Free-electron maser oscillator experiment in the UHF regime

A nonrelativistic electron beam (< 4 keV) travels in this experiment in a non-dispersive waveguide along a planar undulator and an axial magnetic fields. The electron beam has a Gaussian pulse shape with a 1 ms pulse width. Two distinct radiation bursts are observed during the electron energy sweep. Each burst contains a different range of microwave frequencies. One burst corresponds to the FEM interaction, at ∼ 0.8 GHz. The other burst corresponds to the cyclotron resonance interaction, at ∼ 5 GHz. This experiment demonstrates an FEM operation in an extremely long wavelength (37.5 cm) in the UHF regime.