Strong field approximation and its modifications as evolution equations

Abstract

We describe an approach based on the view of the well-known strong-field approximation (SFA) as an evolution equation. From this point of view the SFA is a nonhomogeneous evolution equation with the inhomogeneous term which determines the departure of the approximate evolution driven by the SFA from the evolution driven by the exact ab initio time-dependent Schrödinger equation (TDSE). A modification of this nonhomogeneous evolution equation making the inhomogeneous term smaller produces results for the photoelectron spectra which agree quantitatively well with the TDSE results for a system with the Coulomb interaction (we use hydrogen as an example).