Optics and Spectroscopy (v.110, #4)

The electron-impact excitation of even levels of Tm II from the ground level of the thulium atom is studied by the method of extended crossing beams with recording the optical emission of excited ions. At the exciting electron energy of 50 eV, 54 excitation cross sections are measured. In the electron energy range of 0–200 eV, 12 excitation optical functions are recorded. The most probable channels of the excitation process are discussed.

Near-threshold electron-impact ionization of calcium atoms by J. E. Kontros; I. V. Chernyshova; O. B. Shpenik (500-507).
The electron-impact ionization of calcium atoms is studied in the near-threshold energy range (from 6.11 to 16 eV). Experiments were performed by the method of intersecting electron and atomic beams with the recording of formed positive calcium ions. The electron beam (ΔE 1/2 = 0.15 eV) was formed using a hypocycloidal electron monochromator. An analysis of the specific features of ionization cross sections revealed a contribution from the excitation and decay of low-lying autoionization atomic states, which converge to the excitation thresholds of the 3d, 4p, and 5s ionic levels, and resonances (long-lived states of negative ions). The specific features of cross sections are identified using the experimental and theoretical data on photoionization (photoabsorption).

Simple, rapid and highly sensitive spectrofluorimetric methods were developed for the determination of venlafaxine in pure and pharmaceutical preparations. The proposed methods were based on the reaction of venlafaxine as n-electron donor with π-acceptors namely, p-bromanil and p-chloranil. The method for the determination of venlafaxine over a concentration range of 5–100 and 5–150 ng/mL, for p-bromanil and p-chloranil methods, respectively. The intra- and inter-day precisions were satisfactory, the relative standard deviations did not exceed 1.69%. The proposed method was successfully applied to the determination of venlafaxine in its pharmaceutical preparations with good accuracy; the mean recovery percentages were 99.80%. The results were compared favorably with those of the reference method.

Polarization properties of porous gold and silver films by E. B. Kaganovich; S. A. Kravchenko; L. S. Maksimenko; E. G. Manoilov; I. E. Matyash; O. N. Mishchuk; S. P. Rudenko; B. K. Serdega (513-521).
Using the method of polarization modulation of electromagnetic radiation and the Kretschmann geometry, we perform comparative studies of surface plasmon resonance in porous and continuous gold and silver films. The spectral dependences of the polarization difference of the reflection coefficients of nano-composites are obtained for the first time and are supplemented by angular characteristics of this parameter. We show that these dependences characterize particular features of the optical properties related to the structure, morphology, and topology of porous films. We reveal that surface plasmon-polaritons and local plasmons in porous films can be excited both by radiation that is p polarized with respect to the plane of incidence, as is the case with continuous films, and by s polarized radiation. We demonstrate that the measurement results can yield information on the structural properties of films, such as their thickness, roughness height, degree of dispersion of nanoparticles, and so on.

We studied the spectral-luminescent characteristics of the luminescence of mixed-ligand polypyridine-phosphine complexes of ruthenium(II) cis-[Ru(bpy)2(PPh3)X](BF4) n with ligands 2,2′-bipyridyl (bpy) and triphenylphosphine (PPh3) and X = Cl, Br, CN, NO 2 , NH3, MeCN, pyridine (py), 4-aminopyridine (pyNH2), and 4,4′-bipyridyl (4,4′-bpy) in a 4: 1 EtOH-MeOH alcoholic mixture at 77 K. The radiative and nonradiative deactivation rate constants of the lowest electronically excited state of the complexes are determined. We find that triphenylphosphine has a greater effect on the photophysical characteristics of ruthenium(II) complexes compared to π-acceptor strong-field ligands, such as MeCN, CN, and NO 2 . At the same time, the characteristics of complexes cis-[Ru(bpy)2(PPh3)X] n+ considerably depend on the nature of the second monodentate ligand X, which is coordinated to ruthenium(II), and correlate with its position in the spectrochemical series of ligands.

