Vol 123, No 6 (2017)

The spectroscopic constants (vibrational, rotational, and centrifugal) and the radiative parameters (Einstein coefficients for spontaneous emission, oscillator strengths for absorption, Franck–Condon factors, R_v'v" centroids, and wavenumbers of rotational lines) of rovibronic transitions in the systems of bands B¹Π–X¹Σ⁺ (0 ≤v'≤ 25, 0 ≤v"≤ 49, j = 0, 30, 50, 60, 70) of the LiCs molecule, as well as the radiative lifetimes of the excited electronic state, are calculated. Calculations are performed based on semiempirical potential curves constructed in this work. The calculated spectroscopic constants are compared with experimental values. The radiative lifetimes are calculated for the first time.

A procedure for separating the torsional and rotational motions for molecules with two identical planar tops on a linear core is considered for the example of the allene molecule C₃H₄ in the ground electronic state.

The spectra and amplitude–time characteristics of the radiation of studied Sn and Fe-doped Ga₂O₃ crystals excited with a runaway electron beam and an excilamp with a wavelength of 222 nm were investigated. The main contribution to the luminescence of samples in the region of 280–900 nm under excitation with a beam was shown to be made by cathodoluminescence. In the Fe-doped crystal, a new cathodeand photoluminescence band was detected within a wavelength range of 650–850 nm. In the Sn-doped crystal, Vavilov–Cherenkov radiation was detected in the region of 280–300 nm using a monochromator and a photomultiplier.

The electronic-absorption and luminescence spectra and the kinetics of relaxation of photocurrent in GaSe single crystals and thin films doped with boron atoms are experimentally investigated. Crystals are doped either in the course of synthesis or upon growing single crystals by the Bridgman method. Thin GaSe films are obtained by thermal evaporation of the compound preliminarily doped with boron. An absorption band with the maximum at λ = 925 nm, which is attributed to boron contaminations, is revealed from the comparison of the electronic-absorption spectra of a GaSe crystal and thin films doped with boron. When the crystals are excited with Nd:YAG laser pulses of a duration of 12 ns, it is established that recombination of nonequilibrium current carriers in pure crystals occurs through rapid and slow recombination channels and in crystals doped with boron only through rapid channels. In the region near λ = 932 nm, photoluminescence is observed in the crystals doped with boron, and its half-bandwidth is 15 Å.

A Zn(II) complex with N,N'-bis(5-bromosalicylidene)ethylenediamine exhibiting intense visible blue luminescence is synthesized. It is found that the zinc complex fluoresces at 293 K in both polycrystalline form and in solutions (λ_max = 440 and 450 nm, respectively); the relative fluorescence quantum yields of the complex are determined in dilute ethanol, dimethylformamide, and dimethylsulfoxide solutions.

This paper reports the pH-dependent growth of copper oxide (CuO) nanoparticles by wet chemical precipitation method using pH value of the samples as the only variable parameter. The phase purity, morphology, optical behavior, and elemental analysis of synthesized nanoparticles are shown to be critically dependent on the pH of the samples. Scanning electron microscope (SEM) results shows that a higher pH results well-defined CuO nanoflakes. X-ray powder diffraction (XRD) results disclosed that the growth of pure CuO with monoclinic structure at higher pH 8, whereas mixed phase was formed at lower pH 7. The average crystallite size of samples prepared at pH 8 to 10 was varying from 23.36 to 25.78 nm. The infrared spectroscopy showed that the O–H stretching peaks become narrow with an increase in the pH value. Optical results revealed the existence of the sharp absorption edges with precise excitonic features and photoluminescence bands both located at visible and near infrared spectral region attributed to the excellent optical behavior and narrow size distribution of particles. The additional near infrared band in photoluminescence spectrum located at 860 nm is attributed the defect-related luminescence. The growth mechanism of CuO nanostructures was discussed in the light of our findings.

Using the method of the Green’s function for a wave equation, it is shown that, in a one-dimensional geometry, the field emitted by a resonant medium that is composed by a system of coupled or free charges is proportional not to the acceleration of charges, as is usually assumed, but, rather, to their velocity that they acquire as a result of the action of a light pulse on initially stationary charges. This feature opens up new opportunities for the generation of ultrashort pulses of one-cycle and subcycle durations, as well as for the diagnostics of media and materials using such ultrashort pulses.

