Propagation effect in atom excitation by ultrashort and intense laser pulses

We study hydrogenlike target excitation by a traveling electromagnetic pulse. The spatial size of the pulse l=cτ (c is the speed of light and τ is the pulse duration) is assumed to be comparable or less than the characteristic size of the initially occupied atomic state. When propagating through the atom, the pulse is shown to transform the electron wave function “slice by slice.” These transformations lead to electron transitions between states with Δm=±1 which are forbidden in the dipole approximation. The case of linear polarization is considered. It is found that magnetic-level excitation probabilities are small for the hydrogen atom, but can be more significant for the hydrogenlike multicharged ions.