Optics and Spectroscopy (v.120, #3)

Electromagnetically Induced Transparency in Potassium Vapors: Features and Restrictions by A. Sargsyan; P. A. Petrov; T. A. Vartanyan; D. Sarkisyan (339-344).
Features of electromagnetically induced transparency (EIT) in potassium vapors at the D1 line of the 39K isotope are studied. EIT resonances with a subnatural width of 3.5 MHz have been recorded upon excitation by two independent narrow-band diode lasers in a 1-cm-long cell filled with a natural mixture of potassium isotopes and buffer gas. The splitting of EIT resonances in potassium vapors in longitudinal and transverse magnetic fields has been studied for the first time. The splitted components also have a subnatural width. The smallness of the coupling factor of the hyperfine structure in 39K atoms leads to a transition to the Paschen—Back regime at relatively weaker magnetic fields than in the case of Cs, Rb, and Na atoms. Practical applications of the phenomena under study are noted. The theoretical model well explains the experiment.

The dissociation CO2(X 1Σ) + M → CO(X 1Σ) + O(3P) + M and recombination CO(X 1Σ) + O(3P) + M → CO2(X 1Σ) + M processes are considered with the spin—orbit coupling taken into account in the ground and several excited states of the CO2 molecule. Because of the specific features of mutual position of potential energy surfaces of the CO2 molecule in the ground and several excited states and the large values of spin—orbit interaction matrix elements, which causes the quantum nonadiabatic transition of the molecule from one state to another, these processes become effectively spin-allowed and the rate constants for the nonadiabatic reactions have large values. The proposed dissociation and recombination mechanisms include reactions involving singlet—triplet crossings.

LED-Based Fourier Transform Spectroscopy: the HD16O Absorption Spectrum in the Range of 11200–12400 cm−1 by L. N. Sinitsa; V. I. Serdyukov; E. R. Polovtseva; A. P. Shcherbakov; B. A. Voronin; A. D. Bykov (352-358).
The vibrational—rotational spectrum of the HD16O molecule is studied within the range of 11200−12400 cm−1. The spectrum is recorded by an IFS-125M Fourier spectrometer with a resolution of 0.05 cm−1. The measurements are performed using a multipass White cell. A light-emitting diode is used as a radiation source. The signal-to-noise ratio was about 104. The centers, intensities, and half-widths of the spectral lines are determined by fitting to the experimental data by the least-squares method. A linelist containing more than 1500 lines is created. The results obtained are compared with the experimental data of other authors.

Theoretical Analysis of the Fluorescence Spectra of 7-Azaindole and Its Tautomer by G. N. Ten; O. E. Glukhova; M. M. Slepchenkov; V. I. Baranov (359-366).
The electronic—vibrational fluorescence spectra of the first, S 01 L b, and second, S 01 L a, electronic transitions of 7-azaindole and its tautomer for an isolated state have been calculated. Specific features of structural changes in 7-azaindole and its tautomer upon electronic excitation are determined. Vibrational spectra are assigned for the ground state, and the vibrational structure of fluorescence spectra is interpreted. It is shown that the intensity redistribution between the 6a and 6b oscillations, which is observed in the fluorescence spectrum of the S 01 L b transition in 7-azaindole, can be explained as a result of intensity borrowing (according to the Herzberg—Teller mechanism) from the 1 L a state.

Double-pulse laser induced breakdown spectroscopy (DP-LIBS) of aluminum sample is studied experimentally in orthogonal configuration in air. In this configuration, two schemes of reheating and pre-ablation are examined and the results are compared with single pulse one. The effect of delay time between two laser pulses on emission line intensities of plasma is investigated. Some of the parameters that have been involved in different mechanism of signal enhancement such as plasma temperature, sample heating effects, atmospheric effects, and modification of the ablation dynamics are more discussed. Investigation of the effect of laser pulse energy on emission line intensities in single pulse LIBS experiment demonstrate that because of saturation effects the intensities will not increase necessarily by increasing the laser pulse energy. Moreover, the results show that the electron temperature and rate of mass removal in orthogonal configuration of DP-LIBS is higher than that of single pulse with the same total energy. It is suggested that for correct comparison between single and double pulse results, the optimum pulse energy in single pulse should be considered. Overall, our results demonstrate that under optimized conditions the signal enhancement is much more in pre-ablation configuration than re-heating configuration.

