Fast-wave interactions with an electron film at cyclotron resonance

A thin film of electrons lying upon an emitting surface is established by a relatively weak, normal, steady electric field and a relatively strong, tangential, steady magnetic field. The interactions of this film with an unslowed, normally-polarized electromagnetic wave are investigated theoretically and experimentally for wave frequencies in the region of eB/2¿m. Under appropriate conditions, the wave energy may be increased, decreased, or converted to a steady current. These effects may be considered as interactions of radiation with a bulk medium at a frequency critical to the medium, suggesting millimetre-wave applications not requiring minute cavities or slow-wave structures. Experiments at wavelengths near 8 mm qualitatively confirm many features of the theory.