目 录

一光学与工程 1

1 Cloaking device uses ordinary lenses to hide objects across continuous range of angles 1 2 Brighter images more efficient LCD displays New polarizing filter transits more light 1 3 Scientists light the way for future electronic devices 2 4 New materials for more powerful solar cells 3 5 New research lights the way to super-fast computers 4 二光子学 5

6 Record high data accuracy rates for phase-modulated transmission 5 7 Scientists discover novel metamaterial properties within hexagonal boron nitride 6 8 Optical watermills control spinning light 7 9 Creating bright X-ray pulses in the laser lab 8 10 There and back again Extending optical storage lifetime by retrieving photon echoes from

semiconductor spin excitations 9 11 1-X-ray powder diffraction beamline at NSLS-II takes first beam and first data 12 二量子物理 14

12 Spiral laser beam creates quantum whirlpool 14 13 Twisted light waves sent across Vienna 14 三纳米物理 16

14 Magnetic fields and lasers elicit graphene secret 16 15 Engineers efficiently mix light at the nanoscale 17 16 Two good things that are better together STM combined with X-ray synchrotron microscopy 18 17 Method for symmetry-breaking in feedback-driven self-assembly of optical metamaterials 19 四技术与应用 21

18 Ultra-short X-ray pulses explore the nano world 21 19 Tiny magnetic sensor deemed attractive 22 20 Robotics meet X-ray lasers in cutting-edge biology studies 22 21 Multilaboratory collaboration brings new X-ray detector to light 23 22 Technology helps improve production of laser-heated hard disk drives with enhanced storage capacities

24 23 Worlds first photonic pressure sensor outshines traditional mercury standard 24 24 Northrop Grumman Sets World Record with One-Terahertz Circuit Achieves One Trillion Cycles per

Second 26 25 XEI Scientific launches the revolutionary Evactron EP plasma cleaning system 26 26 Two Photons Strongly Coupled by Glass Fibre 27 27 New technique to help produce next generation photonic chips 28 28 Breakthrough in flexible electronics enabled by inorganic-based laser lift-off 28 29 Exploring extraordinary optical transmission in a plasmonic cavity 29 30 Engineers make sound loud enough to bend light on a computer chip 30 五其他 31

31 New evidence for exotic predicted superconducting state 31 32 Caltech Rocket Experiment Finds Surprising Cosmic Light 32 33 ORNL materials researchers get first look at atom-thin boundaries 33 34 Topological insulators promising for spintronics quantum computers 34 35 Study details laser pulse effects on behavior of electrons 35

一光学与工程

1 Cloaking device uses ordinary lenses to hide objects across continuous range of angles

简介罗切斯特大学在新研制的装置中使用了既便

宜又容易获取的材料详细情况已发表在《光学快讯》

上该装置应用潜力很大比如用于外科手术可以

透过手看见正做的手术部位卡车司机可以看见驾驶盲

点

A side view The laser shows the paths that light rays travel

through the system showing regions that can be used for cloaking an object Credit Adam Fenster University of Rochester

Inspired perhaps by Harry Potters invisibility cloak scientists have recently developed several waysmdashsome simple and some involving new technologiesmdashto hide objects from view The latest effort developed at the University of Rochester not only overcomes some of the limitations of previous devices but it uses inexpensive readily available materials in a novel configuration Thereve been many high tech approaches to cloaking and

the basic idea behind these is to take light and have it pass around something as if it isnt there often using high-tech or exotic materials said John Howell a professor of physics at the University of Rochester Forgoing the specialized components Howell and graduate student Joseph Choi developed a combination of four standard lenses that keeps the object hidden as the viewer moves up to several degrees away from the optimal viewing position

This is the first device that we know of that can do three-dimensional continuously multidirectional cloaking which works for transmitting rays in the visible spectrum said Choi a PhD student at Rochesters Institute of Optics

The details of the device are now published in the journal Optics Express

Many cloaking designs work fine when you look at an object straight on but if you move your viewpoint even a little the object becomes visible explains Howell Choi added that previous cloaking devices can also cause the background to shift drastically making it obvious that the cloaking device is present

In order to both cloak an object and leave the background undisturbed the researchers determined the lens type and power needed as well as the precise distance to separate the four lenses To test their device they placed the cloaked object in front of a grid background As they looked through the lenses and changed their viewing angle by moving from side to side the grid shifted accordingly as if the cloaking device was not there There was no

discontinuity in the grid lines behind the cloaked object compared to the background and the grid sizes (magnification) matched

University of Rochester PhD student Joseph Choi is pictured with

a multidirectional perfect paraxial cloak using four lenses Credit Adam Fenster University of Rochester

The Rochester Cloak can be scaled up as large as the size of the lenses allowing fairly large objects to be cloaked And unlike some other devices its broadband so it works for the whole visible spectrum of light rather than only for specific frequencies

Their simple configuration improves on other cloaking devices but its not perfect This cloak bends light and sends it through the center of the device so the on-axis region cannot be blocked or cloaked said Choi This means that the cloaked region is shaped like a doughnut He added that they have slightly more complicated designs that solve the problem Also the cloak has edge effects but these can be reduced when sufficiently large lenses are used

In their paper Howell and Choi provide a mathematical formalism for this type of cloaking that can work for angles up to 15 degrees or more They use a technique called ABCD matrices that describes how light bends when going through lenses mirrors or other optical elements

While their device is not quite like Harry Potters invisibility cloak Howell had some thoughts about potential applications including using cloaking to effectively let a surgeon look through his hands to what he is actually operating on he said The same principles could be applied to a truck to allow drivers to see through blind spots on their vehicles

Howell became interested in creating simple cloaking devices with off-the-shelf materials while working on a holiday project with his children Together with his 14 year-old son and Choi he recently published a paper about some of the possibilities and also demonstrated simple cloaking with mirrors like magicians would use in a brief video

httpphysorgnews2014-11-cloaking-device-ordinary-lenses-rangehtml

2 Brighter images more efficient LCD displays New polarizing filter transits more light

简介美国尤他大学工程师们研发出一种偏光滤

1

光电技术情报 2015年第1期（总第6期）

一光学与工程

1 Cloaking device uses ordinary lenses to hide objects across continuous range of angles

简介罗切斯特大学在新研制的装置中使用了既便

宜又容易获取的材料详细情况已发表在《光学快讯》

上该装置应用潜力很大比如用于外科手术可以

透过手看见正做的手术部位卡车司机可以看见驾驶盲

点

A side view The laser shows the paths that light rays travel

through the system showing regions that can be used for cloaking an object Credit Adam Fenster University of Rochester

Inspired perhaps by Harry Potters invisibility cloak scientists have recently developed several waysmdashsome simple and some involving new technologiesmdashto hide objects from view The latest effort developed at the University of Rochester not only overcomes some of the limitations of previous devices but it uses inexpensive readily available materials in a novel configuration Thereve been many high tech approaches to cloaking and

the basic idea behind these is to take light and have it pass around something as if it isnt there often using high-tech or exotic materials said John Howell a professor of physics at the University of Rochester Forgoing the specialized components Howell and graduate student Joseph Choi developed a combination of four standard lenses that keeps the object hidden as the viewer moves up to several degrees away from the optimal viewing position

This is the first device that we know of that can do three-dimensional continuously multidirectional cloaking which works for transmitting rays in the visible spectrum said Choi a PhD student at Rochesters Institute of Optics

The details of the device are now published in the journal Optics Express

Many cloaking designs work fine when you look at an object straight on but if you move your viewpoint even a little the object becomes visible explains Howell Choi added that previous cloaking devices can also cause the background to shift drastically making it obvious that the cloaking device is present

In order to both cloak an object and leave the background undisturbed the researchers determined the lens type and power needed as well as the precise distance to separate the four lenses To test their device they placed the cloaked object in front of a grid background As they looked through the lenses and changed their viewing angle by moving from side to side the grid shifted accordingly as if the cloaking device was not there There was no

discontinuity in the grid lines behind the cloaked object compared to the background and the grid sizes (magnification) matched

University of Rochester PhD student Joseph Choi is pictured with

a multidirectional perfect paraxial cloak using four lenses Credit Adam Fenster University of Rochester

The Rochester Cloak can be scaled up as large as the size of the lenses allowing fairly large objects to be cloaked And unlike some other devices its broadband so it works for the whole visible spectrum of light rather than only for specific frequencies

Their simple configuration improves on other cloaking devices but its not perfect This cloak bends light and sends it through the center of the device so the on-axis region cannot be blocked or cloaked said Choi This means that the cloaked region is shaped like a doughnut He added that they have slightly more complicated designs that solve the problem Also the cloak has edge effects but these can be reduced when sufficiently large lenses are used

In their paper Howell and Choi provide a mathematical formalism for this type of cloaking that can work for angles up to 15 degrees or more They use a technique called ABCD matrices that describes how light bends when going through lenses mirrors or other optical elements

While their device is not quite like Harry Potters invisibility cloak Howell had some thoughts about potential applications including using cloaking to effectively let a surgeon look through his hands to what he is actually operating on he said The same principles could be applied to a truck to allow drivers to see through blind spots on their vehicles

Howell became interested in creating simple cloaking devices with off-the-shelf materials while working on a holiday project with his children Together with his 14 year-old son and Choi he recently published a paper about some of the possibilities and also demonstrated simple cloaking with mirrors like magicians would use in a brief video

httpphysorgnews2014-11-cloaking-device-ordinary-lenses-rangehtml

2 Brighter images more efficient LCD displays New polarizing filter transits more light

简介美国尤他大学工程师们研发出一种偏光滤

1

光电技术情报 2015年第1期（总第6期）

镜能传输更多的光引领移动设备显示器的发展方向

他们制造的滤镜使用聚集镓离子束把硅晶片蚀刻成纳

米柱和纳米穴其滤光功能与标准滤光镜别无二致但

滤光量增加了近 30

University of Utah electrical and computer engineering associate

professor Rajesh Menon holds up a piece of silicon that has been etched with microscopic pillars and holes to create a polarized filter He leads a team of researchers that hellip

University of Utah engineers have developed a polarizing filter that allows in more light leading the way for mobile device displays that last much longer on a single battery charge and cameras that can shoot in dim light

Polarizers are indispensable in digital photography and LCD displays but they block enormous amounts of light wasting energy and making it more difficult to photograph in low light

The Utah electrical and computer engineering researchers created the filter by etching a silicon wafer with nanoscale pillars and holes using a focused gallium-ion beam This new concept in light filtering can perform the same function as a standard polarizer but allows up to nearly 30 percent more light to pass through says U electrical and computer engineering associate professor Rajesh Menon The study is being published in Novembers issue of Optica a new journal from The Optical Society

Sunlight as well as most ambient light emits half of its energy as light polarized along a horizontal axis and the other half along a vertical axis A polarizer typically allows only half of the light to pass because its permitting either the horizontal or vertical energy to go through but not both Meanwhile the other half is reflected back or absorbed but the resulting image is much darker Polarizers are widely used by photographers for example to reduce glare in the image They also are used in LCD displays to regulate what light passes through to create images on the screen

When you take a picture and put the polarized filter on you are trying to get rid of glare Menon says But most polarizers will eliminate anywhere from to 60 to 70 percent of the light You can see it with your eyes

Yet with Menons new polarizer much of the light that normally is reflected back is instead converted to the desired polarized state he says The U researchers have been able to pass through about 74 percent of the light though their goal is to eventually allow all of the light to pass through

LCD displays on devices such as smartphones and tablets have two polarizers that ultimately throw away

most of the light when working with the liquid crystal display If one can increase that energy efficiency that is a huge increase on the battery life of your display Or you can make your display brighter Menon says

Menons team validated their concept using a polarizer that is only 20 by 20 micrometers and tested with only infrared light But they plan to increase the size of the filter use it with visible light and figure out a way to make it more cost effective to manufacture Menon says the first marketable applications of this technology could be available in five to 10 years The technology also could be a boon for photographers who want to bring out more detail in their pictures while shooting in low-light situations and for scientists using microscopes and telescopes to visualize obscure phenomenon

httpphysorgnews2014-11-brighter-images-efficient-lcd-polarizinghtml

3 Scientists light the way for future electronic devices

简介英国南安普顿大学光电研究中心的研究人员

成功演示了如何用玻璃制成体积小运行快耗电少的

电子设备这项研究的应用潜力是制造出运行更快效

率更高的电子设备缩小手机平板电脑及台式电脑的

体积降低能耗变废热为电能

Researchers from the Optoelectronics Research Centre

(ORC) at the University of Southampton have demonstrated how glass can be manipulated to create electronic devices that will be smaller faster and consume less power

The research published in the journal Nature Communications has the potential to allow faster more efficient electronic devices further shrinking the size of our phones tablets and computers and reducing their energy consumption by turning waste heat into power

Working in collaboration with the Advanced Technology Institute at the University of Surrey and the University of Cambridge ORC scientists Dr Jin Yao and Dr Behrad Gholipour have made prototype devices that use light to bring together different computing functions into one component

This work builds on contributions from Dr TaeHoon Lee at Cambridge who performed molecular-dynamics simulations on the materials to better understand their structure and Dr Mark Hughes at Surrey who has been studying the effect of dopants on glasses for a number of years and measured the electrical current generated by light in these devices

2

光学与工程

Silicon is reaching its fundamental limits soon we will be unable to reduce the silicon chip any smaller or decrease the power consumption of these devices Using a family of materials called chalcogenides a glass material integral to data technologies such as CDs and DVDs Dr Yao and Dr Gholipour are looking beyond the silicon chip for the next generation of materials which could replace traditional semiconductors and the conventional electronics that power todays electronic devices

By doping a chalcogenide glass in this case a material based on germanium and selenium and forming a multilayer structure with electrical contacts Dr Gholipour was able to show the same switching behaviour seen in silicon transistor but in a device made entirely from glass

Dr Gholipour explains Non-equilibrium doping within chalcogenide glasses enables a unique information processing platform within one material system This allows traditional electronic computing along with memory functionality which opens up the optical spectrum from the visible far into the infrared for next generation optoelectronic and fully optical computing applications

This work builds on Dr Behrads PhD work for which he won the UK Engineering and Physical Sciences Research Councils (EPSRC) prestigious ICT Pioneer prize in the area of information in 2011

Using similar materials Dr Yao formed long strips of different types of chalcogenides connecting each end together to form a chain of materials

Dr Yao says When one end of the structure is hotter than the other as might occur near the battery of your phone or computer a voltage is produced through a process known as the thermoelectric effect This work for which a patent has been now been applied has the potential to make our electronic devices more efficient

The key behind these advances is the doping of the chalcogenides Chalcogenide glass though semiconducting is normally a material which is deficient in electrons leaving holes or vacancies where an electron should be To compete with silicon doping through ion implantation provided by Surreys Ion Beam Centre has allowed the transformation of the material to one with an excess of electrons These two variations of the same material form the basis of all transistors Equally as important the ion implant process remains compatible with traditional semiconducting processes where the process is an established technology

While such material changes have been demonstrated before in chalcogenides this work has significantly opened up the range of compositions that this effect can be achieved and reduced the amount of doping needed by over 100 times

Research group leader Professor Dan Hewak says The key result though is that we are now demonstrating a range of highly functional but very different devices in a single material platform The future of these materials is bright and we are now in the process of consolidating our

chalcogenide glass research into a single interdisciplinary centre dedicated to the advancement of these fascinating materials

The University of Southampton has a 25-year history of working with chalcogenides demonstrating the first chalcogenide optical fibre in 1995 the first chalcogenide laser a few years later as well as making important advances in the use of these compounds in solid state memory active metamaterials and in medical and aerospace applications

httpphysorgnews2014-11-scientists-future-electronic-deviceshtml

4 New materials for more powerful solar cells 简介罗塞教授和他的研究团队研发出一种含铋

铬铁及氢元素的新材料这些多铁材料吸收太阳辐射

具有独一无二的电磁性能在太阳能技术领域有广阔应

用前景在电子传感器和闪存驱动器等器件的应用方面

具有很大的潜力目前该团队着力用这些材料为传统的

单晶硅太阳能电池镀膜可增加电池的寿命并提高

18mdash24的效能 Applying a thin film of metallic oxide significantly

boosts the performance of solar panel cellsmdashas recently demonstrated by Professor Federico Rosei and his team at the Eacutenergie Mateacuteriaux Teacuteleacutecommunications Research Centre at Institut national de la recherche scientifique (INRS) The researchers have developed a new class of materials comprising elements such as bismuth iron chromium and oxygen These multiferroic materials absorb solar radiation and possess unique electrical and magnetic properties This makes them highly promising for solar technology and also potentially useful in devices like electronic sensors and flash memory drives The results of this research are discussed in an article published in Nature Photonics by researcher and lead author Riad Nechache

The INRS research team discovered that by changing the conditions under which a thin film of these materials is applied the wavelengths of light that are absorbed can be controlled A triple-layer coating of these materialsmdashbarely 200 nanometres thickmdashcaptures different wavelengths of light This coating converts much more light into electricity than previous trials conducted with a single layer of the same material With a conversion efficiency of 81 reported by Nechache and his coauthors this is a major breakthrough in the field

The team currently envisions adding this coating to traditional single-crystal silicon solar cells (currently available on the market) They believe it could increase maximum solar efficiency by 18 to 24 while also boosting cell longevity As this technology draws on a simplified structure and processes as well as abundant and stable materials new photovoltaic (PV) cells will be more powerful and cost less This means that the INRS teams breakthrough may make it possible to reposition silicon PV cells at the forefront of the highly competitive solar energy market

3

光电技术情报 2015年第1期（总第6期）

httpphysorgnews2014-11-materials-powerful-solar-cellshtml

5 New research lights the way to super-fast computers

简介《自然通讯》杂志发表了一项新的研究成果

演示了通过操控玻璃生成一种材料能使计算机用光传

输信息这一研发结果在将来能够增加计算机处理速度

及处理能力英萨里大学协同剑桥大学和南安普顿大学

共同研究发现这项研究有可能改变无定形氧属化物的

电子性能即玻璃材料与数据技术的整合物如 CD 光

盘和 DVD 光盘 New research published today in the journal Nature

Communications has demonstrated how glass can be manipulated to create a material that will allow computers to transfer information using light This development could significantly increase computer processing speeds and power in the future

The research by the University of Surrey in collaboration with the University of Cambridge and the University of Southampton has found it is possible to change the electronic properties of amorphous chalcogenides a glass material integral to data technologies such as CDs and DVDs By using a technique called ion doping the team of researchers have discovered a material that could use light to bring together different computing functions into one component leading to all-optical systems

Computers currently use electrons to transfer information and process applications On the other hand data sources such as the internet rely on optical systems the transfer of information using light Optical fibres are used to send information around the world at the speed of light but these signals then have to be converted to electrical signals once they reach a computer causing a significant slowdown in processing

The challenge is to find a single material that can effectively use and control light to carry information around a computer Much like how the web uses light to deliver information we want to use light to both deliver and process computer data said project leader Dr Richard Curry of the University of Surrey

