【作者】 黄巍；

【导师】 薛平；

【作者基本信息】 清华大学 ， 物理学， 2012， 博士

【摘要】 在极端场强、超低温度等极端物理条件下，光场与物质的相互作用会呈现一系列全新的物理现象，随着高新技术的发展，使得在实验室就可实现这样得特殊条件。离子、原子、分子的囚禁、冷却和操控以及外加强场、等离子体等条件下原子分子结构和动力学行为研究，是当今国际上原子分子物理学的主要研究领域。一方面激光冷却技术的发展，使得极低温度的原子体系已经成为一个重要的实验工具。通过光电离冷原子的方法，可以得到近强耦合的超冷等离子体，这一全新的体系对于研究高温高密强耦合等离子体以及等离子体中的原子物理过程具有重要价值。而激发态光电离截面是激发态原子光电离过程及生成超冷等离子体的重要参数。另一方面，等离子体环境会影响激光与原子的相互作用，当强场超短脉冲激光与原子作用时，等离子体屏蔽效应会影响高次谐波产生的全部三步过程。本论文的具体工作包括实验和理论两个部分。实验上，搭建了一套基于磁光阱的冷原子光电离实验系统。本人参与了磁光阱系统的搭建工作，并负责完成了以FPGA卡为核心的时序控制系统的研发和电离光系统的设计和实现。在冷原子光电离实验中，用多种和磁光阱原子动力学行为相关的实验方法，首次测量并得到了电离光波长为405nm、450nm、473nm时⁸⁷Rb原子5P_3/2态的绝对光电离截面。实验研究表明，激发态比例因子是光电离截面测量结果的主要误差来源；同时，因为电离光光斑要大于冷原子云的尺寸，实际起电离冷原子作用的电离光功率要比平均功率大，实验中需要对测量得到的电离光功率进行修正，修正系数与电离光光斑、冷原子云的尺寸有关。理论上，用库仑波函数离散变量表象和二阶劈裂算符时间演化直接非微扰求解三维含时薛定谔方程的方法，首次系统研究了等离子体对强场超短脉冲激光与原子相互作用微观过程的影响。计算结果表明，等离子体对原子电离速率及电离机制、连续态电子在激光场和中心势作用下的运动过程以及电子与离子复合的三个过程都有影响。表现在高次谐波发射谱和由高次谐波得到的阿秒脉冲串都随着德拜屏蔽常数的取值不同而发生改变。更多还原

【Abstract】 Under extrem strong field, ultra-low temperature and such specialconditions, the laser-matter interaction will cause several brand new physicphenomenons. As high and new technologis developed quickly, theseextraordinary states can be achieved in larboratory. Today, the internationalatom and molecule physics study include two main areas. One is the trapping,cooling and manipulation of ion, atom and molecule. And the other is thestructure or dynamic behavior of atom and molecule under additional strongfield or plasma. First, the development of laser-cooling technich makes thesystem of ultra-low temperature atoms become an important experiment tool.Through photoionization cold atoms, the near strong coupled ultra-coldplasma can be obtained. This new plasma system is useful in study hightemperature and high density strong coupled plasma and atom physics inplasma environment. And photoionization cross section of excited atom stateis a crucial parameter in the process of excited atom photoionization andcreation of ultra-cold plasma. Second, the laser-atom interaction in the plasmaenvironment displays some different characters. Especially, when theultra-short strong field laser pulse applied on the atom, the plasma screeningeffect can influence on the whole three-steps. The work in this thesis consistsby two parts, experiment and theory.On the aspect of experiment, the experimental apparatus system of coldatom photoionization based on magneto-optical trap is build up. The writerparticipated in the set-up work of magneto-optical trap. And responsible fordesigning and realizing the time-sequence control system in which the FPGAcard is core component. Futhermore, the photoionization system is completedindependently. In the experiment of cold atom photoionization, some methodsrelated to the atom number dynamic in the magneto-optical trap are employed.The first results of⁸⁷Rb5P_3/2state absolute photoionization cross section atwavelength405nm.450nm and473nm are acquired. We find that the uncertainty of excited factor is the principal error source. And the actualintensity of ionization laser photoionizing the cold atom is stronger than themeasured average intensity. This is caused by the larger size of ionizationlaser spot comparing with the cold atom cloud. Concerning the size ofionization laser profile and cold atom cloud, a coefficient is used to correctthe ionization laser intensity.On theory aspect, the coulomb wave function discrete variablerepresentation and the second-order split-operator method is applied to solve3D TDSE directly and non-pertubatively. Then plasma effect on themicroscopy processes of interaction between strong field ultra-short pulselaser and atom is studied systematically and firstly. The computation resultsrepresent that the plasma screening effect is valid in all three-steps. The atomionization rate, even the ionization mechanism is changed. And the continuumstate electron movement govered by the laser field and potential is affected bythe plasma. Last, the plasma screening effect influent the electron-ionrecombination. As a result, the HHG power spectrum and attosecond pulsetrain hava different characteristics when the value of Debye screeningparameter altered.更多还原