Passive mode locking and formation of dissipative solitons in electron oscillators with a bleaching absorber in the feed
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MOLECULES, OPTICS
Passive Mode Locking and Formation of Dissipative Solitons in Electron Oscillators with a Bleaching Absorber in the Feedback Loop N. S. Ginzburg*, E. R. Kocharovskaya, M. N. Vilkov, and A. S. Sergeev Institute of Applied Physics, Russian Academy of Sciences, ul. Ul’yanova 46, Nizhny Novgorod, 603950 Russia *e-mail: [email protected] Received July 1, 2016
Abstract—The mechanisms of passive mode locking and formation of ultrashort pulses in microwave electron oscillators with a bleaching absorber in the feedback loop have been analyzed. It is shown that in the group synchronism regime in which the translational velocity of particles coincides with the group velocity of the electromagnetic wave, the pulse formation can be described by the equations known in the theory of dissipative solitons. At the same time, the regimes in which the translational velocity of electrons differs from the group velocity and the soliton being formed and moving along the electron beam consecutively (cumulatively) receives energy from various electron fractions are optimal for generating pulses with the maximal peak amplitudes. DOI: 10.1134/S1063776116150085
those in which the translational velocity of electrons differs from the group velocity of a short microwave pulse (soliton) formed. In this case, the microwave pulse slips over the electron beam and cumulatively receives energy from various electron fractions.
1. INTRODUCTION The possibility of formation a periodic sequence of ultrashort pulses with a peak power considerably exceeding the generation power in stationary regimes in microwave electron generators with a bleaching absorber in the feedback loop was demonstrated in [1, 2]. The pulse generation mechanism is analogous to the method of passive mode locking widely used in laser physics [3–5]. At the same time, the interpretation of isolated short pulses generated in such conditions as dissipative solitons is well known in laser physics; such solitons are formed due to the balance between amplification, nonlinear absorption, harmonic generation, and dispersion of group velocities [6–15]. It is well known that dissipative solitons belong to the effects of self-organization in self-oscillatory systems [6, 8, 15]. This study aims at demonstrating that analogous mechanisms can be responsible for the formation of short pulses in electron oscillators. It is shown that actually the pulse generation dynamics is completely described by the equations known in the theory of dissipative solitons in the particular case when the translational velocity of particles coincides with the group velocity of the electromagnetic wave (group synchronism regime). At the same time, the specific features of the electron–wave interaction associated with motion of the active medium (electron beam) are important for applications. It was found that the optimal regimes for generating pulses with the maximal peak powers are
2. MODEL OF ELECTRON OSCILLATOR WITH A HIGH-Q CAVITY AND SATURATING ABSORBER To demonstrate analogy with optica
