Optics and Spectroscopy (v.109, #4)

Specific features of Zeeman structure of configurations 2p 55g of Ne I and 3p 55g of Ar I by G. P. Anisimova; O. A. Dolmatova; E. A. Efremova (483-485).
The energies of Zeeman sublevels of the 2p 55g configuration of the neon atom and the 3p 55g configuration of the argon atom are calculated for different values of the magnetic quantum number M (mainly for M = 0, ±1, and ±2) and magnetic field strength that vary in the range of 0–100 kOe. Values of the fields of crossings (ΔM = ±1 and ±2) and anticrossings (ΔM = 0) of magnetic components are determined. The regions of the strong nonlinearity of the dependence of Zeeman sublevel energies on the magnetic field strength are revealed. The gyromagnetic ratios are determined from the level splitting in the linear region (H ∼ 0.05 Oe).

Application of Raman scattering to study of anisotropy of molecular ensembles by M. B. Krasil’nikov; O. I. Rozhdestvenskiĭ; A. G. Smolin; O. S. Vasyutinskiĭ (486-492).
A general expression is obtained for the Raman scattering intensity in an ensemble of diatomic molecules for an arbitrary geometry of the experiment as a function of the anisotropy of angular distribution of molecular axes. In its derivation, the irreducible representation of the density matrix of molecules was used. It is shown that, in the Raman scattering experiments on the study of the anisotropy of molecular ensembles, a significant contribution to the signal is made, not only by the second-order terms 〈cos2θ〉, but also by the fourth-order terms proportional to 〈cos4θ〉, which should be taken into account to correctly interpret the experimental data. Convenient experimental geometries are proposed that allow the anisotropy of a molecular ensemble to be investigated.

The first results of measurements and analysis of excitation spectra of the λlum = 3250 Å luminescence corresponding to I2(D0 u +X0 g + ) transition as well as luminescence at λlum = 3400 Å, where I2(D′2 g A′2 u and/or β1 g A1 u ) transitions occur, observed after three-step, λ1 + λ f + λ1, λ1 = 5321–5508.2 Å, λ f = 10644.0 Å, laser excitation of pure iodine vapour and I2 + Xe mixtures at room temperature via MI2 vdW complexes, M = I2, Xe, of the I2(0 g + , 1 u (bb)) valence states correlating with the third, I(2 P 1/2) + I(2 P 1/2) (I2(bb)), dissociation limit are presented. Luminescence spectra in the λlum = 2200–3500 Å spectral range are also analyzed. Strong luminescence from the I2(D) and, probably, I2(D′ and β) states is observed. We discuss three alternative mechanisms of optical population of the IP state. In our opinion, the mechanism including the MI2 complexes is the most probable.

The first results of measurements and analysis of excitation spectra of the I2(D0 u +X0 g + ) and I2(D0 u +X0 g + and/or β1 g → A1 u ) luminescence, observed after three-step, λ1 + λ f + λ1, λ1 = 5508–5530 Å, λ f = 10644.0 Å, laser excitation of pure iodine vapour and I2 + Xe mixtures at room temperature via bound parts of the I2(0 g + , 1 u (bb)) valence states correlating with the third, I(2 P 1/2) + I(2 P 1/2), dissociation limit and their MI2 vdW complexes, M = I2, Xe, are presented. Luminescence spectra in the λlum = 2200–5000 Å spectral range are also analyzed. Strong luminescence from the I2(D, γ, D′, and/or β) states is observed, though the two latter may be populated in optical transitions in a free iodine molecule if hyperfine coupling of the I2(0 g + and 1 u (bb)) state rovibronic levels occurs. We discuss possible mechanisms of optical population of the IP state.

The linearity of the Stark shift of the lines CII 3920 Å and CII 2747 Å of singly ionized carbon in the range of electron densities from 4 × 1017 to 4 × 1018 cm−3 was revealed as a result of the spectroscopic study of a plasma jet of a capillary and slit discharges with an evaporating wall. A substantial excess of the calculated shift over the measured one with agreement in their signs was noted. A difference was found in the character of the dependence of the Stark width and shift on the electron density under the conditions of strong interparticle interaction.

