中红外强激光场中准直分子的阈上电离实验研究

The comprehension of tunnel ionization is of fundamental importance in the study of strong field atomic and molecular ionization dynamics. Rescattering model, based on electron tunnel ionization, provides an intuitive physical insight into various experimental phenomena ralated to ionization. However, the occurence of electron tunnel in intense laser field has not yet been experimentally confirmed and poses a great challenge to experimentalist. In this project, the above-threshold ionization process of aligned molecules in intense mid-infrared laser pulses will be exlored. With the help of the self-made time-of-flight photoelectron spectrometer, we will illustrate the existence of the tunnel exit by investigating the dependence of the high-energy electron cutoff position on the molecular alignment angle. This project will shed light on the information of tunnel exit. It will be beneficial to a comprehensive investigation of tunneling ionization and the understanding of many physical problems that have been explained by rescattering model.

对隧穿电离的认识是理解强激光场原子分子电离动力学的基础。基于电子隧穿电离假设的重散射模型为强场电离相关现象提供了直观的物理图象。然而人们对强场隧穿电离这一基本物理过程的理解尚不完善，有待更加深入的研究。本项目拟利用中红外波长的飞秒激光器，对准直分子的阈上电离开展实验研究。利用自主搭建的基于飞行时间原理的高分辨光电子能谱仪实验系统，结合分子准直技术，我们将研究光电子能量截止位置随分子取向角度的关系，探讨分子中不同轨道电子电离的隧穿出口的变化。本项目研究成果有可能对利用重散射模型解释的许多物理问题的理解产生影响，并加深我们对强场原子分子隧穿电离过程的理解。

本项目拟围绕准直分子的阈上电离高能光电子开展研究。在本项目资助下，我们实现了氮气和氧气分子的准直，准直程度为0.7，达到研究领域内较好水平。在研究过程中，结合国际最新研究形势，我们对研究内容进行了适当调整。首次实验研究了长波长（1500 nm）圆偏振飞秒激光中随机取向氧气分子的电离抑制现象，结合S矩阵理论分析，阐明了分子轨道效应对分子电离抑制的重要作用。

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