Plasma-based x-ray lasers

J ZhangInstitute of Physics, CAS, Beijing 100080

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Visible Light Lasers vs. X-Ray Lasers

1. Laser medium: atoms and molecules 2. Wavelength: visible range3. High-Reflecting/Low Trans- mirror: exist4. Cavity is possible: many passes=>small gain required5. Coherence properties: high

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Visible Light Lasers vs. X-Ray Lasers

Still stimulated emissionUtilizing the inverse populations between energy levels of ions.• Wavelength of soft XRL: several~tens nanometers• Laser medium: highly ionized plasmas=>energy consuming• (Wavelength of x-ray laser) ~ (drive energy)-4

• High-Reflecting mirror is difficult to achieve• No Cavity: single pass, ASE =>huge gain required• Strict requirement on uniformity along the plasma

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Necessary Conditions for X-Ray Lasers

1. Specific ions utilized:high photon energy, relatively high abundance, Ne-or Ni-like ions used.

2. Electrons of high density and high temperature: ionization, excitation3. Spatial and temporal overlap of electron density distribution,

temperature distribution, Ion density distribution, pumping photons4. Temporal overlap requirement vs. ion energy level life-span:

traveling-wave pumping technique.5. No HR mirrors for cavity, single-pass amplification: huge gain

requirement, =>high electron density with smooth spatial distributionprofile for necessary long propagation.

6. Coherence properties: multi-modes, long propagation in gain medium is probably a method to achieve high spatial coherence.

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Laser transition

4p

4d

3d10 Ni-like ions

Strong radiationdecay

3d

Laser transition

Monopole collisionalexcitaion

3s

3p

2p6 Ne-like ions

Strong radiationdecay

2p

Ne-like x-ray lasers Ni-like x-ray lasers

Specific ions: => Short wavelength (30-250eV); Qusai-steady state configuration, population inversion between 3p(4d) - 3s (4p)

Necessary Conditions for X-Ray Lasers

1s22s22p6 1s22s22p63s23p63d84s2

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High electron density and temperature: => for abundant specific ions production and population inversion formation, Ti

Necessary Conditions for X-Ray Lasers

22Ti’s Ionization E(eV) of electrons

10 2.16240E+02

11 2.63909E+02

2.92014E+02

7.89623E+02

8.69645E+02

9.52577E+02

1.03842E+03

12

13 (10th)

14

15

16

Ti, Upper-lower level Energy (eV)

2p63p(J=0): 6.21581E+02 eV

2p63s(J=1): 5.19976E+02 eV

47Ag’s Ionization E(eV) of electrons

3.80590E+02

4.10540E+02

4.45870E+02

5.15370E+02

9.00000E+02

9.54480E+02

1.00820E+03

1.06630E+03

19 (28th)

5.19976E+02 eV(J=1):

6.21581E+02 eV(J=0):

Ag, Upper-lower level Energy (eV)

0 500 1000 1500 20000.0

0.5

1.0

1.5

2.0

2.5

<δv>

(x10

-10 cm

3 /s)

Electron Temperature (eV)

Electron collision excitation rate

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Variables’ Spatial and temporal overlap : => for optimum x-ray laser beam output; Te, De, Distribution of specific ions

Necessary Conditions for X-Ray Lasers

Electron density

Ne-like Tiabundance

Overlap of electron density and Ne-like Ti ion distribution with different laser configurations

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Single pass amplification : => huge gain required; smooth electron density profile necessary; long gain medium necessary

Necessary Conditions for X-Ray Lasers

Gain Region

De

x

ce NNn −= 1

220 4/ emNc πω=

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Two Main Goals for the Development of X-Ray Lasers

1. Lasing action at a wavelength as short as possible

Invention of maser at microwave in 1954

Invention of laser at infra red and visible light range in 1960

Theoretical ideas about laser at X-rays in 1960

Experimental observation of X-ray lasers in 1984

First saturated operation of X-ray lasers at 19.6 nm in 1992

First saturated operation at a wavelength shorter than 10 nm in 1996

Saturated x-ray laser at 5.8 nm in 1997, approaching the water window

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Two Main Goals for the Development of X-Ray Lasers

2. X-ray lasers driven by smaller drivers with higher repetition rate

OFI/Recombination Pumping X-ray Lasers in 1993

Capillary Discharge X-ray lasers in 1994

OFI/Collisional Pumping x-ray laser in 1995

Table-top x-ray laser, more efficiencySaturated x-ray lasers produced using several J