The possibility of the giant enhancement of hyper-Raman scattering by molecules adsorbed on rough metal surfaces is demonstrated. The theory is based on the qualitative consideration of electromagnetic field enhancement near some model rough surfaces and individual irregularities, as well as on the quantum-mechanical features of dipole and quadrupole interactions of light with molecules (as in the theory of surface-enhanced Raman scattering), proposed by the author. A consideration of symmetric molecules makes it possible to obtain selection rules for surface-enhanced hyper-Raman scattering (SEHRS) spectra and establish such a regularity as the occurrence of strong forbidden lines (which are due to totally symmetric vibrations); these lines are transformed according to unitary irreducible representation in molecules with the symmetry groups C nh , D, and higher. An analysis of the data in the literature for trans-1,2-bis (4-pyridyl)ethylene and pyridine molecules shows that their spectra can be explained in terms of the dipole-quadrupole theory of SEHRS. At the same time, the analysis of the SEHRS spectra of pyrazine revealed the presence of strong forbidden bands due to totally symmetric vibrations. This finding substantiated the proposed theory, which makes it possible to interpret the entire spectrum in detail. These results are in good agreement with the general mechanism of the optical effects enhanced by molecules adsorbed on metal surfaces, which was developed by the author.

Shape distortions of magneto-optical resonances in emission of an extended source are considered. The shape deformation of the magneto-optical structures is shown to be created by a longitudinal spatial inhomogeneity of the magnetic field. A simple procedure of taking into account distortions and of determining positions of resonances on the magnetic field scale and their widths is proposed.

Electromagnetically induced transparency and two-photon absorption in the ladder system in thin columns of atomic vapors by A. Sargsyan; M. G. Bason; D. Sarkisyan; A. K. Mohapatra; C. S. Adams (529-537).
Experimental results of the study of processes of electromagnetically induced transparency (EIT) and two-photon absorption (TPA) are presented for the ladder Ξ-system obtained using the 5S-5P-nD, mS system of levels of the 85Rb and 87Rb atoms with n = 5, 26, and 27 and m = 39 and 48. To perform these studies, a high-temperature optical cell was designed with several regions with the following thicknesses L: 2 mm, 0.7 mm, and the region of 2–6 μm. The advantages of using thin cells over ordinary cells several centimeters thick are demonstrated. It is shown that the EIT resonance parameters for n = 5, 26, and 27 deteriorate insignificantly for thickness down to 700 μm. The TPA is recorded with the cell thickness decreasing down to L = 6 μm. It is shown that using the EIT and TPA processes makes it possible to measure the hyperfine and fine structures of highlying atomic levels. The influence of the cell walls is appreciable in recording the EIT resonances in the system 5S-5P-39S with L = 0.7 mm and in the system 5S-5P-48S with L = 2 mm. Possible applications of the processes studied are indicated.

In the temperature range of T = 150–400 K, the dependence of spectral widths (cm−1) on temperature, 182 + 0.38(±0.01)T and 217 + 0.48(±0.01)T, respectively, has been obtained for dimole emission of O2(a, 0) + O2(a, 0) → O2(X, 1) + O2(X, 0) + hν (λ = 703 nm) and O2(a, 0) + O2(a, 0) → O2(X, 0) + O2(X, 0) + hν (λ = 634 nm). It was shown that the ratio of dimole emission rate constants does not depend on temperature in the range of 150–400 K and is 1.06 ± 0.01.

For in-plane spin states (s = z, y), the rate constants K dg s of the nonradiative energy degradation T 1S 0 of the lowest triplet T 1 state of naphthalene (NPH) and its dichloro-substituted derivatives at positions 1,4- and 2,3- of the molecule (1,4-NPH and 2,3-NPH) are calculated. A simple model is proposed for calculations that is based on the nonadiabatic approximation and uses all the out-of-plane vibrational modes of the molecule as promoting vibrational modes. As a result of calculations, the dependences of the rate constants K dg and K dg s on the positions of chlorine atoms in the molecule are obtained, which are consistent with the known data of magnetooptical measurements. The inversion of the ratio K dg z : K dg y in the 1,4-NPH and 2,3-NPH molecules is established.

