Том 125, № 3 (2018)

The structural, energy, and optical properties of charged and neutral molecular clusters (MCs) of silver Ag_n (n = 2–5) have been simulated within the density functional theory (DFT). It has been shown that the electronic absorption spectrum of neutral MCs is shifted toward lower energies compared to the charged ones. The strengths of the oscillators of neutral MCs are mainly larger than the ones of charged MCs. A comparison of the simulation results with the previously obtained experimental ones for glasses with silver MCs has been carried out.

A consistent quantum-mechanical approach is used to calculate a fluorescence signal from a cold atomic ensemble excited by pulsed radiation and exposed to a DC electric or magnetic field. The short time Fourier transform is used to analyze the spectral composition of this signal and to investigate its changes over time after the end of excitation. It is demonstrated that external fields substantially change both the shape of the spectrum and its dynamics. The discovered effects are explained as being the result of action of these fields on the spectrum of states of the two-atomic quasi-molecular clusters that randomly form in disordered ensembles.

It is shown that the appearance of double-valued wave functions in constructing the discrete-spectrum classification of coordinate motions in molecules with a linear core and two identical tops using the CNPI-group methods is the consequence of a physically incorrect determination of the action of symmetry operations on variables of a configuration space of the molecule.

Experiments on IR Fourier spectrometry of a Nafion polymer membrane swollen in water are described. The dynamics of Nafion swelling is studied in relation to the deuterium content in water. It has turned out that, if the polymer swells in waters with different deuterium contents, a considerable confinement effect is observed, which, in this case, manifests itself in that the transmittance of IR radiation of water that is enclosed within a region with a size of ~100 μm differs from that of water that is inside nanometer pores of the polymer membrane. In addition, the transmittance of Nafion swollen in water measured at a wavelength of λ = 1.92 μm (spectral minimum) experiences a local minimum in the deuterium concentration range 10² < C < 10³ ppm, irrespective of the soaking time of the polymer in deuterated water. Finally, the effect of the deuterium substitution of the residual water present in the volume of the membrane has been revealed.

The energy band structure of a LiNaSO₄ has been calculated within the framework of density functional theory for space group P31c. It has been established that bandgap width E_g in the GGA approximation is 5.49 eV. The valence band top is generally formed of oxygen p-electrons, while the conduction band bottom is composed of lithium and sodium s-states. The effect of the cationic substitution Na → K → Rb → NH₄ on the electron structure of LiBSO₄ group crystals is considered. Based on the calculated dielectric functions, the spectral dependences of the refractive indices and extinction coefficient of a crystal were calculated and compared with experimental data.

The spectral and kinetic properties of water–ethanol photochromic systems of photochromic compounds from the classes of spiropyrans, spirooxazines, chromenes, and diarylethenes with and without silica nanoparticles have been comparatively studied. It has been found that, depending on the structure of a compound, its molecules can interact either chemically or physically with the surface of nanoparticles.

Existing models of zinc oxide luminescence in the visible spectral region are considered and comparatively analyzed. Experiments are performed with ceramics obtained from initial ZnO powder and ZnO powders annealed in vacuum (ZnO-vac) and in air (ZnO-air). The luminescence characteristics of the ceramics, namely, emission and excitation spectra, kinetics, and temperature stability, are studied. The ZnO-vac ceramics exhibits green luminescence caused by neutral oxygen vacancies. The luminescence of ZnO-air ceramics is shifted to the red and is presumably related to residual lithium impurity. The ceramics differ in the luminescence excitation spectra, time characteristics, and temperature stability.

This paper is devoted to an analysis of the frequency dispersion of dielectric permittivity in order to establish the physical meaning of the dispersion parameters α and β in the Havriliak–Negami model. It is found that parameter α is associated with the spectrum broadening of relaxation time τ. Examples with the appearance of a dispersion with parameter α of about 0.4 and 0.7 are presented. A conclusion is drawn that disorder creates a broadening of the relaxation times. Dispersion parameters α and β are introduced to preserve the unified relaxation time. The possibility of the analysis of experimental results on the basis of the Debye model in order to obtain the relaxation time distribution and determine parameters α and β according to the log(τ_HN/τ) chart is shown.

The diffraction phenomena associated with the limited aperture size of an incident wave are considered on the basis of a theoretical method for studying the reflection of a plane electromagnetic wave from a plane-layered multifilm structure with homogeneous films. The proposed theory is applied to the analysis of the sensitivity of sensors based on surface waves.

