A numerical model of pulsed parametric generation in a ring three-mirror optical parametric oscillator (OPO) based on KTiOPO₄ (KTP) crystals has been developed. It involves solving a system of coupled truncated equations describing parametric generation in a ring resonator with three crystals using boundary conditions for the field amplitudes and initial conditions corresponding to the level of quantum noise. It is shown that for the conditions implemented in the experiments, the numerical model satisfactorily quantitatively describes the energy, temporal, and spatial characteristics of pulses of the signal wave radiation and their dependence on the energy of pump radiation pulses and parameters of the OPO resonator. Based on the analysis of the results of numerical simulation, conditions are formulated that ensure efficient (efficiency >40%) generation of high-power pulses of signal wave radiation without destruction of KTP crystals.

The dependence of the initial transmission S0 of passive Q-switch based on Cr⁴⁺:YAG crystal on temperature T has been experimentally investigated. It has been shown that the initial transmission is increased from 16.3 to 24.0 % with temperature changes from –40 to +60°С. The resulting curve S0(Т) is approximated by a straight line with a slope ratio of 0.076 %/degree. At a constant pumping level, the energy of the generated pulses E of the Nd:YAG laser decreases from 100 to 90 mJ, and the pulse duration t increases from 9.3 to 12.0 ns with an increase in the T value in a given interval. The numerical calculations of the E(T) and τ(T) curves agree with the experimental data. The results obtained make it possible to more accurately predict the results of the temperature tests of compact diode-pumped neodymium lasers.

The paper presents the results of experiments on the observation of frequency locking by cesium vapor resonant transition, which was placed in the cavity of a titanium-sapphire laser. The radiation frequency of a titanium-sapphire laser was tuned near the DII absorption line of Cs 852 nm. In this case, the simultaneous generation on the absorption line in the coherent mode locking regime and generation at the frequency specified by the spectral selector were demonstrated. Passive losses of the laser cavity on the selector frequency are less than the losses on the frequency of absorption transition of Cs. This unusual result is discussed from the point of view of the effect of intracavity narrow-band absorption on the emission spectra of broadband lasers and the effect of spectrum “condensation”.

A brief review is presented on theory of surface enhanced Raman scattering (SERS) with metaldielectric structures and results of its application for cultural heritage studies with paintings as the representative example. Successful SERS application to 20 inorganic pigments detection in microcrystalline form is reported with 10—100-fold sensitivity enhancement using 1 μg probes.

A method has been developed for sol-gel encapsulation of hemoglobin in the deoxygenated T-conformation followed by saturation of the protein with molecular oxygen (О₂). A set-up for sol-gel encapsulation of hemoglobin under anaerobic conditions has been made. Kinetics for the bimolecular recombination of O₂ with encapsulated hemoglobin stabilized predominantly in the oxygenated T-conformation (in an ensemble of oxygenated T-conformers) was recorded for the first time by time-resolved absorption spectroscopy. The developed method allows to study in detail the O₂-binding properties of non-equilibrium conformational states of hemoglobin, which will make a significant contribution to understanding the mechanism of regulation of O₂ binding by both native human hemoglobin and artificial oxygen carriers.

Calibration of concentrations of C, Mn, Si, Cr, Ni, and Cu by the low-resolution laser induced breakdown spectroscopy is made in reference to low-alloy steels etalons. Data preprocessing in the form of spectrum normalization at Fe II 252.0609 nm emission line wavelength and baseline correction, as well as spectral variables selection with an original method of searching combination moving window for the partial least squares method made it possible to build multivariate calibration models for all considered elements with the following characteristics: for C (in the concentration range up to 0.7%) the value of root-meansquare error and residual predictive deviation is 0.04 % and 4.7, Mn (up to 1.9%) – 0.02 % and 24.8, Si (up to 0.9%) – 0.01 % and 12.9, Cr (up to 1%) – 0.01 % and 21.8, Ni (up to 0.7%)– 0.007 % and 23.3, Cu (up to 0.5%) – 0.006 % and 23.2, respectively. Models are quantitative (residual predictive deviation > 3) for all six elements considered, including carbon.

