Optics and Spectroscopy (v.91, #5)

Optical spectra of hydrogen plasma at electron concentrations above 1019 cm−3 by T. V. Gavrilova; V. P. Aver’yanov; Y. Vitel; L. G. D’yachkov; Yu. K. Kurilenkov (667-674).
The optical spectra of a dense (nonideal) plasma formed in a pulsed discharge in a closed quartz capillary were studied. The emission spectra of pure hydrogen plasma at a temperature of 23000 K and an electron concentration of ∼1.5×1019 cm−3, twice the value achieved earlier, were obtained. The plasma diagnostics was carried out by spectroscopic methods taking into account the radial inhomogeneity of the plasma column. The spectral intensity measured in the Balmer region (300–800 nm) was found to be lower than that calculated by the model of weakly nonideal plasma, an effect not observed at lower densities. Possible reasons for the discrepancy between the experiment and the calculation were considered. One of them being the specific density effect of a relative rise in plasma transmission with increasing density.

Results of experiments on photoionization of excited sodium atoms in the 4d state in the field of nanosecond pulses of a Nd:YAG laser are reported. The dependence of the photoionization signal for the given atomic state on the ionizing pulse energy was obtained. The experimental results are compared with the model calculations of the saturation curve for the photoionization signal.

Calculations of the main components of the absolute solvation shift of Δυ a, f, R optical absorption, emission, and Raman spectra of molecules in the gas-solution phase transition for solutions of several diatomic (HCl, DCl, H2, D2) and polyatomic (anthracene, 3-and 4-aminophthalimide) substances in some polar and nonpolar solvents are presented. The calculations are made by a new method of the semiempirical theory, which was proposed by the author earlier and makes such calculations possible for the first time. It is shown that the given theory adequately describes the photophysical effect under study and provides a correct prediction of the values of Δυ a, f, R , which differ for different systems by more than three orders of magnitude (from several inverse centimeters for vibrational spectra of H2 and D2 to many thousands of inverse centimeters for electronic fluorescence spectra of solutions of aminosubstituted derivatives of phthalimide).

The effect of triplet-state quenchers on the kinetics of triplet-triplet annihilation (TTA) of Mg-phthalocyanine (Mg-Phc) is studied. It is found that the rate constant of triplet-state quenching caused by TTA increases with increasing concentration [Q] of quenchers. The maximum values of the relaxation parameter of triplet states are proportional to [Q]2. The experimental data correspond to TTA with the formation of TT complexes from molecules in triplet states. The proportionality of the decay rate of TT complexes into molecules in the ground state to [Q]2 suggests that two quenching molecules are required for quenching one TT complex. It seems that the complex contains two locally excited triplet states of individual molecules. The spin correlation time in the triplet state seems to be longer than the average lifetime of complexes (≤10−4 s). The quenching probability of triplet states in complexes (caused, in particular, by the energy of charge transfer) is lower than the probability of intermolecular triplet energy transfer to the quencher levels.

It is shown by electron absorption spectroscopy methods that the reduction of Pd-octaethylporphin does not touch the unfilled d x 2-y 2 orbitals of metal. In the reduction products (mono-and dianions), excess electrons are distributed on the lowest vacant molecular e g (π*) orbital of the ligand. This does not contradict the results of the quantum-chemical calculation of electronic states of neutral Pd-porphyrins by the extended Hückel method that are presented in the literature. Differences in electronic absorption spectra of π-anions of Pd and Zn complexes are attributed to the distortion of the plane geometry of the tetrapyrrole skeleton due to the displacement of the Pd(II) ion from the macrocycle plane. Mono-and dianions of their Pd complex lose the ability to be luminescent. The emissive capacity is reconstructed in the product of π-dianion protonation, which is called phlorin-anion (π-monoanion of Pd-octaethylporphin phlorin). As the temperature is decreased from room temperature to 77 K, the fluorescence spectrum of this product becomes narrower, its peak shifts to the blue region, and the quantum yield of luminescence increases. Specific features of the spectral properties of phlorin-anion are described by conformational changes in the excited state. Phlorin-anion was found to quench luminescence of neutral Pd-octaethylporphin molecules at room temperature.