This has eluded researchers for decades but now we have now shown how a widely used glass can be manipulated to conduct negative electrons as well as positive charges creating what are known as pn-junction devices This should enable the material to act as a light source a light guide and a light detector - something that can carry and interpret optical information In doing so this could transform the computers of tomorrow allowing them to effectively process information at much faster speeds

The researchers expect that the results of this research will be integrated into computers within ten years In the short term the glass is already being developed and used in next-generation computer memory technology known as

CRAM which may ultimately be integrated with the advances reported httpphysorgnews2014-11-super-fasthtml

光学与工程

4

二光子学

6 Record high data accuracy rates for phase-modulated transmission

简介光波相位可被延时其延时量可用数据段来

表示科学家们通过实验沿着单根光纤记录下来一组

新的光波传输数据为每秒 255 万亿比特他们设计了一

个检测方案比最好的传统探测仪的错误率要低 25 倍

这一检测方案在信息技术领域具有重要的应用价值比

如可以用较少的电进行远程信息传送

By passing it through a special crystal a light waversquos

phase---denoting position along the waversquos cycle---can be delayed A delay of a certain amount can denote a piece of data In this experiment light pulses can be delayed by a zero hellip We want data Lots of it We want it now We want it to be cheap and accurate

Researchers try to meet the inexorable demands made on the telecommunications grid by improving various components In October 2014 for instance scientists at the Eindhoven University of Technology in The Netherlands did their part by setting a new record for transmission down a single optical fiber 255 terabits per second

Alan Migdall and Elohim Becerra and their colleagues at the Joint Quantum Institute do their part by attending to the accuracy at the receiving end of the transmission process They have devised a detection scheme with an error rate 25 times lower than the fundamental limit of the best conventional detector They did this by employing not passive detection of incoming light pulses Instead the light is split up and measured numerous times

The new detector scheme is described in a paper published in the journal Nature Photonics

By greatly reducing the error rate for light signals we can lessen the amount of power needed to send signals reliably says Migdall This will be important for a lot practical applications in information technology such as using less power in sending information to remote stations Alternatively for the same amount of power the signals can be sent over longer distances

Phase Coding Most information comes to us nowadays in the form of

light whether radio waves sent through the air or infrared waves send up a fiber The information can be coded in several ways Amplitude modulation (AM) maps analog information onto a carrier wave by momentarily changing

its amplitude Frequency modulation (FM) maps information by changing the instantaneous frequency of the wave On-off modulation is even simpler quickly turn the wave off (0) and on (1) to convey a desired pattern of binary bits

Because the carrier wave is coherentmdash-for laser light this means a predictable set of crests and troughs along the wavemdash-a more sophisticated form of encoding data can be used In phase modulation (PM) data is encoded in the momentary change of the waves phase that is the wave can be delayed by a fraction of its cycle time to denote particular data How are light waves delayed Usually by sending the waves through special electrically controlled crystals

Instead of using just the two states (0 and 1) of binary logic Migdalls experiment waves are modulated to provide four states (1 2 3 4) which correspond respectively to the wave being un-delayed delayed by one-fourth of a cycle two-fourths of a cycle and three-fourths of a cycle The four phase-modulated states are more usefully depicted as four positions around a circle (figure 2) The radius of each position corresponds to the amplitude of the wave or equivalently the number of photons in the pulse of waves at that moment The angle around the graph corresponds to the signals phase delay

(Left) the four possible phase-delayed states The inherent

uncertainty of the states is suggested by the extent of the fuzziness of fuzzy balls depicting the four states This fuzziness causes some overlap of the different states and leads hellip

The imperfect reliability of any data encoding scheme reflects the fact that signals might be degraded or the detectors poor at their job If you send a pulse in the 3 state for example is it detected as a 3 state or something else Figure 2 besides showing the relation of the 4 possible data states depicts uncertainty inherent in the measurement as a fuzzy cloud A narrow cloud suggests less uncertainty a wide cloud more uncertainty False readings arise from the overlap of these uncertainty clouds If say the clouds for states 2 and 3 overlap a lot then errors will be rife

In general the accuracy will go up if n the mean number of photons (comparable to the intensity of the light pulse) goes up This principle is illustrated by the figure to the right where now the clouds are farther apart than in the left panel This means there is less chance of mistaken readings More intense beams require more power but this mitigates the chance of overlapping blobs

光电技术情报 2015年第1期（总第6期）

5

Twenty Questions So much for the sending of information pulses How

about detecting and accurately reading that information Here the JQI detection approach resembles 20 questions the game in which a person identifies an object or person by asking question after question thus eliminating all things the object is not

In the scheme developed by Becerra (who is now at University of New Mexico) the arriving information is split by a special mirror that typically sends part of the waves in the pulse into detector 1 There the waves are combined with a reference pulse If the reference pulse phase is adjusted so that the two wave trains interfere destructively (that is they cancel each other out exactly) the detector will register a nothing This answers the question what state was that incoming light pulse in When the detector registers nothing then the phase of the reference light provides that answer hellip probably

That last caveat is added because it could also be the case that the detector (whose efficiency is less than 100) would not fire even with incoming light present Conversely perfect destructive interference might have occurred and yet the detector still firesmdash-an eventuality called a dark count Still another possible glitch because of optics imperfections even with a correct referencendashphase setting the destructive interference might be incomplete allowing some light to hit the detector

The way the scheme handles these real world problems is that the system tests a portion of the incoming pulse and uses the result to determine the highest probability of what the incoming state must have been Using that new knowledge the system adjusts the phase of the reference light to make for better destructive interference and measures again A new best guess is obtained and another measurement is made

As the process of comparing portions of the incoming information pulse with the reference pulse is repeated the estimation of the incoming signals true state was gets better and better In other words the probability of being wrong decreases

Schematic for the adaptive quantum receiver The incoming signal

pulse is made to interfere with the signal from a local oscillator (which is itself coordinated with the reference pulse used to encode the original signal) and the hellip

Encoding millions of pulses with known information values and then comparing to the measured values the scientists can measure the actual error rates Moreover the error rates can be determined as the input laser is adjusted so that the information pulse comprises a larger or

smaller number of photons (Because of the uncertainties intrinsic to quantum processes one never knows precisely how many photons are present so the researchers must settle for knowing the mean number)

A plot of the error rates shows that for a range of photon numbers the error rates fall below the conventional limit agreeing with results from Migdalls experiment from two years ago But now the error curve falls even more below the limit and does so for a wider range of photon numbers than in the earlier experiment The difference with the present experiment is that the detectors are now able to resolve how many photons (particles of light) are present for each detection This allows the error rates to improve greatly

For example at a photon number of 4 the expected error rate of this scheme (how often does one get a false reading) is about 5 By comparison with a more intense pulse with a mean photon number of 20 the error rate drops to less than a part in a million

The earlier experiment achieved error rates 4 times better than the standard quantum limit a level of accuracy expected using a standard passive detection scheme The new experiment using the same detectors as in the original experiment but in a way that could extract some photon-number-resolved information from the measurement reaches error rates 25 times below the standard quantum limit

The detectors we used were good but not all that heroic says Migdall With more sophistication the detectors can probably arrive at even better accuracy

The JQI detection scheme is an example of what would be called a quantum receiver Your radio receiver at home also detects and interprets waves but it doesnt merit the adjective quantum The difference here is single photon detection and an adaptive measurement strategy is used A stable reference pulse is required In the current implementation that reference pulse has to accompany the signal from transmitter to detector

Suppose you were sending a signal across the ocean in the optical fibers under the Atlantic Would a reference pulse have to be sent along that whole way Someday atomic clocks might be good enough says Migdall that we could coordinate timing so that the clock at the far end can be read out for reference rather than transmitting a reference along with the signal

httpphysorgnews2014-11-high-accuracy-phase-modulated-transmissionhtml

7 Scientists discover novel metamaterial properties within hexagonal boron nitride

简介美国海军研究实验室协同其他几个国家的大

学及研究机构共同研究并演示了六边氮化硼独特的超

材料性能可用于光通信高分辨成像矫正红外相机

及探测仪等新型纳米尺光设备

光子学

6

Twenty Questions So much for the sending of information pulses How

about detecting and accurately reading that information Here the JQI detection approach resembles 20 questions the game in which a person identifies an object or person by asking question after question thus eliminating all things the object is not

In the scheme developed by Becerra (who is now at University of New Mexico) the arriving information is split by a special mirror that typically sends part of the waves in the pulse into detector 1 There the waves are combined with a reference pulse If the reference pulse phase is adjusted so that the two wave trains interfere destructively (that is they cancel each other out exactly) the detector will register a nothing This answers the question what state was that incoming light pulse in When the detector registers nothing then the phase of the reference light provides that answer hellip probably

That last caveat is added because it could also be the case that the detector (whose efficiency is less than 100) would not fire even with incoming light present Conversely perfect destructive interference might have occurred and yet the detector still firesmdash-an eventuality called a dark count Still another possible glitch because of optics imperfections even with a correct referencendashphase setting the destructive interference might be incomplete allowing some light to hit the detector

The way the scheme handles these real world problems is that the system tests a portion of the incoming pulse and uses the result to determine the highest probability of what the incoming state must have been Using that new knowledge the system adjusts the phase of the reference light to make for better destructive interference and measures again A new best guess is obtained and another measurement is made

As the process of comparing portions of the incoming information pulse with the reference pulse is repeated the estimation of the incoming signals true state was gets better and better In other words the probability of being wrong decreases

Schematic for the adaptive quantum receiver The incoming signal

pulse is made to interfere with the signal from a local oscillator (which is itself coordinated with the reference pulse used to encode the original signal) and the hellip

Encoding millions of pulses with known information values and then comparing to the measured values the scientists can measure the actual error rates Moreover the error rates can be determined as the input laser is adjusted so that the information pulse comprises a larger or

smaller number of photons (Because of the uncertainties intrinsic to quantum processes one never knows precisely how many photons are present so the researchers must settle for knowing the mean number)

A plot of the error rates shows that for a range of photon numbers the error rates fall below the conventional limit agreeing with results from Migdalls experiment from two years ago But now the error curve falls even more below the limit and does so for a wider range of photon numbers than in the earlier experiment The difference with the present experiment is that the detectors are now able to resolve how many photons (particles of light) are present for each detection This allows the error rates to improve greatly

For example at a photon number of 4 the expected error rate of this scheme (how often does one get a false reading) is about 5 By comparison with a more intense pulse with a mean photon number of 20 the error rate drops to less than a part in a million

The earlier experiment achieved error rates 4 times better than the standard quantum limit a level of accuracy expected using a standard passive detection scheme The new experiment using the same detectors as in the original experiment but in a way that could extract some photon-number-resolved information from the measurement reaches error rates 25 times below the standard quantum limit

The detectors we used were good but not all that heroic says Migdall With more sophistication the detectors can probably arrive at even better accuracy

The JQI detection scheme is an example of what would be called a quantum receiver Your radio receiver at home also detects and interprets waves but it doesnt merit the adjective quantum The difference here is single photon detection and an adaptive measurement strategy is used A stable reference pulse is required In the current implementation that reference pulse has to accompany the signal from transmitter to detector

Suppose you were sending a signal across the ocean in the optical fibers under the Atlantic Would a reference pulse have to be sent along that whole way Someday atomic clocks might be good enough says Migdall that we could coordinate timing so that the clock at the far end can be read out for reference rather than transmitting a reference along with the signal

httpphysorgnews2014-11-high-accuracy-phase-modulated-transmissionhtml

7 Scientists discover novel metamaterial properties within hexagonal boron nitride

简介美国海军研究实验室协同其他几个国家的大

学及研究机构共同研究并演示了六边氮化硼独特的超

材料性能可用于光通信高分辨成像矫正红外相机

及探测仪等新型纳米尺光设备

光子学

6

Periodic arrays of cone-shaped hexagonal boron nitride

nanoantennas depicted magnified image above were used to confine hyperbolic polaritons in all three dimensions This enabled the researchers to fundamentally probe the novel optical helliphellip

US Naval Research Laboratory (NRL) scientists in collaboration with researchers from the University of Manchester UK Imperial College London University of California San Diego and the National Institute of Material Science (NIMS) Japan have demonstrated that confined surface phonon polaritons within hexagonal boron nitride (hBN) exhibit unique metamaterial properties that enable novel nanoscale optical devices for use in optical communications super-resolution imaging and improved infrared cameras and detectors Metamaterials are artificial composites of various materials designed to exhibit optical properties not anticipated in nature One such property is hyperbolicity whereby a material exhibits both metallic- and dielectric-like optical responses simultaneously along different crystal axes These hyperbolic metamaterials are the basis for many potential applications such as hyperlenses used for imaging of nanoscale objects not observable using conventional optics

Our examination into the characteristics of hBN reveal the first experimental observation of sub-diffractional guided waves confined in all three dimensions using a natural hyperbolic material said Joshua Caldwell PhD Electronics Science and Technology Division Power Electronics Branch This may in turn lead to the development of disruptive technologies such as the nanoscale equivalent of an optical fiber due to the volume-bound confinement of sub-diffractional modes within hBN

Optic phonons or crystal vibrations that can be excited with infrared light can also be used to confine light to dimensions much smaller than the wavelength of light while maintaining record-high efficiencies These surface phonon polaritons are analogous to electron oscillations in metals or doped-semiconductors called plasmons but offer the benefit of low losses and operation in the infrared to terahertz spectral regions

As a van der Waels crystalmdasha layered crystal structure similar to graphene or graphitemdashhBN was demonstrated to be two orders of magnitude more efficient than hyperbolic metamaterials shown to date says Caldwell Unlike metallicdielectric hyperbolic metamaterials hBN also provides the additional functionality of both types of hyperbolicity allowing both the in-plane and out-of-plane

crystal axes to behave metallic- (reflective) or dielectric-like (transparent) simply by changing the wavelength of the exciting light This mixing of both types of hyperbolic behavior is to this point unique and allowed the fundamental comparison of antennas within these two regimes

Using the natural hyperbolic behavior of hBN the researchers were able to demonstrate that light could also be confined within optical antennasmdashup to 86 times smaller than the wavelength of light for instance confinement of 68 micrometers of light into a 008 micrometer tall antennamdashwhile maintaining record-high efficiencies due to the low-loss nature of the dielectric crystal

The researchers were able to further demonstrate that the resonance wavelength of the hyperbolic polaritons confined within these antennae was dependent only upon the aspect ratio (heightdiameter) and was nominally independent upon the actual size andor shapemdashdemonstrating that antennas could be defined for a given application simply by controlling this ratio thereby making them compatible to a wide array of device form-factors This could enable frequency selective operation and nanophotonic circuits as well as provide an operational material for mid-infrared imaging of nanoscale objects

The research team also demonstrated that the resonance response exhibited not a single mode but four separate series and according to Caldwell a change in the wavelength andor the angle of the incoming light with respect to the sample surface could isolate each series providing the first complete description of these novel three-dimensionally confined hyperbolic polariton modes

Further discoveries found these breakthroughs could have an impact in areas such as enhanced infrared or molecular spectroscopy improved functionality for nanophotonic circuits and devices for use in infrared cameras detectors and weapons guidance systems and tailored thermal emission sources

httpphysorgnews2014-11-scientists-metamaterial-properties-hexagonal-boronhtml

8 Optical watermills control spinning light 简介科学家对控制波导中电磁波的传播方向进行

研究并证实了无论顺向还是逆向传播整个过程的效

果都很好这一研究成果开辟了通信安全的革新和高速

计算技术研发的新道路

Scientists at Kings have built on research they

conducted last year to achieve previously unseen levels of

7

光电技术情报 2015年第1期（总第6期）

control over the travelling direction of electromagnetic wave in waveguides and proved that the process works equally well in reverse opening up the way for the development of technologies that could revolutionise secure communications as well as high speed computing

In a paper published today in Nature Communications the team demonstrates that light waves propagating along a surface will induce the spinning of electrons in a nearby nanoparticle

When speaking of spin in optics one can think of the spinning wheel of a watermill as an illustration of the rotating motion of the electric field vector representing the light field Assuming the water wheel analogy the teams discovery is equivalent to demonstrating that a flow of water in the canal will cause the water wheel to spin thus acting as a water mill The team showed that the direction of propagation of the original wave determined the spinning sense of the electrons This is only possible thanks to a very specific property of light waves guided along a surface which does not generally exist in free space paving the way to a new understanding and new applications of spin on these guided light waves

Dr Francisco Rodriacuteguez-Fortuntildeo from the Department of Physics and one of the studys authors said It has been very encouraging for us to experimentally confirm that this optical watermill was working just as we expected This reinforces our determination to search for new insights and novel applications of spin in guided light

In the experiment the team first generated a light wave propagating along the surface of a thin gold film This wave called a surface plasmon was then directed at a gold nanoparticle placed on the same surface The interaction between them resulted in a fast spinning motion of the electrons inside the nanoparticle in synchrony with the lights frequency The radiation from the circular motion of the electrons in the particle was subsequently detected and its polarization analysed confirming experimentally the reversibility of spin conservation

By selecting the direction of propagation of the surface wave in such a miniaturized setup the researchers have at their disposal a flexible and integrated way to control light spin opening new avenues for all kinds of spinoptical devices Last year in a paper published in Science they demonstrated that the direction of spinning electrons inside a nanoparticle determine the propagation direction of light along a nearby surface

httpphysorgnews2014-11-optical-watermillshtml

9 Creating bright X-ray pulses in the laser lab 简介这篇文章介绍了维也纳技术大学对 X 射线脉

冲进行实验的过程和结果以及未来在这方面的研究计

划科学家们在此之前就致力于建造一个长波长激光系

统维也纳技术大学研究人员在他们实验的前期阶段就

做出了 08 微米的激光器波长是该实验室现有激光脉

冲的 5 倍其 X 射线转化流量则有 25 倍之高这个研

究团队到目前为止所制成的激光是世界上最亮的他们

计划研究并生成波长更长的激光同时还要增加激光器

产生光脉冲的比率

An optical table at the Photonics Institute (TU Wien)

To create X-raysmdashshort wave radiationmdashscientists at TU Vienna start out with very long wavelengthsmdashinfrared laser Long wavelength laser pulses rip atoms out of metal and accelerate them which leads to emission of X-rays

X-rays are widely used in medicine and in materials science To take a picture of a broken bone it is enough to create a continuous flux of X-ray photons but in order to study time-dependent phenomena on very short timescales short X-ray pulses are required One possibility to create short hard X-ray pulses is hitting a metal target with laser pulses The laser rips electrons out of the atoms and makes them emit X-ray radiation Electrical engineers at the Vienna University of Technology (TU Wien) together with researchers from Berlin have drastically increased the flux of X-ray photons using a newly developed mid-infrared laser system This new table-top X-ray source will allow more accurate measurements in many fields of research

Long Waves and Short Waves Hard x-ray radiation is light with a wavelength in the

range of picometers - much shorter than the wavelength of visible light But in order to create this extremely short wave radiation Professor Andrius Baltuskas team (Photonics Institute Electrical Engineering TU Wien) starts out with a quite different kind of light They created a high-intensity infrared laser system with a wavelength of 4 micrometers - which is a wavelength much longer than visible light

