Laser-assisted inelastic electron-atom collisions

We study the inelastic scattering, accompanied by the transfer of L photons, of fast electrons by hydrogen and helium atoms in the presence of a laser field. A detailed analysis is made of the excitation of the n=2 and n=3 states of atomic hydrogen, and of the 1 ${}_{}{}^1{}_{}{}^{}$S–$2^1$S and 1 ${}_{}{}^1{}_{}{}^{}$S–2 ${}_{}{}^1{}_{}{}^{}$P transitions in helium. It is shown that the ‘‘dressing’’ effect due to the dipole distortion of the target by the laser field produces important modifications of the cross sections at small momentum transfers for S-S and S-D transitions. However, this dressing effect is reduced in the case of S-P transitions. Our results exhibit qualitative differences from the case of laser-assisted elastic collisions; this is mainly due to the possibility of intermediate resonances in the laser-atom interaction during the collision event.