Theory of atomic excitation and ionization by ultrashort laser pulses

An alternative momentum-space representation (‘‘impulse representation’’) well adapted to the evaluation of converged nonperturbative solutions of the nonrelativistic time-dependent Schrödinger equation for atoms subject to intense, ultrashort laser pulses is described. Exact expressions for survival, excitation, and ionization probabilities and photoelectron energy spectra are presented for the case of a hydrogen atom struck by a δ-function pulse. A method for the extension of such calculations to realistic ultrashort pulses is described, based on a Sturmian basis expansion of the time-dependent Schrödinger wave function.