Luminescence kinetics of linear polymer molecules with chromophores randomly distributed along the chain by E. N. Bodunov; M. N. Berberan-Santos; J. M. G. Martinho (694-703).
Luminescence kinetics of chromophores randomly attached to an isolated flexible polymer chain is studied. In the static case, when the polymer chain does not change its conformation during the donor excited-state lifetime, analytical equations are derived for the luminescence kinetics of both ideal and nonideal polymer chains. The conditions are formulated when the inhomogeneous broadening should be taken into account. For the dynamic case, the diffusion and hopping mechanisms of the polymer motion are studied.

A general approach and results of specific calculations of conjugated vibronic absorption and fluorescence spectra of “soft” molecules subjected to conformational transitions are presented. The vibronic spectra of these molecules exhibit significant anomalies such as a large energy gap between the fluorescence and absorption spectra, a strong deviation from the mirror symmetry, etc., which cannot be explained within the framework of the theory of vibronic spectra based on single-well adiabatic potentials.

A study is conducted of the static shift and the splitting of the photoluminescence and electroluminescence polarized bands of uniaxial impurity molecules, embedded into uniaxial polymer films with axial or in-plane orientation of the impurity subsystem or into the vitreous phase of a nematic liquid crystal. Dependences of the band shift and the splitting on the type of alignment of impurity molecules, the polarization of transition moments in absorption and emission, and the host-impurity anisotropic interactions of different ranks are established. For both types of host matrices, characteristic features of orientational statistics of impurity molecules at a high degree of orientation ordering are studied. These features are revealed in a qualitative difference between the dependences of positions and splittings of polarized impurity fluorescence bands on the order parameter of the impurity molecules axially ordered in stretched polymer films and relevant dependences in nematic glasses. Specific features of the polarized impurity-related photoluminescence and electroluminescence in the matrices under study, observed experimentally, are interpreted.

Interrelation between optical and magneto-optical properties of MnSbBi(Pt, Co) films by V. G. Kravets; L. V. Poperenko; I. V. Yurgelevich (724-728).
Results of the study of optical and magneto-optical properties of MnSbBi(Pt, Co) films in a spectral region of 360–820 nm are reported. It is shown that the multilayer MnSbBi(Pt, Co) films obtained by magnetron sputtering possess considerable optical rotation in the geometry of the polar Kerr effect, which is as large as 0.5°–0.7° upon 5-h annealing of the films at 350°C. The spectral dependences measured for the magnitude of the polar Kerr effect showed that these films may be used for laser data recording in the short-wavelength spectral region, which substantially increases the recording density. Studies of the film structure by X-ray and electron diffraction analysis showed that the films have a polycrystalline structure, with granules 15–40 nm in size. Possible causes of a large magnitude of Kerr effect are analyzed.

Photon avalanche in a doped quantum well by E. Yu. Perlin (729-734).
The possibility of a photon avalanche in a doped quantum well irradiated by IR light is predicted. The proposed model includes the three lowest size-quantization subbands. The exciting IR light frequency is assumed to be in resonance with the transition between the second and third subbands. Probabilities of the Auger transitions responsible for the avalanche-like multiplication of electrons in excited states are calculated for the above-threshold light intensities (j>j th). By numerically solving the rate equations for electron populations in the three subbands, it is shown that the values j th in quantum wells with the free-carrier densities n 0∼1012 cm−2 are of the order of hundreds of kilowatt per square centimeter and do not depend on the rates of phototransition between the first and second subbands. Characteristic times of establishing the quasi-equilibrium distributions of electrons over the subbands lie in the picosecond range and steeply increase at near-threshold intensities.

