| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 97 === We present an ab initio study of the time-dependent density-functional theory (TDDFT) with proper asymptotic long-range potential for nonperturbative treatment of multi-photon processes of diatomic molecules in strong laser field. For accurate and efficient treatment of the TDDFT equations, the generalized pseudospectral method (GPS) is extended to two-center molecules system. The procedure allows nonuniform and optimal spatial grid discretization of the Hamiltonian in prolate spheroidal coordinates and the time propagation using the split-operator technique in the energy representation.
The multiphoton ionization and high-order harmonic generation (HHG) of diatomic molecules N2, CO, and O2 in intense short laser pulse fields are calculated in detail. We observe both the electronic binding energy and the orientation of the orbitals affect the ionization rate. In the analysis of HHG, the highest occupied molecular orbital (HOMO) has dominant contribution, but accurate results have to be obtained with all-electron study. The CO molecule has a small permanent dipole moment cause the different nonlinear optical response to homonuclear molecules such as generating both even and odd harmonics.
We also practice the optimal control theory using time-dependent targets on the two-level system with use of the conjugate gradient algorithm, therefore greatly reducing the number of iterations to reach convergence.
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