基于临界密度等离子体透镜的激光脉冲整形研究

Shaping laser pulse by near-critical density plasma lens would significantly enhance the laser intensity, which would improve laser acceleration efficiency and further beam quality. This project is intended to study laser shaping based on near-critical density plasma lens. The low intensity pre-pulse or laser background will firstly interact with near-critical density target such as carbon nanotube and near-critical density plasma will be generated with laser and target parameters optimized. Then the high intensity main pulse will interact with the resulting near-critical density plasma and form near-critical density plasma lens, which would further enhance laser intensity. Through this project, new technical method for laser shaping by near-critical density plasma lens would be achieved and higher laser intensity would be promised for laser acceleration, which would further improve the efficiency of laser acceleration.

通过临界密度等离子体透镜实现对强场激光脉冲的整形，有望显著提高激光光强，进而改善激光加速效率和束流质量。本项目拟开展基于临界密度等离子体透镜的激光脉冲整形研究。通过优化激光参数与靶材参数，使强度较低的激光预脉冲或激光本底首先与碳纳米管等典型临界密度靶材相互作用产生临界密度等离子体，之后使强度更高的激光主脉冲与已产生的临界密度等离子体相互作用形成临界密度等离子体透镜，从而实现激光强度提升。希望通过本项目的开展，获得实现临界密度等离子体聚焦透镜脉冲整形的有效技术途径，获取更高强度激光脉冲用于激光加速，以期使激光加速进一步向更高效转换效率迈进。

本项目基于团队已有的200TW激光系统开展基于临界密度等离子体透镜激光脉冲整形研究，改善了激光加速效率和束流质量。首先针对200TW激光系统在等离子体透镜产生所需脉冲质量方面做了深入研究与改造：设计并实现了高效非真空交叉偏振波系统，在此基础上进一步详细研究了交叉偏振波光谱特性，为临界密度等离子透镜实验提供了高对比度激光脉冲；通过对激光光谱的合理调制实现了激光有效最高峰值的运行，这为后续实验提供了最高激光光强。在对激光性能进行研究改造的同时，针对激光诊断脉冲宽度的需求，设计并研制了高精度单发实时脉宽诊断装置。最后，设计并搭建了适用于临界密度等离子体透镜产生的烧蚀脉冲打靶系统，利用烧蚀脉冲制备临界密度等离子体透镜并对强场激光脉冲整形，通过激光加速实验获得了电量和能量都有显著增强的质子束，表明了等离子透镜对强场激光脉冲光强增强效应，从而提供了一种提高激光加速更高转换效率，产生更高束流品质的方案。