用于产生水窗波段圆偏振阿秒脉冲的非周期性多层膜反射镜的设计研究

The generation of attosecond pulse is currently an international research hotspot. Although the pulse width of an attosecond pulse generated experimentally can be as narrow as 43 as, the polarization state of the attosecond pulse is linearly polarized. The circularly polarized attosecond pulse in the water window is an important tool for studying the ultrafast chiral-specific dynamics in molecules, X-ray magnetic circular dichroism spectroscopy and other cutting-edge scientific issues, and attracts increasing attention in the field of attosecond science. However, due to the limitation of recombination conditions of the electron during high-order harmonics generation, the generation of circularly polarized attosecond pulse in the water window is a bottleneck problem in this field. To solve this problem, the aperiodic Cr/Sc multilayer mirror is designed using genetic algorithm as a broadband reflective mirror, which can achieve polarization conversion of light in the water window from linearly polarized state to circularly one. Based on transfer matrix method and Fourier transform method, the characteristics of designed aperiodic Cr/Sc multilayer mirror in frequency and time domains are analyzed, and the physical mechanism of generating circularly polarized water-window attosecond pulse is studied. Through the research of this project, it can solve the bottleneck problem that the attosecond pulse is developing toward the water-window region and the circular polarization state, and promote the application of attosecond pulse.

阿秒脉冲的产生是目前国际上的研究热点，尽管实验上产生的阿秒脉冲的脉冲宽度可窄至43as，但其偏振态都是线偏振的。位于水窗波段的圆偏振阿秒脉冲，因其是研究分子中的超快手性特异性动力学与X射线磁圆二向色性光谱等前沿问题的重要工具，是阿秒科学领域中更引人关注的研究对象。然而，受到高次谐波产生过程中电子复合条件的限制，水窗波段圆偏振阿秒脉冲的产生是该领域的一个瓶颈问题。针对该问题，本项目旨在通过遗传算法设计非周期性Cr/Sc多层膜结构，从而获得在水窗波段可实现线偏振光与圆偏振光转换的宽带高反射镜，并且基于传输矩阵法与傅里叶变换法分析所设计非周期性多层膜反射镜的频域与时域特性，研究利用其产生圆偏振水窗阿秒脉冲的物理机理。通过本项目的研究，可以解决目前阿秒脉冲朝着水窗波段以及圆偏振态方向发展的瓶颈问题，对拓展阿秒脉冲的应用具有重要的意义。

水窗波段圆偏振阿秒脉冲是研究分子中的超快手性特异性动力学与X射线磁圆二向色性光谱等前沿问题的重要工具。本项目针对在水窗波段实现线偏振光与圆偏振光转换的宽带高反射镜开展研究工作，发展了水窗波段非周期性多层膜的设计程序，获得了一种同时调控水窗波段宽带光源两个偏振分量振幅与相位的新算法，掌握了基于非周期性多层膜设计水窗波段宽带圆偏振片的方法，了解了非周期性Cr/Sc多层膜结构的水窗波段宽带圆偏振片的频域与时域特性，明确了其实现偏振态调控的物理机理。相关研究成果帮助和促进了多层膜光学在阿秒科学中的应用，为基于多层膜结构的阿秒脉冲调控提供了新思路和新方法。在本项目支持下发表学术论文5篇、会议论文2篇，培养研究生5名，包括1名毕业研究生，完成了项目的既定目标。