The possibility of spectroscopic identification of substitution solid solutions formed via solvothermal synthesis of molybdenum-vanadium mixed oxide was demonstrated. The method is based on the investigation of the shift of the n(V=O) absorption band due to reduction of vanadium centers in the mixed oxide upon partial substitution of vanadium with molybdenum in the crystalline lattice.

The complex analysis of histological preparations of the colon without pathology, chronic colitis and surgical material of primary colorectal adenocarcinomas, taking into account the survival of patients after standard treatment using confocal Raman microspectroscopy with spatial resolution was presented. It is shown that the main difference in the spectra of normal and pathologically altered tissues are the positions and relative intensities of vibrational bands at frequencies of 1248, 1537, 1587, and 1620 cm–1. The analysis of spectral changes was carried out within the framework of the Stark effect assuming changes in the local electric field in epithelial cells during oncogenesis.

Based on modern models of the exciton-phonon coupling, the analysis of experimental temperature dependences (77–293 K) of absorption and photoluminescence spectra for semiconductor quantum dots (QD) CdSe/ZnS was carried out. It was proven that the formation of the first excitonic transition absorption band takes place with participation of optical phonons of the CdSe core presumably, while photoluminescence properties reflect the interaction with optical phonons of ZnS layer. In the frame of the quantum-mechanical model the photoluminescence quenching for CdSe/ZnS QDs of various sizes was analysed upon formation of nanoassemblies with porphyrin molecules. It was shown that the quenching rate constant decreases with the rise of QD size, and in conditions of quantum confinement the quenching process is due to the electron of excited electron-hole pair tunnelling to the QD surface with the subsequent localization on surface traps.

The dependences of the fluorescence intensity and anisotropy of molecular rotors SYBR Green (SG) and double-stranded DNA with 10, 20, and 100 base pairs on their relative concentration in solutions, as well as on the viscosity of the medium, were studied. It was shown that an increase in the fluorescence intensity with an increase in the SG concentration and subsequent reaching a constant value is associated with an initial increase in the number of SG molecules intercalated in DNA and a further process of saturation and the formation of nonfluorescent states. To explain the sharp drop in fluorescence anisotropy due to the Förster intramolecular energy transfer between DNA-bound SG molecules, a generalized model was developed that takes into account both internal rotations and rotational diffusion of molecular complex as a whole. The proposed model made it possible to calculate universally the obtained experimental dependences of the fluorescence anisotropy on the viscosity of the medium at various dye/DNA ratios and to estimate the Förster energy transfer rates.

The spectral and photophysical parameters for the family of hydrophobic metallocomplexes of phthalocyanines and porphyrins, which were incapsulated in polymeric micelles, has been studied in water solutions at 293 K. The fluorescent characteristics of above mentioned compounds with light ions of Mg(II) and Zn(II), as it was found, have weak differences between the values of main photophysical parameters in water-micellar solutions relatively to the same values in organic solvents. In contrast, the encapsulation of the porphyrins with heavy Pd(II) and Pt(II) ions into polymeric micelles leads to a significant increase in the values of quantum yields and phosphorescence lifetimes in water-micellar solutions relatively to the same characteristics in organic solvents. It was shown that these differences were due to the spin-orbital coupling effect for compounds with Pd(II) and Pt(II) ions, as well as, significant decreasing of the efficiencies quenching of triplet states by molecular oxygen upon encapsuling of compounds in polymeric micelles. The luminescent parameters for the studied compounds depend on the nature of the polymeric micelles and the structure of the studied compounds.