The morphology of Ga₂O₃ layers deposited on a silicon substrate by pulse laser deposition is studied using scanning electron microscopy in the thickness range of 30–200 nm. Using spectroscopic ellipsometry in the wavelength range from 250 to 900 nm, the thickness of layers and dispersion of their optical parameters (complex pseudodielectric function ε, refractive and absorptive indices) have been determined and the fraction of voids has been estimated in the scope of the Bruggeman effective medium approximation. In the spectrum of the imaginary part ε₂, there is observed an increase in values in the region of energy E = 4.8 eV corresponding to the direct interband transition in the Ga₂O₃ structure. X-ray structure analysis showed the presence of peaks typical for the β-Ga₂O₃ structure. The results of the investigations can be used for the formation of wide-bandgap gallium oxide layers in developing devices of power electronics and in creating optoelectronic devices for the UV range.

Current approach demonstrates the suppression of optical side-lobes and the contraction of the main lobe in the composite image of two object points of the optical system under the influence of defocusing effect when an asymmetric phase edges are imposed over the apodized circular aperture. The resolution of two point sources having different intensity ratio is discussed in terms of the modified Sparrow criterion, functions of the degree of coherence of the illumination, the intensity difference and the degree of asymmetric phase masking. Here we have introduced and explored the effects of focus aberration (defect-of-focus) on the two-point resolution of the optical systems. Results on the aberrated composite image of closely spaced objects with amplitude mask and asymmetric phase masks forms a significant contribution in astronomical and microscopic observations.

The results of numerical solution of the lidar equation for Raman scattering of light by molecules of hydrogen sulphide in the direction of 180° under detecting molecules of hydrogen sulfide in the atmosphere with concentration at a level of 1016 cm^–3 from a platform in space at heights of the order of hundreds of kilometers in the synchronous photon counting mode have been presented. It is shown that, for such a variant of a lidar and level of concentration of the investigated molecules, the duration of measurement at a wavelength of the laser radiation of 405 nm and altitude range of 100–600 km lies in the range of 0.14–4.9 s. The development of new schemes of lidars opens up additional possibilities for remote detection of low concentrations of hydrogen sulfide molecules from space.

The possibility of a complex approach for studying changes in the system of blood microcirculation and metabolic processes in the biotissue of lower extremities using optical noninvasive methods of laser doppler flowmetry (LDF), fluorescence spectroscopy, and diffuse reflectance spectroscopy in combination with different modes of heating tests has been assessed. Seventy-six patients with type 2 diabetes mellitus, with 14 patients having visible trophic foot impairments, and 48 healthy volunteers have been examined. The parameters of LDF signals and spectra of fluorescence intensity and diffuse reflectance for foot skin have been analyzed. Statistically significant differences in the recorded parameters between the groups under study have been found. It has been concluded that combined application of noninvasive methods of spectroscopy could be used for diagnostics of complications both upon the occurrence of preliminary symptoms of diabetes, when pathological changes are still reversible, and in the presence of impairments to prevent aggravation of the disease and select an adequate correction of the treatment.

A technology for multivalued holographic measurement of a plane angle—a holographic prism, which serves as the basis for a device for calibrating the testing tools for navigational equipment under rolling— has been developed. The holographic prism is a miniature sample of photosensitive material, which contains a system of superimposed holographic gratings, and a laser the radiation of which passes through gratings to form a fan of diffracted beams. The fan in a prism based on a calcium fluoride (fluorite) crystal with color centers contained six out-of-plane beams radiating from a region with a hard-to-localize center. This fact hindered calibration of the measure and its application in the testing device. The use of photothermo-refractive glass as a material for preparing a sample and recording a system of holograms in it makes it possible to eliminate the drawbacks of fluorite-based prism. The number of holograms rises up to 21, the fan becomes in-plane, and its center is localized in a small region, with a size of several tenths of the sample thickness (1–2 mm). The fan beams are energetically homogeneous, and each can be identified when using the fan in a testing device.

The backscattering of light from spherical surfaces characterized by one and two-scale roughness reliefs has been investigated. The analysis is performed using the three-dimensional Monte-Carlo program POKS-RG (geometrical-optics approximation), which makes it possible to take into account the roughness of objects under study by introducing local geometries of different levels. The geometric module of the program is aimed at describing objects by equations of second-order surfaces. One-scale roughness is set as an ensemble of geometric figures (convex or concave halves of ellipsoids or cones). The two-scale roughness is modeled by convex halves of ellipsoids, with surface containing ellipsoidal pores. It is shown that a spherical surface with one-scale convex inhomogeneities has a flatter backscattering phase function than a surface with concave inhomogeneities (pores). For a sphere with two-scale roughness, the dependence of the backscattering intensity is found to be determined mostly by the lower-level inhomogeneities. The influence of roughness on the dependence of the backscattering from different spatial regions of spherical surface is analyzed.