结合消闲置光原理的多通腔结构参量放大器研究

Optical parametric chirped-pulse amplification (OPCPA) has been widely used in ultrashort high intense laser systems for providing ultra-broad bandwidth as well as high temporal contrast. In order to further apply its technology advantages and build a high performance laser frond-end, this project proposes two novel multi-pass cavity structures based on the principle of idler pulse elimination during parametric amplification: F-P cavities multi-pass structure and ring cavity multi-pass structure. Applying the new structures has the following significant advantages to make up the defects of OPCPA in picosecond and nanosecond domains such as low conversion efficiency, energy instability, parametric bandwidth narrowing because of phase mismatching and spatial coupling offset in engineering applications: <1>enlarging the phase-matching bandwidth due to short single-pass crystal length; <2>increasing conversion efficiency as a result of idler pulses elimination after each pass in order to avoid energy back-conversion; <3>the phase-mismatch factor will not accumulate after each pass so that the entire phase-matching bandwidth is as large as that of single-pass; <4>improving the output stability owing to simple structure; <5>flexible to integrated with temperature-controlled or electric-controlled group-velocity-mismatching (GVM) compensation units, easy to fabricate a high gain, high temporal contrast ps/fs modular-grade OPCPA front-end. This project can provide comprehensive technical support for on-built ultrashort high intensity OPCPA systems in the whole spectrum domain all over the world, and we expect to fabricate a commercial-grade ultra-broadband laser front-end with high stability and high efficiency.

啁啾脉冲光参量放大技术由于大增益带宽和高信噪比等优点在超短超强激光系统中得到了广泛的应用。为更进一步发挥技术优势，建造高性能前端种子源，本申请课题提出了基于消闲置光原理的多通腔参量放大结构：法波腔多通结构与环形腔多通结构。在皮秒域与纳秒域，针对工程应用中出现的转换效率偏低、能量不稳定、级间空间耦合偏移、光谱失配窄化以及群速失配等不足，采用该新型腔结构有以下显著优势：<1>单通之内晶体很短可以大幅度提高匹配带宽；<2>多通之间完全消除闲置光能够防止信号光能量耦合回流，显著提高转换效率；<3>多通之间相位失配因子不累加，整体匹配带宽与单通带宽相等；<4>结构简单提高输出稳定性；<5>可灵活搭配温控/电控群速失配补偿单元，集成高增益高信噪比ps-OPCPA模块化前端。本申请课题研究可在多个光谱波段内，为国内外在建超短超强激光系统的光参量放大器提供技术支持，有望建成商品级高稳定高效率超宽带前端。

超短超强激光光源是未来数十年内超短超强激光领域极其重要的发展方向，将为强场真空非线性结构、带电粒子激光加速、光核物理和阿秒物理等研究领域提供前所未有的强大工具，推动基础研究进入更深更广的层次。光参量啁啾脉冲放大技术已经成为该类光源产生的重要途径。本课题进行了基于消闲置光原理的多通腔参量放大结构探索，主要的研究内容与成果，包括： 1）完成建立数值分析理论模型，得到各类OPAC的合适参数；2）利用SGII-5PW前端OPA平台，搭建基于LBO与YCOB的CFP-OPA放大构型，在YCOB的构型中，在泵浦光400mJ情况下，实验测量信号光能量达到229mJ，转换效率高达57%的世界最高纪录；光谱宽度达到120nm能量输出稳定性<1% RMS，能量稳定性优于泵浦光能量稳定性，该指标远远高于本课题的预期实验指标（泵浦-信号转换效率>40%，能量输出稳定性<5% RMS）；3）完成OPCPA的OPF信噪比实验研究，在800nm波段的高增益>8次方量级的放大器中，首次获得了SNR达到11次方的国际最高指标，该指标较2007年的报道提高了3个量级，并对OPF的抑制机理做出相应的探索；4）完成了基于YCOB晶体的高性能OPCPA实验研究，基于YCOB晶体级联方案，国际上首次同时实现高增益10^9、转换效率>40%、带宽>100nm、测量得到压缩脉宽<20fs；5）基于GGG晶体交叉偏振波产生技术的高信噪比、大能量、超宽带光源产生技术理论研究；6）基于高掺氘率DKDP晶体的高能数拍瓦级OPCPA输出能力实验论证研究，实验显示，高掺氘率（>95%）DKDP晶体可以为数PW级OPCPA装置建设提供末级主放大增益介质。在该项目的支持下，发表SCI文章10篇，EI文章1篇，专利3项，培养博士研究生3名。上述研究成果可以满足工程化需求，对该领域激光装置建设具有重要意义。