In terms of excitation creation and annihilation operators of the Jaynes-Cummings model, acting in the representation of dressed states, the Hamiltonian is written which describes the character of the spectrum of excitations of two modes, representing a quantum analog of the classical behavior of two interacting one-dimensional anharmonic oscillators, namely, the field and atomic oscillators. The anharmonicity is caused by the nonlinearity of the oscillator interaction and manifests itself in the dependence of the frequencies of both modes on the number of excitations, i.e., on the energy. It is shown that an external deterministic force, acting on the system during a certain time t 0, transfers it from a vacuum state to a coherent state or from one of the coherent states to another coherent state. The probability of the transition from the vacuum state to the coherent state with a given number of excitations represents the Poissonian distribution for the number of excitations formed in the (atom + field) system by the end of action of the external force. It was found to be proportional to the excitation time t 0.

The characteristic equation for the Mueller matrix of an arbitrary nondepolarizing optical system is obtained and solved. Polarization eigenstates for all types of nondepolarizing systems are studied. An efficient method for obtaining eigenvectors of matrices as functions of eigenvalues is described.

Based on the near-field effect in the transition layer, a theoretical interpretation is given of experiments on Brewster light reflection from surfaces of certain liquids. The analysis is performed within the framework of the concept of a discrete-continuous dielectric, with allowance made for the fields of atomic dipoles discretely distributed inside the Lorentz sphere surrounding the point of observation.

Raman scattering from a rotating aerosol particle by P. P. Poluéktov (757-761).
The spectrum of Raman scattering of monochromatic radiation from a rotating particle of aspherical shape and the scattering function are calculated for various Stokes and anti-Stokes scattering components. The possibility of determining the size and of reconstructing the shape of the particle from characteristics of Raman scattering is demonstrated. This investigation is applicable to rotating spherical particles with nonuniform structure.

The propagation of electromagnetic waves through a layer of a naturally gyrotropic medium found in a magnetic field is studied. The problem is solved mathematically using 4×4 Berreman matrices. The Berreman Δ matrix and exact Jones reflection () and transmission () matrices are constructed. The reflectivity, the transmittance, the azimuth, and the ellipticity of polarization of the transmitted wave are calculated. Specific features of the irreversibility of waves are studied. It is shown that multiple reflections in a finite layer lead to a manifold increase in irreversibility, which makes possible the use of such systems as optical diodes working in reflection or as unidirectional reflectors. It is shown that three eigenmodes are excited in such media under certain conditions. The relation between the azimuths of transmitted and incident waves is found and specific features of the relation are analyzed.

A systematic theory of the dynamics of the Fredericksz transition in the oscillating magnetic field is constructed for a wide frequency range. Using this theory, one can make a smooth change from static to highfrequency fields and analyze specific features accompanying it. A specific feature of the system in an alternating magnetic field is the appearance of resonant oscillations of the reorientation angle. Oscillations of director orientation decrease in amplitude, i.e., are smoothed with increasing external-field frequency.

Methods of polarization filtering, correlation processing, and wavelet analysis of coherent images of physiologically normal and necrotically changed (myocardium infarct) muscular tissues are considered. A technique of early optical diagnostics of the appearance of these biological objects and the course of their degenerative-dystrophic changes is proposed.

Comparative investigation of the effect of heat and optical radiation on the structure of island metal films by optical fluctuation microscopy by A. M. Bonch-Bruevich; T. A. Vartanyan; N. B. Leonov; S. G. Przhibel’skii; V. V. Khromov (779-785).
Variations in the structural parameters of island sodium films on the quartz surface, caused by heating or exposure to optical radiation, are investigated by the optical method proposed earlier. A correct scheme of processing the measured data is developed. It is shown that to determine the structure parameters, the measurements of both the mean values and fluctuations of transmission and reflection coefficients of the film and of their correlator are required. It is also demonstrated that under a number of assumptions, it is possible to determine the character of the process of evaporation of islands and to reveal the evolution of the distribution function by using the data of measurements. It was found experimentally that variations in the structural parameters of a film during its evaporation caused by heating of the substrate or irradiation by light can noticeably differ. This fact is explained by a difference in the mechanisms of action of heating and irradiation on an island.

A method for the recording and optical processing of two-exposure photographic images of projected fringes is proposed and experimentally tested, which makes possible an arbitrary control of the width and orientation of interference contour lines. Using this method at the stage of optical processing one can visualize both changes in the microrelief of the surface under study and the relief itself, which considerably increases the information content of the studies.

