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1、激光专业英语2讲解n n本课程是本课程是激光加工专业的必修课激光加工专业的必修课。本课程的学习，目的在。本课程的学习，目的在于帮助学生在专业学习和研究中更好地应用英语，以逐步于帮助学生在专业学习和研究中更好地应用英语，以逐步达到能用英语较熟练地阅读本专业的文献资料及适应其他达到能用英语较熟练地阅读本专业的文献资料及适应其他科技交流活动的需要。科技交流活动的需要。n n本课程的教学基本要求本课程的教学基本要求:n n学习常用学习常用激光工程激光工程英语词汇、术语；英语词汇、术语；n n掌握科技英语的特点；掌握科技英语的特点；n n提高运用英语从事提高运用英语从事激光激光工程相关的阅读、写作、会话
2、工程相关的阅读、写作、会话的能力。的能力。n n本课程由本课程由二二个部分组成：个部分组成：n n第一部分偏重于第一部分偏重于激光激光英语文章的英语文章的英汉翻译英汉翻译n n第二部分偏重于第二部分偏重于激光激光英语文章的英语文章的汉英翻译汉英翻译n n课程第一部分的目标：课程第一部分的目标：n n帮助学生能用英语较熟练地阅读本专业的文献资料帮助学生能用英语较熟练地阅读本专业的文献资料n n在方法上，选择本专业内几个通用的理论或技术基础在方法上，选择本专业内几个通用的理论或技术基础问题为背景，要求学生问题为背景，要求学生通过直接阅读原版技术资料掌通过直接阅读原版技术资料掌通过直接阅读原版技术资
3、料掌通过直接阅读原版技术资料掌握相关的知识和技能握相关的知识和技能握相关的知识和技能握相关的知识和技能n n通过阅读本专业典型技术资料对相关领域内的常用通过阅读本专业典型技术资料对相关领域内的常用科科科科技英语词汇、术语技英语词汇、术语技英语词汇、术语技英语词汇、术语有一个初步印象有一个初步印象教学参考书教学参考书 n n激光和电光学激光和电光学(英文版英文版)C.C.Davis)C.C.Davis主编主编 世界图书出版公世界图书出版公司司n n电子科学与技术专业英语电子科学与技术专业英语.光电子技术分册光电子技术分册 张爱红主张爱红主编编 哈尔滨工业大学出版社哈尔滨工业大学出版社激光激光英语
4、英语n nUnit 1 fundamentals of lasersn nUnit 2 Basic Constructions of Lasersn nUnit 3 properties of laser beamsn nUnit 4 properties of laser beamsn nUnit 5 laser oscillation in optical resonatorn nUnit 6 Solid-State Lasersn nUnit 7Solid-State Lasers（continue）激光激光英语英语n nUnit 8 gas dynamic lasersn nUnit
5、9 q-switchingn nUnit 10 Laser Technologyn nUnit 11 Laser Machining Processesn nUnit 12 Laser Weldingn nUnit 13 Laser Cuttingn nUnit 14 Laser drilling and marking激光激光英语英语n nUnit 15 measurement with a lasern nUnit 16 laser radarn nUnit 17 optical communicationsn nUnit 18 other applications of lasersTe
6、xt 1 fundamentals of lasers Optical Amplification 1、To understand the operation of a laser we have to know some of the principles governing the interaction of radiation with matter.1 1光放大光放大 要了解激光器如何运转，就必须弄清楚决定要了解激光器如何运转，就必须弄清楚决定辐射辐射与物质相与物质相互作用的有关原理互作用的有关原理。n n2 2、Atomic systems such as atoms,Atomic
7、 systems such as atoms,ions ions,and,and molecules molecules can exist only in discretecan exist only in discrete energy states.energy states.A change from A change from one energy state to another,called a one energy state to another,called a transitiontransition,is is associated withassociated wit
8、h either the emission or the absorption of a either the emission or the absorption of a photonphoton.The wavelength of the.The wavelength of the absorbed or emitted absorbed or emitted radiation is given by Bohrs radiation is given by Bohrs frequency frequency relationrelation 原子系统，诸如原子、离子和分子，只存在于分立
9、的能态，从原子系统，诸如原子、离子和分子，只存在于分立的能态，从一个能态到另一个能态的变化称为跃迁，它伴随着光子的发一个能态到另一个能态的变化称为跃迁，它伴随着光子的发射或吸收射或吸收.波尔频率关系式给出了吸收或发射辐射的波长波尔频率关系式给出了吸收或发射辐射的波长。n n3、where E2 and E1 are twowhere E2 and E1 are two discrete energy levels discrete energy levels,V21 is,V21 is the frequency,and h is the the frequency,and h is the
10、Plancks constantPlancks constant.An.An electromagnetic waveelectromagnetic wave whose frequency whose frequency V V2 21 1 corresponds tocorresponds to an energy gap of such an atomic system can interact with it.an energy gap of such an atomic system can interact with it.n n E E2 2一一E E1 1=h hv21v21式
11、中，式中，E E2 2,E1,E1是两个离散的能级，是两个离散的能级，v21v21为频率，为频率，h h是普朗克常量，与这一原子系统的能隙相对应的是频率为是普朗克常量，与这一原子系统的能隙相对应的是频率为u u2121的电磁波，该电磁波与原子系统能够相互作用的电磁波，该电磁波与原子系统能够相互作用.n n4、At At thermal equilibrium thermal equilibrium,the lower energy states in,the lower energy states in thethe material are more heavily populated th
12、an the higher material are more heavily populated than the higher energy states.A wave interactingenergy states.A wave interacting with the substance will with the substance will raise the atoms or molecules from lower to higher raise the atoms or molecules from lower to higher energyenergy levels a
