By calculation of the classical Newton-Lorentz equation and neglecting the
radiation reaction, we find that when an electron is scattered by an intens
e continuous monochromatic laser beam (Q = eE/(m(e)wc) > 0.1 in the interac
tion region), there can be not only momentum transfer but also noticeable e
nergy transfer between the free electrons and the laser beam. This kind of
inelastic effect comes from nonlinear Compton scattering.