超快强激光场中原子非绝热电离动力学

With the rapid development of femtosecond laser technique, the pulse duration is approaching the single optical cycle limit. In such a ultrashort laser electric field pulse, the ionization dynamics of atoms cannot be described with the adiabatic approximation very well. Recently, the nonadiabatic ionization process (NIP) attracted a lot of concerns. The relevant works concentrated on the molecular dissociation processes and high order harmonic generation processes, however, little attention has been paid to NIP of high order above threshold ionization (HATI), nonsequential double ionization (NSDI), neutral excited atoms acceleration (NEAA), and the momentum distributions of photoelectrons from tunnelling process (MDPE), where NIP may play important roles according to the published theorectial works. In this project, we will perform an experimental investigation on the NIP in the HATI, NSDI, NEAA, and MDPE processes. The significance of NIP will be revealed with this study concerning the dependence of HATI, NSDI, NEAA, and MDPE on laser electric field parameters, such as pulse duration, wavelength, intensity. We hope this investigation will deepen our understanding on the interaction of laser electric field and atoms and molecules.

随着飞秒激光技术的发展，飞秒激光的脉宽已减少至接近单个光学周期。在如此之短的激光电场中，原子的电离过程已经不能用绝热近似来描述。近年来，原子分子体系在飞秒激光场中非绝热电离过程越来越受到人们的重视。然而，目前的研究主要集中在分子解离过程和高次谐波的产生过程中，对于目前广受关注的高阶阈上电离、非顺序双电离、中性原子加速以及隧穿电离电子动量分布方面却很少有相关研究开展，尽管已有研究表明这些现象中同样可能存在非绝热过程。本项目计划结合实验和理论方法，研究以上提到的四种现象中的非绝热过程，通过研究这些现象随着激光脉宽、波长、光强等因素的演化，并与相关理论进行对比，从而揭示非绝热动力学过程的重要性。相关研究有望加深人们对激光场与原子分子相互作用过程的理解。

原子分子超快电离过程中的非绝热效应目前已经成为备受关注的热点话题。按照申请书的计划，本项目将考察非绝热效应是如何影响隧穿出口的动量和空间分布，以及非绝热效应在高阶阈上电离、非顺序双电离过程以及中性原子产生及加速过程中的表现。本项目严格按照申请书的计划开展研究，本项目研究了非绝热效应是如何影响椭圆偏振激光场中光电子产量随着激光椭偏率演化的曲线。并利用目前对于非绝热效应的理解，发展了一套包含非绝热效应的激光光强标定方案。本项目发展了探测中性激发态原子的技术方案，实验研究了高阶阈上电离能谱随着激光光强和脉宽的演化情况，实验研究了非顺序双电离过程的电子关联动量分布和二维电子动量分布。