Spectral Properties and Photodynamic Activity of Complexes of Polycationic Derivative of Fullerene C60 with Xanthene Dye Fluorescein by A. I. Kotel’nikov; A. Yu. Rybkin; N. S. Goryachev; A. Yu. Belik; P. A. Troshin (379-385).
Using spectrophotometry and stationary and kinetic fluorimetry, we have shown that xanthene dye fluorescein forms complexes with polycationic derivative of fullerene in aqueous solutions mainly due to electrostatic interactions. It is found that efficient quenching of singlet excited states of dye occurs in the structure of these complexes due to the transfer of excitation or electron from dye to fullerene. As a result, the photodynamic activity of the newly formed complex is much higher than that of fluorescein and fullerene derivative. This effect makes it possible to predict the formation of new-generation hybrid photodynamic preparations using dyes excited only into a singlet state; as a result, directed searches for these dyes are significantly facilitated.

The synthesis and the spectral and luminescent properties of N-(3-methoxysalicylidene)-o-anisidine and its Zn(II) complex are presented. It is found that Schiff base in solution has the E(anti)-configuration, and the zinc complex fluoresces in solution and the polycrystalline state at 77 and 293 K.

The [Ir(bt)2(S^S)], [Ir(bt)2(S^N)], and [Ir(bt)2(CH3CN)2]PF6 complexes, where (bt) is a deprotonated form of 2-phenylbenzothiazole and (S^S) and (S^N) are diethyldithiocarbamate, O-ethyldithiocarbonate, 2-mercaptobenzothiazolate, 2-mercaptobenzoxazolate, and 2-mercaptopyridinate ions, and the effect of Hg(II), Cu(II), Cd(II), and Zn(II) cations on the optical characteristics of these complexes are studied by electron absorption spectroscopy and emission spectroscopy. A hypsochromic shift of the absorption and phosphorescence bands of complexes in substituting the (S^S) and (S^N) chelating ligands with acetonitrile ligands is attributed to a lower energy of d Ir orbitals compared with the mixed d Ir/p(S) orbitals. It is shown that the presence of Hg(II) cations results in a hypsochromic shift of the absorption and phosphorescence bands of complexes [Ir(bt)2(S^S)] and [Ir(bt)2(S^N)] because of an effective reaction of substitution of chelating ligands to acetonitrile ligands.

Optical Properties of Zinc(II) and Boron(III) Dipyrrinates with Different Structures by A. Yu. Nikonova; R. T. Kuznetsova; Iu. V. Aksenova; E. N. Tel’minov; G. V. Mayer; N. A. Dudina; E. N. Nuraneeva; E. V. Antina (395-402).
The spectral luminescent, photophysical, photochemical, lasing, nonlinear optical, and sensor characteristics of a series of new synthesized complexes of zinc and difluoroborate with dipyrrines of different structure have been studied. It is found that many of these compounds exhibit stimulated emission in different solvents when excited by the second (532 nm) and third (355 nm) harmonics of a Nd:YAG laser in the range of 548–692 nm. It is shown that not only efficient fluorophores belonging to dipyrrine difluoroborates (with a quantum fluorescence yield close to 1), but also compounds with a fluorescence yield equal to 0.3, generate laser radiation with a high resource; phosphorescence is also observed along with fluorescence. Transmission of UV radiation (355 nm) is shown to decrease with an increase in the pulsed excitation power density; this is a manifestation of nonlinear optical properties. The change of phosphorescence signal in dependence of the composition of the gas mixture around a solid-state sample colored by dipyrrinate complexes indicates that a number of the compounds under consideration exhibit sensor abilities.

