Theory of intense-field ionization and above-threshold ionization of helium through multiple resonances

Abstract
We present a quantitative theory of ionization and above-threshold ionization of He by short (subpicosecond), intense laser pulses. The calculations include the effect of bound states shifting through resonance during the pulse as well as the switching of the process from six to seven photons due to the shift of the ionization threshold. The results are in good agreement with and add further insight into recent experimental data.