Showing papers on "Light scattering published in 1988"
Book•
03 May 1988
TL;DR: In this article, surface plasmons on smooth surfaces were used for light scattering at rough surfaces without an ATR device, and surface plasmon on gratings for enhanced roughness.
Abstract: Surface plasmons on smooth surfaces.- Surface plasmons on surfaces of small roughness.- Surfaces of enhanced roughness.- Light scattering at rough surfaces without an ATR device.- Surface plasmons on gratings.- Conclusions.
4,890 citations
TL;DR: An advanced, thoroughly documented, and quite general purpose discrete ordinate algorithm for time-independent transfer calculations in vertically inhomogeneous, nonisothermal, plane-parallel media for Atmospheric applications ranging from the UV to the radar region of the electromagnetic spectrum is summarized.
Abstract: The transfer of monochromatic radiation in a scattering, absorbing, and emitting plane-parallel medium with a specified bidirectional reflectivity at the lower boundary is considered. The equations and boundary conditions are summarized. The numerical implementation of the theory is discussed with attention given to the reliable and efficient computation of eigenvalues and eigenvectors. Ways of avoiding fatal overflows and ill-conditioning in the matrix inversion needed to determine the integration constants are also presented.
3,257 citations
TL;DR: It is shown how various well-known asymptotic power laws in S(q) are obtained from the above theory, and the theory is compared with experimental results on x-ray scattering from a polished Pyrex glass surface.
Abstract: The scattering of x rays and neutrons from rough surfaces is calculated. It is split into specular reflection and diffuse scattering terms. These are calculated in the first Born approximation, and explicit expressions are given for surfaces whose roughness can be described as self-affine over finite length scales. Expressions are also given for scattering from liquid surfaces, where it is shown that ``specular'' reflections only exist by virtue of a finite length cutoff to the mean-square height fluctuations. Expressions are also given for the scattering from randomly oriented surfaces, as studied in a typical small-angle scattering experiment. It is shown how various well-known asymptotic power laws in S(q) are obtained from the above theory. The distorted-wave Born approximation is next used to treat the case where the scattering is large (e.g., near the critical angle for total external reflection), and its limits of validity are discussed. Finally, the theory is compared with experimental results on x-ray scattering from a polished Pyrex glass surface.
2,031 citations
TL;DR: The discrete dipole approximation (DDA) was extended to incorporate the effects of radiative reaction and to allow for possible anisotropy of the dielectric tensor of the material as mentioned in this paper.
Abstract: The discrete dipole approximation (DDA), a flexible method for computing scattering of radiation by particles of arbitrary shape, is extended to incorporate the effects of radiative reaction and to allow for possible anisotropy of the dielectric tensor of the material. Formulas are given for the evaluation of extinction, absorption, scattering, and polarization cross sections. A simple numerical algorithm based on the method of conjugate gradients is found to provide an efficient and robust method for obtaining accurate solutions to the scattering problem. The method works well for absorptive, as well as dielectric, grain materials. Two validity criteria for the DDA are presented. The DDA is then used to compute extinction cross sections for spherical graphite grains and to calculate extinction cross sections for nonspherical graphite grains with three different geometries. It is concluded that the interstellar 2175 A extinction feature could be produced by small graphite grains which should have aspect ratios not far from unity. 35 references.
1,457 citations
TL;DR: A phenomenological model, which exploits the diffusive nature of the transport of light, is shown to be in excellent agreement with experimental data for several different scattering geometries, and the dependence on geometry provides an important experimental control over the time scale probed.
Abstract: We obtain useful information from the intensity autocorrelations of light scattered from systems which exhibit strong multiple scattering. A phenomenological model, which exploits the diffusive nature of the transport of light, is shown to be in excellent agreement with experimental data for several different scattering geometries. The dependence on geometry provides an important experimental control over the time scale probed. We call this technique diffusing wave spectroscopy, and illustrate its utility by studying diffusion in a strongly interacting colloidal glass.
977 citations
TL;DR: In this article, the authors present a theoretical description of the scattering of a Gaussian beam by a spherical, homogeneous, and isotropic particle, based on the Bromwich method and closely following Kerker's formulation for plane-wave scattering.
Abstract: We present a theoretical description of the scattering of a Gaussian beam by a spherical, homogeneous, and isotropic particle. This theory handles particles with arbitrary size and nature having any location relative to the Gaussian beam. The formulation is based on the Bromwich method and closely follows Kerker’s formulation for plane-wave scattering. It provides expressions for the scattered intensities, the phase angle, the cross sections, and the radiation pressure.
