Vol 127, No 2 (2019)

Absorption of probe laser radiation by a mixture of even isotopes of neon in a gas discharge plasma is investigated by the method of magnetic scanning of 3s₂–2p₄ transition. The contours of absorption lines of isotopes are resolved by means of numerical modeling. It is discovered that, upon decrease in relative concentration of one of the isotopes, its contribution to absorption is replaced by gain. The effect is found to be caused by radiative transfer of excitation energy between atoms of different kinds in the absence of a difference in level energies (the process known as optical pumping). The effect of this mechanism turned out to be substantial for the upper level transitions from which to the ground state are allowed while being absent for the lower level of the transition from which such transitions are forbidden although other decay channels are available.

The dependences of the rotational contributions to the effective dipole moment of the H₂O molecule on vibrational quantum number \({{{v}}_{2}}\), which corresponds to the large-amplitude bending vibration of the molecule, have been determined numerically. Different representations for the dipole moment surface of the H₂O molecule and different potential functions that determine the set of vibrational states E(\({{{v}}_{2}}\)) have been used in calculations. The effect of the calculated contributions on the broadening and shift of H₂O lines induced by the pressure of argon, krypton, hydrogen, and helium has been analyzed. It has been shown that this effect is significant for the shift of rotational lines and for the shift of lines from the vibrational bands for which the difference between the values of rotational quantum number K_a from the upper and lower states of the transition is greater than or equal to 3.

A theory of the imaginary part of isotropic polarizability induced by dipole–dipole interactions between isotropically polarizable particles has been developed on the basis of diagram technique. A classification of single infrared resonances corresponding to the cases of allowed absorption and absorption induced by intermolecular interactions has been proposed. A summation of the diagram contributions describing the change in the intensity of the allowed absorption due to the effect of the reaction field of the environment has been carried out for the dipole–induced dipole (DID) scheme. The strict results obtained in such a way contradict the Onsager–Bettcher model, which is semiempirical. The numerical estimates show that the role of the reaction field in the observed changes in the intensity of the vibrational bands of the simplest model systems (HCl and HBr in inert solvents) is small and decreases with increasing solvent particle size, which indicates the inadequacy of the DID and Onsager–Bettcher models to the experimental data.

Raman light scattering on phonons and polaritons is measured in a gallium phosphide sample. An unfocused beam of a 532-nm single-mode laser was used for excitation. A scattered radiation was collected using a mobile mirror of a small diameter, which allowed us to measure spectra of scattered light in a 0.6°–8° range of scattering angles with a total angular spread of 0.4°. For different crystallographic directions, intensities of polarized components of the Raman light scattering on longitudinal, transverse phonons and polaritons were measured in the region of a strong dispersion of the polaritonic branch for three fixed axial scattering angles. Components of scattering on longitudinal optical phonons and polaritons have a strong dependence on a crystallographic direction, as predicted by theory, and the component of scattering on transverse optical phonons did not depend on a crystallographic direction. It was found that the intensity of scattering on transverse optical phonons correlates with a width of a spectral line of scattering on polariton. A mechanism explaining this correlation is proposed.

New high efficiency luminescence films that convert UV radiation in a wavelength range of 220–410 nm into the europium ion luminescence are first obtained using a supramolecular diamond-containing complex of europium(III) with bathophenanthroline. The films allow the degree of radiation monochromaticity to be tuned at the main band of Eu³⁺ ions, centered at 615 nm. The excitation spectrum profile, as well as the half-width of the main emission band at 615 nm (a ⁵D₀–⁷F₂ transition) and the quantum yield values (in a range of ~0.3–0.8), is found to depend on the type of matrix material. The optical materials presented in the present work are promising candidates for the design of various light-emitting devices, such as screens, indicators, solar concentrators, organic LEDs, and laser media.

Amorphous carbon (a-C) thin films are synthesized using a nonequilibrium method of ion-plasma sputtering of a graphite target under argon atmosphere at a constant plasma current. The local structure of carbon films is studied by the Raman spectroscopy method. Using the normal distribution in the decomposition of the Raman spectra, it is found that a peak typical for a phonon density of states with sp³ bond hybridization appears in the frequency region of 1260 cm^–1 at synthesis temperatures of less than 150°C. In addition, the influence of the dimensions of nanostructures composed of sp² sites on the width of optical bandgap and their correlation with the results of X-ray photoelectron spectroscopy (XPS) in a-C films is shown.

Plasmon-coupled luminescence of rhodamine 6G dye molecules on a thin nickel film has been studied experimentally and theoretically. The spatial distribution of fluorescence of dye molecules, which is calculated using the transfer matrix method for describing flat-layered media, is in good agreement with the experimental diagrams obtained for the spatial distribution of radiation with different polarization. The coupling efficiency between the luminophore and nickel film plasmons is experimentally determined.

A technique for detecting and measuring the weak optical anisotropy has been proposed and experimentally implemented. The strontium tetraborate activated by ytterbium ions, which is considered to be an amorphous glass, has been investigated and its anisotropy comparable with the instrumental errors of ellipsometer goniometers has been found and measured. The proposed approach is based on a previously developed effective and relatively simple method, in which the contribution of the surface (transition) layer to the formation of the resulting beam is essentially smaller than the contribution of the bulk material. The relations between the ellipsometer measuring zones have been used. Some important aspects of the optical and mechanical alignment of the ellipsometers have been described as applied to the weak anisotropy investigations.

