超大功率固态激光器的介质温度场分析

Analysis on temperature field of laser crystal in a super high power solid-state laser

利用有限元分析的方法，对在二极管抽运的超大功率（10～100kW或更高）Nd^3＋：CGG板状激光器的热稳态（CW）和热容量（Heat Capacity）两种工作模式中的激光晶体的温度场分布，及其随工作时间变化情况进行了模拟分析，为热透镜效应提供了详尽的基础数据．研究表明，在热稳态模式下，加大冷却气体的流速可以改善晶体温度分布，减小热透镜效应，但改善程度有限；在热容量模式下，激光的发射和冷却过程在时间上分离，减小晶体应力和光学畸变，改善了输出激光质量．尺寸为10cm×10cm×2cm单片晶体在26．6、38．6、53．2和66．5kW的抽运下，晶体最高温度分别为70．6、93．6、121．0和146．8℃，准连续工作时间分别为7．8、8.5、9．0和12．4S，该结果与实验测量相符合．由此得到：在热容量模式中，单片厚度为2cm的Nd^3＋：CGG输出功率面密度的极限为170-200W／cm^2．

The temperature field distribution and its changes with time were simulated and analyzed by finite-element method, for a super high power （10 100 kW or higher） Nd^3＋ ：GGG slab laser pumped by laser diodes in two working modes, namely heat steady-state （CW） and heat capacity. The results show that in CW mode, increasing the flow rate of cooling gas can improve the temperature distribution of the crystal and reduce the thermal lensing effect, but the improvement is limited： for heat capacity mode in which lasing and cooling are separated by time, the crystal stress and optical distortion can be minimized, thus improving the quality of lasing beam. Analysis shows that when the heat-capacity laser works, the crystal temperature increases gradually and then reaches a maximum. With a crystal size of 10 cm×10 cm×2 cm and pumped with 26.6, 38.6. 53.2 and 66.5 kW. the maxima are 70.6. 93.6. 121.0 and 146.8 ℃, and the durations are 7.8, 8.5. 9.0 and 12.4 s, respectively. Based on the simulation and comparison with prior experimental data, it is expected that the maximum output power flux from a single 2 cm-thick Nd^3＋. GGG will be between 170 and 200 W/cm^2 in the heat capacity mode. This work provides enough data for the study of thermal lensing effect.