On the theory of “Inversionless” free-electron maser

We develop a linear theory of cyclotron parametric instability in systems that are classical analogs of quantum inversionless lasers. Interaction of bichromatic radiation with an ensemble of classical electron oscillators having a modulated distribution function is considered taking into account that the cyclotron-resonance conditions is valid both for each of the two spectral components at high harmonics and for their beat wave. It is shown that the ballistic restructuring of the modulated fraction of the electrons leads to stabilization of the instability. In this case, a peculiar nonreciprocal regime of the parametric particle-field interaction is realized in which the evolution of the high-frequency wave is independent of the low-frequency mode, though the former wave affects the behavior of the latter one.