Optics and Spectroscopy (v.122, #6)

The structure and vibrational spectral parameters of a complex of HF with the planar (H2CO)2 dimer by V. P. Bulychev; A. M. Koshevarnikov; K. G. Tokhadze (851-858).
Equilibrium nuclear configurations of the planar formaldehyde homodimer (H2CO)2 and the (H2CO)2···HF complex are determined in the MP2/6-311++G(3df, 3pd) approximation taking into account the superposition error of basis sets of monomers. Harmonic values of the frequencies and intensities of fundamental transitions between vibrational states of these hydrogen-bonded complexes were calculated using the Gaussian 09 package of programs. Anharmonic values of the frequencies and intensities of the ν(H–F) stretching vibration and several intermolecular vibrations in the (H2CO)2···HF trimer were obtained from variational solutions of one-, two-, and three-dimensional vibrational Schrödinger equations. The anharmonic influence of the C=O and hydrogen bond O···H–F stretching vibrations, as well as of librational vibrations of monomers, on the spectral parameters of the strongest ν(H–F) absorption band of trimer was studied.

The relaxation parameters of the lines of the P, Q, and R branches of the ν1 ammonia ν1 band are calculated in the case of self-broadening. In the case of doublets, the effects of collisional interference of the doublet components have been taken into account. It is shown that the cross-relaxation parameters of the components can reach ~60% of the values of the self-broadening coefficients, which gives rise to the narrowing of the components and indicates that the isolated line approximation is inapplicable. Comparison with experimental data is made. Good agreement for self-broadening coefficients is obtained. In the case of the self-shift coefficients, discrepancies are considerable in both magnitude and sign, and it is impossible to elucidate their reasons without invoking additional experimental data.

New sub-Doppler resonances at central frequencies of atomic (molecular) transitions that appear in the spectrum of absorption of the probe optical radiation under the influence of optical pumping propagating in the orthogonal direction through a relatively narrow area of a cylindrical cell containing dilute gas medium are discovered and analyzed. These resonances are induced by specific optical pumping of atoms as they fly freely from the inner cell surface through the pumped region toward the probe optical beam. The obtained mathematical relations are used to investigate the dependence of the discussed resonances on the intensity and spatial distribution of the localized optical pumping. The proposed method could allow reducing the Doppler broadening of the detected spectral lines by the factor equal to the ratio of the effective width of the narrow pumped region to the cell radius. The obtained results may find application in high-resolution spectroscopy of atoms (molecules), as well as for laser-frequency stabilization by using the discovered sub- Doppler resonances.

Influence of the degree of neutralization of acrylic acid and cross-linking agent on optical properties and swelling of sodium polyacrylate by I. V. Gredyukhina; L. V. Plotnikova; N. S. Balbekin; M. S. Kulya; N. V. Petrov; A. P. Nechiporenko; M. V. Uspenskaya (877-879).
Optical characteristics of polymerization products under variable degrees of neutralization of acrylic acid (AA) and cross-linking agent and at a fixed content of redox components have been studied by IR spectroscopy of frustrated total internal reflection and THz spectroscopy. The results of the analysis show that absorption of IR radiation and dispersion of THz radiation for the samples under study depend on the degree of AA neutralization, which predetermines the mechanism of structure formation of hydrogels, refractive index, and degree of their limited swelling. It is found that the dependences of the refractive index of dry compact hydrogels and the degree of limited swelling of ground polymer samples on the content of neutralizing agent in solutions of the reaction systems have a symbatic character.

Infrared reflection-absorption spectra of thin films of α-crystalline hexafluoroethane deposited on a gold-plated copper mirror are measured at temperatures of 70 and 80 K. The bands corresponding to strong in the dipole absorption vibrations ν5 and ν10 have complex contours, the shape of which is explained in terms of the resonant dipole–dipole interaction between identical spectrally active molecules of the crystal. Splittings of the complex ν5 and ν10 bands are explained taking into account two effects: the Davydov splitting and the LO–TO splitting of the strong modes. Bands of the asymmetric 13С12СF6 isotopologue in the absorption spectrum of the crystal exhibit an anomalously large isotope shift as compared with the shift in the spectrum of free molecules. This anomaly is explained by intermolecular resonant dipole–dipole interaction of asymmetric 13С12СF6 isotopologue with molecules of the environment, consisting of the most abundant 12C2F6 isotopologue. The correctness of the given interpretation is confirmed calculating these three effects in the model of resonant dipole–dipole interaction.

