Study on an unmagnetized plasma-loaded two-stage backward wave oscillator and free electron laser

A free-electron laser pumped by electromagnetic wave (EM-FEL) is a type of laser that uses a high-power electromagnetic wave as a wiggler to generate short wavelength radiation. It has potential to produce higher frequency radiation with low energy electron beams than a free-electron laser with a magnetostatic wiggler. Y. Carmel et al. (1983) and G. G. Denisov et al. (1984), observed the EM-FEL radiation at millimeter wavebands with a relativistic backward-wave oscillator (RBWO) at 3 cm as the electromagnetic wiggler. Z. Liang (1995) reported the results of an electromagnetically pumped FEL with a separated FEL interaction region from the RBWO. A plasma-filled RBWO with a strong guiding magnetic field enhances the peak power over the vacuum case by a factor of up to 8, and the peak power of an EM-FEL with a frequency from 12 GHz to 26 GHz was measured in the experiment simultaneously. In this paper, we report the experimental and simulation results of an unmagnetized plasma-loaded BWO and free-electron laser.