Showing papers on "Light scattering published in 1982"

Advances in Infrared and Raman Spectroscopy

Abstract: Infrared Spectroscopy of the Electrode-Electrolyte Solution Interface Infrared Spectral Studies of DNA Conformations Vibrational Analysis of the Retinal Isomers A Unified View of Raman, Resonance Raman and Fluorescence Spectroscopy (and their Analogues in Two-Photon Absorption) Magnetic Raman Optical Acitivity The Resonance Raman Effect and Depolarization in Vibrational Raman Scattering Low Frequency Depolarized Light Scattering from Liquids and Solutions.

Lightning rod effect in surface enhanced Raman scattering

Abstract: The electromagnetic model of Gersten and Nitzan1 of the surface enhanced Raman scattering is discussed. The ’’lightning rod’’ effect is taken up in some detail. (AIP)

Self-Consistent Results for a GaAs/Al x Ga 1-x As Heterojunction. I. Subband Structure and Light-Scattering Spectra

Abstract: The subband structure of a two-dimensional electron system at a GaAs/Al x Ga 1- x As heterojunction interface is calculated. Many-body exchange and correlation effects are taken into account in the local density-functional approximation. They are shown to be unimportant but not negligibly small. Spectra of light scatterings are also calculated. Results are in reasonable agreement with existing experiments.

Mode amplitudes in dynamic light scattering by concentrated liquid suspensions of polydisperse hard spheres

Abstract: This paper concerns the dynamic light scattering by suspensions of polydisperse hard spherical particles. It is concluded that for relatively high volume fractions and fairly narrow distributions, the light scattering correlation function should, to a good degree of approximation, be composed of two independent modes with well‐separated decay times. The faster decaying mode describes collective stochastic compression–dilation motions and is present even for a monodisperse system. The slower decaying mode describes the exchange of different species. The relative mode amplitudes are calculated in the Percus–Yevick approximation for hard spheres. The two decay times of fast and slow mode are associated with diffusion coefficients D+ and D−, respectively. In the case of scattering power polydispersity D+ and D− are rigorously identified with collective and self‐diffusion, respectively. In the case of size polydispersity D+ and D− can be associated with ‘‘average’’ collective and self‐diffusion coefficients. The considerations are limited to zero scattering wave vector and volume fractions above 0.15. Comparison with experimental results from other papers are in favor of the theory.

Plasma dispersion in a layered electron gas: A determination in GaAs-(AlGa) As heterostructures

Abstract: The dispersion of the plasma frequency of layered electron gases in GaAs-(AlGa) As heterostructures was determined by inelastic light scattering. The measured dispersions differ from that in two- and three-dimensional plasmas. They are linear in the in-plane component of the wave vector. This observation confirms predictions of theoretical models.

New display based on electrically induced index‐matching in an inhomogeneous medium

Abstract: The operation of a new light modulation device that employs electric field controlled light scattering in an inhomogeneous medium is described. The orientation of a nematic liquid crystal, contained in micrometer sized inclusions in a nonabsorbing solid, is changed to produce a varying refractive index. When the refractive index of the liquid crystal matches that of the solid, the composite medium is nonscattering and transparent. If the refractive indices do not match, the medium is scattering and opaque. High contrast ratios have been measured for transmitted light with a response time of a ∼1 ms. The application of this technique to passive display devices is discussed.

Polarized light scattering by hexagonal ice crystals: theory.

Abstract: A scattering model involving complete polarization information for arbitrarily oriented hexagonal columns and plates is developed on the basis of the ray tracing principle which includes contributions from geometric reflection and refraction and Fraunhofer diffraction. We present a traceable and analytic procedure for computation of the scattered electric field and the associated path length for rays undergoing external reflection, two refractions, and internal reflections. We also derive an analytic expression for the scattering electric field in the limit of Fraunhofer diffraction due to an oblique hexagonal aperture. Moreover the theoretical foundation and procedures are further developed for computation of the scattering phase matrix containing 16 elements for randomly oriented hexagonal crystals. Results of the six independent scattering phase matrix elements for randomly oriented large columns and small plates, having length-to-radius ratios of 300/60 and 8/10 microm, respectively, reveal a number of interesting and pronounced features in various regions of the scattering angle when a visible wavelength is utilized in the ray tracing program. Comparisons of the computed scattering phase function, degree of linear polarization, and depolarization ratio for randomly oriented columns and plates with the experimental scattering data obtained by Sassen and Liou for small plates are carried out. We show that the present theoretical results within the context of the geometric optics are in general agreement with the laboratory data, especially for the depolarization ratio.

