环流态分子高次谐波偏振特性及其操控研究

Generation of circularly polarized or highly elliptically polarized high harmonics provides an powerful tool to detect the chiral and magnetic features of matters and monitor the related ultrafast dynamics, and has been a hot topic. However, how to obtain the high yield and high mean ellipticity simultaneously is still an unsolved problem. Generating the high harmonics with prepared current-carrying molecules will be a promising way. In this project, we will study the polarization features of high harmonics from current-carrying molecules with the time-dependent density functional theory. We will reveal the mechanism of high harmonic generation from current-carrying molecules, discuss the dependence of polarization features of high harmonics on the current-carrying state and the driving field, and explore methods to control the polarization of high harmonics. Based on these studies, we will develop a new scheme to generate efficient broadband circularly or highly elliptically polarized high harmonics. The study in this project will help people better understand the strong-field dynamics of current-carrying states, and establish a theoretical foundation for generating practical efficient circularly polarized or highly elliptically high harmonics.

圆偏、大椭偏高次谐波的产生为人们深入研究物质的手性、磁性特征及相关超快动力学过程提供了有力的探测工具，已成为当前的研究热点。然而，目前如何在宽的频谱范围内同时获得大的平均椭偏率和高的产率仍是一个亟待解决的问题。通过制备环流态分子来产生高次谐波将有望解决这一问题。在本项目中，我们将基于含时密度泛函理论开展环流态分子高次谐波偏振特性的研究，揭示环流态分子高次谐波产生的机制，探讨谐波偏振特性对不同环流态、驱动激光场的依赖关系，探索操控环流态分子高次谐波偏振特性的方法与规律。在此基础上，发展基于环流态分子产生高效宽带圆偏、大椭偏高次谐波的新方案。该项目的研究对于人们更加深刻的理解环流态强场动力学特性具有重要的意义，为产生实用高效的圆偏、大椭偏高次谐波奠定了理论基础。

大椭偏阿秒光源的产生将为人们研究手性、磁性超快动力学过程提供有力的探测工具，然而目前如何有效获得这种光源仍是一个亟待解决的问题。针对这一问题，本项目提出利用环流态与强激光相互作用的高次谐波产生过程，探索产生高效宽带大椭偏阿秒脉冲光源的方法。我们首先研究了环流态在强激光场驱动下的环流态动力学过程，发现了超快环流反转现象以及环流态间的干涉现象。在此基础上，提出了利用单环流态、简并的双环流态、混合气体等在线偏或二维激光场驱动下高效地获得宽带大椭偏阿秒脉冲的方法，以及产生旋向以亚拍赫兹超快反转的新型椭偏阿秒光源的方法。此外，基于双色圆偏光驱动环流态穿过简并点的动力学过程，我们发现并证明了Aharonov-Ananadan相位并不像过去认为的那样一定会在绝热极限下收敛于Berry相位，具有重要的理论意义。