激光专业英语2讲解课件.ppt

Laser Specified English,2011年8月,训练课变成我猜我猜我猜猜猜的节目了,本课程是激光加工专业的必修课。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。本课程的教学基本要求:学习常用激光工程英语词汇、术语；掌握科技英语的特点；提高运用英语从事激光工程相关的阅读、写作、会话的能力。,本课程由二个部分组成：第一部分偏重于激光英语文章的英汉翻译第二部分偏重于激光英语文章的汉英翻译课程第一部分的目标：帮助学生能用英语较熟练地阅读本专业的文献资料在方法上，选择本专业内几个通用的理论或技术基础问题为背景，要求学生通过直接阅读原版技术资料掌握相关的知识和技能通过阅读本专业典型技术资料对相关领域内的常用科技英语词汇、术语有一个初步印象,教学参考书,激光和电光学(英文版)C.C.Davis主编 世界图书出版公司电子科学与技术专业英语.光电子技术分册 张爱红主编 哈尔滨工业大学出版社,激光英语,Unit 1 fundamentals of lasersUnit 2 Basic Constructions of LasersUnit 3 properties of laser beamsUnit 4 properties of laser beamsUnit 5 laser oscillation in optical resonatorUnit 6 Solid-State LasersUnit 7Solid-State Lasers（continue）,激光英语,Unit 8 gas dynamic lasersUnit 9 q-switchingUnit 10 Laser TechnologyUnit 11 Laser Machining ProcessesUnit 12 Laser WeldingUnit 13 Laser CuttingUnit 14 Laser drilling and marking,激光英语,Unit 15 measurement with a laserUnit 16 laser radarUnit 17 optical communicationsUnit 18 other applications of lasers,Text 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光放大 要了解激光器如何运转，就必须弄清楚决定辐射与物质相互作用的有关原理。,2、Atomic systems such as atoms,ions,and molecules can exist only in discrete energy states.A change from one energy state to another,called a transition,is associated with either the emission or the absorption of a photon.The wavelength of the absorbed or emitted radiation is given by Bohrs frequency relation 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，它伴随着光子的发射或吸收.波尔频率关系式给出了吸收或发射辐射的波长。,3、where E2 and E1 are two discrete energy levels,V21 is the frequency,and h is the Plancks constant.An electromagnetic wave whose frequency V21 corresponds to an energy gap of such an atomic system can interact with it.E2一E1=hv21式中，E2,E1是两个离散的能级，v21为频率，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u21的电磁波，该电磁波与原子系统能够相互作用.,4、At thermal equilibrium,the lower energy states in the material are more heavily populated than the higher energy states.A wave interacting with the substance will raise the atoms or molecules from lower to higher energy levels and thereby experience absorption.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高能级，即为吸收.,5、The operation of a laser requires that the energy equilibrium of a laser material be changed such that energy is stored in the atoms,ions,or molecules of this material.This is achieved by an external pump source which transfers electrons from a lower energy level to a higher one.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、离子或分子之中.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.,6、The pump radiation thereby causes a population inversion”An electromagnetic wave of appropriate frequency,incident on the inverted laser material,will be amplified because the incidentphotons cause the atoms in the higher level to drop to a lower level and thereby emit additional photons.As a result,energy is extracted from the atomic system and supplied to the radiation field.The release of the stored energy by interaction with an electromagnetic wave is based on stimulated or induced emission.泵浦辐射导致“粒子数反转”.使频率适中的电磁波入射到该“反转的”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。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先存储的能量，这是以受激发射或感应发射为基础的.,7、Stated very briefly,when a material is excited in such a way as to provide more atoms(or molecules)in a higher energy level than in some lower level,the material will be capable of amplifying radiation at the frequency corresponding to the energy level difference.The acronym laser derives its name from this process:Light Amplification by Stimulated Emission of Radiation.”简言之，当材料受到激励，使得它的原子(分子)在高能级的分布多于低能级时，该材料就能够以与能级差相应的频率使辐射放大.英文中的“激光”正是“受激辐射光放大”之略语.,8、Boltzmanns Statistics According to a basic principle of statistical mechanics,when a large collection of similar atoms is in thermal equilibrium at temperature T,the relative populations of any two energy levels E1 and E2,such as the ones shown in Fig.1.1,must be related by the Boltzmann ratio波尔兹曼统计根据统计力学的基本原理，当大量近似的原子在温度T处于热平衡状态时任何两个能级E:和E:的相关粒子数(如图1.1所示)一定与波尔兹曼比值有关。,9、,10、Population InversionAccording to the Boltzmann distribution(1.7),in a collection of atoms at thermal equilibrium there are always fewer atoms in a higher-lying level EZ than in a lower level Ei.Therefore the population difference N1一N2 is always positive.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E2的原子数比低能级E1原子数少，因而粒子数差N1一N2总是正值。,11、The essential condition for amplification is that there are more atoms in an upper energy level than in a lower energy level,i.e.,for amplification,放大的基本条件是上激光能级的原子数比低能级的多，即为了得到放大，必须有,12、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 both states is equal is called the inversion threshold.这种跃迁产生的负粒子数差N2-g2N1/g1，称为粒子数反转.显然，粒子数反转是一种反常现象.在热平衡状态从来没有观测到这种现象.两个能态的粒子数相等的点称为“反转阂值”。,Exercise,Translate the following sentences into Chinese.1The Three-Level System Figure 1.6 shows a diagram which can be used to explain the operation of an optically pumped three-level laser,such as ruby.Initially,all ions of the laser material are in the lowest level 1.Excitation is supplied to the solid by radiation of frequencies which produce absorption into the broadband 3.,图1.6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子都处在最低能级l，当这些材料在某些频率的辐射激励下，能级1的粒子吸收辐射跃迁到宽带能级3.这样，泵浦灯使原子从基能级上升到“泵浦”带。即能级3.,2、The Metastable LevelAfter this brief introduction to the energy level structure of solid-state lasers we can ask the question,what energy level scheme must a solid possess to make it a useful laser?As we have seen in the previous discussion,the existence of a metastable level is of paramount importance for laser action to occur.The relatively long lifetime of the metastable level provides a mechanism by which inverted population can be achieved.前文简要地介绍一f固体激光器的能级结均，可能会有人问:“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?”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.亚稳态能级相对长的寿命提供了一种实现粒f数反转的机理。,