Optics and Spectroscopy (v.115, #5)

Using the methods of a symmetry group chain, construction of a rigorous, combined description of the torsional motions of exchange and nonexchange types in the ground electronic state of the trimethylborane molecule B(CH3)3 is considered.

The FT-IR and micro-Raman spectra of three n-alkyltrimethylammonium bromides (dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and hexadecyl(cetyl)trimethylammonium bromide (CTAB)) in powder form were recorded in the regions 4000–550 cm−1 and 3200–300 cm−1, respectively. The optimized geometries and vibrational frequencies of DTAB, TTAB and CTAB have been carried out with ab initio Hartree-Fock (HF) and density functional theory method B3LYP calculations with the 6–31 G (d, p) basis set in the ground state. The comparison of the observed fundamental vibrational frequencies and calculated results for the fundamental vibrational frequencies of DTAB, TTAB and CTAB indicate that the scaled B3LYP method is superior compared to the scaled HF method.

Excitation of lowest electronic states of thymine by slow electrons by I. V. Chernyshova; E. J. Kontros; P. P. Markush; O. B. Shpenik (645-650).
Excitation of lowest electronic states of the thymine molecules in the gas phase is studied by elec- tron energy loss spectroscopy. In addition to dipole-allowed transitions to singlet states, transitions to the lowest triplet states were observed. The low-energy features of the spectrum at 3.66 and 4.61 eV are identified with the excitation of the first triplet states 13 A′ (π → π*) and 13 A″ (n → π*). The higher-lying features at 4.96, 5.75, 6.17, and 7.35 eV are assigned mainly to the excitation of the π → π* transitions to the singlet states of the molecule. The excitation dynamics of the lowest states is studied. It is found that the first triplet state 13 A′(π → π*) is most efficiently excited at a residual energy close to zero, while the singlet 21 A′(π → π*) state is excited with almost identical efficiency at different residual energies.

Decay of electronic excitations in CdS and CdS/ZnS colloidal quantum dots: spectral and kinetic investigations by M. S. Smirnov; D. I. Stasel’ko; O. V. Ovchinnikov; A. N. Latyshev; O. V. Buganov; S. A. Tikhomirov; A. S. Perepelitsa (651-659).
Using the spectral methods of induced absorption, luminescence, and photostimulated luminescence flash, we have experimentally investigated processes of decay of electronic excitations in CdS colloidal quantum dots and in CdS/ZnS “core-shell” systems synthesized in gelatin by the sol-gel method. It has been shown that the decay of electronic excitations in colloidal quantum dots of this type is predominantly related to a fast localization of nonequilibrium charge carriers on surface defects and their subsequent recombination during times on the order of units and tens of picoseconds. The passage to core-shell systems eliminates, to a large extent, surface defects of the core, some of which are luminescence centers. However, upon using the sol-gel synthesis, a noticeable fraction of luminescence centers are formed in the interior of the CdS quantum dot, which, as well as in the case of CdS/ZnS systems, ensures localization of exciton, blocks its direct annihilation, and maintains recombination radiation.

Optical properties of 2D nanocomposite-based photonic crystals with a lattice defect are studied. The nanocomposite comprises metallic nanospheres dispersed in a transparent matrix and is characterized by an effective resonant permittivity. Transmission spectrum for s-polarized waves at oblique incidence is calculated. Spectral manifestation of the splitting of the defect mode when its frequency coincides with the resonant frequency of the nanocomposite is studied. The essential dependence of the splitting on the angle of incidence and concentration of metallic nanospheres in the nanocomposite matrix is established. Specific features of spatial distribution of the electric field intensity in defect modes of crystals are analyzed.

Transmission and spectral properties of short optical plasmon waveguides by I. L. Rasskazov; V. A. Markel; S. V. Karpov (666-674).
We study the spectral and transmission properties of optical waveguides in the form of different chain configurations of spherical Ag nanoparticles that can be synthesized under conditions of selective deposition on a dielectric substrate from a nanocolloid.

An optical method for measuring nanoparticle size by N. G. Kokodii; M. V. Kaydash; V. A. Timaniuk (675-678).
We describe a method for determining the size of nanoparticles and their optical constants that is based on analysis of the spectrum of extinction of light by these particles. We show that the results of our mathematical modeling agree well with the experimental data.

