光电子学优秀PPT.ppt

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1、光电子学光电子学第1页，本讲稿共71页Chapter 7 Some Specific Laser Systems Introduction Laser,that is light amplification by stimulated emission of radiation,have much predominance(优势优势)compared with common light,because laser come into being(形成形成,产生产生)in condition of stimulated by external light or electricity,the p

2、rocess 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 Diodereversion反转反转,逆转逆转第2页，本讲稿共71页雷射种类m第3页，本讲稿共71页雷射种类 continuedcontinued第4页，本讲稿共71页雷射应用第5页，本讲稿

3、共71页the characteristics of laser are that:(1)、high luminance(亮度亮度)lasers luminance is 100000 much than sun lights.(2)、simplicity of light(单色单色,homochromy)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,靛青

4、靛青)and purple.第6页，本讲稿共71页 (3)(3)、high high correlationcorrelation (相关性相关性)Lasers frequency,phase,direction of Lasers frequency,phase,direction of librations librations(振动振动振动振动)are all are all coherent(coherent(一致的一致的一致的一致的),),so its correlation is very high.so its correlation is very high.(4)(4)、st

5、rong directionstrong direction Common light is emitted towards Common light is emitted towards far and nearfar and near(四面八方四面八方四面八方四面八方),but the ),but the laser beam transmit directed(laser beam transmit directed(定向的定向的定向的定向的).and laser.and laser radiationradiations(s(发散发散发散发散)angle angle is very s

6、mall,it close to parallel light.because laser radiations angle is is very small,it close to parallel light.because laser radiations angle is very small,it can transmit far from lamp-house(very small,it can transmit far from lamp-house(光源光源光源光源).).第7页，本讲稿共71页 Owing to the advantages of laser,on the h

7、igh road of Owing to the advantages of laser,on the high road of information in future,it can be applied far and wide(information in future,it can be applied far and wide(广泛的广泛的广泛的广泛的)：for examplefor example,fiber is primary channel to translate data in ,fiber is primary channel to translate data in

8、 the high road of information.At the same time,laser beam the high road of information.At the same time,laser beam can be made much thin than fiber,so the fiber can use laser can be made much thin than fiber,so the fiber can use laser beam translate information in it.beam translate information in it

9、.第8页，本讲稿共71页All kinds of lasers第9页，本讲稿共71页7.1 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.第10页，本讲稿共71页Lasing Principle第11页，本讲稿共71页induce 感应spontaneous自发的stimulate刺激，激发第12页，本讲稿共71页On t

10、he condition of balance,the distribution of particle numbers in E2 and E1 has:From the viewpoint(观点观点)of energy,we know that when a particle transits to low energy from high energy,it will release a photon:It is the same process form low energy to high energy.7.1-17.1-2第13页，本讲稿共71页n nThe characteris

11、tics about The characteristics about spontaneousspontaneous(自发的自发的)radiation:radiation:un-ruled,spontaneous,stochastic(un-ruled,spontaneous,stochastic(随机的随机的随机的随机的),in a word it is an un-),in a word it is an un-correlative(correlative(相关的相关的相关的相关的)radiation and a noiseradiation and a noise.n nThe ch

12、aracteristics about excitated(The characteristics about excitated(激发激发激发激发)radiation:there are four uniform aspects,the same polarized direction(there are four uniform aspects,the same polarized direction(偏偏偏偏振方向振方向振方向振方向),the same frequency,the same phase and the same),the same frequency,the same p

13、hase and the same radiated direction.radiated direction.第14页，本讲稿共71页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 students.One night wh

14、ile discussing job enrichment,the teacher asked if any of us would be happy doing what we did that day for the asked 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,the rest of our lives.A student in the back raised his

15、 hand.Surprised,the teacher asked him,What did you do today?Smiling,he said,I teacher asked him,What did you do today?Smiling,he said,I took off from work.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人和一些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富化的问题。我们半工半读的学生。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