Impurity cathodoluminescence of oxygen-containing LiF crystals by L. A. Lisitsyna; V. I. Korepanov; V. M. Lisitsyn; A. E. Eliseev; N. N. Timoshenko; A. K. Dauletbekova (529-533).
Cathodoluminescence of oxygen-containing LiF crystals (LiF-O, LiF-O,OH, LiF-WO3) is studied by pulsed spectrometry with nanosecond resolution upon excitation of crystals by a single electronbeam pulse at 15 K.

Optical, nanostructural, and biophysical properties of Zn-induced changes in human erythrocyte membranes by A. Ya. Khairullina; T. V. Ol’shanskaya; D. S. Filimonenko; N. M. Kozlova; Yu. M. Garmaza; E. I. Slobozhanina (534-540).
We studied changes in the surface of erythrocyte membranes exposed to the action of zinc sulfate in the concentration range of 0.1–2.0 mM/l using methods of light scattering, spectrofluorimetry, and atomic force microscopy. Using the spectrofluorimetry method, we revealed a dose-dependent increase in the fluorescence intensity of a fluorescamine probe incorporated into erythrocyte membranes modified by zinc ions, which is indicative of an increase in the level of NH2 groups on the cell surface. Using atomic force microscopy, we revealed changes in the surface topography of erythrocyte membranes exposed to the action of zinc sulfate in the concentration range of 0.1–2.0 mM/l. By performing a correlation analysis, we revealed that the correlation length of the autocorrelation function of the erythrocyte surface irregularity profile directly related to the fluorescence intensity of fluorescamine incorporated into erythrocyte membranes (r = 0.9, p < 0.05) modified by zinc ions. We showed that, in the zinc sulfate concentration range of 0.1–2.0 mM/l, zinc oxides form in erythrocyte membranes, which is confirmed by the appearance of an absorption band at 330–340 nm and by an increase in the light scattering. At more considerable concentrations, we identified absorption bands characteristic of zinc protein complexes in erythrocyte membranes. A considerable decrease in the elongation of the scattering indicatrix of erythrocyte membranes caused by luminescence correlates with the content of zinc proteins. Polarization measurements confirm the enhancement of the aggregation of protein complexes observed by the atomic force microscopy method. The proposed complex approach can be used in studies on the action of various abiotic factors on biological cells.

Molecular Stark effect spectroscopy of diflavonol and inhomogeneous broadening of its electronic spectra in erythrocyte membranes by N. A. Nemkovich; W. Baumann; Yu. V. Kruchenok; G. I. Kurilo; V. G. Pivovarenko; A. N. Rubinov (541-549).
Using spectroscopy of the molecular Stark effect and fluorescence spectroscopy, we study the characteristics of diflavonol 3,7-dihydroxy-2,8-di(4-dimethylaminophenyl)-4H,6H-pyrano[3,2-g]chromene-4,6-dione (DFME), which demonstrates intramolecular charge and proton phototransfer. In the ground state, this dye has only one form and, in the excited state, it has two forms, i.e., normal and phototautomeric. We found that, for the normal form of DFME, the transition dipole moment that is responsible for the absorption (m a ), the dipole moment in the equilibrium ground state (μ g ), and the change of the dipole moment upon transition of the molecule in the excited Franck-Condon state (Δ a μ) are parallel. In the ground equilibrium state, the dipole moments in 1,4-dioxane and cyclohexane are equal to μg = 12.2 × 10−30 C m and μ g = 11.0 × 10−30 C m, respectively. Upon excitation, they increase by Δ a μ = 61 × 10−30 C m and Δ a μ = 50.2 × 10−30 C m in these solvents. We study the spectral characteristics of DFME in organic solvents and erythrocyte membranes. A spectral inhomogeneity of DFME in erythrocyte ghosts is found. The inhomogeneous broadening of fluorescence spectra is manifested as a long-wavelength shift of the band of the normal form of DFME by 1640 cm−1 upon excitation at the red edge of the absorption spectrum.

