Materials XV Winter School-seminar on microwave electronics and radiophysics

Present research is focused on the dynamics of the perturbation of semiconductor superlattice (SL) reference state near the generation threshold as for the case of influence of titled magnetic field as for the case when the magnetic field is absent. The evolution of the considered perturbation is described with the help of linearized evolution operator. It has been shown that increase of the applied voltage leads to decrease of the attenuation coefficient, which becomes zero in bifurcation point where stationary state loses it’s stability.

Shaping of femtosecond laser pulses of petawatt level with plasma layers is analyzed. It is shown that, for electron density exceeding the critical density by several times, it is possible to generate asymmetrical pulse with the amplitude of the first half­cycle, which is practically equal to the maximal amplitude of the pulse. These pulses are necessary for effective generation of relativistic electron mirrors. Spatial structure of the pulse transmitted through a plasma layer is corresponding qualitatively to the field structure after diffraction of the same initial pulse on a slit.

The non­autonomous generation of chaotic microwave pulses in the wideband chaos oscillators is experimentally investigated. Nonlinearity of a spin­wave transmission line is a cause of chaotic dynamics of the spin­wave chaos oscillator and nonlinearity of a TWT amplifier is a cause of chaotic dynamics of the other chaos oscillator. It is shown, that in both cases, the generation of chaotic microwave pulses is observed when an external pulse­modulated microwave signal has a certain power level and its carrier is detuned from a central frequency of a chaotic signal.

The results of preliminary 3D fully electromagnetic simulation of microwave generator with virtual cathode and external feedback loop (virtode) are discussed in this paper. The feedback is realized by the velocity modulation of electron beam in the accelerating gap of electron gun with the electromagnetic signal taken with output cavity placed in the virtual cathode area.

The simulation results of multi­segment permanent magnet magnetic focusing system for clinotrons in submillimeter range have been presented. The visualization of magnetic field distribution in the gap between the system magnetic poles was done with the help of computer simulations. The simulation results are compared with those obtained experimentally. The magnetic field distribution curves of both single segment and whole multi­segment magnetic system are presented.

The paper describes results of experimental investigations on a formation of bright and dark envelope solitons with pulsed, monochromatic and two­frequency excitation of microwave spin waves in a magnetic film periodic structure – a magnonic crystal. The envelope solitons were excited at particular frequencies in the vicinity of magnonic bandgaps formed due to the Bragg resonance.

The exact dispersion equation of electromagnetic modes propagating in structures that include tangentially magnetized ferrite film with surfaces bordered on media with different permittivity is derived. In the low­wavenumber range the comparison of the theoretical calculation with the experimental measurement of dispersion of magnetostatic surface waves propagating in the layered structures of such  types as dielectric­tangentially magnetized ferrite film of yttrium iron garnet–gadolinium gallium garnet is made.

Classification of electronic oscillators and amplifiers has been performed based on the ratio between directions of the kinetic energy of electrons and electromagnetic energy flows. It is shown that management of electromagnetic flows, such as through the use of natural diffraction spread and with various modifications of Bragg structures, is an effective method to synchronize the radiation of electron beams with transverse size significantly exceeding the wavelength.