基于双光丝强脉冲内相干性超连续光谱的2微米OPCPA系统前端研究

基于千瓦级掺镱皮秒激光泵浦源的光参量啁啾脉冲放大（OPCPA）技术被认为是可以实现几十拍瓦乃至更高量级激光脉冲的主要技术路线之一。工作在2微米波段的OPCPA系统由于能够驱动惰性气体产生波长位于水窗波段的高通量x射线而备受关注。精确的控制2微米超短脉冲的载波包络相位（CEP）一直是一个极具挑战性的难题。目前最流行的技术是使用皮秒激光脉冲通过超连续光谱产生和差频产生过程直接实现CEP稳定的2微米种子脉冲。这种2微米种子脉冲的CEP稳定性与超连续脉冲的脉冲内相干性密切相关。基于此，本项目提出了一种新方案来实现CEP稳定的种子脉冲。该方案通过透明介质晶体中的双光丝过程实现具有强脉冲内相干性的超连续光谱，并利用该超连续光谱中与泵浦光波长对称的波长对差频产生CEP稳定的2微米种子脉冲，最终我们基于该方案搭建一个CEP稳定的2微米OPCPA前端，并探索该前端的输出特性。

Optical parametric chirped pulse amplification (OPCPA) based on a kilowatt ytterbium-doped picosecond laser pump source is considered to be one of the main techniques for achieving laser pulses with petawatt or even higher levels. The OPCPA system which operates around 2 μm wavelength region has attracted a lot of attention due to the ability of achieving water-window high-flux x-rays through driving noble gases. It is always a challenging to precisely control the carrier envelope phase (CEP) of a 2 μm ultrashort pulse. The most popular technique in a 2 μm OPCPA system front-end is to use the picosecond pump laser pulse directly realize CEP stable seed pulse via supercontinuum generation process and differential frequency generation process. The CEP stability of the generated 2 μm seed pulse is strongly related to the intra-pulse coherence of the supercontinuum pulse. Based on this, we proposes a new scheme to realize the CEP stable seed pulse. The new scheme is based on a strong coherent supercontinuum which is generated via double filament process in a transparent crystal. The 2 μm seed pulse is generated via differential frequency generation process between a frequency pair which is symmetric relative to the wavelength of the pump laser. Based on this scheme, we will develope a CEP stable 2 μm OPCPA front-end and explore its output characteristics.