Off-shell effects in one-photon free-free absorption

Abstract

One-photon free-free absorption amplitudes are derived for electrons scattering from a spinless spherically symmetric target in the dipole approximation. The exact amplitudes are compared to the usual on-shell approximation to the amplitudes. An effect analogous to the Fano effect in bound-free transitions is also found in free-free transitions if off-shell terms are retained in the amplitudes. Methods of detecting the off-shell effects experimentally are discussed.