To mitigate channel-induced degradation in underwater wireless optical communication (UWOC), this study combines theoretical and experimental analyses to characterize 488 nm blue OAM beam propagation across varying temperatures, salinities, and distances. Under short-range conditions, received power decreases monotonically with increasing temperature (10 ∼ 30°C) and salinity (10 ∼ 35 PPT), though overall attenuation remains modest. Notably, salinity fluctuations exerted a more pronounced impact (0.167
This work is devoted to the development and experimental verification of effective methods for compensating dynamic atmospheric distortions of a laser beam propagating through a turbulent medium. A laboratory experiment on the correction of wavefront distortions of laser radiation propagating along a turbulent path in a pavilion was performed, where turbulence was simulated using a fan heater supplying warm air perpendicular to the beam propagation. The distortion compensation was performed using an adaptive optics system with a wavefront tilt corrector and a bimorph deformable mirror. The system efficiency was assessed from the analysis of the far-field intensity distribution. We have shown that the generated turbulent distortions are spectrally similar to Kolmogorov turbulence with a bandwidth of about 30 Hz. For effective compensation of wavefront aberrations, the operating frequency of the adaptive optics system should be 20–30 times higher than the turbulence bandwidth. At a system operating frequency of 1 kHz, the beam divergence was reduced to 1.4 of the diffraction limit. Increasing the frequency to 2 kHz and using FPGA, we attained beam stabilization accuracy of 5 μrad. The results of this work can be used to design high-performance systems related to laser radiation propagation in a turbulent medium.
Detection of coordinates and magnification of a reconstructed holographic image of a particle is quite difficult because of the lack of a strict geometric-optical model of digital holographic imaging. Traditional optics and microscopy usually use lenses for image magnification. In digital holography, magnified images can be generated without mechanical focusing and optical components, for example, by controlling the divergence of illuminating beams. This work discusses optimization of the optical scheme of digital holography for lensless magnification of reconstructed images; justifies the feasibility of using a geometric-optics apparatus in the design of digital holographic systems, and describes their limitations. The results of the work can be used in the design and development of digital holographic microscopy systems and for high-precision reconstruction and analysis of holographic images of particles.
The paper theoretically studies the propagation regimes of narrow (millimeter) laser beams in a Kerr-nonlinear turbulent medium, which simulates the evolution of light inhomogeneities generated under multiple filamentation of high-power laser pulses in corresponding media, by methods of diffraction-beam tubes and diffraction rays. Three propagation regimes are found: self-focusing with generation of a nonlinear focus (beam collapse), self-channeling over a limited distance, and turbulent propagation. An equation for squared beam effective radius is derived, which is of interest for practical applications in nonlinear atmospheric optics.
The problem of aerosol pollution of the atmosphere and associated climate change has become increasingly relevant. Of particular interest are physicochemical properties and structure of atmospheric aerosols. Being an important component of polluted air, aerosols affect various atmospheric processes, the environment, and human health. Analysis of the morphology and composition of aerosol particles enables us to identify the features of their behavior in the atmosphere and determine their origin. This paper studies the composition and morphology of near-surface atmospheric aerosol particles at a year-round monitoring station (Irkutsk) in different seasons of 2024 using scanning electron microscopy and X-ray spectral analysis. The main types of aerosol particles (soot, fly ash, mineral, and biogenic particles) are identified, and their shapes and sizes are determined. It has been established that mineral and biogenic particles predominate in the composition of near-surface atmospheric aerosol in Irkutsk during the warm season, while fly ash and soot particles predominate during the cold season. Brochosomes (fullerene-like structures of biological carbon-containing particles) were detected for the first time in the surface aerosol at the urban Irkutsk station. The results of this study expand our understanding of the morphological properties and composition of individual particles in surface atmospheric aerosol in the urbanized area of the Southern Baikal region.
The main problem in solar energy is reducing optical losses due to light reflection from the surface of photovoltaic cells. This paper numerically studies antireflection properties of nanostructured silicon dioxide (SiO2) coatings deposited on the surface of a solar cell. Two porous antireflection coating types are considered: multilayer assembly of nanospheres and vertical air nanopores embedded in a solid SiO2 layer. The light transmission efficiency is assessed depending on the coating thickness and structure. It is found that the efficiency of solar energy conversion into electricity can significantly vary across different spectral ranges for the same antireflection coating type. It is shown that a coating in the form of vertical nanopores in most cases provides more efficient conversion of incident light compared to a porous layer assembled of nanospheres. The results are important for designing more efficient solar cells and can be used to create antireflection coatings to improve the overall performance of photovoltaic devices.
