Effect of electric field on light scattering by aqueous colloids of diamond and graphite

We present the results of our experimental investigation of light scattering by polydisperse colloids of diamond and graphite. The scattering is studied at a random orientation of particles and in an external radiofrequency electric field, which orients particles along the strength. The average dimensions of particles in both colloids are close to each other and comparable with the wavelength of the incident light. The shape of particles and the optical and electrooptical properties of diamond and graphite colloids are significantly different. We analyze the polarization components of scattered light energy when the light incident on the colloids is linearly polarized. We show that the quadrupole light scattering by isotropic diamond particles has the main effect on angular dependences of depolarization of scattered light. For light scattering by anisotropic graphite particles, the depolarization of scattered light is mainly determined by a particular feature of the dipole scattering of particles. It is shown that, in both colloids, the orientational order of particles considerably reduces the depolarization of light scattered by particles. We show that relative changes in the intensity and depolarization of scattered light, which depend on the scattering angle and polarization direction of light, as well as on the parameters of particles, can be used as a measure of electrooptical effects observed in colloids.     

Specific features of the electrooptical effect and light scattering of water dispersed system of carbon nanotubes

Results of an electrooptical study of a water solution of carbon nanotubes obtained using the catalytic method are presented. It is shown that nanotubes, which anisotropically absorb light, are oriented in an electric field and create a pronounced linear electric dichroism due to light absorption, rather than light scattering (as in the case of colloids with particles with sizes close to that of nanotubes). An analysis of the relaxation dependences of the electric dichroism shows that nanotubes deform, which are oriented in the electric field; in this case, the deformation sublinearly depends on the field amplitude and reaches a limiting value. The relaxation dependence of the field-induced dichroism agrees with the autocorrelation function of depolarized light scattered perpendicular to the incident light flux.     

Light scattering by diamond and graphite nanodisperse systems with their particles orientationally ordered in an electric field

We have presented the results of our investigations of relative changes in the intensity of light scattered by nanodisperse systems that are exposed to the action of an electric field. To orient particles of the systems under study, sinusoidal fields of variable amplitude and frequency from the radiofrequency range were used. We have examined aqueous polydisperse suspensions of diamond and graphite particles. The average sizes of particles in the two suspensions are close to each other and are comparable with the wavelength of the incident light. Graphite particles had the shape of disks, while polycrystalline diamond particles did not have a clearly pronounced shape. Investigations have been conducted not only in the regime of a stationary orientational order of particles in the field, but also in the course of forced and free relaxation of this order. For the graphite nanodisperse system, the normalized-in-amplitude dependences of observed electrooptical effects on the field strength almost do not depend on the scattering angle, whereas, for the diamond nanodisperse system, they considerably vary as this angle changes. Upon relaxation of the orientational order of particles, the time dependences of these effects in both systems change with varying scattering angle. We have compared field and time dependences of scattering-induced effects with analogous dependences of field-induced dichroism.     

Similarity effects in multiple scattering of coherent radiation: Phenomenology and experiments

Based on phenomenological concepts of statistics of effective optical paths for multiple scattering of coherent radiation, an analysis is carried out of similarity effects observed for the dependences of statistical moments of the scattered field on the relaxation parameters with a dimension of reciprocal length. Within the framework of the diffusion approximation, expressions are obtained that describe the autocorrelation function of fluctuations of the scattered-field amplitude, the degree of polarization, and the normalized intensity of scattered light for media with a finite absorption length in the case of forward scattering of coherent radiation in a plane layer of an isotropic scattering medium. The results of the analysis show the similarity of the dependences of these quantities on the corresponding spatial scales. Experiments with model scattering media (aqueous suspensions of polystyrene spherical particles) supported the existence of similarity effects in multiple scattering. An experimental study was made of the relation between the characteristic depolarization length and the transport length for multiple scattering of coherent radiation in a plane layer. The effective value of the radiation diffusion coefficient providing the best agreement between the experimental and the calculated values of parameters of the scattered field is shown to be independent of the absorption coefficient of a medium.     

