Chapter 7 Chapter 7 Some Specific Laser SystemsSome Specific Laser Systems

Introduction Laser , that is light amplification by stimulated emission of radiation , have much predominance( 优势 ) compared with common light , because laser come into being( 形成 , 产生 ) in condition of stimulated by external light or electricity , the process is that the stimulation cause the electron in low energy jump to high energy level .and when the electron in high energy level much than in the low level , that can be said reversion of electron .

Laser Laser DiodeDiode

reversion

反转 , 逆转

雷射种类雷射种类

μm

雷射种类雷射种类 continuedcontinued

雷射应用雷射应用(1)测量 （ a) 直线基准 （ b) 测距装置 （ c) 划线

(2)量测 （ a) 精密的长度测定 （ b) 雷射雷达（ c) 都卜勒流速计 （ d) 缺陷值测 (e) 平面度测

(3)通信 光缆电缆通信

(4)资讯处理 （ a) 光记忆体 （ b) 光计算尺（ c) 印表机（ d) 显示器 (e) 雷射光碟

(5)医疗（ a) 雷射手术刀（ b) 眼睛检查治疗（ c) 皮肤的治疗 （ d) 癌治疗

(6)能量（ a) 核融合（ b) 电路诊断

(7)加工（ a) 钻孔（ b) 切割 （ c) 焊接（ d) 热处理等

the characteristics of laser are that:

(1) 、 high luminance( 亮度 )

laser’s luminance is 100000 much than sun light’s .

(2) 、 simplicity of light ( 单色 ) The laser is very pure , but sun light or white light can be decomposed and got seven pure light , there are red , orange , yellow , green , blue , indigo( 靛 , 靛青 ), purple .

(3) (3) 、、 high high correlationcorrelation (( 相关性相关性 )) Laser’s frequency , phase , direction of Laser’s frequency , phase , direction of librations librations (( 振动振动 ) ) are are

all coherent(all coherent( 一致的一致的 ),),. so its correlation is very high.. so its correlation is very high.

(4)(4) 、、 strong directionstrong direction Common light is emitted towards Common light is emitted towards far and nearfar and near ( ( 四面八方四面八方 ) , b) , b

ut the laser beam transmit directed(ut the laser beam transmit directed( 定向的定向的 )).and laser .and laser radiatiradiationon’s(’s( 发散发散 ) ) angle is very small , it close to parallel light . becaangle is very small , it close to parallel light . because laser radiation’s angle is very small , it can transmit far frouse laser radiation’s angle is very small , it can transmit far from lamp-house (m lamp-house ( 光源光源 ) . ) .

Owing to the advantages of laser , on the high road of infOwing to the advantages of laser , on the high road of information in future , it can be applied far and wide (ormation in future , it can be applied far and wide ( 广泛广泛的的 ) ) ：：

for examplefor example , fiber is primary channel to translate data i , fiber is primary channel to translate data in the high road of information . At the same time , laser ben the high road of information . At the same time , laser beam can be made much thin than fiber , so the fiber can use am can be made much thin than fiber , so the fiber can use laser beam translate information in it .laser beam translate information in it .

All kinds of lasers

7.1 the theory of excitated radiation7.1 the theory of excitated radiation

Laser , that is light amplification by stimulated emission of radiation. So first, we will learn the theory of excitated radiation.

Lasing Lasing PrinciplePrinciple

induce

感应

spontaneous

自发的

stimulate

刺激，激发

On the condition of balance, the distribution of particle numbers in E2 and E1 has:

2

1

exp( )B

n h

n k T

From the viewpoint ( 观点 ) of energy, we know that when a particle transits to low energy from high energy, it will release a photon:

2 1E E h

It is the same process form low energy to high energy.

7.1-1

7.1-2

The characteristics about spontaneous ( 自发的 )radiation:

un-ruled , spontaneous, stochastic ( 随机的 ) , in a word it is an un-correlative ( 相关的 ) radiation and a noise.