Single-photon spectroscopy is used to study photobleaching of graphene quantum dots in aggregated state on a silicon substrate, in polymer matrices and red blood cell membranes. We have established typical photobleaching times and characterized changes in the emission statistics of graphene quantum dots in the single-photon detection regime. We have also found that changing the microenvironment of nanoobjects does not lead to significant correlations of emitted photons. The reported results are important for the implementation of graphene quantum dots in biomedical imaging.

We studied the effect of a heavy chlorine atom added to the aromatic fragment of a 1,3-diketone ligand in Eu³⁺ ion coordination compounds on the spectral and luminescent properties of complex compounds. The data obtained from the absorption, optical excitation, fluorescence and phosphorescence spectra, as well as from the kinetic dependences of the luminescence intensity, allows us to estimate the efficiency of energy transfer processes within the studied compounds. It was found that adding a heavy chlorine atom leads to an increase in the energy of the first excited singlet state from 24500 to 26000 cm^–1 and does not affect the energy of the triplet level of the ligand. Also, adding chlorine leads to a decrease in the nonradiative relaxation constant (from 1290 to 840 s^–1), and consequently increases the luminescence quantum yield up to three times from 23 to 64%. Thereby, a new approach in the rational construction of coordination compounds of Eu3⁺ ions with 1,3-diketones class ligands has been developed, consisting in substitution of hydrogen with heavy chlorine atom in the aromatic fragment of ligand.

Comparative  studies  of  the  effect  of  radiation  from  laser  and  LED  sources  with  the  wavelength of λ = 405 and 445 nm on the metabolic activity of cultured somatic cells were performed. A more pronounced inhibitory effect is observed when exposed to light with λ = 405 nm. The absence of fundamental differences in the action of monochromatic and quasi-monochromatic light is noted. It is shown that the photobiological effect is due to photochemical processes involving various reactive oxygen species, whose contribution to the effects of cell inactivation depends on the time after the termination of irradiation. Porphyrin components were registered for the first time in the fluorescence spectra of the suspension of living cells along with the flavin component. Based on a comparison of the absorption characteristics of flavin and porphyrin sensitizers, as well as data from chemiluminescence analysis and the biological effects of radiation with λ = 405 and 445 nm, it is concluded that the determining contribution to the formation of singlet oxygen in cells when exposed to radiation with λ = 405 nm is made by endogenous porphyrins, characterized by the most intense absorption in this area. The contribution of flavins is more pronounced under the action of radiation with λ = 445 nm, corresponding to the maximum in their absorption spectrum and the minimum absorption of endogenous porphyrins.

The dependencies of the morphology and optical properties of silicon nanostructures on the laser ablation synthesis conditions were established, namely on the laser focusing conditions, laser pulse repetition rate, as well as temperature and composition of the solution. The regularities obtained were used for the development of the method for Si-Ag and Si-Ag-Сu hybrid metal-silicon nanostructures formation. It has been demonstrated that the obtained broadband absorption of the Si-Ag-Cu nanoparticles is promising for the application in nanofluids for photothermal energy conversion of solar radiation.

Silicon layers with a selenium impurity concentration of up to 10²¹ cm^–3, which exceeds the equilibrium solubility limit of this impurity in silicon by 4 orders of magnitude, have been obtained by high-dose ion implantation followed by pulsed laser annealing at pulse energy densities from 0.5 to 2.5 J/cm². The Rutherford backscattering of He⁺ ions showed that, after laser annealing, up to 70% of the implemented impurity atoms are localized at the sites of the silicon crystal lattice. The Si layers hyperdoped with selenium are characterized by increased (up to 45–55%) absorption in the spectral range of 1100–2400 nm. After thermal heat treatment (550 °C, 30 min + 850 °C, 5 min), no increase in IR absorption was found in comparison with the initial silicon. It was explained by the loss of Se as a result of diffusional redistribution. The theoretical evaluation of recrystallization processes of silicon layers amorphized by Se ions as well as dopants redistributions at the equilibrium thermal treatment was done.