Skirmantas Alisauskas working on the experiment

The mid-infrared light emitted by the laser hits a copper plate The intensity of the laser light is so high that electrons are ripped out of the atoms The laser field turns them around accelerates them and eventually makes them

8

光子学

hit the copper again at very high energies During this impact of the electrons returning to the copper plate X-ray radiation is emitted

The flux of the x-ray radiation depends on the wavelength of the laser says Skirmantas Alisauskas (TU Wien) If the laser wavelength is long then every electron spends a lot of time in the laser field before it returns to the copper atoms It has more time to gain energy and hits the copper plate even harder

Building a New Kind of Laser This is why the scientists have focussed their attention

on building long-wavelenth laser systems Previously this experiment was done with a common 08 micrometer laser The wavelength of our laser pulses is five times as long which translates into a 25 times higher x-ray flux says Skirmantas Alisauskas Each laser pulse leads to one billion x-ray photons emitted into all directions

Skirmantas Alisauskas Vienna University of Technology

Creating this laser light was a big technological challenge Building lasers with such long wavelengths is hard but the main problem was making the laser light intense enough says Alisauskas At this wavelength this is the most intense laser light in the world But we want to go even further in the near future

More Pulses per Second The team is planning to go to even longer wavelengths

and they are trying to increase the rate at which the laser can produce light pulses At the moment we have a repetition rate of 20 laser pulses per second That is perfectly fine for a proof of principle but for technological applications we need to increase that - and we already have a few good ideas of how to do this says Prof Andrius Baltuska

X-rays are used whenever the atomic structure of materials has to be investigated As the new x-ray source does not produce a continuous beam but short pulses it can be used for time-resolved measurements

httpphysorgnews2014-11-bright-x-ray-pulses-laser-labhtml

10 There and back again Extending optical storage lifetime by retrieving photon echoes from semiconductor spin excitations

简介研究人员发现皮秒光脉冲与施加弱横向磁场

能将短暂的光激发转换成长时电子自旋态这种诱发的

受激光子共振在亚微秒时间量程上具有宽带宽特点这

些研究及所运用的方法可在未来用于存储设备还有可

能促成半导体纳米基光存储器的制造

Scheme of photon echo experiment and optical properties of

investigated structure (A) The CdTe(CdMg)Te quantum well (QW) is optically excited with a sequence of three laser pulses with variable delays t12and t23 relative to each other The hellip

(Physorg) mdashFor all of their differences classical and quantum communication have at least one thing in common the importance of being able to store optical information That being said optical storage is a complex process that depends largely on the material being used to convert store and retrieve this information in a controllable consistent manner ndash a process especially prone to short optimal memory times when implemented in certain semiconductor quantum structures Recently however scientists at Technische Universitaumlt Dortmund Germany in collaboration with Saint Petersburg State University Russia and Institute of Physics in Warsaw Poland demonstrated magnetic-field-induced long-lived stimulated photon echoes1 ndash coherent optical phenomena in which resonant excitation of a medium by short optical pulses results in a delayed coherent optical flash response ndash in the electronndashtrion system allowed the bidirectional coherent transfer of quantum information in a semiconductor between optical and spin excitations (Trions are excitations comprising three charged quasiparticles ndash emergent phenomena that occur when a microscopically complex system such as a solid behaves as if it contained different weakly interacting particles in free space)

In their study the researchers found that picosecond optical pulses and an applied weak transverse magnetic field led to the transfer of a short-lived optical excitation into a long-lived electron spin state In turn this induced

9

光电技术情报 2015年第1期（总第6期）

stimulated photon echoes with high bandwidth on submicrosecond timescales that exceeded optical excitation lifetime by a factor exceeding three orders of magnitude Moreover the scientists state that the ability to address all three spin components ndashparallel and perpendicular to applied magnetic field ndash as well as the energy level structure of localized trions being identical in quantum wells and self-assembled quantum dots make their approach highly appealing for future memory device applications and may lead to the fabrication of semiconductor nanostructure-based optical memories

Dr Ilya Akimov discussed the paper that he Doctoral Student Lukas Langer and their co-authors from Dortmund St-Petersburg and Warsaw published in Nature Photonics starting with the main challenges in devising a new experimental approach to stimulated photon echoes by transferring the information contained in the optical field into a spin system where it is decoupled from the optical vacuum field A photon echo can be considered as a flash of light initiated in a medium after a sequence of two or more optical pulses Akimov told Physorg Properties of the photon echo pulse ndash that is intensity optical coherence and phase ndash are identical to the properties of the initial pulse therefore this phenomenon can be used to store information in all-optical systems Photon echoes because they occur in structures which rapidly dephase optical excitation in response to the first pulse but with the second pulse reverse the dephasing process

Akimov pointed out that the timescale at which photon echoes can be observed is determined by the period during which optical excitation coherence is preserved This is why photon echoes are coherent he explained If scattering processes are suppressed optical excitation coherence is limited by its lifetime as governed by intrinsic properties of the materials Nevertheless there is a general rule that the more efficient light-matter interaction the faster decay into the ground state will be observed ndash for example faster spontaneous emission due to the optical vacuum field Here we have a dilemma he noted On the one hand wed like to excite the medium quickly with the shortest possible pulse which requires strong light-matter interaction However this limits the timescale at which the photon echoes can be observed The opposite is also true To observe long-lived photon echoes materials with weak light-matter coupling are needed ndash and although semiconductor systems belong to materials with strong light-matter interaction its possible to extend photon echo decay if the optical excitation is transferred into the spin excitation and then recovered back to the optical excitation ndash that is precisely what Akimov and co-authors have accomplished

In order to achieve this goal he said weve used semiconductor quantum wells with excess electrons (A quantum well is a thin layer which can confine quasiparticles ndash emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contains weakly interacting particles in free

space ndash in the dimension perpendicular to the layer surface) Whats key is that the spin excitation coherence time of such electrons decays three orders of magnitude more slowly than the lifetime of optical excitations In our protocol the first pulse leads to optical excitation in semiconductor quantum well next after dephasing of the optical excitation the second pulse transfers optical excitation into the electron spin excitation and finally ndash even after a long delay which can be 1000 times longer than the delay between the first and second pulses ndash we apply the third pulse This third pulse transforms spin excitation back to optical excitation and initiates rephasing so that resulting photon echoes are retrieved from the spin ensemble ndash and therefore the third pulse can be associated with the readout of optical information previously saved by the optical-to-spin transformation induced by the second pulse

The unique feature of photon echoes is that they contain the information about the first optical pulse Akimov pointed out Therefore photon echoes can be used for information technology optical memory applications Moreover its possible to perform not only classical light storage but to use photon echoes for realization of quantum optical memories This is essential he stresses for the development of quantum information and communication systems which use the laws of quantum mechanics to significantly enhance the speed and capacity of future computers

Schematic presentation of the main mechanisms responsible for

magnetic-field-induced stimulated photon echoes (SPE) The whole process comprises three steps 1 pulse 1 creates the optical excitation (initializationmdashconversion of the optical hellip For this reason research on quantum optical memories attracted a lot of attention Akimov told Physorg Current investigations of photon echoes have concentrated primarily on atomic vapors and rare earth crystals with long storage times which are crucial for implementation of robust light-matter interfaces However he noted light-matter coupling is weaker in these systems so operation speed is not as fast as it could be in semiconductors For example he illustrated efficient optical excitation in atomic systems is possible with optical pulses longer than one nanosecond which slow down the operation speed by three orders of magnitude as compared to our protocol ndash and for rare earth crystals the pulse duration should be even longer

10

光子学

In contrast to classical storage quantum memory forbids measurement of the optical field during saving and retrieving processes In other words Akimov said storage of non-classical quantum light ndash such as squeezed light or a single photon ndash should occur without knowing which optical fields have been stored and retrieved because otherwise the quantum state would be irreversibly destroyed during the measurement procedure However our protocol allows quantum storage since transfer between optical excitation and spin excitation does not require state measurement In other words the new protocol transfers a quantum superposition between optically coupled states (optical excitation) and the other pair of states coupled by a magnetic field (spin excitation) In this process no measurement takes place ndash just the transformation between different excitations

Regarding the quantum well the researchers specifically concentrated on an n-doped CdTe(CdMg)Te quantum well where storage time increased from picoseconds to tens of nanoseconds The structures were grown by Prof Grzegorz Karczewski and Prof Tomasz Wojtowiczin the Institute of Physics Polish Academy of Sciences in Warsaw using molecular beam epitaxy (CdTe(CdMg)Te is a cadmium telluride compound in which some of the cadmium is replaced by magnesium) The cadmium telluride semiconductor quantum well structure is a model proof-of-principle system for extending the photon echo delay Akimov told Physorg In such two-dimensional structures the carriers are confined in one direction this results in well-defined spin-level system and clean selection rules for optical transitions Secondly n-type doping of barriers with donors provides excess electrons in the quantum well which again are responsible for long-lived spin excitations

That said while using cadmium telluride quantum wells enabled very clean experiments on the ensemble of trions to be performed because their optical transitions are well isolated spectrally the researchers had to maintain weak optical pulse intensity to prevent interactions between weakly localized trions In order to increase the efficiency and to achieve longer delays for photon echoes it is necessary to try different type of semiconductor nanostructures which can be also based on other compounds Akimov explained One of such candidates is the ensemble of quantum dots where the electrons and holes are localized much more strongly in all three dimensions This is in contrast to quantum wells where strong confinement is present only along one direction

Finally Akimov noted that in semiconductors there are two types of fundamental optical excitations excitons (electron-hole pairs bound by Coulomb interactions) and trions ndash charged excitons consisting of an exciton bound with an excess electron or hole A trion is a three-particle complex and after its decay theres always an excess carrier left he explained In our case we deal with excess electrons which possess spin 12 Therefore in contrast to excitons it is possible to save information about

optical excitation in the spin of the excess electrons left after trion recombination This transformation is only possible when an external magnetic field is applied since it allows us to mix the electronic states in the proper way The most salient advantage of quantum well structures is that exciton and trion resonances are spectrally well separated ndash meaning that picosecond laser pulses let the researchers address only the optical transition from excess electron to trion

For all of these seemingly daunting challenges the researchers key insight was to study photon echoes emitted by trions in semiconductor nanostructures subject to an external magnetic field ndash and by then using a transient four-wave mixing (FWM) technique to measure magnetic-field-induced long-term photon echoes they were able to show that photon echoes can be retrieved from excess electron spin ensembles (Transient four-wave mixing belongs to time-resolved coherent spectroscopy based on non-linear optics whereby interactions between two or three optical pulses in medium produce fourth optical field in the signal) We used ultrashort optical pulses with duration of about one picosecond Akimov explained because efficient optical excitation in semiconductors is possible on the order of 01-1ps In addition he said the experiments had to be performed at extremely low temperatures ndash about two degrees above absolute zero ndash in order to keep the system robust against interactions with phonons (collective excitations similar to quasiparticles in a periodic elastic arrangement of atoms or molecules in condensed matter such as solids and some liquids) as well as to suppress other relaxation mechanisms which could lead to irreversible dephasing of optical and spin excitations and thereby loss of coherence From an experimental point of view he added our primary challenge was combining four-wave mixing with ultrashort picosecond pulses and external magnetic fields at low temperatures

The current study demonstrates that photon echoes can be retrieved from the spin system on the timescale of 10-100 ns However Akimov said this time delay is still too short for practical applications In order to solve this problem we need to extend the decay time of spin excitations There are two possible reasons for decay of spin excitations dephasing of spins and irreversible spin relaxation through decoherence ndash that is due to interaction with the environment The first point can be addressed by means of spin resonance techniques using dynamic decoupling he explained which is an approach largely the same as photon echo but based on periodic excitation of the spin ensemble with microwave pulses which lead to spin echoes In that way it will be possible to keep the spin ensemble of excess electrons free of dephasing and timescales up to tens or even hundreds of microseconds may be achieved However irreversible spin relaxation is more difficult to solve ndash but there are several attempts to reduce hyperfine interaction between nuclear and electron spins One of the solutions would be to use compounds

11

光电技术情报 2015年第1期（总第6期）

with isotopes carrying zero nuclear spin In this case storage times in the milliseconds can be available

In fact Akimov added that the scientists plan to investigate extending the timescale of photon echoes further into the microsecond and millisecond range Well test other nanostructures such as quantum dots with strong trion localization and will search for new materials with suppressed spin excitation decay In addition he said well use spin resonance techniques in order to eliminate spin dephasing in the ensemble of excess electrons

Akimov also mentioned applications beyond optical memory While most applications are related to optical memories where the optical information should be saved and released on demand he said theres another fundamental aspect Our studies combine optical and spin phenomena and in this sense its very interesting to explore our approach for monitoring the time evolution of combined optical and spin excitations

A unique feature of photon echo experiments is the dephasing which already occurs at the initial stage directly after excitation with the first pulse where the sequence of two linearly polarized pulses create comprehensive spin distribution for excess electrons without net spin polarization While each of the electrons has a certain well-defined spin the ensemble spin polarization or average spin is zero ndash and the information about the optical pulses such as polarization and interpulse delay is encoded in the spins of excess electrons This differs from conventional techniques Akimov pointed out For example in well-established pump-probe experiments the non-zero spin polarization in the system is first induced by a circularly polarized pump pulse and then the evolution of the spin in time is probed The scientists therefore believe that their approach based on photon echoes in a magnetic field constitutes an interesting platform for fundamental spin studies

Along these exploratory lines Physorg asked Akimov if given that storage times of seconds or longer might be possible by further exploiting the hyperfine interaction between electrons and nuclei in quantum dots quantum wells and self-assembling quantum dots might at some point be combined in a single quantum system that emulates human short- and long-term memory I think we are still far from that he replied In order to achieve this goal it would be necessary to establish a net of such quantum dot ensembles analogous to cells which would communicate between each other He added that while he does not exclude such possibility he emphasizes that such a quantum system would very complex and would contain and integrate far more than a simple set of quantum nanostructures Several challenging issues such as communication between different ensembles have to be addressed and for that it is necessary to accomplish directed and selective coupling of light at the nanoscale in and out of the cells Accordingly realization of such a network would need integration of photonic crystals or waveguide layers which can be based on semiconductors

Nevertheless he concluded this is a special area of research which deserves a lot of attention

httpphysorgnews2014-10-optical-storage-lifetime-photon-echoeshtml

11 1-X-ray powder diffraction beamline at NSLS-II takes first beam and first data

简介美国国家同步辐射光源 II 的 X 射线粉末衍

射光束线首次捕捉到光这标志着他们的研究进入到了

一个新阶段下一步要做的是尽快将其转化成科技成

果 On November 6 Eric Dooryhee walked into a crowd of

people excitedly talking at the X-ray Powder Diffraction (XPD) beamline beaming an enormous smile The group broke into applause for the enormous achievement they had gathered to celebrate the operators had opened a shutter to the electron storage ring of the National Synchrotron Light Source II and captured light for the first time at the XPD beamline It was the second beamline at NSLS-II to achieve x-ray beam

This is a big day for all of us said Dooryhee the Powder Diffraction Beamline Group Leader The list of acknowledgements he made reflected the huge effort of many support groups across the Photon Sciences Directorate and beyond that made the milestone possible administration and procurement staff surveyors riggers carpenters vacuum specialists mechanical and electrical utilities technicians equipment protection and personnel safety staff x-ray optics metrology experts scientists designers and engineers We couldnt have achieved our first light without the commitment and support of many collaborators around the Lab including work with Peter Siddons and his group who are developing several state-of-the-art detectors for XPD

The XPD core team includes Sanjit Ghose beamline scientist in charge of operating XPD and consolidating its research program Hengzi Wang mechanical engineer John Trunk beamline technician Andrew DeSantis mechanical designer and Wayne Lewis controls engineer

The complexity of this accomplishment came through when Dooryhee talked about the effort put in by Wayne Lewis the controls engineer for XPD

How many motors vacuum gauges and sensors did you have to take ownership of Hundreds Dooryhee asked Lewis wryly smiled and responded Yeah a few

It was Lewis who ultimately opened the shutter allowing the white x-ray beam for the first time to travel through a diamond window and several other components until it was purposely intercepted by a beam stop Both the window and the beamstop emitted a bright fluorescent light once struck by the x-rays and the x-ray footprint at several locations down the beam pipe could thus be imaged and shown on large screens to everyone present

Eventually once commissioning starts a monochromator will select one part of the white beam at a particular color (or wavelength) This one-color

12

光子学

In contrast to classical storage quantum memory forbids measurement of the optical field during saving and retrieving processes In other words Akimov said storage of non-classical quantum light ndash such as squeezed light or a single photon ndash should occur without knowing which optical fields have been stored and retrieved because otherwise the quantum state would be irreversibly destroyed during the measurement procedure However our protocol allows quantum storage since transfer between optical excitation and spin excitation does not require state measurement In other words the new protocol transfers a quantum superposition between optically coupled states (optical excitation) and the other pair of states coupled by a magnetic field (spin excitation) In this process no measurement takes place ndash just the transformation between different excitations

Regarding the quantum well the researchers specifically concentrated on an n-doped CdTe(CdMg)Te quantum well where storage time increased from picoseconds to tens of nanoseconds The structures were grown by Prof Grzegorz Karczewski and Prof Tomasz Wojtowiczin the Institute of Physics Polish Academy of Sciences in Warsaw using molecular beam epitaxy (CdTe(CdMg)Te is a cadmium telluride compound in which some of the cadmium is replaced by magnesium) The cadmium telluride semiconductor quantum well structure is a model proof-of-principle system for extending the photon echo delay Akimov told Physorg In such two-dimensional structures the carriers are confined in one direction this results in well-defined spin-level system and clean selection rules for optical transitions Secondly n-type doping of barriers with donors provides excess electrons in the quantum well which again are responsible for long-lived spin excitations

That said while using cadmium telluride quantum wells enabled very clean experiments on the ensemble of trions to be performed because their optical transitions are well isolated spectrally the researchers had to maintain weak optical pulse intensity to prevent interactions between weakly localized trions In order to increase the efficiency and to achieve longer delays for photon echoes it is necessary to try different type of semiconductor nanostructures which can be also based on other compounds Akimov explained One of such candidates is the ensemble of quantum dots where the electrons and holes are localized much more strongly in all three dimensions This is in contrast to quantum wells where strong confinement is present only along one direction

Finally Akimov noted that in semiconductors there are two types of fundamental optical excitations excitons (electron-hole pairs bound by Coulomb interactions) and trions ndash charged excitons consisting of an exciton bound with an excess electron or hole A trion is a three-particle complex and after its decay theres always an excess carrier left he explained In our case we deal with excess electrons which possess spin 12 Therefore in contrast to excitons it is possible to save information about

optical excitation in the spin of the excess electrons left after trion recombination This transformation is only possible when an external magnetic field is applied since it allows us to mix the electronic states in the proper way The most salient advantage of quantum well structures is that exciton and trion resonances are spectrally well separated ndash meaning that picosecond laser pulses let the researchers address only the optical transition from excess electron to trion