Evolution of the fractal surface of amorphous lead zirconate-titanate films during crystallization

The recrystallization kinetics of amorphous lead zirconate-titanate films prepared by sol-gel technology are investigated experimentally using elastic scattering of light. Sequences of elastic dependences of the scattered light intensity are recorded directly during thermal annealing. The evolution of the morphology of the film surface during annealing is described in terms of the variation of their fractal dimensionalities D _s. The experimental dependences D _s(t) are compared with the results of a computer simulation of the phase transition kinetics in a thin plate (film). Fiz. Tverd. Tela (St. Petersburg) 41, 306–309 (February 1999)     

Evolution of primary radiation defects in ionic crystals

Using pulsed spectrometry with nanosecond time resolution, we have studied the characteristics of creation of induced defects and the relaxation of such defects in the initial stage in ionic crystals, using as examples ten alkali halide crystals with sc and fcc lattices and an MgF₂ crystal in the temperature range 12.5–500 K. We present the transient absorption spectra, the relaxation kinetics for the induced defects over a broad temperature range, the dependences of the creation and relaxation on the excitation flux density. The results of our investigations are generalized in tables and, in the form of the most characteristic dependences, in figures. We describe the model developed for evolution of primary defects, taking into account the main general characteristics observed experimentally and the results of mathematical modeling based on it, which allowed us to put together a general picture for the series of processes determining the evolution of primary defects. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 5–29, November, 1996.     

Propagation of circularly polarized light in media with large-scale inhomogeneities

Small-angle multiple scattering of circularly polarized waves in disordered systems composed of large (larger than the light wavelength) spherical particles is discussed. The equation for Stokes’s fourth parameter V — the difference between the intensities of the left-and right-hand polarized light — is shown to have the form similar to that of the scalar transport equation for intensity I, the only difference being the presence of an additional “non-small-angle” term responsible for depolarization. In the case of small-angle scattering, depolarizing collisions are relatively rare and, in contrast to the scalar case, the problem contains an additional spatial scale, namely the depolarization depth. The polarization degree and helicity of the scattered light are calculated for the case of purely elastic scattering and in the presence of absorption in the medium. For strong absorption, depolarization is shown to follow the transition to the asymptotic regime of wave propagation. The features appearing in strong (non-Born) single scattering are also discussed. Zh. éksp. Teor. Fiz. 115, 769–790 (March 1999)     

Electrooptical effect in polymeric composites containing heterometallic Cu(II)/Mn(II) complexes

We studied the effect of an electric field on the transmission of linearly polarized light through films of composites based on polyvinylbutyral doped with particles of Cu(II)/Mn(II) complexes with “skeleton” and “planar” structures. The action of an electrostatic field causes light absorption to become anisotropic. The effect increases with increasing distance between the cation and anion. Its sign reverses if the spatial structure of the complex is changed. A phenomenological model is proposed according to which the electrooptical properties of the composites are due to a change in the mutual orientation of complex building blocks on exposure to an external electric field. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 481–484, July–August, 2007.     

The effect of multiple scattering in disperse media on polarization characteristics of scattered light

The effect of scattering of different multiplicity on polarization characteristics of scattered light is studied by the Monte Carlo computer simulation technique. The scattering multiplicity distribution versus the direction of scattering and dimensions of the scattering system is obtained for monodisperse systems of spherical particles of different size. The angular dependences of the elements of the light-scattering matrix (LSM) are calculated. It is shown that in a system of spherical particles, specific features of the LSM structure associated with multiple scattering have much in common with similar features of the LSM in systems of nonspherical particles under conditions of single scattering. The angular dependences of the degree of depolarization of the scattered light are studied.     

