Optics and Spectroscopy (v.104, #1)

The effective lifetime of the excited state 32 P 3/2 of sodium atoms corresponding to the transition with λ = 589 nm has been studied numerically. It is shown that the nonmonotonic behavior of the dependence of the Biberman-Holstein escape factor on the optical thickness of sodium vapor measured in the experiment (A. Romberg and H.-J. Kunze, J. Quant. Spectrosc. Radiat. Transfer 39 (2), 99 (1988)) should not be attributed to the manifestation of the effects of partial frequency redistribution.
Keywords: 32.50.+d

Electron-impact excitation of barium atoms from metastable 5 3 D J states by N. A. Margitich; T. A. Snegurskaya; I. I. Shafranyosh (4-9).
The excitation of spectral transitions of barium atoms from the 53 D J states by electron impact has been studied experimentally. The absolute values of the interaction cross sections and their energy dependences have been determined. The results obtained have been compared with theoretical calculations both by the classical Born approximation method and by the R-matrix method using the multiconfiguration Hartree-Fock wave functions of a target.
Keywords: 34.80.Dp

The dissociative excitation of the 4 S°, 4 P°, 4 D°, and 4 F° levels of the manganese atom in collisions of slow electrons iwth manganese dichloride molecules is studied experimentally. It is found that the dissociative excitation cross sections for these levels are larger than the cross sections of direct excitation in the e-Mn collisions. The cross section ratios of the electron-atom and electron-molecule collisions, which characterize the effect of the chemical bond of the manganese atom with the halogen on the absolute excitation cross sections, are determined.
Keywords: 34.90.+q

Analytical expressions for the density of magnetoactive plasma perturbed by circularly polarized relativistically strong laser radiation are obtained.
Keywords: 52.38.Mf

The rotational Rydberg states of polar molecules, which arise as a result of the interaction of a Rydberg electron with core rotations, are considered. A large number of angular momenta in the core-electron system lead to a considerably greater number of possible coupling schemes of these momenta compared to the number of schemes determined by the classical five Hund’s cases for lower excited electron states of molecules. As a result of such detailed Hund’s classification, more than 30 different coupling schemes (Hund’s subcases) are constructed for rotational Rydberg states of molecules. The conditions of their realization are indicated in terms of the relative quantities of intramolecular interactions, for which analytical estimates are presented. For a large number of subcases, analytical expressions for the molecular matrix elements are found. These expressions can be useful in classification of the experimental spectra of highly excited molecules. As an application, for each of the subcases considered, analytical expressions are given, which describe the linear Zeeman effect and the Paschen-Back effect.
Keywords: 33.55.Be

The effect of the highest excited states on the yield of photoproducts that are usually formed upon excitation of the first singlet electronic state of polyatomic molecules is discussed. It is shown that the excitation of molecular objects through the highest singlet states can, in some cases, increase the yield of reaction products. This allows one to estimate the probabilities of reactions from the corresponding states. The consideration concerns a wide range of primary photoreactions, including the electronic density redistribution (the intramolecular electron transfer) in the excited state, the protolytic reactions, the intramolecular proton transfer (the phototautomerization), the hydrogen bond formation, and the formation of excimers and exciplexes. The relations obtained are used to analyze the experimental fluorescence spectra of 3-hydroxyflavone solutions, excited by electromagnetic radiation with different wavelengths in the region of the S 1, S 2, and S 3 absorption bands. The analysis fulfilled shows that the highest singlet states play an important role in the formation of tautomers in 3-hydroxyflavone due to the intramolecular proton transfer.
Keywords: 33.50.Dq

