大口径非线性晶体组合技术的关键问题研究

The broadband and ultra-broadband, high energy laser has broad application prospects. Recently, Acquiring ultrahigh peak power and ultra-broadband laser by using optical parametric chirped pulse amplification (OPCPA) becomes a tendency, many famous laboratories are planning to design and build 10 PW and even 100 PW laser facilities by OPCPA scheme. However, there are a lot science and technology problems in large aperture OPCPA system, because the limited level of crystals growth and manufacture, the problems of obtaining large aperture nonlinear crystals is one of bottlenecks for high energy OPCPA. Our application is aim to the training program of No:23, the research contents for crystal combination are as follows: (1) the influences to the gain spectrum bandwidth, parametric bandwidth and spectrum modulation of amplified pulse; (2) the affects to compression and focus characters for the output pulse; (3) the effects of band gap between crystals to laser beam quality; (4) By analyzing the mechanism of crystal combination technique in ultra-broadband and high energy OPCPA system, we will confirm the parametric requirement for crystal combination, and do related judged experiment. Though this application, we plan to study the main mechanisms, explore the new phenomena and laws in large nonlinear crystals combination techniques, we will also provide theoretical guidance and experimental criterions for solving large aperture nonlinear crystal problems in high energy OPCPA and SHG system.

宽带、超宽带高能激光具有广泛的应用前景。近来，利用光参量啁啾脉冲放大（OPCPA）技术实现超强、超短激光输出逐渐成为一种趋势，采用此技术，国内外许多著名实验室正在计划设计、建造10PW乃至100PW的激光装置。然而，此过程涉及到很多的科学、技术问题，其中由于晶体生长技术水平的限制，如何制备大口径非线性晶体是制约高能OPCPA发展的主要因素之一。本申请针对“培育项目”中的明确目标课题，开展晶体组合技术的相关研究：（1）分析影响信号光增益带宽、参量带宽以及光谱的主要因素；(2)分析影响宽带脉冲压缩信噪比和聚焦特性的因素；（3）研究晶体间缝隙对激光光束质量的影响；（4）依据晶体组合技术影响高能OPCPA的物理机制，分析对晶体的参数要求，开展验证实验。通过本课题的关键问题研究，探索新现象和新规律，为解决宽带、超宽带高能OPCPA和倍频中大口径晶体问题提供理论指引和实验判据。

为了研究高能OPCPA放大和宽带SHG系统中大口径非线性晶体组合技术的可行性，本项目对晶体组合中涉及的主要问题进行了理论和实验研究。首先，建立了能够仿真二阶非线性晶体组合的数值模拟程序；其次，与单块晶体相比较，理论分析了晶体组合中涉及的主要问题：1）晶轴误差等角度误差对带宽的影响；(2)晶体组合过程对光束质量的影响。通过对上述过程的理论分析，设计、加工了满足实验需求的调整机构。对晶轴角度的确定、衍射传输近场光束质量变化趋势和抑制手段、时间同步和组合晶体后的信号光组束控制及宽带SHG等问题进行了实验研究。课题的理论分析和实验结果将对高能量大口径OPCPA和宽带SHG研究提供一定的指导意义。