Stimulated Raman scattering in hydrogen by ultrashort laser pulse in the keV regime

This letter addresses the problem of stimulated Raman excitation of a hydrogen atom submitted to an ultrashort and intense laser pulse in the keV regime. The pulse central frequency omega of 55 a.u. (about 1.5 keV) is in the weakly relativistic regime, omega <= c/a(0) (c is the speed of light in vacuum and a(0) the Bohr radius) and the pulse duration is tau approximate to 18.85 a.u. (about 456 attoseconds). We solve the corresponding time-dependent Schrodinger equation (TDSE) using a spectral approach, retardation (or nondipole) effects are included up to O(1/c), breaking the conservation of the magnetic quantum number m and forcing the resolution of the TDSE in a three-dimensional space. Due to the laser bandwidth, which is of the order of the ionization potential of hydrogen, stimulated Raman scattering populates nlm excited states (n and l are the principal and azimuthal quantum numbers, respectively). The populations of these excited states are calculated and analyzed in terms of l and m quantum numbers, this showing the contributions of the retardation effects and their relative importance. Copyright (C) EPLA, 2016