The influence of energy and pulse interval, the number of double laser pulses on the purposeful formation of the component and charge composition of laser plasma by laser spark spectrometry (LSS-1 spectrometer) has been studied. The processes of formation of mixed nanopowders of copper and aluminum oxides, precursors for the irradiation of nanoceramics and films of CuAlO₂-type copper aluminates under the influence of double laser pulses on a hybrid target consisting of glued aluminum and copper plates made of AD1 and M2 alloys were studied. It is shown that the sequential effect of a series of double laser pulses with the energy of 53 mJ and between the pulse interval of 10 microseconds on a hybrid target makes it possible to obtain precursors for the production of nanoceramics and nanofilms of CuAlO₂-type copper aluminates. To obtain the products formed by the interaction of aluminum and copper ions with oxygen in the air, a closed glass bux was used, where the target was placed. The size of the primary particles, estimated using high-resolution electron microscopy, was mainly from 30 to 45 nm, the particles were collected in agglomerates. The particles have a crystalline structure and a spherical shape. The size and number of fractal aggregates deposited on the substrate placed at the bottom of the cuvette is several times higher than the number of products deposited on the side substrate due to the purely diffusion mechanism of fractal transfer. The main contribution to the change in the intensity of the spectral lines of atoms and ions of Al, Cu, and molecular bands of AlO is made by the interaction of the second pulse with condensation products formed in the channel after the first pulse exposure. With an increase in the number of long-lived fractal aggregates in the air, the intensity of molecular bands and lines of Al III decreases by about 1.5 times, and copper by almost two times, which is associated with the active interaction of long-lived large fractals accumulating in the air with incident radiation.

On the basis of algorithms that take into account the features of a high-speed time-resolving matrix of single photon detectors, the spatio-temporal correlation properties of a pseudo-thermal light source with nanoand microsecond time resolution are studied. It is shown that the change in the degree of coherence of the second order of radiation scattered on a rotating disk with irregularities of different scales can be represented universally using a nonlinear hyperbolic mapping. Based on the presented method, the change in correlations during the transition of the generated photon flux from coherent to pseudo-thermal is studied.

The equations are derived to describe scattering and absorption of light by a normally illuminated monolayer of identical spherical particles in a homogeneous light-absorbing medium (matrix). They are based on the quasicrystalline approximation, mean-field approximation, and multipole expansion of fields and tensor Green’s function in terms of vector spherical wave functions. The results are presented of numerical analysis of the coefficients of coherent transmission and reflection, incoherent scattering, and absorption of composite systems (a monolayer of gold (Au) nanoparticles in fullerene (C₆₀) matrix and a monolayer of silver (Ag) nanoparticles in copper phthalocyanine (CuPc) matrix) in visible spectrum at different concentrations and sizes of particles. The comparison is made of the dependences of the wavelength of the absorption plasmon resonance maximum on the filling factor of the partially ordered monolayer, calculated with (in the quasicrystalline approximation) and without (in the interference approximation) taking into account multiple scattering of waves. The calculation results are in qualitative agreement with the know experimental data on the red-shift of the resonance with increasing in the monolayer filling factor. The derived equations can be used in solving problems of thin-film optics, developing photonic and optoelectronic devices containing absorbing matrices.

The article presents the results of processing the data of measuring the characteristics of the Antarctic aerosol by the Belarusian Antarctic Expedition at the Vechernaya_Hill AERONET station. The data for the entire period of observations from 2008 to 2022 were processed. The Vechernyaya aerosol model was formed, which is a typical aerosol for the coast of Antarctica near Mount Vechernyaya. The model differs significantly from models of Antarctic coastal aerosol proposed in the literature and can be used in various applications, in particular, in atmospheric correction of satellite data.

