基于等离子体强耦合布里渊散射效应的超短脉冲自压缩技术研究

At present, ultrashort and ultrahigh-power lasers are mainly provided by CPA techniques. But further power promotion is restricted by the damage threshold of the optical components. Plasma amplification developed in recent years offers another route for further improvement of the output power and even EW(1000PW) can be obtained (this is because the plasma is free of damage). But three pulses are needed in traditional plasma amplification experiments, including the prepulse ( which is used to produced plasma), pump pulse and seed pulse. Precise temporal and spatial overlap are needed, which makes the experiments extremely complex and results in low efficiency. In our project, a new mechanism named self-compression is proposed, where we use only one single laser pulse to act as the prepulse, pump pulse and seed pulse at the same time. Coupled with the Nd:glass laser technology, multi-kJ femtosecond pulse can be produced in a single beam, which means self- compression has the potential to become the next generation of key technique for high-peak-power ultrashort laser pulse. Research work includes: 1) Deepgoing theoretical analysis and elaborate computer simulation, and the experiment designs. 2) Accumulating experiment experiences in preliminary experiments and finally completing the main experiment to verify self-compression.

目前超短超强脉冲激光采用啁啾脉冲放大技术，进一步功率提升受到光学元件损伤阈值的限制。近年来发展起来的等离子体放大技术为进一步提高脉冲输出功率，实现EW(1000拍瓦)提供了新的途径（由于等离子体不存在损伤阈值问题）。然而以往的等离子体放大实验中采取预脉冲（产生等离子体）、泵浦光和种子光三束短脉冲激光相互作用的形式，三者的时空耦合效果限制了泵浦光向种子光的能量转换效率。本项目提出了一种新的“自压缩”的等离子体放大超短脉冲的技术方案。采用一束光同时作为电离脉冲、泵浦光和种子光，避免了不同光束的时空耦合对转换效率的影响。结合目前成熟的皮秒级钕玻璃激光技术，“自压缩机制”有望产生单束数千焦的飞秒脉冲，成为下一代超高峰值功率超短脉冲的关键技术。研究工作包括：1）通过深层次理论分析、计算机模拟，优化关键实验因素并设计实验方案；2）利用已有钕玻璃皮秒激光装置，完成等离子体短脉冲自压缩的实验验证

超短超强脉冲激光采用啁啾脉冲放大技术，功率提升受到光学元件损伤阈值的限制。等离子体放大技术为进一步提高脉冲输出功率，实现EW(1000拍瓦)提供了新的途径。然而以往的等离子体放大实验中采取预脉冲（产生等离子体）、泵浦光和种子光三束短脉冲激光相互作用的形式，三者的时空耦合效果限制了泵浦光向种子光的能量转换效率。本项目提出了一种新的“自压缩”的等离子体放大超短脉冲的技术方案。采用一束光同时作为电离脉冲、泵浦光和种子光，避免了不同光束的时空耦合对转换效率的影响。主要的研究结果如下：（1）建立流体理论模型，模拟了基于强耦合布里渊散射的短脉冲自压缩过程，分析了热效应和等离子体不稳定性带来的影响。.（2）建立粒子2D理论模型，模拟了不同参数下基于等离子体布里渊散射的超短脉冲自压缩过程。（3）实验上开展了强耦合布里渊验证实验，获得了2%的转换效率以及500fs的压缩量。（4）实验上产生并测量了飞行焦点，并开展了基于飞行焦点的强耦合布里渊自压缩实验，获得了7%的转换效率和明显的能量和光谱放大曲线。