


Vol 121, No 3 (2016)
- Year: 2016
- Articles: 24
- URL: https://ogarev-online.ru/0030-400X/issue/view/10065
Spectroscopy of Atoms and Molecules
Collisions of alkali-metal atoms Cs and Rb in the ground state. Spin exchange cross sections
Abstract
Collisions of alkali-metal atoms 133Cs and 85Rb in the ground state are considered in the energy interval of 10–4–10–2 au. Complex cross sections of the spin exchange, which allow one to calculate the processes of polarization transfer and the relaxation times, as well as the magnetic resonance frequency shifts caused by spin exchange Cs–Rb collisions, are obtained.



Investigation of the bistability in J aggregates upon resonant optical excitation with inclusion of pair correlations between molecules
Abstract
A theory of resonant interaction with radiation of J aggregates based on chains of two-level molecules coupled by the retarded dipole‒dipole interaction has been developed. The effect of pair correlations between the chain molecules on the bistable response of this system under the influence of external resonant radiation has been investigated within the homogeneous chain model. Traditionally, these systems have been described using single-particle density matrices corresponding to each molecule. In this description, twoparticle interactions are represented in the factorized form and do not include correlations between the interacting molecules. In this study, the correlation corrections have been estimated taking into account the influence of only the nearest neighbors, while their values have found to be of the same order of magnitude as the factorized two-particle expectation values for which these corrections have been calculated. As a result, the dipole‒dipole interaction of a particular molecule with the nearest neighbors is so strong that the description of this interaction in the factorized form becomes inappropriate and can be used only for a qualitative analysis of the response of the chain. In order to obtain correct quantitative characteristics, it is necessary to abandon the factorization of the two-particle expectation values, at least for nearest neighbors.



Determination of copper content in soils and ores by laser-induced breakdown spectrometry
Abstract
It is demonstrated that the method of laser-induced breakdown spectrometry can be applied for quantitative determination of the copper content at a level of 500–40000 g/t, typical for copper ores and soil in the outcrop areas. To avoid the self-absorption of the resonance copper lines, we studied the most intense nonresonant lines of copper atoms and ions. It is shown that the Cu I 521.82-nm line is rather intense and provides the linear calibration. The copper detection limit for this line of 280 g/t allows its use for rapid mapping of outcrop areas.



Condensed-Matter Spectroscopy
Spectral and luminescent properties of N,N'-bis(5-bromosalicylidene)-1,3-propylenediamine and its zinc complex
Abstract
Zn(II) complex with N,N'-bis(5-bromosalicylidene)-1,3-propylenediamine, which efficiently luminesce in the blue region of the visible spectrum, is synthesized for the first time. It is found that, at 293 K, azomethine and zinc complex fluoresce in both solution and the polycrystalline state. Fluorescence quantum yields of the compounds in diluted dimethylformamide and dimethylsulfoxide solutions are determined.



Analysis of the electronic, IR, and 1H NMR spectra of conjugated oligomers based on 4,4'-triphenylamine vinylene
Abstract
Two types of conjugated oligomers based on 4,4'-triphenylamine vinylene have been synthesized and characterized by the methods of IR, UV–visible, and 1H NMR spectroscopy. The corresponding spectra have also been simulated theoretically at the density functional theory level with application of the B3LYP and BMK hybrid exchange-correlation functionals. A comparative analysis of the experimental and theoretical spectra of polymers and oligomers has revealed regularities of the manifestation of spectral signals depending on the conjugation chain length and the presence of a substituent in the triphenylamine core. It has been established, in particular, that the absolute intensity of IR bands satisfies a linear dependence with increase in the degree of polymerization; however, no frequency shift is observed at the same time. The position of the main peak in electron absorption spectra demonstrates the bathochromic shift with an increase in the oligomeric chain length due to the narrowing of the energy gap between the boundary molecular orbitals. Based on the theoretical estimation of the hydrogen atoms chemical shifts, the signals of various protons types in the strongly broadened experimental 1H NMR spectra of the bis-(4-iodine phenyl)-phenylamine and N,N-bis-(4-iodine phenyl)-4'-(phenylethynyl)-phenylamine polymerization products have also been identified.