13、nd thereby experience absorption.levels and thereby experience absorption.n n在热平衡时，材料中处于下能态的粒子数远比上能态的多，在热平衡时，材料中处于下能态的粒子数远比上能态的多，电磁波与其发生相互作用，使原子和分子从低能级上升到电磁波与其发生相互作用，使原子和分子从低能级上升到高能级，即为吸收高能级，即为吸收.n n5、The operation of a laser requires that the energy The operation of a laser requires that the energy
14、 equilibrium of a laser material be equilibrium of a laser material be changed such that energy changed such that energy is storedis stored in the atoms,ions,orin the atoms,ions,or molecules of this material.molecules of this material.ThisThis is achieved by an external pump source which is achieved
15、 by an external pump source which transfers electrons from a lower energytransfers electrons from a lower energy level to a higher level to a higher one.one.n n 激光器运转要求改变激光材料的能量平衡，使能量存储于该激光器运转要求改变激光材料的能量平衡，使能量存储于该材料的原子、离材料的原子、离子子或分子之中或分子之中.通过外部泵浦源使激光材料中通过外部泵浦源使激光材料中的粒子从低能态跃迁到高能态的粒子从低能态跃迁到高能态.n n6、Th
16、e pump radiation thereby causes a The pump radiation thereby causes a population population inversioninversion”An An electromagnetic waveelectromagnetic wave of appropriate of appropriate frequency,incident on the inverted laserfrequency,incident on the inverted laser material,will be material,will
17、be amplified because the incidentphotons cause the atoms in amplified because the incidentphotons cause the atoms in the higherthe higher level to drop to a lower level and thereby emit level to drop to a lower level and thereby emit additional photons.As a result,energyadditional photons.As a resul
18、t,energy is extracted from is extracted from the atomic system and supplied to the radiation field.The the atomic system and supplied to the radiation field.The release ofrelease of the stored energy by interaction with an the stored energy by interaction with an electromagnetic wave is based on sti
19、mulatedelectromagnetic wave is based on stimulated or or induced induced emission.emission.n n泵浦辐射导致泵浦辐射导致“粒子数反转粒子数反转”.”.使频率适中的电磁波入射到该使频率适中的电磁波入射到该“反转的反转的”激光材料上，激光材料上，入射光子将促使高能级的原子降落到低能级而发射出附加的光子，形成光波放大。入射光子将促使高能级的原子降落到低能级而发射出附加的光子，形成光波放大。最终，能量从原子系统出来，供给到辐射场最终，能量从原子系统出来，供给到辐射场.原子系统与电磁波相互作用而释放出原子系统与电
20、磁波相互作用而释放出原先存储的能量，这是以受激发射或感应发射为基础的原先存储的能量，这是以受激发射或感应发射为基础的.n n7、Stated very briefly,when a material is excited in such a Stated very briefly,when a material is excited in such a way as to provide more way as to provide more atoms(or molecules)in a higher atoms(or molecules)in a higher energy level t
21、han in some lower level,the materialenergy level than in some lower level,the material will be will be capable of amplifying radiation at the frequency capable of amplifying radiation at the frequency corresponding to the energycorresponding to the energy level difference.The level difference.The ac
22、ronymacronym laser derives its name from this process:Lightlaser derives its name from this process:Light Amplification by Stimulated Emission of RadiationAmplification by Stimulated Emission of Radiation.”.”简言之，当材料受到激励，使得它的原子简言之，当材料受到激励，使得它的原子(分子分子)在高能级的分在高能级的分布多布多于于低能级时，该材料就能够以与能级差相应的频率使辐射低能级时，该材料
23、就能够以与能级差相应的频率使辐射放大放大.英文中的英文中的“激光激光”正是正是“受激辐射光放大受激辐射光放大”之之略语略语.n n8 8、Boltzmanns Statistics According to aBoltzmanns Statistics According to a basic principle basic principle of of statistical mechanicsstatistical mechanics,when a large collection of similar,when a large collection of similar atoms i
24、s in thermal equilibrium at temperature T,the atoms is in thermal equilibrium at temperature T,the relative populations of any two energy levels E1 and E2,relative populations of any two energy levels E1 and E2,such as the ones shown in Fig.1.1,must be related by the such as the ones shown in Fig.1.
