Optics and Spectroscopy (v.92, #6)

Study of europium traces by laser resonance ionization spectroscopy by A. T. Khalmanov; Kh. S. Hamraev; A. T. Tursunov; O. Tukhliboev (815-817).
A three-stage scheme for the excitation of the autoionization state of europium atoms is realized, and the corresponding ionization cross section is determined: σ=6.5×10−10 cm2. Analytical signals from europium atoms are recorded in standard and waste water solutions used in mining noble metals and in the diagnostics of rare-earth elements.

Data on the lifetimes of the vibrational-rotational levels of the excited electronic states of hydrogen molecule (including H2, D2, HD, DT, and T2 isotopomers) are reviewed. All data on the rotational sublevels of the lowest vibrational levels of various electronic states are presented, which were available before June 2001. A comparative analysis of the data obtained by various researchers using different methods (experimental, semi-empirical, and non-empirical) is performed for the first time. The influence of non-adiabatic intramolecular interactions on the dependence of lifetimes of the rovibronic levels of hydrogen molecule on the vibrational and rotational quantum numbers is discussed. A set of reliable data is selected which can be recommended for use in various applications.

Absorption and emission dynamics in concentrated optical ensembles under laser excitation by V. A. Smirnov; G. M. Ermolaeva; V. B. Shilov (851-858).
A new theoretical model describing the emission and absorption dynamics in an ensemble of molecules under intense coherent pulsed pumping is developed on the basis of the concepts of cooperative light-induced luminescence (CLIL). The CLIL development is described within the framework of formalism of the system density matrix in the space of photon wave functions. It is shown that the fast growth of CLIL relates to the development of coherent states of the quantum field in the area of efficient cooperative interactions of molecules (coherence volume). A system of equations for the calculation of CLIL energy, population of excited states, and optical absorption of the system in dependence on the laser pump energy density is solved. The theoretical results obtained are in good agreement with the experimental data.

The effect of an external electric field on narrow spectral holes in S1←S0 absorption bands of molecules of free-base phthalocyanine and its complex with Al in polyvinyl butyral films at 4.2 K was studied. It was found that the average values of the change in the electric dipole moment due to phototransitions in the free-base phthalocyanine and its complex amount to 0.135 and 0.145 D, respectively. Both these values considerably exceed the relevant values for phthalocyanine complexes with Zn and Mg in the same matrix. Possible causes of the observed effects are discussed. Most probably, they are related to the differences in the structure of the central part of phthalocyanine-type molecules.

Raman study of molecular aggregation in liquid dimethyl sulfoxide by F. H. Tukhvatullin; A. Jumaboev; U. N. Tashkenbaev; B. S. Osmanov; Z. U. Mamatov; H. Hushvaktov (866-870).
Parallel I (ν) and perpendicular I (ν) polarized components of the S=O band in the Raman spectrum of liquid dimethyl sulfoxide (DMSO) were found to consist of at least three lines each. The depolarization ratios of these lines are different. Only the high-frequency line remains in both components after high dilution of DMSO with CCl4 10 mol %. All three lines are present in both components even after high dilution of DMSO with nitromethane, with their intensities being changed only slightly. These facts were explained by the occurrence of various molecular aggregates along with individual (monomeric) molecules present in DMSO and its nitromethane solutions. The monomeric molecules are predominant in a highly diluted CCl4 solution. The polarized components of the S=O band of an aqueous DMSO solution point to the presence of H-aggregated formations of two types. The similarity in the molecular structure of DMSO and acetone makes it possible to assume that there are aggregated formations in liquid acetone as well. The small difference in wavenumbers as well as the overlap of the lines belonging to various aggregated formations may lead to the noncoincidence of the peaks of unresolved I (ν) and I (ν) components of the C=O band of acetone.

The isotopically invariant Dunham parameters U mj , Δ mj H and Δ mj Cl were determined by simultaneously fitting the line centers of vibration-rotation transitions of six isotopic HCl forms in the ground electronic state. Fitting included relations between U mj values. The parameters of the isotopically invariant potential of HCl were determined using independent U m0 and U m1 values. The contributions to the vibrational terms of H35Cl caused by violation of the Born-Oppenheimer approximation were calculated.

Fluorescence of the cis-dimers of porphyrins containing ethylene bridges by S. I. Shishporenok; V. S. Chirvony (877-883).
The absorption and fluorescence spectra of solutions of the porphyrin dimers containing ethylene bridges, binding two Zn(II)octaethylporphyrin molecules or one Zn(II)octaethylporphyrin and one octaethylporphyrin molecule into cis conformation, were studied. For both studied cis-dimers, structureless absorption spectra were observed, only in general resembling the spectra of initial molecules, as well as weak fluorescence with a wide bell-shaped spectrum with a maximum at 680–700 nm and a quantum yield of about Φf≈3×10−5, which is three orders of magnitude lower as compared to the fluorescence of initial monomeric porphyrins. A strong dependence of the fluorescence yield on a medium viscosity was revealed. In addition, low-yield irreversible cis-trans photoisomerization of cis-dimers was detected. A mechanism responsible for the strong intramolecular quenching of fluorescence of the porphyrin dimers containing ethylene bridges is suggested to be a conformation transformation in the region of the ethylene bridge, leading the molecular system to the region of “conic crossing” of the energy surfaces of excited and ground electron states.