Sensitization of fluorescence of dye molecules in nanoparticles of metal complexes by S. S. Dudar’; E. B. Sveshnikova; V. L. Ermolaev (553-566).
We studied the dependence of absorption and fluorescence spectra of complexes of Al, In, Sc, Y, and La with dibenzoylmethane and naphthoyltrifluoroacetone, as well as the dependence of sensitized fluorescence of dyes in nanoparticles of these complexes, in relation to the water pH, the ratio between ions and diketones, and the ion selection. We showed that the ability of complexes of ions to form nanoparticles that efficiently sensitize dye molecules incorporated into them is determined by stability constants of these ions with organic ligands and by their ability to compete with the formation of hydroxy complexes of these ions. We found that nanoparticles consist of diketonates of different compositions and that Nile red incorporated into nanoparticles is an indicator of the dependence of the composition of nanoparticles on the selection of the central ion of complexes and conditions of their formation. We revealed that complexes M(diketone)(OH)2 self-assemble into nanoparticles with an admixture of dye molecules and efficiently sensitize dyes upon excitation into absorption bands of complexes. We showed that, at concentrations of rhodamine 6G in water smaller than 50 nM, the use of a solution that contains 50 μM of Al(III), In(III), or Sc(III) + 50 μM of naphthoyltrifluoroacetone makes it possible to increase the sensitivity of the luminescence analysis by 20-fold for the presence of rhodamine 6G in an aqueous solution.

We studied the steady-state fluorescence spectra of solutions of FET (4′-(diethylamino)-3-hydroxyflavone) in acetonitrile that were excited at different temperatures by quanta with different energies located in the range of the main absorption band and in its long-wavelength wing. We found that, at room temperature, the emission intensity ratio of the bands of the normal and tautomeric forms, which are located at 505 and 570 nm, respectively, depends on the excitation wavelength. In the range of the main absorption band 300–360 nm, this ratio remains nearly the same, i.e., 1.45, while, upon excitation in the range of the long-wavelength wing 360–380 nm of the main band, it decreases to 1.33 at a wavelength of 460 nm. In this same range, a long-wavelength excitation effect that is unusual for liquid inviscid solvents at room temperature, i.e., a bathochromic shift of the entire short-wavelength emission band by 11 nm, manifests itself. We propose to explain these dependences using energy diagrams, which take into account the dependence of free energy on the orientational polarization of the polar solvent. The observed effect of the long-wavelength shift of the fluorescence spectrum with increasing excitation wavelength is explained in terms of the inhomogeneous broadening of electronic spectra of polar solutions, and it should be described using the scheme of energy states that takes into account sublevels of orientational broadening due to orientational dipole-dipole interactions of the fluorophore with nearest molecules of the polar solvent, as well as the relation between the fluorophore lifetime in the excited state and the dielectric relaxation time of solvent molecules in the field of the fluorophore dipole.

The experimental low-frequency Raman spectra of paradibromobenzene nanoparticles of 400-60 nm in size have been recorded. The line frequencies decrease with a decrease in the nanoparticle size and the line half-widths change as well. The nanoparticle sizes have been determined with an electron microscope. The nanoparticle structure has been modeled by the molecular-dynamics method and the histograms of lattice-vibration spectra has been calculated by the Dean method. When the nanoparticle sizes change from 400 to 60 nm the lattice parameter along the crystallographic axis a increase, while the parameters along the two other axes decrease. Overall, the nanoparticle structure is similar to that of paradibromobenzene single crystals.

Optical properties of nanoplasmon excitations in clusters of endometallofullerenes by E. K. Alidzhanov; Yu. D. Lantukh; S. N. Letuta; S. N. Pashkevich; I. E. Kareev; V. P. Bubnov; E. B. Yagubskii (578-583).
The optical properties of solutions of endometallofullerenes with lanthanides (Gd@C82, Ce@C82, La@C82, Y@C82) in dimethylformamide are studied. It is found that these solutions luminesce in the visible region. This luminescence is accompanied by enhanced Raman scattering. It is suggested that these processes are related to nanoplasmon excitations in clusters of endometallofullerenes. It is shown that the luminescence spectrum is described by a superposition of three to four Gaussian spectral profiles, whose energy positions and intensities nonmonotonically depend on the energy of excitation quanta. A detailed quantitative dependence of the intensity and shape of the Raman scattering signal on the concentration of endometallofullerenes in the solutions is determined. Comparative measurements are performed for the emission spectra of solutions of simple fullerenes and chromatographically pure endometallofullerenes. Complex investigations show that the visible luminescence and Raman scattering enhancement are only observed in the case of the formation of nanosized anionic complexes of endometallofullerenes in the solution.