A study of the structural and spectral characteristics of free and bound water in kaolinite
Abstract
The dependence of the Si–O stretching vibration line intensity in the IR spectrum of kaolinite on the humidity of this mineral has been experimentally investigated. The experimental data were interpreted on the basis of density functional theory (DFT) calculations with allowance for the real crystallographic features of the kaolinite sample, determined by structural analysis. Some specific features of the intensity behavior in the plastic state are revealed, which can be used to develop techniques for determining its limits. The differences in the O–H bond lengths and H–O–H angles for the H2O molecules adsorbed by basal surfaces and located in the porous space of the mineral are determined. Based on the DFT data, it was found that bond lengths and bond angles for a water molecule adsorbed on the siloxane surface are systematically smaller than for a water molecule adsorbed on the hydroxyl surface.



Optical properties and electronic structure of BiTeCl and BiTeBr compounds
Abstract
Optical properties of BiTeCl and BiTeBr compounds with a strong Rashba spin–orbit coupling are studied in the 0.08–5.0 eV range using the optical ellipsometry method. Fundamental characteristics of the electronic structure are obtained. Similarly to BiTeI, spectra of the imaginary part of dielectric permittivity constant ε2(E) in the energy interval between the plasma edge and the threshold of an intense interband absorption (0.7 eV in BiTeCl and 0.6 eV in BiTeBr) display a fine structure of electronic transitions at 0.25 and 0.55 eV in BiTeCl and 0.20 and 0.50 eV in BiTeBr. These features are assigned to electronic transitions between the bulk conduction zones split by the Rashba spin–orbit interaction. The parameters of the electronic structure of BiTeCl and BiTeBr are compared with the BiTeI compound that was studied earlier. In the BiTeCl–BiTeBr–BiTeI row, the absorption edge and main features of the fundamental absorption exhibit a shift to low energies.



Polarized optical absorption of MnGa2S4 single crystals
Abstract
Optical absorption of MnGa2S4 single crystals is studied at two light polarizations (E ||C and E⊥ C). The polarization splitting of the absorption edge points to a splitting of the valence band of MnGa2S4. A contribution to the crystal-field splitting is made by two factors, namely, by a difference in the pseudopotential of cationic sublattice atoms and by tetragonal compression of the lattice along the C axis. A scheme of optical transitions in MnGa2S4 in the Brillouin zone center is suggested, according to which the optical transitions Г3 + Г4 → Г1 occur in the polarization E ⊥ C, and the Г2 → Г1 transitions occur in the polarization E || C.



The effect of a gas environment on the fluorescence intensity of quantum-dot composite systems
Abstract
The fluorescence kinetics of a composite structure based on colloidal CdSe/ZnS core-shell quantum dots deposited on an array of GaAs nanowires in atmospheres of different gases is studied upon excitation by cw laser radiation. It is suggested that the fluorescence enhancement mechanism consists in the transfer of part of the vibrational energy of quantum dots to surrounding gas molecules due to inelastic collisions.



Inorganic phosphors in lead–silicate glass for white LEDs
Abstract
Luminescent composites of the “phosphor-in-glass” type, based on a highly reflective lead–silicate matrix and fine-grained powders of YAG:Ce3+ and SiAlON:Eu2+ crystals, are developed and synthesized. Phosphor and glass powders are sintered at a temperature of 550°C to obtain phosphor samples for white LEDs. The composites are analyzed by X-ray diffraction and luminescence spectroscopy. The dependence of the light quantum yield on the SiAlON:Eu2+ content in the samples is investigated. A breadboard of a white LED is designed using a phosphor-in-glass composite based on lead–silicate glass with a low glasstransition temperature. The total emission spectra of a blue LED and glass-based composites are measured. The possibility of generating warm white light by choosing an appropriate composition is demonstrated.



Photolysis of light-transforming polymer materials on the basis of europium(III) nitrate with 1,10-phenanthroline and anthranilic acid
Abstract
Light-transforming polymer materials on the basis of europium(III) nitrate with 1,10-phenanthroline and anthranilic acid, having an intense luminescence in the 400–650 nm spectral range, were obtained. It is shown that the photostability of the polymer materials on the basis of the obtained compositions is higher than of polymer materials activated by europium(III) compounds. Luminescent and photochemical characteristics of the obtained polymer compositions are determined by the molar ratio of the dopants: the maximum luminescence intensity and photostability is characteristic for the polymeric material containing europium(III) nitrate with 1,10-phenanthroline and anthranilic acid at a molar ratio of 1: 2.



