Contribution of the bound states and continuum states of an atom in intense laser fields to high harmonic generation

Solving the time-dependent Schrodinger equation for a one-dimensional atom in an intense laser field based on the basis function expansion and a linea r-least-squares fitting method, we examine the influence of the bound state s, continuum states and the interference between them of the model atom on the high harmonic generation. It is found that the main contributions to th e low-energy harmonic generations come from the bound-bound interaction, wh ile the high-energy harmonic generations are from the bound-continuum. inte raction. Beyond the cut-off, the interference of the bound-bound and bound- continuum interactions leads to the disappearance of the harmonic generatio n.