Optics and Spectroscopy (v.122, #5)

An evolutionary particle swarm optimization algorithm for mathematical processing of experimental spectra by D. I. Kamalova; D. Z. Galimullin; M. E. Sibgatullin; M. Kh. Salakhov (687-691).
A particle swarm optimization algorithm is applied for mathematical treatment of Fourier-transform IR spectra of branched copolymers of methyl methacrylate. The efficiency of reconstruction of the spectra using the particle swarm optimization algorithm as compared with the least squares method is illustrated by the example of decomposition of a six-component experimental spectrum.

Quadrupole effects in angular distributions of photoelectrons upon ionization of Kr by X-ray photons by A. V. Merem’yanin; V. E. Chernov; G. E. Gavrilov; Yu. G. Naryshkin; B. A. Zon (692-698).
Implementation of promising control schemes for the intensity and position of X-ray-laser beams with a photon energy up to several tens of kiloelectronvolts requires knowledge of the angular dependence of cross sections for photoionization of noble gas atoms by hard photons. Estimates of quadrupole corrections to the cross section for photoionization of a Kr atom by X-ray photons with an energy of about 25 keV are reported in this paper. An analytic expression for the cross section of the process is parameterized in a compact form convenient for analyzing angular distributions with an arbitrary polarization of a photon beam.

Oscillator strengths for the Rydberg states of NaHe by A. S. Chervinskaya; S. V. Elfimov; D. L. Dorofeev; V. E. Chernov; B. A. Zon (699-704).
The oscillator strengths for Rydberg states of a NaHe molecule are calculated using a semianalytic procedure with the l-coupling effect taken into account (due to the dipole potential of a core). This effect gives rise to nonzero oscillator strengths for transitions forbidden in the atomic model of molecular Rydberg states. The difference between calculations in terms of the atomic model and calculations with consideration of the dipole moment of a core is shown for allowed transitions.

Measurements of parameters of transient gas flows by a diode laser absorption spectroscopy at elevated pressures and temperatures by M. A. Bolshov; Yu. A. Kuritsyn; V. V. Liger; V. R. Mironenko; O. M. Kolesnikov (705-714).
We have developed a prototype of a diode-laser absorption spectrometer for noncontact determination of the temperature and concentration of water vapor in the combustion zone of mixed supersonic flows. The method is based on fast scanning of the radiation frequencies of two diode lasers in different spectral ranges containing several absorption lines of water molecules, determining the integral intensities of selected lines, and calculating the medium temperature from the intensity ratio of these lines. The described version of the spectrometer allows one to determine the parameters of the gas medium at high pressures (up to 3 atm) and temperatures (up to 2000 K). The criterion of selection of the spectral scanning ranges of the lasers is described, which is based on minimizing the error of determining the temperature at the expected experimental measurement accuracy of the integral intensities of lines. A program for selection of appropriate combinations of lines from spectroscopic databases has been developed. An algorithm for obtaining the temperature by fitting experimental spectra and theoretical spectra simulated using databases has been developed. Errors of determining the temperature for different fitting algorithms have been estimated. We show that, for the temperature estimation to be more accurate, it is necessary to take into account maximal possible number of lines lying in the scanning ranges of the two lasers.

Azobenzene Pd(II) complexes with N^N- and N^O-type ligands by M. V. Nikolaeva; An. M. Puzyk; M. V. Puzyk (715-722).
Methods of synthesis of cyclometalated azobenzene palladium(II) complexes of [Pd(N^N)Azb]ClO4 and [Pd(N^O)Azb]ClO4 types (where Azb is the deprotonated form of azobenzene; N^N is 2NH3, ethylenediamine, or 2,2′-bipyridine; and (N^O) is the deprotonated form of amino acid (glycine, α-alanine, β-alanine, tyrosine, or tryptophan)) are developed. The electronic absorption and the electrochemical properties of these complexes are studied.