A new method for measuring the phase delay introduced by a phase plate is substantiated. The method uses an interference ellipsometer that does not require preliminary determination of the direction of the principal axes of the plate. Sources of error in the method are analyzed and components of error are quantitatively estimated. Requirements for the polarization characteristics of a beamsplitter used in the interference ellipsometer are formulated and conditions for decreasing the measurement error are found.

Nonlinear Kerr effect leads to the appearance of a periodic structure in the saturated refractive index of an optical fiber, which corresponds to a standing structure formed by counterpropagating waves in the circuit of a fiber ring interferometer (FRI). If the intensities of counterpropagating waves are slightly different, their reflection from this periodic structure leads to the appearance of a phase shift of interference of counterpropagating waves unrelated to rotation at the FRI output. If a nonmonochromatic radiation source is used in the FRI system, only radiation rereflected from the middle of the circuit makes a contribution to the phase shift. A method for eliminating the influence of the nonlinear Kerr effect on the zero shift of fiber ring interferometers is proposed. This consists in making the middle of the circuit discontinuous. Numerical estimates are made.

Features of the calculation of the autocovariance function (ACF) of an isotropic surface from experiments on measuring the angular dependence of scattered light are analyzed. The analytical extrapolation of the experimentally obtained function of power spectral density (PSD) of the surface relief based on the application of an adequate model for its description is shown to improve the accuracy of calculations of ACF. In this case, the mean-square roughness of the surface microrelief δ TIS 2 determined from the data of total integrated scattering (TIS) allows the quantitative normalization of the ACF to be carried out. In the studies of the structure of a complicated surface (a superposition of isotropic and periodic components), the inclusion of PSD features allows one to carry out adequate statistical analysis by using techniques for calculating the ACF of homogeneous isotropic surfaces. The answer to this question is in the detailed study of experimentally obtained dependences of PSD and identification of their domains corresponding to isotropic scatterers, periodic structures, or characteristic dimensions at the surface. The validity of the proposed approach is confirmed by independent studies with the use of atomic force microscopy (AFM).

Features of the adiabatic population transfer are studied with the spatial evolution of interacting pulses propagating in an optically dense medium of three-level Λ-atoms taken into account. A self-consistent analytical solution describing the spatial-temporal dynamics of interacting short pulses under the conditions of adiabatic population transfer is constructed in the adiabatic approximation with consideration for the first nonadiabatic correction. Practically complete inversion on a forbidden transition determined by coherent (adiabatic) population transfer is shown to take place over a length of the medium, which may exceed the absorption length of a weak probing pulse in the absence of control radiation on the adjacent transition by several orders of magnitude.

Dielectric layers with silver nanoparticles in the bulk, synthesized by the vacuum evaporation of metal onto viscous-flow softened polymer substrates are analyzed. New materials with a nonuniform distribution of nanoparticles over the sample thickness are obtained. Optical characteristics of the composition layers are calculated from the transmission spectra. To calculate the optical spectra, a model of a multilayered plane-parallel film structure is considered. Functions of dielectric constants of separate composition layers are determined using the Bruggeman theory of effective medium. A qualitative agreement between the experimental and simulated optical spectra is achieved taking into account nonuniform distribution of metal nanoparticles over the composition material thickness.

The dependence of attenuation of laser radiation by fullerene-containing solutions on the laser pulse duration is theoretically studied. The investigation is carried out for a wide range of variations in the pulse durations: from 250×10−15 to 10−8 s. The contribution of two mechanisms (reverse saturable absorption and induced scattering associated with thermal nonlinearity) to the attenuation of radiation is studied. It is shown that reverse saturable absorption makes a considerable contribution to the attenuation in the whole range of durations under consideration, whereas induced scattering exists only in the range of durations that are longer than some nanoseconds. It is shown that the law of similarity with respect to the product of the intensity and the pulse duration for attenuation of laser radiation is approximately fulfilled in the whole range of durations, i.e., the attenuation depends on the energy density. Additionally, the elementary theory of reverse saturable absorption is developed and the limiting values of the absorption coefficient and the maximum attenuation are obtained.