Optics and Spectroscopy (v.89, #5)

Specific features of holographic recording of diffraction gratings in thin films of fullerene-containing organic systems by N. V. Kamanina; L. N. Kaporskii; V. N. Sizov; D. I. Stasel’ko (651-653).
Thin films based on fullerene-containing polyimides COANP and PNP were studied using methods of dynamic holography under conditions of Raman-Nath diffraction. A significant increase in the diffraction efficiency of the fullerene-containing samples was detected, and the threshold of the transition from phase grating to amplitude grating was determined. The qualitative explanation of the results is based on the spectral features and the thermal properties of the systems under study.

Results of numerical simulation of the kinetics of excitation of HeI and HeII levels in the buffer region of a high-power gas-discharge capillary optically pumped by resonance emission of a discharge plasma are presented.

The linear polarization of quadrupole emission by the J=2-J 0=0 transition under conditions of laser excitation in a gas medium is studied. Cases of excitation through dipole and quadrupole absorption of monochromatic laser radiation are considered. Taking into account the anisotropy of collisional relaxation, the contributions of polarization moments of the second and fourth ranks, i.e., those with usual and hexadecapole alignments, to the signal of linear polarization of quadrupole emission are calculated. The dependence of this signal on the laser frequency, the density of the gas medium, and the angles determining the orientation of the system of axes of observation of light polarization relative to a laser ray is studied. The numerical calculations of contributions of usual and hexadecapole alignment to the signal of linear polarization are made for the magnetic quadrupole transition J=2-J 0=0 between the states 2p 5(2 P 1 2/0 )3p′[3/2]2 and 2p 5(2 P 1 2/0 )3s 3s′[1/2]0 of neon atoms in the xenon atmosphere.

Precise variational calculations of the energy and diverse physical characteristics are performed for the ground state of a fully nonadiabatic four-particle system—the positronium molecule e+ee+e. The nonlinear exponential parameters of correlated Gaussian basis functions dependent on all interparticle separations are systematically optimized. The dependence of the calculated energy values and the expectation values of interparticle separations (as well as their degrees and Dirac delta functions of interparticle separations) on the basis size N is examined. For N=200, the ground-state energy of the positronium molecule is found to be E=−0.5160028 au. For an extended basis set with N=4700 containing 200 basis functions with the optimized parameters and 4500 additional functions with random values of nonlinear parameters, E=−.5160036 au. At present, this result is the most accurate variational energy value of the positronium molecule, and it demonstrates the high efficiency of optimization of the nonlinear parameters in calculations of atomic-molecular systems. The lifetime of the positronium molecule e+ee+e with respect to electron-positron annihilation is calculated to be τ=2.26×10−10 s.

Based on the methods of symmetry, a description of the Jahn-Teller E-E system in the spectrum of a nonrigid XY3 molecule is constructed.

Approximation of the width of the line profile narrowed by collisions by V. P. Kochanov; I. V. Ptashnik (678-683).
For models of hard and soft (in velocity) collisions, algebraic approximations of the line half-width are determined that depend on parameters of collisional broadening and narrowing and on the Doppler half-width. The average difference between the approximated and the exact values of the half-width do not exceed 0.1%. A simple criterion for determining the correspondence of models of hard and soft collisions to the experimental dependence of the half-width on the buffer gas pressure is proposed.

A new model of line profile is proposed, which simultaneously takes into account hard and soft (in velocity) collisions leading to collisional line narrowing. It is shown that parameters of collisional narrowing and broadening obtained by processing experimental profiles on the basis of the standard model of hard collisions contain almost no contribution of diffraction scattering of molecules by buffer gas particles. The model proposed for the line profile makes possible a correct comparison of frequencies of the collision integral measured by methods of linear and nonlinear spectroscopy.

A review of one-and two-photon counting methods in single impurity center spectroscopy is reported, and advantages and drawbacks of these methods are discussed. The jumps of spectral lines, which are manifested as the so-called spectral trajectories, are discussed. Examples of the use of the theory of two-photon correlators and autocorrelation functions for experimental data processing are presented. Data are reported that demonstrate that the local dynamics of approximately 30% of single impurity centers cannot be described within the framework of the standard tunneling system model suggested by P. Anderson et al. to explain the low-temperature anomalies observed in glasses.

Calculations of the potential energy surfaces of X-OH 2 + cations (X = C, O) by the restricted and unrestricted Hartree-Fock methods (RHF, UHF) taking into account the correlation energy (MP-2) and by the CASSCF method are presented. All cations are found to be rather stable against X-O bond rupture and intermolecular rearrangement. The reaction of electron capture by these cations is studied.

