  Based on strong-field QED in the Furry picture we use the Dirac-Volkov
propagator to derive a compact expression for the differential emission
probability of the two-photon Compton process in a pulsed intense laser field.
The relation of real and virtual intermediate states is discussed, and the
natural regularization of the on-shell contributions due to the finite laser
pulse is highlighted. The inclusive two-photon spectrum is two orders of
magnitude stronger than expected from a perturbative estimate.
