光电子学精品课件

1、光电子学第1页，共71页，2022年，5月20日，17点35分，星期一Chapter 7 Some 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 o

2、r 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 Diodereversion反转, 逆转第2页，共71页，2022年，5月20日，17点35分，星期一雷射种类m第3页，共71页，2022

3、年，5月20日，17点35分，星期一雷射种类 continued第4页，共71页，2022年，5月20日，17点35分，星期一雷射应用第5页，共71页，2022年，5月20日，17点35分，星期一the characteristics of laser are that:(1)、high luminance(亮度) lasers luminance is 100000 much than sun lights . (2)、simplicity of light (单色, homochromy) The laser is very pure , but sun light or white li

4、ght can be decomposed and got seven pure light , there are red , orange , yellow , green , blue , indigo(靛, 靛青) and purple .第6页，共71页，2022年，5月20日，17点35分，星期一 (3) 、high correlation (相关性) Lasers frequency , phase , direction of librations (振动) are all coherent(一致的), so its correlation is very high. (4)、

5、strong direction Common light is emitted towards far and near (四面八方) , but the laser beam transmit directed(定向的).and laser radiations(发散) angle is very small , it close to parallel light . because laser radiations angle is very small , it can transmit far from lamp-house (光源) . 第7页，共71页，2022年，5月20日，

6、17点35分，星期一 Owing to the advantages of laser , on the high road of information in future , it can be applied far and wide (广泛的) ： for example , fiber is primary channel to translate data in the high road of information . At the same time , laser beam can be made much thin than fiber , so the fiber ca

7、n use laser beam translate information in it .第8页，共71页，2022年，5月20日，17点35分，星期一All kinds of lasers第9页，共71页，2022年，5月20日，17点35分，星期一7.1 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

8、，共71页，2022年，5月20日，17点35分，星期一Lasing Principle第11页，共71页，2022年，5月20日，17点35分，星期一induce 感应spontaneous自发的stimulate刺激，激发第12页，共71页，2022年，5月20日，17点35分，星期一On the condition of balance, the distribution of particle numbers in E2 and E1 has:From the viewpoint (观点) of energy, we know that when a particle transits

9、 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，共71页，2022年，5月20日，17点35分，星期一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

10、 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.第14页，共71页，2022年，5月20日，17点35分，星期一Off from work 请假了My personnel-management class consisted mainly of ad

11、ult, working students. One night while discussing job enrichment, the teacher 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 teacher asked him, What did you do today? Smiling, he said, I took off from work

12、.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，“你今天做什么来着？”，学生笑着回答，“我今天请假了”。第15页，共71页，2022年，5月20日，17点35分，星期一7.2 the technology of pumping There are two common pumping technologies: optical pumping(be fit for solid and liquid la

13、ser) and electric pumping.棒灯球形聚光腔椭圆柱形聚光 腔棒灯第16页，共71页，2022年，5月20日，17点35分，星期一7.3 pumping and laser efficiencyAbsorption band or groups of levels3hv30hv21Laser transitionFast decayPump transition跃迁 Figure 7-1 pumping-oscillation cycle of a typical laser第17页，共71页，2022年，5月20日，17点35分，星期一 It is evident fro

14、m 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”.7.3-1第18页，共71页，2022年，5月20日，17点35分，星期一The overall laser efficiency depends on: (1) the fraction of the total p

15、ump 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 f

16、rom about 1 percent to about 30 percent. 第19页，共71页，2022年，5月20日，17点35分，星期一7.4 laser systemsRuby （红宝石）；Nd3+ :YAG 铷-钇铝石榴石neodymium yttrium aluminum garnet ;Nd3+:glass (铷玻璃);He-Ne;CO2;Ar+;氩(argon)Excimer：准分子;Organic-dye ：有机染料第20页，共71页，2022年，5月20日，17点35分，星期一1. Ruby laser(红宝石) Ruby was the first material

17、in which laser action was demonstrated and is still one of the most useful materials material：Al2O3 crystalActive particles :Cr3+ 铬 (chromium) , typical concentrations are 0.05% by weight; Characters:(1) output: (2) The pumping of ruby is usually performed by subjecting it to the light of intense fl

18、ashlamps （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) three-level laser. The lifetime of atoms in

19、the upper laser level E is t2=10-3 s . Each decay results in the (spontaneous) emission of a photon, so t2tspont.第21页，共71页，2022年，5月20日，17点35分，星期一第22页，共71页，2022年，5月20日，17点35分，星期一第23页，共71页，2022年，5月20日，17点35分，星期一The pertinent（相关的）energy level diagramFigure 7-2 Energy levels pertinent to the operation o

20、f a ruby laser第24页，共71页，2022年，5月20日，17点35分，星期一An absorption spectrum of a typical ruby with two orientations of optical 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 1.81019 cm-3;2、 The two

