Electron-atomic-hydrogen elastic exchange collisions in the presence of a laser field

A theoretical study is made of elastic exchange collisions of fast electrons with atomic hydrogen in the presence of a laser. The ratios between exchange and direct differential cross sections in the field-assisted and the field-free cases are compared, using (i) laser-dressed atomic wavefunctions, accounting for the dipole moment induced by the field on the hydrogen ground state; (ii) the eikonal-Born series approximation for the direct scattering amplitude; (iii) a second-order treatment in the electron-electron interaction for the exchange amplitude. It is found that the laser greatly modifies the process, introducing a strong asymmetry between the absorption and emission of photons. (author)