Dynamics of oxide phases on the surface of single- and polycrystalline Pb1 − x Sn x Te films upon their investigation by the raman light scattering method by S. P. Zimin; E. S. Gorlachev; N. V. Gladysheva; V. V. Naumov; V. F. Gremenok; H. G. Seidi (679-684).
We have studied Raman spectra of single- and polycrystalline Pb1 − x Sn x Te (0 ≤ x ≤ 1) films on different substrates in relation to the intensity of the laser action. The composition of oxide phases on the surface of lead-tin telluride films has been described, and their modification as a result of photostimulated oxidation of the surface during measurements of spectra has been analyzed. We have shown that, for films with a small mole fraction of tin telluride (x ≤ 0.26), irrespective of the crystalline state, predominant oxidation of tellurium with the formation of the compound TeO2 takes place during the laser action. In films with a high content of tin, at a laser-action intensity higher than 1000 μW, tellurium dioxide TeO2 on the surface is replaced with tin dioxide SnO2.

Study of the ion mobility in a Li0.03Na0.97Ta0.4Nb0.6O3 solid solution by raman spectra by N. V. Sidorov; N. A. Teplyakova; M. N. Palatnikov (685-689).
We have studied ion mobility in a Li0.03Na0.97Ta0.4Nb0.6O3 solid solution by its Raman spectra. It has been revealed that, as the temperature of the solution is increased to approach the point of the phase transition to a state with a high conductivity with respect to lithium, the lines with frequencies at 77, 118, and 142 cm−1, which refer, respectively, to librations of oxygen octahedra Nb(Ta)O6 as a whole and vibrations of Li and Na ions in octahedra, considerably broaden, decrease in intensity, and smear into the wing of the Rayleigh line. Remaining lines are preserved in the spectrum. We have observed that the width of the line with a frequency of 118 cm−1 depends exponentially on temperature, while the width of the line with a frequency of 142 cm−1 changes linearly with it, which makes it possible to attribute to the line with the frequency of 118 cm−1 to vibrations of Li+ cations, whereas the line with the frequency of 142 cm−1 should be attributed to vibrations of Na+ cations in AO12 cuboctahedra. The average lifetime of Li+ ions in equilibrium positions and the jump barrier have been estimated to be ∼8 × 10−12 s and ∼20 kJ/mol, respectively. This agrees well with the data in the literature on measurements of electric conductivity.

Optical spectroscopy and electronic structure of compounds HoNi5 − x Al x (x = 0, 1, 2) by Yu. V. Knyazev; A. V. Lukoyanov; Yu. I. Kuz’min; A. G. Kuchin (690-695).
The optical properties of the compounds HoNi5 − x Al x (x = 0, 1, 2) have been investigated using the ellipsometric method in the wavelength range from 0.22 to 16 μm. The electronic structure of these intermetallic compounds has been calculated in the local electron-spin density approximation with the correction for strong electronic interactions in the 4f shell of the holmium ions. The experimental dispersion dependences of optical conductivity in the region of interband light absorption have been interpreted based on the results of the calculation of the electron density of states. The plasma and relaxation frequencies of electrons have been determined.

We have considered the possibility of measuring the linear and quadratic (in magnetic field) magnetooptical effects in magnetooptical crystals that are simultaneously exposed to a constant (polarizing) magnetic field and to an alternating magnetic field under conditions of magnetomechanical resonance. The use of a Mueller polarimeter in combination with spectral analysis of the intensity of the light wave at the output of the polarimeter makes it possible to selectively determine elements of the Mueller matrix and minimize the amount of measurements. We have shown that there is a possibility of solving the inverse problem on finding two components of the alternating magnetic field in which a magnetooptical crystal is placed.

Physical, structural, and luminescence studies of Nd3+ doped MgO-ZnO borate glass by W. A. W. Razali; K. Azman; S. Hashim; Yasser Saleh Mustafa Alajerami; S. A. Syamsyir; A. Mardhiah; M. H. J. Ridzwan (701-707).
A series of borate glass of the system xNd2O3-5MgO-20ZnO-(75 − x)B2O3, where x = 0.5, 1.0,1.5, 2.0, and 2.5 was successfully fabricated using melt quench method. The properties of the glass were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), absorption and luminescence spectra. The upconversion properties of Nd3+ doped borate glass were observed by using 574 nm excitation wavelength corresponding to 4 I 15/22 H 114/2 transition. The emission bands centered at 460, 500 and 620 nm which corresponding to the Nd3+ transitions, 4 F 7/24 I 15/2, 2 H 11/24 I 15/2, and 4 F 9/24 I 15/2 respectively were observed at room temperature. The presence of Nd3+ in borate based glass could intensify the upconversion luminescence spectra as it can potentially be used as host materials for upconversion lasers.