For all of these seemingly daunting challenges the researchers key insight was to study photon echoes emitted by trions in semiconductor nanostructures subject to an external magnetic field ndash and by then using a transient four-wave mixing (FWM) technique to measure magnetic-field-induced long-term photon echoes they were able to show that photon echoes can be retrieved from excess electron spin ensembles (Transient four-wave mixing belongs to time-resolved coherent spectroscopy based on non-linear optics whereby interactions between two or three optical pulses in medium produce fourth optical field in the signal) We used ultrashort optical pulses with duration of about one picosecond Akimov explained because efficient optical excitation in semiconductors is possible on the order of 01-1ps In addition he said the experiments had to be performed at extremely low temperatures ndash about two degrees above absolute zero ndash in order to keep the system robust against interactions with phonons (collective excitations similar to quasiparticles in a periodic elastic arrangement of atoms or molecules in condensed matter such as solids and some liquids) as well as to suppress other relaxation mechanisms which could lead to irreversible dephasing of optical and spin excitations and thereby loss of coherence From an experimental point of view he added our primary challenge was combining four-wave mixing with ultrashort picosecond pulses and external magnetic fields at low temperatures

The current study demonstrates that photon echoes can be retrieved from the spin system on the timescale of 10-100 ns However Akimov said this time delay is still too short for practical applications In order to solve this problem we need to extend the decay time of spin excitations There are two possible reasons for decay of spin excitations dephasing of spins and irreversible spin relaxation through decoherence ndash that is due to interaction with the environment The first point can be addressed by means of spin resonance techniques using dynamic decoupling he explained which is an approach largely the same as photon echo but based on periodic excitation of the spin ensemble with microwave pulses which lead to spin echoes In that way it will be possible to keep the spin ensemble of excess electrons free of dephasing and timescales up to tens or even hundreds of microseconds may be achieved However irreversible spin relaxation is more difficult to solve ndash but there are several attempts to reduce hyperfine interaction between nuclear and electron spins One of the solutions would be to use compounds

11

光电技术情报 2015年第1期（总第6期）

with isotopes carrying zero nuclear spin In this case storage times in the milliseconds can be available

In fact Akimov added that the scientists plan to investigate extending the timescale of photon echoes further into the microsecond and millisecond range Well test other nanostructures such as quantum dots with strong trion localization and will search for new materials with suppressed spin excitation decay In addition he said well use spin resonance techniques in order to eliminate spin dephasing in the ensemble of excess electrons

Akimov also mentioned applications beyond optical memory While most applications are related to optical memories where the optical information should be saved and released on demand he said theres another fundamental aspect Our studies combine optical and spin phenomena and in this sense its very interesting to explore our approach for monitoring the time evolution of combined optical and spin excitations

A unique feature of photon echo experiments is the dephasing which already occurs at the initial stage directly after excitation with the first pulse where the sequence of two linearly polarized pulses create comprehensive spin distribution for excess electrons without net spin polarization While each of the electrons has a certain well-defined spin the ensemble spin polarization or average spin is zero ndash and the information about the optical pulses such as polarization and interpulse delay is encoded in the spins of excess electrons This differs from conventional techniques Akimov pointed out For example in well-established pump-probe experiments the non-zero spin polarization in the system is first induced by a circularly polarized pump pulse and then the evolution of the spin in time is probed The scientists therefore believe that their approach based on photon echoes in a magnetic field constitutes an interesting platform for fundamental spin studies

Along these exploratory lines Physorg asked Akimov if given that storage times of seconds or longer might be possible by further exploiting the hyperfine interaction between electrons and nuclei in quantum dots quantum wells and self-assembling quantum dots might at some point be combined in a single quantum system that emulates human short- and long-term memory I think we are still far from that he replied In order to achieve this goal it would be necessary to establish a net of such quantum dot ensembles analogous to cells which would communicate between each other He added that while he does not exclude such possibility he emphasizes that such a quantum system would very complex and would contain and integrate far more than a simple set of quantum nanostructures Several challenging issues such as communication between different ensembles have to be addressed and for that it is necessary to accomplish directed and selective coupling of light at the nanoscale in and out of the cells Accordingly realization of such a network would need integration of photonic crystals or waveguide layers which can be based on semiconductors

Nevertheless he concluded this is a special area of research which deserves a lot of attention

httpphysorgnews2014-10-optical-storage-lifetime-photon-echoeshtml

11 1-X-ray powder diffraction beamline at NSLS-II takes first beam and first data

简介美国国家同步辐射光源 II 的 X 射线粉末衍

射光束线首次捕捉到光这标志着他们的研究进入到了

一个新阶段下一步要做的是尽快将其转化成科技成

果 On November 6 Eric Dooryhee walked into a crowd of

people excitedly talking at the X-ray Powder Diffraction (XPD) beamline beaming an enormous smile The group broke into applause for the enormous achievement they had gathered to celebrate the operators had opened a shutter to the electron storage ring of the National Synchrotron Light Source II and captured light for the first time at the XPD beamline It was the second beamline at NSLS-II to achieve x-ray beam

This is a big day for all of us said Dooryhee the Powder Diffraction Beamline Group Leader The list of acknowledgements he made reflected the huge effort of many support groups across the Photon Sciences Directorate and beyond that made the milestone possible administration and procurement staff surveyors riggers carpenters vacuum specialists mechanical and electrical utilities technicians equipment protection and personnel safety staff x-ray optics metrology experts scientists designers and engineers We couldnt have achieved our first light without the commitment and support of many collaborators around the Lab including work with Peter Siddons and his group who are developing several state-of-the-art detectors for XPD

The XPD core team includes Sanjit Ghose beamline scientist in charge of operating XPD and consolidating its research program Hengzi Wang mechanical engineer John Trunk beamline technician Andrew DeSantis mechanical designer and Wayne Lewis controls engineer

The complexity of this accomplishment came through when Dooryhee talked about the effort put in by Wayne Lewis the controls engineer for XPD

How many motors vacuum gauges and sensors did you have to take ownership of Hundreds Dooryhee asked Lewis wryly smiled and responded Yeah a few

It was Lewis who ultimately opened the shutter allowing the white x-ray beam for the first time to travel through a diamond window and several other components until it was purposely intercepted by a beam stop Both the window and the beamstop emitted a bright fluorescent light once struck by the x-rays and the x-ray footprint at several locations down the beam pipe could thus be imaged and shown on large screens to everyone present

Eventually once commissioning starts a monochromator will select one part of the white beam at a particular color (or wavelength) This one-color

12

光子学

with isotopes carrying zero nuclear spin In this case storage times in the milliseconds can be available

In fact Akimov added that the scientists plan to investigate extending the timescale of photon echoes further into the microsecond and millisecond range Well test other nanostructures such as quantum dots with strong trion localization and will search for new materials with suppressed spin excitation decay In addition he said well use spin resonance techniques in order to eliminate spin dephasing in the ensemble of excess electrons

Akimov also mentioned applications beyond optical memory While most applications are related to optical memories where the optical information should be saved and released on demand he said theres another fundamental aspect Our studies combine optical and spin phenomena and in this sense its very interesting to explore our approach for monitoring the time evolution of combined optical and spin excitations

A unique feature of photon echo experiments is the dephasing which already occurs at the initial stage directly after excitation with the first pulse where the sequence of two linearly polarized pulses create comprehensive spin distribution for excess electrons without net spin polarization While each of the electrons has a certain well-defined spin the ensemble spin polarization or average spin is zero ndash and the information about the optical pulses such as polarization and interpulse delay is encoded in the spins of excess electrons This differs from conventional techniques Akimov pointed out For example in well-established pump-probe experiments the non-zero spin polarization in the system is first induced by a circularly polarized pump pulse and then the evolution of the spin in time is probed The scientists therefore believe that their approach based on photon echoes in a magnetic field constitutes an interesting platform for fundamental spin studies

Along these exploratory lines Physorg asked Akimov if given that storage times of seconds or longer might be possible by further exploiting the hyperfine interaction between electrons and nuclei in quantum dots quantum wells and self-assembling quantum dots might at some point be combined in a single quantum system that emulates human short- and long-term memory I think we are still far from that he replied In order to achieve this goal it would be necessary to establish a net of such quantum dot ensembles analogous to cells which would communicate between each other He added that while he does not exclude such possibility he emphasizes that such a quantum system would very complex and would contain and integrate far more than a simple set of quantum nanostructures Several challenging issues such as communication between different ensembles have to be addressed and for that it is necessary to accomplish directed and selective coupling of light at the nanoscale in and out of the cells Accordingly realization of such a network would need integration of photonic crystals or waveguide layers which can be based on semiconductors

Nevertheless he concluded this is a special area of research which deserves a lot of attention

httpphysorgnews2014-10-optical-storage-lifetime-photon-echoeshtml

11 1-X-ray powder diffraction beamline at NSLS-II takes first beam and first data

简介美国国家同步辐射光源 II 的 X 射线粉末衍

射光束线首次捕捉到光这标志着他们的研究进入到了

一个新阶段下一步要做的是尽快将其转化成科技成

果 On November 6 Eric Dooryhee walked into a crowd of

people excitedly talking at the X-ray Powder Diffraction (XPD) beamline beaming an enormous smile The group broke into applause for the enormous achievement they had gathered to celebrate the operators had opened a shutter to the electron storage ring of the National Synchrotron Light Source II and captured light for the first time at the XPD beamline It was the second beamline at NSLS-II to achieve x-ray beam

This is a big day for all of us said Dooryhee the Powder Diffraction Beamline Group Leader The list of acknowledgements he made reflected the huge effort of many support groups across the Photon Sciences Directorate and beyond that made the milestone possible administration and procurement staff surveyors riggers carpenters vacuum specialists mechanical and electrical utilities technicians equipment protection and personnel safety staff x-ray optics metrology experts scientists designers and engineers We couldnt have achieved our first light without the commitment and support of many collaborators around the Lab including work with Peter Siddons and his group who are developing several state-of-the-art detectors for XPD

The XPD core team includes Sanjit Ghose beamline scientist in charge of operating XPD and consolidating its research program Hengzi Wang mechanical engineer John Trunk beamline technician Andrew DeSantis mechanical designer and Wayne Lewis controls engineer

The complexity of this accomplishment came through when Dooryhee talked about the effort put in by Wayne Lewis the controls engineer for XPD

How many motors vacuum gauges and sensors did you have to take ownership of Hundreds Dooryhee asked Lewis wryly smiled and responded Yeah a few

It was Lewis who ultimately opened the shutter allowing the white x-ray beam for the first time to travel through a diamond window and several other components until it was purposely intercepted by a beam stop Both the window and the beamstop emitted a bright fluorescent light once struck by the x-rays and the x-ray footprint at several locations down the beam pipe could thus be imaged and shown on large screens to everyone present

Eventually once commissioning starts a monochromator will select one part of the white beam at a particular color (or wavelength) This one-color

12

光子学

(monochromatic) x-ray beam will go past the white beam stop and will be reflected off a four-and-a-half-foot long mirror and over to the sample

As we open the shutter the beam is spot on said Dooryhee We find the beam is very stable and we are extremely happy with these start-up conditions thanks to the work accomplished by the Accelerator Division This concludes 5 years of preparation and installation and now is the beginning of a new phase for us We have to commission the entire beamline with the x-rays on get beam safely into the experimental station and transition to science as soon as we can

Part of this open house celebration at XPD was a demonstration of the 250-pound robotic sample changer which will operate within the lead-lined hutch while the x-ray beam is on This robot will be able to perform unmanned and repetitive collection of data on a variety of sample holders in a reliable reproducible and fast way XPD is designed with high throughput efficiency in mind

The robot will also enable landmark experiments of radioactive samples like those proposed by Lynne Ecker of Brookhavens Nuclear Science and Technology Department Ecker was awarded $980000 from the US Department of Energys Nuclear Energy Enabling Technologies program that will enable cross-cutting research at XPD and will fundamentally improve the safety and performance of nuclear reactors

BNL is a truly outstanding environment and our chance

with NSLS-II is to interact with very high-level scientific collaborators across the Laboratory that will enable XPD to host premier work from the Center for Functional Nanomaterials the Nuclear Energy group Chemistry and Physics said Dooryhee And XPD is also planning to accommodate a part of the high-pressure program at NSLS-II that includes a large volume press and diamond-anvil cells that were previously in use at NSLS in collaboration with the COMPRES consortium and Stony Brook University

The XPD beamline research will focus on studies of catalysts batteries and other functional and technological materials under the conditions of synthesis and operation and Dooryhee is optimistic about the science to come He is also excited about the intersection of XPDs scientific program with Brookhavens Laboratory Directed Research and Development (LDRD) program Young active

committed scientists will have access to our beamline and will help us develop new capabilities Current LDRD-XPD partnerships have already led to the invention of a novel slit system for probing the sample with x-rays at well controlled locations and are helping develop a new method called Modulation Enhanced Diffraction

Just before publication of this feature Dooryhee reported that the XPD team managed to condition and focus the x-ray monochromatic beam after only three weeks of commissioning Shown here is the first diffraction image from NSLS-II

The very first scientific sample run on XPD is a new material system TaSe2-xSx mdashSulfur-doped Tantalum Selenidemdashthat is being studied by Cedomir Petrovic in the Condensed Matter Physics and Materials Sciences department at Brookhaven

At low temperature electrons in both the pure TaSe2 and TaS2 compounds spontaneously form into charge density waves (CDWs) like ripples on the surface of a pond but characteristics of the waves (such as the wavelength) are different The question is when you vary composition smoothly from one end of the series to the other end (meaning vary x in TaSe2-xSx) how do the waves cross over from one to the other The surprise is that in between the waves disappear and are replaced by superconductivity ndash the ability of the material to conduct electricity with no resistance

It is like mixing red paint and white paint and instead of getting pink you get blue after mixing said professor Simon Billinge joint appointee with Brookhaven and Columbia University who has been the spokesperson and the chair of the beamline advisory team for the XPD beamline since the inception of the project The data from XPD provides crucial information about how the atomic structure varies with composition which is used to understand the delicate interplay of CDW and superconducting behavior in these materials

As well as being interesting in their own right these studies at XPD are important to understand the phenomenon of unconventional high-temperature superconductivity currently our best hope for technological devices for low loss power transmission where a similar interplay of CDW and superconductivity is seen added Dooryhee

httpphysorgnews2014-11-x-ray-powder-diffraction-beamline-nsls-iihtml

13

光电技术情报 2015年第1期（总第6期）

二量子物理

12 Spiral laser beam creates quantum whirlpool 简介澳大利亚国立大学科学家们设计出螺旋激光

束并用于生成混合光物质颗粒涡流

Robert Dall with the spiral laser beam

Physicists at Australian National University have engineered a spiral laser beam and used it to create a whirlpool of hybrid light-matter particles called polaritons Creating circulating currents of polaritons ndash vortices ndash and controlling them has been a long-standing challenge said leader of the team theoretician Dr Elena Ostrovskaya from the Research School of Physics and Engineering

We can now create a circulating flow of these hybrid particles and sustain it for hours

Polaritons are hybrid particles that have properties of both matter and light The ability to control polariton flows in this way could aid the development of completely novel technology to link conventional electronics with new laser and fibre-based technologies

Polaritons form in semiconductors when laser light interacts with electrons and holes (positively charged vacancies) so strongly that it is no longer possible to distinguish light from matter

The team created the spiral beam by putting their laser through a piece of brass with a spiral pattern of holes in it This was directed into a semiconductor microcavity a tiny wafer of aluminium gallium arsenide a material used in LEDs sandwiched between two reflectors

The vortices have previously only appeared randomly and always in pairs that swirl in opposite directions said Dr Robert Dall who led the experimental part of the project

However by using a spiral mask to structure our laser we create a chiral system that prefers one flow direction Therefore we can create a single stable vortex at will

The brass mask used to create the spiral laser beam The spiral is

created by a circular pattern of holes of increasing size

These vortices are an example of quantum fluid behaviour in which the polaritons coalesce into a rare state of matter known as a Bose-Einstein condensate

As well as being a window into the quantum world these polaritonic vortices could be used to construct extremely sensitive detectors of electromagnetic fields similar to SQUIDS (Superconducting QUantum Interference Devices) Dr Ostrovskaya said

They could also be employed as quantum information carriers

The ANU team has pioneered the study of microcavity polaritons in Australia and hope their success will inspire other research groups around the country

Polaritonics is a rapidly developing research field all around the world We hope we can build a network of groups researching these devices across Australia and joining the international effort Dr Ostrovskaya said

httpphysorgnews2014-11-spiral-laser-quantum-whirlpoolhtml

13 Twisted light waves sent across Vienna 简介维也纳大学与量子光学和量子通信研究院的

研究人员组成的团队在维也纳市上空 3公里范围内进行

了扭曲光波传送实验这是首次在室外大距离范围内进

行的扭曲光波传送实验研究人员是用绿激光束通过雷

达塔上的透镜进行纠缠态光波传送的这一实验有利于

研究人员在传统通信及量子通信领域进行研究以便充

分利用光数据承载能力进行实际应用

The 3 kilometer free-space experiment was performed in the city of

Vienna from ZAMG (Zentralanstalt fuumlr Meteorologie und Geodynamik Central Institute for Meteorology and Geodynamics) to our institute IQOQI Picture of an alignment laser hellip

A group of researchers from Austria have sent twisted beams of light across the rooftops of Vienna

It is the first time that twisted light has been transmitted over a large distance outdoors and could enable researchers to take advantage of the significant data-carrying capacity of light in both classical and quantum communications

The results of the experiment have been published today 12 November in the Institute of Physics and German Physical Societys New Journal of Physics and are accompanied by a video abstract which can viewed below

Previous research has shown that if a beam of a certain colour or wavelength of light is twisted into a corkscrew

量子物理

14

shape the number of channels that data can be transmitted through can be drastically increased Instead of using one wavelength of light as one channel of communication the light can be theoretically twisted with an infinite number of turns with each configuration acting as a single communication channel

This twisting characteristic known as orbital angular momentum (OAM) has been exploited by researchers in the past with some showing that it can be used to transmit 25 terabits of data per secondmdashthe carrying capacity of more than 66 DVDsmdashthrough an optical fibre

Yet optical fibres are not always suitable or available for certain types of communication where light is usedmdashsuch as Earth to satellite communicationsmdashso researchers have been trying to send twisted light over free space whilst at the same time avoiding disturbances from air turbulence So far this has only been achieved over small distances in the lab

In the current study the researchers from the University of Vienna and the Institute for Quantum Optics and Quantum Information used a green laser beam to send twisted light through a lens on top of a radar tower at the Central Institute for Meteorology and Geodynamics in Vienna

The researchers sent 16 different twisted configurations of a specific wavelength of light to a receiver 3 km away at the University of Vienna A camera was used to capture the beams of light and an artificial neural network was deployed to reveal the pattern and remove any possible disturbances that may have been caused by air turbulence

httpphysorgnews2014-11-viennahtml

15

光电技术情报 2015年第1期（总第6期）

三纳米物理

14 Magnetic fields and lasers elicit graphene secret

简介科学家首次研究被誉为ldquo奇特材料rdquo的石墨烯

在磁场中的电子运动发现了令人费解的现象来自柏

林法国捷克和美国的科学家们用一个模型对他们所

观察到的现象进行了详细的描述对此现象的理解有利

于新型激光器的制造

This is a model of the electron redistribution through Auger

scattering that HZDR researchers discovered in graphene Scientists at the Helmholtz-Zentrum

