反旋双色椭偏场中Ar非次序双电离电子关联的强度依赖

Intensity-dependent electron correlation in nonsequential double ionization of Ar atoms in counter-rotating two-color elliptically polarized laser fields

本文利用三维经典系综模型研究了反向旋转双色椭偏(two-color elliptically polarized,TCEP)场中Ar原子非次序双电离(nonsequential double ionization,NSDI)的电子关联特性和再碰撞动力学.数值结果显示随激光强度的增大,电子对在x方向的关联动量分布从位于第一象限的V形结构逐渐演变成主要分布于二、四象限的弧形结构,最后过渡到主要位于第一象限的近原点分布.其主要的关联行为从正相关演变成反相关再到正相关.两脉冲组成的复合电场波形呈现出三叶草的形状,即1个周期的电场由3个不同方向的“叶片”组成,每个“叶片”称为一个波瓣,根据时间演化的顺序分别将其称为波瓣1、波瓣2和波瓣3.轨道分析发现,NSDI事件中单电离主要发生在波瓣1和波瓣3,且随强度的增大波瓣1的贡献越来越大,波瓣3的贡献越来越小.相应地电子主要从20°和175°两个方向返回母离子,且随强度的增大,20°附近返回的电子逐渐增多,175°附近返回的电子逐渐减少.

Electron correlation behaviors and recollision dynamics in nonsequential double ionization(NSDI)of Ar atoms in a counter-rotating two-color elliptically polarized(TCEP)field are investigated by using a threedimensional classical ensemble model.The numerical results show that the correlated momentum distribution of electron pairs in the x-axis direction evolves from a V-shaped structure in the first quadrant at the low intensity,to an arc-shaped structure mainly located in the second and fourth quadrants at moderate intensity,finally to a distribution near the origin located in the first quadrant in the high intensity.With the laser intensity increasing,the dominant correlation behavior evolves from correlation to anti-correlation and finally reverts back to correlation.The combined electric field traces out a trefoil pattern,i.e.the waveform in a period shows three leaves in different directions.Each leaf is called a lobe.The electric field recursively evolves from lobe 1 to lobe 2 and to lobe 3.Unlike the counter-rotating two-color circularly polarized fields,the combined fields from two elliptical fields do not have the spatial symmetry.Amplitudes of the three field lobes and the angles between them are different.Furthermore,the back analysis of NSDI trajectories shows that the single ionization in NSDI events mainly occurs in lobe 1 and lobe 3,and the contribution from lobe 1 increases and that from lobe 3 decreases with the increase of the intensity.Correspondingly,the free electrons mainly return to the parent ion from 20°and 175°.With the laser intensity increasing,the electrons returning from 20°gradually increase and those returning from 175°gradually decrease.In order to further understand the correlation behaviors of electron pairs in the x-axis direction,the NSDI events triggered off by single ionization from different lobes are separately discussed.With the increase of laser intensity the correlation behavior of NSDI events triggered off by single ionization from field lobe 1 evolves from anti-correlation behavior to correlation behavior,but the correlation behavior of NSDI events induced by single ionization from field lobe 3 evolves from correlation behavior to anti-correlation behavior.With the laser intensity increasing,the NSDI events induced by single ionization from field lobe 1 increase gradually,but those from field lobe 3 decrease.This results in that the total dominant correlation behavior evolves from correlation to anti-correlation and finally reverts back to correlation as the laser intensity increases.