The characteristics about excitated( 激发 )radiation:

there are four uniform aspects, the same polarized direction ( 偏振方向 ), the same frequency, the same phase and the same radiated direction.

Off from work Off from work 请假了请假了My personnel-management class consisted mainly of adult, working My personnel-management class consisted mainly of adult, working

students. One night while discussing job enrichment, the teacher astudents. One night while discussing job enrichment, the teacher asked if any of us would be happy doing what we did that day for thsked if any of us would be happy doing what we did that day for the rest of our lives. A student in the back raised his hand. Surprised, e rest of our lives. A student in the back raised his hand. Surprised, the teacher asked him, "What did you do today?" Smiling, he said, the teacher asked him, "What did you do today?" Smiling, he said, "I took off from work.""I took off from work."

我曾参加过一个员工管理培训课程，我们班上基本上都是成年我曾参加过一个员工管理培训课程，我们班上基本上都是成年人和一些半工半读的学生。一天晚上我们在课上讨论工作丰人和一些半工半读的学生。一天晚上我们在课上讨论工作丰富化的问题。我们的老师问我们当中有没有人愿意一辈子做富化的问题。我们的老师问我们当中有没有人愿意一辈子做今天所做的事情。坐在教室最后面的一个学生举起了手。老今天所做的事情。坐在教室最后面的一个学生举起了手。老师觉得很惊奇，于是问那个学生，“你今天做什么来着？”，师觉得很惊奇，于是问那个学生，“你今天做什么来着？”，学生笑着回答，“我今天请假了”。学生笑着回答，“我今天请假了”。

7.2 the technology of pumping7.2 the technology of pumping

There are two common pumping technologies: optical pumping(be fit for solid and liquid laser) and electric pumping.

棒 灯

球形聚光腔 椭圆柱形聚光 腔

棒 灯

7.3 pumping and laser efficiency7.3 pumping and laser efficiency

Absorption band or groups of levels

3

hv30hv21

Laser transition

Fast decay

Pump transition跃迁

Figure 7-1 pumping-oscillation cycle of a typical laser

It is evident from this figure that the minimum energy input per output photon is hv30 , so the power efficiency of the laser cannot exceed:

to which quantity we will refer as the “atomic quantum efficiency”.

21

30atomic

7.3-1

The overall laser efficiency depends on:

(1) the fraction of the total pump power that is effective in transferring atoms into level 3 ；

（ 2 ） the pumping quantum efficiency defined as the fraction of the atoms that once in 3, make a transition to 2.

The product of the last two factors, which constitutes an upper limit on the efficiency of optically pumped lasers, ranges from about 1 percent to about 30 percent.

7.4 laser systems Ruby Ruby （红宝石）；（红宝石）；

Nd3+ :YAG 铷 - 钇铝石榴石 neodymium yttrium aluminum gar

net ; Nd3+:glass ( 铷玻璃 );

He-Ne;

CO2;

Ar+; 氩 (argon)

Excimer ：准分子 ;

Organic-dye ：有机染料

1. 1. Ruby Ruby laser(laser( 红宝石红宝石 )) Ruby was the first material in which laser action was de

monstrated and is still one of the most useful materials

materialmaterial ：： AlAl22OO33 crysta crystallActive particles :Active particles :CrCr3+ 铬 铬 (chromium)(chromium) , typical concentrations , typical concentrations are 0.05% by weight;are 0.05% by weight;

Characters:Characters: (1) output: (1) output: 0.6943o m (2) (2) The pumping of ruby is usually performed by subjecting it to the light of intense flashlamps （电灯泡） (quite similar to the types used in flash photography) ( 闪光摄影术 ). And A portion of this light that corresponds in frequency to the two absorption bands 4F2 and 4F1 is absorbed, thereby causing Cr3+ ions to be transferred into these levels. (3) (3) three-level laser. The lifetime of atoms in the upper laser level E is t2=10-3 s . Each decay results in the (spontaneous) emission of a photon, so t2≈tspont..

