Passive mode locking in masers with non-equidistant spectra.

It is shown that in simplest models the shape of a short pulse traveling in a plasma maser system with a nonequidistant spectrum can be described by the Haus equations with complex coefficients. The quasi-linear interaction between waves and particles is found to be equivalent to a slow saturable absorber in lasers, and the cubic nonlinearity is found to be equivalent to a rapid absorber. Analytic soliton solutions of the generalized Haus equations, which correspond to pulse sequences with a high off-duty factor, are obtained. Regularities of the wave-spectrum drift within the limits of a single pulse are elucidated. The approach considered can be used to describe processes in laboratory plasma cyclotron masers and some types of lasers, and to study the origin of several natural electromagnetic radiation components of the magnetospheres of earth and Jupiter.