激光淬火过程中光的干涉和衍射结构的热作用研究

A study on the thermal effect of the interference and diffraction fringes of laser beam in the process of laser heat treatment

为提高激光热处理的质量，国内外利用光束分割再重新复合的方法，研究成功不少光学系统。由于激光是高相干光，光的干涉及衍射结构使复合光斑的功率密度分布复杂化，严格研究热处理过程中光与材料的相互热作用变得非常困难．在文献￣［１］中，我们从一个简单的光学系统研究出发，从理论上证明，当光的干涉和衍射条纹的间距相较于作用光斑的尺寸而言甚小时，可以忽略这些条纹结构对金属材料热处理的影响，并可以利用几何光学所预言的激光功率密度分布来进行有关的热学计算，为使这个结论更具有一般性，本文导出便于使用的判断光的干涉及衍射结构的热影响可否忽略的表达式，同时给出实验结论。

To obtain desirable beam energy repartition and enhance the quality of laser beat treatment, many optical systems have been developed in different parts of the world by means of splitting an initial beam and recombining the resulted sub-beams in the interaction plane, Because of the high coherence nature of laser,the energy repartitions of the recombined beams are made much more complicated by the inter-ference and diffraction fringe structures. A detailed analysis of the thermal interaction between laser beam and the target materials is thus becoming more diffcult.In ref.￣[1],a theoretical calculation based on a simple optical system showed that the influence of the interference and diffraction fringes on the result of laser heat treatment can be neglected and provided that the intervals between these fringes are small relative to the size of the incident beam, and under such circumstances temperature field can be calcu-lated using the energy repartition predicted by geometricaloptics, To genernalize this conclusion,the present paper gives mathematical expressions which can be conveniently used to determine whether or not the interference and diffraction fringes can be safely neglected.The results of experimental verifications are also presented.