Improving KFR Theory by Dressing Atomic Initial States

This paper is devoted to nonperturbative theoretical treatments for the above-thresholdionization (ATI) phenomena. It is shown that the bare atomic initial state approximation in Keldysh-Faisal-Reiss (KFR) theory leads to a fundamental theoretical difficulty and thus, has to be modified by properly dressing the atomic initial state with an. appropriate laser-electron interaction term. The analytical result of the improved S-matrix for general situations is obtained and is applied to hydrogen Is-state with linearly polarized laser of various intensities. The numerical simulations of our applications indicate that the improved theory is not only more reasonable on theoretical aspect, but also closer to experimental measurements.