


Vol 127, No 5 (2019)
- Year: 2019
- Articles: 28
- URL: https://ogarev-online.ru/0030-400X/issue/view/10114
Spectroscopy and Physics of Atoms and Molecules
The Effect of Fluorine Substituents on the Intra- and Intermolecular Interaction Parameters of 1,4-Distyrylbenzene Molecules
Abstract
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.



Optical Radiation of Atmospheric Pressure Plasma Jets Excited by a Barrier Discharge
Abstract
The luminescence spectra of plasma jets formed by a barrier discharge at atmospheric pressure in argon–air and helium–air mixtures have been studied experimentally in the spectral region of 270–900 nm. It is shown that the emission spectra of plasma jets are represented mainly by electronic-vibrational transitions of the second positive system of neutral nitrogen molecules in the ultraviolet range of the spectrum. The radiation powers of the studied mixtures are compared.



Narrowing of the Absorption Line of Light Alkali Metal Atoms in an Atmosphere of Heavy Inert Gases at Growing Radiation Intensity
Abstract
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.



Physically Correct Configuration Spaces in the Description of the Internal Dynamics of a Rigid Molecule
Abstract
A family of configuration spaces in the description of the internal dynamics of a rigid molecule has been considered. It has been shown that the requirement of the physical correctness of the description leads to serious restrictions for such spaces. In particular, only spaces satisfying the Eckart condition are allowed for a nonlinear rigid molecule.



Dynamic Polarizabilities of Diatomic Molecules: A Comparison of the ab initio and Density Functional Theory Methods with the Reduced-Added Green Function Method of the Quantum Defect Theory
Abstract
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.



Comparison of the Radon–Nikodym Method with a Multistage Relaxation Model in the Analysis of the Fluorescence Dynamics of a Cold Atomic Ensemble
Abstract
The fluorescence of cold atoms, cooled to ultra-low temperatures and excited by pulsed laser radiation, is calculated. The fluorescence of cold atoms is calculated based on the solution of the non-steady-state Schrödinger equation for a combined system of atoms and an electromagnetic field. A universal function is proposed in the work showing the deviation of the fluorescence decay at the end of the pulse from the single-exponential model. To analyze the dynamics of fluorescence, a Radon–Nikodym method has been used based on the studies on the eigenvalues of a matrix constructed on the basis of the fluorescence signal. It is shown that a correlation exists between the parameter of distribution asymmetry inherent in signal matrix eigenvalues, and the temporal law of fluorescence decay. As an alternative method of fluorescence analysis, a multistage relaxation model is used, caused by collective multiatomic effects. The values of characteristic amplitude and relaxation time both at short times (“superradiance”) and at long times (“subradiance”) have been found.



Spin-Dependent Vibrational Spectra of the Gd@C60 Endohedral Metallofullerene
Abstract
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.



On the Selectivity of Population of the Neon Excited Levels in the Decaying He–Ne Plasma
Abstract
The results of a spectroscopic study of the afterglow of a pulsed discharge in a He–Ne mixture are presented, showing the unique selective population of the upper level of the 2p54p configuration (3p1 in Paschen’s notation) of a neon atom at a helium pressure of tens of Torr. The main measurements were conducted under conditions of competition between the excitation transfer from metastable He atoms (21S0) and the dissociative recombination of HeNe+ ions with electrons as sources of excited atoms. Helium pressure PHe ≈ 0.08–20 Torr, neon PNe ≈ 0.0005–0.003 Torr, the electron density [e] < 1011 cm–3. The results of the experiment indicate the existence of a mechanism that forms with an increase of helium pressure such a distribution of populations over 2p54p levels, in which more than 60% of the radiation flux of 2p53s ← 2p54p transitions is concentrated in one spectral line of 352.0 nm.



Spectroscopy of Condensed States
Phonon Spectrum of La2Zr2O7: ab initio Calculation
Abstract
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.



Spectral-Luminescent Properties of Mixed-Ligand Europium(III) Complexes with p-Methylbenzoic Acid
Abstract
The spectral-luminescent properties of europium(III) complexes with p-methylbenzoic acid and nitrogen- and phosphorus-containing neutral ligands of compositions [Eu(p-MBA)3 · D]2 · xH2O and [Eu(p‑MBA)3 · 2H2O]n, where p-MBA is the anion of p-methylbenzoic acid and D is 1,10-phenanthroline (phen), 2,2' dipyridyl (dipy), triphenylphosphine oxide (tppo) (х = 0), hexamethylphosphortriamide (hmpa) (x = 1), or benzotriazole (bt) (x = 2) are studied. The electronic absorption spectra, the luminescence excitation spectra, and the Stark structure of 5D0−7Fj ( j = 0–2) electronic transitions in low-temperature luminescence spectra of complex europium(III) p-methylbenzoates are analyzed. It is found that the excitation energy transfer to europium ions occurs from the levels of both p-methylbenzoic acid and neutral ligands.



Optical Properties of Nonstoichiometric Silicon Oxide SiOx (x < 2)
Abstract
The optical properties of amorphous nonstoichiometric silicon oxide (SiOx) 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 SiOx 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 SiOx structure for ab initio calculations is proposed and describes well the experimental optical spectra. Ab initio calculations of the dependences of the SiOx refractive index and band gap on stoichiometry parameter x are performed.