Absorption and fluorescent properties of pyrylium compounds: II. Spectra and cross sections for absorption from the ground and excited states of the structurally rearranged form by A. M. Bonch-Bruevich; R. Gadonas; E. N. Kaliteevskaya; V. Krasauskas; A. Pyalakauskas; T. K. Razumova; A. D. Roshal’; A. N. Tarnovskii (712-720).
The nonstationary absorption of solutions of 2,4,6-substituted pyrylium salt is studied by the pump-probe method. The solutions in methylene chloride are studied upon picosecond pumping and probing with different time delays. The solutions in methyl ethyl ketone are studied upon pumping and synchronous probing by nanosecond pulses. It is shown that excitation of the initially nonplanar molecule causes its structural rearrangement. As a result, substituent 2 enters into the pyrylium ring plane and two nonstationary conformers are formed that differ in the position of substituent 6. The motion upon structural rearrangement has a small amplitude, and localization of molecular orbitals changes only slightly. The temperature dependence of the nonstationary absorption is studied in the range from 293 to 223 K. The spectra and cross sections are measured for transitions from the S0 and S1 states. In addition, the activation energies and kinetic parameters of the rearrangement in the ground and excited states are determined. Experimental data are compared with theoretical calculations of the transitions from the S1 state. It is shown that a partial flattening of conformer molecules results in the long-wavelength shift of the bands and an increase in the cross sections for transitions localized on a flat part of the molecule and does not change parameters of the band localized on the molecular part that did not change upon the rearrangement but remained nonplanar.

Spectral and luminescent properties of mixed-ligand complexes of palladium(II) and 7,8-benzoquinoline by M. V. Puzyk; V. S. Kotlyar; N. V. Antonov; Yu. A. Ivanov; M. A. Ivanov; K. P. Balashev (721-723).
Spectral and luminescent properties of mixed-ligand palladium(II) complexes—[PdBhq(μ-Cl)]2, [PdBhqEn]ClO4, and [PdBhqBpy]ClO4, where Bhq stands for the 7,8-benzoquinoline ion—were studied. The absorption spectra of these complexes in the 25000–40000-cm range were found to have a number of spin-allowed transitions of the 1(π-π*) type involving orbitals of the 7,8-benzoquinoline ligand. The luminescent characteristics of these compounds in a glass-forming matrix at 77 K are primarily determined by the participation of the 3(π-π*) states of the 7,8-benzoquinoline ligand.

Study of spectral properties of zinc phthalocyanines used as sensitizers in photodynamic therapy by N. E. Koval’skaya; N. A. Kuznetsova; O. L. Kaliya; N. S. Gretsova; I. V. Sokolova (724-726).
Some features of the influence of the structure of water-soluble zinc phthalocyanines on their spectral parameters and state in solutions are studied. It is shown that the position of the long-wavelength electronic absorption band only weakly depends on the type of ionogen substituents in the zinc phthalocyanine macrocycle. It is found that the state of the dye in aqueous solution substantially depends on the type of a substituent in the dye macrocycle.

The spectral and luminescent properties of solutions of perylenetetracarboxylic acid (PTCA), its ionic forms, and its aggregates and complexes with rare-earth ions are studied. The mechanisms of the fluorescence quenching of PTCA upon complex formation are discussed. It is concluded that the complex formation in such systems is of the intrasphere type. Comparison between the measured intracomplex-deactivation energies of the fluorescing states of PTCA and pyrene tetrasulfonate indicates that the metal-ligand interaction is more efficient in carboxylic complexes.

A perturbation theory for determining the stability characteristics of spatial optical solitons with a 2D transverse profile in a transparent medium with a weak saturation of nonlinear refractive index is developed. For Kerr nonlinearity, a new solution of linearized equations for weak soliton perturbations is found. Using this solution, an expression for the stability characteristic is deduced, which, in the case of unstable solitons, determines their decay length and, in the case of stable solitons, shows the presence of perturbations with anomalously weak damping (internal modes) and determines their oscillation period.

The lateral shift of a light beam reflected from the interface between an optically transparent dielectric and a medium for which the frequency dependences of the real and imaginary parts of the permittivity have a resonant form is investigated. At certain radiation frequencies and angles of incidence, a negative displacement of the reflected beam along the interface takes place.

Modulation instability of a two-mode packet of strongly interacting waves by I. O. Zolotovskiĭ; D. I. Sementsov (742-745).
The conditions for the appearance of modulation instability of a two-wave packet formed by two unidirectional strongly interacting modes traveling in a two-mode fiber waveguide are studied. The possibility of the existence of modulation instability in the region of normal dispersion and the effect of the initial conditions of fiber excitation on the development of modulation instability are demonstrated.

Nonreciprocity in the state of polarization in an inhomogeneously anisotropic crystal is discovered, and the main characteristics of this effect are studied. The effect consists in the appearance of asymmetry of components of the Stokes vector for radiation traveling in forward and backward directions. It is shown to be caused by the presence of a nonlinear gradient of mechanical stress. The effect is theoretically analyzed using the model of a sample whose inhomogeneity is caused by the presence of sections with linear and circular birefringence placed in a series. The theoretical conclusions qualitatively agree with experimental results obtained for a silicon single crystal using the polarization modulation technique.

