Ponderomotive forces and stimulated Compton scattering of free electrons in a laser field

The relationship between ponderomotive forces and stimulated Compton scattering is investigated. It is shown that an electron interacting with a coherent classical light field experiences an action of both ponderomotive forces and forces arising from the stimulated Compton scattering. Both of these forces are shown to be expressed in terms of a single function interpreted as the ponderomotive potential. Ponderomotive forces are shown to exist only if both electron and light states have at least some degree of coherence they disappear if either the electron wave function is a pure plane wave or the field state is a pure quantum-electrodynamical state with definite numbers of photons (a pure Fock state). Stimulated Compton scattering is shown to depend also on the degree of coherence of the light field and of the free-electron wave function. Specific calculations are carried out for the plane-focused stationary Gaussian beam and for the stationary evanescent wave. Critical fields are found at which ponderomotive forces and forces arising due to the stimulated Compton scattering become of the same order of magnitude.