原子发射高次谐波的优化控制和动力学分析  

The optimal control and dynamical analysis of high-order harmonic generation from atom

作　　者：王国利[1] 李鹏程[1] 李小勇[2] 赵松峰[1] 周效信[1] WANG GuoLi LI PengCheng LI XiaoYong ZHAO SongFeng ZHOU XiaoXin(College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China Experimental Center, Northwest University for Nationalities, Lanzhou 730030, China)

机构地区：[1]西北师范大学物理与电子工程学院,兰州730070 [2]西北民族大学实验中心,兰州730030

出　　处：《中国科学：物理学、力学、天文学》2017年第3期2-13,共12页Scientia Sinica Physica,Mechanica & Astronomica

基　　金：国家自然科学基金(编号:11264036;11364038;11364039;11564033);甘肃省高等学校基本科研业务费专项基金资助项目

摘　　要：原子分子在强激光场中发射的高次谐波是一种新型的便捷型光源,目前已在众多研究领域展现出了非常诱人的应用前景.本文综述了针对高次谐波转换效率低而对其进行优化控制的常用方法和结果,结合波形整形技术和遗传算法等演化算法,人们可以对高次谐波进行各种目的性的控制,特别是利用近年发展成熟的波形合成技术,可将谐波场的强度提高1个数量级以上,或者在不降低强度的基础上将谐波截止位置扩展2倍以上.最后介绍了一种全新的用于高次谐波分析的时频变换方法——同步压缩技术(Synchrosqueezing Transform,SST),该变换技术为理解和探索电离阈值附近及以下高次谐波发射的动力学过程提供了强有力的工具.High-order harmonic generation （HHG） is a frequency up-conversion process in which an ultrafast femtosecond laser pulse at high intensity interacts with atom or molecule. HHG covers the wider wavelength spectral regions of extreme ultraviolet （XUV）, soft X-ray and even hard X-ray. With the high photon flux, the HHG promises to be a attractive broadband tabletop light source, and a number of interesting applications of HHG have been demonstrated in many research fields. In this paper, we review some common methods and results on the optimal control of HHG to improve its low photon flux. HHG can now be controlled for different purposes, i.e., extending the cutoff energy, increasing the efficiency of the high-harmonic conversion process, and selecting single or range of harmonics, by combining the technologies of femtosecond temporal and spatial laser pulse shaping, waveform synthesizing and evolutionary algorithm, such as genetic algorithm and optimal control theory. Selective generation of a single harmonic can now be achieved both in hollow fiber, long gas cell and gas jet. We show that by using the newly developed waveform synthesis with two-color laser fields, the harmonic yield can be enhanced by more than one order without increasing the total laser energy, or the harmonic cutoff can be extended about two times without losing harmonic yield, even after considering the propagation effects. These progresses will exert a far-reaching impact on strong field physics. To optimize the HHG processes, a detailed understanding of the corresponding dynamics is essential. We also introduce a new time-frequency （TF） analysis technique, the synchrosqueezing transform （SST）, which is used to reveal the quantum dynamics of HHG. Compared with the classical type of TF methods, such as the Gabor transform, the Morlet wavelet transform, the SST can be applied to explore the dynamical origin of near- and below-threshold harmonic emission.

关 键 词：高次谐波 优化控制 脉冲整形 波形合成 动力学分析 

分 类 号：O562[理学—原子与分子物理]