Model calculations for an atom interacting with an intense, time-dependent electric field

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Abstract
We have performed a set of numerical calculations of the one-dimensional, time-dependent Schrödinger equation in order to study the interaction of an intense, electromagnetic field with a model atom. We approximate the atom by a local, square-well potential and the electromagnetic wave by an oscillating electric field. We investigate the multiphoton-absorption process that leads to the ‘‘above-threshold’’ ionization (ATI) phenomenon. We not only examine the ionization probability and electron-energy distributions within the field but also the effects of spatial and temporal boundaries that represent the finite dimensions of a laser pulse. We observe all the main features of the ATI behavior from the shifting of the peaks to their disappearance. In addition, we find differences in the positions of the peaks according to how the electron exits the field region. We also explore resonant ionization as well as Volkov wave packets and the recombination process.