This article presents an improved internet-accessible expert system, SLON, for analyzing high-resolution molecular spectra. It was developed in the Laboratory of Molecular Spectroscopy of Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences. SLON expert system is based on a neural network capable of decision making when analyzing combination differences formed by groups of molecular transitions from different rotational sublevels of the ground state to the same excited vibrational-rotational state. The set of features used by the neural network for distinguishing the correct combination difference from random realizations is improved; restrictions on the size of an analyzed spectrum are removed; the format of used databases is now universal and enables expanding the class of molecules under study. An up-to-date multi-platform user interface enables this software to be running Windows and Linux systems. The operating principles, operational experience, and prospects for the development of the created expert system are discussed.
Chloroform is one of dangerous air pollutants. To control it in the atmosphere by absorption spectroscopy, it is necessary to know the position of its spectral lines. In this work, the absorption spectra of CH37Cl3 isotopologue of gaseous chloroform are measured using a high-resolution nonstationary spectrometer in the frequency range 118–175 GHz, where spectroscopic data for this compound are absent. The identification of the chloroform lines presented in the literature and assigned to the vibrational state ν2 of CH35Cl3 is refined; their belonging to CH37Cl3 isotopologue is shown. The experimental results are compared with our theoretical estimates of absorption line centers of the rotational spectrum of this molecule in the same spectral range. Absorption lines of CH37Cl3 isotopologue in the ground state were detected and identified in the spectral subranges near 131.4, 137.6, 150.1, and 156.4 GHz. Based on the experimental spectra, we have estimated the molecular constants B = 3129.56 MHz, DJ = 1.34 kHz, and DJK = −2.25 kHz with RMSE = 7.84 × 10−2 MHz, which determine transition frequencies in absorption spectra near 150.1 and 156.4 GHz more accurately than molecular constants given in the literature (B = 3129.61 MHz, DJ = 1.37 kHz, and DJK = −2.28 kHz with RMSE = 11.55 × 10−2 MHz). The results can be used for controlling the atmospheric content of chloroform.
The analysis of a spectrum of 15N18O molecule recorded in the region 5100–5500 cm−1 was performed, and 187 positions of rotational lines were found in the vibrational band 3–0 of the main transitions between the electronic states 2Π1/2 and 2Π3/2 with the maximal rotational quantum number J = 32.5. For the first time, Λ-splitting was observed in this band. The positions and relative intensities of both the resolved component of Λ-doublets and unresolved doublets were determined. A joint weighted processing of all known vibrational-rotational transition frequencies in the microwave and infrared spectral regions was carried out. As a result, Dunham type constants were determined for 15N18O isotopologue in the ground electronic state. Using the found constants, predictive calculations of the rotational line positions of all bands corresponding to vibrational transitions between states with v ≤ 3 and J ≤ 37.5 were carried out. The experimental data obtained in this study provide new spectroscopic information about 15N18O isotopologue and enrich fundamental knowledge about nitrogen monoxide molecule.
Acquisition of high-quality satellite information is important for solving a wide range of problems in monitoring the Earth surface, such as estimation of forest health, agricultural productivity, and others. To perform accurate atmospheric correction (elimination of the distorting influence of the atmosphere) of satellite images of the Earth surface, it is crucial to consider various factors that influence received signals, including non-Lambertian surface reflectance (the difference between surface reflection and Lambert’s law according to which radiation is equally reflected in all directions and depends only on the irradiance of the surface and the reflectance). In some algorithms, non-Lambertian reflection is taken into account after solving a problem in the Lambertian reflection approximation. In this case, the assumption is used that the adjacency effect (i.e., the effect of received radiation reflected from surface areas adjacent to the observed one and scattered in the atmosphere) is formed only by Lambertian surfaces. Our calculations show that at meteorological range of visibility SM ≤ 6 km, neglect of contribution of non-Lambertian reflection produces an error in the reflectance of no higher than 20.3
The question of how forest ecosystems influences climate parameters is of growing scientific interest. This work analyzes two approaches to the study of interaction between Siberian forests and the atmosphere. Based on the analysis results, we suggest that a four-year cycle in precipitation over forest areas can be caused by tree transpiration. This finding is to help understanding similar cyclic patterns in meteorological data in other regions with large forest ecosystems. The results can be useful for specialists dealing with problems of biosphere-atmospheric interaction.
