Time-dependent analysis of few-photon coherent control schemes

We investigate the coherent control of nonresonant two-photon excitation and (2 + 1) photon ionization processes from the time-dependent perspective. To this end, we have solved the time-dependent Schrodinger equation for a hydrogen atom interacting with an ultraviolet laser field. Results are obtained for symmetric and antisymmetric phase distributions leading to dark and bright pulses, for which the temporal field distributions consist of many subpulses. For the two-photon excitation process, it is found that at intermediate time between the subpulses, the population in the excited state can exceed the final state population and, in particular, is nonzero for dark pulses. The results for the (2 + 1) photon ionization closely follow those for the excitation process, which shows that the ionization of the electron proceeds as a resonant process via the excited state in all cases considered.