Photoluminescence of water-soluble CdSe/ZnS nanoparticles in complexes with cationic and anionic polyelectrolytes by N. Strekal’; O. Kulakovich; A. Belyaev; V. Stsiapura; S. Maskevich (50-56).
The data on the influence of polyelectrolytes on the photon emission probability of water-soluble CdSe/ZnS nanoparticles are obtained. The decrease in the photoluminescence quantum yield of nanoparticles occurring upon their transfer to aqueous solutions from toluene (in the course of solubilization) depends on the ionic nature of an agent applied for the replacement of trioctylphosphine oxide residues on the surface of nanoparticles. It turns out that such a cationic modifying agent as cysteamine leads to an insignificant (∼10%) decrease in the photoluminescence quantum yield of nanoparticles. The use of such an anionic agent as mercaptoacetic acid causes a significant (∼80%) decrease in the quantum yield and the average decay time of photoluminescence. For nanoparticles modified by mercaptoacetic acid (anionic nanoparticles), this decrease is partially compensated if these particles interact with polyelectrolytes whose backbone is oppositely charged (cationic polyelectrolytes), such as polyallylamine and polydiallyldimethylammonium chloride. In this case, the photoluminescence quantum yield shows a reverse increase by 40%, remaining the same within a matter of months or longer. In contrast to this, cationic nanoparticles, only slightly quenched by cysteamine at the stage of solubilization, are appreciably degraded in complexes with anionic polyelectrolytes in solutions and upon immobilization of complexes on a substrate, so that their photoluminescence quantum yield irreversible decreases to zero within a few days. Possible mechanisms of the effects observed are discussed and their consideration in polyelectrolyte-based molecular lithography.
Keywords: 78.67.Bf

The behavior of the positions and shapes of the fluorescence bands of di-, tetra-, and hexamethine merocyanine dyes with 3H-indolyliden (dyes 1–3) and benzoimidazolyliden (dyes 4–6) as electron-donating substituents and malononitrile as an electron-accepting substituent is studied by the method of moments in solvents of different polarity. The solvatofluorochromic shifts have been found to be smaller than the solvatochromic shifts not only for negatively solvatochromic merocyanines 4–6, but also for dyes 1–3 whose solvatochromism is positive. For dyes 4–6, cases of a change of the sign of solvatofluorochromism with respect to the sign of solvatochromism are revealed. These nontrivial effects are accounted for by transitions between the polyene and polymethine electronic structures of merocyanines in the fluorescence state S 1 that occur with increasing medium polarity. In contrast to the absorption spectra of merocyanines 1–3, an increase in the chain length results in an increase in the vinylene shifts in the fluorescence spectra of these dyes, as well as in a decrease in the deviations and in the narrowing of the bands. This is explained by the fact that the electronic structure of these merocyanines in the S 1 state is closer to that of the ideal polymethine (the cyanine limit) than in the S 0 state. The fluorescence bands of merocyanines 4–6 are observed to be broader compared to the absorption bands. This broadening is caused by a change in the relation between intermolecular and vibronic interactions during absorption and emission of light. The interactions of these types have a decisive effect on the behavior of the Stokes shifts and fluorescence quantum yields of merocyanines 1–6.
Keywords: 33.50.Dq; 31.70.Dk

The cation of 2-phenylpyridinate ethylenediamine of platinum(II) is immobilized from a water solution on the surface of a cation-exchange membrane. A nonlinear dependence of the luminescence intensity of the obtained material on humidity is determined.
Keywords: 78.55.-m

The temperature dependences of the fluorescence characteristics of three forms (normal, tautomeric, and anionic) of 3-hydroxyflavone in methanol upon selective excitation in different UV ranges are studied. The fluorescence of all the forms undergoes temperature quenching, whose efficiency depends on the excitation energy. It is found that the intensity ratio of the fluorescence of different forms also varies with temperature; the excitation regions in which these variations are most pronounced are determined. The highest temperature sensitivity is observed for the luminescence intensity ratio of the normal and tautomeric forms upon excitation in the region of 280 nm, this ratio continuously increasing from 0.5 to 1.0 in the temperature range of 20–70°C. The dependence found allows one to measure the temperature of the solution in some temperature regions with an error of ∼1 ± 0.5% with the help of a standard Hitachi F-2500 spectrofluorimeter.
Keywords: 33.50.Dq