The pertinentThe pertinent （相关的）（相关的） energy level diagraenergy level diagramm

Figure 7-2 Energy levels pertinent to the operation of a ruby laser

An absorption spectrum of a typical An absorption spectrum of a typical ruby with two orientations of optical ruby with two orientations of optical

field relative to the c axis is shown as: field relative to the c axis is shown as:

1 、 The 300K data were derived from transmittance measurements on pink ruby with an average Cr ion concentration of 1.8×1019 cm-3;

2 、 The two main peaks corresponds to absorption into the useful 4

F1 and 4F2 bands, which are responsible for the characteristic (ruby) color.

跃迁截面被定义为单位体积中单位反转（颠跃迁截面被定义为单位体积中单位反转（颠倒）的吸收系数。倒）的吸收系数。

1 2( ) ( ) ( )N N

The absorption coefficient is :The absorption coefficient is :

Where is the transition cross section which is defined Where is the transition cross section which is defined as as the absorption coefficient per unit inversion per unit volume and has consequently the dimension of area.

7.4-1

Figure 1Figure 1 The detailed plot of the absorption near the The detailed plot of the absorption near the laser emission wavelength is :laser emission wavelength is :

Sample was a pink ruby laser rod having a 900 c-axis orientation with respect to the rod axis and a Cr concentration of 1.58×1019cm-3

Figure 2 The width v of the laser transition as a function of temperature

At room temperature :△V=11cm-1

The helical （螺旋状的） flashlamp surrounds the ruby rod （棒） . The flash excitation is provided by the discharge （卸下） of the charge （电荷） stored in a capacitor bank ( 电容器组 ) across the lamp.

Figure 3 Typical setup of a pulsed ruby laser using flashlamp puming and external mirro

rs.

0

( ) ( )flasht s d

absorption coefficient

of the crystal

Assume that the flash pulse is rectangular ( 矩形的 ) in time and of duration tflash and that it results in an optical flux ( 变迁，通量、流量 ) at the crystal surface having s(v) watts per unit area per unit frequency at the frequency v. If the absorption coefficient is , then the amount of energy absorption by the crystal per unit volume is

( )v

7.4-2

If the absorption quantum efficiency (the probability that the absorption of a pump photon at v results in transferring one atom into the upper laser level) is , the number of atoms pumped into level 2 per unit volume is :

( )

2

0

( ) ( ) ( )flash

sN t d

h

If the lifetime of atoms in level 2 is considerably longer than the flash duration( for example : t2=3×10-3 s , tflash≈5×10-4 s), the spontaneous decay out of level 2 during the time of the flash pulse can be neglected, and then N2

represents the population of level 2 after the flash.

7.4-3

2. Nd2. Nd++:YAG:YAG(Y(Y33AlAl55OO1212)) laser lasermaterialmaterial ：： YAG YAG 铷 - 钇铝石榴石 yttrium aluminum garnet

Active particles :Active particles :NdNd3+3+

Characters:Characters:

1. the laser emission occurs at at room temperature1. the laser emission occurs at at room temperature1.0641o m 2. Four-level laser2. Four-level laser

3. Spontaneous lifetime t3. Spontaneous lifetime tspont spont =5.5×10=5.5×10-4-4ss4. The room temperature cross section at the center of the laser tra4. The room temperature cross section at the center of the laser transiton:nsiton: and larger than rubyand larger than ruby

19 29 10 cm ＝20 2

ruby 1.22 10 cm ＝

Transiton crossTransiton cross section section 跃迁截面被定义为单跃迁截面被定义为单位体积中单位反转（颠倒）的吸收系数。位体积中单位反转（颠倒）的吸收系数。

2. Nd2. Nd++:YAG:YAG(Y(Y33AlAl55OO1212)) laser lasermaterialmaterial ：： YAG YAG 铷 - 钇铝石榴石 yttrium aluminum garnet

Active particles :Active particles :NdNd3+3+

Characters:Characters:

