Abstract
Free-free transitions have been observed in electron-argon scattering in the presence of the radiative field of a CO2 laser. The ratio of the free-free and elastic differential cross sections has been determined at a scattering angle of 160 degrees and electron energies of 5, 11.15 and 16 eV. Good agreement was found with the soft-photon approximation at 11.15 and 16 eV. At 5 eV the correspondence was not as good, possibly indicating the expected failure of this approach towards lower electron energies.