Nonsequential double ionization (NSDI) of atoms driven by parallel-polarized two-color (PPTC) fields composed of two equal-intensity multiple-cycle laser pulses is investigated using a three-dimensional classical ensemble model. The ion momentum distribution shows pronounced asymmetry and strongly depends on the relative phase of the two pulses. The ion momentum distributions exhibit a double- or not yet observed triple-hump structure, depending on the relative phase of the two pulses. More interestingly, the three peaks of the ion momentum distribution correspond to the first-returning recollision, the odd-returning recollision (without the first returning recollision), and the even-returning recollision. This means that the number of electron returnings is mapped onto the ion momentum distribution. The information about the number of electron returnings can be directly retrieved from the observed ion momentum distribution in the PPTC field with equal intensities. Moreover, the proportions of the three types of trajectories in NSDI, the returning energy of the ionized electron, and the ionization mechanism can be well manipulated by changing the relative phase of the two pulses.

中文翻译：

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强场非顺序双电离中电子返回动力学对离子动量谱的印记

使用三维经典系综模型研究了由两个等强度多周期激光脉冲组成的平行偏振双色（PPTC）场驱动的原子的非顺序双电离（NSDI）。离子动量分布显示出明显的不对称性，并且很大程度上取决于两个脉冲的相对相位。离子动量分布呈现出双峰或尚未观察到的三峰结构，具体取决于两个脉冲的相对相位。更有趣的是，离子动量分布的三个峰值对应于第一次返回重碰撞、奇数返回重碰撞（没有第一次返回重碰撞）和偶数返回重碰撞。这意味着返回的电子数量映射到离子动量分布上。关于电子返回次数的信息可以直接从观察到的等强度PPTC场中的离子动量分布中获得。而且，通过改变两个脉冲的相对相位，可以很好地控制NSDI中三种轨迹的比例、电离电子的返回能量以及电离机制。