Dissipative solitons in electron oscillators with a saturable absorber

Abstract

We analyze the mechanisms of passive mode locking and ultrashort pulse generation in microwave electron oscillators with a bleaching absorber in the feedback loop. It is shown that in the group synchronism regime, where the translational velocity of particles coincides with the group velocity of an electromagnetic wave, the formation of pulses obeys the equations known in the theory of a dissipative soliton which is widely used for the description of the femtosecond pulse formation in laser physics. At the same time, in electron oscillators, for the formation of pulses with the maximum amplitude, beneficial conditions in which the translational velocity of the particles is different from the group velocity of the wave and the generated soliton moving along the electron beam consecutively (cumulatively) extracts energy from various electron fractions are required. In this case, the soliton can be generated in both hard and soft excitation modes. It is shown that nonlinear absorption can be provided in the additional unit installed in the feedback loop, in which an independent electron beam interacts with the radiation under the Kompfner dip conditions.