Spectroscopic and laser characteristics of new efficient luminophores for a wide spectral range based on complexes of dipyrrolylmethene derivatives with difluorine borate by R. T. Kuznetsova; Yu. V. Aksenova; T. A. Solodova; D. E. Bashkirtsev; T. N. Kopylova; E. N. Tel’minov; G. V. Mayer; M. B. Berezin; A. S. Semeikin; S. L. Yutanova; E. V. Antina; S. M. Arabei; T. A. Pavich; K. N. Solovyov (708-716).
We have studied the spectral-luminescent, lasing, photochemical, and endurance characteristics of a series of new efficiently emitting difluorine borate complexes with dipyrrolylmethenes of different structures. Experimental data have been obtained in polar and nonpolar organic solvents and in solid polymer films involving the participation of silicate structures. We have discussed relations of the structure of investigated compounds and formed solvates with their optical characteristics, and have given guidelines on the use of particular compounds as active media of tunable lasers for determining spectral ranges.

Spectroscopic and proton-acceptor properties of biologically active molecules of benzoic acid and its derivatives by G. B. Tolstorozhev; M. V. Bel’kov; T. F. Raichenok; I. V. Skornyakov; O. I. Shadyro; S. D. Brinkevich; S. N. Samovich; O. K. Bazyl’; V. Ya. Artyukhov; G. V. Mayer (717-726).
We have measured the absorption, fluorescence, fluorescence excitation spectra, fluorescence quantum yields, and IR Fourier-transform spectra of aromatic acids in solutions. We have considered spectroscopic particular features of benzoic acid, its hydroxylated and methoxylated derivatives. Using quantumchemistry methods, we have calculated and interpreted electronic spectra. Data of calculations have been compared with experimental results. We have ascertained the main channels and mechanisms of photophysical relaxation processes in the molecules under study. Proton-acceptor properties of molecules of aromatic acids have been evaluated. We have analyzed in detail mechanisms by which hydrogen bonds are formed, intramolecular charge redistribution is realized, and the electron density of oxygen atoms changes. Spectroscopic indications of participation of oxygen-containing groups in intramolecular interactions and in intermolecular interactions with the formation of cyclic dimers have been revealed.

We present results of our systematic investigation and comparative analysis of the spectral-kinetic properties of absorption and fluorescence of two series of related planar porphyrins in liquid media at 293 K, in which deviations from the planarity are caused by contact steric interactions of eight peripheral β-pyrrole methyl (−CH3) or ethyl (−C2H5) groups with a successively increasing number (from one to four) and varying position of meso-phenyl (Ph) substituents in the porphyrin macrocycle. It is substantiated that considerable differences between the spectral-kinetic properties of absorption and fluorescence of the octaethyl- and octamethylporphyrin molecules, which have the same number of meso-phenyl substituents, are caused by fundamentally different roles played by β-ethyl and β-methyl groups, which differ in volume and which determine differences in the character of steric interactions and the efficiency of the dynamic relaxation of the tetrapyrrole macrocycle. It is revealed that there is a difference between calculated f theor and experimentally determined f exp values of the fluorescence probability, which is caused by conformational rearrangements of spatially distorted porphyrin macrocycles in the S 1 excited state, which reduce the oscillator strength and lower the energy of the long-wavelength transition S 0S 1. It is found that the chemical nature, the size, and the number of bulky -CH3 or -C2H5 β-pyrrole groups affect weakly rate constants of fluorescence quenching by molecular oxygen and do not create noticeable steric hindrances for contact interactions of the oxygen molecule with the π-conjugated system of the tetrapyrrole macrocycle.

It has been shown that the two-electron mechanism of nonlinear optical absorption considered in the first two parts of our study, even at laser radiation intensities j ∼ 103-104 W/cm2 in the case of nanosecond pulses, can lead to almost complete absorption of light by crystals that are transparent to weak radiation of the same wavelength. A number of materials that can exhibit the considered effects have been described.