On the scattering of light by a Mie scatter center located on the axis of an axisymmetric light profile

Abstract: A formalism to compute the scattered intensities from an isotropic, homogeneous, spherical, non-magnetic particle located on the axis of an axisymmetric incident light profile using Bromwich functions is reported. This formalism is expressed in a way similar to the one given by Kerker (1969) for classical Lorenz-Mie theory.

Attractive interactions in critical scattering from non-ionic micelles

Abstract: We have studied the temperature-dependent critical scattering of both light and neutrons from aqueous solutions ofn-octyl pentaoxyethylene glycol monoether (C8E5). We show that the assumption of a short-ranged temperature-dependent attractive pair potential between approximately spherical micelles of constant size permits a quantitative analysis of the neutron scattering data. The analysis, which is undertaken using current liquid-state theory and is in analytic form, contains only one free parameter, the depth of the attractive potential. We find that a potential with a range of only a fraction of a nm is sufficient to generate spatial correlations over tens of nm as the attractive potential deepens on approaching the critical temperature. The analysis also provides a semi-quantitative understanding of the light scattering data as a function of concentration and temperature, and leads to a qualitative prediction of the form of the phase diagram. Numerical values obtained are consistent with the hypothesis that the primary effect of raising the temperature is to lower the degree of structure of water near the micelle surface, allowing increased van der Waals attraction due to closer contact.

Light scattering by a fluid in a nonequilibrium steady state. II. Large gradients

Abstract: The equations derived in the first paper of this series for the correlation functions of mass, momentum, and energy densities are solved for a fluid subject to a large temperature gradient. The shape and intensity of the Rayleigh line show deviations from equilibrium that are proportional to the square of the temperature gradient. The deviations of the intensity of each Brillouin line from its equilibrium value as a function of the temperature gradient is obtained for the optimal scattering geometry. The intensity of one of these two Brillouin lines shows a maximum or minimum as a function of the temperature gradient, depending on the sign of the temperature derivatives of the coefficient of sound attenuation and thermal conductivity and on the orientation of the momentum transfer between fluid and light with respect to the temperature gradient. Further, the difference in intensity of the two Brillouin lines is found to be about three times smaller than predicted by the linear theory, consistent with the experiments of Beysens et al. Since all these results are due to mode-coupling effects, an experimental verification would constitute the first observation of mode-coupling effects away from criticality. The connection between (a) the mode-coupling effects responsible for the changes in the intensities of the Rayleigh and Brillouin lines, (b) the long-time tail contributions to the transport coefficients, and (c) the nonexistence of a virial expansion of the transport coefficients is discussed.

Covalently bonded high refractive index particle reagents and their use in light scattering immunoassays

Abstract: Novel particle reagents for light scattering immunoassays are provided. The particle reagents are high refractive index shell-core polymers covalently bonded to compounds of biological interest or analogs thereof. A method of measuring unknown concentrations of these compounds of biological interest by measuring changes in turbidity caused by particle agglutination or its inhibition is also provided.

Aggregation of dipalmitoylphosphatidylcholine vesicles

Abstract: Quasi-elastic and 90 degrees light scattering were used to study the aggregation of dipalmitoylphosphatidylcholine vesicles at temperatures below the gel-liquid-crystalline phase transition as a function of concentration, temperature, and size. Increased vesicle concentration did not appreciably change aggregate size but did change the total number of aggregates in a manner consistent with a bimolecular collisional mechanism for the conversion of aggregates to fused vesicles. Increased temperature decreased aggregation, indicating that the disaggregation rate constant increased faster than the aggregation rate constant. As a function of size, aggregation decreased slightly from small to 700 A diameter vesicles and increased considerably for 950 A diameter vesicles. A model of the interaction of small vesicles below the gel-liquid-crystalline phase transition is presented in which aggregation precedes fusion and collision between aggregates triggers fusion.

