Atomic Structure And Photoionization Cross Section Calculations And Study Of Absorption Spectroscopy Of Cold Atoms In A MOT

With the development of calculation technologies, theoretical calculations havebeen playing important roles in atomic and molecular physics. Based on the varia-tion principle, many methods have been developed in atomic structure calculations. Ahigh quality complete basis set is essential to the calculation of atomic structures andrelated physical parameters. Such as photoionization cross sections in photoionizationprocess. Photoionization processes play important roles in plasma physics, laser physic-s, atmospheric science and astrophysics. The photoionization cross sections are theindispensable parameters in the relative fields. Excited-state photoionization processesare important in plasma discharges, laser-guided plasmas. In recent years, with the de-velopment of laser cooling and trapping techniques, there has been an increased interestin the study of photoionization cross sections of excited states.We present how to construct quasi-complete basis sets by using the full-relativisticGraspVU program package, which is based on the multi-configuration Dirac-Fockmethod. The relativistic configuration interaction calculations are carried out by usingthe quasi-complete basis sets to consider adequate correlations. The relativistic retar-dation efect of electromagnetic interactions and the quantum electron dynamic correc-tions are also included. Our calculation results of He agree well with other theoreticalresults and experimental results, which validates our calculation scenario is applicable.Our calculations are full relativistic, and can be extended to high Z helium-like ionsin which the relativistic efect is important. We elucidate the mechanism of the inter-esting fine-structure splittings for the1s2p³P_0,1,2states along the helium isoelectronicsequence（Z≤36）, i.e. the competitions between the spin-orbit interactions and theBreit interactions which represent the relativistic retardation efect of electromagneticinteractions. Our scenario of constructing quasi-complete basis sets can be used in anymany-electron atomic system. We calculated the energy levels of Mg and elucidated themechanism of its interesting fine-structure splittings of3³D and4³D levels.The alkali-metal atoms as quasi-one electron systems have been proven to be animportant and interesting testing ground for theoretical descriptions of photoionizationprocesses. Many experimental works have been done. There are few theoretical calcu-lations for the excited-state photoionization cross sections. We measured the photoion- ization cross sections of5p_3/2of Rb in MOT and calculated the photoionization crosssections of low-lying states of Rb by using R-matrix method. Our results agree withother experimental and theoretical results within the error bars. Note that, our scenari-o of constructing quasi-complete basis sets for atomic calculations can be applied inR-matrix calculations.In precision measurement, the iterations between fields and atoms must be con-sidered. Coherent field interacting with the multi-level atoms can lead to quantum in-terference, which could make significative physical phenomenon. As the typical one,the electromagnetically induced transparency（EIT） efect has been of great interest forthe unique optical properties, such as the high transmission, steep dispersion, and soon. The cold atom media has become the research focus in quantum optics and atomicphysics due to its low Doppler-broaden efect and decoherent efect by the collision.The absorbtion spectroscopy of cold⁸⁷Rb in a magneto-optical trap are measured witha weak probe beam. The absorbtion reduction dip due to EIT efect are observed, and atheoretical description is given by a four-level and three-light system.