The comparison of high-order harmonic generation of H in a circularly polarized laser pulse combined with a terahertz field and with a static electric field

Abstract

By solving a two-dimensional time-dependent Schrödinger equation we investigate high-order harmonic generation (HHG) for the molecular ion in a circularly polarized laser pulse (CPLP). A comparison is made between a HHG in a CPLP combined with a terahertz (THz) field and with a static electric field. When the CPLP is combined with a static electric field, it is observed that a double-plateau structure appears, and the harmonic spectrum presents large modulation. With the CPLP with a THz field, a continuum spectrum with a spectral width of about 137 eV from 102 eV to 239 eV can be achieved. The HHG process is studied using the semi-classical three-step model and time-frequency analysis. Our studies show that only one trajectory contributes to HHG when a THz field is added. Furthermore, we present the temporal evolution of the probability density of an electron wave packet, which shows the recombination of electrons at different times.