Roles of Coulomb potentials in below- and above-threshold harmonic generation for a hydrogen atom in strong laser fields

Abstract

We study the effects of Coulomb potentials on high-harmonic generation from a hydrogen atom exposed to strong laser fields by numerically simulating the time-dependent Schrodinger equation. Different roles played by the Coulomb potential in the generation of above-threshold harmonics (ATHs) and below-threshold harmonics (BTHs) are distinguished. By gradually screening the Coulomb potential, we find that the BTHs are greatly suppressed, but the ATHs do not change sensitively. Meanwhile, the screening of the Coulomb potential may modify the interference structure of the BTHs, which are induced by the bound–bound states transition and continuum-bound states transition. This study gives an intuitive picture describing the response of a bound or free electron in a laser-dressed Coulomb potential.