The Influence of the Properties of an Aqueous Medium on Dimegin Aggregation
Abstract
The influence of the properties of an aqueous medium on aggregation of dimegin, photoditazine, and radachlorin is comparatively studied. It is noted that the molar extinction nonlinearly depends on the concentration of photosensitizer in solution and the degree of nonlinearity is different for the pharmaceutical form of solutions and solutions prepared with the use of freeze-dried photosensitizer powders. It is shown that the use of surfactants (Pluronic F-127 and polyvinylpyrrolidone) somewhat reduces problems related to aggregation of photosensitizers under study.



Generation of Droplet Quasi-Bessel Beams Using a Semiconductor Laser
Abstract
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.



Physical Optics
Geometrical Optics of a Twist-Oriented Nematic Liquid Crystal with Anisotropic Absorption
Abstract
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.



Holography
Recording Polarization Holograms in Polymer Films with Azo Dyes and Azo Polymers
Abstract
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.



Nonlinear Optics
A Phase-Modulated Two-Component Pulse in a Dispersive Medium
Abstract
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.



A Modified Drude–Lorentz Model That Enables Taking into Account Topological Characteristics of a Medium
Abstract
The Drude–Lorentz model, which makes it possible to describe a nonlinear response of a dielectric or conducting medium, can be suited for the description of nonlinear nonresonant responses of some exotic media: topological insulators, a Weil semimetal, or a Dirac metal. A generalized Drude–Lorentz model and its simplified version, in which topological effects are taken into account to a minimum extent, are presented. As an example of application of the simplified model, the second-order nonlinear conductivity is derived, which is responsible for the second harmonic generation and the effect of optical rectification. It is shown that the ratio of the topological conductivity to the ordinary linear conductivity contains constants that are proportional to the fine structure constant and the axion field gradient.



Quantum Optics
Controlled Logic Gate Based on a Four-Node Linear Hybrid Cluster State
Abstract
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.



Optical Materials
The Influence of Proton Irradiation on Properties of Glass with ITO Coating
Abstract
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.



Application of Fe–graphene Oxide Nanocomposite to Improve SERS Intensity of Polyaromatic Hydrocarbons
Abstract
Raman spectroscopy is used to provide a structural finger-print by which molecules can be identified. SERS technique offers many orders of magnitude enhancement in initial weak Raman signal of some molecules. To detect Raman signal of pyrene, magnetic properties of iron nanoparticles (Fe NPs) was employed along with graphene oxide (GO). Significant differences were discovered in performance of five different SERS substrates which were prepared using magnetized and non-magnetized Fe NPs-GO nanocomposites (FNRC) and Ag nanoparticles. UV-Vis, Raman and FE-SEM analysis presented complete formation of Ag-NPs, GO and FNRCs. The quantity of enhancement measured showed different enhancements from 1.09 up to 3.54 times for pyrene solution on magnetized Fe NP-GO nanocomposite. SERS enhancement showed a reverse relation with GO/Fe precursor rate. Raman shift suggested formation of new bonds. 2.017 RSD factor presented very fast performance only 10 seconds after irradiation of magnetized FNRCs.



Optics of Low-Dimensional Structures, Mesostructures, and Metamaterials
Influence of Electric and Magnetic Fields on Interband Luminescence in Semiconductor Quantum Wires
Abstract
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.



Optical Coefficients of Nanoscale Copper Films in the Range of 9–11 GHz
Abstract
The reflectance, transmittance, and absorption coefficient of ultrathin copper films on a quartz substrate have been measured in a waveguide at frequencies of 9–11 GHz. Films less than 5 nm thick are oxidized almost completely and transparent to microwave radiation. A conducting layer is formed at a film thickness above 5 nm; however, the reflectance increases with thickness in the range of 5–15 nm more slowly than is yielded by calculations using the model conductivity of a continuous film. These results can be explained by the film morphology.



Optical Properties of Nanocomposites Based on Zinc and Tin Sulfides in Nanoporous Silicate Glass
Abstract
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.



An Ellipsometric Study of Thin-Film Structures of Amorphic Hydrogenized Carbon and Gold Nanoparticles
Abstract
Optical сonstants of an amorphous hydrogenated carbon (a-C:H) film and its hybrid structure with granular gold film before and after annealing at 300°C have been investigated by spectral ellipsometry. Dispersions n(λ) and k(λ) of the a-C:H film and its thickness have been identified using the Cauchy approximation. The spectral features of the layer of Au plasmon nanoparticles deposited on the a-C:H surface have been modeled in the form of an effective medium and Lorentz oscillator. The parameters of the films and their thickness have been determined by fitting the calculated spectra to the ψ(λ) and Δ(λ) ellipsometric spectra. The obtained data have been used to determine the Lorentz oscillator parameters in the model of an a‑C:H/Au two-layer structure. The intensity of the maxima in the n and k spectra increased, their position shifted to the blue region, and the half-width of the bands decreased as a result of the a-C:H/Au structure annealing. The observed changes in ellipsometric spectra are fully consistent with the spectrophotometric data of this structure.



High-Precision Optical Measurements and Metrology
The Effect of the Limited Aperture of an Emitter on the Width and Divergence Angle of a Laser Beam
Abstract
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.



Optics of Surfaces and Interfaces
Decay Kinetics of Thermal Radiation Emitted by Surface Layers of Carbon Materials under Pulsed Laser Excitation
Abstract
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).



Plasmonics
Plasmon-Stimulated Photodoping in the Thin-Layer As2S3–Ag Structure
Abstract
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.



Applied Optics
Assessing Fatigue Damage in Organic Glass Using Optical Methods
Abstract
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.


