Perturbative expansions for laser-atom interactions

We analyze the interaction of a one-active electron system with a strong laser field. In order to extract information about the interaction mechanisms, it is important to consider perturbative expansions of the ionization probability amplitude in terms of the Coulomb potential. Based on some of Faddeev ideas, we introduce a new perturbative series that involves both the Coulomb and the Volkov propagators. We show that for photon energies higher than the ionization potential, the series converges rapidly towards the exact result as calculated by solving numerically the time-dependent Schrödinger equation. In the same conditions, the well known strong field approximation series is shown to diverge