1. the laser emission occurs at at room temperature1. the laser emission occurs at at room temperature1.0641o m 2. Four-level laser2. Four-level laser

3. Spontaneous lifetime t3. Spontaneous lifetime tspont spont =5.5×10=5.5×10-4-4ss4. The room temperature cross section at the center of the laser tra4. The room temperature cross section at the center of the laser transiton:nsiton: and larger than rubyand larger than ruby

19 29 10 cm ＝20 2

ruby 1.22 10 cm ＝

5. The optical gain constant is approximately 75 times that of ruby, 5. The optical gain constant is approximately 75 times that of ruby, so the oscillation threshold is very low ,and that can explains the easso the oscillation threshold is very low ,and that can explains the easy continuous operation of this laser compare to ruby.y continuous operation of this laser compare to ruby.6. The absorption responsible for populating( 移民 , 粒子 )the upper laser level takes place in a number of bands between 13000 and 25000 cm-1 .

钕钕 -- 钇铝石榴石激光器 钇铝石榴石激光器 (( 亚格激光器亚格激光器 ) )

图 图 2 : 2 : power supply power supply 电源电源 电源为电源为 YAGYAG 激光器提供高电压及其它控制电压 激光器提供高电压及其它控制电压

图 图 3 :3 : resonator 谐振腔谐振腔 仪器中使用的谐振腔是平凹腔，它是提供光学正反馈的必要条件，光子在谐仪器中使用的谐振腔是平凹腔，它是提供光学正反馈的必要条件，光子在谐

振腔中往返多次被放大，形成受激辐射的光放大――激光。它的两端均是可振腔中往返多次被放大，形成受激辐射的光放大――激光。它的两端均是可以调节的，因为很多原因都可以造成谐振腔失谐，比如热膨胀、振动等。若以调节的，因为很多原因都可以造成谐振腔失谐，比如热膨胀、振动等。若激光器一旦失谐，即光线没有经过足够放大就逸出腔外，这时必须借助于其激光器一旦失谐，即光线没有经过足够放大就逸出腔外，这时必须借助于其它准直仪器进行调整，以重新找回原来的谐振状态。它准直仪器进行调整，以重新找回原来的谐振状态。

图 图 4 : 4 : 泵浦源和冷却系统泵浦源和冷却系统 泵浦源的作用是将粒子从低能级泵浦源的作用是将粒子从低能级 E1E1 抽运到激发态抽运到激发态 E3E3 ，， E3E3 上的粒上的粒

子通过无辐射跃迁迅速转移到亚稳态子通过无辐射跃迁迅速转移到亚稳态 E2E2 ，而，而 E2E2 是一个寿命较长是一个寿命较长的能级，这样不断积累；而的能级，这样不断积累；而 E1E1 又不断地减少，从而实现于又不断地减少，从而实现于 E2E2 间间 EE11 粒子数的反转。实验中采用的是氙灯泵浦，实际产品是将氙灯和粒子数的反转。实验中采用的是氙灯泵浦，实际产品是将氙灯和掺钕的钇铝石榴石晶体集成在一起而且密封以防射线向外射出。 掺钕的钇铝石榴石晶体集成在一起而且密封以防射线向外射出。