583 citations
TL;DR: This dissertation aims to provide a history of web exceptionalism from 1989 to 2002, a period chosen in order to explore its roots as well as specific cases up to and including the year in which descriptions of “Web 2.0” began to circulate.
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283 citations
TL;DR: In this paper, the first observation of Bragg scattering of sodium atoms from a standing light wave was reported and quantitatively predicted the amplitude of various Bragg orders as a function of the light's detuning and power, and the interaction time.
Abstract: We report the first observation of Bragg scattering of sodium atoms from a standing light wave. We also present a theory which quantitatively predicts the amplitude of the various Bragg orders as a function of the light's detuning and power, and the interaction time. The analog of the Pendello$uml---sung effect, previously observed in Bragg scattering of neutrons from crystals, is predicted and qualitatively observed for first-order Bragg scattering of atoms from a standing light wave.
279 citations
TL;DR: The scattering matrix, differential cross section, and total cross section for supramicrometer-size nematic droplets in a polymeric matrix are derived in the anomalous-diffraction approach and indicate strong dependence of the diffraction patterns on wavelength and droplet structure.
Abstract: The scattering matrix, differential cross section, and total cross section for supramicrometer-size nematic droplets in a polymeric matrix are derived in the anomalous-diffraction approach. Scattering patterns are calculated in detail for three different nematic-director configurations: one characteristic of a droplet in a strong external field, the other characteristic of a droplet outside the field in the case of normal surface anchoring, and the third characteristic of an isotropic droplet with a surface-induced nematic layer. The results, which are presented graphically, indicate strong dependence of the diffraction patterns on wavelength and droplet structure. The possibilities of determining droplet size and nematic-director structure from experimental light scattering data are discussed. Special attention is paid to the possibility of the detection of the surface-induced nematic ordering.
195 citations
TL;DR: In this article, a detailed experimental study of coherent backscattering of light from aqueous suspensions of polystyrene microspheres is presented, focusing on the effects of particle size, of absorption due to added dye and of light polarization on the shape and height of the backscatter cone.
Abstract: A detailed experimental study of coherent backscattering of light from aqueous suspensions of polystyrene microspheres is presented. Emphasis is on the effects of particle size, of absorption due to added dye and of light polarization on the shape and height of the backscattering cone. For parallel polarization of incident and scattered beams, the scalar diffusion theory, parametrized by the transport mean free path l*, agrees well with our data up to surprizingly large scattering angles (ql * ~ 1) and quantitatively accounts for the rounding of the cones due to absorption. No deviations from the usual Gaussian statistics of scattered fields is observed up to λ/l* ∼ 0.1.
195 citations
TL;DR: The dynamics of the sol-gel transition is probed by use of quasielastic light scattering, and a type of critical dynamics is observed that is associated with a divergent friction, rather than a singularity in a thermodynamic quantity.
Abstract: The dynamics of the sol-gel transition is probed by use of quasielastic light scattering. A type of critical dynamics is observed that is associated with a divergent friction, rather than a singularity in a thermodynamic quantity. Several novel effects are reported, including power-law time decay of the intensity autocorrelation function, critical slowing down of the average relaxation time, and observation of a fractal time set in the scattered field.
TL;DR: Values of sigma(s) obtained by measuring the collimated transmittance of dilute RBC suspensions illuminated with a He-Ne laser agreed with those predicted by Mie theory and were consistently greater than those obtained experimentally by making angular scattering measurements in a goniometer.
Abstract: Two important optical properties of red blood cells (RBCs), their microscopic scattering cross sections sigma(s), and the mean cosine of their scattering angles micro, contribute to the optical behavior of whole blood. Therefore, the ability of Mie theory to predict values of sigma(s) and was tested by experiment. In addition, the effect of red blood cell size on sigma(s) and micro was investigated in two ways: (1) by studying erythrocytes from the dog, goat, and human, three species known to have different RBC sizes and (2) by allowing the RBCs from each species to shrink or swell osmotically. Values of sigma(s) obtained by measuring the collimated transmittance of dilute RBC suspensions illuminated with a He-Ne laser agreed with those predicted by Mie theory. Moreover, measured as values were directly proportional to RBC volume. By contrast, values of from Mie theory were consistently greater than those obtained experimentally by making angular scattering measurements in a goniometer. Thus Mie theory appears to yield adequate values for the RBC's microscopic scattering cross section, but by treating the RBC as a sphere with an equal volume, Mie theory fails to take the RBC's anisotropy into account and thus yields spuriously high values for micro.