Infrared spectroscopy and tunneling of protons in crystals with hydrogen bonds by V. M. Timokhin; V. M. Garmash; V. A. Tedzhetov (889-895).
Infrared (IR) spectra of a number of crystals with proton conductivity have been investigated. The width of the band gap is determined, and most lines of the IR absorption spectra are identified. A direct proof of the existence of protons, defects ОН–and Н3О+, molecules of adsorbed and crystallization water in the crystals grown in ordinary and in heavy water is also carried out. The transparency of the rectangular potential barrier for protons is calculated, and the possibility of tunneling and translational diffusion of protons in wide-band-gap crystals is shown.

Absorption and resonant light-scattering spectra of nanoparticles (NPs) of silver, and their complexes with water-soluble Cu(II)-5,10,15,20-tetrakis(4-N-methylpyridinium)-porphyrin (CuTMpyP4) and Fe(II)-5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (FeTSPP) have been compared. It is shown that in the presence of cationic CuTMpyP4, the band of surface plasmon resonance in the absorption and resonant scattering spectra of silver NPs is shifted to the long-wavelength region that is associated with the agglomeration of the particles caused by the Coulomb attraction between the silver particles and the porphyrin molecules. Addition of anionic FeTSPP to the silver NP solution does not lead to any spectral changes. The observed effect of silver-NP association induced by the cationic porphyrin can be used to develop an optical method for the detection of nanoparticles in solutions.

Formation of H a - hydrogen centers upon additive coloration of alkaline-earth fluoride crystals by E. A. Radzhabov; A. V. Egranov; R. Yu. Shendrik (901-905).
The mechanism of coloration of alkaline-earth fluoride crystals CaF2, SrF2, and BaF2 in calcium vapors in an autoclave with a cold zone is studied. It was found that the pressure in the autoclave upon constant evacuation by a vacuum pump within the temperature range of 500–800°C increases due to evaporation of metal calcium. In addition to the optical-absorption bands of color centers in the additively colored undoped crystals or to the bands of divalent ions in the crystals doped with rare-earth Sm, Yb, and Tm elements, there appear intense bands in the vacuum ultraviolet region at 7.7, 7.0, and 6.025 eV in CaF2, SrF2, and BaF2, respectively. These bands belong to the Ha - hydrogen centers. The formation of hydrogen centers is also confirmed by the appearance of the EPR signal of interstitial hydrogen atoms after X-ray irradiation of the additively colored crystals. Grinding of the outer edges of the colored crystals leads to a decrease in the hydrogen absorption-band intensity with depth to complete disappearance. The rate of hydrogen penetration inside the crystal is lower than the corresponding rate of color centers (anion vacancies) by a factor of tens. The visible color density of the outer regions of the hydrogen-containing crystals is several times lower than that of the inner region due to the competition between the color centers and hydrogen centers.

Spontaneous luminescence of Eu3+ ions in porous Y2O3 nanospheres by S. V. Zaitsev; Yu. V. Ermolaeva; N. A. Matveevskaya; I. I. Zver’kova; A. V. Tolmachev (906-911).
A study of the luminescence of Eu3+ ions in Y2O3 nanospheres indicates a significant influence of the porous structure of nanoparticles on the luminescence of dopant ions. It is shown that filling the nanopores of initially porous Y2O3 nanospheres shortens the decay time of the spontaneous luminescence of doping europium ions. The change in the decay time is associated with the change in the effective refractive index of the porous nanospheres.

The luminescence spectra of Cr3+ and Eu3+ ions embedded in mullite ceramic samples are studied. The samples were annealed at temperatures from 600 to 1200°С. Beginning at a temperature of 890°С, the spectra demonstrated the presence of a newly formed crystal phase. At temperatures from 920 to 1200°С, the crystalline form manifested itself as a stable mullite phase. A temperature of 920°С corresponded to a sharp change in the symmetry of the crystal field around Eu3+ (phase transition). The parameters of the spectral lines of ions were used to estimate the mullite crystal-lattice disorder and the residual deformations in ceramic samples. The spread of the mullite crystal-lattice parameter is determined as |Δа/а| ≈ 0.028 and is independent of the annealing temperature.

The main mechanisms of the visible electroluminescence (EL) of porous silicon are reviewed. Characteristics of photoluminescence and EL of diode structures based on porous silicon are compared. Metals having a smaller value of the electron work function (3.6 eV, Mg) than do Al and Au are proposed as the material for making contacts in such diode structures to increase the efficiency of their EL in the visible region of the spectrum. The main problems and prospects of light-emitting devices based on porous silicon are formulated.

The results of studying optical-absorption and spectral curves of photoconductivity in MnGaInS4 single crystals are presented for two light polarizations (E || C and EC). The intrinsic absorption edge and the band-gap width of MnGaInS4 single crystals in polarized light are determined. The anisotropy of optical absorption and photoconductivity spectrum of MnGaInS4 single crystals is observed. It is suggested that the polarization splitting of the absorption edge is related to the splitting of the MnGaInS4 valence band.

