为了精确测量激光晶体的动态热焦距, 提出了一种指示光偏振变换测量方法。基于几何光学成像理论, 建立了热透镜动态热焦距的表达式。将准直的指示光往返两次通过具有热透镜效应的激光晶体, 利用偏振变换的方法使测量光束有效的从光路中分离出来, 采用CCD相机对被测光束进行探测。搭建了激光晶体的动态热焦距的实验测量装置, 分别测量了端面泵浦和侧面泵浦两种工作状态激光晶体的动态热焦距, 最后分析了实验测量的误差。结果表明: 利用指示光偏振变换法测量激光晶体的热焦距, 测量误差仅为0.8 mm, 能够满足激光器谐振腔设计要求。

To measure accurately dynamic thermal focus length of laser crystal in solid state laser, a new and accurate method for measuring dynamic thermal focus length by means of the indicator light polarization converted was presented in the paper. A formula of dynamic thermal focus length was established based on imaging theory of geometrical optics. An indicator light was traveled through laser medium which possessed thermal lens effect round trips. The measuring beam was separated from the optical path by a method of polarization converted. Then, the measuring beam was detected by CCD camera. The experiment setup for measuring dynamic thermal focus length of laser crystal was put up and the dynamic thermal focus length of laser crystal end-pumped and side-pumped were measured respectively. The measuring error was analyzed at last. The result showed that the measuring error of dynamic thermal focus length is only 0.8 mm by means of the indicator light polarization conversion, and the error can completely meet the design requirements for laser cavity.