Atomic and molecular multiphoton processes in intense laser fields.

摘要

To advance this strong-field atomic and molecular physics, this dissertation aims at developing both new theoretical formalisms and accurate computational methods for ab initio nonperturbative studies of atomic and molecular processes in intense and superintense laser fields. The new methods developed allow the first in-depth and precision studies of strong-field phenomena of both one- and many-electron systems, including multiphotonionization (MPI), multiple high-order harmonic generation (HHG) and x-ray laser, and coherent control of quantum dynamics, etc. The main achievements are summarized below: (a) A generalized pseudospectral method (GPS) is developed for precision calculations of the electronic structure of both atomic and two-center molecular systems, involving optimal non-uniform spatial grid discretization of the Hamiltonians. (b) A complex-scaling GPS procedure is developed for general treatment of the energies and lifetimes of resonance states. The procedure is applied to the first converged non-Hermitian Floquet study of the complex quasienergies of molecular ions in intense low-frequency laser fields. (c) A new time-dependent method is developed for accurate solution of time-dependent Schrödinger equation and applied to the calculation of HHG spectra of Na in intense mid IR laser fields. (d) A genetic algorithm procedure is devised for the optimization of HHG emission by adjusting the incident laser pulse amplitude and phase. The new concept of “intra-atomic” phase matching on the sub optical cycle is confirmed for the first time. (e) A steady-state self-Interaction-free density functional theory is developed for general and accurate treatment of the electronic structure of Rydberg atoms and many-electron molecular systems. (f) A self interaction-free time-dependent density-functional theory (TDDFT) is developed, allowing general and nonperturbative treatment of quantum dynamics of many-electron molecular systems in intense laser fields for the first time. (g) Similar TDDFT procedures are extended to the first study of MPI and HHG of multi-electron N₂ molecules in intense laser fields. The results reveal the competition of two different effects on MPI/HHG, namely, orbital orientation and binding energy from individual valence electron orbital. (Abstract shortened by UMI.)