Luminescence spectroscopy of excitons and antisite defects in Lu3Al5O12 single crystals and single-crystal films by Yu. Zorenko; T. Voznyak; V. Gorbenko; T. Zorenko; A. Voloshinovskiĭ; V. Vistovsky; M. Nikl; K. Nejezchleb; V. Kolobanov; D. Spasskiĭ (75-87).
The nature of the intrinsic luminescence of the lutetium aluminum garnet Lu3Al5O12 (LuAG) has been analyzed on the basis of time-resolved spectral kinetic investigations upon excitation of two model objects, LuAG single crystals and single-crystal films, by pulsed X-ray and synchrotron radiations. Due to the differences in the mechanisms and methods of crystallization, these objects are characterized by significantly different concentrations of LuAl antisite defects. The energy structure of luminescence centers in LuAG single crystals (self-trapped excitons (STEs), excitons localized near antisite defects, and LuAl antisite defects) has been established. For single-crystal LuAG films, grown by liquid-phase epitaxy from a Pb-containing flux, the energy parameters of the following luminescence centers have been determined: STEs in regular (unperturbed by the presence of antisite defects) sites of the garnet lattice and excitons localized near Pb2+ ions. The structure of the luminescence centers, related to the background emission of impurity Pb2+ ions, has also been established in the UV and visible ranges. It is suggested that, in contrast to the two-halide hole self-trapping, a self-trapped state similar to STEs in simple oxides (Al2O3, Y2O3) is formed in LuAG; this state is formed by self-trapped holes in the form of singly charged O ions and electrons localized at excited levels of Lu3+ cations.
Keywords: 78.55.-m

Interaction of molecular and polymolecular forms of a dye by A. V. Tyurin; V. P. Churashov; S. A. Zhukov; L. I. Manchenko; T. F. Levitskaya; O. I. Sviridova (88-94).
A luminescence method is proposed, which makes it possible to control interactions between molecular and polymolecular forms of a dye in AgHal emulsions, responsible for the self-desensitization of the first and second kinds. This allows one to determine an optimal concentration of a dye upon its application. An anomalously delayed anti-Stokes fluorescence of a molecular dye, which is responsible for self-desensitization of the second kind, is observed for the first time upon excitation of J aggregates of the dye. A mechanism for the self-desensitization of the first kind is proposed, which is connected with interactions between the J aggregate of a dye and dye molecules adsorbed on its surface.
Keywords: 78.55.-m

Slow light and slow current by V. S. Zapasskiĭ; G. G. Kozlov (95-98).
It is shown that the effect of hole-burning under conditions of coherent population oscillations as well as the light pulse delay in a saturable absorber (a modification of the so-called slow light effect) can be interpreted, in a comprehensive way, in terms of the intensity spectrum of the light and intensity-related susceptibility of the medium. The physical content of these effects is illustrated by a simple electric circuit with a non-linear resistor which realizes a full analog of the saturable absorber. In this case the effect of hole-burning in the absorption spectrum of the medium is converted into the effect of hole-burning in the frequency dependence of resistance of the resistor and the effect of slow light into the effect of slow current.
Keywords: 42.65.-k

Specific features of the nonstationary transmission of two pulses exciting biexcitons from the ground state in a thin semiconductor film are studied. It is shown that one of the incident rectangular pulses is totally reflected from the film, whereas the second pulse passes through it as through an absolutely transparent medium. Criteria for appearance of a stationary bistable transmission are determined.
Keywords: 78.66.-w

The possibility of phase control over coupling of Bose-condensed atoms into molecules is justified. It is shown that the time evolution of stimulated Raman atom-molecule conversion is determined significantly by the initial densities of particles and by the initial phase difference between material and electromagnetic waves.
Keywords: 42.50.Rh; 67.40.-w