Photoluminescence of CaGa2S4:Pr Polycrystals by B. G. Tagiev; S. A. Abushov; O. B. Tagiev (403-407).
The photoluminescence (PL) and PL excitation spectra of CaGa2S4 polycrystals doped with praseodymium are studied in the regions of the activator absorption and the fundamental absorption of the host. It is found that the PL excitation spectrum consists of two regions: broadband absorption in the range of 200-380 nm corresponding to the fundamental absorption of the host and the narrow-band absorption of the dopant in the range of 430–515 nm. The luminescence spectra are different for different excitation wave-lengths, which occurs because Pr3+ ions substitute divalent cations occupying different crystallographic positions in the host crystal lattice.

PVP Assisted Shape-Controlled Synthesis of Self-Assembled 1D ZnO and 3D CuO Nanostructures by Fozia Z. Haque; Mohammad Ramzan Parra; Hafsa Siddiqui; Neha Singh; Nitu Singh; Padmini Pandey; K. M. Mishra (408-414).
Self-assembled one-dimensional (1D) zinc oxide (ZnO) rods and three-dimensional (3D) cupric oxide (CuO) cubes like nanostructures with a mean crystallite size of approximately 33 and 32 nm were synthesized through chemical route in the presence of polyvinylpyrrolidone (PVP) under mild synthesis conditions. The technique used for the synthesis of nanoparticles seems to be an efficient, inexpensive and easy method. X-Ray diffraction patterns confirmed well crystallinity and phase purity of the as prepared samples, followed by the compositional investigation using Fourier Transform Infrared (FT-IR) spectroscopy. The formation of ZnO nanorods and CuO nanocubes like structures were through Scanning Electron Microscopy (SEM) images. The mechanism and the formation factors of the self-assembly were discussed in detail. It was clearly observed from results that the concentration of precursors and PVP were important factors in the synthesis of self-assembly ZnO and CuO nanostructures. These self-assembly nanostructures maybe used as novel materials in various potential applications.

Spectral and Luminescence Properties of Sols and Coatings Containing CdS/ZnS QDs and Polyvinylpyrrolidone by K. S. Evstrop’ev; Yu. A. Gatchin; S. K. Evstrop’ev; K. V. Dukel’skii; I. M. Kislyakov; N. A. Pegasova; I. V. Bagrov (415-422).
Spectral and luminescence properties of sols and composition coatings containing cadmium and zinc sulfides and high-molecular polyvinylpyrrolidone have been studied. It is shown that the absorption spectra of colloidal solutions in the UV spectral range are determined by the quantum-confinement effect and exhibit a dependence of the absorption edge on the size of cadmium sulfide nanocrystals. The size of forming particles of metal sulfides has been found to decrease with an increase in the relative content of polyvinylpyrrolidone. It is shown that the order of mixing of the initial components when synthesizing sols also determines the difference in the size of forming particles and their spectral properties.

Controlling the Radiation Parameters of a Resonant Medium Excited by a Sequence of Ultrashort Superluminal Pulses by R. M. Arkhipov; M. V. Arkhipov; P. A. Belov; I. Babushkin; Yu. A. Tolmachev (423-433).
We investigate the possibility of controlling the radiation parameters of a spatially periodic one-dimensional medium consisting of classical harmonic oscillators by means of a sequence of ultrashort pulses that propagate through the medium with a superluminal velocity. We show that, in the spectrum of the transient process, in addition to the radiation at a resonant frequency of oscillators, new frequencies arise that depend on the period of the spatial distribution of the oscillator density, the excitation velocity, and the angle of observation. We have examined in detail the case of excitation of the medium by a periodic sequence of ultrashort pulses that travel with a superluminal velocity. We show that it is possible to excite oscillations of complex shapes and to control the radiation parameters of the resonant medium by changing the relationship between the pulse repetition rate, the medium resonant frequency, and the new frequency.

The effect of an external dc electric field on the two-dimensional extremely short optical pulse propagating in a zigzag carbon nanotube array was investigated. The electromagnetic field evolution in the investigated nanotube system is described by the Maxwell equations. Using numerical simulation, the interaction between the pulse electromagnetic field and the external electric field applied to the carbon nanotube array is analyzed.