Experimental results on frequency conversion of images by dynamic holograms and diagnostics of semiconductor materials, photorefractive and activated crystals based on transient gratings method are presented. The possibility of visualization of infrared 3D images in real time is shown. Spectral regularities of short (hundreds of microseconds) and long-lived (seconds) lattice recordings in photorefractive bismuth silicate crystals are established. The results of measurements of the diffusion coefficient of excitation energy and lifetime of excited states are presented. A technique for compensation of induced anisotropy in active laser media and measuring the coefficient of thermal diffusivity of thin-film and bulk thermoelectrics based on lead telluride is proposed.

Stokes polarimetry was used to evaluate the birefringence of nanoporous alumina films. The transmittance of the film and the degree of polarization of the transmitted radiation were measured for the angles of incidence at which the phase difference of the orthogonal polarized components of the transmitted radiation reach to λ/4 or λ/2. Using the Maxwell—Garnet model, the porosity and pore radii of the films were estimated. The possibility of creating achromatic phase plates with a variable phase difference of the orthogonal polarized components of the transmitted radiation, which can function as a quarter-wave and half-wave plates, based on a nanoporous alumina film, is shown.

The polarization selectivity of a double DNA-like helix with respect to waves with left and right circular polarization at a resonance characteristic of the periodic structure is confirmed by modeling. As an example, helices of various lengths consisting of two and a half and twenty and a half turns are considered, while the wavelength of the incident field is approximately equal to the length of the helix turn. The effect consists in a radically different ability of a double DNA-like helix to reflect waves with right or left circular polarization at the resonance under consideration. The predominant intensity is a reflected wave with such a direction of circular polarization, in which the electric vector is twisted in space in the opposite direction relative to the double helix. Consequently, on the basis of a double DNA-like helix, an electromagnetic wave polarizer can be created that converts an incident linearly polarized wave into a reflected wave with circular polarization. The electromagnetic forces of interaction between helix strands at three states of polarization of the incident wave are calculated, which also confirms the polarization selectivity of a double DNA-like helix as an element of metamaterials and as an object with great possibilities of use in optics.

A new electrically controlled photonic liquid crystal device, a twist q-plate for generation of a given number of polarization and phase optical singularities on the wavefront of a light beam in a wide spectral range, has been proposed. The ability of the developed element to function in two modes has been experimentally demonstrated: generation of a given number of singularities or generation of a Gaussian beam and application of this element in a scheme of optical tweezers. A theoretical model has been developed to determine the range of control voltage of achromatic functioning of the proposed element.

Two-dimensional organic-inorganic hybrid lead halide perovskites are of interest for photovoltaic and light emitting devices due to their relative stability when compared to bulk lead halide perovskites and favorable properties that can be tuned. Tuning of the material can be performed by adjusting halide composition or by taking advantage of confinement effects. Here we use density functional theory and excited state dynamics treated by reduced density matrix method to examine the effects that varying the thickness of the perovskite layer has on the ground state and excited state photo-physical properties of the materials, further we explore the effects of a vertical heterostructure of perovskite layers. Nonadiabatic couplings were computed based on the on-the-fly approach along a molecular dynamic trajectory at ambient temperatures. Density matrix-based equation of motion for electronic degrees of freedom is used to calculate the dynamics of electronic degrees of freedom. We find that the vertical stacking of two-dimensional perovskites into heterostructures shows an increase in photoluminescence intensity by two orders of magnitude when compared to the individual two-dimensional perovskites.

Mineral pigments are commonly used in cultural relics, which makes the analysis of mineral pigments helpful in such research. It is complicated and time-consuming work to establish the data set of mineral pigment Raman spectra, so it is necessary to study the method of data augmentation. In this paper, two methods of augmenting Raman spectra data are explored – translation transformation, adding noise; expanding the size of the data set from 20 to 320 – then a convolutional neural network model is proposed and trained with the expanded data set. Experimental results showed that the accuracy of the model can reach 100% when the SNR of the test set is not less than 40 dB.

