Effects of laser polarization in laser-assisted electron-helium inelastic collisions: a Sturmian approach

The influence of linearly and circularly polarized laser fields on the dyna mics of fast electron-impact excitation in atomic helium is discussed. A de tailed analysis is made in the excitation of 2(1)S, 3(1)S and 3(1)D dressed states of helium target. By using a semiperturbative treatment with the St urmian basis expansion, we take into account the target atom distortion ind uced by a laser field. Important differences appear between the angular dis tributions depending on the different states of polarization, in particular the circular polarization presents an experimental interest. We give new f eatures (intermediate resonances) for both polarizations, concerning the n = 2 states of helium for emission and the n = 3 for the absorption, in term s of laser frequency. Qualitative differences from the case of laser-assist ed elastic collisions have been found.