Том 125, № 1 (2018)

Using a tunable CO₂ laser, unsaturated absorption coefficients in pure CO₂ and binary CO₂ gas mixtures with inert gases He, Ar, Kr, and Xe in a 1 : 2 ratio at 100 Torr were measured at the central frequencies of the R(8), R(22), P(8), P(22), and P(32) CO₂ spectral lines of the 10⁰0-00⁰1 transition at 300–700 K. The coefficients of the collisional broadening of the CO₂ spectral lines by He, Ar, Kr, and Xe are determined. The obtained temperature dependences of the collisional broadening coefficients are approximated by power functions with two different degrees.

The interaction of spin-polarized cesium atoms with cesium and rubidium atoms under conditions of optical orientation of atoms is considered. On the basis of data on spin-exchange complex cross sections in the Cs–Cs and Cs–Rb systems, a calculation of a magnetic resonance frequency shift of cesium atoms in a Cs–Rb mixture, as well as comparison of the calculated values of the frequency shift with experimental data, is performed.

Raman scattering spectra in the frequency range of 5–75 cm^–1 in lithium niobate samples with various structural imperfections were obtained. It is shown that the intensity of quasi-elastic light scattering on the wing of the Rayleigh line demonstrates an exponential dependence on the concentration of large-scale defects in the samples. Calibration curves for the intensity of quasi-elastic scattering dependence at low frequencies on the acoustic quality factor are constructed.

Particular features of the geometrical and electronic structure of six possible conformers of dansylamide ((CH₃)₂N–C₁₀H₆–SO₂NH₂) are considered. The electronic absorption spectra of the conformers of dansylamide in the free state and taking into account the influence of an aqueous solvent (in terms of the PCM model) are calculated by the TDDFT method. It is shown that, as a result of taking into account solvation, the electronic absorption spectra of the conformers exhibit a bathochromic shift, and the difference in the values of λ of the conformers reaches 16 nm. The calculated electronic absorption spectra in an aqueous medium agree qualitatively with the obtained experimental spectra. An analysis of molecular orbitals involved in the first three electronic transitions of the conformers is carried out. It is suggested that the broadening of the band with λ_max = 326 nm in the experimental spectrum may be caused by the presence of dansylamide conformers in the aqueous solution. It is shown that the calculated values of λ in the electronic absorption spectra of dansylamide in the aqueous solvent depend substantially on the DFT functional type.

The absorption and thermoluminescence spectra and their relaxation in pure and praseodymium-doped LuAG crystals are comparatively studied to determine the contribution of intrinsic and impurity defects before and after irradiation by ⁶⁰Co γ-quanta with an average energy of 1.25 MeV, dose rate of 0.8 Gy/s, and dose of 10³ Gy at 310 K. The existence of intrinsic F⁺ defects with a typical absorption band at 375 nm and impurity Cr⁴⁺ centers absorbing at 285, 420, 490, and 595 nm in both LuAG and Pr:LuAG samples before irradiation is related to the crystal-growth technology and the impurity composition of the charge. An increase in the concentration of F⁺ and Cr⁴⁺ centers after γ-irradiation is caused by charging of neutral F centers and changing of the electronic state (valence) of Cr³⁺ impurity centers. Formation of antisite defect complexes Lu_Al³⁺–V_O, which are responsible for a luminescence band at 335 nm, is suggested. The first broad peak at 340 K on the thermoluminescence curves of both samples after irradiation with a dose of 10³ Gy is related to liberation of charge carriers from shallow trapping levels; thermal activation and radiative recombination with emitting centers begin at 310 K, which places the upper limit on the temperature range of application of these scintillation crystals.

Tilted fiber Bragg gratings with different tilt angles have been inscribed in single-mode isotropic optical fiber with an increased photorefractivity using Talbot interferometer and KrF-excimer laser system. Their spectra are studied. Using a confocal laser scanning luminescent microscope the images of gratings in transmitted light were obtained. The calculated dependence of the slope angle of the grating recorded in the Talbot interferometer on the angle between the strokes of the interference pattern created in the interferometer and the transverse section of the optical fiber is experimentally verified.

The review discusses the possibility of obtaining highly effective relief-phase structures on silver halide photographic emulsions and dichromated gelatin layers by irradiating initially recorded holographic structures with short-wave UV radiation.

