The stimulated Cerenkov interaction and its applications

Reviewed are the results of two experiments in which momentum modulation of a relativistic electron beam by laser fields using the stimulated Cerenkov interaction was measured, and coherent Cerenkov radiation from the optically bunched electron beam was observed. In the first experiment, light at 1.06 μm from a 30 MW Nd:YAG laser intersected 102 MeV electrons at an angle of 18 mrad in hydrogen gas, which was used as the phase-matching medium. The change in the electron-beam energy spectrum in the presence of the laser was measured, together with its functional dependence on the index of refraction of the phase-matching medium. In the second experiment, the same laser intersected 55.9 MeV electrons at an angle of 17 mrad, again in hydrogen gas. Coherent Cerenkov radiation at the second harmonic of the laser frequency (0.532 μm) was measured and indicated that the electrons were bunched on the order of the laser wavelength as a result of being velocity modulated by the laser. Applications of these results, such as development of optical klystrons and laser-driven particle accelerators, are considered. The characteristics of these devices and possible design configurations are discussed.