Elastic scattering, absorption, and surface-enhanced Raman scattering by concentric spheres comprised of a metallic and a dielectric region

Abstract: Elastic scattering by a small inhomogeneous sphere, comprised of two concentric spherical regions, may be abnormally low if the dielectric constant of the external medium is intermediate between those of the two regions. When one of these regions is a metal with a real negative dielectric constant, there may also be very large enhancement of the scattering due to excitation of a dipolar surface plasmon. For a sphere in which the metallic region is silver, the incident radiation can be tuned over a range of optical wavelengths to give a variation of ${10}^{6}$ in scattering cross section. Such objects may exhibit very large surface-enhanced Raman scattering with excitation profiles sharply dependent upon the relative thickness of the spherical shell.

Measurements of temporal and spatial sequences of events in periodic precipitation processes

Abstract: A series of new experiments on Liesegang ring (or band) formation is presented which is concerned with the temporal and spatial evolution of the process of structure formation. We have chosen NH4OH and MgSO4 to form rings of Mg(OH)2 precipitate in a gelatin gel, as well as KI and Pb(NO3)2 for periodic precipitation of PbI2 in an agar gel. A temporal sequence of events during the entire period from the start of a Liesegang experiment in a test tube to the completion of the final ring pattern has been determined at many locations in the tube by visual observations and by measurements of transmitted light, of scattered light, of deflection of the transmitted light beam, and of gravity effects. After diffusion of one electrolyte into the gel medium containing the second electrolyte results in an ion product larger than three times the solubility product, at any and all points in space, we observe the onset of homogeneous nucleation of colloidal particles by a steplike increase of the index of refraction. The colloid concentration and the particle number density at the nucleation site are estimated to be 10−2 mol/l and 1015 to 1016 cm−3, respectively. Nucleation is followed by the growth of colloidal particles which gives rise to distinct light scattering (turbidity). Both nucleation and colloid formation take place in space continuously; the fronts of these phenomena move through the system and obey a simple diffusion law. A substantial time interval after their passage, there arises a localized gradient of the index of refraction at the prospective ring positions which indicates onset of structure formation by means of a focusing mechanism. While the localized gradient becomes more pronounced and narrower in space, the turbidity in the regions on either side of the ring location decreases, which indicates a depletion in colloidal material in the neighboring zones. Eventually, a sharp band of visible precipitate appears, which is clearly separated from the preceding ring. We conclude that the ring formation is a postnucleation phenomenon in that structure arises from a spatially continuous region of colloid a long time after nucleation has occurred, and propose that it is associated with the autocatalytic growth of colloidal particles. The location of rings is not determined by the spatial pattern of nucleation and colloid deposition as predicted by the Ostwald–Wagner–Prager theory. Our conclusions are supported by experiments on the influence of gravity on the ring locations, which provide evidence for the existence of colloidal particles of several hundred angstroms in size for a substantial fraction of the time required for the formation of a visible structure.

Light scattering and absorption as methods of studying cell population parameters

Abstract: When a collimated beam of light encounters a system of biological cells or structures, part of the light may be absorbed, part is scattered, and the rest is transmitted. Transmitted and scattered light are measured to obtain information about the cells. Optical methods are among the most powerful tools for remotely and unobtrusively obtaining information about a sample suspension. Absorp­ tion measurements routinely provide information about compounds within the cells. The experimental data is interpreted in terms of empiri­ cal spectra of solutions of the compounds involved. Scattered light is a source of information about the morphological properties of cells and large subcellular structures: size, shape, state of aggregation, etc. EffeCts of scattering have similarly been interpreted on the basis of empirical evidence. This review treats scattering and absorption by populations of cells and large subcellular structures (particles) in dilute suspension. These particles are generally larger than the wavelength of the light; they are in the Lorenz-Mie light-scattering domain. We omit small particle (molecu­ lar) scattering, quasi-elastic scattering (which reveals particle size, etc, from diffusion theory), single particle scattering techniques, and effects that involve the measurement of linear or circular polarization. We consider only certain fundamental problems in scattering by populations that have received too little attention.

Light scattering in graphite intercalation compounds

Abstract: Light scattering in graphite intercalation compounds gives key insights into the physics of these layered structures. In this chapter a review is presented of experimental Raman scattering studies and their interpretation based on models of the lattice dynamics of pristine and intercalated graphite. The periodic layer structure of intercalation compounds makes it possible to model the dynamical matrix by a Brillouin zone folding of the pristine graphite matrix. The stage dependence of the Raman-active modes is reported which correlates with a stage dependent strain. Resonant enhancement of the scattering cross-section permits observation of modes related to the intercalate layer. Explicit results are obtained for the internal modes of Br2 molecules in the graphite-Br2 system. Stage I alkali metal compounds show a lineshape of the Breit-Wigner-Fano form which implies a coupling between a sharp vibrational mode and a Ramanactive continuum. Second-order Raman scattering results for intercalated graphite are reported. A brief summary is also given on Raman scattering studies of intercalated graphite fibers, adsorbed molecules on graphite surfaces and ion-implanted graphite.

