SGⅡ-5 PW激光系统大能量光参量放大器光束近场分布均匀性

Analysis on Near-Field Distribution Uniformity of High Energy Optical Parametric Chirped Pulse Amplifier in SGⅡ-5 PW System

为了提高神光Ⅱ 5PW(SGII-5PW)超短脉冲激光系统的运行安全性,针对大能量光参量啁啾脉冲放大(OPCPA)光束近场分布均匀性问题,从理论上进行了数值模拟,并与实验数据进行了对比分析。在1PW级放大器模拟中,以预放大器以及神光Ⅱ大能量抽运脉冲的测量数据为基础,利用参量耦合波方程组数值模拟方法,得到了近场填充因子与光通量对比度在光参量放大过程中的演变,并结合转换效率与输出稳定性进行讨论,得到了对应于高光束质量、高转换效率与高稳定性的非线性晶体长度优化范围,结果还表明抽运光对放大后光束均匀性影响较大,进一步提升神光Ⅱ第7路光束质量是大幅提升第2级OPCPA(OPCPA-Ⅱ)光束均匀性的切实途径。

In order to improve the operation security of Shenguang II 5 PW （SGII-5 PW） ultrashort pulse laser system, the near-field distribution uniformity of large energy optical parametric chirped pulse amplification （OPCPA） beam is numerically simulated, and the simulation results are compared with experimental results. In the 1 PW amplifier, based on the measurement data of the preamplifier and the SGII high energy pump pulse, the evolution of the near field fill factor and the fluence beam contrast in optical parametric amplification process are presented by numerical simulation of parametric coupling wave equations. The conversion efficiency and the amplification stability are also discussed. The optimal range of nonlinear crystal length, in which high beam quality, high conversion efficiency and high stability can be achieved simultaneously, is obtained. The results also indicate that the pump light greatly affects the amplified beam uniformity. Enhancement of the SGII 7th beam quality is a practical way to improve the beam uniformity of second stage OPCPA.