Electron-hydrogen collisions with dressed target and Volkov projectile states in a laser field

Abstract

Cross sections for the 1S-2S and 1S-2P0 transitions in laser-assisted e--H(1S) collisions are calculated in both the multichannel eikonal treatment and the Born wave approximation, as a function of impact energy and laser field intensity. The laser considered is a monotonic, plane-polarized CO2 laser (photon energy=0.117 eV) with the polarization direction parallel to the initial projectile velocity. The first part of this paper confines the laser perturbation to the bound electrons of the atom. A semiclassical Floquet approach is used to dress the hydrogen atom in this soft-photon weak-field regime, and is shown to reveal a concise description of the laser-assisted collision. The Floquet dressing is compared to dressing by the traditional time-dependent perturbation theory, showing that the perturbative approach gives an incomplete description of the laser interaction, and cannot predict the distinct features provided by the Floquet approach. The second part of this paper extends the laser perturbation to the projectile electron, and the familiar Volkov dressed states are used.