The process of
multiphoton ionization (MPI) of atomic and molecular
species has been a subject of intensive experimental
and theoretical
studies in recent years. Advancement in high-power short-pulse laser
techniques has been driven rapid progress in this field. Theoretical
description of
ionization process occuring in laser fields has been
developed. In this paper, computational procedure in quantum formalism
to treat MPI process of atomic targets in strong laser fields is
outlined. MPI process treat nonperturbatively as a decay phenomenon by
solving a coupled set of the Lippmann-Schwinger integral equation. A
complete set of field-free atomic states use As a building block of the
theory. This approach enable to provide both the total and differential
cross-sections of MPI of atoms with one or two electrons. For
application, the proposed procedure apply to a simple model of
multiphoton ionization from a square well potential and to hydrogen
atom.