21、main peaks corresponds to absorption into the useful 4F1 and 4F2 bands, which are responsible for the characteristic (ruby) color.第25页，共71页，2022年，5月20日，17点35分，星期一第26页，共71页，2022年，5月20日，17点35分，星期一跃迁截面被定义为单位体积中单位反转（颠倒）的吸收系数。 The absorption coefficient is :Where is the transition cross section which is

22、defined as the absorption coefficient per unit inversion per unit volume and has consequently the dimension of area. 7.4-1第27页，共71页，2022年，5月20日，17点35分，星期一Figure 1 The detailed plot of the absorption near the laser emission wavelength is :Sample was a pink ruby laser rod having a 900 c-axis orientati

23、on with respect to the rod axis and a Cr concentration of 1.581019cm-3第28页，共71页，2022年，5月20日，17点35分，星期一Figure 2 The width v of the laser transition as a function of temperatureAt room temperature :V=11cm-1第29页，共71页，2022年，5月20日，17点35分，星期一 The helical （螺旋状的）flashlamp surrounds the ruby rod （棒）. The fla

24、sh 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 mirrors.第30页，共71页，2022年，5月20日，17点35分，星期一absorption coefficient of the crystalAssume that the flash pu

25、lse 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 volu

26、me is 7.4-2第31页，共71页，2022年，5月20日，17点35分，星期一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 :If the lifetime of atoms in level 2

27、 is considerably longer than the flash duration( for example : t2=310-3 s , tflash510-4 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第32页，共71页，2022年，5月20日，17点35分，星期一2. Nd+:YAG(Y3Al5

28、O12) lasermaterial：YAG 铷-钇铝石榴石 yttrium aluminum garnet Active particles :Nd3+Characters: 1. the laser emission occurs at at room temperature2. Four-level laser3. Spontaneous lifetime tspont =5.510-4s4. The room temperature cross section at the center of the laser transiton: and larger than ruby Tran

29、siton cross section 跃迁截面被定义为单位体积中单位反转（颠倒）的吸收系数。第33页，共71页，2022年，5月20日，17点35分，星期一2. Nd+:YAG(Y3Al5O12) lasermaterial：YAG 铷-钇铝石榴石 yttrium aluminum garnet Active particles :Nd3+Characters: 1. the laser emission occurs at at room temperature2. Four-level laser3. Spontaneous lifetime tspont =5.510-4s4. The

30、 room temperature cross section at the center of the laser transiton: and larger than 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 easy continuous operation of this laser compare to ruby.6. The absorptio

31、n responsible for populating(移民,粒子)the upper laser level takes place in a number of bands between 13000 and 25000 cm-1 .第34页，共71页，2022年，5月20日，17点35分，星期一钕-钇铝石榴石激光器 (亚格激光器) 第35页，共71页，2022年，5月20日，17点35分，星期一第36页，共71页，2022年，5月20日，17点35分，星期一图 2 : power supply 电源电源为YAG激光器提供高电压及其它控制电压 第37页，共71页，2022年，5月20日，

32、17点35分，星期一图 3 : resonator 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。第38页，共71页，2022年，5月20日，17点35分，星期一图 4 : 泵浦源和冷却系统泵浦源的作用是将粒子从低能级E1抽运到激发态E3，E3上的粒子通过无辐射跃迁迅速转移到亚稳态E2，而E2是一个寿命较长的能级，这样不断积累；而

33、E1又不断地减少，从而实现于E2间E1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 Y3Al5O12 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，以保证其正常工作的温度。第39页，共71页，2022年，5月20日，17点35分，星期一图 5 : 半导体激光器指示光路1 第40页，共71页，2022年，5月20日，17点35分，星期一图 6 : 半导体激光器指示光路2 第41页，共71页，2022年，5月20日，17点35分，星期一图 7 : 调Q晶体及电源它是一个电光

34、调制器，是由一个电光晶体、偏振片组成，其中偏振片由于反射的作用，即起到起偏器作用又起到检偏器作用。在加电时，驱动泵浦源，此过程为粒子积累阶段，腔内损耗大，低Q值；在粒子数反转达到最大值时，退除电光晶体上的电压，Q值突然增加，形成巨脉冲。电光晶体的电源采用的是退压式电源。 第42页，共71页，2022年，5月20日，17点35分，星期一 The quality factor of the resonator is defined universally as: Where is the stored energy, is the resonant frequency, and is the po

35、wer 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，共71页，2022年，5月20日，17点35分，星期一图 8 : 倍频晶体它是一个非线形元件，在该实验中可以使YAG输出的1064nm的红外光变成532nm 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。 第44页，共71页，2022年，5月20日，17点35分，星期一Figure 4 Energy-level diagram of Nd3+

