Showing papers on "Light scattering published in 1995"

Liquid crystal dispersions

Abstract: Methods for Film Formation: Emulsification Methods Phase-Separation Methods. Droplet Configurations: Methods for Probing Droplet Structure Catalogue of Droplet Structures Transformations between Droplet Structures Gels and Porous Glasses. Electro-Optical Effects: Light Scattering Dichroic Effects Droplet Reorientation Fields Response Times Hysteresis and Persistence Effects Film Dielectric Properties Nonlinear Optical Effects. Applications: Projection Displays Direct-View Displays Light-Valve Applications.

Optical models for direct volume rendering

Abstract: This tutorial survey paper reviews several different models for light interaction with volume densities of absorbing, glowing, reflecting, and/or scattering material. They are, in order of increasing realism, absorption only, emission only, emission and absorption combined, single scattering of external illumination without shadows, single scattering with shadows, and multiple scattering. For each model the paper provides the physical assumptions, describes the applications for which it is appropriate, derives the differential or integral equations for light transport, presents calculation methods for solving them, and shows output images for a data set representing a cloud. Special attention is given to calculation methods for the multiple scattering model. >

Resonance light scattering : a new technique for studying chromophore aggregation

Abstract: Light scattering experiments are usually performed at wavelengths away from absorption bands, but for species that aggregate, enhancements in light scattering of several orders of magnitude can be observed at wavelengths characteristic of these species. Resonance light scattering is shown to be a sensitive and selective method for studying electronically coupled chromophore arrays. The approach is illustrated with several examples drawn from porphyrin and chlorin chemistry. The physical principles underlying resonance light scattering are discussed, and the advantages and limitations of the technique are reviewed.

Development of a distributed sensing technique using Brillouin scattering

Abstract: This paper reviews the developments of a distributed strain and temperature sensing technique that uses Brillouin scattering in single-mode optical fibers. This technique is based on strain- and temperature-induced changes in the Brillouin frequency shift. Several approaches for measuring the weak Brillouin line are compared. >

Photoacoustic ultrasound (PAUS)--reconstruction tomography.

Abstract: The theoretical underpinnings of photoacoustic ultrasound (PAUS) reconstruction tomography are presented. A formal relationship between PAUS signals and the heterogeneous distribution of optical absorption within the object being investigated is developed. Based on this theory, a reconstruction approach, analogous to that used in x‐ray computed tomography, is suggested. Initial experimental results suggest that this approach produces ‘‘reasonable’’ reconstructions for absorbers distributed within a narrow plane embedded within a highly scattering medium.

Nature of light scattering in dental enamel and dentin at visible and near-infrared wavelengths

Abstract: The light-scattering properties of dental enamel and dentin were measured at 543, 632, and 1053 nm. Angularly resolved scattering distributions for these materials were measured from 0° to 180° using a rotating goniometer. Surface scattering was minimized by immersing the samples in an index-matching bath. The scattering and absorption coefficients and the scattering phase function were deduced by comparing the measured scattering data with angularly resolved Monte Carlo light-scattering simulations. Enamel and dentin were best represented by a linear combination of a highly forward-peaked Henyey–Greenstein (HG) phase function and an isotropic phase function. Enamel weakly scatters light between 543 nm and 1.06 μm, with the scattering coefficient (μs) ranging from μs = 15 to 105 cm−1. The phase function is a combination of a HG function with g = 0.96 and a 30–60% isotropic phase function. For enamel, absorption is negligible. Dentin scatters strongly in the visible and near IR (μs ≅ 260 cm−1) and absorbs weakly (μa ≅ 4 cm−1). The scattering phase function for dentin is described by a HG function with g = 0.93 and a very weak isotropic scattering component (~2%).