Correlations for dilute hard core suspensions

Abstract: The generalized Smoluchowski equation is solved exactly for two particles interacting via a hard core potential in one, two, and three dimensions without the hydrodynamic interaction. From this solution coherent and incoherent intermediate scattering functions, memory functions, and transport coefficients are calculated. While many results relating to mutual diffusion are known, new results relating to self‐diffusion are presented. These are compared with other exact and approximate results. The ’’hydrodynamic regime’’ for dynamic light scattering is discussed.

Effects of polydispersity, branching and chain stiffness on quasielastic light scattering

Abstract: Aspects of polarized coherent quasi-elastic scattering by dilute macromolecular solutions are discussed. Effects of polydispersity, branching and chain stiffness are considered, particularly in respect to the observable first cumulant of the dynamic structure factor and its dependence on the scattering angle. A combination of integrated and time-resolved scattering data yields the maximum information.

Light scattering of bovine serum albumin solutions: Extension of the hard particle model to allow for electrostatic repulsion

Abstract: The light scattering of bovine serum albumin (BSA) has been measured at protein concentration up to 90 g/L and at pH values between 4.4 and 7.6. The dependence of scattering on both protein concentration and pH may be quantitatively accounted for by a simple extension of the hard-sphere model for protein solutions [Ross, P. D. & Minton, A. P. (1977) J. Mol. Biol.112, 437–452] allowing for electrostatic repulsions between molecules. According to the extended model, the radius of the effective hard spherical particle representing BSA varies with the net electrical charge of the BSA molecule in a manner which may be calculated from electrostatic theory.

Light-scattering study of DNA condensation: Competition between collapse and aggregation

Abstract: Light-scattering studies were done to investigate the DNA collapse transition, a large and discontinuous reduction in the radius of gyration. Of particular concern was differentiating the compaction of a single DNA molecule from aggregation. Solutions of RK2 plasmid DNA (Mr = 37 × 106) or bacteriophage T7 DNA (Mr = 25 × 106) were titrated with the condensing reagents spermidine in aqueous solvent or magnesium ion in ethanol–water solvent. The transition was followed by the change in scattering at a single angle or by the change in the angular dependence of scattering. At concentrations below 1 μg/mL, only aggregation could be detected by observation at a single angle; therefore, to study the collapse transition, it was necessary to measure the angular dependence of scattering. The intensities measured between the angles 30° and 60° were fit to known scattering functions. At low concentrations of the condensing reagent, the data were consistent with the scattering function of a random coil. On the other hand, during the transition at higher reagent concentrations, the curve that fit the data required two components—the scattering function for a random coil with a large radius of gyration, plus that for a sphere with a radius about one-fifth of that of the coil. The fractional concentration of the sphere increased with increasing condensing-reagent concentration. This two-component behavior is in apparent contrast to the situation with a more flexible polymer such as polystyrene, in accord with theoretical predictions. At still higher reagent concentrations, aggregation was apparent. Condensation to a collapsed state was reversible without hysteresis, while dissolution of the aggregated state nearly always occurred with hysteresis. Qualitative agreement between the observed DNA collapse transition and the theoretical phase diagram presented in the preceding paper was found, although the light-scattering results did not show quantitative agreement with the simple theoretical model.

Light emitting optical fiber assemblies and method for forming the same

Abstract: The light emitting optical fiber assemblies include light emitting panels that employ a nonwoven geometric grid of light emitting optical fibers which can be arranged to permit air to pass through the panel or to define apertures providing access through the panel. Also, such nonwoven fiber grids can be arranged to permit the panels to be cut or sectioned without losing all light emitting capability. Panels are provided which include the encapsulation of light emitting fibers in a light transmitting laminate, and the laminate is provided with light scattering formations which permit light to be emitted from the encapsulating layer. The panels and other light emitting units are provided with light or electromagnetic radiation from lightpipe harness assemblies which are designed to supply light to a plurality of use devices.