掺钕的钇铝石榴石晶体 掺钕的钇铝石榴石晶体 Y3Al5O12 Y3Al5O12 是激光器的增益介质，即载体。是激光器的增益介质，即载体。

冷却系统是为泵中的掺钕的钇铝石榴石晶体提供水冷系统，以保证冷却系统是为泵中的掺钕的钇铝石榴石晶体提供水冷系统，以保证其正常工作的温度。其正常工作的温度。

图 图 5 : 5 : 半导体激光器指示光路半导体激光器指示光路 1 1

图 图 6 : 6 : 半导体激光器指示光路半导体激光器指示光路 2 2

图 图 7 : 7 : 调调 QQ 晶体及电晶体及电源源

它是一个电光调制器，它是一个电光调制器，是由一个电光晶体、偏是由一个电光晶体、偏振片组成，其中偏振片振片组成，其中偏振片由于反射的作用，即起由于反射的作用，即起到起偏器作用又起到检到起偏器作用又起到检偏器作用。在加电时，偏器作用。在加电时，驱动泵浦源，此过程为驱动泵浦源，此过程为粒子积累阶段，腔内损粒子积累阶段，腔内损耗大，低耗大，低 QQ值；在粒子值；在粒子数反转达到最大值时，数反转达到最大值时，退除电光晶体上的电压，退除电光晶体上的电压，QQ值突然增加，形成巨值突然增加，形成巨脉冲。电光晶体的电源脉冲。电光晶体的电源采用的是退压式电源。 采用的是退压式电源。

The quality factor of the resonator is defined universally as:

/Q

P d dt

Where is the stored energy, is the resonant frequency, and is the power dissipated. By comparing 4.7-4 and 4.7-1 we obtain:

/P d dt

cQ t

4.7-4

4.7-5

被浪费的

tc is the decay lifetime (photon lifetime)

图 图 8 : 8 : 倍频晶体倍频晶体 它是一个非线形元件，在该实验中可以使它是一个非线形元件，在该实验中可以使 YAGYAG 输输

出的出的 1064nm1064nm 的红外光变成的红外光变成 532nm 532nm 的可见光段的可见光段的绿光，使人们在不同激光波长的获取方法上又的绿光，使人们在不同激光波长的获取方法上又开辟了新的道路。 开辟了新的道路。

Figure 4Figure 4 Energy-level diagram of Nd Energy-level diagram of Nd3+3+ in YAG in YAG

• The lower laser level is at E2≈2111cm-1 from the ground state. so that at room temperature its population is down by a factor of exp(-E2/kT) ≈e-10 from that of the ground state and can be neglected.

Figure 5Figure 5 The spontaneous The spontaneous emission spectrum of the laser emission spectrum of the laser

transition at transition at 1

0 64 m －＝1. 0

The width of the gain linewidth at room temperature is △v≈6 cm-1

3. Neodymium(3. Neodymium( 钕钕 )-Glass Laser)-Glass Laser materialmaterial ：： glassglass Active particles :Active particles :NdNd3+ 3+ ionion Characters: Characters: 1.Four-level laser1.Four-level laser

3. the lower level is approximately 1950 cm-1 above the ground state (基态 ). 4. The fluorescent linewidth can be measured off directly and ranges, for th

e glasses shown , around 300 cm 300 cm-1 -1 ，， this width is approximately a factor of 50 larger than that of Nd3+ in YAG. This is due to the amorphous ( 无定形的，无组织的 ) structure of glass, which causes different Nd3+ ions to “see” slightly different surroundings.

5. 5. Different ions consequently radiate at slightly different frequencies, causing a broadening of the spontaneous emission spectrum.

1.06o m 2. 1.54um Er 玻璃激光器

Figure 6Figure 6 Energy-level diagram for the ground Energy-level diagram for the ground

statestate

The state involved in laser emission at 1.059um for Nd3+ in a rubidium potassium barium silicate glass

Neodymium (Neodymium ( 钕钕 ))rubidium [rubidium [ 化化 ]] 铷铷potassium [potassium [ 化化 ]]钾钾barium barium 钡钡Silicate Silicate 硅酸盐硅酸盐

Figure 7 The absorption bands responsible for pumping the laser level

The probability that the absorption of a photon in any of these bands will result in pumping an atom to the upper laser level (that is, the absorption quantum efficiency) has been estimated at about 0.4.

