Bulletin of the Russian Academy of Sciences: Physics最新文献

The authors discuss results from studying the effect 2D processes have on the bunching of electrons in high-power single-beam relativistic klystrons. Data are presented on the maximum achievable efficiency of such devices. Results are presented from a numerical analysis of the structure and magnitude of wake fields of relativistic electron bunches as a function of the degree of compression of bunches and the energy of electrons.

A brief analysis is performed of theoretical constructions related to studying the formation of two-color parametric solitons in the mode of second harmonic generation. Spatial, temporal, and spatiotemporal two-color solitons of different types are considered, including bright, dark, and bright–dark wave objects.

The quasi-energy of Dirac electrons in the electromagnetic field of bichromatic radiation is calculated using the Floquet formalism. The possibility of the law of charge carrier dispersion being altered by its interaction with a wave of a high-frequency electric field is demonstrated. The existence of the second harmonic ensures anisotropy of the modified law of dispersion in the momentum space.

It was demonstrated that oscillations in the dependence of the acoustic radiation force on the distance between a focusing piezoelectric source and a spherical scatterer can be reduced by adding a layered structure consisting of plane-parallel acrylic glass plates to the space between the transducer and the scatterer. It was experimentally confirmed that the formation of standing waves, which cause oscillations, is minimized by absorbing and scattering acoustic waves reflected from the source. The ability to control the oscillation level by varying the number of plates was shown. The theoretically calculated radiation force levels in the presence of the layered structure agree with those measured.

Results are presented from numerical parametric calculations based on a finite-difference solution of two-dimensional Navier–Stokes equations for a viscous incompressible fluid in a closed square region heated from the side. Gravitational convection is modeled for a wide range of defining dimensionless parameters: Grashof number (0 < {text{Gr}} < {{10}^{8}}), Prandtl number ({text{1}}{{{text{0}}}^{{ - 2}}} < {text{Pr}} < {{10}^{2}}), concentrational Grashof number (0 < {text{G}}{{{text{r}}}_{{text{C}}}} < {{10}^{8}}), and Schmidt number ({text{1}}{{{text{0}}}^{{ - 2}}} < {text{Sc}} < {{10}^{2}}). Results from modeling show the nonmonotonic nature of the dependence of the vertical stratification in temperature and concentration on the Grashof numbers, along with dynamics of the formation of steady-state oscillatory convective flows of a viscous liquid. For intense laminar convection, there is a narrow range of Grashof numbers that depends non-linearly on the Prandtl number. In this range, the steady convective flow has an ordered oscillatory periodic pattern caused by metastable changes in the stable state of secondary macro-vortices on the heated and cooled boundaries, and their subsequent movement along the closed boundary layer. When the Grashof numbers are raised even more, the periodic convective flow regime becomes a chaotic oscillatory and then turbulent regime.

We demonstrate the application of a custom-built polarization holographic microscope (PHM) for comprehensive characterization of laser-fabricated and self-assembled optical elements. We investigate two distinct material platforms: silver-doped zinc oxide (ZnO:Ag) sol–gel films structured by femtosecond direct laser writing, and self-assembled torons, namely soft topological solitons, in chiral nematic liquid crystals (LCs). The PHM enables single-shot, multi-wavelength (450, 532, 660 nm) reconstruction of the full Jones matrix, providing complete amplitude, phase, and polarization information. For ZnO:Ag films, we show that laser writing induces programmable dichroism and birefringence, characterized by a spectrally dependent phase shift (e.g., +π/4 at 450 nm and –π/8 at 660 nm between orthogonal Jones matrix components), establishing a foundation for all-dielectric metasurfaces. For torons, PHM analysis of torons in 25 µm LC cells reveals complex ring structure of the corresponding phase and light intensity distributions and confirms the robustness of their optical functions (e.g., vortex generation) across the visible spectrum.

Silicon nanoparticles decorated with small gold (Au) inclusions are of potential interest as agents for efficient photothermal conversion in tumor hyperthermia applications. In this work, we present the technology for synthesizing a suspension of composite silicon–gold (Si/Au) nanoparticles with a core-satellite type morphology. They are quasi-spherical with the mean diameter of up to 75 nm and relative size dispersion not exceeding 32%, while the decorating Au inclusions range in size of 5–15 nm. Fabrication is implemented through a dual-stage laser ablation technique employing a porous silicon target, ethanol (first stage) and a water-ethanol solution with chloroauric acid HAuCl₄ (second stage) as buffer media. The fabricated composite Si/Au nanoparticles possess a high degree of crystallinity and exhibit moderate colloidal stability in water.

We presented a novel, maskless approach for fabricating copper electrodes on flexible polyimide substrates using direct laser metallization (DLM) from deep eutectic solvents (DES). The DLM process utilizes localized thermochemical reactions driven by a picosecond pulsed laser to convert DES precursors into conductive copper structures with precise patterning. Key parameters such as laser power density, scanning speed, and DES layer thickness were optimized to achieve uniform copper lines with excellent electrical conductivity and mechanical flexibility. The fabricated electrodes demonstrated remarkable stability under bending tests, showing less than 5% variation in resistance, which confirms their suitability for flexible pressure and strain sensor applications in wearable electronics and human–machine interfaces. This is the first demonstration of copper structures produced on polyimide via DES-based DLM with proven functional performance, highlighting its potential as a scalable, cost-effective method for next-generation flexible electronic device manufacturing.

The prospects for studying photoswitching of amphiphilic spiropyrans using IR spectroscopy have been demonstrated. The comparison of analytical capability of the method in studying the photochromism of spirocompounds in the liquid phase and in the solid state using an attenuated total reflection sensor has been carried out. It has been shown that infrared spectroscopy allows to analyze the structural characteristics of photosensitive molecules in various isomeric forms, as well as to obtain information about their conformation and intermolecular interactions.

The advancement of integrated nanophotonics requires the development and characterization of materials with high refractive indices and low optical losses. Van der Waals (vdW) materials, particularly transition metal dichalcogenides (TMDs) such as WSe₂ and MoSe₂, exhibit giant optical anisotropy and high refractive indices (n > 4) in the near-infrared range, making them promising candidates for next-generation photonic circuits. However, accurately determining their anisotropic optical constants, especially the out-of-plane component, is challenging due to the limited size of exfoliated flakes and the limitations of far-field techniques. This study details the application of scattering-type scanning near-field optical microscopy (s‑SNOM) for the nanoscale characterization of these materials. The principles of s-SNOM, including the excitation and detection of waveguide modes in planar vdW structures, are discussed. By analyzing the interference fringes generated by propagating modes, the effective mode index is determined. We demonstrate this methodology using WSe₂ and MoSe₂ flakes, where the experimental effective indices are compared with theoretical models. This comparison confirms the necessity of accounting for giant optical anisotropy and validates the out-of-plane dielectric constants, illustrating the efficacy of s-SNOM for the comprehensive optical characterization of vdW materials.