Issue 4, 2025

Investigation of the features of Bose-Einstein condensation of unitary polaritons in crystalline and photonic-crystalline media

V. V. Volkova, D. A. Gavrilovets, A. D. Kotova, M. A. Kulagina, V. V. Filatov

Unitary (transparently associated, transparent) polaritons are quanta of the electromagnetic field in matter for which interaction with the phonon subsystem leads to an effective refractive index equal to unity ("unitary", hence the name). The material medium for such light quanta is optically identical to a vacuum, which makes transparent polaritons extremely interesting both for controlled illumination of optical media and for modeling nonlinear vacuum optical processes in matter (such as, for example, γ→a). In this paper, the possibilities of condensation of transparently associated polaritons in periodic material media (crystalline and photonic crystalline) are investigated and the characteristic features for crystalline and photonic crystalline cases are clarified. It has been established that condensation of transparently associated polaritons in the visible region of the spectrum is impossible in ordinary (non-photonic) crystals, however, in photonic crystals, on the contrary, it can be realized at any required wavelength. The results obtained are interesting for obtaining tunable coherent optical generation based on the parametric optical process γγ → a(φ',φ")→γ'y', in which an intermediate (axion-like) bipolariton a is synthesized and destroyed, and the frequency of useful radiation γ'"is tuned" by auxiliary phonons φ' and φ".

Development of an algorithm for constructing a wheel profile and detecting surface defects during wheel-rail interaction

K. G. Arinushkina$^{1,3}$, P. I. Tsomaev$^{2,3}$, V. V. Davydov$^{1,2}$, I. Yu. Saveliev$^3$

The global growth of rail transportation contributes to economic development, but at the same time increases the safety requirements for rolling stock. Wheelset defects, which are the cause of most accidents, remain a key risk factor. To detect them in a timely manner, a comprehensive analysis of the wheel surface is required, including image collection, restoration of damaged areas and accurate measurement of geometric parameters. Optical systems are used for timely detection of defects, which allow for real-time monitoring of the surface. However, the effectiveness of such systems largely depends on the algorithms used to calculate and evaluate the parameters. The presented paper considers the relevance of developing an improved data processing algorithm for monitoring the main parameters of the wheels in order to improve the accuracy of diagnosing rolling surface defects.

Laser spectroscopy of ZnS nanoparticles during their synthesis in reverse microemulsions

R. R. Volkov$^1$, I. V. Plastinin$^2$

In this study, the methods of Raman spectroscopy, dynamic light scattering (DLS) and absorption spectroscopy in the ultraviolet region were used to study reverse microemulsions in which the reaction of synthesis of ZnS nanoparticles was carried out. According to the DLS data, the size of reverse micelles in the microemulsions did not exceed 5 nm, and the size of the synthesized ZnS nanoparticles did not exceed 3 nm. It was shown that the size of reverse micelles does not depend on the presence of precursors and nanoparticles inside the micelles. Using absorption spectroscopy, it was found that the size of nanoparticles synthesized in the microemulsions was equal to 2.8 ± 0.2 nm, which is consistent with the DLS data. Using Raman spectroscopy, it was shown that the change in the intensity of the SO stretching band of the ZnSO4 precursor correlates with the change in the concentration of SO42- ions inside the micelle cores, which allows it to be used to control the precursor content in the reaction medium with synthesized nanoparticles. In addition, it was shown that the interaction of water molecules with hydrophilic AOT groups leads to a change in the shape of the SO AOT stretching band and its shift to the region of lower wavenumbers. The results of the studies provide for the development of methods for remote and express laser diagnostics of micellar nanoreactors

Application of Domain Adaptation for Diagnostics of Natural Waters by Raman Spectroscopy

L. S. Utegenova$^1$, K. A. Buzanov$^2$

Determination of ionic composition and concentration of substances in river and waste water is an important scientific and practical task of environmental monitoring. In this paper, the problem of determining the concentrations of Zn2+, Cu2+, Li+, Fe3+, Ni2+, NH4+, SO42- и NO3- ions in aqueous solutions is solved using Raman spectroscopy and artificial neural networks (NN). Raman spectroscopy allows to perform rapid and remote analysis of multicomponent liquid media in real time. However, spectral analysis faces a number of problems due to the complex chemical composition of natural waters and the presence of fluorescent background caused by dissolved organic substances. Therefore, NN must be used. In the study, the transfer learning method is implemented for the purpose of domain adaptation of the NN, based on preliminary training of models on a representative sample of spectral data that do not contain a fluorescent component (source domain), and further additional training of the NN on spectra with a fluorescent background (target domain). This approach made it possible to increase the efficiency of model training and the accuracy of determining ion concentrations in real river waters (Moscow River, Yauza, Bitsa, Setun).