Dresden-Rossendorf (HZDR) have studied the dynamics of electrons from the wonder material graphene in a magnetic field for the first time This led to the discovery of a seemingly paradoxical phenomenon in the material Its understanding could make a new type of laser possible in the future Together with researchers from Berlin France the Czech Republic and the United States the scientists precisely described their observations in a model and have now published their findings in the scientific journal Nature Physics

Graphene is considered a wonder material its breaking strength is higher than steel and it conducts electricity and heat more effectively than copper As a two-dimensional structure consisting of only a single layer of carbon atoms it is also flexible nearly transparent and approximately one million times thinner than a sheet of paper Furthermore shortly after its discovery ten years ago scientists recognized that the energy states of graphene in a magnetic field - known as Landau levels - behave differently than those of semiconductors Many fascinating effects have been discovered with graphene in magnetic fields but the dynamics of electrons have never been studied in such a system until now explains physicist Dr Stephan Winnerl from HZDR

The HZDR researchers exposed the graphene to a four-Tesla magnetic field - forty times stronger than a horseshoe magnet As a result the electrons in graphene occupy only certain energy states The negatively charged particles were virtually forced on tracks These energy levels were then examined with free-electron laser light pulses at the HZDR The laser pulse excites the electrons into a certain Landau level A temporally delayed pulse then probes how the system evolves explains Martin Mittendorff doctoral candidate at the HZDR and first author of the paper

Electron redistribution surprises scientists The result of the experiments has astonished the

researchers This particular energy level into which new electrons were pumped using the laser gradually emptied Winnerl illustrates this paradoxical effect using an everyday example Imagine a librarian sorting books on a bookshelf with three shelves She places one book at a time from the lower shelf onto the middle shelf Her son is simultaneously helping by taking two books from the middle shelf placing one of them on the top shelf the other on the bottom The son is very eager and now the number of books on the middle shelf decreases even though this is precisely the shelf his mother wishes to fill

With intense light from the HZDRs free-electron lasers materials

can be examined on the atomic level Because there were neither experiments nor theories

regarding such dynamics before the Dresden physicists initially had difficulty interpreting the signals correctly After a number of attempts however they found an explanation collisions between electrons cause this unusual rearrangement This effect has long been known as Auger scattering but no one expected it would be so strong and would cause an energy level to become depleted explains Winnerl

This new discovery could be used in the future for developing a laser that can produce light with arbitrarily adjustable wavelengths in the infrared and terahertz ranges Such a Landau-level laser was long considered impossible but now with graphene this semiconductor physicists dream could become a reality says Winnerl enthusiastically

Berlin researchers calculate complex model for Dresden experiments

After the fundamental model used in the experiments had worked satisfactorily the precise theoretical work followed which was carried out at the Technical University Berlin Berlin scientists Ermin Malic and Andreas Knorr confirmed using complex calculations the Dresden groups assumptions and provided detailed insights into the underlying mechanisms The HZDR researchers additionally cooperated with the French High Magnetic Field Laboratory in Grenoble (Laboratoire National des Champs Magneacutetiques Intenses - LNCMI) the Charles University Prague and the Georgia Institute of Technology in Atlanta (USA)

纳米物理

16

httpphysorgnews2014-11-magnetic-fields-lasers-elicit-graphenehtml

15 Engineers efficiently mix light at the nanoscale

简介宾夕法尼亚大学研究人员设计出纳米线系

统为解决光子系统中输入光混频奠定了基础

Light emitted from the underside of the cavity THe dotted outlines

represents the orientation of the cadmium selenide nanowire The race to make computer components smaller and

faster and use less power is pushing the limits of the properties of electrons in a material Photonic systems could eventually replace electronic ones but the fundamentals of computation mixing two inputs into a single output currently require too much space and power when done with light

Researchers at the University of Pennsylvania have engineered a nanowire system that could pave the way for this ability combining two light waves to produce a third with a different frequency and using an optical cavity to amplify the intensity of the output to a usable level

The study was led by Ritesh Agarwal professor of materials science and engineering in Penns School of Engineering and Applied Science and Ming-Liang Ren a post-doctoral researcher in his lab Other members of the Agarwal lab Wenjing Liu Carlos O Aspetti and Liaoxin Sun contributed to the study

It was published in Nature Communications Current computer systems represent bits of

informationmdashthe 1s and 0s of binary codemdashwith electricity Circuit elements such as transistors operate on these electric signals producing outputs that are dependent on their inputs

Mixing two input signals to get a new output is the basis of computation Agarwal said Its easy to do with electric signals but its not easy to do with light as light waves dont normally interact with one another

A schematic of the optical cavity

The difficulty inherent in mixing light may seem counterintuitive given the gamut of colors on TV or computer screen that are produced solely by combinations of red green and blue pixels The yellows oranges and purples those displays make however are a trick of perception not of physics Red and blue light are simply experienced simultaneously rather than combined into a single purple wavelength

So-called nonlinear materials are capable of this kind of mixing but even the best candidates in this category are not yet viable for computational applications due to high power and large volume constraints

A nonlinear material such a cadmium sulfide can change the frequency and thus the color of light that passes through it Ren said but you need a powerful laser and even so the material needs to be a many micrometers and even up to millimeters thick That doesnt work for a computer chip

To reduce the volume of the material and the power of the light needed to do useful signal mixing the researchers needed a way to amplify the intensity of a light wave as it passed through a cadmium sulfide nanowire

The researchers achieved this through a clever bit of optical engineering partially wrapping the nanowire in a silver shell that acts like an echo chamber Agarwals group had employed a similar design before in an effort to create photonic devices that could switch on and off very rapidly This quality relied on a phenomenon known as surface plasmon resonance but by changing the polarization of the light as it entered the nanowire the researchers were able to better confine it to the frequency-altering nonlinear part of the device the nanowire core

By engineering the structure so that light is mostly contained within the cadmium sulfide rather than at the interface between it and the silver shell we can maximize the intensity while generating the second harmonic Ren said

Like a second harmonic played on a guitar string this meant doubling the frequency of the light wave Information in a photonic computer system could be encoded in a waves frequency or the number of oscillations it makes in a second Being able to manipulate that quality in one wave with another allows for the fundamentals of computer logic

We want to show we can sum two frequencies of lightAgarwal said so we simplified the experiment By taking one frequency and adding it to itself you get double the frequency in the end Ultimately we want to be able to

17

光电技术情报 2015年第1期（总第6期）

tune the light to whatever frequency is needed which can be done by altering the size of the nanowire and the shell

Most important however was that this frequency mixing was possible on the nanoscale with very high efficiency The researchers optical cavity was able to increase the output waves intensity by more than a thousand times

The frequency-changing efficiency of cadmium sulfide is intrinsic to the material but it depends on the volume of the material the wave passes through Agarwal said By adding the silver shell we can significantly decrease the volume needed to get a usable signal and push the device size into the nanoscale

httpphysorgnews2014-11-efficiently-nanoscalehtml

16 Two good things that are better together STM combined with X-ray synchrotron microscopy

简介俄亥俄大学阿尔贡国家实验室的研究团队将

扫描隧道显微镜与同步 X 射线结合起来在铜表面获得

2 纳米分辨率的独立镍簇化学指纹图谱并研制出成像

工具在材料和生物科学领域有很大发展潜力

Localized x-ray cross-section of a Ni island (a) Perspective

three-dimensional view of a STM topography scan (110 times 60 nm2 minus1 V 1 nA) (b) Height profile of the line shown in the topography scan (c) X-ray cross section of a single hellip

(Physorg) mdashOver the past three decades scanning tunneling microscopy (STM) has rapidly become a major component of the condensed matter physics toolbox While STM can provide vast quantities of data about the electronic structural and magnetic properties of materials at atomic resolution its Achilles heel is its inability to characterize elemental species But a team from Argonne National Laboratory and Ohio University has found a way around this limitation by combining STM with the spectroscopic versatility of synchrotron x-rays achieving

chemical fingerprinting of individual nickel clusters on a copper surface at a resolution of 2 nm creating a powerful and versatile nanoscale imaging tool with exciting promise and potential for the materials and biological sciences Their work was published in Nano Letters

Working at the Center for Nanoscale Materials (CNM)X-ray Science Division 26-ID beamline of the US Department of Energys Advanced Photon Source the researchers took advantage of some new technological innovations developed by Argonne researchers

However the team had to overcome some experimental hurdles to combine STM with synchrotron x-rays The resolution and sensitivity of STM can be adversely affected by photoejected electrons from the sample interfering with the measurement of tunneling effects

The Argonne researchers invented and patented a nanofabricated smart tip for the scanning tunneling microscope that sharply focuses detection of electrons solely to those collected at the scanning tip where it interacts with the sample ignoring the background electrons from the sidewalls of the tip The various coatings for the smart tip were grown at the CNM and then the tip apex was exposed via focused ion beam milling carried out at the CNM Electron Microscopy Center (EMC) (The APS CNM and EMC at Argonne are Office of Science user facilities)

A diagram of the imaging setup featuring the STM smart tip and

an image of Ni clusters (green) on the Cu surface (red) The smart tip consists of a sharp conducting tip (green) coaxially coated by an insulating layer (gray) a thin seed hellip

The team also developed a filter circuit that separates the chemical and magnetic data from the x-ray-induced currents and topographical data from conventional tunneling effects into two channels allowing them to be recorded separately without mutual interference

Using the markedly enhanced resolution and sensitivity made possible with these advances in synchrotron x-ray tunneling microscopy (SX-STM) the ArgonneOhio University experiment team analyzed nickel clusters deposited on a copper surface Usually because chemical fingerprinting using x-rays is based on photoionization cross sections such measurements are averaged over a rather wide surface area and depth But the new technique

18

纳米物理

was able to image and obtain a photoionization cross section of a single nickel cluster on the sample surface with 2-nm resolution

We have demonstrated a world record in the spatial resolution of chemical imaging using synchrotron x-ray scanning tunneling microscopy said Saw-Wai Hla a co-author of the Nano Letters article

This has a tremendous impact for many scientific areas including materials science chemistry and energy materials said co-author Volker Rose

Both that remarkable resolution and the precise chemical fingerprinting of individual nickel nanoclusters were also clearly evident in the topographic images of the sample surface even down to the height of a single atom The experimenters note that the thickness of individual clusters appears to have no effect on the contrast intensity of their chemical signature They suggest that because tunneling is a local effect sensitive only to the topmost layer of materials this phenomenon as observed topographically results from the tunneling of x-ray excited photoelectrons from states between the Fermi level and the work function

While the current experiments were conducted at room temperature the researchers anticipate achieving even better resolution in SX-STM at far lower temperatures

Even in its present form the techniques demonstrated here can revolutionize nanoscale imaging in realms far beyond materials science including electronics and biology By overcoming the inherent limitations of both STM and x-ray microscopy this new work has also combined the strengths of each to create a powerful and versatile imaging tool with an exciting promise and potential

httpphysorgnews2014-11-good-stm-combined-x-ray-synchrotronhtml

17 Method for symmetry-breaking in feedback-driven self-assembly of optical metamaterials

简介加利福尼亚伯克利大学研究团队首次成功实

现对称破裂用他们的新方法可以获得独特的电磁回

应研究结果发表在《自然纳米技术》上题目为光

超材料反馈驱动自组装的对称破裂

Simulation of feedback driven self-assembly in mass assembly-line

The tilted network indicates aqueous flow in space (blue reservoir) The plasmon gauged potential (red) phothermally dissociates unwanted assemblies and re-assembles into the desired dimers

Physorg) mdashIf you can uniformly break the symmetry of nanorod pairs in a colloidal solution youre a step ahead of the game toward achieving new and exciting metamaterial properties But traditional thermodynamic -driven colloidal assembly of these metamaterials which are materials defined by their non-naturally-occurring properties often result in structures with high degree of symmetries in the bulk material In this case the energy requirement does not allow the structure to break its symmetry

In a study led by Xiang Zhang director of Berkeley Labs Materials Sciences Division he and his research group at the University of California (UC) Berkeley achieved symmetry-breaking in a bulk metamaterial solution for the first time Zhang and his group demonstrated self-assembled optical metamaterials with tailored broken-symmetries and hence unique electromagnetic responses that can be achieved via their new method The results have been published in Nature Nanotechnology The paper is titled Feedback-driven self-assembly of symmetry-breaking optical metamaterials in solution

We developed an innovative self-assembly route which could surpass the conventional thermodynamic limit in chemical synthetic systems explains Sui Yang lead author of the Nature Nanotechnology paper and member of Zhangs research group Specifically we use the materials own property as a self-correction feedback mechanism to self-determine the final structure

This led the group to produce nanostructures that have historically been considered impossible to assemble

The widely used method of metamaterial synthesis is top-down fabrication such as electron beam or focus ion beam lithography that often results in strongly anisotropic and small-scale metamaterials

People build metamaterials using top-down methods that include light exposure and electron beam exposure which are inefficient and costly says Xingjie Ni another lead author on the paper If we want to use metamaterials we need to develop a way to build them cheaply and efficiently

The bottom-up route fills these requirements Starting with a solution of colloidal nanorods Yang and Ni built on the common self-assembly technique used to build nanoparticles The twist that they added was to introduce a feedback mechanism by which to obtain the desired product

The desired product when synthesizing colloidal gold nanorods which are stabilized during growth to obtain preferential bonding along longitudinal facets is pairs of rods or dimers that are shifted by a certain amount their symmetry is uniformly broken

When you have this reaction you get all kinds of products You have a pair of nanorods with no shift at all relative to one another or a pair that are shifted too much or not enough This is a typical process and is governed by thermodynamics explains Yang

19

光电技术情报 2015年第1期（总第6期）

The team used a laser to excite the plasmonic resonance of specific particles produced in the reaction This allowed them to separate out the un-desired resonances indicating nanorod pairs that are not shifted the desired amount and dissociate those pairs using heat from the excitation

Only the desired resonance survives in this process Ni says Then the reaction can be repeated to produce more of the desired broken-symmetry particles based on their plasmonic signature Clear distinction in resonance profiles makes this a highly selective method

This is a brand new self-assembly fabrication method that people can commonly employ we use the materials own properties to drive nanostructure formation in solution This has the intrinsic value of making many structures in one batch

The method developed in Zhangs research group can be applied to many other nanoparticles indeed almost any structure that can self-assemble could be produced in this way This solves the problem of achieving large scale symmetric breaking and can open the door to new properties and applications

The unique feedback mechanism leads to precisely controlled nanostructures with beyond conventional symmetries and functionalities

As a demonstration in our paper we have synthesized a new class of symmetry-breaking optical metamaterials that have isotropic electromagnetic responses and can be used in a number of important applications such as subwavelength imaging optical cloaking and sensing says Yang

In contrast to the conventional wisdom that a materials structure determines its properties we provocatively suggest that the physical properties of materials by design may dictate the evolution of self-assembly and self-determine the structures of bulk materials concludes Zhang

httpphysorgnews2014-11-method-symmetry-breaking-feedback-driven-self-assembly-opticalhtml

20

纳米物理

四技术与应用

18 Ultra-short X-ray pulses explore the nano world

简介科学家们利用超短极强 X 射线闪光灯ldquo抓拍rdquo微小几何结构如分子中的原子排列等要想达到增强

空间和瞬时清晰度的目的需进一步掌握 X 射线的精确

持续时长及亮度一个国际科学家研究团队已经攻克了

这个难题他们首次直接对超短 X 射线闪光子峰进行测

量并确认了他们的预测即每单个闪光持续时间大约

800 阿秒

Undulator hall of Linac Coherent Light Source at SLAC

Ultra-short and extremely strong X-ray flashes as produced by free-electron lasers are opening the door to a hitherto unknown world Scientists are using these flashes to take snapshots of the geometry of tiniest structures for example the arrangement of atoms in molecules To improve not only spatial but also temporal resolution further requires knowledge about the precise duration and intensity of the X-ray flashes An international team of scientists has now tackled this challenge

X-ray flashes are a unique scientific tool They are generated by accelerating electrons to very high energy levels in kilometer-long vacuum tubes so-called linear accelerators and then deflecting them with specially arranged magnets In the process the particles emit X-ray radiation that is amplified until an ultra-short and intensive X-ray flash is released

Researchers use these X-ray flashes to resolve structures as small as one ten billionth of a meter (01 nanometer) in size That is roughly the diameter of a hydrogen atom In this way biomolecules for example can be imaged at extremely high resolution providing new insight into the nano cosmos of nature

Using two quickly sequenced flashes the researchers can even obtain information on structural changes during reactions The first laser flash triggers a reaction while the second measures structural changes during the reaction For this it is essential to know the precise duration and temporal intensity distribution of the X-ray flashes However hitherto it has not been possible to measure the ultra-short pulses directly

Researchers at the Technische Universitaumlt Muumlnchen (TUM) the Hamburg Center for Free-Electron Laser Science (CFEL) and the Max Planck Institute of Quantum

Optics (MPQ) in Garching in collaboration with other colleagues have now developed just such a methodology The respective experiments were done at the SLAC National Accelerator Laboratory in California (USA) by a team headed by Professor Reinhard Kienberger Dr Wolfram Helml (TUM) and Dr Andreas Maier (CFEL)

The scientists determined the duration of the X-ray flashes by modifying a process originally developed to measure ultra-short flashes of light The physicists directed the X-ray flashes into a vacuum chamber filled with a few atoms of an inert gas There they superimposed the flashes with 24 micrometer wavelength pulses of infrared light

When the X-ray flashes hit a gas atom they knock electrons out of the innermost shell setting them free After being liberated the electrons are accelerated or decelerated by the electrical field of the infrared light pulse The change in an electrons velocity is a function of when the light intercepts the electron and thus of the electrical field strength at the moment of ionization

Since electrons are set free during the full duration of an X-ray flash electrons emitted at different points in time feel different field strengths of the periodically oscillating infrared light As a result they are accelerated at varying rates The physicists can then calculate the duration of the original X-ray flash from the different arrival times of the electrons in a detector

Using this approach the researchers determined that the average pulse duration doesnt exceed four and a half femtoseconds ndash a femtosecond is a millionth of a billionth of a second (10-15 seconds) In addition the researchers obtained insight into the structure of the X-ray flashes

A characteristic of the intense X-ray flashes generated in free-electron lasers is their randomly changing pulse form A typical X-ray pulse comprises multiple contiguous shorter X-ray spikes The number and intensity of these spikes varies from one shot to the next

For the first time ever the researchers managed to measure these ultra-short sub-peaks directly and confirm predictions that the individual flashes last only around 800 attoseconds ndash an attosecond is a billionth of a billionth of a second (10-18 seconds) The new methodology allows the detailed direct temporal measurement of X-ray pulses and augments methodologies for determining pulse shape and length indirectly from the structure of the electron packets used to generate the flashes

The enhanced X-ray pulse measurement technology may also find application at the new Center for Advanced Laser Applications (CALA) at the Garching campus Researchers there are working on among other things generating even shorter X-ray pulses using high-energy lasers Pulses with a duration of only a few attoseconds would allow researchers to take snapshots of even faster processes in nature like the movement of electrons around atomic nuclei