We have analyzed the influence of the angle between the wave vectors of two incident waves (the opening angle) and of the type of the anisotropy of a nonlinear layer on the shape of the directivity pattern of a sum-frequency harmonic generated by the two plane elliptically polarized electromagnetic waves from a thin spherical optically nonlinear layer deposited on the surface of a dielectric spherical particle placed in a dielectric. Our analysis has shown that, if the radius of the thin spherical nonlinear layer is small, the shape of the directivity pattern will change significantly with increasing opening angle only for some types of anisotropy: the main lobes shift toward the direction that is opposite to the direction of the sum of the wave vectors of the incident waves. For three types of anisotropy, the directivity patterns have similar shapes. We have also found that, for one of the types of the anisotropy, the shape of the directivity pattern remains unchanged upon a change in the opening angle. The mathematical properties of functions describing the spatial distribution of the generated harmonic have been determined. In particular, it has been found that, upon incidence of linearly polarized waves on a thin nonlinear spherical layer that possesses either solely chiral or solely nonchiral nonlinear properties, linearly polarized radiation of the sum-frequency harmonic is generated.

Dithioazaspiroheterocyclic derivatives are synthesized by condensing dithiols with piperidin-4-one in the presence of catalytic amounts of Lewis acids. Acrylic dithioazaspiroheterocyclic derivatives are obtained by the reaction with acryloyl chloride. The polymerization of monomers yields transparent polymer films of optical quality. The refractive indices for the synthesized monomers and polymers are in the range of n = 1.59–1.64.

A spherically symmetric lens with a negative refractive index, which can be invisible from the point of view of geometrical optics, is considered. Expressions describing the profile of the refractive index and ray trajectories in the lens, as well as some results of numerical modeling of plane wave scattering by the lens in the rigorous statement of the problem, are presented. It is detected that, unlike in the case of an invisible lens with a positive refractive index, the minima of the radar cross section in the forward direction corresponding to invisibility for the lens with a negative index occur at integer, rather than semi-integer, values of the electric radius, and that their depth is smaller because of the astigmatism associated with focusing of rays on the axis. Some results characterizing influence of losses in the lens on the level of the radar cross-section minima are also presented.

Water-soluble conjugates based on semiconductor quantum dots ZnS:Mn with chlorin e6 have been created. It has been established by optical spectroscopy that effective energy transfer (~35%) from quantum dots to chlorin e6 is observed in the resulting conjugates.

High-Z nanoparticles can increase the absorbed radiation dose if they are accumulated in tumor cells. The quantitative measure of this radiosensitization effect is the dose enhancement factor (DEF), that is, the ratio of the doses absorbed in the presence and in the absence of nanoparticles. In the present work, the values of the dose enhancement factors of Ta₂O₅, HfO₂, and CeO₂ ceramic nanoparticles were calculated analytically for monochromatic radiation of the X-ray energy range (1–180 keV) and for low-energy sources for brachytherapy: ¹⁰³Pd (mean energy, 20.6 keV), ¹²⁵I (26.7 keV), and ¹³¹Cs (30.4 keV). For all types of nanoparticles in the concentration of 5 mg/mL, the values of the dose enhancement factor were high both for monochromatic radiation and for brachytherapy sources. The highest DEF values of ~1.7 were obtained for nanoparticles of tantalum oxide. For brachytherapy sources, the highest dose enhancement factors (1.48 to 1.67) were obtained for Ta₂O₅ and HfO₂ nanoparticles. These results confirm that ceramic nanoparticles are promising dose modifying agents for radiotherapy.

A method for correcting the influence of light attenuation processes in biological tissues on their fluorescent images is proposed. The transfer function that takes into account the radiation losses in the medium at the wavelengths of excitation and emission of fluorescence is calculated analytically, depending on the transport scattering index and the hemoglobin tissue index. The latter is determined on the basis of a color image of the tissue in reflected visible light. Verification of the developed method was carried out on the basis of computer simulation of fluorescent images of biological tissue by the Monte Carlo method.

A robust approach of laser-induced breakdown spectroscopy (LIBS) in ambient air has been employed to investigate concentration of the trace elements in fennel seeds (saunf) via generation of plasma through the second harmonic of solid state Nd: YAG pulsed laser 532 nm. Spectral emissions of saunf plasma were acquired with resolution of 0.06 nm in spectral range of 200–720 nm. The experimental determination showed the existence of elements namely, Ca, Al, K, Fe, S, P, Mg, Mn, Sr, Na, and Zn in the sample. However, no toxic elements such as Pb, Cr etc. were perceived. The relative concentrations of detected elements were measured through the intensity of the strongest peak, intensities of every emission from every specie, and calibration free (CF)-LIBS. To indorse the experimental determinations of LIBS, a comparative study was carried out with the outcomes of atomic absorption spectroscopy (AAS). The results of LIBS and AAS were compared by the statistical treatment.

The photoluminescence spectra of three crystalline phase modifications of aromatic amino acid tryptophan are compared: the left phase of L-tryptophan, the right phase of D-tryptophan, and the racemic phase of DL-tryptophan. The photoluminescence spectra were recorded using a fiber-optic procedure, a small-size FSD-8 spectrometer, and a data processing system that enables comparison of the analyzed spectrum with the spectrum of a reference substance. Photoluminescence was excited by a pulsed-periodic ultraviolet laser at a wavelength of 266 nm.