基于冷靶反冲离子动量谱仪的原子分子超快动力学研究

发布时间：2018-03-05 23:01

本文选题：冷靶反冲离子动量谱仪　切入点：少周期飞秒激光脉冲　出处：《中国科学院研究生院(武汉物理与数学研究所)》2016年博士论文　论文类型：学位论文

【摘要】：随着激光技术的发展,特别是超短激光脉冲的出现,激光与物质相互作用进入一个全新的领域。用飞秒脉冲光作为轰击粒子与目标粒子相互作用,如果能够掌握作用前后粒子的状态信息,就可以实现原子分子内部电子动力学的飞秒超快测量。本论文基于冷靶反冲离子动量谱仪(COLTRIMS)结合载波-包络相位稳定的周期量级飞秒激光器系统,系统的开展了氢分子在少周期激光场下的双电离动力学行为研究,以及原子电离过程中载波-包络相位效应研究。主要内容如下：1.自主建设了一套用于原子分子超快动力学研究的COLTRIMS系统。其主要包括三个部分,真空系统,超声分子束和离子电子动量测量系统。文中分别对各个部分的搭建过程和工作原理进行了阐述。完成后的COLTRIMS在真空度、分子束冷却温度和离子电子探测系统的测量范围和精度都达到国际先进水平,为开展原子分子内部超快动力学的研究奠定了坚实基础。2.实验上研究了氢分子在超短脉冲激光场驱动下的双电离动力学行为。双电离过程中产生的两个质子的动能释放谱,可以用于分辨导致双电离的不同通道。通过测量不同激光参数(如激光强度,激光偏振和脉冲宽度)下的动能释放谱,结果显示在长脉冲激光场下(即25 fs),主要有两种路径导致双电离,即电荷共振增强电离和重碰撞导致的双电离。另外,可以通过改变激光脉冲的光强来调控这两个过程。而在5 fs激光脉冲下,只有重碰撞导致的双电离过程存在,特别是这一过程只有来自第一次返回轨道重碰撞导致的双电离通道,利用如此短的脉冲为研究亚周期尺度的分子动力学提供一个有效的手段。3.分别从实验上和理论上研究少周期激光脉冲下原子电离过程中的载波-包络相位效应。实验上,通过测量不同载波-包络相位下氩一价离子和氩二价离子的动量分布,展示离子左右出射不对称性系数随载波-包络相位的变化曲线是简单的正弦函数振荡。更有趣的是随着激光光强的增加一价离子的不对称性曲线相对右移,另外二价离子的不对称性曲线与一价离子的不对称性曲线之间的相移也会随着光强的增加而发生变化。理论上,我们使用半经典理论、SFA理论和CVA理论系统模拟了原子单电离过程中的载波-包络相位效应。通过对比不同理论模拟的结果,发现CVA理论可以定性重复实验结果。通过比较CVA理论与SFA理论模拟的结果,发现库仑势影响光电子发射的左右不对称性,导致CVA理论与SFA理论模拟的结果不一致以及不同光强下不对称性系数随载波-包络相位的变化曲线的相移。在Simple man模型下,阐明上述结果是由于库仑势对前向散射电子的明显影响而造成的。
[Abstract]:With the development of laser technology, especially the emergence of ultrashort laser pulses, the interaction between laser and matter has entered a new field. If you can grasp the state of the particles before and after the action, In this paper, a periodic femtosecond laser system based on cold target recoil ion momentum spectrometer (COLTRIMS) and carrier envelope phase stability can be realized. The double ionization dynamics of hydrogen molecules in a small period laser field has been studied systematically. The main contents are as follows: 1. A set of COLTRIMS system for the study of ultrafast dynamics of atoms and molecules has been built. The system consists of three parts: vacuum system. Ultrasonic molecular beam and ion electron momentum measurement system. The construction process and working principle of each part are described in this paper. The vacuum degree of the finished COLTRIMS is obtained. The measurement range and accuracy of the molecular beam cooling temperature and ion electron detection system have reached the international advanced level. 2. The double ionization kinetics of hydrogen molecules driven by ultrashort pulse laser field is studied experimentally. The kinetic energy release spectra of two protons produced in the process of double ionization are studied. Can be used to identify different channels leading to double ionization. By measuring kinetic energy release spectra at different laser parameters, such as laser intensity, laser polarization, and pulse width, The results show that there are two main paths leading to double ionization under long pulse laser field (i.e. 25fsN), namely charge resonance enhanced ionization and double ionization caused by heavy collision. These two processes can be regulated by changing the light intensity of the laser pulse. In the case of a 5 fs laser pulse, only double ionization processes caused by heavy collisions exist. In particular, this process comes only from the double ionization channels resulting from the first re-entry orbit heavy collision, The use of such short pulses provides an effective means for studying subperiodic scale molecular dynamics. 3. The carrier envelope phase effect in the atomic ionization process under a small period laser pulse is studied experimentally and theoretically. The momentum distributions of argon monovalent ions and argon bivalent ions at different carrier envelope phases were measured. It is shown that the variation curve of ion left and right emission asymmetry coefficient with carrier envelope phase is a simple sinusoidal oscillation. More interesting is the relative right shift of the asymmetry curve with the increase of laser intensity. In addition, the phase shift between the asymmetry curve of bivalent ions and that of monovalent ions also changes with the increase of light intensity. We use semiclassical theory and CVA theory to simulate the carrier envelope phase effect in atomic mono ionization process. It is found that the CVA theory can qualitatively repeat the experimental results. By comparing the results of CVA theory and SFA theory, it is found that Coulomb potential affects the left and right asymmetry of photoelectron emission. The results of the simulation of CVA theory and SFA theory are inconsistent, and the phase shift of asymmetry coefficient with carrier envelope phase under different light intensities. In the Simple man model, It is shown that these results are due to the obvious influence of Coulomb potential on the forward scattering electrons.
【学位授予单位】：中国科学院研究生院(武汉物理与数学研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O437

【参考文献】