Longitudinal pumping and grazing incidence pumpingSaturated operation of x-ray laser at 18.9 nm using 150mJ at 10 Hz

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Development of X-Ray Lasers------first observation

1. Theory: Transition between 2p53p(J=0) 2p53s(J=1) dominates in Ne-like ionsExcitation rates from 2p6 to 2p53p is larger than that from 2p6 to 2p53s;Transition to 2p53p(J=0) through direct monopole excitationTransitions to other levels primarily fed by cascades and recombinations

Dominating lines: Which transition dominates x-ray spectra

1. 12. Experiments: Transition between 2p53p(J=2) 2p53s(J=1) dominates in Ne-like ions

Matthews’s first observation of xrlamplification

Phys. Rev. Lett. 54, 110 (1985)

Amplified transitions:(2p3/23p3/2)J=2->(2p3/23s)J=1(2p1/23p3/2)J=2->(2p1/23s)J=1

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Development of X-Ray Lasers------exploding foil targets

Dominating lines: Lack of predicted lines is due to x-ray’s refraction? Modulating density: Exploding foil targets minimizing the refraction problem.

Rosen’s exploding foil target technique,Observing amplification of transitions (J=2->1)No predicted (J=0->1) dominating.

Problem of dominating lines is closely related to the physical processes in the plasma medium.

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Development of X-Ray Lasers------prepulse technique

Electron Density: Prepulse technique produces smooth electron densityat high density region where J=0->1 lasing takes place

Ne-like Se

Nilson’s experiments with prepulseNilson’s experiments with multi-pulses

Pre-pulse advantages: 1. Produce uniform plasma column with proper electron density, allowing long propagation and

sufficient amplification for saturated output; 2. Preformed plasmas cool down so that driving laser can be absorbed directly in the gain region;

Electron density

Without Prepulse

With prepulse

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Development of X-Ray Lasers------xrl saturation output

Saturation output: Saturation output indicates the stimulated emission extracts the maximum power possible for an excited plasmas; Necessary for applications; All utilize prepulse technique.

Neon-like ions:Transition J=2->1 Transition J=0->1

Ge 23.6nm Ti 32.6nm

Ge 23.2nm Fe 25.5nm

Se 20.6nm Zn 21.2nm

Y 15.5nm Ge 19.6nm

5.86nmDy

7.3nmSm

12.0nmSn

13.2nmCd

14.0nmAg

14.7nmPd

18.9nmMo

20.3nmNb

Nickle-like ion systems:

Driving laser configuration and target configuration are essential for saturation output of xrl.

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Development of X-Ray Lasers------Refraction compensation

Double targets: for compensation of the x-ray beam refraction

Double 75 ps pulse separated by 2.2 ns.Focused intensity on target 1~4x10 13 W/cm -2.

Demonstration of Saturation in a Ni-like Ag X-Ray laser at 14 nm; Zhang et al, PRL 78, 3856 (1997)

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Development of X-Ray Lasers------Approaching water window

Water window wavelength: for coherent biological x-ray imaging

Saturated Amplification in Ni-like Sm at 7 nmZhang et al, Science 276, 1097 (1997)

0

0.2

0.4

0.6

0.8

1

20 40 60 80 100 120 140 160 180 200 220 240

ProteinWater

Tran

smis

sion

Wavelength (?

AgInSn

Sm

TaYb

Gd

Dy

W

Water Window

Y GeLLNL(94)RAL(97)

RAL(97)

RAL(96)

Planned at RAL (99)

GeRAL(92)SIOM(92)

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A g x-ray laser In x-ray laser Sn x-ray laser Sm x-ray laser Dy x-ray laser

W avelength 14 .0 nm 12.6 nm 12.0 nm 7.3 nm 5.8 nm

Gain Coefficient 7.2 cm-1 9.0 cm-1 11.5 cm-1 8.4 cm-1 8 .9 cm-1

Divergence angle 2.1 mrad 2.2 mrad 2.7 mrad 1.2 mrad 1.6 mrad

Deflection angle 4.5 mrad 0.9 mrad 1.2 mrad 1.0 mrad 1.4 mrad

Output Energy 90 µJ 300 µJ 690 µJ 313 µJ 500 µJ

Output Intensity 6.9x1010 W ·cm-2 8.0x1010 W ·cm-2 9.7x10 10 W ·cm-2 2.0x1011 W ·cm-2 3 .0x1011 W ·cm-2

