Low loss quasioptical cavity for a two-stage free electron laser (fel). Technical report

A quasioptical cavity consisting of a cylindrical, metallic, overmoded, TE sub 01 waveguide between two spherical end mirrors will be used to contain long-wavelength (approx. 1 mm) pump radiation in a two-stage free electron laser. The major loss mechanism is found to be mode conversion. Two different modified cavities are shown to suffer negligible mode conversion, and two more possible approaches, with low mode conversion and additional advantages, are discussed.