在CdSe晶体光参量振荡器(OPO)中, 泵浦激光经过晶体后产生大量废热, 使CdSe晶体出现明显热透镜效应, 从而导致泵浦激光的光斑半径在晶体内部不断变小, 最终降低了晶体的损伤阈值和OPO的输出功率。本文利用COMSOL软件对高重频脉冲激光泵浦CdSe晶体进行多物理场建模, 完成了CdSe晶体热透镜效应仿真, 通过参数优化, 发现对流系数与晶体最大温度成反比, 与晶体后端面和焦点的光斑半径成正比, 聚焦位置随对流系数增加趋于稳定。单脉冲能量和重复频率与晶体最大温度和焦点的光斑半径成正比, 与晶体后端面光斑半径和聚焦位置成反比。准直激光光斑半径与晶体最大温度成反比, 与晶体后端面光斑半径、聚焦位置和焦点光斑半径成正比。该研究解决了CdSe OPO中晶体后端面光斑半径难以直接测量的问题, 为优化CdSe晶体热透镜效应提供了理论依据。

In the optical parametric oscillator (OPO) based on CdSe crystal, a large amount of waste heat is generated when the pump laser passes through the crystal, resulting in a significant thermal lens effect in CdSe crystal, which causes the spot radius of the pump laser smaller inside the crystal, and finally reduces the damage threshold of the crystal and the output power of the OPO. The thermal lens effect simulation of CdSe crystal pumped by high frequency pulsed laser is completed by COMSOL software in this paper. Through parameter optimization, it is found that the convection coefficient is inversely proportional to the maximum temperature of the crystal, directly proportional to the spot radius of the back face and focus of the crystal, and the focus position tends to be stable with the increase of convection coefficient. The single pulse energy and repetition frequency are directly proportional to the maximum temperature of the crystal and the spot radius of the focus, and inversely proportional to the spot radius and the focus position at the back end of the crystal. The collimated laser spot radius is inversely proportional to the maximum temperature of the crystal, and directly proportional to the spot radius, focus position and spot radius of the back end of the crystal. This study solves the problem that the laser spot radius at the back end of CdSe OPO crystal is difficult to measure directly, and provides a theoretical basis for optimizing the thermal lens effect of CdSe crystal.