Physical optics of photonic crystals by S. G. Rautian (112-120).
A one-dimensional harmonic model of a photonic crystal is considered using the methods of physical optics. The theoretical formalism is based on the notion of the Fresnel volume reflection and the system of two first-order differential equations, which are equivalent to the wave equation. Using the Rayleigh layer as an example, it is shown that the volume reflection plays a role of the friction, similar to the friction in oscillations of a pendulum, and, in a strongly inhomogeneous medium, can suppress field oscillations and turn the group velocity to zero. In the approximation of small modulation factor, the models of two, four, and six waves are considered. In the two-wave model, the dispersion relation contains a zone of inhomogeneous waves, whose width is determined by the Fresnel reflection coefficient from one period. The refinement in terms of the four-wave or six-wave model yields only a small correction to the position of the zone, retaining its width unchanged. The wavenumber as a function of frequency is described by a circle inside the zone of inhomogeneous waves and by a hyperbola outside this zone. Mathematically, the method used is significantly simpler than those based on the application of the Floquet theorem to the wave equation. It is shown that the notion of forbidden zones is inconsistent with respect to photonic crystals, and the term zones of inhomogeneous waves is proposed instead.
Keywords: 42.25.Bs; 42.70.Qs

The optical scheme of a simple resonator is transformed into a sequence of local interferometers. The phase length of a local interferometer is determined by the optical thickness of the thin-film dielectric coating on the surface of one of the mirrors. The spectral characteristic of the instrumental function is formed by parameter fitting. The experimental results are presented.
Keywords: 42.25.Hz

The possibility of generating beams with longitudinally periodic polarization properties is considered.
Keywords: 42.55.-f; 42.60.Jf

Effect of broadband incoherent light on the photoresponse of lithium niobate crystals by A. V. Syui; V. I. Stroganov; V. V. Krishtop; V. V. Likhtin (126-129).
The effect of broadband incoherent light on the local photoresponse of lithium niobate crystals has been experimentally investigated. It is shown that a previously induced electric field affects the dependence of the photovoltage on time and impurity type and concentration. The pyroelectric effect significantly influences the photoprocesses in lithium niobate crystals, especially in the initial stage of illumination.
Keywords: 72.40.+w; 77.70.+a; 42.70.Nq

A new criterion—transmission capacity in the unsaturated gain regime—is proposed for comparing the quality of glasses for erbium-doped fiber amplifiers, considered as an element of an optical communication system. It is shown that, according to the criterion for the highest transmission capacity, amplifiers based on alumino-phosphate-silicate and zinc-sodium-germanate-silicate fibers are preferred for systems with separate C and L bands, respectively. In broadband systems, the highest transmission capacity is observed in amplifiers based on tellurite fibers.
Keywords: 42.25.Bs; 42.79.-e; 42.79.Gn; 42.81.-i

The hologram recording in low-viscosity liquid photopolymerizing compositions with a neutral component is studied theoretically and experimentally. A diffusion model of redistribution of the composition components that takes into account the polymer mobility at the initial stage of photopolymerization is proposed. It is shown that the use of methanol as a neutral component significantly increases the diffraction efficiency.
Keywords: 42.70.Ln

Skin spectrophotometry under the islet photothermal effect on the epidermal permeability by A. A. Gavrilova; V. V. Tuchin; A. B. Pravdin; I. V. Yaroslavsky; G. B. Altshuler (140-146).
The results of experimental investigation of an increase in the epidermal barrier permeability are presented. The results are obtained using the method based on the creation of permeability microzones (islets) during the local thermal action on stratum corneum. It is shown that the epidermal barrier permeability considerably increases under the island photothermal effect and application of various clearing agents. Detailed spectrophotometric investigations of skin under the conditions of a partial violation of the epidermis barrier functions due to the island effect and introduction of various immersion agents in the skin are presented. The effect of various conditions of the object illumination on the dynamics of spectra is analyzed. A common behavior of the dynamics of the spectra of all kinds during clearing is revealed. Possible mechanisms accompanying the optical clearing process under the island photothermal effect are discussed.
Keywords: 42.62.Be