The influence of donor–acceptor properties of tert-butyl-, 2.6-dimethylphenyl-, and 4-bromophenyl-isocyanides (BuNC, XylNC, BpNC), ethylenediamine (En), and diethyldithiocarbamate ions (Dtc–) on the 1H and 13C NMR, IR, optical, and electrochemical characteristics of Ir(III) complexes with metalated 4-(4-bromophenyl)-2-methyl-1,3-thiazole is studied. Enhancement of the donor properties of BpNC, XylNC, BuNC, En, and Dtc ligands leads to a bathochromic shift of metal-to-ligand charge transfer (MLCT) bands and to a decrease in the difference between the one-electron oxidation and reduction potentials of complexes. The bathochromic shift of the low-temperature phosphorescence of complexes in frozen (77 K) solutions with increasing donor properties of BpNC, XylNC, BuNC, En, and Dtc–ligands is caused by a decrease in the admixture of MLCT to the intraligand excited state of {Ir(bptz)2}. Quenching of the phosphorescence of complexes in liquid solutions is attributed to the thermally-induced population of excited dd* states with subsequent nonradiative deactivation.

Photochromic properties of modified nanodiamonds by O. V. Venidiktova; T. M. Valova; V. A. Barachevsky; A. O. Ait; P. V. Lebedev-Stepanov; A. Ya. Vul; L. S. Koltsova; A. I. Shienok; N. L. Zaichenko (729-734).
A functionalization of the surface of detonation nanodiamonds by photochromic spirocompounds from the classes of spiropyrans and spirooxazines has been carried out for the first time. A comparative study of the interaction of nanodiamonds with positive and negative potential is performed by the spectral–kinetic method, which shows the possibility of surface modification by only functionalized molecules of spirocompounds with the formation of surface proton complexes. This is confirmed by the hypsochromic shift of the absorption bands of the photoinduced merocyanine forms of adsorbed molecules of spirocompounds and by the decrease of the speed of their dark relaxation to the initial state in the presence of nanodiamonds with a negative potential.

Optical transitions in KPb2Cl5:Tb3+ crystals are studied experimentally and theoretically. The absorption cross-section spectra are plotted and the oscillator strengths of transitions from the ground terbium state to excited multiplets are determined. Intensity parameters Ωt for KPC:Tb3+ are determined by the Judd–Ofelt method to be Ω2 = 2.70 × 10–20 cm2, Ω4 = 7.0 × 10–20 cm2, and Ω6 = 0.72 × 10–20 cm2. These values were used to calculate such characteristics of spontaneous radiative transitions as oscillator strengths, probabilities of radiative transitions, and radiative lifetimes. The emission spectra of KPb2Cl5:Tb3+ crystals upon UV excitation and the decay kinetics of luminescence from the excited 5 D 3 and 5 D 4 levels are studied experimentally, the lifetimes of these levels are determined, and the dependences of the rates of nonradiative relaxation from the excited 7 F j (j = 0–5), 5 D 4, and 5 D 3 levels to lower-lying terbium levels are calculated. It is shown that the population of the 5 D 4 level in KPC:Tb3+ crystals occurs according to a cascade scheme, which leads to quenching of the 5 D 3 level. The calculated data agree well with the known experimental rates of multiphonon nonradiative transitions for Dy:KPC, Nd:KPC, Er:KPC, Tb:KPB, and Nd:KPB crystals. It is shown that transitions in the near-IR (3–6 μm) region in double halide crystals (MPb2Hal5) are almost unquenched and the rates of nonradiative relaxation of excited levels spaced by energy gaps ΔE ji > 1000 cm–1 are W ji NR < 103s–1. This circumstance suggests that it is possible to obtain stimulated emission in KPb2Cl5:RE3+ crystals in the IR spectral region up to 6 μm.

The results of measuring the spectra of polystyrene samples in the IR range (4000–400 cm–1) obtained by transmission, specular reflection, frustrated total internal reflection, and diffuse reflection have been compared. Polystyrene samples in the form of a thin film, a bulk sample, and foamed polystyrene have been investigated. The frequencies of the strongest bands in the spectra obtained by the methods under comparison are shown to depend on the anomalous dispersion in the vicinity of these bands and the specific features of structural chemical composition of the polystyrene–air interfaces. The presence of these interfaces is most pronounced in the reflection methods.