Dielectric Receiving Antenna with Optical Signal Readout Based on a Whispering-Gallery Mode Resonator

B. K. Reznikov$^1$, E. S. Minin$^1$, T. A. Kotov$^1$, E. V. Polyakova$^1$, N. Yu. Kolybelnikov$^1$, S. S. Gryzulev$^1$

This article explores a novel type of antenna — dielectric resonator antennas (DRAs) based on whispering-gallery-mode (WGM) nanophotonic resonators, which demonstrate exceptionally high resistance to electromagnetic interference (EMI) and are entirely free from metallic components. Due to the ultra-high quality factors of WGM resonators and the effective overlap between radio-frequency and optical fields inside the dielectric resonator, optical signal modulation by an RF field is achieved without the use of metal electrodes. The paper discusses the operating principles, modulation parameters, and implementation schemes of such antennas, highlighting their potential for the development of highly sensitive, compact, and EMI-immune next-generation radio-photonic antenna systems.

Investigation of Phase Modulation of an Analogue Temperature Signal in a Single-Mode Fibre

B. K. Reznikov

This article investigates the influence of temperature fluctuations on the performance of optical fibre communication systems. In the context of climate change, increasing environmental challenges, and the rising density of communication infrastructure, maintaining optimal system parameters---especially over long distances in harsh climates such as mountainous terrain or the Far North—poses significant difficulties. The research focuses on the characterisation of Rayleigh scattering losses ($\alpha_{RS}$) in single-mode optical fibres fabricated by different technological methods (VAD and MCVD), with varying germanium dioxide (GeO${}_2$) doping concentrations. A linear empirical relationship between $\alpha_{RS}$ and the relative refractive index difference ($\Delta$) was established based on experimental data. A dedicated experimental setup was developed to study the effect of temperature on scattering losses using a 10~km length of fibre exposed to controlled temperature conditions. Measurements demonstrated that $\alpha_{RS}$ increases significantly with higher GeO${}_2$ concentrations at sub-zero temperatures. However, in fibres with 3.5---5 mol~\% GeO${}_2$, the losses remain low enough to ensure long-distance data transmission without amplification. The findings suggest that thermal stabilisation may be unnecessary for systems operating in moderate cold climates. The article also discusses the influence of temperature variations on the phase modulation of analogue signals in fibre-optic communication lines.

A. A. Gajna$^1$, A. A. Mozhaiko$^2$

The paper investigated the accuracy of temperature measurements during laser hardening of structural steel using a thermal imager operating in the mid-infrared range (8-14 microns). Experiments were conducted on installations equipped with fiber lasers, LENS 750 and ЛС-10. Several factors have been identified that affect the accuracy of measurements. These include the reflection of laser radiation, the camera resolution, incorrectly adjusted emission coefficients, and the interaction between laser radiation and air during discharge. In order to improve the accuracy, several methods have been proposed. These methods include the use of optical filters, optimization of the observation distance, and correction of emission coefficients. The study's results indicated the need for comprehensive calibration of the system in order to ensure accurate surface temperature measurement.

A. A. Mikheeva$^1$, A. A. Turkin, A. A. Marmalyuk

Today, amplified spontaneous emission (superluminescence) is an important effect both in injection lasers and in superluminescent diodes. In the latter, this phenomenon allows achieving the widest emission spectrum of the device at a sufficiently high output power, which is an undeniable advantage for a wide class of practical applications. Due to the relevance of the problem of creating broadband superluminescent diodes (SLDs), it seems promising to analyze the best way to broaden the spectrum of these devices depending on the design of their active region. To do this, it is necessary to carry out theoretical modeling of optical gain in various designs of SLD active regions, as well as to study the behavior of the spontaneous radiative recombination rate with increasing wavelength in these structures. When constructing the gain spectrum, it is possible to draw a conclusion about which optical transitions in the quantum well make the greatest contribution to the gain at a certain injection current. The analysis of such important effects allows to construct the calculated spectra of the SLD output power and to calculate the width of each spectrum at half-height at different injection currents. In addition, in order to understand which of the active media designs allows to create an effective broadband superluminescent diode, it is necessary to analyze the magnitude of the spectral dip between the maxima in the corresponding emission spectrum. The work shows that the broadest SLD with a small spectral dip can be created on the basis of one quantum well, in which two optical transitions are involved in the emission process.

