Temporal coherent control of two-photon ionization by a sequence of ultrashort laser pulses

We study two-photon ionization of a hydrogen atom by a sequence of two 10-fs laser pulses whose photon energy is slightly lower than the ionization threshold, based on direct solution of the time-dependent Schodinger equation. Although the Rydberg wave packet formed by the first pulse quickly disintegrates before the Kepler time, it can be further ionized by the second pulse when the latter coincides with the return of a fragment of the wave packet. The ionization yield and the peak position can be coherently controlled by the time delay between the two pulses.