Photoluminescence of Ca(Al x Ga1–x )2S4:Eu2+ compounds by B. G. Tagiev; O. B. Tagiev; E. G. Asadov (757-763).
Photoluminescence (PL) observed in solid solutions of Ca(Al x Ga1–x )2S4:Eu2+ (x = 0.1–0.3) is studied. It is shown that the increase in emission intensity by 18% is caused by changes in the x values and electronic 5d → 4 f transitions in Eu2+ ions. A change in the position of the emission spectrum or its partial shift toward shorter wavelengths is due to an increase in the aluminum concentration and a decrease in the crystal field energy. The energy of the zero phonon line E 0, redshift D, and the Stokes shift ΔS are determined. A decrease in the photoluminescence intensity maximum and an increase in the half-width of the spectrum are found in the temperature range of 10–300 K. The efficiency of emission at temperatures of 20 and 300 K is almost independent of the excitation power density of up to ~104 W/cm2. The luminescence lifetime of Eu2+ ions was 383, 357, 346, and 333 ns for x = 0, 0.1, 0.2, and 0.3, respectively.

Luminescence and sensory properties of PMMA films doped with a boron chelate by A. G. Mirochnik; E. V. Fedorenko; I. G. Nagornyi; O. A. Starovoit (764-767).
The optical sensory properties of polymethylmethacrylate films doped with 2,2-difluoro-4-methylnaphtho-[2,1-e]-1,3,2-dioxaborine (1) for water vapor are found. A mechanism of the optical response is proposed: water molecules contribute through hydrogen bonds to the dissociation of aggregates of 1 having intense excimer luminescence of J-aggregates. A sharp quenching of luminescence is observed. The spectrum of the films after exposure to water vapor corresponds to the monomer luminescence of 1.

Specific properties of the radiation emitted by a spatially modulated resonance medium excited by an ultrashort light pulse propagating through the medium at a variable superluminal velocity are analyzed. In so doing, frequencies different from that of the resonance transition of the medium may appear in the emission spectrum. It is demonstrated that, in contrast to an earlier studied case of medium excitation at constant velocity, variation of the excitation velocity leads to generation of a spectral continuum, the boundaries of which are determined by the range of variation of the medium-excitation velocity.

We have considered the dynamics of soliton-like pulses and stable frequency-modulated self-similar pulses in an active medium with saturable nonlinearity and a parabolic refractive-index profile. We show that, based on gaining gradient fibers with a parabolic distribution of the refractive index and saturable nonlinearity, it is possible to create complexes that ensure generation of laser pulses with a high (above 1 TW) peak power.

Quantum dynamics of intracavity third-subharmonic generation by S. T. Gevorkyan; M. S. Gevorkyan (784-790).
The quantum dynamics of the mean number of photons and quantum entropy of interacting modes, as well as the Wigner function of the stationary state of the fundamental mode and the third subharmonic mode has been investigated for the intracavity third-subharmonic generation. It is shown that the quantum dynamics of the system depends strongly on the nonlinear coupling coefficient between the modes. It is also demonstrated that, in the steady-state limit, depending on the intermodal coupling coefficient, the fundamental mode can be either in a pure coherent state, or in a squeezed state, or in a pure vacuum state. The third subharmonic mode in the subthreshold regime of generation of this mode is in the vacuum state. The Wigner function is squeezed over three sides of an equilateral triangle (squeezed vacuum). The quantum entropy of this state is nonzero. It is also shown that the third subharmonic mode, depending on the nonlinear coupling coefficient in the steady-state limit, can be localized in the three-component state with the same probability of detecting a field in each coherent component of the state and with the presence of quantummechanical interference between the state components. The mean number of photons in this state is smaller than unity. Depending on the nonlinear coupling coefficient, the third subharmonic mode can also be localized in the three-component state, which is a statistical mixture of three squeezed states.

