卷 125, 编号 6 (2018)

The fine-structure parameters are calculated by a semiempirical method for six \(1sng\) configurations of a helium atom using new refined energy values. After diagonalization of second-rank energy-operator matrices (levels \(^{3}{{G}_{4}}\) and \(^{1}{{G}_{4}}\)), the discrepancies between the calculated and experimental energy values are virtually equal to zero. The main concern was with the study of the Zeeman structure in order to determine the gyromagnetic ratios for all four levels of configurations. This is topical because analogous experimental data are absent for the studied configurations. The gyromagnetic ratios can be calculated only in the linear region. This region has been established for all the considered configurations. The specific features of Zeeman splitting—crossings and anticrossings of magnetic sublevels—were also studied. The data obtained can serve as a guide for further experimental studies.

The circular dichroism effect has been investigated for atomic transitions of the Rb D₁ line in magnetic fields of up to 3 kG using circularly polarized σ⁺ and σ⁻ radiation. The process of selective reflection from a 350-nm-thick nanocell has been used, which makes it possible to form narrow atomic lines and observe separately the behavior of individual transitions. Two groups consisting of six (⁸⁵Rb atoms) and four (⁸⁷Rb atoms) transitions are formed in magnetic fields B > 0.5 kG upon σ⁺ and σ⁻ laser excitation. All transitions have been identified. It is shown that the strongest transitions for ⁸⁷Rb and ⁸⁵Rb atoms in magnetic fields of up to several kG are formed under σ⁻ irradiation. A further increase in the magnetic field makes it possible to attain the Paschen–Back regime on a hyperfine structure, for which the probabilities of transitions upon σ⁺ and σ⁻ excitation become identical. The theoretical model and experiment are in good agreement.

Using a hypocycloidal electron spectrometer, the total scattering cross section of slow (0–9 eV) electrons and the dissociative electron attachment cross section for thymine molecules in the gas phase were measured. The ionization cross section for a thymine molecule was studied in the energy range of 9–32 eV. Some features were found in the scattering cross section, caused by the formation and decay of short-lived states of the molecular negative ion. Three of them (E = 0.32, 1.71, and 4.03 eV) relate to shape resonances; the others, which are observed for the first time, refer to the Feshbach resonances (or core-excited resonances). In the total dissociative attachment cross section in the energy range of E < 4 eV, a clear structure is observed due to the formation of a negative ion (T–H)^–, and a less intense structure associated with the total contribution of fragment thymine ions is found above 4 eV. The correlation of the features found in the total scattering cross section and in the dissociative attachment cross section is assessed. The absolute total scattering cross section was obtained by normalizing the measured curve to the theoretical calculation. In the total ionization cross section, features are observed that are associated both with the effect of the formation of fr-agment ions and with ionization due to the ejection of electrons from the orbitals of the outer shell of the molecule.

The band spectrum and density of states of the Tl₄CdI₆ crystal have been investigated. Based on theoretical calculations, the electron and hole effective masses have been determined, the localization of the minimum band gap has been found, the origin of the conduction and valence bands has been established, and the nature of the direct-gap transition has been disclosed. Photoluminescence spectra and photoluminescence band excitation spectra at a temperature of 90 K have been experimentally detected. The identification and nature of the observed bands are discussed.

The thermal stability of surface plasmon resonance in a-C:H〈Ag〉 and a-C:H〈Ag + TiО₂〉 nanocomposite films is studied. The films were deposited by ion-plasma magnetron sputtering of a combined graphite-metal target in the atmosphere of the argon and methane mixture. The structure and optical properties of nanocomposite films were studied using transmission electron microscopy and optical spectroscopy, respectively. It is found that surface plasmon resonance in the a-C:H〈Ag + TiО₂〉 films persists to the annealing temperature of 450°C in argon atmosphere, whereas in a-C:H〈Ag〉 films, surface plasmon resonance disappears at the annealing temperature of 350°C. It is shown that annealing at 350°C leads to the significant increase in the diameter of silver nanoparticles in the structure of the a-C:H〈Ag〉 films. In the a-C:H〈Ag + TiO₂〉 films, along with the appearance of silver nanoparticles with a large diameter, silver nanoparticles with a small diameter are present, which remain after annealing at this temperature. The higher thermal stability of surface plasmon resonance in the a-C:H〈Ag + TiО₂〉 films is explained by the presence of TiO₂ nanoparticles in the structure of films, which inhibit the coalescence of silver nanoparticles at high temperatures.