Conversion Efficiency 6.0x10 -7 2 .0x10-6 9 .0x10 -6 2 .1x10-6 6 .0x10-6

Charateristics of X-ray Lasers国家

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Requirements for Divers

100 kJ, 20 ps to 1 ns, 120 TW 10 beams of 74 cm diameter 527 nm, 351 nm (large KDP crystals) Dismantled in 1999

Nova laser system:

Saturated operation of x-ray laser using~ kJ drive energy

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Requirements for Drivers

1 ns, 2.6 kJ, 2.6 TW, 1054 nm

< 1 ps, 100 TW, 1054 nm

1 kJ, 527 nm Nd:glass disk amplifier

Vulcan laser facility:

Saturated operation of x-ray laser using~ 100J drive energy

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Advantages of low driving energy requirementsProposed by Afanasiev, Shlyaptsev (1989)Demonstrated by Nickles, et al (1995)Prepulse + ∼1 ps, 1-10 J pumping

Transient Collisional Excitation (TCE), Table-Top XRLs

Gain Saturation Regime for Laser-Driven Tabletop, Transient Ni-like Ion X-Ray LasersDunn et al, Phys. Rev. Lett. 84, 4834 (2000)

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TCE Requirement for Driver Systems

Wavelength: 1054nm, 5 J, 5 ns; 5 J, 1 ps, 0.0017 Hz

COMET laser facility: Saturated operation of x-ray laser using~ several J drive energy

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Longitudinal Pumping

Highly Directive 18.9 nm Ni-like Mo XRL at 150 mJ PumpingOzaki et al, Phys. Rev. Lett. 89, 253902 (2002)

Demonstration of a Hybrid Collisionally Pumped Soft XRLJanulewicz et al, Phys. Rev. A 63, 033803 (2001)

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Grazing Incidence Pumping (GRIP)

Target

optimum gain region

On-axisx-ray laser

Preformed plasma1 ps Grazing

Incidence Pumping

200 ps

Wavelength: 800nm Short pulse duration: 80 fsLow Power: 300 mJ @ 10 Hz High Power: 15 J @ 2 shots/hr

High-Repetition-rate Grazing-Incidence Pumped X-Ray Laser Operating at 18.9 nmR. Keenan et al, Phys. Rev. Lett. 94, 103901 (2005)

GRIP COMETParameters XRL XRLPump (J): 150 mJ 5 JXRL (J): 10 nJ >10 µJPhotons: 109 1012

Rate (Hz): 10 0.004λ (nm): 18.9 12 - 47Source (µm2): 9 ´20 25 ´100Div. (mrad2): 3 ´5 2.5 ´10Pulse (ps): 2 2 - 8Peak B*: 2.0 ´1023 1.6 ´1025

Average B*‡: 3.7 ´1012 1.3 ´1011

* [Ph. mm-2 mrad-2 s -1 (0.1% BW) -1]‡ For 10 Hz operation

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Grazing Incidence Pumping (GRIP)

1. Grazing-incidence pumping scheme helps increase the path length and energy absorption efficiency

2. Each partition of the 300ps pulse is reflected and dump most of its energy at the turning point

3. Long gain region with a shallow electron density gradient

GRIP advantages:国

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Preformed plasma:

Grazing Incidence Pumping (GRIP)

Modulations of electron density:

• Peak intensity is 1x1011W/cm2

• Peak time is 360ps• 5ns delay time • Prepare an initial plasma (no Ne-like ions)

Second grazing incidence prepulse preparing the plasma

Comparison of density profilesIn normal incidence scheme andIn grazing incidence scheme.

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Grazing Incidence Pumping (GRIP)

Modulations of electron density:

1. Optimum intensity 3x1014W/cm2

2. Maximum gain coefficient happens at the turning point of the main pulse, the same spatial position as the valley 2

3. Valley 2 can work as a channel for the propagation and amplification of x-ray laser beams

De

Gain

Near-field Far-field

Field distributionof xrl beam

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Requirements for Drivers

Wavelength, Pulse width: 800nm, 80 fsEnergy @ 1ω : 300 mJ @ 10 Hz;

15 J @ 2 shots/hrIntensity (25µm x 1.0 cm): 1015 W cm-2;

5 x 1016 W cm-2

LLNL JANUSP laser:

Saturated operation of x-ray laser at 18.9 nm ~ 150mJ drive energy

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2001年－建成20TW飞秒激光装置—极光二号

640mJ/30fs, 20TW=2x1013W, 聚焦功率密度 >3x1019W/cm2

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2006年将建成200TW飞秒激光装置—极光三号

6J/30fs, 200TW=2x1014W, 聚焦功率密度 >3x1020W/cm2

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Discharge Pumped Table-Top XRLs

Discharge pumped H2 laser at 116.1 nm (Waynant, 1972) Discharge pumped Ar laser at 46.9 nm (Rocca et al., 1994)Saturated amplification (1996) Repetitive operation (1998), Application to plasma diagnostics (1998) Full spatial coherence (2000) Desk-top XRL (2002)

Full Spatial CoherenceLiu et al, ICXRL-2000, Pr2-123.