The spectral and temporal characteristics of the fluorescence of the anionic form of some 3-hydroxiflavones in different solvents are studied. This form is observed under selective excitation in the region of the long-wavelength slope of the main absorption band, and its spectrum consists of a wide structureless band lying between the short- and long-wavelength fluorescence bands of these molecular probes. The fluorescence excitation spectra of the anionic form differ from the corresponding spectra of the normal and tautomeric forms. The addition of water to the solution leads to a gradual fluorescence quenching which is static or belongs to the second kind according to Vavilov’s classification, i.e., occurs in the ground state.

Magnetic field effect on ultra short pulse propagation in system of carbon nanotubes by M. B. Belonenko; N. G. Lebedev; E. N. Galkina; O. J. Tuzalina (557-561).
A problem of ultra short optical pulses behavior in a system of carbon nanotubes with applied magnetic field parallel to the nanotube axis was considered. The electromagnetic field was explored under the Maxwell equations. And the electronic system of the carbon nanotubes was quantum and mechanically investigated in the case of low temperatures. The distributional pattern of the ultra short pulses and their collision were established by means of numerical modeling.

The separation of variables method (SVM), which uses a spheroidal basis, is proposed. According to this method, fields are presented in the form of expansion in terms of spheroidal functions. The previously conducted analysis of various methods using a spherical basis showed that the SVM is applicable in a broader area for numerical calculations, while the proposed approach using a spheroidal basis yields reliable results in the case of spheroids with a high degree of asphericity where other methods and approaches cannot be used. Importantly, the method includes an SVM that uses a spherical basis as the limiting case. Thus, the proposed method has all chances of being highly efficient for calculation of optical characteristics of various nonspherical particles in a wide range of parameters of the formulated problem.

The results of analytical modeling of the resonant excitation of evanescent harmonics in a medium formed by parallel metallic nanorods taking into account the spatial dispersion are presented. Analytical expressions are derived for the reflection and transmission coefficients, as well as for the amplitudes of electromagnetic waves inside the medium. These expressions are compared to similar expressions that were previously obtained using a local model of an ultimately anisotropic material without taking into account the spatial dispersion. The obtained expressions are simplified for various partial cases, including the superresolution imaging of a source that is located at a considerable distance from the metamaterial layer. A layer of a medium composed from finitesized wires is numerically simulated and it is demonstrated that, due to the effect of resonant excitation of evanescent spatial harmonics in the layer, subwavelength details of an object that is considerably distant from the layer can be distinguished inside of the layer.

Transmission of polarized light through turbid media by E. E. Gorodnichev; S. V. Ivliev; A. I. Kuzovlev; D. B. Rogozkin (586-594).
The depolarization of light in multiple-scattering media with large (larger than the light wavelength) inhomogeneities is considered. The polarization state of the scattered light is described in the principal-mode approximation. Using the Fokker-Planck model, the polarization and intensity distribution of light are calculated in the vicinity of an inhomogeneity in the shape of an absorbing half-plane. The results of the calculations agree with the experimental data on transmission of light through turbid media.

We obtain equations for the Bragg regime of acoustooptic diffraction of light in two-dimensional photonic crystals. We determine applicability conditions of the single-wave approximation, in which it is sufficient to take into account only one Fourier component of each of Bloch waves involved in the acoustooptic interaction. In the single-wave approximation, we obtain formulas that make it possible to estimate the acoustooptic figures of merit of a photonic crystal. We show that, in a photonic crystal, higher acoustooptic figures of merit can be achieved than in the materials that make up the crystal.

Additive coloring of CaF2 optical ceramic by A. S. Shcheulin; A. I. Ryskin; A. E. Angervaks; P. P. Fedorov; V. V. Osiko; A. A. Demidenko; E. A. Garibin; A. N. Smirnov; K. V. Dukel’skii; I. A. Mironov (604-608).
The specificity of additive coloring of CaF2 optical ceramic (formation of color centers in it and photothermochemical transformation of these centers in colored ceramic samples) has been considered. Under the same coloring conditions, this process occurs more slowly in ceramics rather than in crystals; at the same time, the limiting concentration of color centers that can be introduced into ceramics is much higher. The photothermochemical transformations of color centers in crystals and ceramics, which occur under illumination at different wavelengths and upon heating, have been studied. The specific features of introduction of color centers into ceramic and their transformation under illumination and heating are likely to be related to the mass twinning of ceramic grains.