However X-ray flashes provide not only basic research with new perspectives Medicine could also profit from the technology Ultra-short laser-like X-ray pluses serve not

21

光电技术情报 2015年第1期（总第6期）

only the investigation of the fastest physical processes at the core of matter but could because of their extremely high intensity also be used to destroy tumors following X-ray diagnosis explains Reinhard Kienberger professor for laser and X-ray physics at TU Muumlnchen and leader of the research consortium

httpphysorgnews2014-11-ultra-short-x-ray-pulses-explore-nanohtml

19 Tiny magnetic sensor deemed attractive 简介超感磁力传感器技术大量应用于探测未爆原

子弹地下管道地球物理勘测甚至大脑及心脏成像

等如图美国国家标准技术研究所研究的芯片级磁力

计其传感器只有大米粒那么高其顶部最宽的块状部

件是一个封闭的透明电池里边封装的是铷原子蒸汽

The NIST chip-scale magnetometer The sensor is about as tall as

a grain of rice The widest block near the top of the device is an enclosed transparent cell that holds a vapor of rubidium atoms

Ultra-sensitive magnetic sensor technology pioneered at PML may soon be commercialized for a host of applications from detection of unexploded bombs and underground pipes to geophysical surveying and perhaps even imaging of the brain and heart

In late October 2014 Geometrics of San Jose CA announced a technology license and development agreement with Texas Instruments to develop miniature magnetometers derived from work done by scientists in PMLs Atomic Devices and Instrumentation Group

The original prototype device produced in 2004 with funding from the US Defense Advanced Research Projects Agency featured a sensor about the size of a grain of rice that could measure changes in magnetic fields as small as one-millionth of the Earths field and required minimal electrical power

The device works by detecting tiny shifts ndash caused for example by magnetic properties of buried metals ndash in the way laser light interacts with an atomic vapor

httpphysorgnews2014-11-tiny-magnetic-sensor-deemedhtml

20 Robotics meet X-ray lasers in cutting-edge biology studies

简介美国斯坦福直线加速中心的科学家将目前

最亮的 X 射线激光器与机器人相结合开展了对蛋白质

的前沿问题研究使用机器人和其他自动化部件并运用

X 射线激光脉冲精确地选取样本进行研究能加速完成

纳米级晶体蛋白质三维结构映射等

This illustration shows an experimental setup used in

crystallography experiments at SLACs Linac Coherent Light Source X-ray laser The drum-shaped container at left stores supercooled crystal samples that are fetched by a robotic arm and hellip

Scientists at the Department of Energys SLAC National Accelerator Laboratory are combining the speed and precision of robots with one of the brightest X-ray lasers on the planet for pioneering studies of proteins important to biology and drug discovery

The new system uses robotics and other automated components to precisely maneuver delicate samples for study with the X-ray laser pulses at SLACs Linac Coherent Light Source (LCLS) This will speed efforts to map the 3-D structures of nanoscale crystallized proteins which are important for designing targeted drugs and synthesizing natural systems and processes

A new way to study biology This is an efficient highly reliable and automated way

to obtain high-resolution 3-D structural information from small sizes and volumes of samples and from samples that are too delicate to study using other X-ray sources and techniques said Aina Cohen who oversaw the development of the platform in collaboration with staff at LCLS and at SLACs Stanford Synchrotron Radiation Lightsource (SSRL) both DOE Office of Science User Facilities

She is co-leader of the Macromolecular Crystallography group in the Structural Molecular Biology (SMB) program at SSRL which has used robotic sample-handling systems to run remote-controlled experiments for a decade

The new setup at LCLS is described in the Oct 31 edition of Proceedings of the National Academy of Sciences It includes a modified version of a goniometer a sample-handling device in use at SSRL and many other synchrotrons as well as a custom version of an SSRL-designed software package that pinpoints the position of crystals in arrays of samples

技术与应用

22

Equipment used in a highly automated X-ray crystallography system at SLACs Linac Coherent Light Source X-ray laser The metal drum at lower left contains liquid nitrogen for cooling crystallized samples studied with LCLSs intense X-ray hellip

LCLS with X-ray pulses a billion times brighter than more conventional sources has already allowed scientists to explore biological samples too small or fragile to study in detail with other tools The new system provides added flexibility in the type of samples and sample-holders that can be used in experiments

Rather than injecting millions of tiny randomly tumbling crystallized samples into the path of the pulses in a thin liquid stream ndash common in biology experiments at LCLS ndash the goniometer-based system places crystals one at a time into the X-ray pulses This greatly reduces the number of crystals needed for structural studies on rare and important samples that require a more controlled approach

Early successes This system adapts common synchrotron techniques for

use at LCLS which is very important said Henrik Lemke staff scientist at LCLS There is a large community of scientists who are familiar with the goniometer technique

The system has already been used to provide a complete picture of a proteins structure in about 30 minutes using only five crystallized samples of an enzyme moved one at a time into the X-rays for a sequence of atomic-scale snapshots

It has also helped to determine the atomic-scale structures of an oxygen-binding protein found in muscles and another protein that regulates heart and other muscle and organ functions

We have shown that this system works and we can further automate it Cohen said Our goal is to make it easy for everyone to use

Many biological experiments at LCLS are conducted in air-tight chambers The new setup is designed to work in the open air and can also be used to study room-temperature samples although most of the samples used in the system so far have been deeply chilled to preserve their structure One goal is to speed up the system so it delivers samples and measures the resulting diffraction patterns as fast as possible ideally as fast as LCLS delivers pulses 120 times a second

The goniometer setup is the latest addition to a large toolkit of systems that deliver a variety of samples to the LCLS beam and a new experimental station called MFX that is planned at LCLS will incorporate a permanent version

Team effort Developed through a collaboration of SSRLs Structural

Molecular Biology program and the Stanford University School of Medicine the LCLS goniometer system reflects increasing cooperation in the science of SSRL and LCLS Cohen said drawing upon key areas of expertise for SSRL and the unique capabilities of LCLS The combined effort of staff at both experimental facilities was key in this success she said

httpphysorgnews2014-11-robotics-x-ray-lasers-cutting-edge-biologyhtml

21 Multilaboratory collaboration brings new X-ray detector to light

简介美国能源部研究办公室通过协作研究将制

造出独一无二的X射线检测器其可满足对X射线XCS的需求该检测器能进行微秒计时并具有纳米尺敏感

性在取样时能捕捉动态工艺过程协作研究团队将

在传感器上做出第一个无缝组列芯片

The 64-by-64 pixel VIPIC prototype pictured with a sensor on the

bottom and solder bump-bonding bump on top ready to be received on the printed circuit board

A collaboration blending research in DOEs offices of High-Energy Physics (HEP) with Basic Energy Sciences (BES) will yield a one-of-a-kind X-ray detector The device boasts Brookhaven Lab sensors mounted on Fermilab integrated circuits linked to Argonne Lab data acquisition systems It will be used at Brookhavens National Synchrotron Light Source II and Argonnes Advanced Photon Source Lead scientists Peter Siddons Grzegorz Deptuch and Robert Bradford represent the three laboratories

This partnership between HEP and BES has been a fruitful collaboration advancing detector technology for both fields said Brookhavens Peter Siddons

This detector is filling a need in the X-ray correlation spectroscopy (XCS) community which has been longing for a detector that can capture dynamic processes in samples with microsecond timing and nanoscale sensitivity Available detectors have been designed largely for X-ray diffraction crystallography and are incapable of performing on this time scale

In 2006 Fermilabs Ray Yarema began investigating 3-D integrated chip technology which increases circuit density performance and functionality by vertically stacking rather than laterally arranging silicon wafers Then in 2008 Deptuch a member of Yaremas group and Fermilab ASIC Group leader since 2011 met with Siddons a scientist at Brookhaven at a medical imaging conference They discussed applying 3-D technology to a new custom detector project which was later given the name VIPIC (vertically integrated photon imaging chip) Siddons was intrigued by the 3-D opportunities and has since taken the lead on leveraging Fermilab expertise toward the longstanding XCS problem As a result the development

23

光电技术情报 2015年第1期（总第6期）

of the device at Fermilabmdashwhere 97 percent of research funds come through HEPmdashreceives BES funding

A 64-by-64-pixel VIPIC prototype tested at Argonne this summer flaunted three essential properties timing resolution within one microsecond continuous new-data acquisition with simultaneous old-data read-out and selective transmission of only pixels containing data

The results achieved with the prototype have attracted attention from the scientific community

Deptuch noted that this partnership between BES and HEP reflects the collaborative nature of such efforts at the national labs

It truly is a cooperative effort combining the expertise from three national laboratories toward one specific goal he said

The team will grow their first VIPIC prototype tiled seamless array of chips on a sensor to form a 1-megapixel detector The collaboration is targeting a completion date of 2017 for the basic functionality detector Ideas for expanded capabilities are being discussed for the future

httpphysorgnews2014-11-multilaboratory-collaboration-x-ray-detectorhtml

22 Technology helps improve production of laser-heated hard disk drives with enhanced storage capacities

简介目前使用的硬盘驱动器能够容纳数以兆计的

数字数据可是用传统的常规方法很难再生产拥有更大

存储容量的驱动器ldquo热辅助磁记录rdquo可解决这一难题

为此研究人员研发出测试仪器以很高的空间精确度对

激光驱动变化进行测量提高磁刻技术能力增大硬盘

驱动器存储容量

An advanced testing instrument can measure laser-driven

changes to magnetic disk drives with impressive spatial precision

Todays hard disk drives can hold terabytes of digital data but manufacturers are having trouble squeezing more storage capacity into these devices using conventional procedures Now a new technique that promises to solve this impassemdashheat-assisted magnetic recording (HAMR)mdashcan be integrated more efficiently into future hard drives thanks to an analytical tool developed by ASTAR researchers

Data-storing bits inside hard disk drives have to be turned on and off with magnetic fields But as bit sizes diminish to improve storage density the recording heads need stronger and stronger fields to resolve individual magnetic grains Eventually impractically large fields are required to read and write data

The HAMR approach uses a small laser mounted on the disk recording head to heat up the magnetic material before writing to it The increase in temperature reduces the magnetic field intensity necessary for data storage and consequently smaller bit sizes can be used Rapid cooling of the magnetic grains ensures the stability of the freshly recorded data

Researchers are confident that the HAMR technique can lead to 20-terabyte hard drives within a few years if some specific challenges can be overcome One current problem is that accurately testing the temperature-dependent recording in localized regions is difficult Typical analytical methods have to heat up relatively large sample volumes a time-consuming process that can irreversibly damage HAMR media

Hongzhi Yang with a team from the ASTAR Data Storage Institute and the National University of Singapore designed an improved pumpndashprobe laser device to scrutinize HAMR devices The instrument uses an initial intense beam to heat up a localized region of the magnetic disk Then a weaker laser probes the heated region for the micro-magneto-optic Kerr effect (μ-MOKE) a phenomenon that can gauge a materials magnetization state By repeating these measurements with different heating beam conditions the researchers obtained detailed data on HAMR writing reading and magnetic states from specific microscopic spots on the hard drive surfacemdashinformation currently unavailable through other techniques

The challenge in developing this testing instrument was integrating the complex optical and mechanical components to achieve good signal-to-noise ratios and uniform temperature distribution in the media during heating says Yang But compared to traditional bulk-heating techniques our method is much faster allows full disk measurement and avoids annealing effects

The team is confident that this instrument can be incorporated into disk drive manufacturing plants as HAMR captures a larger share of magnetic recording technology

httpphysorgnews2014-11-technology-production-laser-heated-hard-diskhtml

23 Worlds first photonic pressure sensor outshines traditional mercury standard

简介固长光谐振腔压力传感器无论在分辨率

速度还是在大小方面都优于汞基技术可测量通过氮气

腔内光波长度的微妙变化其内有一个外边包着铜的温

控光谐振腔其大小约为 155cmtimes5cmtimes5cm

24

技术与应用

The FLOC inside its copper container with the cover removed

revealing the upper of the two channels For almost 400 years mercury gauges have prevailed as

the most accurate way to measure pressure Now within weeks of seeing first light a novel pressure-sensing device has surpassed the performance of the best mercury-based techniques in resolution speed and range at a fraction of the size The new instrument called a fixed-length optical cavity (FLOC) works by detecting subtle changes in the wavelength of light passing through a cavity filled with nitrogen gas

The FLOC system is poised to depose traditional mercury pressure sensors ndash also called manometers ndash as the standard used to calibrate commercial equipment says the interdisciplinary team of NIST researchers who developed the system and will continue to refine it over the next few years The new design is also a promising candidate for a factory-floor pressure instrument that could be used by a range of industries including those associated with semiconductor glass and aerospace manufacturing

Weve exceeded the expectations we had three years ago says Thermodynamic Metrology Group Leader Gregory Strouse This device is not only a photonic sensor its also a primary standard Its the first photonic-based primary pressure standard And it works

About the size of a travel mug the FLOC has a resolution of 01 mPa (millipascal or thousandths of a pascal) 36 times better than NISTS official US pressure standard which is a 3-meter-tall (about 10-foot) column of liquid mercury that extends through the ceiling of the calibration room

The cavitys range also beats that of the mercury manometer at the low end an impressively wide range that stretches from the millipascal- to hundred thousand pascal-level says Principal Investigator Jay Hendricks of the Thermodynamic Metrology Group Theres no other instrument that can handle so many different ranges and have that high a resolution he continues

The FLOC is 100 times faster than the standard mercury manometer too

It can do in a second what the big mercury manometer takes about a minute and a half to do Hendricks says

Traditional pressure sensors rely on changes to the height of a column of mercury which rises or falls in response to pressure But though accurate and reliable these instruments are bulky and their dependence on

mercury a neurotoxic substance makes them undesirable In fact mercurys hazards have prompted a global effort to cut or phase out this substance from products and manufacturing a goal made manifest by a United Nations Environment Program (UNEP) treaty that has been signed by more than 100 countries

The FLOC system setup with laser-directing optics (right)

copper-enclosed optical cavity (center) and output signal on a computer monitor (left)

The new mercury-free photonic pressure sensor consists of a temperature-controlled optical cavity approximately 155 cm (about 6 inches) long by 5 cm (2 in) by 5 cm (2 in) encased in copper The cavity contains two channels one flooded with nitrogen gas and the other in vacuum A beam of low-power red (633-nm) laser light is locked to each channel meaning it forms a standing wave that self-synchronizes through constant adjustments to its wavelength Some of the light from each channel is allowed to exit the FLOC where the beams combine to form an interference pattern

A change in pressure does not affect the light in the vacuum tube because there is no medium to be affected But it does affect the density of the nitrogen which in turn alters the gass index of refraction or how fast light travels through it And this change in light speed affects the wavelength of the light resonating in the nitrogen-filled channel Though these alterations in wavelength are minute ndash on the picometer level a hundred times smaller than an atom ndash they can be detected in the interference pattern

So far the technique is accurate to within 0005 or 50 parts per million (ppm) which makes it superior to most commercial pressure instruments But this is only a first attempt and Hendricks and his colleagues believe they can do better In the next three years the team will try to drive this accuracy below the 5 ppm range which will allow it to surpass that of the current manometer standard

Hendricks and Strouse see great potential for making the system smaller too ndash perhaps as small as a smartphone someday ndash while further increasing its speed and resolution There are tricks we havent even begun to tap into yet Hendricks says

httpphysorgnews2014-10-world-photonic-pressure-sensor-outshineshtml

25

光电技术情报 2015年第1期（总第6期）

24 Northrop Grumman Sets World Record with One-Terahertz Circuit Achieves One Trillion Cycles per Second

简介诺斯罗谱公司研发出世界最快的集成电路放

大器已收进世界吉尼斯记录该放大器使用 10 级放

大晶体管达到 1 太赫兹工作速度 Northrop Grumman Corporation (NYSENOC) a leader

in advanced microelectronics has developed the worlds fastest integrated circuit amplifier which has been recognized by Guinness World Records The amplifier uses 10 transistor stages to reach an operating speed of one terahertz (1012 Hz) or one trillion cycles per secondmdashsurpassing the companys own performance record of 850 billion cycles per second set in 2012

Terahertz is a slice of the electromagnetic spectrum that lies between microwaves and infrared light waves Researchers have long sought to exploit this tremendously high-frequency band commonly referred to as the terahertz gap but have been unable to detect process and radiate the necessary high-frequency signals without resorting to frequency translation or multiplication

The Northrop Grumman terahertz monolithic integrated circuit (TMIC) effectively bridges this gap by using a super-scaled 25 nanometer gatelength indium phosphide high electron mobility transistor that measures at a gain of 10 decibels at 1 terahertz and nine decibels at 103 terahertz In comparison present day smartphones operate at 1 to 2 gigahertz and wireless networks at 57 gigahertz

Developed on behalf of the Defense Advanced Research Projects Agency (DARPA) the circuit is the culmination of the companys three-phase contract with the agency to demonstrate transistor-based electronics operating at 670 gigahertz 850 gigahertz and 1 terahertz All three milestones were successfully completed by Northrop Grumman within five years

This breakthrough by the Northrop Grumman team could lead to revolutionary technologies such as high-resolution security imaging systems improved collision-avoidance radar communications networks with many times the capacity of current systems and spectrometers that could detect potentially dangerous chemicals and explosives with much greater sensitivity said Dev Palmer program manager Microsystems Technology Office at DARPA

Additional applications could include atmospheric sensing radio astronomy and medical imaging It is also expected to improve system range and reduce size weight and power consumption of existing systems

A decade ago there was no consensus in the scientific community whether an integrated circuit operating at one terahertz was technologically possible said William Deal program manager terahertz electronics Northrop Grumman An interdisciplinary team of scientists and engineers worked together in scaling all facets of our MMIC technology to enable this result Now as a result of DARPAs investment in high-speed transistor processes it

will become routine to fabricate wafers containing thousands of terahertz integrated circuits

DARPA has made strategic investments in terahertz electronics through its High Frequency Integrated Vacuum Electronics (HiFIVE) Sub-millimeter Wave Imaging Focal Plane Technology (SWIFT) and Technology for Frequency Agile Digitally Synthesized Transmitters (TFAST) programs Each program built on the successes of the previous one providing the foundational research necessary for frequencies to reach the terahertz threshold Northrop Grumman has partnered with DARPA on each program

httpwwwglobenewswirecomnewsarchivenocpresspagesnews_releaseshtmld=10104912

25 XEI Scientific launches the revolutionary Evactron EP plasma cleaning system

简介XEI 科学有限公司将革新后的热离子变阻器

清洗系统投放市场这一系统运用了新的等离子清洗方

法是专门为从事物理及材料研究团体设计制作的可

清洗由激光等引起的带电粒子束以及光感面产生的碳

沉积物等 XEI Scientific Inc announces the release of the

Evactronreg EP at the annual meeting of the American Vacuum Society in Baltimore MD This provides a new approach to plasma cleaning designed for those in the physics and materials science communities building and using custom-designed vacuum systems

