Optics and Spectroscopy (v.119, #6)

The equilibrium nuclear configuration and the potential energy and dipole moment component surfaces of an isolated Li+–CO complex are calculated quantum-mechanically in the MP4(SDQ)/6-311++G(3df) approximation. The geometrical parameters and the binding energy of the complex are determined. The frequencies and intensities for the fundamental transitions are calculated in the harmonic approximation. The one-, two-, and three-dimensional anharmonic vibrational Schrödinger equations are solved using the variational method. The energies of states of a three-dimensional vibrational system, anharmonic constants, and the frequencies and intensities of fundamental transitions are determined with the anharmonic interactions taken into account. The changes in the frequency and intensity of the C–O stretching vibration upon the formation of the complex are predicted.

The dependence of energy of an ion accelerated from a thin laser target on its charge is investigated numerically and analytically. It is demonstrated that this dependence is determined by the values of ionization potentials of the target atoms and has a sharper character than those obtained in previous models of ion acceleration. The physical origin of sharper dependence is the relation of ion charge to its initial position in the ionized target. As a result, more highly charged ions turn out to be in the region of stronger accelerating field and thus attain higher energy. For a laser target made of a gold foil, the results obtained with an analytical model are compared to those obtained by means of a two-dimensional simulation, which demonstrated agreement between theoretical and calculated dependences of ion energy on its charge.

The theory of absorption of femtosecond light pulses due to indirect interband transitions in crystals is developed. The absorption occurs due to two-quantum processes with participation of a photon and a phonon. Expressions governing J, the density of energy absorbed during the laser pulse action, and its dependence on laser pulse duration, temperature, and frequency of light are obtained.

Optical spectra and electron–Hole liquid in diamond by E. I. Lipatov; D. E. Genin; V. F. Tarasenko (918-923).
Optical absorption spectra in the spectral range from 200 nm to 15 μm, Raman spectra in the wavenumber range of 100–3700 cm–1, and photoluminescence spectra in the spectral range of 200–850 nm have been studied for five nominally “pure” diamond samples synthesized in different ways. The measurements have been carried out in the temperature range of 80–300 K. Photoluminescence was excited by the KrCl laser radiation at a wavelength of 222 nm with a pulse FWHM of 8 ns and a peak intensity on the sample surface of up to 13 MW/cm2. It is found that, at absorption coefficients of diamond samples below 10 cm–1 in the spectral range of 225–226 nm, their photoluminescence spectra exhibit a radiative recombination band of electron–hole liquid peaked at 240 nm.

PbS molecular clusters and quantum dots (QDs) have been formed by heat treatment in fluorophosphate glasses of the Na2O3–Р2O5–Ga2O3–ALF3–ZnO(S)–PbF2 system, and their spectral-luminescence characteristics have been investigated. It is experimentally shown that the transition from molecular clusters to QDs is accompanied by a stepwise change in the spectrum and luminescence quantum yield. Molecular PbS clusters luminesce in the visible spectral range (1.5–3.5 eV) and QDs luminesce in the IR region (0.6–1.4 eV). The luminescence of molecular PbS clusters is characterized by low quantum yield, which decreases from 10 to 1% with an increase in excitation energy. An increase in nanoparticle size leads to a decrease in the Stokes shift from 80 to 50 meV. The QD luminescence spectrum contains two bands, which are due to transitions from two lower excited states.

Photosensitized generation of singlet oxygen by rhenium(I) complex by A. N. Burchinov; V. M. Kiselev; A. A. Penni; V. V. Khistyaeva (932-937).
The photosensitized generation of singlet oxygen in solutions of rhenium(I) complex fac-[Re(bipy)(CO)3NССН3]+OTf, where bipy=2,2'-bipyridine, in chloride methylene and carbon tetrachloride under continuous LED irradiation in the UV and visible ranges has been investigated.

Raman scattering in lead selenide films at a low excitation level by M. O. Kuzivanov; S. P. Zimin; A. V. Fedorov; A. V. Baranov (938-942).
Raman scattering spectra of epitaxial lead selenide films were measured at low (0.06 mW/μm2) excitation power densities to ensure the absence of photo- and thermal modifications of the film material. It is shown that observed transitions correspond to overtones or combinational tones of PbSe phonon modes implying a high quality of crystalline structure of the material for which the first order Raman effect is prohibited. An increase in incident excitation density leads to the appearance of transitions related to lead oxides, which masks characteristic spectral features of lead selenide.