Modern aspects of small-angle scattering

Abstract: Preface. 1. Some Fundamental Concepts and Techniques Useful in Small-Angle Scattering Studies of Disordered Solids P.W. Schmidt. 2. Instrumentation for Small-Angle Scattering J.S. Pedersen. 3. Reduction of Data from SANS Instruments A.R. Rennie. 4. Modern Methods of Data Analysis in Small-Angle Scattering and Light Scattering O. Glatter. 5. Grazing Incidence Small-Angle X-Ray Scattering: Application to Layers and Surface Layers A. Naudon. 6. Anomalous Small-Angle X-Ray Scattering (ASAXS) A. Naudon. 7. Contrast Variation H.B. Stuhrmann. 8. Metals and Alloys: Phase Separation and Defect Agglomeration G. Kostorz. 9. The Anisotropy of Metallic Systems -- Analysis of Small-Angle Scattering Data A.D. Sequeira, G. Kostorz. 10. Characterization of Porosity in Ceramic Materials by Small-Angle Scattering: VYCOR(R) Glass and Silica Aerogel D.W. Schaefer, R.K. Brow, B.J. Olivier, T. Rieker, G. Beaucage, L. Hrubesh, J.S. Lin. 11. Small-Angle Scattering of Catalysts H. Brumberger. 12. Thermodynamic and Scattering Properties of Dense Fluids of Monodisperse Isotropic Particles: an Information Theory Approach V. Luzzati. 13. Small-Angle Scattering from Complex Fluids E.W. Kaler. 14. Small-Angle Neutron Scattering of Biological Macromolecular Complexes Consisting of Proteins and Nucleic Acids R.P. May. 15. X-Ray and Neutron Small-Angle Scattering on Plasma Lipoproteins P. Laggner. 16. Time-Resolved X-Ray Small-Angle Diffraction with Synchrotron Radiation on Phospholipid Phase Transitions. Pathways,Intermediates and Kinetics P. Laggner, M. Kriechbaum. 17. Polymers in Solution-Flow Techniques P. Lindner. 18. Bulk Polymers A.R. Rennie. Index.

Tooth Color and Reflectance as Related to Light Scattering and Enamel Hardness

Abstract: Tooth color is determined by the paths of light inside the tooth and absorption along these paths. This paper tests the hypothesis that, since the paths are determined by scattering, a relation between color and scattering coefficients exists. One hundred and two extracted incisors were fixed in formalin, mounted in a standardized position in brass holders, and pumiced. A facet was prepared near the incisal edge on the labial plane to allow for Knoop hardness measurements with a 500-gram load. Light scattering by the enamel was measured in a 45°/0° geometry; light scattering by both enamel and dentin was measured in a 0°/0° geometry. The reflection spectrum of the tooth was measured from the labial plane with a spectroradiometer in a 45°/0° geometry, with standard illuminant A and standard illuminant D65. To include all volume-reflected light, we used entire-tooth illumination and small-area measurement. CIELAB color coordinates were calculated from the spectra. Neither spectra nor coordinates showed evid...

Mie and Rayleigh modeling of visible-light scattering in neonatal skin

Abstract: Reduced-scattering coefficients of neonatal skin were deduced in the 450-750-nm range from integrating-sphere measurements of the total reflection and total transmission of 22 skin samples. The reduced-scattering coefficients increased linearly at each wavelength with gestational maturity. The distribution of diameters d and concentration ρ(A) of the skin-sample collagen fibers were measured in histological sections of nine neonatal skin samples of varying gestational ages. An algorithm that calculates Mie scattering by cylinders was used to model the scattering by the collagen fibers in the skin. The fraction of the reduced-scattering coefficient µ(s)' that was attributable to Mie scattering by collagen fibers, as deduced from wavelength-dependent analysis, increased with gestational age and approached that found for adult skin. An assignment of 1.017 for n(rel), the refractive index of the collagen fibers relative to that of the surrounding medium, allowed the values for Mie scattering by collagen fibers, as predicted by the model for each of the nine neonatal skin samples to match the values for Mie scattering by collagen fibers as expected from the measurements of µ(s)'. The Mie-scattering model predicted an increase in scattering with gestational age on the basis of changes in the collagen-fiber diameters, and this increase was proportional to that measured with the integrating-sphere method.

