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.     

A fibre-optic sensor for flocculation detection by electric field light scattering

A laser-based apparatus is described that is able to differentiate between the isolated and flocculated state of colloidal particles in concentrated suspensions. It is based on the principle that the intensity of the scattered light changes when anisodiametric particles are made to rotate and align in an electric field. The system is demonstrated by measurements on kaolinite clay suspensions and can be readily adapted to monitor and control suspensions deflocculation in ‘on-line’ industrial processes.     

Electric field light scattering by flexible linear polyelectrolytes in aqueous solution

Electric field light scattering results on aqueous solutions of linear, flexible NaPSS at minimal ionic strength are reported. Samples of molecular weights between 356 kg/mol and 2870 kg/mol were investigated. With increasing field strength the intensity as a function of wavenumber develops a pronounced oscillating behaviour. Besides the well-known first peak a second maximum is observed at the position at which a weak maximum for some samples already occurs at zero field. The overall intensity strongly depends on the frequency of the electric field. The electro-optical effect shows a maximum at 300 kHz. Increasing the particle concentration gives a large increase of the peak maximum, normalized to concentration. If plotted versus scattering angle the relative intensity increase is maximum for samples of medium molecular weight. The results strongly indicate a stretching and alignment of the chains, thus leading to or enlarging the short range order of the chains. Received 9 April 1999 and Received in final form 18 August 1999     

Effect of electric field on neutron scattering in lead magnoniobate

The temperature dependence of the intensity of the Bragg and the transverse component of quasi-elastic neutron scattering from the single-crystal model relaxor PbMg_1/3Nb_2/3O₃ (PMN) has been studied for various applied electric fields. It is shown that application of a field E>E _th ≈1.6 kV/cm increases the elastic scattering intensity and reduces the intensity of the transverse diffuse-scattering component and that, below 230 K and for E>6 kV/cm, the elastic-scattering intensity saturates while the temperature-dependent part of the transverse diffuse-scattering component becomes practically suppressed. The measured temperature and field dependences of the intensity of type (h00) and (hh0) Bragg reflections provide supportive evidence both for the presence of considerable lead-ion displacements relative to the ideal perovskite sites and for the existence in strong electric fields of an induced transition to the ferroelectric phase below 250 K. Fiz. Tverd. Tela (St. Petersburg) 40, 1905–1910 (October 1998)     

Theory of interband and intraband light scattering in semiconductors in an external electric field

A theory is developed for interband and intraband light scattering in semiconductors in an external electric field. Explicit results are given for a simple two-band model. The field induced change of the interband scattering cross section shows oscillation close to the scattering edge. Intraband scattering being approximately elastic without an external electric field becomes inelastic in the presence of the field. A numerical estimation of the field influence on the scattering cross section is given in both cases.     

Effect of higher-order electric and magnetic multipolar transitions on Rayleigh light scattering in liquids

We calculate the effect of magnetic dipolar transitions, related with the polarizabilities B″, ′, and ″ and electric-quadrupole transitions, related with the polarizabilities C′, ″, and ′, on dynamical Rayleigh light scattering by isotrophic media. To this aim, we introduce molecular scattering factors of the fourth, fifth and sixth orders related with these polarizabilities. For molecules with 76 magnetic point group symmetries these transitions are found to affect the time-dependent intensities and depolarization ratios of scattered light. Among the 76 groups, the molecules belonging to 23 groups exhibit natural (transmission and Rayleigh) optical activity, whereas the point group m shows Rayleigh activity only. The effects in question result moreover from the contribution of magnetic-dipole and electric-quadrupole transitions. For isotropic molecules, the above transitions lead to partial depolarization of the scattered light wave. Our use of i- and c-tensors as well as Hermitian and anti-Hermitian components permits the extension of our discussion to regions of absorption as well as cases of full symmetry of the molecules.     

Heavy particle scattering by atoms in an electric field

Atom—atom collision processes in an electric field are considered. A formula is obtained, in a two-level approximation, for the probability of transitions in which there is a change in the total angular momentum from J=0 to J=1. It is shown that the transition probability is characterized by an anisotropic distribution and a dependence on the electric field strength.V. V. Kuibyshev State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–94, October, 1994.     

Influence of electric field on heterogeneous reactions stimulated by laser light

We present experimental data for vanadium and copper oxidation by cw CO₂ laser light in an external electric field. Direct influence of the external field on the crystallisation process has been demonstrated in both vanadium and copper cases; the oxidation rate and surface morphology depend sensitively on the sign and strength of the external field.     