The applicability of an analog of the extended boundary condition method, which is popular in light-scattering theory, is studied in combination with the standard spherical basis for the solution of an electrostatic problem appearing for spheroidal layered scatterers the sizes of which are small as compared to the incident radiation wavelength. In the case of two or more layers, polarizability and other optical characteristics of particles in the far zone are shown to be undeterminable if the condition under which the appearing systems of linear equations for expansion coefficients of unknown fields are Fredholm systems solvable by the reduction method is broken. For two-layer spheroids with confocal boundaries, this condition is transformed into a simple restriction on the ratio of particle semiaxes a/b< $sqrt 2 $ + 1. In the case of homogeneous particles, the solvability condition is that the radius of convergence of the internal-field expansion must exceed that of the expansion of an analog of the scattering field. Since homogeneous spheroids (ellipsoids) are unique particles inside which the electrostatic field is homogeneous, it is shown that the solution can be always found in this case. The obtained results make it possible to match in principle the results of theoretical and numerical determinations of the domain of applicability for the extended boundary condition method with a spherical basis for spheroidal scatterers.

Influence of thickness on optical properties of titanium layers by H. Kangarlou; M. Motallebi Aghgonbad (753-757).
Titanium layers with different thicknesses of 21, 83.7, and 133 nm and same other deposition conditions were deposited on glass substrates at 300 K, by physical vapor deposition method under high vacuum conditions. The optical reflectance of the layers was measured in the wave length range of 400–800 nm. The optical properties were calculated by using Kramers-Kronig relations. Relation between the optical properties and nanostructure of the layers was investigated. By using Generalized Gradient Approximations in context of plane wave pseudopotentials (norm conserving and ultrasoft) method, band structure calculated and compared with experimental results.

The use of ultrashort laser pulses is a way to increase recoil momentum under laser ablation of materials, because, in this case, the energy deposition per unit volume of the target material is substantially higher due to reduced heat dissipation. By using methods of combined interferometry, we estimated the specific impulse (∼200–900 s), momentum coupling coefficient (∼2 × 10−5−3 × 10−4 Ns/J), laser-energy conversion efficiency to kinetic energy of the gas-plasma flow (∼0.05–0.82), and degree of the gas-plasma flow monochromaticity (∼0.72–0.92) under femtosecond (τ ∼ 45 fs, λ ∼ 800 nm) ablation of refractory metals (Ti, Zr, Mo, and Nb) in vacuum.

Thermophysical and gas-dynamic characteristics of gas-plasma flows induced by ultrashort laser pulses interacting with a thin-film copper target in vacuum were studied experimentally. Using combined laser interferometry and complex processing of experimental data, we estimated the momentum coupling coefficient and the efficiency of laser-energy conversion to kinetic energy, spatiotemporal distributions of the number density and velocities of particles, pressure, and temperature in the gas-plasma flow. We provide comparative analysis of presented data with those found in the literature, which were obtained by other methods.

It is demonstrated that the photodissociation of oxyhemoglobin in cutaneous blood vessels and capillaries allows additional extraction of molecular oxygen, prevents hypoxia, and stimulates aerobic metabolism of cells. On the basis of the studied phenomena, a new optical technology of local oxygenation of tissue directly in the zone of laser irradiation has been developed. It is shown that the efficiency of the proposed method for laser-induced oxygenation of biotissues is comparable with the efficiency of hyperbaric oxygenation, with local action being an additional advantage. Various aspects of the applications of the new technology in modern medicine in which the elimination of local hypoxia is needed are discussed. The proposed optical method for local oxygenation of biotissues makes it possible to solve the hypoxia problem in malignant tissue and substantially increase the efficiency of photodynamic, radiation, and chemical therapy in modern oncology.

Noninvasive determination of spectral depth of light penetration into skin by S. A. Lisenko; M. M. Kugeiko; A. M. Lisenkova (779-785).
A noninvasive method for determining the spectral depth of light penetration into the skin has been developed. It is based on measuring fluxes of radiation reflected from the skin in N Λ ≥ 3 narrow or wide spectral parts and spectral analysis thereof using the regression approach to solving ill-posed inverse problems. The possibility of estimating the spectral depth of light penetration into skin by skin images in three wide spectral parts (red, green, and blue) is demonstrated. Errors of the method are estimated under conditions of general variability of structural-morphological skin parameters, and its resistance to errors of optical measurements is analyzed.