The photoluminescence (PL) performance of thermally annealed PbSe nanocrystalline films has been investigated at different temperatures. The visible PL signals at 655 and 466 nm are observed for the asprepared PbSe films, and the enhanced intensities of the two PL peaks are closely related to the optimized crystallization quality of PbSe nanoparticles after annealing at 50–150°C. However, as the annealing temperature is above 200°C, the severe surface damage of PbSe films induced by the oxide impurity phases and dislocation defects results in the reduction of the crystallinity of PbSe and the lower intensities of PL signals, which have been proved by means of X-ray diffraction (XRD) characterization. In addition, another emission peak at 429 nm is observed at the annealing temperature above 200°C owing to the appearance of the PbO impurity phase, and its intensity strongly depends on the content of the PbO impurity phase, whereas the PL intensity decreases above 350°C owing to the formation of PbSeO_x.

Dy³⁺-doped Li₂CaSiO₄ phosphors were prepared by high temperature solid-state reaction. Structural studies were carried out using X-ray diffraction technique. Scanning electron microscopy was used to get information about the morphology of the prepared samples. Also, photoluminescence analysis of the phosphor samples for different concentrations of the doping ion with variable excitations was presented. When doped with Dy³⁺, Li₂CaSiO₄ emits intense emission bands at 485 and 576 nm (excited at 353 nm). Our study shows that the as-prepared phosphor may be useful in white light-emitting diodes as a bluish component. The corresponding transitions of the doping ion and concentration quenching effect were studied in detail. The CIE 1931 (x, y) chromaticity coordinates (x = 0.24 and y = 0.31) show the distribution of the spectral region calculated from photoluminescence emission spectra.

Trametes versicolor laccase, one of the main enzymes used for the biodegradation of environmental pollutants, has received much attention in the degradation of phenolic pollutants. In this study, the binding energy between the Trametes versicolor laccase and bisphenol E (BPE) is first calculated by means of computational simulation. Moreover, the interaction between Trametes versicolor laccase and bisphenol E is studied with multi-spectroscopy. The results show that bisphenol E can be effectively degraded by crude Trametes versicolor laccase under optimal incubation conditions. The kinetic study is used to characterize the kinetic features of the laccase-catalytic degradation of BPE. The calculation results suggest that the reaction can proceed spontaneously. Spectral analyses show that the secondary structure oflaccaseis changed after the interaction between laccase and bisphenol E. The degradation efficiency of BPE is up to 93.64% after reacting for 6 h, and the maximum catalytic reaction rate is 0.1764 mg/(L·min). The reactions follow a first-order kinetic equation when the initial concentration of the substrate is lower than 5 mol/L.

Laser-induced fluorescence (LIF) is a potential technology for the rapid, sensitive, and selective detection of vitamins. In this study, the LIF spectra (LIFS) of vitamins A, B1, C, D, E, and K1, and their mixtures were investigated under a 266-nm laser excitation via an Nd:YAG laser. The experimental results showed that the LIFS of each vitamin solution had its unique profile. The six vitamins can be distinguished to some extent by the characteristic wavelength region: 320–380 nm for vitamins A and C, 350–440 nm for vitamins D and E, and 400–470 nm for vitamins B1 and K1. Additionally, it can be used for accurate diagnosis by characteristics of LIFS (starting wavelength, spectral range, peak wavelength, maximum intensity, and extinction coefficient) as a complement. Moreover, the features of LIFS can reflect the main vitamin components in the mixture of vitamins to a certain extent when several vitamins coexist. It was found that the spectral range, maximum intensity, and extinction coefficient could report the benzene ring number, double bonds, and OH group in molecules of components in mixtures, which is a discrimination-assisted method for vitamins in a mixture. This paper also proposes a technique to identify individual components in mixtures quantitatively by using LIFS and LIFS parameters. The present study will offer technical support in clinical diagnosis and targeted therapy using vitamins via experimental exploration on detection.