Investigation On Generation Of High-Order Harmonic From Acetylene

High-order harmonic generation (HHG) can be observed as the molecular system is radiated by an intense laser field, and utilizing the molecular HHG, one can image the orbital wave-function of the molecule. In this thesis, adopting the time-dependent Hartree-Fock scheme, the HHG process of acetylene molecule is systematically investigated. And the specific research work mainly includes the following parts:We systematically investigate the time-evolution of the spatial distribution of electrons in different molecular orbits. It is found that there is a big difference between the dynamical evolution of electrons in orbit of inner shell and that in orbit of outer shell, and as for the HOMO orbits, the spatial change of electronic ionization population can be clearly observed.The influence of intensity of incident laser pulse on the HHG is systematically investigated. It is found that, for the acetylene molecule whose internuclear distance is at the equilibrium position, its harmonic spectrum can be divided into three regions according to the energy:in the lower energy region which is below the threshold of ionization, the overall harmonic generation is more intense than the harmonic generation of HOMO (region A); in the energy region which is above the ionization threshold and below the cut-off position given by the three steps model, the overall harmonic generation is identical to that the harmonic generation of HOMO (region B); in the energy region above he cut-off position, the harmonic generation is much more intense than the harmonic generation of HOMO (region C). As for region C, the intensity of harmonic does not change much with the amplitude of electric field, which is mainly attributed to the transition between different orbits, as for region B, the intensity of harmonic increases as the amplitude of electric field increases, which is attributed to the fact that this kind of harmonics is generated in the ionization of the electron in molecule, and as for region A, the intensity of harmonic also increases as the amplitude of electric field increases, however, it does not change much, and this kind of harmonics comes from the dipole transition of bound system.The influence of internuclear distance on the HHG is investigated. In the case of larger internuclear distance, the contribution to HHG from the inner shell will become larger and larger, apart from that from HOMO orbits.