The vibrational frequencies and corresponding intensities have been calculated ab initio for the center of the Brillouin zone of crystalline magnesium, calcium, strontium, and barium nitrates; magnesium nitrate hexahydrate; and calcium nitrate tetrahydrate. The calculation has been performed within the electron- density functional theory using the PBE exchange-correlation functional in the basis of localized atomic orbitals with the aid of the CRYSTAL14 software. The calculated values and the experimental IR and Raman spectral data on strontium and barium nitrates are shown to be in satisfactory agreement. The frequencies of normal long-wavelength vibrations in the nitrates become red-shifted with an increase in the cation atomic mass. The occurrence of several peaks due to the vibrations of hydrogen atoms in water molecules with different dynamic charges is predicted in the IR spectrum of hexahydrate magnesium in the frequency range above 3430 cm–1.

The theory of SERS on semiconductor and dielectric substrates by A. M. Polubotko; V. P. Chelibanov (937-943).
It is demonstrated that the reason for SERS on dielectric and semiconductor substrates is enhancement of the electric field in the regions of the tops of surface roughness with a very small radius or a very large curvature. The enhancement depends on the dielectric constant of the substrate and is stronger for a larger dielectric constant. It is indicated that the enhancement on dielectrics and semiconductors is weaker than on metals with the same modulus of the dielectric constant. The result obtained is confirmed by experimental data on the enhancement coefficients obtained for various semiconductor and dielectric substrates.

Optical and electrical properties of thin NiO films deposited by reactive magnetron sputtering and spray pyrolysis by H. P. Parkhomenko; M. N. Solovan; A. I. Mostovoi; I. G. Orletskii; O. A. Parfenyuk; P. D. Maryanchuk (944-948).
Thin NiO films are deposited by reactive magnetron sputtering and spray pyrolysis. The main optical constants, i.e., refractive index n(λ), absorption coefficient α(λ), extinction coefficient k(λ), and thickness d, are determined. The temperature dependence of the resistance of thin films is found, and the activation energy of films deposited by different methods is determined.

Nonlinear-photonics devices on the basis of the coherent interaction of optical radiation with resonant media (a review) by R. M. Arkhipov; M. V. Arkhipov; A. V. Pakhomov; I. Babushkin; N. N. Rosanov (949-954).
We have examined examples of nonlinear-photonics devices that are based on the coherent interaction of light with matter. Such interaction takes place if the duration of a light pulse is shorter than the relaxation times T 1 and T 2 in a resonant medium and if the strength of the light field is so high that Rabi oscillations arise. Theoretical analysis shows that these systems have a number of advantages compared to similar devices that operate under incoherent interaction conditions of light with matter.

We investigate conditions for the occurrence of a bistable response from a thin layer of an ensemble of two-level inhomogeneously broadened emitters upon their interaction with resonant radiation. A Lorentz correction to the local field that acts on emitters is taken into account. Bistability phase diagrams in the parameter space (inhomogeneous broadening, detuning away from resonance, and local field) are calculated, and the occurrence of optical hysteresis of the system is demonstrated. In addition to this, we study the switching time from the lower stable branch of the bistable characteristics to the upper one and vice versa against the intensity of the driving field, which determines the operation speed of a bistable device. The possibility of using a thin layer of resonant emitters as a multichannel all-optical switch is discussed.

Various recently emerged applications of mid-infrared pulses for high-order harmonic generation in laser plasmas produced on the surfaces of various materials are reviewed. Among them are (a) the highorder harmonic generation in Ag, Sn, fullerene, and graphene nanoparticle-containing plasmas using tunable two-color mid-infrared pulses, (b) efficiency dependence on the generating particle properties in the case of two-color high-harmonic generation of the longer-wavelength radiation in the plasmas, and (c) high-order sum and difference frequency generation using tunable two- and three-color commensurate and incommensurate mid-infrared pumps of graphite plasma. These studies demonstrate the perspectives of the frequency conversion of mid-infrared radiation in the extended laser-produced plasmas.

We have found an analytical expression for the absorption coefficient of electromagnetic radiation in a quantum channel with a parabolic confinement potential. The calculation has been performed using the second-order perturbation theory taking into account the scattering of a quasi-one-dimensional electron gas by ionized impurities. We have analyzed the dependences of the absorption coefficient on the frequency of the electromagnetic radiation and the magnetic field. The appearance of additional resonant peaks, which are caused by scattering by impurities, has been found.

