Studies On Interference Photoelectron Spectra Of Atomic And Molecular Systems Ionized By Extreme Ultraviolet Laser Pulses

Intense laser interaction with atoms and molecules is one of the most important re-search aspects in atomic, molecular and optical physics. With the development of freeelectron laser, high-intensity extreme ultraviolet (XUV) or X-ray light sources have beenachievable. An ultrashort laser pulse with unprecedented high carrier frequency can notonly serve as an efective tool for probing and controlling the microprocess in atoms andmolecules, but also induce some novel physical phenomena. Therefore, research on theinteraction of intense high-frequency laser with atoms and molecules has been paid muchattention in recent years.In2012, P V Demekhin and L S Cedebaum, researchers of Heidelberg University inGermany, theoretically studied the XUV single-photon ionization process of a hydrogenatom. For the first time, interference structures induced by dynamic Stark efect were foundin the photoelectron spectra. On the basis of their pioneering research results, we makedeeper investigation of the interference photoelectron spectra of atomic hydrogen by nu-merical simulation. We discuss the impact of the dipole transition moments and the laserparameters on the interference photoelectron spectra, and explain our findings based on thetheory of dynamic Stark efect. Also, we propose two approaches for approximately calcu-lating the dipole transition moments and checked their validation, which are of significancein numerically simulating the single-photon ionization of other atomic and molecular sys-tems.We further extend our research to the simplest molecule, hydrogen molecular ion H2+,and study the single-photon ionization process of its one-dimensional model by performingwavepacket dynamics simulation. Similar to atomic hydrogen, modulation structures arefound in the photoelectron spectra of hydrogen molecular ion H2+, which is excited by anintense XUV ultrashort pulse. We investigate the impact of the laser parameters on theinterference photoelectron spectra of H2+, and explain our findings qualitatively by usingthe theory of dynamic Stark efect. An approximation theory by neglecting the nuclearmotion is also proposed for molecular systems, and it successfully reveals the connectionand disparity between the photoelectron spectra of atoms and molecules.