36、 in YAG The lower laser level is at E22111cm-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.第45页，共71页，2022年，5月20日，17点35分，星期一Figure 5 The spontaneous emission spectrum of the laser transiti

37、on at The width of the gain linewidth at room temperature is v6 cm-1第46页，共71页，2022年，5月20日，17点35分，星期一3. Neodymium(钕)-Glass Lasermaterial：glassActive particles :Nd3+ ionCharacters: 1.Four-level laser 3. the lower level is approximately 1950 cm-1 above the ground state (基态). 4. The fluorescent linewidt

38、h can be measured off directly and ranges, for the glasses shown , around 300 cm-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. D

39、ifferent ions consequently radiate at slightly different frequencies, causing a broadening of the spontaneous emission spectrum. 2.1.54um Er玻璃激光器 第47页，共71页，2022年，5月20日，17点35分，星期一Figure 6 Energy-level diagram for the ground state The state involved in laser emission at 1.059um for Nd3+ in a rubidium

40、potassium barium silicate glassNeodymium (钕)rubidium 化铷potassium 化钾barium 钡Silicate 硅酸盐第48页，共71页，2022年，5月20日，17点35分，星期一Figure 7 The absorption bands responsible for pumping the laser levelThe probability that the absorption of a photon in any of these bands will result in pumping an atom to the uppe

41、r laser level (that is, the absorption quantum efficiency) has been estimated at about 0.4. Sb 化锑 (antimony)第49页，共71页，2022年，5月20日，17点35分，星期一Figure 8 Lifetime as a function of concentration for two glass series浓度第50页，共71页，2022年，5月20日，17点35分，星期一4. He-Ne laserThe first CW (continuous) laser, as well as

42、 the first gas laser, was one 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: A dc (or rf) discharge is established in the gas mi

43、xture containing typically, 1.0mm Hg of He and 0.1mm Hg of Ne. the energetic electrons in the discharge excite helium (He) atoms into 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

44、 whose lifetimes are 10-4 s and 510-6 s second, respectively. 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

45、 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.第51页，共71页，2022年，5月20日，17点35分，星期一Taking attendance 点名On my first day of classes at my Uni

46、versity I took a front-row seat in my literature course. The professor told us we would be responsible for reading five books, and that he would provide us with a list of authors from which we could choose. Then he ambled over to the lectern (演讲台), took out his class book and began, Baker, Black, Br

47、ooks, Carter, Cook. I was working feverishly (兴奋地)to get down all the names when I felt a tap on my shoulder. The student in back of me whispered, Hes 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”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：

48、“他在点名呢。”第52页，共71页，2022年，5月20日，17点35分，星期一Figure 9 He-Ne energy levels.第53页，共71页，2022年，5月20日，17点35分，星期一Figure 10 Typical gas laser setupthe gas envelope windows are tilted Brewsters angle so radiation with the electric field vector in the plane of the paper suffers no reflection losses at the windows.

49、 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. 第54页，共71页，2022年，5月20日，17点35分，星期一5. carbon dioxide (CO2) laserCharacter: The CO2 laser is representative (典型的)

50、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.第55页，共71页，2

51、022年，5月20日，17点35分，星期一(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 th

52、e internuclear axis. Figure 12 第56页，共71页，2022年，5月20日，17点35分，星期一 vibration manner OCOOOC第57页，共71页，2022年，5月20日，17点35分，星期一 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 stat

53、e of the CO2 molecule can be described by a set of three integers (u1,u2, u3) that correspond respectively to the degree of excitation of the three modes described. the total energy of the molecule is : Where v1,v2,v3 are the frequencies of the symmetric stretch, bending, and asymmetric stretch mode

54、s, respectively.第58页，共71页，2022年，5月20日，17点35分，星期一pumping 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 3、resonant transfer （共振跃迁） 第59页，共71页，2022年，5月20日，17点35分，星期一Figure 11 The

55、low vibrational levels of CO2nitrogen第60页，共71页，2022年，5月20日，17点35分，星期一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) level

56、s 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第61页，共71

57、页，2022年，5月20日，17点35分，星期一the laser levels are all near the ground state, and the atomic quantum efficiency v21/v30 is about 45 percent; 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 lo

58、ng-lived (001) level;a very large fraction of the N2 molecules that are excited by the discharge tend to collect in the u3=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 re

59、presented by:(u3=1)+(000)+K.E.=(u3=0)+(001)N2N2CO2CO2第62页，共71页，2022年，5月20日，17点35分，星期一气体气体 + -后反射镜输出镜冷却液冷却液第63页，共71页，2022年，5月20日，17点35分，星期一6. Ar+ laser 氩 (argon) the Ar+ laser is one of the most important lasers in use today.Characters:1. Transition between highly excited states of the singly ionized argon atom c