Alkali Metal Rydberg Atoms In Strong External Fields

Atoms in highly excited electronic states - Rydberg atoms - are an extremely useful tool to gain insight in atomic dynamics. The study of microwave ionization and transition of Rydberg alkali metal atoms is an active research field due to the possibilities of explaining the experimental results by means of classical chaos, searching for the quantum manifestation of classical chaos, and studying high order multiphoton processes in quantitative ways; meanwhile, studies of atom-field interactions have provided important keys to understanding atomic structure, spin-dependent interactions, and angular momentum coupling schemes in atoms. In this thesis, we study highly excited alkali metal Rydberg atoms under the influence of strong external fields. The main contents are as follows:(1) By a direct approach that is based on the Floquet method plus a kind of atomic potential model, we directly calculate the multiphoton transition probability of Rydberg potassium atom in strong microwave fields; and for the first time we give the theoretical microwave threshold spectra that can be compared with experimental ones. The threshold fields and resonance fields are in good agreement with the experimental ones. Our results confirm that the threshold fields do not exhibit the smooth n dependence and show that, in general, the structure does not appear before the threshold field is achieved in the microwave threshold spectrum except a few special cases.(2) Overcoming the difficulties on calculating radial matrix elements of highly excited states by traditional CA method, we explore a new approach to compute the radial matrix elements of alkali metal Rydberg states with higher principal quantum number n. Using B-spline expansion technique and model potentials, we calculate the radial matrix elements by numerical integration with 16 decimal digits precision. We are able to obtain the radial matrix elements of alkali metal Rydberg states with n up to 145, with five significant digits. However, we can only calculate the radial matrix elements of alkali metal Rydberg states with principal quantum number n<30 by traditional CA method. As a test example, we also compute the positions and widths of the anticrossings for highly excited Stark states of Na with n up to 70.According to the viewpoint of a multi-step or rate-limiting step about microwave ionization of alkali metal atoms, the ionization threshold is determined by the first transition step. Our method can be used to directly and quantitatively study multiphoton . ionization processes.