A method of the power summation for mutually noncoherent pulsed lasers of the same type using time interleaving is proposed and validated experimentally. The method uses an acoustic-optic deflector, which commutates radiation of different sources into one output channel simultaneously with radiation presenting in this channel. It is crucially important that the power of the final output radiation is equal to the power sum of the input sources, and the angular and coordinate parameters of an output beam are the same as that for the input sources. The experiments were carried out with single-mode diode lasers on a wavelength of 1.3 μm using a ТеО₂-crystal-based deflector. The method is appropriate for the power summation for fiber-optic, diode, and solid-state lasers. We have estimated the main interrelated parameters.

Propagation of electromagnetic waves in a medium with zigzag carbon nanotubes is studied. Based on the Maxwell equations, an effective equation for the electromagnetic field vector potential is derived, which takes into account ion oscillations in the dielectric medium with nanotubes. It is found that the pulse shape depends on the character of oscillations of heavy ions, which may absorb the electromagnetic field, and on other parameters of the problem.

The quasi-classical approximation is used to determine the positions of the classical turning points upon motion of an electron that is bound by an image field and a constant homogeneous electric field of the same direction. Power expansions of the coordinates of the turning points in a wide range of electron energies and field strengths are obtained. The mechanism of one-dimensional confinement of an electron, which determines a completely discrete spectrum of states, is described. The dependence of the spatial width of the confinement region on the field strength and electron energy is determined. The dependences of the electron energy in different states on the external field strength are calculated numerically. Quasi-classical quantization is performed, and the dependence of the electron energy on the width of the confinement region is determined. The energy interval of a maximum density of electron states is found, which is determined by the dependence of the width of the confinement region on the electric field strength.

Characteristics of the sensing element of a fiber sensor for evanescent wave mid-IR spectroscopy have been studied within the electromagnetic theory of fiber waveguides by using the problem of determining the concentration of aqueous acetone solutions as an example. A multimode chalcogenide fiber was used as a sensing element. It has been shown that the selective excitation of the fiber modes may provide the possibility to increase the sensitivity of the fiber sensing element, decrease the minimum detectable concentration of a substance in a solution, and enhance the range of measured solution concentrations.

The problem of allocating bands of individual monomers or aggregates of the absorption spectrum of a multicomponent structure arises in the study of molecular layers or organic thin films. Not counting the concentrations of the components, the optical properties of this kind of samples are determined by the tilt of the molecules relative to the substrate surface. Molecular orientation can be determined from the dichroic ratio spectra recorded with the tilt probing of samples. Using the example of the tricarbocyanine dye layers, the following two independent methods for the identification of the spectra of the components from the absorption spectrum of a layer are compared: by comparing the spectra of layers of different thicknesses and based on the dichroic ratio spectra. The effect of laser radiation on the samples, which leads to a change in the dichroic ratio, is studied. Photoinduced changes of the orientation angles of molecules are calculated, which allows one to refine the range of possible values of these angles.

In this study, we demonstrate the possibility of realizing the quantum key distribution system by temporal coding of time-bin qubits that are prepared and measured using unbalanced Mach-Zehnder interferometers. We also show that, to exclude a clear a priori identification of time-bin qubits with equal bases, their encoding with the symbols 0 and 1 can be accomplished by delaying one of them by half the clock interval. The uniqueness of measurements of qutrits in this algorithm is shown to be based on the ability of quantum particles in β-states to interfere with the probability amplitudes at the ports of the system interferometers, as well as the absence of collisions of signaling states of the qutrits in adjacent clock intervals. We describe a method for controlling such collisions, including those that are based on qubits prepared from quasi-one-photon coherent laser states.

The dynamics of polaritons in a microcavity in the parametric oscillator mode, when two pump polaritons turn into the signal and idler polaritons and vice versa, has been studied. The pumping is carried out using two lasers with close frequencies. Analytical solutions of the system of nonlinear differential equations have been obtained. The periodic and aperiodic modes of the transformation of a pair of pump polaritons into signal and idler polaritons have been found.

A facile, efficient and time-saving strategy is proposed to obtain large-area and reliable surface-enhanced Raman scattering (SERS) substrates via artificial heat-treatment of Au nanoparticles or ultrathin Au films sputtered on the silica substrates. Excellent Raman enhancements with the detection limitation down to 10^–9 mol/L are obtained due to the highly-dense plasmonic hot-spots and strong plasmons near-field coupling. Decreased intensity of Raman peaks with the increased sputtering time of Au nanoparticles or ultrathin films mainly originates from the excited and hybridized coupling of multiple surface plasmons. The simple fabrication strategy and superior performance make these substrates promising candidates for the development of inexpensive and reliable SERS substrates.