Inversionless Superradiance and the Duffing Model by I. V. Ryzhov; N. A. Vasil’ev; I. S. Kosova; M. D. Shtager; V. A. Malyshev (440-447).
Superradiance of three-level optical systems with a doublet in the ground state (Λ-scheme) placed in a high-Q cavity is studied theoretically. The conservation laws are obtained, which allow to considerably reduce the dimension of the phase space of the examined model (R11→R5). In the particular case of a degenerate doublet, a mapping that makes it possible to reduce the problem of the three-level superradiance to a Duffing oscillator model (R5→R2) is found. It is shown the possibility to initiate the superradiance generation even in the case when the population of the upper level is smaller than the total population of the lower doublet, i.e., without population inversion on the whole.

We have examined an analog to the extended boundary conditions method (EBCM) with the standard spherical basis, which is popular in light scattering theory, with respect to its applicability to the solution of an electrostatic problem that arises for multilayer scatterers the sizes of which are smaller compared to the wavelength of the incident radiation. It has been found that, in the case of two or more layers, to determine the polarizability and other optical characteristics of particles in the far-field zone, the parameters of the surfaces of layers should obey the condition max{σ1 (j)} < min{σ2 (j)}. In this case, appearing infinite systems of linear equations for expansion coefficients of unknown fields have a unique solution, which can be found by the reduction method. For nonspheroidal particles, this condition is related to the convergence radii of expansions of regular and irregular fields outside and inside of the particle, including its shells—R 1 (j) = σ1 (j) and R 2 (j) = σ2 (j). In other words, a spherical shell should exist in which expansions of all regular and irregular fields converge simultaneously. This condition is a natural generalization of the result for homogeneous particles, for which such a condition is imposed only on expansions of the “scattered” and internal fields—R 1 < R 2. For spheroidal multilayer particles, which should be singled out into a separate class, the EBCM applicability condition is written as max{σ1 (1), σ1 (2), …, σ1 (J−1), σ1 (J)} < min{σ2 (1), σ2 (2), …, σ2 (J−1)} and parameters σ2 (j) of the surfaces of shells are not related to corresponding convergence radii R 2 j of irregular fields. Numerical calculations for two-layer spheroids and pseudospheroids have confirmed completely theoretical inferences. Apart from the EBCM algorithm, an approximate formula has been proposed for the calculation of the polarizability of two-layer particles, in which the polarizability of a two-layer particle is interpreted as a linear combination of the polarizabilities of homogeneous particles that consist of the materials of the shell and core proportionally to their volumes. The range of applicability of this formula is wider than that for the EBCM, and the calculation error is smaller than 1%.

A method for the measurement of the recording/erasing time of dynamic phase gratings that are recorded by phase-modulated beams in photorefractive medium with local response is presented. The method is based on the detection of the intensity modulation of output beams in the course of rerecording of the grating after a shift of the interference pattern by one-half of spatial period. It is demonstrated that a relatively high sensitivity of the method is due to the selective detection of signals at a high frequency and a high efficiency of energy exchange of the recording beams in comparison with the diffraction of the probe beam. The application of the method in dynamic holographic seismographs is discussed.

Antimirror Reflection of a Bounded Planar Optical Waveguide: the String Model by P. Yu. Shapochkin; Yu. V. Kapitonov; G. G. Kozlov (465-471).
The effect of antimirror reflection from a bounded planar optical waveguide is considered. Earlier, it was used for observing the slow light in a Bragg waveguide. Using the proposed theory of this effect, experimentally observed spectral (Gaussian line shape) and angular (Lorentzian angular distribution) properties of the radiation scattered by the bounded waveguide in the antimirror direction are interpreted.

Specific features have been revealed of nonlinear optical processes occurring when the total energy of two photons of a mode-locked Nd3+:YAG laser coincides with the energy of the main electron—hole (exciton) transition in colloidal CdSe/ZnS QDs and the effective self-diffraction of two laser beams arises on the induced diffraction grating.

