Vol 127, No 5 (2019)

We have compared and analyzed the parameters of the Franck–Condon (FC) and Herzberg–Teller (HT) interactions, which form the fine-structure spectra of stilbene, 1,4-distyrylbenzene, and tetrafluorodistyrylbenzene—compounds that are similar in their chemical structures but differ in the length of π-conjugation and in the presence of substituents in their benzene rings. The numerical values of the FC intramolecular interaction constants have been obtained, and, simultaneously, the values of the HT parameter have been found as quantitative values of the projections of the electronic transition vector of the dipole moment onto the normal vibrational coordinates. We have solved the question of transferability of these parameters in the homologous series of stilbene molecules containing the same sets of structural elements, which has made it possible to extend the use of the fragmentary approach to describe the fundamental bands of organic molecules of different homological series and to solve the problem of studying the structure of the spectra of large molecules.

The effect of narrowing of the absorption line of light alkali metal ⁷Li and ²³Na atoms present in an atmosphere of heavy inert gas (xenon) with an increase in the external radiation intensity has been investigated. For ⁷Li atoms at temperature T = 300 K and buffer gas (Xe) pressure \({{p}_{{{\text{Xe}}}}} = 0.002\) Torr, the linewidth at half maximum decreases by a factor of 1.20 with an increase in the radiation intensity from 1 µW/cm² to 2.5 mW/cm². For ²³Na atoms at T = 600 K and \({{p}_{{{\text{Xe}}}}} = 0.01\) Torr, the linewidth at half maximum decreases by a factor of 1.29 with an increase in the radiation intensity from 1 µW/cm² to 6 mW/cm². The effect of field narrowing of the absorption line is due to the following factors. First, the collisional relaxation of the velocities of light resonance particles in an atmosphere of heavy buffer particles is divided into two stages with significantly different durations: relaxation in the velocity direction (fast stage) and relaxation in the velocity magnitude (slow stage). Second, there are no collisional transitions between hyperfine components of the ground state.

The quantum defect theory is used to test the accuracy of the ab initio and density functional theory (DFT) methods in calculations of the dynamic polarizabilities of diatomic molecules. Our testing is restricted only to those variants of these methods which are most accurate in calculations of static polarizabilities. The testing results show that one of the main errors of the ab initio and DFT methods is related to inaccuracies in determining the energies of excited states, where dynamic polarizabilities have resonant maxima.

We present an ab initio calculation of the structures and the IR spectra of the endofullerene Gd@C₆₀ in different spin states. The lines in the IR spectra of Gd@C₆₀ endofullerenes have been found to lie in the range of 10–1540 cm^–1. The frequencies and the intensities of the lines depend on the spin state and molecular symmetry of the endofullerene. The frequencies of coupled vibrations of the metal atom and the carbon cage have been shown to lie in the range of 10–160 cm^–1 and vary significantly with a change in the spin state. The spin dependence of the vibrational spectra of endofullerenes makes it possible to monitor their spin state by measuring the frequencies of their lines in the IR range, which is important for nanoelectronics and quantum-information science.

The crystal structure and the phonon spectrum of a La₂Zr₂O₇ crystal have been investigated in terms of the MO LCAO approach using DFT hybrid functionals that take into account the contribution of the nonlocal exchange within the Hartree–Fock formalism. The frequencies, symmetry species, and intensities of IR and Raman active fundamental vibrations are determined. Elastic constants are calculated. The calculations have been carried out using the new version of the CRYSTAL program—CRYSTAL17—designed to model periodic structures within the MO LCAO approach.

The optical properties of amorphous nonstoichiometric silicon oxide (SiO_x) films of variable composition (x = 0.62–1.92) formed by plasma-enhanced chemical vapor deposition are studied in the spectral range of 1.12–4.96 eV. Spectral ellipsometry showed that the refractive index dispersion character allows one to assign the formed SiO_x films to silicon-like films, dielectrics, or intermediate-conductivity-type films depending on the content of oxygen in the gas phase during synthesis. A model of the SiO_x structure for ab initio calculations is proposed and describes well the experimental optical spectra. Ab initio calculations of the dependences of the SiO_x refractive index and band gap on stoichiometry parameter x are performed.

A method for generation of droplet quasi-Bessel beams using a conical lens with a rounded tip is demonstrated. The study of the longitudinal distribution of the intensity of the obtained quasi-Bessel beam showed that, due to the interference of two wavefronts that occurred as the generating beam passed through the rounded axicon, periodical intensity pulsations that looked like “drops” of light occurred in the resulting beam. These light beams can be used for micromanipulation of biological objects and in super-resolution microscopy. The application of an axicon with a rounded tip for generation of a droplet beam allows considerable simplification and miniaturization of the experimental setup, which paves the way for multiple practical applications.

The spatial dynamics of a polarized light in a smoothly inhomogeneous anisotropic medium with the admixture of an anisotropically absorbing dye was analyzed. A twist-oriented nematic liquid crystal with pleochroic dye was considered as this medium. A system of coupled reduced equations relative to Cartesian components of the electric component of light wave was derived in the geometrical-optics approximation. The system of coupled complex equations was analytically solved and the behavior of a linearly polarized wave in this medium is analyzed in the case of both absorption and amplification. An asymmetric effect of these two processes on a spatial dynamics of light propagation in the medium is found.