16、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。老师觉得很惊奇，于是问那个学生，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？你今天做什么来着？”，学生笑着回答，学生笑着回答，“我今天请假了我今天请假了”。第15页，本讲稿共71页7.2 the technology of pumping There are two common pumping technologies:optical pumping(be fit for solid and liquid laser)an

17、d electric pumping.棒灯球形聚光腔球形聚光腔椭圆柱形聚光椭圆柱形聚光 腔腔棒灯第16页，本讲稿共71页7.3 pumping and laser efficiencyAbsorption band or groups of levels3hv30hv21Laser transitionFast decayPump transition跃跃迁迁 Figure 7-1 pumping-oscillation cycle of a typical laser第17页，本讲稿共71页 It is evident from this figure that the minimum en

18、ergy input It is evident from this figure that the minimum energy input per output photon is hper output photon is hv v3030,so the power efficiency of the laser ,so the power efficiency of the laser cannot exceed:cannot exceed:to which quantity we will refer as the to which quantity we will refer as

19、 the“atomic quantum efficiency”.“atomic quantum efficiency”.7.3-1第18页，本讲稿共71页n nThe overall laser efficiency depends on:The overall laser efficiency depends on:(1)the fraction of the total pump power that is effective in(1)the fraction of the total pump power that is effective in transferring atoms

20、into level 3 transferring atoms into level 3；（2 2）the pumping quantum efficiency defined as the fraction of the the pumping quantum efficiency defined as the fraction of the atoms that once in 3,make a transition to 2.atoms that once in 3,make a transition to 2.n nThe product of the last two factors

21、,which constitutes an upper The product of the last two factors,which constitutes an upper limit on the efficiency of optically pumped lasers,ranges from limit on the efficiency of optically pumped lasers,ranges from about 1 percent to about 30 percent.about 1 percent to about 30 percent.第19页，本讲稿共71

22、页7.4 laser systemsn nRuby Ruby（红宝石）；（红宝石）；（红宝石）；（红宝石）；n nNdNd3+3+:YAG:YAG 铷铷铷铷-钇铝石榴石钇铝石榴石钇铝石榴石钇铝石榴石n nneodymium yttrium aluminum garnet ;n nNdNd3+3+:glass(:glass(铷玻璃铷玻璃铷玻璃铷玻璃););n nHe-Ne;He-Ne;n nCOCO2;2;n nArAr+;氩氩氩氩(argon)(argon)n nExcimerExcimer：准分子准分子准分子准分子;n nOrganic-dye Organic-dye：有机染料有机染料第20

23、页，本讲稿共71页1.Ruby laser(红宝石红宝石)Ruby was the first material in which laser action was Ruby was the first material in which laser action was demonstrated and is still one of the most useful materialsdemonstrated and is still one of the most useful materials material material：AlAl2 2OO3 3 crystal crystal

24、Active particles:Active particles:CrCr3+铬铬铬铬(chromium)(chromium),typical concentrations are ,typical concentrations are 0.05%by weight;0.05%by weight;Characters:Characters:(1)output:(1)output:(2)(2)The pumping of ruby is usually performed by subjecting it to the light of intense flashlamps（电灯泡）（电灯泡）

25、(quite similar to the types used in flash photography)(闪光摄影术闪光摄影术).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 las

26、er level E is t2=10-3 s.Each decay results in the(spontaneous)emission of a photon,so t2tspont.第21页，本讲稿共71页第22页，本讲稿共71页第23页，本讲稿共71页The pertinent（相关的）（相关的）（相关的）（相关的）energy level diagramenergy level diagramFigure 7-2 Energy levels pertinent to the operation of a ruby laser第24页，本讲稿共71页An absorption spe

27、ctrum of a typical ruby with two An absorption spectrum of a typical ruby with two orientations of optical field relative to the c axis is shown orientations of optical field relative to the c axis is shown as:as:1、The 300K data were derived from transmittance measurements on pink ruby with an avera

28、ge Cr ion concentration of 1.81019 cm-3;2、The two main peaks corresponds to absorption into the useful 4F1 and 4F2 bands,which are responsible for the characteristic(ruby)color.第25页，本讲稿共71页第26页，本讲稿共71页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。The absorption coefficient is:The absorption

