中红外激光场下阈上电离能谱中的低能结构

Low energy structure of above-threshold ionization spectra produced by mid-infrared laser pulses

强激光诱导原子阈上电离中的低能结构(low-energy structure,LES)是当前强场领域的研究热点,其背后的动力学过程引起了广泛讨论.本文基于半经典模型、SCTS(semi-classical two-step)量子轨道模型和数值求解含时薛定谔方程(time-dependent Schrödinger equation,TDSE)方法,研究了中红外激光场下Xe原子阈上电离中的LES随激光脉冲宽度的依赖.发现LES随脉冲宽度的减小向更低能量方向移动.分析表明:长脉宽条件下,能谱中的多峰结构(LESn)与电子前向散射的阶次n及电子初始横向动量密切相关,而极低能结构(very-low-energy structure,VLES)主要由更高阶次前向散射的电子轨道贡献;少周期脉冲条件下,LES峰值位置随载波包络相位(carrier-envelope phase,CEP)的移动可归因于激光场矢势和离子实库仑势的共同作用随CEP的变化,其中库仑势导致的电子聚束效应是LES峰形成的主要原因.

The low-energy structure(LES)of above-threshold ionization(ATI)of atoms subjected to an intense laser field is a hot topic in the strong-field atomic physics.The rich physical insights behind LES attract a lot of attention.Based on a semi-classical model,a semi-classical two-step(SCTS)quantum trajectory model and numerical solution of the time-dependent Schrödinger equation(TDSE),we study the pulse-duration dependence of LES for Xe atom subjected to a mid-infrared laser field.It is found that the energy of LES becomes lower for shorter pulse duration.Further analysis shows that in the case of multi-cycle laser field,the LESn structure is closely related to the number of times of forward scattering and the initial transverse momentum.In the case of few-cycle laser pulse,the carrier-envelope phase(CEP)dependence of the peak position of LES is mainly due to the CEP dependence of the influence of both vector-potential of the laser field and the Coulomb potential.In addition,the bunching effect of electrons,caused by Coulomb potential,is the main reason for the formation of LES.