Optical Rheometry of Complex Fluids

Abstract: 1. Propogation of Electromagnetic Waves 2. Transmission by Anisotropic Media: The Jones and Mueller Calculus 3. Reflection and Refraction of Light 4. Total Intensity Light Scattering 5. Chapter 5. Spectroscopic Methods 6. Laser Doppler Velocimetry and Dynamic Light Scattering 7. Microstructural Theories of Optical Properties 1. Design of Optical Instruments 2. Selection and Alignment of Optical Components 3. Applications and Case Studies

Continuous-wave ultrasonic modulation of scattered laser light to image objects in turbid media.

Abstract: Continuous-wave ultrasonic modulation of scattered laser light has been used to image objects in tissue-simulating turbid media for what is to our knowledge the first time. The ultrasound wave focused into the turbid media modulates the laser light passing through the ultrasonic focal zone. The modulated laser light collected by a photomultiplier tube reflects the local mechanical and optical properties in the focal zone. Buried objects are located with millimeter resolution by scanning and detecting alterations of the modulated optical signal. This technique has the potential to provide a noninvasive, nonionizing, inexpensive diagnostic tool for diseases such as breast cancer.

Ultrasonic modulation of multiply scattered light

Abstract: We report the first observation of ultrasonic modulation of multiple light scattering speckles. The modulation at ƒ a = 2 MHz of the temporal field autocorrelation function 〈E(0)E ∗ (t)〉 of the light scattered from concentrated aqueous suspensions of polystytrene beads was measured. In addition, when using ƒ a = 27 MHz , the light intensity spectra measured with a Fabry-Perot interferometer show four inelastic peaks at ƒa and 2ƒa from the principal Rayleigh peak. The modulation amplitudes obtained from both techniques were found to increase with the ultrasonic amplitude and to vary with the mean free path of light in agreement with our simple model.

Optical properties of ocular fundus tissues--an in vitro study using the double-integrating-sphere technique and inverse Monte Carlo simulation.

Abstract: Various models have been published calculating the light transport at the ocular fundus either for interpretation of in vivo reflectance measurements or for the prediction of photocoagulation effects. All these models took the absorption spectra of the pigments located at the ocular fundus, melanin, haemoglobin, xanthophyll, and the photoreceptor pigments, into account. However, light scattering inside the single fundus layers has not been investigated in detail and was, therefore, neglected in the calculations or only considered by very rough approximations. This paper presents measurements on specimens of retina, retinal pigment epithelium, choroid, and sclera using the double-integrating-sphere technique. Absorption coefficients, scattering coefficients, and anisotropy of scattering were calculated by an inverse Monte Carlo simulation from the measured collimated and diffuse transmittance and diffuse reflectance. Conclusions are drawn for the interpretation of fundus reflectance measurements, which are a useful tool in diagnostics and photocoagulation dosimetry.

A hybrid geometric optical-radiative transfer approach for modeling albedo and directional reflectance of discontinuous canopies

Abstract: A new model for the bidirectional reflectance of a vegetation cover combines principles of geometric optics and radiative transfer. It relies on gap probabilities and path length distributions to model the penetration of irradiance from a parallel source and the single and multiple scattering of that irradiance in the direction of an observer. The model applies to vegetation covers of discrete plant crowns that are randomly centered both on the plane and within a layer of variable thickness above it. Crowns assume a spheroidal shape with arbitrary height to width ratio. Geometric optics easily models the irradiance that penetrates the vegetation cover directly, is scattered by the soil, and exits without further scattering by the vegetation. Within a plant crown, the probability of scattering is a negative exponential function of path length. Within-crown scattering provides the source for singly-scattered radiation, which exits with probabilities proportional to further path-length distributions in the direction of exitance (including the hotspot effect). Single scattering provides the source for double scattering, and then higher order pairs of scattering are solved successively by a convolution function. Early validations using data from a conifer stand near Howland, Maine, show reasonable agreement between modeled and observed reflectance.

