The process of resonant multiphoton ionization of a hydrogen atom in the gr
ound 1s state is studied by direct numerical integration of the nonstationa
ry Schrodinger equation for a quantum system in an electromagnetic field. T
he dependence of photoionization probability on the radiation intensity is
found to be nonmonotonic. It is established that the minima of ionization c
orrespond to multiphoton resonances between the ground state and one of the
excited (Rydberg) atomic states perturbed by the laser field. it is shown
that ionization is suppressed due to rearrangement of Rydberg states in a s
trong electromagnetic field and is accompanied by efficient Raman Lambda tr
ansitions, which connect a set of closely lying Rydberg states via the cont
inuum. (C) 2000 MAIK "Nauka/lnterperiodica".