Cyclotron interaction of an electron beam with coparallel luminous waves

The interaction of luminous electromagnetic waves with an electon beam propagating along and gyrating about an external magnetic field parallel with the propagation vector has been investigated theoretically. For highly relativistic beam energies, the synchronism condition gives wave frequencies much higher than the electron gyrofrequency. From the linear and nonlinear analysis of the interaction, the following results have been obtained: (a) power transfer to the wave is possible, (b) the gain spectrum is symmetric about the frequency of synchronism, (c) the total beam energy is available for the interaction, (d) efficiencies up to 10% are easy to obtain, with high frequency upshift, (e) higher efficiencies are attainable in a two-stage operation or with a prebunched beam. This interaction appears to be a viable alternative to the free-electron-laser, in particular in the sub-mm wavelength regime.