Nonlinear and Quantum Optics
Formation of solitons and realization of the superluminality effect upon femtosecond pulse propagation in a medium containing gold nanoparticles
Abstract
Based on computer simulation, we demonstrate the possibility of formation of solitons upon propagation of a femtosecond laser pulse in a medium containing gold nanoparticles in the presence of two-photon light absorption. The solitons are formed when the laser pulse induces a positive phase grating. The speed of solitons substantially exceeds the speed of laser radiation propagating in a linear medium.



Observation of parametric nonadiabatic excitation of collective resonances under femtosecond optical pumping of a dense resonant extended medium without population inversion under the conditions of strong light-matter coupling
Abstract
We experimentally studied the superradiance of the resonant line of rubidium under femtosecond optical pumping of a dense extended medium without population inversion under conditions of strong lightmatter coupling. Substantial self-splitting of superradiance components is observed.



Determination of the stimulated raman scattering threshold for a pump pulse of arbitrary width
Abstract
A theoretical solution to the problem of determining the stimulated Raman scattering (SRS) threshold has been found within the undepleted pump approximation for a pump pulse of arbitrary width, which distinguishes it from the known solutions for the limiting cases of very short (highly transient SRS) and very long (quasi-steady-state SRS) pump pulses with respect to the oscillation dephasing time of the SRS medium. The general formula of the theoretical estimate of SRS threshold, in dependence of not only the pump radiation intensity and the SRS interaction length but also the pump-pulse width, is obtained based on the found solution. The theoretical estimate of the SRS threshold has been shown to be in good agreement with the experimental results on the excitation of picosecond SRS in crystals, which justifies the new express method for estimating the SRS gain in experimental measurements of the picosecond SRS threshold.



Dependence of the time of the appearance of a Stark echo response on irreversible relaxation of a system
Abstract
The dependence of the time of the appearance of a Stark (gradient) echo response on the irreversible transverse relaxation time of a system in the nanosecond range and on the width of the excitation region of an inhomogeneously broadened line has been investigated. It has been shown that the use of nonresonant laser pulses with an artificially created spatial inhomogeneity makes it possible to determine the relaxation time in the nanosecond range from the time of the appearance of a Stark (gradient) echo response, which is a more accurate method than the method of determining the relaxation time from the decay of the intensity by varying time intervals of the exposure to inhomogeneous electromagnetic fields.



Quantization of electromagnetic field and analysis of Purcell effect based on formalism of scattering matrix
Abstract
We have developed a rigorous self-consistent approach for the quantization of electromagnetic field in inhomogeneous structures. The approach is based on utilization of the scattering matrix of the system. Instead of the use of standard periodic Born-Karman boundary conditions, we use the quantization condition implying equating eigenvalues of the scattering matrix (S-matrix) of the system to unity (S-quantization). In the trivial case of uniform medium boundary condition for S-quantization is nothing but periodic boundary condition. S-quantization allows calculating modification of the spontaneous emission rate for arbitrary inhomogeneous structure and direction of the emitted radiation. S-quantization solves the long-standing problem coupled to normalization of the quasi-stationary electromagnetic modes. Examples of application of S-quantization for the calculation of spontaneous emission rate for the cases of Bragg reflector and microcavity are demonstrated.



Physical Optics
Effect of Mannosylerythritol lipid-A on light scattering of AOT/D2O/Octane
Abstract
The light scattering technique is used for the study of interaction of Mannosylerythritol lipid-A on AOT/D2O/Octane. The collective diffusion of AOT/D2O droplets soluble in Octane mixed with lipid is founded from a correlation function of light scattering. We focus on the variation of the dynamic behavior of droplets as a function of the lipid concentrations and the size of droplets. The increase of concentration of Mannosylerythritol lipid-A on microemulsion decreases the dynamic of droplets. The SAXS experiment shows the size and the interaction of the droplets change by increase of Mannosylerythritol lipid-A concentration. A hard sphere model can describe the interaction of lipid with AOT/D2O droplets.