29、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第27页，本讲稿共71页Figure 1Figure 1 The detailed plot of the absor

30、ption near the laser The detailed plot of the absorption near the laser emission wavelength is: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 1.581019cm-3第28页，本讲稿共71页Figure 2Figure 2 The width The width v

31、 v of the laser transition as a function of of the laser transition as a function of temperaturetemperatureAt room temperature:V=11cm-1第29页，本讲稿共71页 The helical（螺旋状的）（螺旋状的）flashlamp surrounds the ruby rod（棒）（棒）.The flash excitation is provided by the discharge（卸下）（卸下）of the charge（电荷）（电荷）stored in a

32、capacitor bank(电容器电容器组组)across the lamp.Figure 3Figure 3 Typical setup of a pulsed ruby laser using flashlamp puming and external mirrors.第30页，本讲稿共71页absorption coefficient of the crystalAssume that the flash pulse is rectangular(矩形的矩形的)in time and of duration tflash and that it results in an optica

33、l flux(变迁，通量、流量变迁，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 7.4-2第31页，本讲稿共71页If the absorption quantum efficiency(the probability that the

34、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 :If the lifetime of atoms in level 2 is considerably longer than the flash duration(for example:t2=310-3 s,tflash510-4 s),the spontaneous decay

35、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第32页，本讲稿共71页2.Nd+:YAG(Y3Al5O12)lasermaterialmaterial：YAG YAG 铷铷-钇铝石榴石钇铝石榴石 yttrium aluminum garnet Active particles:Active particles:NdNd3+3+Characters:Characters:

36、1.the laser emission occurs at at room temperature1.the laser emission occurs at at room temperature2.Four-level laser2.Four-level laser3.Spontaneous lifetime t3.Spontaneous lifetime tspont spont=5.510=5.510-4-4s s4.The room temperature cross section at the center of the laser 4.The room temperature

37、 cross section at the center of the laser transiton:transiton:and larger than ruby and larger than ruby Transiton cross section 跃迁截面被定义为单位体跃迁截面被定义为单位体积中单位反转（颠倒）的吸收系数。积中单位反转（颠倒）的吸收系数。第33页，本讲稿共71页2.Nd+:YAG(Y3Al5O12)lasermaterialmaterial：YAG YAG 铷铷-钇铝石榴石钇铝石榴石 yttrium aluminum garnet Active particles:Ac

38、tive particles:NdNd3+3+Characters:Characters:1.the laser emission occurs at at room temperature1.the laser emission occurs at at room temperature2.Four-level laser2.Four-level laser3.Spontaneous lifetime t3.Spontaneous lifetime tspont spont=5.510=5.510-4-4s s4.The room temperature cross section at t

39、he center of the laser 4.The room temperature cross section at the center of the laser transiton:transiton:and larger than ruby and larger than ruby 5.The optical gain constant is approximately 75 times that of ruby,so the 5.The optical gain constant is approximately 75 times that of ruby,so the osc

40、illation threshold is very low,and that can explains the easy continuous oscillation threshold is very low,and that can explains the easy continuous operation of this laser compare to ruby.operation of this laser compare to ruby.6.The absorption responsible for populating(移民移民,粒子粒子)the upper laser l

41、evel takes place in a number of bands between 13000 and 25000 cm-1 .第34页，本讲稿共71页n n钕-钇铝石榴石激光器(亚格激光器亚格激光器)第35页，本讲稿共71页第36页，本讲稿共71页n n图图 2:power supply 电源电源n n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 第37页，本讲稿共71页n n图图图图 3:3:resonator resonator 谐振腔谐振腔谐振腔谐振腔 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，光子在谐振腔中往仪器中使用的

42、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返多次被放大，形成受激辐射的光放大返多次被放大，形成受激辐射的光放大返多次被放大，形成受激辐射的光放大激光。它的两端均是可以调节的，因为很多激光。它的两端均是可以调节的，因为很多激光。它的两端均是可以调节的，因为很多激光。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。若激光器一旦失谐，即光线没有经原因都可以造成谐振腔失谐，

