Time delay in strong-field photoionization of a hydrogen atom

We study time delay for the process of photoionization of a hydrogen atom in a strong electromagnetic field. We compute this quantity by solving the time-dependent Schrodinger equation. We show that even a moderately strong field can have quite a considerable effect on the time delay. Analysis of the wave-packet motion performed by means of the Gabor transform shows that a simple semiclassical model can explain this phenomenon.