Inelastic fast-electron-hydrogen-atom collision in a laser field.

Abstract

The laser-assisted electron-impact excitation of 2s and 2p dressed states of hydrogen is studied. The interaction of a linearly polarized laser field with the colliding system is treated by the nonperturbative Floquet theory, while the interaction of the fast incident electron with the target atom is treated in the first Born approximation. The nonresonant collision in a low-intensity, low-frequency laser field is dominated by the process with no exchanged photon with the field, while at larger intensities the collision accompanied by the exchange of real or virtual photons is much more important. For the stimulated bremsstrahlung, the 1s\ensuremath{\rightarrow}2s transition is strongly influenced by the resonant coupling between the final 2s and the intermediate 3p states. In the resonant cases, where laser frequency matches a transition frequency between the initial or final and an intermediate state, the collisions with the largest cross section are those in which the projectile induces a dipole transition in the atom.