Radiophysics and Quantum Electronics最新文献

We consider the features of modeling the interaction of electromagnetic waves in the microwave range with nanosized conducting structures, which allow one to theoretically study the dynamics of the development of electrodynamic and thermal phenomena leading to a burn-through of thin films.

We study the polarization characteristics of weather phenomena. An algorithm for estimating the covariance matrix of scattering of volumetrically distributed meteorological objects using an ensemble of Keno matrices is described. Invariants of the covariance matrix of scattering and Keno pre-matrix are analyzed. An algorithm for full polarization scanning by an unpolarized sequence of radio waves is described. Simulation results of differential reflectivity and linear and circular depolarization ratio of rain, downpour, and hail are presented.

We study a selective coaxial launder of an oversized cavity operating at the eigenmode of two higher asymmetric, spatially developed coupled modes in the context of the radiation input into a millimeter-wavelength gyroklystron. The external coaxial cavity is coupled with the internal oversized cavity and microwave sources via azimuthally periodic systems of rectangular holes in both side walls. The relation between the parameters of the coaxial launcher, which ensures the maximum transformation of the feeding-waveguide mode into the eigenmode of the internal cavity, has been found. The fundamental mode TE₁₀ of the rectangular waveguide is transformed into the eigenoscillation of the coupled TE₁₂₂₁ and TE₆₄₁ modes, which rotates azimuthally, with an efficiency of 0.6 in the absence of ohmic losses.

We have formulated a mathematical model for a nonlinear photoacoustic (PA) response of two-layer samples. The features of second-harmonic (SH) generation of a nonlinear PA signal by these samples are studied in detail. Simple expressions for the amplitude of this signal, which describe its dependence on the modulation frequency of the incident beam, as well as on the thermal coefficients of thermophysical parameters and emissivity of the samples, are obtained for the most interesting cases. It was found that only for the case where the first layer is highly absorbing and both layers are thermally thick the frequency dependence of the SH amplitude of the PA signal has the form ω^−5/2 and is described by the function ω^−3/2 in all other cases. Only for nontransparent layers does the thermal coefficient of emissivity of the corresponding layer contribute to the amplitude of this signal.

We present the results of experimental and theoretical studies on the effect of a strong pump wave on a weak probe wave in an acoustic rod resonator (with rigid and soft boundaries) made of annealed polycrystalline copper. The measurements were carried out with simultaneous excitation of the resonator in its first and fourth longitudinal modes. An analytical description of nonlinear effects (changes in the amplitude and frequency of resonant oscillations for a weak wave under the influence of a strong one) is developed within the framework of the hysteretic equation of state for a polycrystalline solid with saturation of amplitude-dependent internal friction. By comparing the experimental and analytical amplitude dependences of the nonlinear effects, we determined the parameters of the hysteresis nonlinearity of annealed copper for various combinations of strong and weak wave frequencies corresponding to the first and fourth resonator modes.

We examine the features of second-harmonic generation (eo–e and oe–o phase matching) and third-harmonic generation (oo–e phase matching) by laser pulses with opposite frequency chirps in the saturation regime, based on numerical simulations. The influence of the material dispersion of the crystal, spectral phase mismatch, and spatial drift on the conversion efficiency and the preservation of the pulse shape at the sum frequency is investigated.

We study resonance scattering of an extraordinary plane electromagnetic wave by a cylindrical magnetic-field-aligned decreased-density irregularity located in a background magnetoplasma. The emphasis is placed on the influence of smoothing the boundary of such an irregularity on the characteristics of its surface and volume plasmon resonances in comparison with the case of a stepwise plasma density profile. The frequency dependences of the amplitude coefficients of the electromagnetic field and the effective scattering and absorption cross sections (per unit length of the cylindrical irregularity) are obtained for different values of the width of the nonuniform region and its radius. A qualitative change in the behavior of the scattering and absorption cross sections is demonstrated, which is caused by energy dissipation at the upper hybrid resonance of the weakly collisional plasma inside the cylindrical irregularity with a monotonic profile of the plasma density, as compared to the case of a similar sharp-walled irregularity.

We present the results of numerical modeling of the interaction of a fraction of heavy charged particles, immersed in a gravitational field and an external uniform electric field, with a weakly conducting charged ascending convective flow within the framework of the approach proposed in (Davydenko et al. in Radiophys. Quantum Electron. 67:423–430, 2024). The features of the instability developing in the system and the characteristics of the emerging small-scale variations of the electric field depending on the parameters of heavy particles are studied. It is shown that the instability growth rate decreases with increasing radius of particles and decreasing absolute value of their charge.

We study the surface photogalvanic effect in a degenerate collisionless electron gas. The surface direct current induced by electromagnetic radiation and flowing along a rigid smooth boundary is calculated for a two-dimensional gas in a semi-infinite quantum well and a three-dimensional gas in a semi-infinite metal slab. The calculations employ two microscopic approaches, namely, the single-particle Schrödinger equation and the Boltzmann kinetic equation. Both approaches yield identical nonzero values of the net surface (edge) current under elliptically polarized radiation. For a linearly polarized wave, the total surface current is zero, marking a key distinction from cases where electron scattering processes are significant. Spatial profiles of the direct current are calculated, revealing that its density decreases as a power law with distance from the edge of the half-plane or semi-infinite slab containing the gas. The exponent varies with the dimensionality of the system and differs between the two approaches. Additionally, the current density exhibits spatial oscillations with a period given by the product of the Fermi velocity and the oscillation period of the radiation field.

We discuss features of the fine structure of the cyclotron radiation spectrum produced by the plasma of an electron cyclotron resonance (ECR) discharge in a wide range of experimental parameters. In a nonequilibrium plasma, a cyclotron instability develops, which leads to the generation of electromagnetic emission bursts in the whistler frequency range. Simultaneously with the generation of whistler waves, low-frequency oscillations were discovered for the first time, which modify the spectrum of high-frequency waves. It is shown that in the presence of low-frequency oscillations, the frequency and amplitude of high-frequency whistler waves are modulated at the frequency of the low-frequency wave. The formation of a broadband spectrum of whistlers with many sidebands in the Fourier spectrum is determined by the nonlinear interaction of high-frequency electromagnetic oscillations with low-frequency plasma waves in the lower hybrid frequency range.