利用有限元分析法结合Fox-Li迭代法, 考虑腔内本征模式与腔镜热形变的相互耦合作用, 计算模拟了正支共焦非稳腔的本征模式分布, 定量分析了高功率激光器腔镜热变形对输出光束质量的影响, 重点讨论了腔镜热变形所引起的腔内本征模式相位特性的变化, 并从波前功率谱密度、Zernike像差系数及光束质量β值等角度对腔镜发生热形变前后的激光器输出光束的光束特性进行比较分析。研究结果表明: 高功率激光器腔镜热形变对输出光束的光束质量会产生一定的影响, 且随着激光输出功率的增大, 镜面热形变引起的输出光束波前相位高频比例及Zernike高阶像差均会有所增大, 波前畸变程度也明显变大, 光束质量逐渐变差。

By using the method of finite element combined with Fox-Li iteration algorithm, the eigenmode in positive-branch confocal unstable resonators has been calculated and simulated, with considering the coupling effect between the eigenmodes of resonators and the thermal distortions of cavity mirrors. The effect of thermal distortions of cavity mirrors on output beam quality of high-power laser has also been analyzed quantitatively. Furthermore, the changes of eigenmode phase characteristics caused by thermal distortions of cavity mirrors have been discussed, and the phase characteristics of output beam with and without thermal distortions have been compared and analyzed from the aspects of the wavefront power spectral density (PSD), Zernike coefficients and β factors of output laser beams. The results show that the output beam quality would be influenced by the thermal distortions of cavity mirrors. The proportion of high frequency part in distorted phase and the high order Zernike aberrations increase with the increasing of output laser power, resulting in the degradation of beam quality of output laser beams.