理论分析了Er:YAG激光晶体的热退偏效应，模拟计算了该晶体棒端面退偏的分布，并进行了偏光干涉实验验证。结果表明，数值模拟和实验结果完全一致，热退偏效应随抽运能量增大而增强，退偏分布呈十字形，最大退偏发生在晶体棒端面上与起偏器偏振方向成45°方位处。同时，还阐明了一种利用临界稳定腔来测量灯抽运脉冲Er:YAG激光器有效热透镜焦距的简单方法，测量出不同抽运功率下Er:YAG晶体的等效热焦距。

The theory of thermal-induced-depolarization is analyzed. The distribution of depolarization is numerically simulated, and the result is verified by the experiment of the polarized light polarization interference. The experimental result is consistent with the numerical one, which shows that the distribution of depolarization in the cross section of Er:YAG rod is a crisscross and increases with the pump energy. The direction of the worst depolarization is along 45° angle with the polarization. A simple way is illustrated to measure the thermal lens focal length of the lamp-pumped Er:YAG laser with the critical stability condition of the cavity. The equivalent thermal focal length of Er:YAG crystal under different pump powers is also measured.