Energy filtration of charge carriers in a nanostructured material based on bismuth telluride

The dependences of the electrical conductivity and thermopower on the size of grains in a nanocrystalline material based on Bi₂Te₃-Sb₂Te₃ solid solutions of the p type have been investigated theoretically and experimentally. The relaxation time in the case of hole scattering by nanograin boundaries in an isotropic polycrystal has been calculated taking into account the energy dependence of the probability of tunneling of charge carriers and the dependence of the scattering intensity on the nanograin size L _n . A decrease in the probability of boundary scattering with an increase in the energy of charge carriers leads to an increase in the thermopower. The dependences of the thermopower and electrical conductivity on the nanograin size, which have been obtained taking into account the boundary scattering and scattering by acoustic phonons, are in good agreement with experimental data. For the material under consideration, the thermopower coefficient increases by 10–20% compared to the initial solid solution at L _n = 20–30 nm. This can lead to an increase in the thermoelectric figure of merit by 20–40%, provided that the decrease in the electrical conductivity and the decrease in the lattice thermal conductivity compensate each other. Despite the absence of a complete compensation, it has been possible to increase the thermoelectric figure of merit for the samples under investigation to ZT = 1.10–1.12.     

Dielectric relaxation in deuterated triglycine sulfate crystals

A study has been made of the slow relaxation of the dielectric permittivity of deuterated triglycine sulfate (DTGS) initiated by application of a dc electric field. The field and temperature dependences of the relaxation time associated with domain-wall motion were obtained. The effect of the internal electric field on relaxation processes is seen in different behavior of the field and temperature dependences under different orientations of the external field. The existence in DTGS crystals of two temperature regions of domain-structure rearrangement lying 7–8 and 15–18 °C below the Curie point has been established. Fiz. Tverd. Tela (St. Petersburg) 40, 1542–1545 (August 1998)     

Four-wave polariton scattering of light in LiNbO3

Four-wave Stokes k-spectra for light scattering on polaritons in lithium niobate crystals with an Mg impurity are studied experimentally. The mechanisms for direct, cascade, coherent, and incoherent four-wave mixing of light are discussed in the course of interpreting the angular dependences of the scattered light intensity. It is shown that the dispersion of the real part of the polariton wave vector and the refractive index of the crystals at the polariton frequencies can be measured with an order of magnitude greater accuracy than by spontaneous three-wave polariton light scattering. A significant discrepancy is found between determinations of the polariton absorption coefficient from the angular spectra of three-wave scattering and four-wave scattering in terms of the model employed here. Zh. éksp. Teor. Fiz. 112, 441–452 (August 1997)     

Magnetooptical method of measuring the characteristics of the reservoir of spin-spin interactions in paramagnets

Based on the phenomenon of coherent spin Raman scattering a magnetooptical method of measuring the characteristics of the reservoir of electronic spin-spin interactions in paramagnets was implemented. A formula relating the intensity of the inelastically scattered light to the temperature of the spin-spin reservoirs under conditions of saturation of the EPR of paramagnetic ions has been derived. For the Ce³⁺ ions in the (Ce_xLa_1−x)₂Mg₃(NO₃)₁₂·24H₂O crystal values of the time of spin-lattice relaxation of the spin-spin reservoir and the local magnetic field have been measured, and a relation between the spin-spin reservoir temperature and the external magnetic field strength under conditions of stationary saturation of the EPR of the Ce³⁺ ions has been obtained. V. I. Ul’yanov-Lenin Kazan State University,18, Lenin St., Kazan, 420008, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 76–81, January–February, 1997.     

Angular structure of radiation scattered by monolayer of polydisperse droplets of nematic liquid crystal

We considered light scattering by a polydisperse ensemble of droplets of a nematic liquid crystal. To model light scattering by a monolayer of polymer-dispersed spherical droplets of a nematic liquid crystal with cylindrical symmetry of its internal structure, we proposed a semianalytical modeling method. The method is based on interference approximation of the theory of multiple wave scattering, anomalous diffraction approximation, and effective-medium approximation. The method takes into account cooperative optical effects in concentrated, partially ordered layers and can be used to analyze the small-angle structure of the intensity of scattered radiation in relation to the concentration, size, polydispersity of liquid crystal droplets, orientation of their optical axes, and refractive indices of the liquid crystal and polymer. The obtained relations can be applied to solving direct and inverse problems of light scattering in composite liquid crystal materials using data of polarization measurements. We present graphical results of solving the direct problem for components of the polarization vector of scattered wave. These results illustrate the formation of an angular structure for monolayers with a high concentration of polydisperse droplets of the liquid crystal in the range of small scattering angles (0 < θ _s ≤ 8°).     

