Quantum mechanical study of high-order harmonic generation from HeH2+ molecule in homogeneous and plasmonic-enhanced laser fields

Abstract

High-order harmonic generation (HHG) from molecular ion HeH2+ in two initial states— (ground state) and (first excited state)—in homogeneous and plasmonic-enhanced laser fields is investigated theoretically. The electron ionization and the enhancement of HHG yield with ground and first excited states as the initial states is studied, and a strong orientation effect for electron ionization in state, which can be used to reach a longer lifetime for the electron in the first excited state during the high harmonic emission, is discovered. In order to investigate the effect of the plasmonic field on the cutoff position of HHG spectra, first the enhancement of laser field in a nano-antenna is calculated and then the interaction of the enhanced field with HeH2+ molecule is studied by solving the time-dependent Schrödinger equation. According to the results, when an HeH2+ molecule in the initial state of is irradiated by a plasmonic polarized laser field with polarization normal to the molecular axis, the HHG yield and cutoff position are enhanced, while the excited state has a long lifetime during the HHG process.