TL;DR: It is found that the approximations of Bruggeman and Maxwell Garnett, the generalization of dynamic effective medium approximation derived by Chylek and Srivastava, and the experimental waveguide method of determination of the effective refractive index lead to an acceptable agreement between calculated and measured values.
Abstract: We have measured the differential scattering cross sections (phase functions I22) and the normalized extinction and scattering cross sections (efficiences) of composite spherical particles. The size parameter x = 2πr/λ was around 2π. Composite spheres consisted of nonabsorbing matrix containing a small amount (1.6 and 2.7% by volume) of highly absorbing inclusions. Such composite particles may represent a realistic model of fog or cloud droplets containing small amounts of carbon or a composite atmospheric aerosol particle. We have compared measured data with those calculated using seven different effective medium approximations. We have found that the approximations of Bruggeman and Maxwell Garnett, the generalization of dynamic effective medium approximation derived by Chylek and Srivastava, and the experimental waveguide method of determination of the effective refractive index lead to an acceptable agreement between calculated and measured values. The reduced χ2 values for these approximations ranged between 0.6 and 2.0. The remaining three approximations (volume averages of refractive indices or dielectric constants and the Maxwell Garnett relation with matrix and inclusion materials interchanged) lead to reduced χ2 values between 4.0 and 12.0 demonstrating a large disagreement between calculated and measured scattering characteristics.
TL;DR: In this article, the effect of time-dependent fluctuations of a medium on the spectral intensity and intensity fluctuations of light scattered from the medium is discussed, and it is shown that the relaxation time depends on the number of scattering events, i.e., on the lengths of the multiple scattering paths, and the scattered intensity thus exhibits a broad range of relaxation times.
Abstract: The effect of time-dependent fluctuations of a medium on the spectral intensity and intensity fluctuations of light scattered from the medium is discussed. In the case that the light is multiply scattered from the medium, it is possible in the diffusion approximation to relate the spectral intensity in the scattered wave to the angular-average structure factor of the medium. The relaxation time depends on the number of scattering events, i.e., on the lengths of the multiple-scattering paths, and the scattered intensity thus exhibits a broad range of relaxation times. The spectral intensity in coherent backscattering is also discussed.
TL;DR: In this paper, the distribution of intensity scattered by a plane mirror placed in the Fresnel region behind a smoothly varying deep random phase screen is calculated for arbitrary angles of incidence of the illuminating beam.
Abstract: The distribution of intensity scattered by a plane mirror placed in the Fresnel region behind a smoothly varying deep random phase screen is calculated for arbitrary angles of incidence of the illuminating beam. It is found that enhancement occurs in the backward direction because of the coherent addition of doubly scattered waves, as in particle-scattering systems, and also as a result of statistical geometrical-optics effects. These effects are largest when reflection takes place near the focusing plane of the phase screen and lead to an enhancement factor proportional to the logarithm of the phase variance introduced by the screen. The coherence and higher-order statistical properties of the scattered wave are briefly examined.
01 Mar 1988
TL;DR: In this paper, the authors studied flame-generated (fumed) silica particles in situ by static and dynamic light scattering and ex situ by transmission electron microscopy, and found that the growth and aggregation of the particles were followed as a function of height in the flame.
Abstract: We studied flame-generated (fumed) silica particles in situ by static and dynamic light scattering and ex situ by transmission electron microscopy. The growth and aggregation of the particles was followed as a function of height in the flame. The scattered intensity appeared to be consistent with a fractal aggregate structure having a fractal dimension of D = 1.49 (smaller than previously reported ex situ measurements of fumed silica) although the data are too limited to determine D with certainty. From the dynamic light scattering results, corrected for polydispersity, the growth trend appeared to deviate from free-molecular behavior for long residence times. From the electron microscopy, we noted a surprising tendency for the silica monomers to shrink with residence time.
TL;DR: In this article, the frequency, width, and intensity of the 1320 cm−1 peak near and above the Neel temperature (960 K) of α-Fe2O3 was investigated.
TL;DR: This new method provides what is to the authors' knowledge the first complete physical description of the classical processes involved in cooperative EM scattering by an aggregate of spheres.