On the interrelation of the characteristic scales of depolarization and decorrelation of optical fields under multiple-scattering conditions

The interrelation of depolarization and decorrelation of optical fields in multiply scattering Brownian media is studied on the basis of the notion of the probability density of optical path lengths of the partial components of the scattered field under multiple-scattering conditions. To describe such media a universal parameter that is independent of the density (concentration) of scattering particles is introduced — the characteristic correlation time. Experimental results obtained with aqueous suspensions of polystyrene beads as model media are presented which demonstrate the constancy of this parameter at different concentrations of scattering particles. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 455–460 (10 April 1998)     

Radiation scattering by finite dielectric cyclinders

The volumetric integral equation formalism (VIEF) is used to determine characteristics of scattering of radiation falling along the axis of dielectric cylinders that scatter the radiation. The spectral dependence of the extinction efficiency factor Q is studied with changes in the length l of the cylinder (300–2200 nm), its width d (100–300 nm), and the refraction index m (1.33–1.65). In the range of angles θ=0–180°, for a cylinder with l=700 nm, d=100 nm, and m=1.33, angular intensity distribution functions i_i and i₂ are calculated for the components of the scattered radiation that are polarized perpendicular and parallel to the plane of observation, respectively. No effect of scattered-radiation depolarization is found. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 256–260, March–April, 1998.     

Raleigh and Mandelshtam-Brillouin light scattering in chalcogenide glasses of the (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>x</Subscript>I<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> system

Raleigh and Mandelshtam-Brillouin light scattering has been investigated in chalcogenide glasses of the (As₂S₃)_xI_1−x system for x = 1.00−0.80. Longitudinal hypersound velocities, adiabatic elastooptical constants (p₁₂)_ad at frequencies of ∼15 GHz, and Landau-Placzek ratios R_LP are found and scattering losses are calculated. Significant iodine additives are shown to result in the appearance of different features in the behavior of concentration dependences of the investigated parameters. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 814–818, November–December, 2008.     

Electrooptic properties of aqueous suspensions of nanotubes based on magnesium hydrosilicate

Nanotubes suspended in a fluid medium have been investigated by the electrooptic method. This method is based on measuring the relative changes in the intensity of light transmitted through a suspension of nanotubes with application of an external electric field. The electrooptic effect (difference in these changes for transmitted light plane-polarized along the external field and perpendicularly to it) is analyzed. For aqueous suspensions of Mg₃Si₂O₅(OH)₄ nanotubes, the field and relaxation dependences of this effect are investigated. An analysis of the results obtained suggests that nanotubes, even when their concentration in water is low, form strong stable aggregates, which, however, can be elongated and enlarged under long-term action of strong rf fields.     

Magnetothermal factor of intersubband relaxation of 2D electrons from a highly doped heterotransition in AlGaAs (Si)/GaAs

Characteristics of the Shubnikov-de Haas transverse magnetoresistance oscillations of 2D electrons in highly dopedAlGaAs(Si)/GaAs heterostructures are investigated in the present paper. Anomalies caused by the occupation of two quantization subbands are revealed for samples with 2D-electron density n_s>7·10¹¹ cm⁻² at T=1.7–16 K and magnetic field induction B up to 7.4 T. The dependences of the normalized oscillation amplitude on the magnetic field show bends that typically displace toward weaker magnetic fields with decreasing temperature and electron density n_s. A nonmonotonic (oscillating) dependence of the Dingle temperature on the experimental temperature is found. These anomalies are interpreted for a model of the occupation of two quantization subbands with electrons. They are caused by the competitive character, of intersubband 2D-electron scattering. Small-angle relaxation times are estimated for 2D electrons of the zero and first quantization subbands. S. A. Esenin Ryazan' State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 52–57, January, 2000.     

Absorption related to reversible rotations in a magnetic fluid

A continuum approximation is used to find the magnetic component of absorption (its frequency, field, and orientation dependences) related to the orientational relaxation of the localized magnetic moments of magnetic particles of a magnetic fluid dispersed in a nonmagnetic fluid in the field of a plane stress wave. Kursk State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 14–17, July, 1997.