The Evactron EP Remote Plasma Source from XEI Scientific uses flowing afterglow cleaning with air to clean carbon compounds from vacuum chambers operating with turbomolecular pumps The unique new system has instant ignition from any vacuum level It uses a low wattage hollow cathode electrode to produce plasma It is compact and affordable Most commercially available remote plasma sources have been designed for semiconductor equipment and thus are usually derated for the plasma cleaning of other vacuum systems Evactron systems were specifically designed for cleaning electron microscopes safely This high rate process cleans in minutes removing carbon acquired during exposure to ambient air system assembly poor vacuum practice etc The removal of carbon speeds pump down times improving instrument performance and stops carbon deposition by lasers and charged particle beams on optics and other sensitive surfaces It prevents cross contamination XEIs plasma R amp D team has designed the EP system to be affordable providing fast reliable high performance cleaning The critical RF generator and impedance matches are the same units used in XEIs fully featured Evactron De-Contaminators Flowing afterglows give high oxygen radical concentrations for fast cleaning due to longer mean free paths in the 2-20 milliTorr region A fixed input gas flow rate removes the need for pressure gauges and variable gas flow valves and control A patent has been applied for the unique and reliable plasma ignition system

26

技术与应用

that works even when the chamber is at very high vacuum at the start For safety a vacuum interlock allows the RF power to be turned only when the unit is inserted into vacuum The unit is CE NRTL Semi-S2 and RoHS compliant The EP system was designed with the purchase price in mind By removing high cost components and designing the unit for easy assembly it is now priced at less than half the cost of full function plasma cleaning systems

The front panel has only one control an onoff switch that turns on the RF power and gas flow in the chamber to start the cleaning plasma A computer interface connection may be used to set cleaning time cycle cleaning and power levels if needed To be used the unit needs to be mounted on a vacuum chamber (NW40 or CF 275 flanges) vacuum and power applied and plasma turned on

httpwwwmaterialstodaycomsurface-scienceproductsxei-scientific-evactron-ep-plasma-cleaning-system

26 Two Photons Strongly Coupled by Glass Fibre

简介维也纳技术大学用超薄玻璃纤维加强两个光

子的相互作用这一方法是量子技术的一个重要新手

段将来要建立一个基于玻璃技术的新系统这是走向

全球量子信息网络的重要一步 At the Vienna University of Technology (TU Wien) two

photons were made to interact strongly using an ultra-thin glass fibre This technique is an important new tool for quantum technology

The light in a glass fibre is coupled to a bottle resonator

Light runs around a bottle-shaped glass fibre about half as thick

as a human hair Two photons in free space do not interact Light waves

can pass through each other without having any influence on each other at all For many applications in quantum technology however interaction between photons is crucial It is an indispensable prerequisite for transmitting information through tap-proof quantum channels or for

building optical logic gates At the Vienna University of Technology (TU Wien) scientists have now succeeded in establishing a strong interaction between two single photons This opens up completely new possibilities for quantum optics The experimental results have now been published in the journal ldquoNature Photonicsrdquo

Interaction Usually Requires Bright Light ldquoIn order to have light interact with light one usually

uses so-called nonlinear mediardquo says Professor Arno Rauschenbeutel (Vienna Center for Quantum Science and Technology Institute for Atomic and Subatomic Physics TU Wien) The light has an effect on the properties of these materials and the material in turn influences the light which leads to an indirect coupling between photons This technique however can only be used at high light intensities when countless photons are involved At TU Wien a system was built which creates a strong interaction between only two photons This interaction is so strong that the phase of the photons is changed by 180 degrees ldquoIt is like a pendulum which should actually swing to the left but due to coupling with a second pendulum it is swinging to the right There cannot be a more extreme change in the pendulumrsquos oscillationrdquo says Rauschenbeutel ldquoWe achieve the strongest possible interaction with the smallest possible intensity of lightrdquo

A Photon in a Bottle To make this possible the photon has to be sent on an

unusual journey An ultra-thin glass fibre is coupled to a tiny bottle-like optical resonator so that light can enter the resonator move in circles and return to the glass fibre This detour through the resonator inverts the phase of the photon a wave crest appears where a wave trough would have been expected When however a single rubidium atom is coupled to the resonator the system is changed dramatically Due to the presence of the atom hardly any light enters the resonator anymore and the oscillation phase of the photon remains unchanged

Two Photons at Once Things change when two photons arrive at the same time

ldquoThe atom is an absorber which can be saturatedrdquo says Arno Rauschenbeutel ldquoA photon is absorbed by the atom for a short while and then released again into the resonator During that time it cannot absorb any other photons If two photons arrive simultaneously only one can be absorbed while the other can still be phase shiftedrdquo From a quantum mechanical point of view the two photons are indistinguishable They have to be considered as a joint wave-like object which is located in the resonator and in the glass fibre at the same time Therefore one cannot tell which photon has been absorbed and which one has passed When both hit the resonator at the same time they thus experience a joint phase shift of 180 degrees Hence two simultaneous photons that interact show a completely different behaviour than single photons

27

光电技术情报 2015年第1期（总第6期）

The Building Blocks of Future Quantum Data-Highways

ldquoThat way a maximally entangled photon state can be createdrdquo says Arno Rauschenbeutel ldquoSuch states are required in all fields of quantum optics ndash in quantum teleportation or for light-transistors which could potentially be used for quantum computingrdquo

A big advantage of the new system is that it is based on glass fibre technology which is already being used for optical communication anyway Nano glass fibres and bottle-resonators are perfectly compatible with existing technologies The creation of a strong deterministic photon-photon-interaction is an important step towards a global quantum information network for the tap-proof transmission of data

httpwwwtuwienacatennewsnews_detailarticle9076

27 New technique to help produce next generation photonic chips

简介英国南安普顿大学研究人员发现能ldquo看见rdquo或者测量光在芯片内的活动新方法称作做超速光调制光

谱技术利用此技术可以在特定时间看见光在芯片中所

处的位置

Ultrafast photomodulation spectroscopy Researchers from the

University of Southampton have developed a new technique to help produce more reliable and robust next generation photonic chips

Photonic chips made from silicon will play a major role in future optical networks for worldwide data traffic The high refractive index of silicon makes optical structures the size of a fraction of the diameter of a human hair possible Squeezing more and more optical structures for light distribution modulation detection and routing into smaller chip areas allows for higher data rates at lower fabrication costs

As the complexity of optical chips increases testing and characterising such chips becomes more difficult Light traveling in the chip is confined in the silicon that is it cannot be lsquoseenrsquo or measured from the outside

Southampton researchers have now developed a new method which will help solve this problem to find out at which time the light in the chip is at which position The technique called Ultrafast photomodulation spectroscopy (UPMS) uses ultraviolet laser pulses of femtosecond duration to change the refractive index of silicon in a tiny area on the photonic chip

Non-contact characterization tools like UPMS are vital for scientist designing complex photonic chips The UPMS

technique is fast and robust and has the potential to be used for industrial testing in the photonics industry

The research is published in the latest issue of the journal Nature Photonics

Dr Roman Bruck from Physics and Astronomy at the University of Southampton and lead author of the study says ldquoMonitoring the transmission of the chip while the refractive index is locally changed gives a precise picture of how the light flows through it This allows testing of individual optical elements on the chip a crucial step in the design optimisation to ensure its flawless operation Because the changes induced by the technique are fully reversible this testing method is non-destructive and after testing the chip can be used for its intended applicationrdquo The research team from Physics and Astronomy and the Optoelectronics Research Centre (ORC) at the University expects to establish the technique as a standard characterisation tool making photonic chips under development more reliable and bringing them into the market quicker

httpwwwsouthamptonacukmediacentrenews2014nov14_208shtmlVHKU_dIYDrN

28 Breakthrough in flexible electronics enabled by inorganic-based laser lift-off

简介弹性电子产品将在下一代电子产品领域独占

熬头韩国科学技术学院的研究团队研究出一种简单的

方法可通过无机基激光垂直发射实现电子产品的高效

操作性能这一研究成果可应用于各种弹性电子产品

比如显示器的驱动电路和无机基能源设备包括蓄电

池太阳能电池自供电设备等

Flexible crossbar memory developed via the ILLO process

Flexible electronics have been touted as the next generation in electronics in various areas ranging from consumer electronics to bio-integrated medical devices In spite of their merits insufficient performance of organic materials arising from inherent material properties and processing limitations in scalability have posed big challenges to developing all-in-one flexible electronics systems in which display processor memory and energy devices are integrated The high temperature processes essential for high performance electronic devices have

28

技术与应用

severely restricted the development of flexible electronics because of the fundamental thermal instabilities of polymer materials

A research team headed by Professor Keon Jae Lee of the Department of Materials Science and Engineering at KAIST provides an easier methodology to realize high performance flexible electronics by using the Inorganic-based Laser Lift-off (ILLO)

The ILLO process involves depositing a laser-reactive exfoliation layer on rigid substrates and then fabricating ultrathin inorganic electronic devices eg high density crossbar memristive memory on top of the exfoliation layer By laser irradiation through the back of the substrate only the ultrathin inorganic device layers are exfoliated from the substrate as a result of the reaction between laser and exfoliation layer and then subsequently transferred onto any kind of receiver substrate such as plastic paper and even fabric

This ILLO process can enable not only nanoscale processes for high density flexible devices but also the high temperature process that was previously difficult to achieve on plastic substrates The transferred device successfully demonstrates fully-functional random access memory operation on flexible substrates even under severe bending

Professor Lee said By selecting an optimized set of inorganic exfoliation layer and substrate a nanoscale process at a high temperature of over 1000 degC can be utilized for high performance flexible electronics The ILLO process can be applied to diverse flexible electronics such as driving circuits for displays and inorganic-based energy devices such as battery solar cell and self-powered devices that require high temperature processes

httpphysorgnews2014-11-breakthrough-flexible-electronics-enabled-inorganic-basedhtml

29 Exploring extraordinary optical transmission in a plasmonic cavity

简介美国墨西哥州立大学研究人员研究出等离子

体腔光传输设备此设备的特点是其混合表面的等离子

极化声子能给出矫正后的 Q 值可用于生物传感器和光

回路

Jayson Briscoe and Sang-Yeon Cho in their lab at New Mexico

State University Researchers at New Mexico State University in the US

have investigated extraordinary optical transmission in a plasmonic cavity The device they have developed features

a hybrid surface plasmon polaritonFabry-Peacuterot cavity which gives an improved Q-factor and demonstrates its suitability for use in biosensors and photonic circuits The main achievement by the team was that of extraordinary optical transmission (EOT) EOT is the surprising phenomenon where a sub-wavelength aperture can transmit considerably more light than would classically be expected The phenomenon is caused by the presence of surface plasmon polaritons

Plasmonic cavities have long been of interest to researchers in the field due to the fact that they are naturally nanoscale and easily miniaturised However high ohmic losses in metal at optical frequencies mean that they have suffered from low q-factors and the US team expect their design to address these issues

Exciting lighting Surface plasmon polaritons (SPPs) are a collective

excitation or quasiparticle involving interactions between charged particles (electrons in a plasma or metal) and electromagnetic fields (light) At a metal-dielectric interface ndash where the real part of the permittivity changes sign ndash the conduction electrons are excited collectively which is described by plasmons If light is incident on the metal polaritons will form and the interaction of the plasmon and the polariton is described through SPPs

In order to generate stable SPP excitations the team manufactured a hybrid cavity that consisted of an array of nano-structured metal rods embedded in a dielectic cavity A Fabry-Peacuterot structure was then introduced across the system ndash effectively two mirrors on either side of the cavity The nanoscale array acts to create the surface plasmons and the photonic standing wave (or mode) created by the Fabry-Peacuterot cavity provides the light that leads to the formation of SPPs

An array of metal nanorods embedded in a dielectric cavity

It has been shown that SPPs are responsible for the effect and the teams array may be introduced into devices to improve transmission Of course the transmission will be maximal at a resonant frequency which in the current device is around 800 nm However changing the dimensions of the array and cavity can tune this resonance

Integration and quality The presence of EOT means that these nanoscale devices

can be used in a wide variety of applications for example as mentioned above integrated photonic circuits As EOT structures are intrinsically nanoscale they lend themselves to integration so could be used in photonic interconnects or waveguides

29

光电技术情报 2015年第1期（总第6期）

Another intriguing possible application is in chemical and biological sensing This is made possible by the relationship between the SPP dispersion and the change in permittivity between the metal and the dielectric The presence of a foreign body biological agent or element will affect the relative permittivity changing the SPP dispersion and so shifting the frequency of the EOT resonance

As the teams cavity demonstrated a 39 improvement in Q-factor they believe that engineered nanostructured devices are on the verge of mainstream commercial application and the possible fields do not just include those mentioned above The insight into hybrid cavity devices they have provided can be applied to research into evermore diverse areas from colloidal quantum dot based sources to spectral engineering and metamaterials

httpphysorgnews2014-11-exploring-extraordinary-optical-transmission-plasmonichtml

30 Engineers make sound loud enough to bend light on a computer chip

简介美国密尼苏达大学的工程研究人员研发出生

成光波和声波的芯片使两者进行交融以实现声音有效

控制光的目的这一新设备平台能够用光纤改进无线通

信系统最终实现用量子物理进行计算研究人员未来

研究计划是实现把声波作为量子计算的信息载体

The figure illustrates a sound wave passing across an integrated

optical waveguide overlaid with a color map of the light field in it During a thunderstorm we all know that it is common to

hear thunder after we see the lightning Thats because sound travels much slower (768 miles per hour) than light (670000000 miles per hour) Now University of Minnesota engineering researchers have developed a chip on which both sound wave and light wave are generated and confined together so that the sound can very efficiently control the light The novel device platform could improve wireless communications systems using optical fibers and ultimately be used for computation using quantum physics

The research was recently published in Nature Communications

The University of Minnesota chip is made with a silicon base coated with a layer of aluminum nitride that conducts an electric change Applying alternating electrical signal to the material causes the material to deform periodically and generate sound waves that grow on its surface similar to earthquake waves that grow from the center of the

earthquake The technology has been widely used in cell phones and other wireless devices as microwave filters

Our breakthrough is to integrate optical circuits in the same layer of material with acoustic devices in order to attain extreme strong interaction between light and sound waves said Mo Li assistant professor in the Department of Electrical and Computer Engineering and the lead researcher of the study

The researchers used the state-of-the-art nanofabrication technology to make arrays of electrodes with a width of only 100 nanometers (000001 centimeters) to excite sound waves at an unprecedented high frequency that is higher than 10 GHz the frequency used for satellite communications

Whats remarkable is that at this high frequency the wavelength of the sound is even shorter than the wavelength of light This is achieved for the first time on a chip said Semere Tadesse a graduate student in the University of Minnesotas School of Physics and Astronomy and the first author of the paper In this unprecedented regime sound can interact with light most efficiently to achieve high-speed modulation

In addition to applications in communications researchers are pursuing quantum physics applications for the novel device They are investigating the interaction between single photons (the fundamental quantum unit of light) and single phonons (the fundamental quantum unit of sound) The researcher plan to use sound waves as the information carriers for quantum computing

httpphysorgnews2014-11-loud-chiphtml

30

技术与应用

五其他

31 New evidence for exotic predicted superconducting state

简介美国布朗大学研究团队找到了 50 年前首次

预测高能超导态的新证据即超导体受强磁场的影响会

产生高能超导态这一发现意味着对许多宇宙现象能够

进行解释比如密集夸克的运动构成原子核的粒子

等 A research team led by a Brown University physicist has

produced new evidence for an exotic superconducting state first predicted a half-century ago that can arise when a superconductor is exposed to a strong magnetic field

PROVIDENCE RI [Brown University] mdash Superconductors and magnetic fields do not usually get along But a research team led by a Brown University physicist has produced new evidence for an exotic superconducting state first predicted a half-century ago that can indeed arise when a superconductor is exposed to a strong magnetic field

ldquoIt took 50 years to show that this phenomenon indeed happensrdquo said Vesna Mitrovic associate professor of physics at Brown University who led the work ldquoWe have identified the microscopic nature of this exotic quantum state of matterrdquo

The research is published in Nature Physics Superconductivity mdash the ability to conduct electric

current without resistance mdash depends on the formation of electron twosomes known as Cooper pairs (named for Leon Cooper a Brown University physicist who shared the Nobel Prize for identifying the phenomenon) In a normal conductor electrons rattle around in the structure of the material which creates resistance But Cooper pairs move in concert in a way that keeps them from rattling around enabling them to travel without resistance

Magnetic fields are the enemy of Cooper pairs In order to form a pair electrons must be opposites in a property that physicists refer to as spin Normally a superconducting material has a roughly equal number of electrons with each spin so nearly all electrons have a dance partner But strong magnetic fields can flip ldquospin-downrdquo electrons to ldquospin-uprdquo making the spin population in the material unequal

ldquoThe question is what happens when we have more electrons with one spin than the otherrdquo Mitrovic said ldquoWhat happens with the ones that donrsquot have pairs Can we actually form superconducting states that way and what would that state look likerdquo

Discrete bands of superconductivity A diagram depicts unpaired spin up electrons

congregating in discrete bands In 1964 physicists predicted that superconductivity

could indeed persist in certain kinds of materials amid a magnetic field The prediction was that the unpaired electrons would gather together in discrete bands or stripes across the superconducting material Those bands would conduct normally while the rest of the material would be superconducting This modulated superconductive state came to be known as the FFLO phase named for theorists Peter Fulde Richard Ferrell Anatoly Larkin and Yuri Ovchinniko who predicted its existence

To investigate the phenomenon Mitrovic and her team used an organic superconductor with the catchy name κ-(BEDT-TTF)2Cu(NCS)2 The material consists of ultra-thin sheets stacked on top of each other and is exactly the kind of material predicted to exhibit the FFLO state

After applying an intense magnetic field to the material Mitrovic and her collaborators from the French National High Magnetic Field Laboratory in Grenoble probed its properties using nuclear magnetic resonance (NMR)

What they found were regions across the material where unpaired spin-up electrons had congregated These ldquopolarizedrdquo electrons behave ldquolike little particles constrained in a boxrdquo Mitrovic said and they form what are known as Andreev bound states

ldquoWhat is remarkable about these bound states is that they enable transport of supercurrents through non-superconducting regionsrdquo Mitrovic said ldquoThus the current can travel without resistance throughout the entire material in this special superconducting staterdquo

Experimentalists have been trying for years to provide solid evidence that the FFLO state exists but to little avail Mitrovic and her colleagues took some counterintuitive measures to arrive at their findings Specifically they probed their material at a much higher temperature than might be expected for quantum experiments

ldquoNormally to observe quantum states you want to be as cold as possible to limit thermal motionrdquo Mitrovic said ldquoBut by raising the temperature we increased the energy window of our NMR probe to detect the states we were looking for That was a breakthroughrdquo

This new understanding of what happens when electron spin populations become unequal could have implications beyond superconductivity according to Mitrovic

It might help astrophysicists to understand pulsars mdash densely packed neutron stars believed to harbor both superconductivity and strong magnetic fields It could also be relevant to the field of spintronics devices that operate based on electron spin rather than charge made of layered ferromagnetic-superconducting structures

ldquoThis really goes beyond the problem of superconductivityrdquo Mitrovic said ldquoIt has implications for explaining many other things in the universe such as behavior of dense quarks particles that make up atomic nucleirdquo