J-aggregates of pseudoisocyanine with long alkyl substituents in thin films: Synthesis, spectral properties, and thermal stability by V. V. Shelkovnikov; Z. M. Ivanova; N. A. Orlova; T. N. Gerasimova; A. I. Plekhanov (884-891).
The formation and properties of J-aggregates in thin solid films of pseudoisocyanines with long N-alkyl groups, obtained by centrifuging from solutions in organic solvents, were studied. It is shown for the first time that nonsymmetric cyanine dyes, containing a C2H5 group at one nitrogen atom and a C10H21, C15H31, or C18H37 group at another nitrogen atom, spontaneously form J-aggregates stable at room temperature and pressing a narrow absorption band with a half-width at half maximum of 200 cm−1. The thermal stability of J-aggregates in thin films of pseudoisocyanines with alkyl substituents decreases in the following order: C2H5-C2H5> C2H5-C6H13>C2H5-C18H37>C2H5-C10H21>C2H5-C15H31. By introducing 1-octadecyl-2-methylquinolinium iodide in the film, it was found that the J-aggregates studied consist of a small number (2–4) of dye molecules.

The optical absorption coefficient γ of a thin film of a Peierls semiconductor has been calculated in the dipole approximation for direct interband transitions as a function of intensity I and central frequency ω0 of a quasi-monochromatic frequency spectrum near the lower optical transition edge. It is shown that the γ(I, ω0) dependence is strongly nonlinear, and within a certain region of I and ω0 variation, not single-valued, which indicates the onset of resonator-free optical bistability with increasing absorption.

The spectral dependences of absorption and emission by an optically dense concentrated system of two-level atoms are studied with allowance made for the cooperative effects. Analytical expressions are derived for the stationary spectrum of resonance fluorescence and the absorption spectrum of a probe signal. The results obtained suggest that the system can have a bistable behavior and its spectral characteristics are significantly modified.

The effect of the temperature dependence of the free-electron radiative recombination time on the onset of absorption optical bistability has been considered within the point-charge model. The existence of multistable states and the possibility of reducing by tens of times the switching temperatures and intensities and the differences between their corresponding values have been revealed. This permits one to reduce considerably the energy expended per switching event and, hence, to increase the speed of response of a bistable system.

A numerical model is presented which allows one, in the geometrical optics approximation, to calculate scattering contributions of specified multiplicity in layers comprised of opaque particles with dull surfaces. For definiteness, the particles are assumed to be spherical with the Lambertian law of light scattering by the particle surface. The greatest scattering multiplicity is restricted, in this model, only by computer capacity. In this paper, the scattering multiplicities up to the sixth order inclusively are studied. Layers of moderate optical thickness, as well as the case of a semi-infinite medium with different particle packing densities, are analyzed for different geometries of illumination and observation. It is shown that for conservative scattering by the particle surface, the contribution of higher-order scattering decreases with increasing order number, which is related to the shadow-hiding effect. The scattering indicatrices of higher orders approach the isotropic case. The even and odd scattering orders show a systematic difference between themselves.

The effect of scattering of different multiplicity on polarization characteristics of scattered light is studied by the Monte Carlo computer simulation technique. The scattering multiplicity distribution versus the direction of scattering and dimensions of the scattering system is obtained for monodisperse systems of spherical particles of different size. The angular dependences of the elements of the light-scattering matrix (LSM) are calculated. It is shown that in a system of spherical particles, specific features of the LSM structure associated with multiple scattering have much in common with similar features of the LSM in systems of nonspherical particles under conditions of single scattering. The angular dependences of the degree of depolarization of the scattered light are studied.

Three-dimensional emission tomography of a scattering plasma by A. V. Likhachov; V. V. Pickalov (924-935).
The three-dimensional emission ray tomography of a plasma partially scattering its self-radiation is considered. The spatial distribution of scattering density and its angular distribution are assumed to be known. The model of projection-data acquisition taking into account single and multiple scattering is constructed. In terms of this model, the problem of determining the distribution of local emission coefficients is posed. For solving this problem, the algorithm based on the Neumann-series expansion of the product of the radiative-transfer operator for a scattering medium and the operator for solving the pure emission problem was proposed. The algorithm was investigated in detail using numerical simulation.

Polarization of spherical waves by A. L. Sokolov (936-942).
Polarization characteristics of waves with a spherical wavefront are analyzed. It is shown that they may be considered as a particular case of polarization-inhomogeneous waves. Polarization analysis of the radiation transmitted by a polarizer and a quarter-wave plate is carried out. Polarization aberrations of a thin Brewster plate are calculated.

Study of the magnetomechanical effect in a gas discharge with the use of dust particles by E. S. Dzlieva; V. Yu. Karasev; A. I. Éikhval’d (943-947).
This paper reports on a test using laser Doppler anemometry of the hypothesis that the magnetomechanical effect involves rotation of the plasma of the positive gas-discharge column in an axial magnetic field. This was done by measuring the velocities of the dust macroparticles dropping in a vertical discharge tube. No rotation of the gas was revealed at a sensitivity of 40 cm/s. The rotation of dust particles suspended in striations and in the trap near the narrowed region of the discharge in a magnetic field was observed. The possible connection of this rotation with the magnetomechanical effect is discussed.

Crosstalks of three-dimensional superimposed holograms, caused by multiple wave diffraction at crossmodulation and intermodulation hologram gratings, were studied. It was shown that the intensity of these interferences depends on the method of data coding in physical parameters of hologram object waves during holographic recording. A coding method efficiently lowering the interference intensity was considered.