Specific symmetry features of dielectric and gyrotropic properties of superlattices comprised of arbitrary crystalline layers are considered. It is shown that by changing the orientation of crystallographic axes of the high-symmetry components of the superlattice with respect to their interfaces, one can obtain structures with induced uniaxial or biaxial anisotropy. Expressions are derived that determine the orientation of optical axes in these structures. Propagation of light beams along directions of the induced binormals is analyzed. The feasibility of and conditions for lensless focusing of an optical beam in superlattices comprised of high-symmetry layers are established.

Determination of optical constants of latex in concentrated suspensions by A. Ya. Khaĭrullina; T. V. Oleinik; L. M. Bui (756-760).
The possibility of taking into account concentration effects in the determination of optical constants of latex in the visible and near IR regions of the spectrum is demonstrated, and the limits of applicability of the methods proposed for this purpose are determined. The limiting concentration of particles in suspensions for which these effects should be taken into account depend on the particle size. Using latex as an example, ways of increasing the accuracy of reconstruction of optical constants of weakly absorbing particles of micron and submicron size are shown. Similar concentration effects can take place in the study of blood substituents, proteins, and other weakly absorbing particles in weakly absorbing media.

Nonlinear transmission of a single-mode optical fiber with a sharp change of core diameter by L. A. Mel’nikov; E. A. Romanova; É. V. Bekker (761-765).
Nonlinear transmission of a cylindrically symmetric weakly guiding single-mode optical fiber with a sharp change of core diameter is estimated in the approximation of weak nonlinearity of the fiber material and is calculated by direct numerical simulation of light propagation. It is shown that an increase or a decrease of nonlinear transmission in comparison with the linear value depends on the way in which the width of the radial mode distribution changes with changing diameter of the structure. Domains of fiber diameters corresponding to an increase of nonlinear transmission in comparison with the linear value are determined.

Generation of light using two-level atoms with initial coherence by V. N. Gorbachev; A. I. Trubilko (766-771).
The Fokker-Planck equation for the Glauber quasi-probability is derived, which describes one-photon generation of light in lasers and micromasers using atoms with initial coherence. Stationary lasing and masing conditions are analyzed. In particular, the case of an inversionless transition is considered. The line shape and the photon statistics are found. The field state for lasing on an inversionless transition is found to be coherent.

Second-harmonic generation in the field of an ultrashort pulse and the propagation of extremely short pulses in a medium with quadratic nonlinearity are analyzed. Second-harmonic generation is analyzed taking into account the effect of second-and third-order group velocity dispersion and dispersion of nonlinear susceptibility up to the second order. Corrections, whose order of smallness is determined by the parameter (ωL t p)−1, where t p is the pulse duration and ωL is the carrier frequency of the pump wave, are obtained. For a large phase mismatch, two new solutions are found that describe the stationary evolution of solitary pump and second-harmonic waves in the regions of both anomalous and normal group velocity dispersions.

Assuming arbitrary correlation between the recorded and read-out fields and taking into account all the effects of inter-and cross-modulation diffraction structures, expressions are derived that describe in the most general form the spatial modulation of the original object and reference waves in the response of thin linear and quadratic off-axis holograms with superimposed recording. Associative data reconstruction is discussed.

The choice of a function approximating the exposure dependence of the amplitude transmission of negative recording media is considered from the standpoint of the theory of measure within the framework of the algebraic model of the system in the geometrical optics approximation. Two processes are taken into account: photodetection in the quasi-linear and the overexposure ranges and light modulation by transparencies made by the method of negative photodetection. Formal construction of the algebra is shown to lead to the approximation by Sugeno negation. Comparison with the approximation by a power polynomial is made.

Wide-band interference filters by Yu. N. Markov (797-798).
Results of calculations are presented that demonstrate the possibility of constructing two-and threecomponent coatings for wide-band interference filters for the medium infrared spectral region with characteristics that could be realized earlier only in four-component interference coatings.

Polarization-based visualization of multifractal structures for the diagnostics of pathological changes in biological tissues by O. V. Angel’skiĭ; A. G. Ushenko; S. B. Ermolenko; D. N. Burkovets; V. P. Pishak; Yu. A. Ushenko; O. V. Pishak (799-804).
The dynamics of the changes in the statistical polarization structure of coherent images of biological tissues are studied for the visualization process of their optically anisotropic (collagen) structure.

Results of calculations of the resolving power (according to Foucault) of optoelectronic imaging systems with incoherent and coherent illumination under the conditions of atmospheric phase distortions are presented. It is suggested that incoherent optical images are formed in the case of incoherent illumination and speckle images are formed in the case of coherent illumination. The shape of objects observed is estimated from these images. The resolving powers are shown to be practically the same in the formation of incoherent optical images and speckle images in the case of strong phase distortions and smoothing of images by a matrix photodetector. At the same time, the limiting resolving power in the formation of incoherent optical images is twice as large as in the formation of speckle images.