Stimulated electromagnetic-wave scattering by a relativistic electron beam in a refracting medium

A theoretical study shows that it is possible to obtain high-frequency coherent radiation by the interaction of a relativistic beam with a lower-frequency electromagnetic wave propagating along the beam and having a phase velocity that is less than the beam velocity. Both the scattered high-frequency field and the original lower-frequency wave are amplified during this interaction. It was also found possible to produce conditions under which the amplitude of the original wave increases rapidly due to the linear instability arising during the interaction with the beam; this results in a significant increment of the scattered-wave amplitude. This process leads to a reduction in the characteristic size of the region in which beam energy is converted into field energy, and makes possible a reduction in the initial power of the original wave.