Kapitza-Dirac effect and nonresonant nonlinear quantum interaction of laser and electron beams

When crossing an electron beam in vacuum with an optical (laser) beam with standing waves, an interaction was redicted known as Kapitz-Dirac effect where the electrons are diffracted at the nodes of the optical field. After the final success of an experiment was reported (Freimund et al. 2001) confirming this classical kind of laser interaction with free electrons, the generalization of this effect (Schwarz-Hora effect) in the presence of a target or medium in the crossing area of the beams is re-considered as a basic non-resonance nonlinear quantum interaction process. The proof is based on a discovery of Peierls and of repeated later measurements agreeing with a quantum threshold for which the theory was elaborated initially. This is confirmed also in connectnion with the quantum theory of 1/f noise. Other aspects for electron acceleration of electrons by lasers may be interesting up to PeV energy using laser pulses of femtosecond (fs) duration and powers from Petawatt (PW) to Exawatt and Zetawatt.