M. M. Leshcheva, A. A. Abashkina, A. A. Sharkov, O. M. Vokhnik

The transformation of intensity distributions occurring as a phase-modulated laser beam propagates is experimentally investigated. The influence of the depth of sinusoidal phase modulation on the transformation of the phase distribution into the intensity distribution occurring at a distance equal to a quarter of the Talbot length is revealed. Periodic self-reproduction of the radiation intensity distributions, the phase of which is modulated according to a periodic fractal law, is registered. The features of the Talbot effect caused by the use of a phase transparency based on the Weierstrass function are revealed.

MEMS-switch with enhanced capacitive ratio for advanced electronic systems

M. O. Morozov$^{1,2}$, I. V. Uvarov$^2$

MEMS switches have great potential for use in advanced radar and communication systems, but their practical implementation is limited by several factors. The capacitance ratio in the closed and open state is usually several units, which does not meet the desired specifications. By adding an intermediate electrode on top of the dielectric layer, the capacitance ratio can be significantly increased. In this study, the capacitive and radio-frequency characteristics of a switch with an intermediate electrode are calculated.

L. A. Barinov$^{1,2}$

It is shown that the laser gravitational wave detector scheme proposed in [Barinov L. A., Khalili F. Ya. // Phys. Rev. D. 2025, https://doi.org/10.1103/7mn7-qm31], which combines the advantages of a quantum speedmeter and tunable optical rigidity, can be adapted for tabletop-scale optomechanical sensors of weak forces. A numerical analysis is performed, and analytical expressions are obtained for the spectral density of quantum noise under parameters typical for modern optomechanical systems with sub-gram-scale mirrors.

Space-like pion off-shell form factors in the Bethe-Salpeter approach

S. G. Bondarenko$^1$, M. K. Slautin$^2$

In the paper, the off-shell electromagnetic pion form factors in the Bethe-Salpeter formalism are considered. The separable kernel of the first rank quark-antiquark interaction is used to solve the equation analytically.The semi-off-shell pion form factors 𝐹1 and 𝐹2, which are related to each other by the Ward-Takahashi identity, are calculated. The obtained off-shell form factors as well as static properties of the pion are compared with the results of other authors

Electromagnetic interactions of massive higher-spin fields in three dimensions

A. A. Sharapov$^1$, D. Y. Shcherbtaov$^2$, E. D. Skvortsov$^{3,4}$

New relativistic wave equations and Lagrangians for massive fields of integer spins in three-dimensional Minkowski space are proposed. The consistent interaction of a massive particle of integer spin with an electromagnetic field subject to the Bogomolny equation is constructed. The derivation of Maxwell's equations as a сonsistency condition of the constructed interaction is considered.

V. O. Galkin$^1$, E. M. Savchenko$^{1,2}$

Masses of ground and radially and orbitally excited states of triply heavy tetraquarks with a pair of open and hidden heavy flavors (charm, bottom) were calculated within the relativistic quark model, based on the quasipotential approach and QCD. A tetraquark is considered as a bound state of a diquark with an antidiquark. Diquarks are treated as color--triplet states. Calculations take into account all relativistic effects (spin--independent and spin--dependent) and finite size of diquarks. Obtained results are compared with the strong fall--apart decay thresholds into a pair of heavy and heavy--light mesons. Tetraquark states that are most promising candidates for experimental searches are identified.

V. O. Galkin$^1$, A. O. Nemtyrev$^2$

In recent decades, significant experimental progress has been achieved in studying decays of hadrons containing heavy quarks. In particular, the branching fractions of the exclusive semileptonic and rare decays of both charm and bottom mesons and baryons were measured. In this paper, we present the results of a study of the rare decay of $\Xi_{b}^-\rightarrow\Xi^-l^+l^-$. The form factors parameterizing the weak current matrix elements between baryonic states are calculated within the framework of the relativistic quark model based on the quasipotential approach and quantum chromodynamics. The calculation of the differential and total decay widths, as well as the asymmetries and polarization characteristics of the decays, is carried out on the basis of the helicity formalism. The calculations were performed both with the account of the long-range contributions of charmonium vector resonances to the Wilson coefficients and without their account. Predictions for decay widths for 3 generations of leptons have been obtained.