Electronic and vibrational energy transfer processes taking place in molecular complexes in a polymer are investigated under dual-wavelength (visible at λ = 532 nm and IR at wavelength λ = 10.6 μm) laser photoexcitation of eosin molecules (С = 4 × 10^–4 М) in air and without it (р ≈ 10^–4 Torr) in thin polyvinyl butyral (PVB) films containing silver nanoparticles (R ≈ 36 nm) prepared by laser ablation. Generation of singlet oxygen, singlet–triplet annihilation, and enhancement of plasmon quenching of dye fluorescence are studied. Thermal-energy transfer processes in thin PVB films following pulsed IR excitation are simulated, and the temperature conductivity coefficients of the polymer films in the presence of silver nanoparticles are calculated. Low-temperature processes in PVB films containing dye molecules taking place after IR excitation are investigated, and the mechanism for accelerating intercombination S₁ → Т₁ transitions as a result of thermal heating and intramolecular vibrational-energy distribution is explained.

The effect of hydrate number on the structural changes, thermal properties, and ionic (molecular) mobility character in NH₄ZrF₅ ⋅ H₂O, NH₄ZrF₅ ⋅ 0.75H₂O crystal hydrates have been investigated by the methods of IR, Raman, nuclear magnetic resonance (NMR) (¹H, ¹⁹F, including ¹⁹F MAS), and TG-DTA spectroscopy. Differences in crystal hydrate structures—anion structure, molecular state of water, and O–H⋅⋅⋅F, N–H⋅⋅⋅F hydrogen bond strengths—have been corroborated by IR and Raman spectroscopy data. Isotropic chemical shifts of magnetic inequivalent positions have been determined and attributed to crystal structures of the studied compounds by the method of ¹⁹F MAS NMR. It has been established that the removal of water molecules from NH₄ZrF₅ ⋅ H₂O and NH₄ZrF₅ ⋅ 0.75H₂O results in the transformation of chain or layered structures accompanied by the increase of the number of bridge bonds while retaining or increasing the dimensionality of the anion structural motif. According to the ¹H NMR data, the NH\(_{4}^{ + }\) cation diffusion in NH₄ZrF₅ occurs only in the temperature range of 370–520 K.

The photophysical properties of three photosensitizers—dimegine, photoditazine, and radachlorin—have been comparatively examined. For dimegine and photoditazine, two techniques have been used to measure the singlet oxygen generation quantum yields and the quenching constants of singlet oxygen by dimegine and photoditazine, as well as the dimegine fluorescence quantum yield.

Multilayer graphene has been obtained by ultrasonic splitting of graphite microparticles in a surface-active solvent that is a mixture of nonane and water and a surface-active surfactant, which provides dispersion of graphene in hydrophilic systems, has been selected. The chemical structure of the obtained materials has been investigated by IR Fourier spectroscopy. Possible mechanisms of the influence of inorganic surfactants (sodium liquid glass) on the graphene, the type of relations that arise between it and the graphene surface, and possible areas of its application have been discussed.

Boron carbide (B₄C) is a semiconducting material that finds a wide range of industrial and optoelectronic applications because of its unique structural and physical properties. In the present work, boron carbide synthesized from natural precursors such as cotton and aloe vera are subjected to optical emission studies. The morphology of the samples is understood from the field emission scanning electron microscopic images and the optical bandgap from the ultraviolet visible spectrum. The fluorescence emission from the samples is studied using photoluminescence spectra. The CIE plot and power spectrum of fluorescence emission from the samples throw light into the color perception and the spectral distribution of energy revealing the potential of the samples for optoelectronic applications.

