A free-electron laser (FEL) oscillator experiment operating with a low-energy, low current (< 4 keV, < 0.5 A) pulsed electron beam is presented in this paper. In the table-top FEL oscillator constructed in our laboratory, the electrons travel along a planar undulator ((lambda) w equals 2 cm) and an axial magnetic field, and interact with TEM-mode electromagnetic waves. The FEL output signal is observed at approximately 40 cm wavelength in the UHF regime.
"Extremely long wavelength free-electron laser experiment", Proc. SPIE 2557, Intense Microwave Pulses III, (8 September 1995); doi: 10.1117/12.218560; https://doi.org/10.1117/12.218560