Theoretical Studies On Electron Dynamics Of Hydrogen Atom And Molecule In Intense Laser Fields

Intense laser interaction with atoms and molecules attracts a lot of attention. And it is a frontier of physical research. The latest researches in this area is available for detecting and controlling of the physical processes of materials on a time scale of attosecond and a spatial scale of angstrom. Nowadays, the laser pulse width becomes shorter and shorter, reaching only a few optical cycles, and its strength is comparable with atomic internal Coulomb force. With such intense laser field, there are many non-linear physical phenomena: tunneling ionization, above threshold ionization, non-sequential double ionization, high-order harmonics generation, and so on. As research on these issues deepening, more and more new questions are constantly being raised. In this paper, we employ the theoretical tool of solving time-dependent Schr?dinger equation, combining with semi-classical quantum trajectory analysis, and study the electronic dynamic process of the single-active-electron approximation quantum systems of atoms or molecules in intense laser field for interplaying the physical phenomena: high order harmonics generation, single attosecond pulses emission and above threshold ionization.First, we develop a program for solving three-dimensional time-dependent Schr?dinger equation for single-active-electron atoms in intense laser fields, which benefits the numerical methods of solving the Schr?dinger equation. When a linearly polarized laser acts with hydrogen atoms, the atomic system manifests a prevailing spherical symmetry. The atomic orbitals are expanded in spherical harmonics. The radial degrees of freedom are discretized using a FEM-DVR with a product basis of Lobatto shape functions. Making full use of the features of sparse and block structure of the Hamiltonian matrix, we spin-off and regroup the matrix to facilitate parallel computing efficiently.Secondly, we theoretically study the electron dynamic process of high-order harmonics generation and produce attosecond pulses by continuum wave packets interference when hydrogen atoms are shined by super intense laser fields, by solving the time-dependent Schr?dinger equation. When the intensity of the laser is up to the over-barrier regime, the ground state of the hydrogen atom will be depleted empty. The continuum wave packets with different energy back to the parent ion are interfered with each other and high-order harmonics emit. According to this physical mechanism, by using a two-color laser field to control the quantum trajectory of the electron and intensity of the continuous wave packet, we separate the harmonics generated from continuum-continuum and continuum-bound wave packets interference in harmonic spectrum. Further, by adjusting the relative carrier envelope phase of the two-color laser pulses, we can obtain a shorter single attosecond pulse by superposing the high harmonics from continuous wave packets interference.Third, we put forward a solution of shielding certain bound states to participate in the evolution when solving 3D time-dependent Schr?dinger equation, and apply it to the theoretical calculations. The solution is based on the short iterative Lanczos method for time-dependent evolution. The numerical results of simulating atomic Xe in intense laser field by using this solution are in good agreement with the experiment. Meanwhile, we apply this solution to study the process of above threshold ionization and find the influence of the difference of electronic orbital on the photoelectron spectrum theoretically.Finally, we demonstrate the red and blue shift of the photoelectron energy spectrum of hydrogen molecular ion in a few cycles extreme ultraviolet laser pulse. It is caused by the periodic change of the ground state population of electron of molecular ion in momentum space. For different nuclear distance, when the electronic population of ground state in in momentum space corresponding to the frequency around the center frequency of laser field is diminishing, the energy spectrum of photoelectron is red shift. Otherwise, the energy spectrum of photoelectron is red shift.