少光周期激光场中非次序双电离关联电子动力学研究

发布时间：2018-10-09 09:30

【摘要】：强场原子分子非次序双电离是强场物理科学中重要的基本过程。由于电离过程中双电子体现强烈的关联性,开展强场非次序双电离研究,对人们深入理解强场过程,进一步认识微观世界中阿秒时间尺度动力学的物理本质有重要的意义。本文主要研究了少光周期激光脉冲驱动的原子分子非次序双电离,重点关注激光脉宽、强度和波长等可控激光参数对关联电子发射细节的影响。全文的研究内容如下:研究了关联电子动力学对激光脉宽的依赖,计算结果显示,在平均CEP情况下,激光脉宽为4个光周期时,关联电子末态纵向(沿激光场偏振方向)动量分布主要集中在第一、三象限,并呈现清晰的V型结构。随激光脉宽的增加,更多的关联电子动量分布集中在第二、四象限。在绝对CEP=0情况下,随激光脉宽的增加,关联电子末态动量分布的不对称性随激光脉宽的增加不断弱化。通过反演分析发现,电子关联行为与第二个电子的电离时间相位密切相关,同时,双电离时间相位分布由单区域演变为双区域,导致关联电子末态动量分布的不对称性随激光脉宽的增加不断弱化。研究了少光周期激光脉冲驱动的氮分子非次序双电离中关联电子行为对激光强度和波长的依赖特性。计算结果显示,在近红外激光脉冲下,随激光强度的增加,关联电子末态动量分布由四个象限均匀分布演变为在一,三象限集中分布。与之不同的是,在中红外激光脉冲下,随激光强度的增加,关联电子动量分布由一,三象限集中分布演变为四个象限均匀分布。通过向后分析轨迹发现,占主导地位的电离机制的改变是动量谱变化的主要原因。但是,随激光波长的增加,再碰撞时间相位向激光电场峰值附近移动,这导致在高激光强度、长波长情况下,相当一部分关联电子对沿相反方向发射。研究了高能电子电离动力学对激光强度的依赖。计算结果显示,高能电子对的产率随着激光强度增加先快速增高随后缓慢降低。正二价离子动量分布随激光强度的增加而发生显著的变化,呈现单峰—三峰—双峰的结构变化。反演分析双电离轨迹发现,高能电子的产生主要与第二个电子的电离动力学密切相关。同时,随激光强度增加,占主导地位的双电离通道发生改变,这导致纵向离子动量谱的结构变化。
[Abstract]:Non-ordered double ionization of strong field atoms and molecules is an important basic process in strong field physics. Due to the strong correlation of double electrons in the process of ionization, it is of great significance for people to understand the process of strong field and further understand the physical essence of time-scale dynamics of attosecond in the microcosm. In this paper, the influence of controlled laser parameters such as laser pulse width, intensity and wavelength on the detail of correlated electron emission is studied. The main contents of this paper are as follows: the dependence of correlation electron dynamics on laser pulse width is studied. The calculated results show that the laser pulse width is 4 photoperiod on average in the case of CEP. The longitudinal (along the polarization direction of laser field) momentum distribution of the related-electron terminal states is mainly concentrated in the first and third quadrants with a clear V-shaped structure. With the increase of laser pulse width, more correlated electron momentum distributions are concentrated in the second and fourth quadrants. In the case of absolute CEP=0, with the increase of laser pulse width, the asymmetry of the momentum distribution of the related-electron terminal state weakens with the increase of laser pulse width. Through inversion analysis, it is found that the electron correlation behavior is closely related to the ionization time phase of the second electron, and the double ionization time phase distribution evolves from a single region to a double region. The asymmetry of the momentum distribution in the final states of the correlated electrons is weakened with the increase of the laser pulse width. The dependence of correlated electron behavior on laser intensity and wavelength in non-ordered double ionization of nitrogen molecules driven by laser pulses with less photoperiod was studied. The calculated results show that with the increase of laser intensity, the momentum distribution of the final states of correlated electrons evolves from four quadrants to one and three quadrants under near-infrared laser pulses. In contrast, with the increase of laser intensity, the momentum distribution of correlated electrons evolves from one and three quadrants to four quadrants under the middle infrared laser pulse. It is found that the change of dominant ionization mechanism is the main reason for the change of momentum spectrum. However, with the increase of the laser wavelength, the phase of the recollision time moves towards the peak of the laser electric field, which results in a large number of correlated electron pairs emitting in the opposite direction under the condition of high laser intensity and long wavelength. The dependence of high energy electron ionization dynamics on laser intensity is studied. The calculated results show that the yield of high energy electron pairs increases rapidly and then decreases slowly with the increase of laser intensity. The momentum distribution of positive bivalent ions changes significantly with the increase of laser intensity, showing a single peak, three peaks and two peaks. It is found that the generation of high energy electrons is closely related to the ionization dynamics of the second electron. At the same time, with the increase of laser intensity, the dominant double ionization channel changes, which leads to the structural change of longitudinal ion momentum spectrum.
【学位授予单位】：信阳师范学院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O562

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