热透镜效应对固体激光器的性能影响很大,准确测量热透镜焦距对固体激光系统的设计有重要意义。考虑热致双折射效应,利用等效谐振腔的g参数坐标图进行分析,推导了三种不同腔型结构下径向热透镜焦距和切向热透镜焦距系数的计算方法,分析并得出了测量热透镜焦距系数所需的腔型结构。实验采用Nd∶YAG作为激光晶体,三组激光二极管互呈120°侧向抽运。实验结果表明,在非对称平-平腔中,当激光晶体相对于两面腔镜位置不同时,谐振腔输出功率会出现不同的变化趋势,测量出径向热透镜系数为31.76 m·W和切向热透镜系数为42.26 m·W。实验验证了理论分析的正确性。

Thermal effect has large influence on the performance of a solid-state laser, and the exact measurement of thermal focal length means a lot to solid-state laser system design. Considering the thermal-induced birefringence, the g parameter coordinate system is analyzed, the formulas of radially polarized and azimuthally polarized focal lengths in three different cavity structures are deduced and the proper cavity structure to get the thermal focal length coefficients is presented. In experiment Nd∶YAG rod is side-pumped with three laser diodes positioned with 120° respectively. Experimental results show that in asymmetric flat-flat resonators, when the laser crystal′s position is varied relative to two cavity mirrors, the output power changes in different way, and the radially polarized and azimuthally polarized focal lengths are 31.76 m·W, 42.26 m·W measured respectively.