31

光电技术情报 2015年第1期（总第6期）

httpsnewsbrowneduarticles201410superconductivity

32 Caltech Rocket Experiment Finds Surprising Cosmic Light

简介美国宇航员在其国家航空和宇宙航行局亚轨

道火箭上进行的空间实验中探测到弥散的宇宙光比已

知宇宙星系产生的光更多未来的实验可能测试出那些

弥散在宇宙星系间的ldquo流浪之星rdquo Using an experiment carried into space on a NASA

suborbital rocket astronomers at Caltech and their colleagues have detected a diffuse cosmic glow that appears to represent more light than that produced by known galaxies in the universe

The researchers including Caltech Professor of Physics Jamie Bock and Caltech Senior Postdoctoral Fellow Michael Zemcov say that the best explanation is that the cosmic lightmdashdescribed in a paper published November 7 in the journal Sciencemdashoriginates from stars that were stripped away from their parent galaxies and flung out into space as those galaxies collided and merged with other galaxies

The discovery suggests that many such previously undetected stars permeate what had been thought to be dark spaces between galaxies forming an interconnected sea of stars Measuring such large fluctuations surprised us but we carried out many tests to show the results are reliable says Zemcov who led the study

Although they cannot be seen individually the total light produced by these stray stars is about equal to the background light we get from counting up individual galaxies says Bock also a senior research scientist at JPL Bock is the principal investigator of the rocket project called the Cosmic Infrared Background Experiment or CIBER which originated at Caltech and flew on four rocket flights from 2009 through 2013

In earlier studies NASAs Spitzer Space Telescope which sees the universe at longer wavelengths had observed a splotchy pattern of infrared light called the cosmic infrared background The splotches are much bigger than individual galaxies We are measuring structures that are grand on a cosmic scale says Zemcov and these sizes are associated with galaxies bunching together on a large-scale pattern Initially some researchers proposed that this light came from the very first galaxies to form and ignite stars after the Big Bang Others however have argued the light originated from stars stripped from galaxies in more recent times

CIBER was designed to help settle the debate CIBER was born as a conversation with Asantha Cooray a theoretical cosmologist at UC Irvine and at the time a postdoc at Caltech with [former professor] Marc Kamionkowski Bock explains Asantha developed an idea for studying galaxies by measuring their large-scale structure Galaxies form in dark-matter halos which are over-dense regions initially seeded in the early universe by inflation Furthermore galaxies not only start out in these

halos they tend to cluster together as well Asantha had the brilliant idea to measure this large-scale structure directly from maps Experimentally it is much easier for us to make a map by taking a wide-field picture with a small camera than going through and measuring faint galaxies one by one with a large telescope

Cooray originally developed this approach for the longer infrared wavelengths observed by the European Space Agencys Herschel Space Observatory With its 35-meter diameter mirror Herschel is too small to count up all the galaxies that make the infrared background light so he instead obtained this information from the spatial structure in the map Bock says

Meanwhile I had been working on near-infrared rocket experiments and was interested in new ways to use this unique idea to study the extragalactic background he says The extragalactic infrared background represents all of the infrared light from all of the sources in the universe and there were some hints we didnt know where it was all coming from

In other words if you calculate the light produced by individual galaxies you would find they made less than the background light One could try and measure the total sky brightness directly Bock says but the problem is that the foreground Zodiacal light due to dust in the solar system reflecting light from the sun is so bright that it is hard to subtract with enough accuracy to measure the extragalactic background So we put these two ideas together applying Asanthas mapping approach to new wavelengths and decided that the best way to get at the extragalactic background was to measure spatial fluctuations on angular scales around a degree That led to CIBER

The CIBER experiment consists of three instruments including two spectrometers to determine the brightness of Zodiacal light and measure the cosmic infrared background directly The measurements in the recent publication are made with two wide-field cameras to search for fluctuations in two wavelengths of near infrared light Earths upper atmosphere glows brightly at the CIBER wavelengths But the measurements can be done in spacemdashavoiding that glowmdashin just the short amount of time that a suborbital rocket flies above the atmosphere before descending again back toward the planet

CIBER flew four missions in all the paper includes results from the second and third of CIBERs flights launched in 2010 and 2012 from White Sands Missile Range in New Mexico and recovered afterward by parachute In the flights the researchers observed the same part of the sky at a different time of year and swapped the detector arrays as a crosscheck against data artifacts created by the sensors This series of flights was quite helpful in developing complete confidence in the results says Zemcov For the final flight we decided to get more time above the atmosphere and went with a non-recovered flight into the Atlantic Ocean on a four-stage rocket (The data from the fourth flight will be discussed in a future paper)

其他

32

Based on data from these two launches the researchers found fluctuations but they had to go through a careful process to identify and remove local sources such as the instrument as well as emissions from the solar system stars scattered starlight in the Milky Way and known galaxies What is left behind is a splotchy pattern representing fluctuations in the remaining infrared background light Comparing data from multiple rocket launches they saw the identical signal That signal also is observed by comparing CIBER and Spitzer images of the same region of sky Finally the team measured the color of the fluctuations by comparing the CIBER results to Spitzer measurements at longer wavelengths The result is a spectrum with a very blue color brightest in the CIBER bands

CIBER tells us a couple key facts Zemcov explains The fluctuations seem to be too bright to be coming from the first galaxies You have to burn a large quantity of hydrogen into helium to get that much light then you have to hide the evidence because we dont see enough heavy elements made by stellar nucleosynthesismdashthe process occurring within stars by which heavier elements are created from the fusion of lighter onesmdashwhich means these elements would have to disappear into black holes

The color is also too blue he says First galaxies should appear redder due to their light being absorbed by hydrogen and we do not see any evidence for such an absorption feature

In short Zemcov says although we designed our experiment to search for emission from first stars and galaxies that explanation doesnt fit our data very well The best interpretation is that we are seeing light from stars outside of galaxies but in the same dark matter halos The stars have been stripped from their parent galaxies by gravitational interactionsmdashwhich we know happens from images of interacting galaxiesmdashand flung out to large distances

The model Bock admits isnt perfect In fact the color still isnt quite blue enough to match the data But even so the brightness of the fluctuations implies this signal is important in a cosmological sense as we are tracing a large amount of cosmic light production

Future experiments could test whether stray stars are indeed the source of the infrared cosmic glow the researchers say If the stars were tossed out from their parent galaxies they should still be located in the same vicinity The CIBER team is working on better measurements using more infrared colors to learn how the stripping of stars happened over cosmic history

In addition to Bock Zemcov and Cooray other coauthors of the paper On the Origin of Near-Infrared Extragalactic Background Light Anisotropy are Joseph Smidt of Los Alamos National Laboratory Toshiaki Arai Toshio Matsumoto Shuji Matsuura and Takehiko Wada of the Japan Aerospace Exploration Agency Yan Gong of UC Irvine Min Gyu Kim of Seoul National University Phillip Korngut a postdoctoral scholar at Caltech Anson

Lam of UCLA Dae Hee Lee and Uk Won Nam of the Korea Astronomy and Space Science Institute (KASI) Gael Roudier of JPL and Kohji Tsumura of Tohoku University The work was supported by NASA with initial support provided by JPLs Directors Research and Development Fund Japanese participation in CIBER was supported by the Japan Society for the Promotion of Science and the Ministry of Education Culture Sports Science and Technology Korean participation in CIBER was supported by KASI

httpwwwcaltecheducontentcaltech-rocket-experiment-finds-surprising-cosmic-light

33 ORNL materials researchers get first look at atom-thin boundaries

简介美国国立橡树岭实验室首次直接观察到一维

边界分离原子量级厚度的石墨烯与六边氮化硼的行为

研究团队计划继续研究边界的磁性能等

Scientists at the Oak Ridge National Laboratory have made the

first direct observations of the electronic behaviors of a one-dimensional boundary separating atom-thin graphene and hexagonal boron nitride materials

Scientists at the Department of Energyrsquos Oak Ridge National Laboratory have made the first direct observations of a one-dimensional boundary separating two different atom-thin materials enabling studies of long-theorized phenomena at these interfaces Theorists have predicted the existence of intriguing properties at one-dimensional (1-D) boundaries between two crystalline components but experimental verification has eluded researchers because atomically precise 1-D interfaces are difficult to construct

ldquoWhile many theoretical studies of such 1-D interfaces predict striking behaviors in our work we have provided the first experimental validation of those interface propertiesrdquo said ORNLrsquos An-Ping Li

The new Nature Communications study builds on work by ORNL and University of Tennessee scientists published in Science earlier this year that introduced a method to grow different two-dimensional materials ndash graphene and boron nitride ndash into a single layer only one atom thick

The teamrsquos materials growth technique unlocked the ability to study the 1-D boundary and its electronic properties in atomic resolution Using scanning tunneling microscopy spectroscopy and density-functional calculations the researchers first obtained a comprehensive picture of spatial and energetic distributions of the 1-D interface states

33

光电技术情报 2015年第1期（总第6期）

ldquoIn three-dimensional (3-D) systems the interface is embedded so you cannot get a real-space view of the complete interface ndash you can only look at a projection of that planerdquo said Jewook Park ORNL postdoctoral researcher and the lead author of the work ldquoIn our case the 1-D interface is completely accessible to real-space studyrdquo

ldquoThe combination of scanning tunneling microscopy and the first principles theory calculations allows us to distinguish the chemical nature of the boundary and evaluate the effects of orbital hybridization at the junctionrdquo said ORNLrsquos Mina Yoon a theorist on the team The researchersrsquo observations revealed a highly confined electric field at the interface and provided an opportunity to investigate an intriguing phenomenon known as a ldquopolar catastropherdquo which occurs in 3-D oxide interfaces This effect can cause atomic and electron reorganization at the interface to compensate for the electrostatic field resulting from materialsrsquo different polarities

ldquoThis is the first time we have been able to study the polar discontinuity effect in a 1-D boundaryrdquo Li said

Although the researchers focused on gaining a fundamental understanding of the system they note their study could culminate in applications that take advantage of the 1-D interface

ldquoFor instance the 1-D chain of electrons could be exploited to pass a current along the boundaryrdquo Li said ldquoIt could be useful for electronics especially for ultra-thin or flexible devicesrdquo

The team plans to continue examining different aspects of the boundary including its magnetic properties and the effect of its supporting substrate

The study is published as ldquoSpatially resolved one-dimensional boundary states in graphenendashhexagonal boron nitride planar heterostructuresrdquo Coauthors are ORNLrsquos Jewook Park Jaekwang Lee Corentin Durand Changwon Park Bobby Sumpter Arthur Baddorf Mina Yoon and An-Ping Li the University of Tennesseersquos Lei Liu Ali Mohsin and Gong Gu and Central Methodist Universityrsquos Kendal Clark

httpwwwornlgovornlnewsnews-releases2014ornl-materials-researchers-get-first-look-at-atom-thin-boundaries

34 Topological insulators promising for spintronics quantum computers

简介美国普渡大学研究人员发现了确凿的证据

证明用拓谱绝缘子材料能使自旋电子器件和实用量子

计算机的技术功能更加强大普林斯顿大学和德州奥斯

丁大学研究团队在这方面的研究进一步证实了拓谱绝

缘材料的这一重要特性

Purdue University doctoral student Yang Xu lead author of a new research paper on topological insulators an emerging class of materials that could make possible spintronic devices and practical quantum computers far more powerful than todays technologies is shown here inspecting devices made from topological insulators under a microscope before electrical measurements

WEST LAFAYETTE Ind ndash Researchers have uncovered smoking-gun evidence to confirm the workings of an emerging class of materials that could make possible spintronic devices and practical quantum computers far more powerful than todays technologies

The materials are called topological insulators Unlike ordinary materials that are either insulators or conductors topological insulators are in some sense both at the same time - they are insulators inside but always conduct electricity via the surface Specifically the researchers have reported the clearest demonstration of such seemingly paradoxical conducting properties and observed the half integer quantum Hall effect on the surface of a topological insulator

This is unambiguous smoking-gun evidence to confirm theoretical predictions for the conduction of electrons in these materials said Purdue University doctoral student Yang Xu lead author of a paper appearing this week in the journal Nature Physics

Yong P Chen a Purdue associate professor of physics and astronomy and electrical and computer engineering led a team of researchers from Purdue Princeton University and the University of Texas at Austin in studying the bismuth-based material

This experimental system provides an excellent platform to pursue a plethora of exotic physics and novel device applications predicted for topological insulators Chen said

For example by further combining topological insulators with a superconductor which conducts electricity with no resistance researchers may be able to build a practical quantum computer Such a technology would perform calculations using the laws of quantum mechanics making for computers much faster than conventional computers at certain tasks such as database searches and code-breaking

One of the main problems with prototype quantum computers developed so far is that they are prone to errors Chen said But if topologically protected there is a mechanism to fundamentally suppress those errors leading to a robust way to do quantum computing

The topological insulators were synthesized at Purdue and fabricated into electrical devices at the Birck Nanotechnology Center in the universitys Discovery Park

The researchers for the first time demonstrated a three-dimensional material with an electrical resistance not dependent on the thickness of the material a departure from conventional behavior Whereas electrons usually have a mass in the case of topological insulators the conducting electrons on the surface have no mass and are automatically spin polarized leading to the unique

34

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half-integer quantum Hall effect observed and also making the material promising for various potential applications

Topological insulators could bring future computing platforms based on spintronics Conventional computers use the presence and absence of electric charges to represent ones and zeroes in a binary code needed to carry out computations Spintronics however uses the spin state of electrons to represent ones and zeros

Compounds based on bismuth antimony telluride and selenide are the cleanest and most intrinsic topological insulators demonstrated so far with no measurable amount of undesirable conduction inside the bulk that often spoils the topological conduction properties in earlier topological insulator materials Chen said

The researchers also found evidence consistent with the conduction of electrons being topologically protected meaning its surface is guaranteed to be a robust conductor Studying thin-slab-shaped samples cut from this material down to ever decreasing thickness while observing the conductance the researchers found that the conductance - which occurs always and only at the surface - barely changes

For the thinnest samples such topological conduction properties were even observed at room temperature paving the way for practical applications Xu said

The paper was authored by Xu Purdue research scientist Ireneusz Miotkowski who created the high-quality materials Princeton postdoctoral research associate Chang Liu Purdue postdoctoral research associate Jifa Tian UT Austin graduate student Hyoungdo Nam Princeton graduate student Nasser Alidoust Purdue graduate student Jiuning Hu Chih-Kang Shih Jane and Roland Blumberg Professor at UT Austin M Zahid Hasan a Princeton professor of physics and Chen

In addition to the material growth and electrical measurements performed by the Purdue researchers the Princeton and UT Austin groups contributed to this study by performing advanced characterizations that further confirmed important properties of the material as a topological insulator

httpwwwpurdueedunewsroomreleases2014Q4topological-insulators-promising-for-spintronics-quantum-computershtml

35 Study details laser pulse effects on behavior of electrons

简介一个国际研究团队演示了从氦原子发射的两

个电子的发射角度取决于激光脉冲磁场并计算出电子

在左旋和右旋两种条件下分开的角度的差异进一步确

认这种效果出现的条件是原子受到足够短且强脉冲的

碰撞此研究论文已在《物理简讯》上发表其研究结

果会帮助物理学家对一些基础的和普遍的物理问题进

行研究 By solving a six-dimensional equation that had

previously stymied researchers University of Nebraska-Lincoln physicists have pinpointed the

characteristics of a laser pulse that yields electron behavior they can predict and essentially control Its long been known that laser pulses of sufficient intensity can produce enough energy to eject electrons from their ultrafast orbits around an atom causing ionization

An international team led by the UNL researchers has demonstrated that the angles at which two electrons launch from a helium atom can depend on whether a laser pulses electric field is right- or left-handedmdashthat is whether it rotates clockwise or counterclockwise The researchers have also calculated the distinct range of angles at which the electrons depart under both conditions

The authors further confirmed that this effect which they have coined nonlinear dichroism appears only when an atom is struck by a sufficiently short intense pulse featuring an elliptically shaped electric field

The study published in the journal Physical Review Letters specifically determined that pulses capable of producing this effect last no longer than 200 attoseconds Counting to one second by intervals of 200 attoseconds per second would take roughly 1585 million yearsmdashlonger than the span that has passed since the end of Earths Jurassic period

The goal in laser atomic physics is to control electron motion and also image it said Anthony Starace a George Holmes University Professor of physics who co-authored the study To do that one needs probes that are much faster than the time scale on which electrons move

However Starace noted that the exceptionally short duration of attosecond laser pulsesmdashand the resulting quantum-scale interactionsmdashcan obscure the mechanics underlying laboratory outcomes

When things happen on such fast time scales experimentalists dont always know what theyve achieved he said They cannot see how electrons make atomic and molecular transitions So they need means to ascertain How did we do that or What did we have there

The teams paper Starace said should help laser physicists address this fundamental and prevalent issue

This has applications for timing electron processes Starace said On our human time scale we think in terms of minutes but these phenomena take place over inconceivably short fractions of a second The question is Are they 10 attoseconds One hundred A thousand No one knows With these results we can explore theoreticallymdashand fairly exactlymdashthe question of how long electron transitions and processes take

By identifying and measuring nonlinear dichroism Starace said the teams study also offers a new signature that quantum physicists can use to classify experimentally produced laser pulses and verify their results

If the experimentalists measure this new effect they will have information as to how long their pulses are what polarization their pulses have and what the shape of their electric field is Starace said These are means to characterize their pulses

35

光电技术情报 2015年第1期（总第6期）

According to Starace the study represents a significant step toward an even larger goal of laser physics manipulating the most fundamental components of matter in the known universe

If experimentalists can finally produce such pulses reliably this new effect allows great control over the way electrons move Starace said If we hit a target with the short attosecond pulses that have a particular duration and polarization we can tell the electrons whether to go one way or another This is humankinds dream of controlling electrons rather than just watching them

Jean Marcel Ngoko Djiokap research assistant professor of physics laid the path to the teams findings by programming the first code capable of accounting both for the interactions between two laser-influenced electrons and the complexity of electric fields that move in multiple dimensions

Normally theorists assume an electric field oscillates in one direction only which reduces the scale of the computation Starace said With elliptical polarization the electric field sweeps around in a plane This adds another dimension to the problem which greatly increases the numerical complexity and the difficulty of doing the calculation Marcel has solved this problem

Starace likened the teams computational approach to climbing aboard the elliptical merry-go-round of the laser pulses electric field Performing calculations from this perspectivemdashrather than the stationary perspective of those watching from outsidemdashultimately streamlined the problem he said

If youre on a merry-go-round people on the sidelines see you spinning aroundmdashbut to you the horse youre sitting on is stationary Starace said What Marcel has done is move the calculation from the laboratory frame (of reference) to this rotating frame so that all we see is linearly polarized one-dimensional light The whole thing becomes simpler

httpphysorgnews2014-11-laser-pulse-effects-behavior-electronshtml

36

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