43、比如热膨胀、振动等。若激光器一旦失谐，即光线没有经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，这时必须借助于其它准直仪器进行调整，以重新找回原来的谐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。振状态。振状态。振状态。第38页，本讲稿共71页n n图图图图 4:4:泵浦源和冷却系

44、统泵浦源和冷却系统泵浦源和冷却系统泵浦源和冷却系统n n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抽运到激发态抽运到激发态E3E3，E3E3上的粒子通过上的粒子通过上的粒子通过上的粒子通过无辐射跃迁迅速转移到亚稳态无辐射跃迁迅速转移到亚稳态无辐射跃迁迅速转移到亚稳态无辐射跃迁迅速转移到亚稳态E2E2，而，而，而，而E2E2是一个寿命较长的能级，这样不断是一个寿命较长的能级，这样不断是一个寿命较长的能级，这样不断是一个寿命较长的能级，这样不断积累；而积累；而积累；而积累；而E1E1又不断地减少，

45、从而实现于又不断地减少，从而实现于又不断地减少，从而实现于又不断地减少，从而实现于E2E2间间间间E1E1粒子数的反转。实验粒子数的反转。实验粒子数的反转。实验粒子数的反转。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。集成在一起而且密封以防射线向外射出。集成在一起而且密封以防射线向外射出。集成在一起而且密封以防射线向外射出。n n掺钕的钇铝石榴石晶体掺钕的钇铝石榴石晶体

46、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。是激光器的增益介质，即载体。是激光器的增益介质，即载体。n n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。作的温度。作的温度。作的温度。第39页，本讲稿共71页n n图 5:半导体激光器指示光路1 第40页，本讲稿共71页n n图 6:

47、半导体激光器指示光路2 第41页，本讲稿共71页n n图图图图 7:7:调调调调QQ晶体及电源晶体及电源晶体及电源晶体及电源n n它是一个电光调制器，是由它是一个电光调制器，是由它是一个电光调制器，是由它是一个电光调制器，是由一个电光晶体、偏振片组成，一个电光晶体、偏振片组成，一个电光晶体、偏振片组成，一个电光晶体、偏振片组成，其中偏振片由于反射的作用，其中偏振片由于反射的作用，其中偏振片由于反射的作用，其中偏振片由于反射的作用，即起到起偏器作用又起到检即起到起偏器作用又起到检即起到起偏器作用又起到检即起到起偏器作用又起到检偏器作用。在加电时，驱动偏器作用。在加电时，驱动偏器作用。在加电时，驱

48、动偏器作用。在加电时，驱动泵浦源，此过程为粒子积累泵浦源，此过程为粒子积累泵浦源，此过程为粒子积累泵浦源，此过程为粒子积累阶段，腔内损耗大，低阶段，腔内损耗大，低阶段，腔内损耗大，低阶段，腔内损耗大，低QQ值；值；值；值；在粒子数反转达到最大值时，在粒子数反转达到最大值时，在粒子数反转达到最大值时，在粒子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，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，形成巨脉值突然增加，形成巨脉值突然增加，形成巨脉值突然增加，形成巨脉冲。电光晶体的电源采冲。电光晶体的电源采冲。电光晶体的电源采冲。电光晶体的电源采用的是退压式电源。用的

49、是退压式电源。用的是退压式电源。用的是退压式电源。第42页，本讲稿共71页 The quality factor of the resonator is defined universally as: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:4.7-44.7-5被浪费的tc is the decay lifetime(photon lifetime)第43页，本讲稿共71页n n图图 8:8:倍频晶

50、体n n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YAG输出的输出的1064nm的红外光变成532nm 的可见光段的绿光，使的可见光段的绿光，使人们在不同激光波长的获取方法上又开辟了新的道路。人们在不同激光波长的获取方法上又开辟了新的道路。第44页，本讲稿共71页Figure 4 Energy-level diagram of Nd3+in YAG The lower laser level is at The lower laser level is at E22111cmE22111cm-1-1 from the ground from the ground