Band formation in mixtures of oppositely charged colloids driven by an ac electric field

We present experiments on pattern formation in a Brownian system of oppositely charged colloids driven by an ac electric field. Using confocal laser scanning microscopy we observe complete segregation of the two particle species into bands perpendicular to a field of sufficient strength when the frequency is in a well-defined range. Because of its Brownian nature the system spontaneously returns to the equilibrium mixture after the field is turned off. We show that band formation is linked to the time scale associated with collisions between particles moving in opposite directions.     

Effect of absorption on light scattering by agglomerated debris particles

We study the influence of material absorption on light scattering by agglomerated debris particles whose sizes are comparable with the wavelength. We find that the angular profile of linear polarization is extremely sensitive to the imaginary part of refractive index, and there are some unique features that may assist in the retrieval of physical properties of particles using remote-sensing techniques. Most notably, the position of the positive polarization maximum α_max changes monotonically with the imaginary part of refractive index, allowing it to be used to characterize this property. In addition, the amplitude of the negative polarization branch (NPB) is significantly greater for dielectric particles than for non-dielectric particles. It disappears in the transition region between dielectric and conducting particles before reappearing as the imaginary part of the refractive index is increased further. Further increasing the imaginary part of the refractive index may see the NPB disappearing and reappearing in quasi-periodic fashion. This recurrent NPB has a much smaller amplitude than that of dielectric particles. This suggests that the cometary circumnuclear haloes, which have significant NPBs, cannot contain significant quantities of absorbing particles. In addition, combined observations suggest that the polarization maximum of circumnuclear haloes are relatively small P_max～12%, and occur at relatively small phase angles α_max～60°, which is also consistent with dielectric particles.     

Electro- and magneto-optical measurements of electric field strength in magnetic colloids based on liquid dielectrics

The distribution of the electric field strength in liquid dielectrics containing colloidal magnetite particles was investigated based on the data of electro- and magneto-optical experiments. It is shown that the field distribution between plane-parallel electrodes is nonuniform. The dependences of the field enhancement in the near-electrode region on the temperature and average field strength in the cell are determined. The parameters of the near-electrode space charge are calculated based on the data of optical experiments.     

水下光场的迭代求解

水体对光线的散射是水下图像质量劣化的重要因素,为了定量分析在特定光源照射下水体散射的影响,建立了光线水下传输的散射模型,以此为基础推导出求解水下光场分布的Fredholm积分方程.在水中光线能量随距离的增大呈指数规律衰减,基于此,在水体体散射函数为常数的情况下,给出了有边界条件时该积分方程的数值迭代求解方法,得到高精度...     

Effect of multiple scattering on the critical electric field for runaway electrons in the atmosphere

A simple method for taking into account the multiple Coulomb scattering in construction of a separatrix (the line separating the regions of runaway and decelerating electrons in an electric field) is described. The desired line is obtained by solving a simple transcendental equation.     

Effect of built-in electric field on electron Raman scattering in InGaN/GaN coupled quantum wells

Electron Raman scattering (ERS) in wurtzite In_xGaN_1−x/GaN coupled quantum wells (CQWs) is investigated by effective-mass approximation and second-perturbation approach, including a strong built-in electric field (BEF) effect due to the piezoelectricity and spontaneous polarization. The dependence of differential cross-section (DCS) on structural parameters of CQWs is studied. Our results show that the strong BEF gives rise to a remarkable reduction of the DCS, which is around three orders smaller than that of the CQWs without BEF. With the presence of the BEF, the emitted photon energy decreases about 10 times as a consequence of quantum-confined Stark effect.     

Interband light absorption by a semiconductor in a pulsing electric field

The light absorption by a semiconductor, placed in a pulsing electric field of arbitrary amplitude and pulse duration is considered. The calculation of the absorption coefficient is carried out on the ground of the effective mass method for direct optical transitions between two simple parabolic bands. The calculated absorption coefficient is valid for photon energies both greater and lesser than the semiconductor forbidden bandwidth.     

Rayleigh scattering of light by two-dimensional electrons in a high magnetic field

Resonance Rayleigh scattering of light by a two-dimensional electron system in the ultraquantum limit is investigated. The scattering process under study involves electronic states belonging to the two spin sublevels of the zero Landau level. It is shown that the main contribution to resonance Rayleigh scattering originates from the fluctuations of the random potential in the quantum well hosting the two-dimensional system.     

Effect of an electric field on crystallization

The effect of an electric field on crystallization of dielectrics is examined. It is shown by the techniques of thermodynamics that an electric field has a substantial effect on the parameters of crystallization, the number of centers, the critical dimensions, and the work and rate of nucleus formation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 29–32, April, 1977.