Spectral properties of zinc sulfide sols stabilized by high-molecular polyvinylpyrrolidone by S. K. Evstrop’ev; Yu. A. Gatchin; K. S. Evstrop’ev; K. V. Dukel’skii; I. M. Kislyakov (943-947).
Spectral properties of zinc sulfide sols stabilized by high-molecular polyvinylpyrrolidone have been studied. It is shown that the absorption spectra of colloidal solutions in the UV spectral range are determined by the quantum-confinement effect, exhibiting a dependence of the absorption edge on the size of zinc sulfide nanocrystals.

Optical methods for hydrogen degassing monitoring in urban conditions by E. V. Timchenko; P. E. Timchenko; L. A. Zherdeva; N. V. Tregub; E. A. Selezneva; V. N. Yakovlev (948-954).
Results of a study of variations in optical parameters of bioindicators that grow in the regions of hydrogen degassing in Samara are presented. Raman spectroscopy and confocal fluorescence microscopy were used as the main methods of the study. Features of Raman spectra of plants that grow in zones with presence/ absence of deep hydrogen emissions have been ascertained. The main variations have been recorded at wavenumbers of 1380, 1522, 1547, and 1600 cm–1, which are responsible for stretching vibrations in lignin and β-carotene and chlorophyll a and cellulose in plant leaves. Confocal fluorescence microscopy showed an increase in the chloroplasts in leaves of plants which grow at hydrogen degassing territories. An optical coefficient was introduced, on the basis of which the Samara region was monitored.

The morphology and the structural and chemical properties of crystalline formations appearing on the surface of commercial quartz glasses at the beginning of the induction stage upon heating at temperatures of 1000–1300°C are studied by optical polarization microscopy, μ-Fourier transform infrared spectroscopy, and X-ray diffraction. It is shown that crystalline island nuclei induce crystallization not only in the local environment of the surface layer, but also in the glass bulk at a depth of up to ≈200 μm. Crystalline nuclei in the center of islands often have an imperfect crystal structure formed by intermediate mesophases based on individual low-symmetry SiO4 tetrahedra. However, the induced phase at the periphery of these nuclei has a well-ordered crystal structure consisting mainly of α-SiO2 (quartz) and/or α-cristobalite. The proportion of these two phases depends on the glass heating temperature, namely, at 1000°C, the induced structure for the most part contains α-SiO2, while α-cristobalite dominates at 1300°C.

Evolution of the electronic structure and optical properties of iron-based Heusler alloys by E. I. Shreder; A. D. Svyazhin; A. A. Makhnev (969-973).
The optical properties of Heusler alloys Fe2 MeAl (Me = Ti, V, Cr, Mn, Fe, Co, or Ni) and Fe2MnSi have been studied, and their optical spectra have been calculated. Substitution for the Me atom is found to cause significant changes in the band-energy spectrum, especially in the vicinity of the Fermi level. These changes are accompanied by considerable variations in the optical characteristics of alloys. The optical properties of Fe2 MeAl alloys (Me = Ti, Fe, Co, or Ni) are typical of metals. The anomalous behavior of the optical properties of alloys with Me = V, Cr, or Mn is determined by the electronic states at the Fermi level.

Down-conversion in ytterbium-doped NaGd(MoO4)2 crystals by K. A. Subbotin; D. A. Lis; Yu. N. Osipova; A. V. Khomyakov; D. A. Nikolaev; V. A. Smirnov; E. V. Zharikov; I. A. Shcherbakov (974-981).
A series of NaGd(MoO4)2 single crystals doped with various Yb3+ concentrations (from 0.5 to 30 at %) is grown. The optical absorption spectra of the crystals are measured within the range from 800 to 1200 nm and used to calculate the actual concentrations of Yb in the samples. The luminescence of crystals is studied under UV excitation. It is found that there exist two types of active centers that are not directly related to Yb3+ ions and exhibit broadband luminescence in the visible spectral region. In addition, UV excitation of crystal gives rise to Yb3+ luminescence in the region of 1 μm owing to nonradiative excited-state energy transfer from, probably, donor centers of the host to ytterbium. The character of the dependence of the UV-excited luminescence of Yb on its concentration in the samples, in comparison with the corresponding dependence measured under IR excitation, points to the occurrence of cooperative down-conversion in crystals with high ytterbium concentrations, which means that the excited-state energy of donors is simultaneously transferred to two Yb3+ ions. In other words, excitations are multiplied; i.e., the quantum yield of this down-conversion exceeds unity.

