Kroll-Watson low-frequency approximation revisited

In this paper we discuss the low-frequency approximation and the role of th e off-shell effects in the laser-assisted potential scattering of electrons and illustrate this with the scattering by the three-dimensional square we ll potential. It appears that the off-shell effects are the manifestation o f the diffractive character of small-angle laser-assisted electron-atom sca ttering, which is likely to be responsible for the observed discrepancy bet ween the results of the Wallbank and Holmes experiment [1] and the Kroll-Wa tson theory [2].