Parametric interaction and compression of optical pulses in field of high-power pump wave by I. O. Zolotovskiĭ; R. N. Minvaliev; D. I. Sementsov (584-589).
It is shown that, in the undepleted pump approximation, the nonlinear problem of the three-wave parametric interaction under the conditions of phase mismatch can be reduced to a problem of linear interaction of the signal and idle waves with a strong low-frequency pump wave. The whole wave packet formed by the two waves breaks down to partial pulses whose dynamics is controlled by effective dispersion parameters. This can be accompanied by the compression of either one of the pulses that comprises the wave packet or the whole wave packet.

Controlling the parameters of photon nanojets of composite microspheres by Yu. E. Geints; A. A. Zemlyanov; E. K. Panina (590-595).
We consider the spatial and amplitude characteristics of PNJ forming in the neighborhood of the shadow surface of micron-sized composite particles consisting of a nucleus and a shell with various refraction indices when laser radiation scatters on them. We study the longitudinal and transverse dimensions of a photon flux and its peak intensity depending on the microparticle shell thickness. We show that a certain choice of the refraction index of the shell relative to the nucleus in two-layer composite spherical microparticles can significantly lengthen the forming PNJ or increase their peak intensity. The width of the photon flux during this changes insignificantly.

Integral equations for photonic-crystal fibers by M. V. Davidovich; Yu. V. Stefyuk (596-607).
The integral and integro-differential equations for photonic-crystal waveguides (fibers) with both infinite and finite quasi-periodic dielectric coatings have been obtained, with previous consideration of the equations for 2D periodic photonic crystals with magnetodielectric and metallic inclusions. The corresponding numerical results are presented.

Time dynamics of the nematic liquid crystal director in the field of a sequence of rectangular pulses by R. B. Alaverdyan; A. L. Aslanyan; L. S. Aslanyan; G. S. Gevorgyan; V. B. Pakhalov (608-612).
We study theoretically and experimentally the Freedericksz transition in a sequence of rectangular pulses. We show the dependence of the accumulation effect on the pulse filling coefficient. We demonstrate that at a constant energy value in a pulse, the accumulation phenomenon substantially depends on the pulse repetition frequency. An analytical consideration of the initial stage of development of orientational instability fully confirms the conclusions of numerical analysis. The results of experiment agree well with the conclusions of theoretical analysis.

We present the results of measuring the scattering matrix of a water suspension of zinc oxide at a wavelength of 0.63 μm in the range of scattering angles of 15–150°. The angle dependences of matrix elements were measured using a laser polarimeter, the optical scheme of which contained two electro-optical modulators. We compare the measurement results with calculation data for spherically symmetric scatterers. We demonstrate that at a dimensional parameter value of 1.8, in interpreting the data using the model of spherically symmetric scatterers, it is possible to determine the parameters of particle distribution of a zinc oxide suspension with an error of 30%.

Real-time mode asymmetrization of two-wave interference pattern profile by V. Yu. Venediktov; V. A. Laskin; V. A. Savinov (622-624).
The interferogram was digitally transformed in experiment (its fringe profile was asymetrized) in a real-time mode on the base of particularly local (point-to-point) information.

The eigen and noneigen (leaky) modes of a three-layer planar integrated optical waveguide are described. The dispersion relation of a three-layer planar waveguide and other dependences are derived, and the cutoff conditions are analyzed. The diagram of propagation constants of the guided and radiation modes of an irregular asymmetric three-layer waveguide and the dependence of the electric field amplitudes of radiation modes of substrate on vertical coordinate in a tantalum integrated optical waveguide are presented. The operating principles of an absorption integrated optical waveguide sensor are investigated. The dependences of sensitivity of an integrated optical waveguide sensor on the sensory cell length, the coupling efficiency of the laser radiation into the waveguide, the absorption cross-section of the studied material, and the level of additive statistical noise are investigated. Some of the prospective areas of application of integrated-optical waveguide sensors are outlined.

Path-averaged differential meter of atmospheric turbulence parameters by L. V. Antoshkin; N. N. Botygina; O. N. Emaleev; P. A. Konyaev; V. P. Lukin (635-640).
A path-averaged differential meter of the structure constant of the atmospheric refractive index, C n 2 , has been developed and tested. The results of a model numerical experiment on measuring C n 2 and the horizontal component of average wind velocity transverse to the path are reported.

A method is proposed for improving the accuracy of measuring the wedge angle of transparent plates using a lateral-shear holographic interferometer. Consecutive processing of a pair of interferograms with doubled number of interference fringes leads to reduction of the observational error by a factor of two compared to traditional interferometric methods. Data on the experimental validation of the method are presented.