抑制高峰值功率皮秒激光放大系统Nd:YAG中的自聚焦效应

全固态皮秒放大器的平均输出功率易受到增益晶体中自聚焦效应的影响。通过引入补偿元件砷化镓（GaAs）片可以避免自聚焦效应造成的损伤，关于砷化镓的抑制机理对高峰值功率Nd:YAG晶体皮秒放大器系统的进行理论分析和实验研究。以公式计算得到了GaAs材料的非线性折射率系数，并由数值模拟给出了在抑制自聚焦的最佳效果下GaAs片厚度与Nd:YAG棒长度的关系。在入射皮秒激光束中心波长为1 064 nm、重复频率为1 kHz、峰值功率密度为12 GW/cm2的条件下，进行了不同厚度（200 m和550 m） GaAs片对抑制Nd:YAG棒自聚焦损伤的实验研究。通过优化GaAs片的厚度，该补偿方法在高峰值功率皮秒脉冲条件下，特别是对于Nd:YAG放大器显示出较高的效率。关键词:自聚焦效应；非线性折射率系数；光学损伤； B积分

Suppressing self-focusing effect in high peak power Nd:YAG picosecond laser amplifier systems

The output average power of all-solid-state picosecond amplifier suffered from self-focusing effect existed in the gain crystals. Through introducing the compensation element-gallium arsenide(GaAs)plate, the damage due to self-focusing effect has been avoided and the suppressing mechanism has been studied through theoretical analysis and experimental research for high peak power Nd:YAG crystal picosecond amplifier systems. The nonlinear refractive index coefficient of GaAs was obtained by calculation, and the relationship between the thickness of GaAs plate and the length of Nd:YAG rod under the optimal effect of suppressing self-focusing was given by numerical simulations. Under the condition that the center wavelength of the incident picosecond laser beam is 1 064 nm, the repetition frequency is 1 kHz, and the peak power density is about 12 GW/cm2, experiments on the effect of GaAs plates with different thicknesses(200 m and 550 m) to reduce the self-focusing damage in Nd:YAG rod have been completed. With optimization of thickness of the GaAs plate, the compensation method demonstrates high efficiency under high peak power picosecond pulses condition especially for Nd:YAG amplifier.