The optical properties of a composite material consisting of a thin polymer film, which is activated by semiconductor CdSe/ZnS quantum dots (QDs) and silver nanoparticles, on a transparent dielectric substrate have been investigated. It is revealed that the presence of silver nanoparticles leads to an increase in the QD absorption (by a factor of 4) and in the fluorescence intensity (by a factor of 10), whereas the fluorescence time drops by a factor of about 10. Excitation of the composite medium by a pulsed laser is found to result in narrowing of the fluorescence band and a sublinear dependence of its intensity on the pulse energy. In the absence of silver nanoparticles, the fluorescence spectrum of QDs is independent of the excitation-pulse energy density, and the fluorescence intensity depends linearly on the pulse energy in the entire range of energy densities, up to 75 mJ/cm2.

The Influence of the Molecular Structure of Cyanine Dye on the Component Composition of Molecular Layers by E. N. Kaliteevskaya; V. P. Krutyakova; T. K. Razumova; A. A. Starovoitov (482-491).
The formation of the component composition of symmetric cationic cyanine dyes on glass is studied. The absorption spectra of layers of three homologous series of dyes with end heterocyclic groups of different spatial and chemical compositions are measured, and the absorption spectra of monomer components and aggregates are separated. The component compositions of layers of different thicknesses are compared. It is shown that the widening of the absorption spectra of molecular layers against the spectra of ethanol solutions of these compounds is caused mainly by the formation of various monomer stereoisomers and molecular aggregates and their interaction with the substrate surface and the neighborhood. The number of isomer forms and their relative concentrations depend on the layer thickness, the electron donor ability and spatial structure of end groups, and the cation conjugation chain length. The influence of the anion manifests itself only in the concentration ratio of the formed monomers and a small shift of the maxima of their absorption bands. The increase in the number of monomer forms produced in the layer corresponds to the increase in the conjugation chain length. Spatial obstacles created by heterocyclic groups inhibit the formation of definite stereoisomers, which reduces the number of components of the layer.

Laser Spectrometric Measurement System for Local Express Diagnostics of Flame at Combustion of Liquid Hydrocarbon Fuels by V. D. Kobtsev; D. N. Kozlov; S. A. Kostritsa; V. V. Smirnov; O. M. Stel’makh; A. A. Tumanov (492-499).
A laboratory laser spectrometric measurement system for investigation of spatial distributions of local temperatures in a flame at combustion of vapors of various liquid hydrocarbon fuels in oxygen or air at atmospheric pressure is presented. The system incorporates a coherent anti-Stokes Raman spectrometer with high spatial resolution for local thermometry of nitrogen-containing gas mixtures in a single laser shot and a continuous operation burner with a laminar diffusion flame. The system test results are presented for measurements of spatial distributions of local temperatures in various flame zones at combustion of vapor—gas n-decane/nitrogen mixtures in air. Its applicability for accomplishing practical tasks in comparative laboratory investigation of characteristics of various fuels and for research on combustion in turbulent flames is discussed.

Combination of FTIR and SEM for Identifying Freshwater-Cultured Pearls from Different Quality by Somruedee Satitkune; Natthapong Monarumit; Chakkrich Boonmee; Aumaparn Phlayrahan; Kittiphop Promdee; Krit Won-in (500-504).
The freshwater-cultured pearl (Chamberlainia hainesiana species) is an organic gemstone mainly composed of calcium carbonate mineral including calcite, aragonite and vaterite phases. Generally, the quality of freshwater-cultured pearl is based on its luster. The high luster pearl is full of the aragonite phase without vaterite phase. On the other hand, the low luster pearl consists of aragonite and vaterite phases. These data could be proved by the Fourier Transform Infrared (FTIR) spectroscopy combined with the scanning electron microscopy (SEM). As the results, the high luster pearl similarly shows the FTIR spectrum of aragonite phase, and also, it shows the hexagonal shape of aragonite for the SEM image. On the other hand, the FTIR spectrum of low luster pearl has been pointed to the mixture component among aragonite and vaterite phases, and based on the SEM image; the irregular form is also interpreted to the mixture of aragonite and vaterite phases. This research concludes that the quality of freshwater-cultured pearls can be identified by the combination data of FTIR spectra and SEM images. These techniques are suitable for applied gemology.