Analysis of periodic spectral gaps observed in the tuning range of free-electron lasers with a partial waveguide

Abstract

A phenomenon of “spectral gaps” is observed in far-infrared free-electron lasers using partial waveguiding: the laser power falls down to zero at some particular wavelengths, whatever the beam adjustments are. We show that this effect is related to a periodic increase of the cavity losses, with a period depending on the dimensions of the waveguide. A code including diffraction effects exhibits good agreement with the measurements.