Vol 123, No 2 (2017)

An analytical expression describing the frequency shift of nonsoliton pulses in a nonlinear Raman-active medium is obtained by the method of moments. The regime of propagation in which the central frequency of the signal falls into the region of zero group-velocity dispersion is analyzed.

The necessary conditions for nonlinear excitation of higher-order modes in a single-mode step-index optical fiber are analyzed. The cutoff conditions for such an optical waveguide are investigated taking into account Kerr nonlinearity. The minimal power of optical pulses required for fulfilling the necessary conditions for nonlinear excitation of higher-order modes in a single-mode step-index fiber is calculated as a function of the normalized frequency. The allowed ranges of variation of the normalized frequency and optical-radiation power are estimated. It is demonstrated that the conditions necessary for nonlinear excitation of a higher-order mode in a step-index single-mode optical fiber can be created for optical pulses shorter than 500 fs.

Radiation and thermal processes in skin exposed to solar radiation are simulated based on the diffusion model of radiative-conductive heat exchange. Using the model proposed for the parameters corresponding to radiation with a wavelength of 800 nm, the contributions of thermal radiation induced by the skin and the reflection and refraction effects are estimated, and the photoprotective properties of titanium dioxide nanoparticles (TiO₂) when introduced into the stratum corneum are studied.

Analytic expressions for the probability density of states of a molecule with internal rotation and the probability of finding the state in the potential well are derived for the first time. Two methods are proposed for assigning conformers to potential wells. A quantitative measure of localization and delocalization of a state in the potential well is introduced. The rotational symmetry number is generalized to the case of asymmetric rotation. On the basis of the localization criterion, a model is developed for calculating the internal rotation contribution to thermodynamic properties of individual conformers with low rotational barriers and/or at a high temperature.

Geometrical and electronic structure and optical properties of several substituents and derivatives of 1,8-naphthosultam are studied by quantum-chemical DFT and TDDFT. It is found that the substituents –NO₂, –CF₃, and –N(CH₃)₂ affect the geometrical and electronic structure the most. It is shown that the Stokes shift is greatest (≈260 nm) for compounds with the strong donor substituent –N(CH₃)₂, while strong acceptor substituents provide a quite small Stokes shift. The dependence of the Stokes shift on the difference in energies of the frontier orbitals of the ground and excited states of molecules is found. Of the 1,8-naphthosultam substituents considered, compounds with –N(CH₃)₂ substituent, which emit in the biological window region, can be advised for use in optical bioimaging. The results can be used as a basis for the development and creation of new functional materials and biologically active compounds.

We have quantitatively analyzed the vibronic parameters of two cross-conjugated δ-dimethylaminoketones. The presence of the –N(CH₃)₂, C=O, and –NO₂ groups in the benzene ring has been shown to affect the manifestation of the vibronic parameters of characteristic bands that describe the state (vibrations, types of deformation upon excitation) of polyene systems with aromatic rings. Data on the influence of the nature of the substituent on the parameters of intra- and intermolecular interactions in the examined compounds have been presented.

The technique for recording Raman spectra in uranium compounds using a probe minispectrometer with a multielement radiation detector has been developed. A selective filter, which reflects exciting laser radiation and transmits Raman signals, has been used to suppress the exciting radiation. It is shown that the technique developed makes it possible to record Raman spectra from a small amount (~10^–5 g) of sodium uranyl-acetate polycrystals in a wide spectral range for several seconds.

The optical properties of RuAl₂ and RuGa₂ intermetallic compounds have been investigated in the spectral range of 0.22–14 μm. The nature of interband light absorption has been interpreted based on a comparative analysis of calculated and experimental frequency dependences of optical conductivity. The data obtained confirm the existence of pseudogaps with a width of ~0.8 eV localized at the Fermi level in the electron densities of states of these materials, which was predicted in previous energy-band calculations.

The nonlinear spectroscopy using harmonic generation in the extreme ultraviolet range became a versatile tool for the analysis of the optical, structural and morphological properties of matter. The carbon-contained materials have shown the advanced properties among other studied species, which allowed both the definition of the role of structural properties on the nonlinear optical response and the analysis of the fundamental features of carbon as the attractive material for generation of coherent short-wavelength radiation. We review the studies of the high-order harmonic generation by focusing ultrashort pulses into the plasmas produced during laser ablation of various organic compounds. We discuss the role of ionic transitions of ablated carbon-containing molecules on the harmonic yield. We also show the similarities and distinctions of the harmonic and plasma spectra of organic compounds and graphite. We discuss the studies of the generation of harmonics up to the 27th order (λ = 29.9 nm) of 806 nm radiation in the boron carbide plasma and analyze the advantages and disadvantages of this target compared with the ingredients comprising B₄C (solid boron and graphite) by comparing plasma emission and harmonic spectra from three species. We also show that the coincidence of harmonic and plasma emission wavelengths in most cases does not cause the enhancement or decrease of the conversion efficiency of this harmonic.

We consider the excitation by a dipole of metallic photonic crystals—systems of infinitely extended parallel-oriented metallic cylinders with a small circular cross section. Based on the rigorous statement of the problem, analytical expressions are obtained that make it possible to give a simple estimate of frequencies that determine the band gap edges in the spectrum of eigenstates of such a crystal and, also, to describe the amplitude characteristics of radiation in the low-frequency range, in which the approximations used in our study are correct. We compare our results with those obtained by strictly numerical simulation.

The possibilities of correcting the functional properties of nonlinear optical limiters based on carbon nanoparticles using polymer dopants have been considered. The results of analyzing the characteristics of nonlinear optical limiting of a suspension of carbon black with addition of sodium dodecylbenzene sulfonate and polyvinyl alcohol are given. The forms in which particles exist in the suspension have been investigated by different physicochemical methods. Optical measurements have confirmed the efficiency of these additives.

The operation principles of interferometric waveguide sensors have been considered. A comparison of the sensitivity of the two-mode sensors with waveguides of oxide and chalcogenide glass has been performed. The advantages of the two-mode sensors with waveguides made of a material with high refractive index have been shown. It has been shown that the sensors with waveguides made of chalcogenide glass have a sensitivity three orders of magnitude higher.

A series of studies devoted to the theoretical justification and development of methods and tools for angular measurements based on the use of multiple sources of optical beams with a small angular aperture is continued. The source used in this study is a holographic prism: a fluorite single crystal with a system of superimposed holograms recorded in its bulk, which generates a series of diffracted small-angle beams in the form of a flat fan under illumination by a reference laser. This fan has a high spatial stability, including constancy of angles between any pair of fan beams in a wide range of external conditions. Based on the previously introduced notion of an effective beam axis, potential exact methods for measuring angles between fan beams are considered, and a coordinate method using a coordinate measuring machine and a CCD recorder is substantiated and implemented. The accuracy of the proposed method is analyzed. It is shown that its errors can potentially be reduced to a level of 1″ or even less.