Том 25, № 1 (2017)

Six absorption bands of Tm³⁺:Sc₂SiO₅ crystal have been investigated by decomposing each absorption band into a series of Lorentzian peaks. Polarized light of two polarizations was transmitted in three perpendicular directions through a crystal shaped as a parallelepiped with polished faces. The results are presented in the form of tables containing the parameters of the found Lorentzian peaks: central wavelength, width, and height.

A particular analytical solution to the nonintegrable problem of plane electromagnetic wave propagation through an isotropic gyrotropic nonlinear medium is found in the form of elliptically polarized breather. The intensity ratio for the circularly polarized components of this wave, which remains constant during propagation, can be used to determine the ratio of local and nonlocal nonlinear susceptibilities describing the Kerr nonlinearity and its spatial dispersion.

The energy spectrum of a new-type quantumwell composed of gapless graphenes with identical work functions and different Fermi velocities is investigated. Symmetric and asymmetric quantum wells are considered. In a symmetric well, there is always at least one bound state. In an asymmetric well, a bound state appears, beginning at a certain finite momentum. A possibility of appearance of boundary states is investigated.

Using the linear approximation, we consider beam instabilities like a collective and a singleparticle stimulated Cherenkov effect developing in a longitudinally bounded electrodynamic system near its nontransparency band, i.e., when the electromagnetic wave excited by the beam has a zero group velocity. A dispersion equation is obtained which determines instability development increments with allowance for the exit of the radiation from the electrodynamic system. Solutions to the dispersion equation for various parameters of the electron beam and the electrodynamic system are investigated.

A plasma maser that does not use a strong magnetic field for transporting a relativistic highcurrent electron flow is calculated within the particle-in-cell model. Tuning of the average radiation frequency from 3 to 7GHz with a single pulse spectrum width of 2 to 3GHz is demonstrated. The power of a radiation pulse with a duration up to 70 ns is from 0.5 to 0.7GW at the efficiency of 4 to 6%.

The plasma relativistic generator (PRG) at the Sinus 550-80 accelerator has a number of unique properties, such as the single- and multiple-pulse (up to 50 pulses per second) generation modes, generation of microwave pulses with a duration of up to 80 ns and frequencies of 2 to 25GHz, and generation of monochromatic and wide-spectrum radiation. The carrier frequency and the spectrum width can be controlled by varying the experimental parameters, e.g., the plasma density. To investigate the PRG operation modes, appropriate devices for detection of the PRG microwave radiation are needed. In this work, numerical models of antennas with different geometrical parameters are developed using the Ansoft HFSS 13.0 CAD and an antenna with the optimum parameters is proposed for measuring microwave radiation spectra in the desired frequency range at a power level of 50 to 100MW.

The previously proposed method for selecting groups of single-type wave fieldmodes in oceanic waveguides, based on a double Fourier transform of the interference pattern formed by a moving sound source, is theoretically substantiated. This procedure, which is possible due to the invariance of the frequency shift of field maxima with respect to the numbers of interfering single-type modes, leads to spectral density localization. The sizes of acceptable localization domain and spectral density distribution are estimated. The results of a natural experiment on application of this procedure to problems of detection of a sound source and estimation of its radial velocity and distance from receiver are reported.

The motion of long surface waves above a sloping bottom has been calculated within the shallow-water approximation. It is shown that, if the linear solution is known, the nonlinear corrections, up to the eighth order, can be expressed in terms of the derivatives of the functions determining the linear solution. An analytical solution for the free-surface elevation in the near-shore area is constructed.