25、1,must be related by the Boltzmann ratioBoltzmann ration n波尔兹曼统计波尔兹曼统计n n根据统计力学的基本原理，当大量近似的原子在温度根据统计力学的基本原理，当大量近似的原子在温度T T处于热处于热平衡状态时任何两个能级平衡状态时任何两个能级E:E:和和E:E:的相关粒子数的相关粒子数(如图如图1.11.1所示所示)一一定与波尔兹曼比值有关。定与波尔兹曼比值有关。n n9 9、n n1010、Population InversionPopulation Inversionn nAccording to the Boltzmann dis
26、tribution(1.7),in a collection According to the Boltzmann distribution(1.7),in a collection of atoms at thermal equilibrium there are always fewer atoms of atoms at thermal equilibrium there are always fewer atoms in a higher-lying level EZ than in a lower level Ei.Therefore in a higher-lying level
27、EZ than in a lower level Ei.Therefore the population difference N1the population difference N1一一N2 is always positive.N2 is always positive.n n 根据波尔兹曼分布，对于一热平衡条件下的原子集合，高能级根据波尔兹曼分布，对于一热平衡条件下的原子集合，高能级E2E2的原子数比低能级的原子数比低能级E1E1原子数少，因而粒子数差原子数少，因而粒子数差N1N1一一N2N2总是总是正值。正值。n n1111、The essential condition The
28、essential condition for amplification is that for amplification is that there are more atoms in anthere are more atoms in an upper energy levelupper energy level than in a than in a lower energy levellower energy level,i.e.,for,i.e.,for amplification,amplification,n n放大的基本条件是上激光能级的原放大的基本条件是上激光能级的原子数
29、比低能级的多，即为了得到放子数比低能级的多，即为了得到放大，必须大，必须有有n12、The resulting negative sign of the population difference(N2-g2N1/g1)on that transition is called a population inversion.Population inversion is clearly an abnormal situation;it is never observed at thermal equilibrium.The point at which the population of bot
30、h states is equal is called the inversion threshold.n n这种跃迁产生的负粒子数差这种跃迁产生的负粒子数差N2-g2N1/g1N2-g2N1/g1，称为粒子，称为粒子数反转数反转.显然，粒子数反转显然，粒子数反转是一种反常现象是一种反常现象.在热平在热平衡状态从来没有观测到这种现象衡状态从来没有观测到这种现象.两个能态的粒子数两个能态的粒子数相等的点称为相等的点称为“反转阂值反转阂值”。Exercise Translate the following sentences into Chinese.Translate the following
31、 sentences into Chinese.1 1The Three-Level SystemThe Three-Level System Figure 1.6 shows a diagram which can be used to explain Figure 1.6 shows a diagram which can be used to explain the operation of an optically pumped three-level laser,the operation of an optically pumped three-level laser,such a
32、s ruby.Initially,all ions of the laser material aresuch as ruby.Initially,all ions of the laser material are in in the lowest level 1.Excitation is supplied to the solid by the lowest level 1.Excitation is supplied to the solid by radiation of frequenciesradiation of frequencies which produce absorp
33、tion into which produce absorption into the broadband 3.the broadband 3.n n图图1.61.6是一幅简图，可以用它来解释红宝石等光泵是一幅简图，可以用它来解释红宝石等光泵浦的三能级激光器。最初，激光材料内所有的原浦的三能级激光器。最初，激光材料内所有的原子都处在最低能级子都处在最低能级l l，当这些材料在某些频率的辐，当这些材料在某些频率的辐射激励下，能级射激励下，能级1 1的粒子吸收辐射跃迁到宽带能级的粒子吸收辐射跃迁到宽带能级3.3.这样，泵浦灯使原子从基能级上升到这样，泵浦灯使原子从基能级上升到“泵浦泵浦”带。带。即
34、能级即能级3.3.n n2 2、The Metastable LevelThe Metastable Leveln nAfter this brief introduction to the energy level structure After this brief introduction to the energy level structure of solid-state lasers we can ask the question,what energy of solid-state lasers we can ask the question,what energy level
35、 scheme must a solid possess to make it a usefullevel scheme must a solid possess to make it a useful laser?As we have seen in the previous discussion,the laser?As we have seen in the previous discussion,the existence of a metastable level is of existence of a metastable level is of paramountparamou
36、nt importance importance for laser action to occur.The relatively long lifetimefor laser action to occur.The relatively long lifetime of the metastable level provides a mechanism by which of the metastable level provides a mechanism by which inverted population can be achieved.inverted population ca
37、n be achieved.前文简要地介绍一前文简要地介绍一f f固体激光器的能级结均，可能会有人问固体激光器的能级结均，可能会有人问:“:“固体必须具有固体必须具有什么样的能级结构，才能制成有用的激光器呢什么样的能级结构，才能制成有用的激光器呢?”?”正如前文讨论过的那样，正如前文讨论过的那样，亚稳态能级的存在对于激光作用的发生是至关重要的亚稳态能级的存在对于激光作用的发生是至关重要的.亚稳态能级相对长亚稳态能级相对长的寿命提供了一种实现粒的寿命提供了一种实现粒f f数反转的机理数反转的机理。此课件下载可自行编辑修改，仅供参考！此课件下载可自行编辑修改，仅供参考！感谢您的支持，我们努力做得更好！谢谢感谢您的支持，我们努力做得更好！谢谢