Above-threshold-ionization spectra from the core region of a time-dependent wave packet: An ab initio time-dependent approach

We present a method for accurate and efficient treatment of the time-dependent Schrodinger equation and electron energy and angular distributions after above-threshold multiphoton ionization. The procedure does not require propagation of the wave packet at large distances, making use of the wave function in the core region. It is based on the extension of the Kramers-Henneberger picture of the ionization process while the final expressions involve the wave function in the laboratory frame only. The approach is illustrated by a case study of above-threshold ionization of the hydrogen atom subject to intense laser pulses. The ejected electron energy and angle distributions have been calculated and analyzed. We explore the electron spectrum dependence on the duration of the laser pulse and carrier-envelope phase.