Research On The Photoionization Of Atom In A Magneto-Optical Trap Or In Plasma

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.