Principles of high-contrast energy modulation and microbunching of electron beams

Recent advancements in ultra-short-pulse terawatt IR/visible/UV laser technology have made it possible to consider particle-beam energy modulation schemes in which the practical field amplitudes of the laser and undulator fields in an ultrarelativistic electron bunchʹs average rest frame can attain comparable magnitudes. This parameter regime, well outside the radiation field strengths attainable by conventional free electron lasers, makes possible the exploitation of “relativistic interferometry”, viz., the phenomenon of high-contrast interference, to isolate regions in the longitudinal space of an electron bunch on the order of one laser wavelength. In this paper we review selected requirements on the laser and undulator fields to generate highly efficient microbunching followed by coherent radiation at a substantially reduced wavelength. Conditions on the electron beam quality, as well as selected possibilities for new modes of operation, are summarized.