X-ray spectral diagnostics of synthetic lanthanide silicates by A. N. Kravtsova; A. A. Guda; A. V. Soldatov; J. Goettlicher; V. K. Taroev; A. A. Kashaev; L. F. Suvorova; V. L. Tauson (982-986).
Potassium and rare-earth (Eu, Sm, Yb, Ce) silicate and aluminosilicate crystals are hydrothermally synthesized under isothermal conditions at 500°C and a pressure of 100 MPa. The chemical and structural formulas of the synthesized compounds HK6Eu[Si10O25], K7Sm3[Si12O32], K2Sm[AlSi4O12] · 0.375H2O, K4Yb2[Si8O21], and K4Ce2[Al2Si8O24] are determined. In addition, a synthesis product with Eu, in which the dominant phase is assumed to be K3Eu3+[Si6O15] · 2H2O, is studied. The oxidation state of lanthanides in the silicates under study is determined based on X-ray absorption near-edge structure spectroscopy. The Eu L 3-, Sm L 3-, Yb L 3-, and Ce L 3-edge X-ray absorption spectra of the studied silicates and reference samples are recorded using a Rigaku R-XAS laboratory spectrometer. As reference samples, Eu2+S, Eu3+F3, Eu 2 3+ O3, Sm 2 3+ O3, Yb 2 3+ O3, Yb3+F3, Yb3+Cl3, Ce 2 3+ O3, and Ce4+O2 are used. Comparison of the absorption edge energies of lanthanide silicates and reference samples shows that Eu, Sm, Yb, and Cе in all the samples studied are in the oxidation state 3+. The synthesized silicates will supplement our knowledge of possible rare-earth minerals existing in hydrothermal systems, which is important for analyzing the distribution spectra of rare elements, which are widely used for diagnostics of geochemical processes and determination of sources of ore materials.

XRD, FT-IR, and DFT study on a novel ethyl derivative of 3-hydroxy-2-quinoxalinecarboxylic acid by Serdar Badoğlu; Ersin Temel; Şenay Yurdakul; Orhan Büyükgüngör (987-996).
The novel ethyl derivative of 3-hydroxy-2-quinoxalinecarboxylic acid has been synthesized for the first time, characterized by FT-IR spectroscopy and single-crystal X-Ray diffraction. The crystal packing is achieved by inter-molecular C–H···N, C–H···O and N–H···O type hydrogen bonds, which play an important role in the formation of the 3D supramolecular network of the title compound. The geometries and vibrational frequencies of the title compound in monomer and dimer forms were investigated by density functional theory calculations employing the B3LYP hybrid functional. The calculation results are in accordance with the experimental data. In addition, the theoretical electronic properties like natural bond orbital (NBO) charges and frontier molecular orbitals were presented.

We have obtained luminescent complex compounds of europium(III) with quinaldic acid and β- diketones of composition Eu(Quin)2β-dic • Н2О, where Quin is the anion of quinaldic acid, and β-dic is the anion of acetylacetone (acac), benzoylacetone (bzac), or dibenzoylmethane (dbm). The spectral properties of the obtained compounds have been examined. The joint presence of quinaldic acid and β-diketone in the coordination sphere of europium(III) leads to a broadening of the absorption spectral range of the investigated complex compounds. We have found that the “anomalous” Stark structure of luminescence spectra and the luminescence quenching of complexes at 300 K are determined by the occurrence of a high-lying ligand–europium(III) charge-transfer state.

Three-dimensional motion of the center of the localized structure of atomic Bose–Einstein condensate in a dynamic trap has been analyzed. The transverse and longitudinal motions of the structure center are separated within the approximation of Newtonian-type mechanical equation. The transverse-motion equations are solved for the axisymmetric and quadratic transverse potentials.

Control of parameters of quantum memory for light in a cavity configuration by V. V. Kuz’min; A. N. Vetlugin; I. V. Sokolov (1004-1009).
Control of time dependences of waveforms is important for the application of optical signals in the nonclassical state that are recorded in various quantum-memory devices. Matching of waveforms at the signal detectors is needed for measurements using optical mixing (homodyne detection), detection of entangled states, etc. Earlier results for cavity quantum memory on an ensemble of cold atoms show that the waveform of the strong control field can be changed in such a way that the profile of optical signal recorded and readout from a collective atomic spin is convenient for measurements. In the course of recording, the control field provides the suppression of the reflection loss of the input signal related to the destructive interference of the signal and local field at the coupling mirror (impedance matching). Using an example of memory reading, we show that impedance matching provides additional possibilities for variations in the control field and allows efficient generation of output quantum signals with predetermined waveforms convenient for experimental measurements.