A review of the current progress in fiber optics for the mid-infrared range of the spectrum (2.0–50.0 µm) is performed. The problem in development of infrared (IR) optical fibers with the extended working-wavelength range also having increased radiation resistance, is substantiated. The study of diagrams of AgBr–TlI and AgBr–TlBr_0.46I_0.54 quasi-binary section of the AgBr–AgI–TlBr–TlI four-component system was conducted. Areas of homogeneity of solid solutions were revealed. An experimental technique was developed for determining the refractive index depending on the wavelength by the spectroscopic method for crystals of new compositions. The resistance of the studied materials to ionizing radiation was revealed. The photonic crystal structures based on metal-halide systems under consideration were simulated and single-mode optical fibers of the modelled structure with an increased mode field were produced by extrusion. It was found that the working spectral range of AgBr–TlI optical fibers is from 4 to 25 μm. The options for using the obtained IR light guides are considered.

Commonly, a surface wave traveling along the interface between isotropic media has a spin moment that lies in the plane of the interface and is perpendicular to the direction of propagation. Here, we show that, if one of the two media is a topological insulator, the spin moment vector has a component that is normal to the surface of the interface and is proportional to odd integers. The appearance of the normal component of the spin moment is associated with the topological magnetoelectric effect, as a result of which the polarization of the wave changes upon passage through the interface.

We present the results of a study of milk as a complex biological fluid. The simultaneous occurrence of both direct and reverse sedimentation associated, respectively, with the protein and fat components of milk is demonstrated. Digital holographic interferometry enables the determination of the spatial and temporal changes in the refractive index of the suspension under study caused by fractionation processes with an accuracy of 10^–6, which exceeds the capabilities of other research methods. The results can be used to create a mathematical model of biological fluid fractionation processes and to develop physical models (phantoms) of such systems.

Laser ablation of the materials immersed in liquid environment has been established as an advanced method for formation of the stable nanoparticles, especially those which cannot be synthesized by chemical methods. We review the studies of four metal (Ag, Ti, Co, Ni) nanoparticles synthesized during laser ablation in different liquids. The correlation between strong nonlinear optical response of silver nanoparticles out of plasmon resonance and efficient third harmonic generation in the plasmas containing silver nanoparticles is discussed. The change of sign of the nonlinear refraction with variation of the wavelength and duration of probe laser pulses is analyzed. The studies of third-order nonlinear optical processes (saturable absorption, reverse saturable absorption, two-photon absorption and nonlinear refraction) in the titanium and cobalt nanoparticles synthesized by laser ablation of bulk materials in water, toluene and ethylene glycol are discussed. The concurrence of different nonlinear absorption processes in nanoparticle-containing suspensions is analyzed. We discuss the two-photon absorption and nonlinear refraction studies of the nickel nanoparticles in water using femtosecond laser pulses at 400 and 800 nm. Third harmonic generation from the Ni nanoparticles contained plasma using picosecond and femtosecond pulses as heating radiation and femtosecond probe pulses is analyzed.

A modified Z-scan method for determining the nonlinear refractive index of colloidal quantum dots in the near-IR spectral range in the resonant excitation mode is proposed. It is demonstrated that the thermal effects related to heating of the solution due to strong light absorption can be mitigated by reducing the probing pulse repetition rate. The nonlinear refractive index of colloidal lead sulfide quantum dots is found to be on the order of 10^–16 cm²/W.

The probabilities of different types of optical processes involved in the formation of a photon avalanche in type-I heterostructures with deep quantum wells are calculated. The processes include two-electron transitions with participation of a photon, phototransitions between electronic states of size-quantized subbands and continuum of band states, and two-photon interband transitions in quantum wells. The obtained probabilities will be used in the forthcoming parts of the study for analysis of photon-avalanche kinetics.

The electric area of a radiation pulse, which is defined as a time integral of the electric field strength, is interpreted as a mechanical moment of the Lorentz force acting on a unit electric charge upon its interaction with the radiation pulse. Correspondence between the classical mechanics law of conservation of momentum and the change in the moment of force upon the interaction of a quantum object with an intense extremely short radiation pulse is demonstrated. The high efficiency of acceleration of charged particles with quasi-unipolar radiation pulses is confirmed.

The Raman spectra and the temperature dependence of the electrical resistance of graphene oxide in the process of continuous heating and cooling in an argon atmosphere in the temperature range of 300–550 K are studied. The D and G bands in the Raman spectra are described, and their nature is determined. A decrease in the D-band intensity after thermal treatment is related to a decrease in the concentration of oxygen-containing groups. This leads to a decrease in electrical resistance with increasing temperature. It is found that the resistance is independent of temperature in the range of 300–370 K, which testifies to a thermal stability of graphene oxide resistance.

