20-MW desktop free-electron laser at THz frequencies

We numerically study the generation of periodically bunched electrons from a 6 MeV photocathode electron gun driven by a beat-wave laser with a beat frequency at THz frequencies. We then inject the electrons into a single-pass FEL undulator. Due to the prebunched electrons, the quick build-up of the FEL power can overcome the space-charge debunching force. With nominal beam parameters and an initial bunching factor of 0.2, the FEL can reach nearly 20-MW saturation power at 4 THz in a ~0.5 m distance in the wiggler. The length of this 20MW THz FEL, from the beginning of the electron gun to the end of the undulator, is less than a meter.