SATURATION OF HARMONIC-GENERATION IN ONE-DIMENSIONAL AND 3-DIMENSIONAL ATOMS

A commonly used numerical technique for calculating the harmonic spect rum emitted by an atom exposed to an intense laser pulse is the direct integration of the Schrodinger equation. We compare the spectra calcu lated using two different models. The first is in one dimension with a n approximate hydrogenic soft-core potential and the second is in thre e dimensions with a Coulomb potential. We use realistic laser pulse co nditions (100 fs, 800 nm) and intensities at which there is significan t ionization, leading to a saturation of the harmonic-generation proce ss. Although the ionization rates in the two models differ, the harmon ic spectra and the positions of the cutoff are remarkably similar. Onl y a relatively small number of angular momentum states is needed in th e three-dimensional calculation to give a reliable estimate of the cut off, even for intensities at which there is strong ionization.