An optimal radiation wavelength for scanning marine surface from air is found, which provides minimal radiation absorption, parasitic fluorescence, beam divergence, and scattering in the water column. These parameters depend on the laser type used. The research focused on water samples from the Black Sea collected 200 m from the shore immediately before the experiment and water samples stored for one year in light-protected hermetically sealed containers. For both sets of samples, the following characteristics were examined: scattering phase function, spectral transmittance, laser beam divergence, particle size distribution of organic matter in the samples, and its effect on fluorescence spectra. Commercial semiconductor lasers with wavelengths of 450, 520, and 660 nm were used. The study shows a 450-nm laser to be optimal for underwater sounding tasks since it exhibits the lowest radiation attenuation in the water column (0.5 dB/m), the smallest scattering spot, and minimal fluorescence. Organic particles do not significantly affect hydrooptical properties of seawater in the both sets of samples. The results can be used in the design of above-water and underwater laser sounding systems for marine surface analysis.
Natural gamma radiation easily penetrates into the cells of a human body and destructively affects all structures causing a wide range of diseases. It also plays an active role in the atmosphere by participating in electrical processes and origination of ions, which affects cloud formation, precipitation, radiation balance, etc. There are very few measurements of the vertical distribution of gamma background over the Russian territory. This paper summarizes the results of aircraft sounding in 2003–2025. Based on the analysis of the long-term data, an average vertical profile of this parameter has been calculated, which shows its nonlinear increase with altitude. In the surface air layer, this parameter varied within 0.03–0.25 μSv/h with the average over the period under study being 0.11 μSv/h. At an altitude of 10 km, the gamma background varied in the range 2.18–2.80 μSv/h, and the average was 2.35 μSv/h. The analysis of the latitudinal distribution revealed the belt 60°–70° N with high gamma radiation values; the gamma background was lower to the south and north of that belt. The data analysis has also revealed a weak annual gamma background variation with a maximum in November and a minimum in August, which is not typical for other atmospheric parameters. The results can be useful for choosing the range and uncertainty of developed radiation protection devices and means, as well as for assessing the probability of origination of radiative effects.
Stratospheric aerosol, the main component of which are volcanogenic particles, is one of key factors influencing the global climate. The role of aerosol emitted into the stratosphere during wildfires is underestimated. Consideration of the effect of stratospheric aerosol produced by wildfires into climate models leads to significant uncertainties and highlights the need in in-depth study of this phenomenon. This work discusses the results of lidar monitoring of stratospheric aerosol dynamics over Tomsk, Western Siberia, in 2025, with an emphasis on the study of disturbances in the stratospheric aerosol component caused by wildfires. Ground-based lidar sensing in June 2025 detected aerosol layers in the stratosphere over Tomsk at altitudes of 10–17 km. The trajectory analysis and satellite data on wildfires have shown that these aerosol layers could consist of combustion products, including soot transported into the stratosphere by pyrocumulative clouds formed in late May and early June 2025 over severe wildfires covering parts of Canada and the United States. These results are of interest for studying climate changes in Western Siberia.
Stratospheric polar vortices, which form over the polar regions in late autumn, are large-scale cyclonic structures whose stability in the winter-spring period determines the scales and depth of spring ozone depletion. Using the vortex delineation method based on ERA5 reanalysis data, we studied the features in the vertical dynamics of the Arctic and Antarctic polar vortices in 2020 during their anomalous strengthening, which was accompanied by deep and prolonged ozone depletion in the Arctic and Antarctic. In particular, we examined the synchronicity in temporal changes at different stratospheric levels. The polar vortex breakdown in 2020 was observed from late spring to early summer spreading from top downward over 1‒2 months. The dynamics of the Arctic polar vortex showed three peaks of activity, spreading from the upper to the lower stratosphere within a month. The dynamics of the Antarctic polar vortex clearly showed one peak of activity spreading from the upper to the lower stratosphere over a period of 2 months. The anomalous duration of the westerly phase of the quasi-biennial oscillation in the middle stratosphere has been proposed as a possible reason for the unprecedented strengthening of the polar vortices in 2020. The results can be used to assess the risks of increasing ground-level UV-B radiation which is dangerous for the biosphere.
