Vol 25, No 2 (2017)

The averaged Lagrangian method has been used to derive an analytical solution in the form of planar light bullets for the system of equations describing the second-harmonic generation in a medium with anomalous dispersion. The stability of this solution is confirmed by the simulation for different relations between the nonlinearity, diffraction, and dispersion in the cases of input pulses at both frequencies and at only the fundamental frequency.

The angular dependence of the intensity and contrast of the radiation of laser diodes (LDs) with a CW power of 1.25 W has been investigated in the above-threshold mode. An original method for detecting fundamental lasing is used to analyze the mode structure of the LD radiation at low pump currents. It is shown that this radiation contrast measurement makes it possible to detect the LD degradation in earlier stages than in power measurements.

The coupling of doubly split ring resonators in the GHz range has been experimentally, analytically, and numerically studied in order to design a metamaterial with dominant electrical coupling as a model of nanoscale metamaterials. An example of propagation of GHz electroinductive waves in a metamaterial is demonstrated.

The possibility of applying paratellurite, iodic acid, and lithium iodate crystals in acousto-optics in the THz range has been investigated. The transparency windows of these crystals and their refractive indices in the THz range have been determined. The acousto-optic figures of merit of these materials are calculated for different acousto-optic interaction geometries.

Properties of surface plasmon polariton waves are theoretically studied in structures containing topological insulators with the axion effect. The effect of axion properties on dispersion, localization, and polarization of plasmon polaritons is analyzed. A possibility of determining the axion effect from the variation in the plasmon-polariton polarization is shown, and conditions for enhancement of polarization effects are revealed in waveguide structures of the dielectric−metal−dielectric type.

We describe mechanisms of microwave pulse shortening in radiation sources with the power of about 10⁸ W based on interaction between relativistic electron beams of nanosecond duration and preformed plasma. The shortening is mainly due to the electron return flow through the plasma, which leads to a multiple decrease in the linear gain of the microwave by the relativistic electron beam and in the reflection coefficient of the plasma wave that provides the generator feedback. The ways to eliminate the effect of microwave pulse shortening are proposed.

The problems of magnetic resonance imaging (MRI) of objects having a very wide spectrum of the nuclear magnetic resonance, where signals from all its lines are difficult to detect, have been investigated. It is proposed to carry out MRI using frequency-selective pulses. A method for setting optimally the pulse parameters and the start time of induction signal detection is described. The calculation results are compared with the MRI data obtained for a fluorocarbon compound.

Ultrasonic separation of two immiscible liquids under microgravity conditions has been demonstrated on example of liquid mixtures of FC-70 or FC-72 with silicone oils of 1.5 or 1.0 cSt viscosities, respectively. A 3-MHz focused ultrasound beam was utilized to form an emulsion from these liquid combinations, and a plane wave of the same frequency served to separate (demix) fluids. Droplet deformation under pulsed ultrasound in microgravity conditions is reported, and the observed singular behavior is discussed.

The possibilities of the method for detecting a noise source, estimating its radial velocity and its distance from the receiver, based on the double Fourier transform of the interference pattern formed during motion, have been considered for a single-receiver configuration. It is shown that, as compared to a signal with a uniform spectrum, the limiting values of the input signal-to-noise ratio, at which the noise source can be localized, increase by about half. The results of a computational experiment are presented. A comparative analysis of the noise immunity of the algorithm applied to signals with uniform and noise spectra is performed.