Sb 〈化〉锑 (antimony)

Figure 8Figure 8 Lifetime as a function of Lifetime as a function of concentration for two glass seriesconcentration for two glass series

浓度

4. He-Ne laser4. He-Ne laser The first CW (continuous) laser, as well as the first gas laser, was o

ne in which a transition between the 2S and the 2P levels in atomic Ne resulted in the emission of 1.15um radiation .Since then transitions in Ne were used to obtain laser oscillation at 0.6328um and at 3.39um.

Characters: Characters: 1. A dc (or rf) discharge is established in the gas mixture containing t

ypically, 1.0mm Hg of He and 0.1mm Hg of Ne. 2. the energetic electrons in the discharge excite helium (He) atoms in

to a variety of excited states. In the normal cascade of these excited atoms down to the ground state, many collect in the long-lived metastable states ( 亚稳态 ) 23S and 21S whose lifetimes are 10-4 s and 5×10-6 s second, respectively.

3. Since these long-lived (metastable) levels nearly coincide in energy with the 2S and 3S levels of Ne, they can excite Ne atoms into these two excited states. This excitation takes place when an excited He atom collides with (碰撞 ) a Ne atom in the ground state and exchanges energy with it. The small difference in energy is taken up by the kinetic ( 动力学的 ) energy of the atoms after the collision. This is the main pumping mechanism in the He-Ne system.

Taking attendance Taking attendance 点名点名On my first day of classes at my University I took a front-row seOn my first day of classes at my University I took a front-row se

at in my literature course. The professor told us we would be at in my literature course. The professor told us we would be responsible for reading five books, and that he would provide responsible for reading five books, and that he would provide us with a list of authors from which we could choose. Then hus with a list of authors from which we could choose. Then he ambled over to the lectern (e ambled over to the lectern ( 演讲台演讲台 )), took out his class boo, took out his class book and began, "Baker, Black, Brooks, Carter, Cook..." I was wk and began, "Baker, Black, Brooks, Carter, Cook..." I was working feverishly (orking feverishly ( 兴奋地兴奋地 ))to get down all the names when I fto get down all the names when I felt a tap on my shoulder. The student in back of me whispereelt a tap on my shoulder. The student in back of me whispered, "He's taking attendance." d, "He's taking attendance."

大学的第一天，文学课我坐在了前排。教授告诉我们这学期必大学的第一天，文学课我坐在了前排。教授告诉我们这学期必须得读五本书，他提供我们可供选择的作者名单。随后他缓步须得读五本书，他提供我们可供选择的作者名单。随后他缓步走上讲台，拿出课本，“贝克、布莱克、布鲁斯、卡特、库克走上讲台，拿出课本，“贝克、布莱克、布鲁斯、卡特、库克…”为了写下所有的名字，我不得不疯狂的作着记录。这时有…”为了写下所有的名字，我不得不疯狂的作着记录。这时有人轻轻的拍我肩膀，坐在我后面的学生悄悄告诉我：“他在点人轻轻的拍我肩膀，坐在我后面的学生悄悄告诉我：“他在点名呢。”名呢。”

Figure 9Figure 9 He-Ne energy He-Ne energy levels.levels.

Figure 10Figure 10 Typical gas laser setup Typical gas laser setup

the gas envelope windows are tilted Brewster’s angle so radiation with the electric field vector in the plane of the paper suffers no reflection losses at the windows. This causes the output radiation to be polarized in the sense shown, since the orthogonal polarization undergoes reflection losses at the windows and, consequently, has a higher threshold.

B

5. 5. carbon dioxide (COcarbon dioxide (CO22) laser) laser

Character:

The CO2 laser is representative (典型的 ) of the so-called molecular laser in which the energy levels of concern involve the internal vibration of the molecules---that is , the relative motion of the constituent ( 组成的 ) atoms. The atomic electrons remain in their lowest energetic states and their degree of excitation is not affected.

