Guiding and superradiance effects in ensembles of electrons-oscillators

The induced emission of localized ensembles of electrons-oscillators in the free space has been studied. It has been found that the guiding effects take place during propagation of wave beams along the electron beams that play the role of open active waveguides. In the linear stage of the interaction the quasisurface modes are generated, and in the nonlinear stage, the wave beam broadens and the electromagnetic energy is emitted into the outer space. There occurs stochastic retardation of particles interacting with the ensemble of electromagnetic waves which propagate at various angles to the system axis, and this can increase the efficiency of the system as compared to the closed waveguides. The effects of superradiance have been found in the bunches of electrons-oscillators that form moving active resonators. The development of thresholdless instabilities leads to bunching of electrons and their coherent emission. This emission is quasimonochromatic in the intrinsic frame of reference and a multifrequency one in the laboratory frame. If the translational velocity of a bunch is close to the velocity of light, then the radiant power is concentrated predominantly in the short-wave component.