A comparison of relativistic Cherenkov-FELs, orotrons and undulator FELs as radiation sources in the sub-millimeter region

Undulator free-electron lasers, Cherenkov-FELs and orotrons are compared as coherent radiation sources in the sub-millimeter wavelength range. Electrodynamics and the “beam-field” interaction of the devices are considered. The dependencies of the small-signal gain on the interaction length, radiation frequency and other parameters are analyzed. Using the idea of the optical klystron, the relativistic double-grating orotron (DOR) is introduced. It consists of two short gratings with a flight gap between them and a quasi-optical cavity to form the coherent electromagnetic fields on the gratings. The analysis of the DOR gain shows the possibility to obtain sub-millimeter wavelength generation with a simple relativistic device.