Formation kinetics of volume holograms in reversible photochromic media by A. S. Shcheulin; A. E. Angervaks; A. I. Ryskin (609-616).
The specific features of recording a volume hologram in a photochromic reversible medium, which is characterized by simultaneous occurrence of hologram recording and relaxation, have been considered by the example of two ion crystals, i.e., cadmium fluoride with bistable gallium centers and calcium fluoride with color centers.

Additive coloring rate and intensity for pure and doped fluorite crystals by A. S. Shcheulin; T. S. Semenova; L. F. Koryakina; M. A. Petrova; A. E. Angervaks; A. I. Ryskin (617-623).
The mechanism of the additive coloring of calcium fluoride crystals, both pure and doped with I- and III-group elements, has been investigated. The coloring rate and intensity and the dependences of these parameters on the experimental conditions, vapor mixture pressure, and temperature have been experimentally determined. It is shown that the concentration of anion vacancies/electrons that can be introduced into crystals is in the range of 1017–1018 cm−3; in crystals with a high concentration of rare earth ions, the limiting concentration can be an order of magnitude higher.

Optical method for detecting variations of the magnetic field strength by M. V. Bolshakov; A. V. Ershov; N. D. Kundikova (624-629).
A method of detecting the magnetic field variation is proposed and implemented experimentally. The method employs the rotation of the speckle pattern of light transmitted through an optical fiber that is placed into a longitudinal magnetic field and the recording of a holographic grating in a photorefractive crystal using the speckle field. The possibility of detecting the shape of a 0.15-s magnetic field pulse is demonstrated experimentally.

Control of spectral lines weakly absorbed by atmosphere in continuous wave chemical HF lasers by I. A. Fedorov; Yu. P. Maksimov; A. P. Zhevlakov (630-636).
The behavior of two lines P 1-0(11) and P 2-1(8) weakly absorbed by the atmosphere is experimentally investigated in the spectra of cw chemical multikilowatt HF lasers of five types that differ in size and construction scheme of the nozzle array. It is shown that the intensity of these lines can be controlled within certain limits by varying the gas-dynamic regime of the laser operation, the chemical composition of the active medium, the orientation of the optical axis of the cavity and the cavity feedback factor, and the construction of the nozzle array.

We analyze the interference between two processes of higher harmonic generation (HHG) in plasma containing mixtures of different materials (silver and gold nanoparticles, as well as graphite and boron). We find that, for mixtures and individual ingredients, the limiting orders of generated harmonics of laser radiation approximately coincide with one another. At the same time, for plasma torches formed by the ablation of mixtures of materials, the HHG efficiency is considerably reduced compared to the case of the frequency transformation of laser radiation in individual ingredients of these mixtures as a result of destructive interference in the former case. We demonstrate a considerable spectral broadening of harmonics generated in laser plasma with pulses passed through filaments formed in air. In this case, the HHG efficiency increases fourfold (from 3 × 10−6 to 1.2 × 10−5) compared to the case of radiation free of phase and frequency modulation. The generation of harmonics is also observed upon the passage of 120-fs laser pulses through plasma containing fullerenes. In this case, the limiting value of generated harmonics achieves the 33rd order. The efficiency of harmonics in fullerene plasma considerably exceeds a similar process in silver plasma.

The determination of optical characteristics of biological tissues by the temporal distribution of an ultrashort laser pulse passed through a homogeneous scattering layer is considered. Four nonstationary models used to describe passing of laser pulses through a highly scattering medium are compared for the first time. The domains of applicability for the diffusion models are determined. It has been shown that the determination of optical characteristics of highly scattering media by experimental temporal distributions leads to different numerical values depending on the used model. Nevertheless, any of these models can be used because the performed study does not permit one to give preference to any of them. However, in determining optical characteristics of the scattering samples, it is necessary to specify the used model, as well as the conditions under which the initial experimental data (in particular, the thickness of the layer of a studied sample) are obtained.