An optico-mechanical model describing the coherent (directed) transmittance and the degree of polarization of forward-transmitted light by a polymer film with elongated liquid-crystal (LC) drops has been developed. This model, based on the Foldy–Twersky and anomalous-diffraction approximations, makes it possible to analyze the optical response of a film under extension as a function of the film thickness, refractive index of the polymer, the sizes and anisometry parameters of liquid-crystal drops, their concentration, internal structure, polydispersity, and orientation of optical axes. The model is verified based on the comparison of numerical and experimental data for the inverse modification of interfacial anchoring by an ion-forming surfactant. The internal drop structure is determined by solving the problem of minimizing the volume free energy density. A comparative analysis of the calculated transmittance and degree of polarization for films with uniform homeotropic and modified inhomogeneous interfacial anchoring is performed. The spectral polarization characteristics of a film with elongated LC drops and single-domain internal structure, formed under mechanical extension with the aid of surfactants, are investigated.

Refractometry of Rb2ZnCl4 crystals under uniaxial pressure by V. I. Stadnik; V. B. Stakhura; B. V. Andrievskii (995-1001).
The influence of uniaxial pressures applied along the main crystallophysical directions on the dispersion and temperature dependences of the refractive index n i of Rb2ZnCl4 crystals has been investigated. The n i value is found to be rather sensitive to uniaxial pressures, whereas uniaxial stress does not change the character of the dispersion and temperature dependences of n i. The pressure-induced changes in electronic polarizability αі, refraction R, and the parameters of UV oscillators are studied for mechanically deformed Rb2ZnCl4 crystals. The contributions of the UV and IR oscillators to the changes in n i at different temperatures, in different spectral regions, and under different mechanical stresses are estimated. The points of paraelectric–incommensurate–commensurate phase transitions (PTs) are found to undergo a significant pressure-induced shift to different temperature regions, depending on the pressure-application direction.

Application of whispering-gallery-mode optical microcavities for detection of silver nanoparticles in an aqueous medium by A. A. Samolenko; G. G. Levin; V. L. Lyaskovskii; K. N. Min’kov; A. D. Ivanov; I. A. Bilenko (1002-1004).
The results of an experimental investigation of a sensor intended for detection and measurement of concentration of nanoparticles in an aqueous medium, which is based on optical-dielectric whispering-gallery-mode microcavities, are presented. Variation of the frequency and Q-factor of the eigenmodes of the microcavity upon its interaction with silver nanoparticles is studied. It is demonstrated that this type of sensor can be used for measurement of infinitesimally low concentrations of nanoparticles.

Up-conversion in an Er-containing nanocomposite and microlasers based on it by N. O. Sobeshchuk; I. Yu. Denisyuk (1005-1007).
The results of an investigation of three-dimensional polymer microcavities doped with inorganic luminescent particles are presented. Microlasers in the form of rectangular parallelepipeds were fabricated based on the SU8 2025 photoresist by means of compact UV lithography. Luminescent particles containing erbium oxide were obtained by low-temperature synthesis of the corresponding chlorides in a nonaqueous medium. The obtained spectra confirm the presence of a narrowband laser radiation exhibiting a Stokes shift.

Polarization analysis of the beam-steering device of quantum optical systems by A. S. Akent’ev; M. A. Sadovnikov; A. L. Sokolov; G. V. Simonov (1008-1014).
Polarization analysis of the laser radiation of quantum optical systems intended for pulsed laser ranging of satellites orbiting the Earth is conducted. The polarization states of laser radiation at the output of a laser rangefinder for different azimuth and elevation angles of satellites are determined. Problems related to controlling polarization losses upon reflection from the dielectric mirrors of the quantum optical system and reduction of error of laser ranging by using circularly polarized laser radiation are analyzed. It is confirmed that it is effective to use circularly polarized laser radiation for laser ranging of satellites orbiting the Earth.

A study of muscular tissue of animal origin by reflection-spectroscopy methods by L. V. Plotnikova; A. P. Nechiporenko; S. M. Orekhova; P. P. Plotnikov; A. L. Ishevskii (1015-1018).
A comparative analysis of the spectral characteristics of the surface of muscular tissue of animal origin (pork) and its main components has been performed by the methods of diffuse reflection electronic spectroscopy (DRES) and frustrated total internal reflection IR spectroscopy. The experiments have shown that the application of the DRES method makes it possible to detect more pronounced changes in the surface optical characteristics of muscular tissue and obtain electronic spectra containing information about the component composition of its main parts under successive extraction of sarcoplasmic materials, myofibrillar proteins of the actomyosin complex, and stroma mucopolysaccharides.

Erratum to: “A highly efficient white-light-emitting diode based on a two-component polyfluorene/quantum dot composite” by S. V. Dayneko; P. S. Samokhvalov; D. Lypenko; G. I. Nosova; I. A. Berezin; A. V. Yakimanskii; A. A. Chistyakov; I. Nabiev (1020-1020).