•(a) the molecule is at rest; (b) the atoms vibrate along the internuclear (原子核间的 ) axis in a symmetric manner; (c) the molecules vibrate symmetrically along an axis perpendicular (垂直的 ) to the internuclear axis the bending(弯曲 )mode. In (d) the atoms vibrate asymmetrically along the internuclear axis.

Figure 12

vibration mannervibration manner

O C O

O OC

the mode (d) is referred to as the asymmetric stretching (拉伸 ) mode. In the first approximation one can assume that the three normal modes are independent of each other, so the state of the CO2 molecule can be described by a set of three integers (v1,v2,v3) that correspond respectively to the degree of excitation of the three modes described.

the total energy of the molecule is :

1 2 3 1 1 2 2 3 3( , , ) ( 1/ 2) 1/ 2 1/ 2E v v v hv v hv v hv v

Where v1,v2,v3 are the frequencies of the symmetric stretch, bending, and asymmetric stretch modes, respectively.

pumping mannerpumping mannerThere have three processes to excite CO2 molecular to the upper level which is 001 level.

1 、 straightforward collision between two electrons

2 、 step by step transition

2 2(000) (001)CO e CO e

2 2 2 2(000) (00 ) (001) (00 1)CO CO n CO CO n

3 、 resonant transfer （共振跃迁）

2 2 2 2(000) ( 1) (001) ( 0)CO N v CO N v

Figure 11 The low vibrational levels of CO2nitrogen

Figure 7-17 (a) Some of the low-lying vibrational levels of the carbon dioxide (CO2) molecule, including the upper and lower levels for the 10.6μm and 9.6μm laser transitions. (b) Ground state (v=0) and first excited state (v=l) of the nitrogen molecule, which plays an important role in the selective excitation of the (001) CO2 level.

The upper laser level (001) is thus one in which only the asymmetric stretch mode ,figure 7-18 (d), is excited and contains a single quantum hv3 of energy.

The laser transition at 10.6um takes place between the (001) and (100) levels of CO2 . The excitation is provided usually in a plasma ( 等离子体 ) discharge that, in addition to CO2 typically contains N2 and He. The CO2 laser possesses a high overall working efficiency of about 30 percent. This efficiency results primarily from three factors:

carbon dioxide Nitrogen helium

1. the laser levels are all near the ground state, and the atomic quantum efficiency v21/v30 is about 45 percent;

2. a large fraction of the CO2 molecules excited by electron impact cascade down the energy ladder from their original level of excitation and tend to collect in the long-lived (001) level;

3. a very large fraction of the N2 molecules that are excited by the discharge tend to collect in the v=1 level.

The slight deficiency in energy (about 18 cm-1 ) is made up by a decrease of the total kinetic energy of the molecules following the collision. This collision can be represented by:

(v=1)+(000)+K.E.=(v=0)+(001)

气体 气体

2 2, ,CO N He

+ -

后反射

镜

输出镜

冷却液 冷却液

6. Ar6. Ar+ + laser laser 氩 氩 (argon)(argon) the Ar+ laser is one of the most important lasers in use tod

ay. Characters:

1. Transition between highly excited states of the singly ionized argon atom can be used to obtain oscillation at a number of visible (or near visible) wavelengths between 0.35um and 0.52um.

2. The Ar+laser can be operated in a pure Ar discharge that contains no other gases. The excitation mechanism involves collisions with energetic (4---5eV) electrons. Since the mean electron energy is small compared to the energy of the upper laser level (20eV above the ground state of the ion), it is clear that pumping is achieved by Multiple collisions of Ar+ ground state ions with electrons followed by a number of cascading paths.

氩氩氪氪离子激光器离子激光器 华东师范 华东师范

氩氪离子激光器 氩氪离子激光器 ((南京三乐光电子有限公司南京三乐光电子有限公司 ) )

氩氪离子激光器 氩氪离子激光器 ((南京三乐光电子有限公司南京三乐光电子有限公司 ) )

Figure 13 The pertinent energy level scheme

The most prominent transition

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now and discuss their applies.now and discuss their applies.

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