Based on polymers with the addition of azo dyes as chromophores and azopolymers with the same covalently linked chromophores, recording media for polarization holography are created and their properties are studied when recording holograms of a plane wave front with parallel and perpendicular polarization of recording rays. It is found that the diffraction efficiency and the storage time of holograms are much longer in recording media with films of azo polymers in comparison with polymeric solid solutions of azo dyes. In the latter case, the energy of light is spent only for the trans–cis isomerization of azo dye molecules during exposure of holograms and the polymer chains do not undergo deformation with the formation of a surface relief in the polymer film. Therefore, it is preferable to use recording media based on solid solutions of azo dyes in dynamic polarization holography.

A theory of optical two-component pulse of self-induced transparency in a dispersive medium has been developed. Using the generalized version of the perturbative expansion method, the system of material equations for an ensemble of two-level atoms and the wave equation in a dispersive medium are reduced to coupled nonlinear Schrödinger equations. A solution in the form of a phase-modulated two-component \(0\pi \) pulse is obtained. The pulse components oscillate at the sum and difference frequencies in the vicinity of the carrier-wave frequency. Explicit analytical expressions for the parameters and formation conditions of a nonlinear wave, which depend on the dispersive properties of the medium, are presented. Known results are obtained for a particular case.

In the case of a large amount of computation, a situation may arise when the intermediate results of calculations need to be stored for a given time. In this work, we show how to create a hybrid atomic-field cluster state and create a controlled gate in such a way that the results of calculations are recorded under long-lived degrees of freedom of an atomic ensemble and can be stored for a long time.

Changes in the surface morphology and optical properties of the samples of K208 glass with an ITO film are studied after the effect of protons with an energy of 20 keV and a dose of 0.2–1.0 mC/cm² at a proton current density of 9 nA/cm². It is shown experimentally that the presence of the ITO film affects the character of morphology changing and is the main reason for the degradation of the sample optical properties at the proton irradiation.

Interband optical transitions in quantum wires have been theoretically investigated in the model of parabolic potential in electric and magnetic fields directed perpendicular to the nanowire axis. The frequency dependences of the luminescence intensity have been calculated considering the interaction of carriers with a rough surface and with long-wave acoustic oscillations. The graphs of the frequency dependence of the luminescence intensity at different values of electric and magnetic fields, the dependences of the luminescence half-width on the wire radius have been obtained. A comparison with the experiment has also been made.

The spectra of optical density, luminescence, and Raman scattering of crystalline micro- and nanodendrites of zinc and tin sulfides in silicate nanoporous glass (NPG) with an average pore size of 25 nm have been presented. Sulfide nanodendrites have been synthesized by sulfiding zinc and tin nanodendrites grown in the pores of the NPG by electrolysis. It has been shown that the luminescence of nanodendrites is caused by defects in the crystal lattice. The main bands of the Raman spectrum of nanodendrites are related to transverse and longitudinal vibrational modes of hexagonal ZnS (wurtzite) and stretching modes of the 2H polytype of SnS₂ with a hexagonal elementary cell. The obtained results can be used in the creation of chemical and biological sensors, as well as in photovoltaics and photocatalysis.

The conditions necessary for the correct measurement of the width and divergence angle of a laser beam have been determined with consideration for the finite dimensions of the aperture of an emitter by the method based on the estimation of initial spatial moments. It has been shown that the severe requirements disregarded in the corresponding developed standards are imposed on the shape of the spatial intensity distribution in a laser beam cross section in this case.

The decay of thermal radiation emitted by surface layers of carbon materials excited by pulses of a Q-switched neodymium laser is investigated experimentally and theoretically. It is discovered that the decay curves can be approximated with satisfactory accuracy by a sum of two exponential components with decay times of about 10 and 100 ns. Changes in the decay curves under sample irradiation by a sequence of laser pulses can be interpreted as being the result of redistribution of intensities of these two components. Based on the results of computer simulation, the conclusion is drawn that the glow-decay time is determined by the ratio of the penetration depth of the laser radiation and the thermal-diffusion length, which creates an opportunity to determine the coefficient of temperature conductivity in a thin surface layer of the studied material at high temperatures (thousands of Kelvins).

The effect of the excitation of surface plasmon polaritons at the silver–chalcogenide glass interface upon the photostimulated diffusion of silver into chalcogenide was studied for the first time. A high-frequency aluminum diffraction grating with a period of 248.5 nm and a deposited two-layer Ag–As₂S₃ structure was used to excite plasmons. The process of photostimulated diffusion of silver into the chalcogenide layer is accelerated (that is, the photosensitivity of such a structure increases) when a surface plasmon polariton is excited during exposure at the Ag–As₂S₃ interface. The photostimulated changes in the optical characteristics of the structure, including at the initial stage of the photodiffusion process, were monitored by recording the dynamics of changes in the characteristics of plasmon excitation with exposure time.

On the basis of fragments of time-averaged speckle images registered with no stopping of cyclic loading, the features of nucleation, onset, and propagation of a crack in the bulk of a transparent prismatic sample with a sharp V-shaped notch have been found. It has been shown that the first signs of fatigue damage occur not at the top of the notch, but at a distance of 400 μm from it in the sample center within an area with a diameter of 200 μm. After the beginning of the development (“onset”) of the crack, the size of the zone of irreversible processes exhibits an increase by an order of magnitude. The distribution of the refractive index and the density around the crack has been studied based on changing speckle images and with the use of ellipsometry. It has been shown that the maximum value of relative change in density being at least 2 × 10^–3, is located near the crack. The speckle method can serve a basis for the development of nondestructive testing tools and techniques that make it possible to assess the time preceding crack onset according to the changing rate and the limiting values of the refractive index and material density, as well as according to other parameters affecting the change in the optical paths of waves within small areas about 10 μm in size.