The form of a quasi-optical equation for a beam of monochromatic radiation propagating through a layer of a weakly absorbing linear medium is analyzed. It is concluded that the standard form of this equation should be modified using an “effective diffusion coefficient.”

The impact of a polychromatic field on a two-level medium is considered in the limit of small amplitudes. In the indicated limit, we obtained asymptotic expansions of the polarization spectra of an arbitrary order of smallness. These polarization spectra were compared with the results of the numerical solution of the density matrix equation. Compared to numerical calculation methods, the asymptotic expansion offers an analytical estimation of the contribution of each individual component of a polychromatic field and a description of the intermode interaction. However, with an increase in the intensity of the driving field, the computational efficiency of the method decreases, since, to achieve the required accuracy, it is necessary to increase the order of the asymptotic expansion.

Transparent ZnO–MgO–Ag₂O coatings are formed on glasses by the polymer–salt method, and the optical properties of these coatings are studied. The optical properties of the films are studied by optical spectroscopy and photoluminescence. The structure of the oxide coatings is studied by X-ray diffraction analysis and scanning electron microscopy. It is found that an increase in the silver concentration in the coatings leads to a decrease in the band gap width of the material. It is shown that the films are characterized by a high transparency in the visible spectral region and can generate singlet oxygen under action of UV radiation (370 nm) and blue light (405 nm).

Studies published in the period from 2014 to 2018 that are aimed at creating nondispersive and photoacoustic IR gas analyzers with LED radiation sources based on А³В⁵ heterostructures and operating in a range of wavelengths from 3 to 5 μm are reviewed. Potential of gas analysis equipment based on the aforementioned LEDs for detecting CO, CO₂, methane, and other gases is analyzed.

The interaction of an electromagnetic H wave with a thin metal film has been calculated with allowance for the ellipsoidal Fermi surface and constancy of the electron mean free path for different angles of incidence of the electromagnetic wave θ and different coefficients of specular reflection q₁ and q₂ at reflection of electrons from the film surfaces. The metal film is between two media with permittivities ε₁ and ε₂. The dependences of reflectance R, transmission T, and absorption A on the effective mass of conduction electrons have been analyzed.

We propose a scheme of a universal block of broadband quantum memory consisting of three ring microresonators forming a controllable frequency comb and interacting with each other and with a common waveguide. We find the optimal parameters of the microresonators showing the possibility of highly efficient storage of light fields in this memory block and we demonstrate the procedure for gluing several memory blocks for increasing the spectral range of the composite quantum memory while maintaining high efficiency.

An ellipsometric method for reconstructing the thickness compositional profile in thin heterostructure nanolayers grown by molecular beam epitaxy on the basis of a cadmium–mercury–tellurium compound has been developed. The method is based on solving an inverse ellipsometric problem with the replacement of part of an inhomogeneous layer with a homogeneous medium with specially selected optical constants. The numerical simulation has confirmed the correctness of this replacement and efficiency of the developed algorithm. Using this method, the active region of a heterostructure consisting of five HgTe quantum wells separated by wide-gap CdHgTe spacers has been investigated. Based on the results of continuous in situ ellipsometry measurements performed during the heterostructure growth, the compositional profiles for all the five sequentially grown quantum wells have been calculated and the high reproducibility of the thickness dependences of their composition has been demonstrated.

We present the results of in vivo optical immersion clearing of human skin by aqueous solutions of some immersion agents (ribose, glucose, and fructose monosaccharides and glycerol), obtained using optical coherence tomography (OCT). To assess the efficiency of optical clearing, we determined the values of the rate of change of the light scattering coefficient, obtained using the averaged A-scan of the OCT signal in the derma section at a depth of 350–700 μm. A good correlation was observed between the rate of change of the light scattering coefficient and the potential of the optical clearing. Using complex molecular simulation of the interaction of a number of immersion clearing agents with collagen mimetic peptide (GPH)₃ using classical molecular dynamics and quantum chemistry, we found correlations between the efficiency of optical clearing and the energy of intermolecular interaction of cleaning agents with a fragment of collagen peptide.

Future development of the method of immersion optical clearing of biological tissues—this method is widely used in the study of the morphology and pathologies of tissues in vitro and considered promising for in vivo applications in biophysical research and medicine—requires knowledge of the details of interaction of immersion liquids with the tissue, in particular, the characteristics both of the tissue dehydration process, which is caused by the osmotic effect of the immersion liquid, and the process of diffusion of the immersion agent (IA) into the tissue. The optical properties of skin dermis, eye sclera, tendon, and many other tissues are determined by the properties of collagen bundles, abundant in these tissues. In the present work, a convenient and reliable technique for monitoring the optical properties and geometry of collagen bundles in the course of their immersion clearing in vitro, based on optical coherence tomography (OCT), is proposed. The main advantage of this technique is that it allows one to monitor changes in the geometric and optical properties of the tissue simultaneously, without interrupting the natural course of the immersion clearing process, and to obtain reliable estimates of the characteristic times and rates of both the process of tissue dehydration and process of diffusion of the IA into the tissue.