Most measurements of aerosol attenuation of the atmosphere are carried out in the visible and near-infrared regions of the spectrum. However, many atmospheric optics tasks require data on the spectral behavior of aerosol extinction coefficients in the visible and IR regions, including the atmospheric “transparency window” 8–12 μm. In this regard, models that make it possible to calculate attenuation in the IR region based on measurements in the visible region are of great interest. A one-parameter model of the spectral behavior of the aerosol extinction coefficient for the surface air layer is suggested. The input parameter of the model is the aerosol extinction coefficient at a wavelength of 0.55 μm or the meteorological visibility range Sm. The model enables one to calculate the mean aerosol extinction coefficient in the wavelength range 0.44–12 μm at meteorological visibility range Sm > 8 km. The model can be used to evaluate the efficiency of different optical systems and to separate aerosol attenuation into submicron and coarse components.
In connection with the global warming problem caused by the increase in the concentration of greenhouse gases in the atmosphere, estimating the potential of different ecosystems for the sequestration of atmospheric carbon dioxide on both regional and global scales is a topical problem. In this work, the balance of natural carbon dioxide fluxes throughout Sverdlovsk region is considered. An integral estimate of net CO2 absorbed from the atmosphere by regional ecosystems over 2020–2022 is obtained for the first time using an original NorthFlux machine learning model, where spectra data from the MODIS satellite sensor, meteorological data of retrospective climate analysis, and satellite data on the classification of the underlying surface vegetation are used as input. The data on the amount of anthropogenic CO2 emissions is taken from the inventory of greenhouse gas emissions in Sverdlovsk region. The transboundary transfer of carbon dioxide is estimated using a balance equation for CO2 fluxes in the atmospheric column and data on the average annual rate of increase in the CO2 concentration in the regional atmosphere obtained from ground-based Bruker IFS 125M high-resolution measurements at the Kourovka Astronomical Observatory in 2012–2024. It has been found that the sequestration of atmospheric CO2 by ecosystems of Sverdlovsk region ranges from 10.9 to 15.2
Imaging in the visible spectral range of processes in media transparent only to IR radiation requires the use of active IR-to-visible converters. In this work, we simulate the conversion of IR radiation into the visible based on competition between transitions in Mn vapor active media with the use of a spatiotemporal kinetic model of an active medium. We estimate the conversion efficiency for continuous and pulsed input IR signals in a wide range of signal power for different pulse frequencies (from 2 to 20 kHz). We show the pulsed mode and pulse frequencies lower than an optimal frequency in terms of amplified spontaneous emission power to be optimal for this conversion. The measurable conversion efficiency is higher than 10 for medium-size GDT. Our results confirm the usability of a bistatic Mn vapor laser monitor for negative imaging of processes in a medium transparent for IR radiation, i.e., a possibility of creating a narrowband pulsed IR-to-visible converter.
Effective monitoring of tropospheric ozone requires lidar systems, operation of which depends on the quality of dielectric mirrors used in the UV region, where traditional coatings are subject to accelerated degradation. We have designed a dielectric mirror with high reflectance at a wavelength of 266 nm for UV lidar systems for ozone monitoring. A multilayer interference coating was manufactured based on HfO2 and SiO2 and optimized using experimental dispersion data. The effect of thermal annealing on the optical properties of the coating is studied, and a temperature threshold is detected, above which the coating structure degrades. The results can be used in the design of highly efficient optical elements for UV differential absorption lidars and other laser systems which require UV dielectric mirrors.
We investigated a dual-point pumped Nd:YAG laser that emits two beams, where the dual-point pumping occurs through the birefringent walk-off effect of pump light in a uniaxial crystal. By using dual-point pumping, two-beam and parallel oscillations were obtained, where the two beams were orthogonally polarized, and the polarization direction of each beam was identical to that of the corresponding pumping point. The polarization extinction ratio of an ordinary light pumped beam was 31.75 dB, and the polarization purity of extraordinary light pumped beam was 31.25 dB. Compared to that of conventional single-point pumps, the slope efficiency of the output power increased from 16