Abstract: An outline is provided of the derivation of an order-of-scattering technique that we apply here for the first reported time to the study of light scattering by two or more interacting spheres. This new method provides what is to our knowledge the first complete physical description of the classical processes involved in cooperative EM scattering by an aggregate of spheres. In addition, the algorithms that it employs are often more efficient than those used in an already established method. Comparisons between selected calculations and experimental results are made for linear chains of three and five spheres, and effects of particle orientation are investigated theoretically.
TL;DR: In this paper, a light scattering study is presented on static and dynamic interactions between monodisperse, charged silica spheres suspended in an optically matching, salt free mixture of ethanol and toluene up to volume fractions of 10%.
Abstract: A light scattering study is presented on static and dynamic interactions between monodisperse, charged silica spheres suspended in an optically matching, salt free mixture of ethanol and toluene up to volume fractions of 10%. The static structure factor S(K), well described by calculations in the RMSA approximation, is combined with the wave vector (K) dependent (short‐time) diffusion coefficient De(K) to give the function H(K) which represents the hydrodynamic interactions. From H(K), obtained for the first time for charged particles, we conclude that the long‐range electrostatic repulsion between the spheres has a pronounced influence on the hydrodynamics of large‐scale, collective particle motions, whereas small‐scale single‐particle diffusion is relatively unaffected.
TL;DR: In the last fifteen years, a variety of laser-based, light-scattering techniques have been developed for the measurement of local temperature in gaseous flows, including spontaneous vibrational and rotational Raman scattering, Rayleigh scattering, and laser-induced fluorescence as mentioned in this paper.
TL;DR: Erythro-aggregometer is a Couette viscometer which was developed to measure aggregation parameters of red blood cells based on the analysis of the light intensity backscattered by a blood suspension.
Patent•
28 Sep 1988
TL;DR: In this article, a gas sample is placed in a cell and a laser beam is passed through the cell, which is detected by collection channels (60). Light scattered by the gas sample contains inelastic Raman and elastic scattered light.
Abstract: The concentration of multiple polyatomic gases are determined by Raman light scattering. A gas sample is placed in a cell (26, 50) and a laser beam (18) passed through the cell (26, 50). A portion of the light scattered by the gas sample is detected by collection channels (60). Light scattered by the gas sample contains inelastic Raman and elastic scattered light. Each channel (60) contains a laser line rejection filter (216) which attenuates the elastic scattered laser signals and an interference filter (217) which is specific to the transmission of one or more specific Raman lines. Each interference filter (217) is selected to a specific wavelength which is characteristic of Raman scattering from a particular polyatomic gas. Optical signals representative of these specific Raman lines are sensed by optical detectors (219) and processed into simultaneous visual readouts indicative of the intensity and concentration of each of the polyatomic gas molecules present in the gas sample.
TL;DR: The results demonstrate that reliable white blood cell differentiation of the four most clinically relevant leukocyte can be obtained by measurement of light scattering properties of unstained leukocytes.
Abstract: Measurement of the depolarized orthogonal light scattering in flow cytometry enables one to discriminate human eosinephilic granulocytes from neutrophilic granulocytes. We use this method to perform a four-parameter differential white blood cell analysis.
A simple flow cytometer was built equipped with a 5-mW helium neon laser that measures simultaneously four light scattering parameters. Lymphocytes, monocytes, and granulocytes were identified by simultaneously measuring the light scattering intensity at angles between 1.0° and 2.6° and angles between 3.0° and 11.0°. Eosinophilic granulocytes were distinguished from neutrophilic granulocytes by simultaneous measurement of the orthogonal and depolarized orthogonal light scattering.
Comparison of a white blood cell differentiation of 45 donors obtained by the Technicon H-6000 and our instrument revealed good correlations. The correlation coefficients (r2) found were: 0.99 for lymphocytes, 0.76 for monocytes, 0.99 for neutrophilic granulocytes, and 0.98 for eosinophilic granulocytes. The results demonstrate that reliable white blood cell differentiation of the four most clinically relevant leukocytes can be obtained by measurement of light scattering properties of unstained leukocytes.
TL;DR: A Monte Carlo simulation and the Three-Parameter Model of the submarine light field are used to analyze the effect of water Raman emission at 520 nm in clear ocean waters and a new optical parametrization for clear ocean water is proposed.
Abstract: A Monte Carlo simulation (the NORDA optical model) and the Three-Parameter Model of the submarine light field are used to analyze the effect of water Raman emission at 520 nm in clear ocean waters. Reported optical anomalies for clear ocean waters at longer wavelengths (520 nm +) are explained by the effects of water Raman emission, and the simulation results are confirmed by Biowatt-NORDA observations made in the Sargasso Sea. A new optical parametrization for clear ocean water is proposed.
