研究了非均匀泵浦状态下径向偏振光束的退偏机理及补偿方法。理论分析表明，非均匀泵浦条件下各向同性晶体横截面内由热致剪应力引起的剪切向热致双折射是导致径向偏振光退偏的主要原因。设计实验依次采用薄膜偏振片（TFP）测量法和纯度测量法评价了径向偏振光在非均匀泵浦条件下的退偏，其中TFP测量法用于检测径向偏振光的整体退偏，纯度测量法用于检测径向偏振光的局部退偏。在泵浦峰值功率1.1 kW下，两种评价方法测得的退偏量分别为2.34%和2.53%。基于理论分析和评价方法的结果，在退偏补偿方案的设计中采用相位调制与空间模式匹配相结合的方法，将径向偏振光的退偏量优化了59%，并获得脉冲能量为19.36 mJ，纯度为90.13%的皮秒径向偏振光，光束质量因子M²为3.8。

A high-power, Joule-class, nanosecond temporally shaped multi-pass ring laser amplifier system with two neodymium-doped phosphate glass (Nd:glass) laser heads is demonstrated. The laser amplifier system consists of three parts: an all-fiber structure seeder, a diode-pumped Nd:glass regenerative amplifier and a multi-pass ring amplifier, where the thermally induced depolarization of two laser heads is studied experimentally and theoretically. Following the injection of a square pulse with the pulse energy of 0.9 mJ and pulse width of 6 ns, a 0.969-J high-energy laser pulse at 1 Hz was generated, which had the ability to change the waveform arbitrarily, based on the all-fiber structure front end. The experimental results show that the proposed laser system is promising to be adopted in the preamplifier of high-power laser facilities.

Thermal stress can induce birefringence in a laser medium, which can cause depolarization of the laser. The depolarization effect will be very severe in a high-average-power laser. Because the depolarization will make the frequency doubling efficiency decline, it should be compensated. In this paper, the thermal characteristics of two kinds of materials are analyzed in respect of temperature, thermal deformation and thermal stress. The depolarization result from thermal stress was simulated. Depolarization on non-uniform pumping was also simulated, and the compensation method is discussed.