Dynamic analysis of the parametric-resonance effect in the exciton region of a spectrum by L. Yu. Nadkin; P. I. Khadzhi; K. D. Lyakhomskaya (791-798).
The pump-probe method of studying of the optical properties of a semiconductor in the exciton region of a spectrum is considered theoretically taking into account the exciton–photon and elastic exciton–exciton interactions. It is shown that the concentration of excitons, and the susceptibility of the medium are mainly determined by the detuning from the exciton resonance and the magnitude of the pump field. The values of the parameters corresponding to the observed parametric resonance are obtained and the dynamic analysis of the found solutions is carried out.

Light absorption by a single spherical crystalline silicon (c-Si) particle and by monolayers of submicron c-Si particles arranged in triangular lattice is examined within the wavelength range from 0.28 to 1.12 μm. Data for spectral and integrated (over the terrestrial solar spectral irradiance “Global tilt” ASTM G173-03) absorption coefficients of monolayer demonstrating the possibility to enhance light absorption by a particulate active layer of crystalline silicon are presented. They are calculated in the quasicrystalline approximation of the theory of multiple scattering of waves. It is shown that in the narrow wavelength intervals (up to 10 nm) the spectral absorption coefficient of monolayer can be more than 100 times larger than the one of the plane-parallel plate of equal volume of material. Some results on the transmittance and reflectance of partially ordered monolayer are presented as well. The potentialities of light absorption enhancement in a single monolayer and three-monolayer system are considered.

The values of optical anisotropy of two series of thermotropic nematic liquid crystalline complexes based on the ions Eu+3, Gd+3, Tb+3, and Dy+3 have been determined. Even–odd alternation of optical anisotropy with an increasing number of protons in ions of lanthanides has been observed. It is established that, in the considered series of lanthanidomesogens, optical anisotropy is more sensitive to changes in the ligand structure of complexes than to the variation of the complexing agent.

The influence of an external electric field on the propagation of light waves in cholesteric liquid crystal cells by E. V. Aksenova; A. A. Karetnikov; A. P. Kovshik; E. S. Krainyukov; A. V. Svanidze (816-825).
The specific features of light transmission in a cholesteric liquid crystal (LC) cell with a director rotated by 90° have been investigated. In this structure, where a light wave is incident at a large angle with respect to the LC surface, the light is reflected (refracted) in the LC layer near the opposite boundary. It is shown that the application of an electric field changes the character of extraordinary wave refraction, as a result of which light starts passing through a cell. The transmission threshold voltage is determined, and its dependence on the angle of incidence of light is obtained. The dependence of the transmitted-light intensity on the voltage across the cell is obtained as well. The same dependences are also derived by numerical calculations with allowance for the turning points and extinction.

Dynamic billiards for particles with inelastic reflections by V. D. Vinokurova; N. N. Rosanov (826-834).
The one-dimensional dynamics of particles that move between a stationary and a harmonically oscillating mirror have been analyzed analytically and numerically taking into account inelastic collisions of particles with mirrors. It has been shown that, in such “billiards,” in contrast to the case of elastic collisions, asymptotically stable periodic regimes are established, including the regime of periodic sticking of a particle to the oscillating mirror, as well as regimes of dynamic chaos.

Analysis of the Purcell effect in the waveguide mode by S-quantization by K. A. Ivanov; A. R. Gubaidullin; K. M. Morozov; M. E. Sasin; M. A. Kaliteevskii (835-842).
A method for calculating the spontaneous-emission probability for arbitrary layered structures in the waveguide mode has been developed based on the scattering matrix formalism. The results of calculating the mode Purcell factor for the TE and TM modes of a planar waveguide are shown. Analytical estimates for the mode Purcell factor are obtained, and the conditions for achieving maximum amplification of spontaneous emission in a waveguide are determined.

Thermooptical processes in the window of a high-power gas laser by M. V. Rogozhin; V. E. Rogalin; M. I. Krymskii (843-849).
We have developed a mathematical model of thermomechanical and thermooptical processes that proceed in the output window of a continuous gas laser of a multikilowatt power. Optimal parameters have been determined at which the output window not only successfully withstands an extreme radiation load, but also ensures the radiation coupling with a minimum possible divergence. We have used numerical modeling to analyze the properties of the most promising materials used in high-power СО2, СО, and oxygen–iodine lasers.