卷 121, 编号 5 (2016)

The problem of changes in the energy level classification of a nonrigid molecule upon a change in its equilibrium configurations, in the case in which different possible geometries of such configurations correspond to different point groups, is considered for the example of the nonrigid dimethylacetylene molecule CH₃C₂CH₃ in the ground electronic state.

Atomic argon spectrum in the range of 1200–2000 cm^–1 has been recorded by time-resolved Fourier transform spectroscopy. The lines have been identified using the oscillator strengths calculated by the quantum-defect method. Previously unknown energies of the 6h levels of Ar I have been found from the spectrum.

Main patterns of structure formation of composite liquid crystal (LC) media and their classification according to the percentage content of liquid crystal and polymer are considered. Their properties are compared with the properties of homogeneous LC layers and the opportunities of their practical use in optical modulators are discussed. It is shown that, at small (10 wt %) monomer concentrations in the composite, its polymerization leads to formation of a thin-wall network which separates the liquid crystal into domains and provides an uniform orientation in the bulk. The polymer network increases the elasticity of the layer and decreases the relaxation time, but the devices usually work in polarized light and use the same principle as the devices filled with pure LC; i.e. the phase of the light or its polarization changes due to a change in the effective refraction index. However, the division of the LC volume into relatively autonomous domains also allows one to create a polarization-independent device based on the scattering effect. By increasing the relative content of the monomer, it is possible to ensure formation of a porous polymer matrix with inclusions of isolated from each other LC droplets. Such polymer-dispersed LC in its initial state either scatter the light of any polarization and becomes transparent state when an electric field is applied, or, with the use of special methods, the switch-off and switch-on states are swapped (“reverse mode” devices). The main advantages of the composite media are independence of polarization, mechanical strength, and small relaxation times, while the main disadvantages are increased power consumption, high polarization-independent optical losses, and significantly lower contrast. Possible ways to increase the contrast are described.

The IR photoabsorption cross section of a semiconductor nanoparticle has been calculated. Light is absorbed by conduction electrons and trapped electrons in the volume and surface of the nanoparticle. Electron concentrations have been obtained by minimizing the total free energy of charges in the system. The photoabsorption cross section has two characteristic maxima corresponding to the absorption by conduction electrons and by trapped electrons in the nanoparticle volume. The number of trapped electrons on the surface is relatively small, so that they do not contribute to the total cross section.

We have studied the IR polarized reflection spectra of LiCaAlF₆ crystal in the range of 50–2000 cm^–1 and have obtained parameters of dipole phonons. In order to calculate the electronic and vibrational properties of the crystal, we have applied the density functional method with the basis sets of Gaussian functions and plane waves. We have shown that the structure of electronic bands has a direct energy gap. The projected densities of electronic states of atoms, the Born effective charges, and the Mulliken populations have been found to be consistent with the ionic–covalent character of cation–fluorine interatomic bonds. The dielectric properties in high and low-frequency limits have been calculated. We have examined the longitudinal–transverse splitting of dipole modes and have revealed a phonon with an inverted splitting. The theoretical IR reflection and Raman spectra have been found to agree well with experiment. Based on the analysis of the dispersion of phonons in the Brillouin zone, we have revealed an effect of the “quasi-doubling” of the crystal cell along the z axis due to the competing interactions of atoms with nearest and next neighbors. We have found that phonons with frequencies higher than 500 cm^–1 are separated by an energy gap and have predominantly stretching character of vibrations.

The optical properties of fluorophosphate glasses with CdSe quantum dots are studied. Secondary heat treatment at a temperature exceeding the glass transition temperature resulted in the formation of quantum dots with sizes of 3.7–6.2 nm. The influence of the semiconductor component concentration on the spectral-luminescent characteristics of glasses is shown. It is experimentally demonstrated that glasses with a lower CdSe concentration have a higher absolute luminescence quantum yield.

The problem of control for the quantum statistics of dissipative vortex optical solitons when using the Raman scheme of spin-flip transitions in an optical fiber doped with narrow-bandgap semiconductor quantum dots is considered. The possibility of forming individual bounded nonclassical quadrature squeezed light regions appearing within the spatial profile of a formed vortex soliton is demonstrated.

The problem of dynamics of propagation of extremely short optical pulses (light bullets) with a Bessel cross section in inhomogeneous medium of carbon nanotubes has been considered. It is numerically shown that the optical pulse propagation is stable and steady.

The modified Ambartsumyan method of addition of layers is used for solving the problem of oblique light propagation through a layer of gyrotropic metamaterial in the field of two counterpropagating ultrasonic waves. It is shown that the studied system can operate as a tunable optical diode. The possibility of controlling the system parameters by changing the parameters of ultrasonic waves is studied.

The optical properties of multilayer bimetallic films composed of silver and gold nanoparticles have been investigated. The dependence of the transmission spectra of the films on their morphology is demonstrated. A finite-difference time-domain (FDTD) simulation has confirmed that there is a dependence of the transmission spectra on the average distance between particles and the number of deposited layers.

It is shown that effects of self-visualization of transparent objects and self-inversion of nontransparent ones are possible when an illuminating beam passing through them is focused into a (weakly) absorbing air medium at the initial stage of the thermal self-action of the beam. A model experiment was carried out in an optically thick cell with air at atmospheric pressure with addition of a small quantity of molecular bromine as a partial radiation absorber. The required power for the implementation of the processes was P = 200 mW at wavelength λ = 0.53 µm.

Scheme of an LED optrode for detecting sulfur dioxide in the air is considered. The components of the device are (1) a glass plate coated with a copolymer film of n-decylmethacrylate and styrene sulfonate with ion-coupled cation of the brilliant green dye, (2) an LED emitting at a wavelength of 655 nm, and (3) a metal housing. The nominal static conversion function of the device and its sensitivity are analyzed on the basis of mathematical modeling. It is established that the maximum sensitivity in determining the sulfur dioxide concentration in the air is achieved in the case in which the glass plate of the optrode is covered with a polymer film characterized by a specific value of the optical density in pure air containing no sulfur dioxide. For example, for a sulfur dioxide concentration close to zero, the film optical density should be close to one. The presented results allow one to make an optrode suitable for ensuring environmental and sanitaryhygienic safety. The device provides the ability to create analyzers for the measurement of sulfur dioxide in air that have small overall dimensions, power consumption, and cost.