Cherenkov free-electron laser

Cherenkov radiation, produced by mild to moderately relativistic electron beams as they traverse dielectric-loaded surface-wave resonators, can be used as the basis of a free-electron laser. Devices of this kind have now been operated at wavelengths ranging from the cm to the far-infrared region of the spectrum. Recent work is summarized. Three different accelerator types and a range of operating voltages have been employed. Pulse-line accelerators (PLA) and pulse transformers (PT) have been used in the mm-sub mm regime. At shorter wavelengths, compact radio-frequency accelerators can be employed. This summary reviews a 5 MandV microtron accelerator-driven experiment. The electron beam consists of a train of 25-ps-long micropulses spaced at the period of the 3-Ghz accelerating field and the resonator consists of a pair of opposing trough guides. One of the trough surfaces is coated with a thin polyethylene film. The film thickness, together with the beam energy determine the operating wavelength. In the present experiment, a 2-micrometer film and the 5-MeV beam give a design wavelength of 100 micrometers.