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Saturated XRLs国家

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More efficient XRLs with higher repetition rate

Require evaluation of different pumping geometries for x-ray lasers

Pu

mp

ing

En

erg

y (J

) Rep

etition

Rate (H

z)

Matthews 5 kJ 1984Nilsen 1 kJ 1993Zhang 150 J 1997Nickles 10 J 1997Tommassini 30 J 1999Li 0.15 J 2000Sebban 0.5 J 2001Ozaki 0.15 J 2002

XRL Pump Energy, Rep. Rate Efficiency vs Pumping Pulse Duration

Work Pulse Year Efficiency, εDa Silva 200 ps 1993 1.5 x 10-6

Zhang 75 ps 1997 6 x 10 -7

Warwick 7 ps 1998 1 x 10 -6

Dunn 1.2 ps 2000 1.7 x 10 -6

Sebban 35fs 2001 7 x 10 -8

Sebban 30 fs 2002 2 x 10 -8

Keenan 1.5 ps 2004 7 x 10 -8

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Demonstrated Applications

Main characteristics:

High brightnessHigh coherenceShort pulseShort wavelengthsHigh penetration

Main applications:

Microscopy Science, 258, 269 (1992)

Holography Science, 238, 517 (1987)

Radiography PRL, 76, 3574 (1996)

Deflectometry Science, 265, 514 (1994)

Interferometry Science, 273, 1093 (1996).

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Two-dimensional plasma-imaging

X-ray-laser-backlit image of an accelerated foilShort pulse duration is required togive high spatial resolution

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X-ray laser interferometer for probing high-density,long-scale length plasmas

Electron density measurements of high density plasmas using soft XRL interferometryDa Silva et al, Phys. Rev. Lett. 74, 3991 (1995)

Picosecond X-Ray Laser Interferometryof Dense PlasmasR. F. Smith et al, Phys. Rev. Lett. 89, 065004 (2002)

Shorter wavelengths, high spatial conference are required.

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X-ray microscope images of rat sperm nucleiprepared using different rechniquesShort wavelengths in the Water Window required

Resolution ~ 550

X-ray laser microscopy of biological samples国家

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Applications to Material Science

Time-resolved photoelectron spectroscopyNelson et al, Proc. SPIE 5197, 168 (2003)

Electric field induced surface changeZeitoun et al, Nucl. Inst. Meth. A 416, 189 (1998)

Surface modification with intense XUV irradiationRocca et al, Proc. SPIE 5197, 174 (2003)

Phase transition of ferroelectric domainsTai et al, Phys. Rev. Lett. 89, 257602 (2002).

106℃118℃119℃120℃121℃

24℃

130℃

(a)

(b)(c)(d)(e)(f)

(g)

(h)

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X-ray laser radiography

Measurement of single mode imprint by EUV laser radiographyWolfram et al, Phys. Plasmas 5, 227 (1998)

0 10050 150 0 10050 150 0 10050 150

0-25 25 0-25 25 0-25 25

Position at target (µm)

Mode number (200 µm square)

a) 2ω static RPP b) 2ωSSD c) 2ω ISI

XUVradiograph

2-D FFT ofradiograph

X-ray laser radiography of thin foilsimprinted by different smoothing techniques

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101

102

103

104

10-15 10 -14 10-13 10-12 10-11 10-10 10-9 10-8 10-7

X-ray lasers

Time (s)

•Fundamental processes in Femtosecond time scale: Molecular dynamics, spin dyn. Lattice dyn. Etc.Unexplored areas

•Shorter wavelengths:applications in wider areas of sciences

Science 274, 201(1996)

Future Direction of Plasma XRLs国家

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Summary

FEL X-ray Lasers and Plasma X-ray lasers are Allies

towards the same goals and for similar user community

Many technologies to share

high synchronization, stability, phase control etc

More Close Collaboration between Two Families is expected

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