毕业论文英文文献及中文翻译 学生姓名： 学号： 10051041 学 院： 信息与通信工程学院 专 业： 光电信息工程 指导教师： 2014年 6 月Three Dimensional photo-thermal Deflection of Solids UsingModulated CW Lasers : Theoretical DevelopmentM. Soltanolkotabi and M. H. NaderiPhysics Department ， Faculty of Sciences ， University of Isfahan， Isfahan， IranAbstract In this paper，a detailed theoretical treatment of the three dimensional photo-thermal deflection ，under modulated cw excitation ， is presented for a three layer system( backing-solid sample-fluid). By using a technique based on Greens function and integral transformations we find the explicit expressions for laser induced temperature distribution function and the photo-thermal deflection of the probe beam. Numerical analysis of those expressions for certain solid samples leads to some interesting resultsI. Introduction photo-thermal techniques evolved from the development of photoacousticspectroscopy in the 1970s. They now encompass a wide range of techniques andphenomena based upon the conversion of absorbed optical energy into heat . When ansource is focused on the surface of a sample ， part or all of the incident energy is absorbeenergy d by the sample and a localized heat flow is produced in the mediumfollowing a series of nonradiative deexcitation transitions . Such processes are theorigins of the photo-thermal effects and techniques . If the energy source is modulated，a periodic heat flow is produced at the sample . The resulting periodic heat flow in the material is a diffusive process that produces a periodic temperature distribution called a thermal wave . Several mechanisms are available for detecting ，directly or indirectly ， thermal waves . These includes gas-microphone photoacoustic detection of heat flow from the sample to the surrounding gas; photo-thermal measurements of infrared radiationemitted from the heated sample surface ; optical beam deflection of a laser beamtraversing the periodically heated gaseous or liquids layer just above the sample surface ; laser detection of the local thermoelastic deformations of the surface; and interferometric detection of the thermoelastic displacement of the sample surface . In particular， the two last schemes of thermal wave detection which form the basis of photo-thermal deformation spectroscopy (PTDS) are becoming the most widely exploited ， the principal reason being that they offer avaluable mean for measuring optical and thermal parameters of materials ，such asoptical absorption coefficient and thermal diffusivity . The photo-thermal deformation technique is simple and straightforward. A laser beam (pump beam) of wavelength within the absorption range of the sample is incident on the sample and it is absorbed . The sample gets heated and this heating leads ， through thermoelastic coupling ， to an expansion of the interaction volumewhich in turn causes the deformation of the sample surface. The resulting thermoelastic deformation of the surface is detected by the deflection of a second ，weaker laser beam (probe beam). Ameri and his colleagues were among those who have used first ， both the laser interferometric and laser deflection techniques for spectroscopic studies onamorphous silicon.Their method restricted to low to moderate modulation frequencies. Opsal et al have used thermal wave detection for thin film thickness measurements using laser beam deflection technique. They have obtained temperature distribution function for what is called 1-D temperature distribution function. In their analysis they assumed both probe and pump beams incident normal to the sample surface. Miranda obtained sample temperature distribution by neglecting transient as well as the dc components of the temperature distribution function . On the other hand ，the theory of photo-thermal displacement under pulsed laser excitation in the quasistatic approximation has been given by Li .Zhang and collaborators have investigated the more general case of dynamic thermoelastic response under short laser pulse excitation . Moreover， Cheng and Zhang have considered the effect of the diffusion of photo-generated carriers in semiconductors on the photo-thermal signal.In this paper ， we present a detailed theoretical analysis of the deflection process in three dimensions，for a three layer system consisting of a transparent fluid ，an optically absorbing solid sample ， and a backing material . It is assumed that the system is irradiated by a modulated cw laser beam .The theoretical treatment of photo-thermal deflection can be devided into two parts. In Sec II.A we will find the 3D laser-induced temperature distribution within the three region of the system ， due to the absorption of the pump beam. Our mathematical approach is based on Greens function and integral transformations . In