Cerenkov Free-Electron Laser: A Critical Review and Progress Report

摘要

Presented is a summary of the basic scaling relations which apply to Cerenkov free-electron laser operation, together with a description of a 100 micrometer wavelength experiment currently in progress. A Cerenkov free-electron laser (C-FEL) consists of a thin, dielectric-film-loaded waveguide resonator and an electron beam with a suitable kinetic energy. When the beam moves parallel to the surface of the dielectric at a velocity greater than the light speed in the film material, it emits both spontaneous and stimulated Cerenkov radiation. When mirrors of sufficient reflectivity are added to the film-guide structure, the stimulated radiation process is unstable. Current modulation on the beam will grow as the beam traverses the resonator. The bunching occurs in the retarding phase of the axial component of the electric field stored in the resonator, and continues to grow until the modulation index approaches unity. At this point beam electron orbits, viewed from a frame moving with the phase velocity of the wave, no longer progress past wave crests. The film-guide structure supports a TM mode which is evanescent in the direction perpendicular to the guide surface. Thus as the desired operating wavelength is decreased, an invariant overlap of the beam's transverse profile and the resonator mode can be maintained, provided that the beam energy is increased. Reprints.