TL;DR: In this paper, the authors studied the dynamics of concentration fluctuation in a deuterated polystyrene/poly(vinylmethylether) blend system by the reverse quench light scattering techniques.
Abstract: The dynamics of concentration fluctuation in a deuterated polystyrene/poly(vinylmethylether) blend system has been studied by the temperature jump and also by the reverse quench light scattering techniques. The growth or decay rate R(q) in Cahn–Hilliard–Cook’s equation is almost proportional to the square of scattering wave vector. This indicates that the interfacial free energy contribution to the concentration fluctuation dynamics in the wavelength range examined is very small. The interdiffusion coefficient D which has been obtained as a function of temperature, is continuous at the phase separation boundary. The mobility M, which can be extracted from D by combining the results of both statics and kinetics has an Arrhenius type of temperature dependence on both sides of the phase boundary.
TL;DR: In this paper, a time-domain light scattering study of acoustic and mountain modes in glycerol is reported by using light-scattering angles between 089° and 889°, a wide range of acoustic frequencies is sampled.
Abstract: A time‐domain light scattering study of acoustic and Mountain modes in glycerol is reported By using light‐scattering angles between 089° and 889°, a wide range of acoustic frequencies is sampled The data also yield information about time‐dependent density responses to stress and to heat (the latter is the time‐dependent thermal expansion) These responses are associated with the Mountain mode and provide additional information about structural relaxation dynamics A theoretical framework is presented which can treat these experiments as well as ultrasonics and specific heat spectroscopy The time or frequency dependences of the elastic modulus, heat capacity, and pressure response to temperature change are all accounted for and appear to be significant The experimental results are fit best with a distribution of relaxation times which is somewhat less asymmetric than a Cole–Davidson distribution The width of the distribution (on a logarithmic frequency scale) does not change significantly in the 20
TL;DR: The inclusion of scattering anisotropy in the theoretical model represents an improvement over the usual diffusion description and predictions of space irradiance utilizing the transport approximation show good general agreement with experimental space irradiances results.
Abstract: Understanding the distribution of light in tissue is necessary for dosimetry in photodynamic therapy of malignant tumors. Attenuation measurements from implanted fiber optic sources in R3327-AT (rat prostate) tumors show that light penetration is greatest in the direction of the beam itself and least in the backward direction. This anisotropy of the overall optical distribution persists to distances of at least 2 cm from the source and is a result of strong anisotropy in the scattering phase function. The inclusion of scattering anisotropy in the theoretical model represents an improvement over the usual diffusion description. Predictions of space irradiance utilizing the transport approximation show good general agreement with experimental space irradiance results. The specific optical constants used in the model are consistent with actual measured values of scattering, absorption, and attenuation coefficients. The theory can be applied to other optical sources. >
TL;DR: In this article, the optical properties of soot particles are inferred in the visible and infrared part of the spectrum, and the effects of agglomeration and temperature in the determination of optical properties are assessed.
Abstract: Measurements of dynamic light scattering along with classical scattering/extinction as a function of the wavelength for a rich propane/oxygen flame are presented. Spectral optical properties of soot particles are inferred in the visible and infrared part of the spectrum. Particle size distribution. number densities and volume fractions of soot are determined and comparisons are made with predictions of existing models for the soot optical constants. The effects of agglomeration and temperature in the determination of the optical properties are assessed and a new set of dispersion constants for the optical properties of flame soot is presented.
TL;DR: Comparisons with a comparably extensive experimental study published by Zerull in 1976 reveal remarkable qualitative similarities, even though Zerull used greatly different shapes from the authors', augurs well for the eventual development of a general theory of nonspherical scattering.
Abstract: The calculated angular scattering properties of over 250 randomly oriented nonspherical Chebyshev particles are examined for the effect of three factors: size; concavity vs convexity; and amount of deformation from a sphere. Both shape and size averaging are performed to reveal general features of the angular scattering not discernible for particular shapes and sizes. Comparisons with a comparably extensive experimental study published by Zerull in 1976 reveal remarkable qualitative similarities, even though Zerull used greatly different shapes from ours. This augurs well for the eventual development of a general theory of nonspherical scattering, although such a theory must account for concavity in addition to the amount of deviation from a sphere; and it cannot be entirely deterministic, as the third paper in this series will argue.