“Wandering” soliton in a nonlinear photonic crystal by T. M. Lysak; V. A. Trofimov (1010-1014).
On the basis of computer simulation, we demonstrate the possibility of a new type of “wandering” solitons implementation in nonlinear periodic layered structures. “Wandering” soliton moves across the layers, repeatedly changing its direction of motion due to the reflection from the photonic crystal (PC) boundaries with the ambient medium. The initial soliton is located inside a PC and occupies several of its layers. Its profile can be found as the solution of the corresponding nonlinear eigenvalue problem. “Wandering” solitons are formed as a result of a large perturbation of the wave vector, which leads to the soliton motion across photonic crystal layers. In the process of reflection from the boundary with the ambient medium, the soliton partly penetrates into the ambient medium at a depth equal to the width of several PC layers. A slow return of light energy, which previously left the PC, can take place at this moment.

To create a hybrid-aligned structure of a dual-frequency nematic liquid crystal (LC), we have obtained an approximate analytical solution of the system of equations that describes the dynamics of reorientations of the director under the action of a control electric signal of an arbitrary shape. Formulas obtained have been used to simulate a symmetric optical response of the LC structure for a sinusoidal electric pulse. It has been shown that, in terms of the used approximations, the results of the analytical calculation agree well with results of computer simulation and with experiment in the case of small deformations of the LC layer.

Properties of the T matrix in the Rayleigh approximation by V. G. Farafonov; V. I. Ustimov (1022-1033).
We have examined the properties of the T matrix in the Rayleigh approximation (i.e., in the electrostatic problem) for axisymmetric particles using an analog of the extended boundary condition method (EBCM). The T matrix can be constructed by two methods. In the first method, the field inside of the particle is initially determined and then the “scattered” field is found. In terms of the second approach, the problem is formulated straight for the scattered field. Theoretically, the two schemes are equivalent. Based on the refined analysis of a vast amount of numerical calculations for Chebyshev particles and pseudospheroids, it has been shown that, taking into account the influence of calculation errors, the second approach is much more efficient than the first one for determining the scattered field and the T matrix taking into account its symmetric character. Numerical investigations of the range of applicability of the EBCM have unambiguously confirmed theoretical inferences. Namely, the T matrix can be constructed by the EBCM only if there exists a nonempty intersection of analytical continuations of the expansions of the scattered and internal fields in terms of spherical functions. In other words, the radii of convergence of these expansions should satisfy the condition R 1 < R 2, which depends only on the particle shape.

Formation of 3D structures in a volumetric photocurable material via a holographic method by N. D. Vorzobova; V. G. Bulgakova; V. O. Veselov (1034-1037).
The principle of forming 3D polymer structures is considered, based on the display of the 3D intensity distribution of radiation formed by a hologram in the bulk of a photocurable material. The conditions are determined for limiting the cure depth and reproducing the projected wavefront configuration.

Particularities of optical pumping effects in cold and ultra-slow beams of Na and Cs in the case of cyclic transitions by M. Bruvelis; A. Cinins; A. Leitis; D. K. Efimov; N. N. Bezuglov; A. S. Chirtsov; F. Fuso; A. Ekers (1038-1048).
The time-dependent population dynamics of hyperfine (HF) levels of n 2 p 3/2 states is examined for cyclic transitions in alkali atoms. We study a slow and cold atomic beam of Na (n = 3) and Cs (n = 6), taking into account the long interaction time of light with atoms (~200 μs) inside the resonant laser beam. Simple analytical expressions for the populations of the excited states and for the intensities of the absorption lines are derived for a three-level system model. We show that at moderate pump laser power the mixing of HF levels is sufficient to form a flow of population from a cyclic transition to partially open transitions. We discuss various phenomena associated with the evolution of optical pumping that cannot be explained by general analysis of two-level system model.

Spectral and temperature characteristics of light transmission in solutions of chemical indicators by V. D. Gavrichev; A. L. Dmitriev; G. Karacharov; Yu. T. Nagibin (1049-1051).
Spectral and temperature characteristics of light transmission in water solutions of chemical indicators— bromophenol blue, bromothymol blue, and cresol red—were measured in the wavelength range of 500–750 nm and the temperature range from 20 to 90°С. It was demonstrated that these solutions can be applied in optical fiber thermometers with continuous reading which are not affected by strong external electromagnetic fields.

Determination of the director pretilt angle at liquid-crystal layer boundaries by polarimetric and crystal rotation methods in the same cell by A. A. Karetnikov; L. P. Amosova; D. A. Vakulin; N. A. Karetnikov; A. P. Kovshik; I. P. Kolomiets; E. I. Ryumtsev (1052-1055).
The pretilt angle of the director at the liquid crystal–glass interface is determined with the polarimetric and crystal rotation methods. The polarimetric method has been modified with the aim of increasing the measurement accuracy. The results obtained with the modified polarimetric method are verified with the use of reference plane-parallel iceland spar plates with known pretilt angles of the optical axes. It is shown that the pretilt angles found with the crystal rotation and modified polarimetric methods coincide within the measurement accuracy.