大口径高通量验证实验平台片状放大器热致退偏效应研究

Investigation on Depolarization of Slab Amplifiers on Integration-Test-Bed

氙灯抽运将导致钕玻璃内产生不均匀温升，这是产生应力退偏的根本原因。热致应力退偏效应将直接降低系统效率、影响光束质量，因此确定片内的温度分布以及应力分布，准确预测由此带来的光束退偏特性并合理设计光束填充因子是十分重要的。介绍了我国第一台单束输出能力超过万焦耳的惯性约束聚变激光驱动器中大口径高通量验证实验平台片状放大器的热致退偏效应，通过理论模拟计算获得了钕玻璃片内三维温升分布、应力分布与由此导致的退偏分布特性。结果表明，片状放大器在5．28％／cm平均小信号增益系数输出的情况下整个光束口径内的应力双折射是很小的，但方光束的四个角部处的应力双折射较严重，最大的退偏量约为0．13％，该结果与劳伦斯·利弗莫尔实验室实验测得的结果基本一致。输出的激光近场结果表明，片状放大器热致退偏效应可满足大能量装置输出设计要求。

Xenon lamp-pumped Nd： glass will result in uneven temperature rise, which will produce thermal stress birefringence and induce depolarization. Depolarization will directly reduce the system efficiency, beam quality. So, it is important to confirm the temperature distribution and stress distribution, to accurately predict the resulting depolarization of the beam, and to design rational beam filling factor. Based on the electro-optical conversion model, we used three-dimensional ray tracing to obtain the distribution of thermal power source, with heat conduction theory, we calculated the three-dimensional temperature distribution of the laser glass and the stress distribution and the resulting depolarization distribution. The results show that the stress birefringence within the beam diameter is small, but the four corners of square beam department of the stress birefringence are more serious, with the largest depolarization about 0.13 %. The results are consistent with the experimental results of Lawrence Livermore national laboratory. The near field results of output laser show that the thermal induced depolarization of the slab amplifiers satisfies the output design demand of high energy equipment.