Ultrasonic diffraction of Bessel light beams in uniaxial gyrotropic crystals
Abstract
Specific features of the acousto-optic diffraction of Bessel light beams propagating in the vicinity of the optical axis of a uniaxial gyrotropic crystal have been investigated. The dependences of the diffraction efficiency on the acousto-optic interaction length, ultrasound power, and polarization state of the incident Bessel light beam have been analyzed using the coupled-wave equations and the overlap-integral method. It is shown that polarization-independent diffraction of Bessel light beams is observed in paratellurite crystals, when the Bragg diffraction efficiency is independent of the polarization state of the incident beam. The physical reason for this diffraction has been established (both theoretically and experimentally) to be simultaneous implementation of two processes of anisotropic scattering, at which the Bragg synchronism conditions are satisfied for orthogonal polarized Bessel beams with elliptical polarization.



Analytical solution of the direct problem of ellipsometry for some profiles of optical constants of inhomogeneous layers
Abstract
Differential equations that describe the reflection of polarized light from an optically inhomogeneous medium are considered. In the approximation of small variations of the refractive index, analytical expressions for the reflection coefficients are obtained for both types of polarization for the exponential and harmonic profiles of the optical constants. The accuracy of the obtained expressions is estimated by numerical simulation. It is found that analytical formulas describe well the behavior of the ellipsometric parameters of periodic structures based on Hg1–xCdxTe with a sinusoidal profile of the refractive index.



Formation of periodic phase structures in a photopolymerizable layer by nonstationary light beams
Abstract
Photopolymerization of a composite containing a nonpolymerizable component under the action of nonstationary optical radiation is studied. It is shown that the diffusion displacement of the nonpolymerizable component at the illuminated region boundary is caused by the appearance of the monomer concentration gradient, which, in turn, is induced by nonuniform photoinitiation. The action of radiation with a nonstationary intensity distribution makes it possible to form a periodic refractive index structure in the volume of the photopolymerizable material. The possibility of optical formation of polymer phase gratings by moving the shadow boundary stepwise along the polymerizable layer is studied numerically and experimentally.



A study of refraction of a cylindrical laser beam in stratified liquid
Abstract
Refraction of a cylindrical laser beam in a transition layer at the interface of two liquids with different optical characteristics is studied theoretically and experimentally. A theoretical basis for calculations of the beam trajectory in the transition layer of stratified liquid is given. Two- and three-dimensional images (2D and 3D refractograms) of a cylindrical laser beam inside and outside the media are obtained on the basis of a tangential model of the refractive index profile. The influence of the parameters of the laser beam and media on the appearance of refractograms is studied and the optimal experimental conditions are selected with the use of computer simulation. A scheme of the setup for recording digital 2D refractogram and experimental results are presented. Algorithms for digitizing experimental images and for their comparison with calculated refractograms to determine the refractive index profile in the transition layer based on the tangential model are developed.



Geometrical and Applied Optics
An imaging Fourier transform spectroradiometer with a multi-element photodetector for the spectral range of 7–14 μm
Abstract
The construction and principle of operation of a imaging Fourier transform infrared spectroradiometer (FTIR spectrometer) equipped with a cooled 32-area photodetector designed for spectral analysis of open atmospheric paths are considered. The main technical characteristics of the Fourier spectrometer are reported. The technique of visualization of the detected vapor cloud is described. The results of field experiments using the imaging FTIR spectrometer are shown. Based on these results, the dynamics of motion of the cloud of material has been investigated, its angular and linear velocities have been estimated, and data on propagation of the cloud of material and change in its angular sizes in air have been obtained. A technique for analyzing data provided by two FTIR spectrometers is given, based on which one can estimate the size of the cloud and the distance to it from each device. It is shown that the results of detection of the cloud of material by the imaging FTIR spectrometer can be used to predict the propagation of material under study in space.



The influence of an external cavity on the emission spectrum of a mercury germicidal lamp
Abstract
The spectrum of emission from the cylindrical duralumin cavity of a TUV 8wG8 T5 UV industrial germicidal mercury lamp is studied. It is shown that, due to reflection from the inner surface of the cavity and reabsorption in the gas discharge, the resonance line of a mercury atom is significantly weakened. The dependence of the resonance line intensity on the discharge current has a maximum, and the discharge current corresponding to the intensity maximum depends on the reflection coefficient of the inner surface of the cavity.



Thermal deformations of a glass spherical satellite
Abstract
The effect of the kind of the reflecting coating of a glass spherical satellite on thermal deformations caused by the solar irradiation is considered. Two types of coating deposited on one of the hemispheres are considered: aluminum with a protective layer of bakelite varnish and interference dielectric coating for two orientations of the satellite orbit. Structures of a multilayer dielectric coating and technologies of its deposition are described.