The optical properties of thin films based on unsubstituted and tetrafluoro-substituted zinc phthalocyanines synthesized by physical vapor deposition are studied within the wavelength range of 250–1000 nm. Spectroscopic ellipsometry shows that films based on zinc phthalocyanines have uniform thicknesses and optical parameters, strongly absorb visible light, and have characteristic absorption peaks corresponding to electronic transitions in the system of conjugated double bonds of phthalocyanine rings. Introduction of fluorine substituents into peripheral positions of the zinc phthalocyanine molecule leads to an increase in light absorption and a shift of the main absorption maximum to longer wavelengths (bathochromic shift). The absorption spectra are described using the Lorentz–Drude dispersion model. It is shown that the films based on a mixture of phthalocyanines can be well described using the Bruggeman effective medium model.

A rigorous formulation of a theoretical method for investigating reflection of a plane electromagnetic wave from a flat-layered structure in the Kretschmann configuration is presented. Excitation of a surface wave is investigated taking into account diffraction effects caused by the finite aperture of the incident wave. Attention here is paid to application of the developed theory for investigating the Goos–Hänchen effect. Interference of surface plasmon waves upon their excitation on the surface of a metal film is analyzed. Possible applications of the obtained results are discussed.

Colloidal ternary quantum dots of AgInS₂ and AgInS₂/ZnS were synthesized in water in the presence of mercapto alkyl carboxylic acid. Selective size separation of AIS and AIS/ZnS hydrophilic nanoparticles was performed as well as the ligand exchange by thiolated methoxypolyethylene glycol molecules having an amphiphilic nature. The influence of nanocrystal size, composition and surface molecules on the optical properties of QDs was studied.

Circular dichroism (CD) spectra of liquid crystalline dispersions formed as a result of phase exclusion of double-stranded DNA molecules from aqueous-salt-poly(ethylene glycol)-containing solutions were studied at room temperature and under heating. Based on the CD spectra, it is possible to distinguish dispersions with cholesteric packing of DNA molecules from those with hexagonal DNA packing. Heating of DNA dispersions with hexagonal packing led to the appearance of an abnormal band in their CD spectra, which indicated a novel phase transition: from hexagonal to the re-entrant cholesteric packing of DNA molecules in individual particles of these dispersions. At room temperature, the spectra of such dispersions did not contain the abnormal band. By concentration of particles of liquid crystalline DNA dispersions using low-speed centrifugation, liquid crystalline DNA phases were obtained and their optical textures in thin layers were investigated. It was found that the spatial organization of DNA molecules in individual particles of dispersions formed in aqueous-salt-poly(ethylene glycol)-containing solutions may differ from their packing in macroscopic phases.

The properties of optical materials usable in the terahertz (THz) spectral range, which is the boundary between the optical and radio ranges, are examined. The relevance of the research field associated with the optics of THz devices is largely governed by intensified activity on creating lasers operating in the THz range and the discovery of substantial problems in the use of optical materials for these applications in general. The present study is devoted to analyzing the properties—especially optical properties—of the THz materials used. The characteristics are given, and the physical, chemical, and optical properties of conventional and new materials, including crystalline (silicon, sapphire, quartz, diamond, germanium, and silicon carbide), as well as a number of polymers (polymethylpentene, polyethylene, and polytetrafluoroethylene), are discussed and compared.

A local tomography by differential interface contrast (DIC) projections is proposed for optical studies of the internal structure of transparent objects. The advantage of local tomography is that it allows quickly calculating the desired distribution in the point or area of interest without a complete reconstruction of the entire cross section. To obtain quantitative DIC-projections, a tomographic microscope with a transverse shear interferometer is developed, in which the method of phase steps for phase recovery is implemented. A procedure is proposed for normalizing projection data on geometric moments from DIC-projections. It is theoretically shown and confirmed by computer simulation that the total image from the DIC-projections is proportional to the Hilbert transform from the original function describing the object, and the application of the inverse Hilbert transform to this image leads to the restoration of the tomogram of the object. The results of reconstructing a tomogram of a ball made of silicon dioxide by its experimental DIC-projections are presented. Comparison of the simulation results with the experimental results showed their close agreement.