Light scattering optical waveguide method for detecting specific binding events

Abstract: A waveguide binding assay method involves detecting the scattering of light directed into the waveguide, the scattering being the result of scattering labels specifically bound to the waveguide within the penetration depth of an evanescent wave. The waveguide may be transparent plastic or glass and the binding is typically by oligonucleotide hybridization or immunological capture. Light scattering labels include colloidal metals or non-metals, including gold, selenium and latex. A light absorbing member consisting of dye or concentrated particles may also be employed to enhance signal. Real-time binding and dissociation can be monitored visually or by video imaging, such as with a CCD camera and frame grabber software. Hybridization mismatches of as few as one base can be distinguished by real-time melting curves.

Radiative Transfer in Cirrus Clouds. Part III: Light Scattering by Irregular Ice Crystals

Abstract: A new Monte Carlo/geometric ray-tracing method has been developed for the computation of the scattering, absorption, and polarization properties of ice crystals with various irregular structure, including hollow columns, bullet rosettes, dendrites, and capped columns. The shapes of these ice crystals are defined by appropriate geometric models and incident coordinate systems. The incident photons are traced with a hit-and-miss Monte Carlo method and followed by geometric reflection and refraction on the crystal boundary. Absorption has been accounted for by means of stochastic procedures. Computation of the phase matrix elements and normalization of the phase function have been carried out using the results derived from rays that undergo reflections and refractions and from Fraunhofer diffraction using projected cross section areas for irregular ice crystals. Numerical results are presented for visible and near-infrared wavelengths. It is shown that irregular ice crystals scatter more in forward ...

X-Ray photon correlation spectroscopy study of Brownian motion of gold colloids in glycerol.

Abstract: We report x-ray photon correlation spectroscopy studies of the static structure factor and dynamic correlation function of a gold colloid dispersed in the viscous liquid glycerol. We find a diffusion coefficient for Brownian motion of the gold colloid which agrees well with that extrapolated from measurements made with visible light, but which was determined on an optically opaque sample and in a wave-vector range inaccessible to visible light.

Temperature Dependence of Triton X-100 Micelle Size and Hydration

Abstract: Quasi-elastic light scattering spectroscopy was used to measure the mutual diffusion coefficient, D m , of Triton X-100 micelles in aqueous solution and the translational diffusion coefficient, D p , of mesoscopic probes in the same solutions. We apply conventional hydrodynamic treatments of diffusion under the assumption that Triton X-100 minimal micelles are adequately represented as hard spheres. D m and D p measured at a series of surfactant concentrations are used to infer the micelle radius, am, aggregation number, N, and degree of hydration, δ, for temperatures 10≤T≤50 o C. As T is increased toward the cloud point, am and N increase, the increase in N being especially dramatic above 40 o C. δ at first increases but then tends to saturate with increasing T

Experimental Evidence for Recurrent Multiple Scattering Events of Light in Disordered Media

Abstract: The interest in the field of multiple light scattering in disordered media has gone through an enormous revival after it was recognized that interference effects can be important, even after many scattering events. Several interference phenomena like weak localization [1] and short and long range spatial correlations in intensity fluctuations are the focus of today’s research [2]. The phenomenon of weak localization is sometimes seen as a precursor to strong or Anderson localization of light [3], which would be the light counterpart of Anderson localization of electrons. The approach to a strong localization transition in a medium with strong disorder manifests itself as a reduction of the diffusion coefficient, eventually to zero. Localization in three dimensions of microwaves has been reported [4]. It is still a challenge to find experimental evidence for strong localization of light. In all multiple scattering phenomena that have been observed so far, recurrent scattering of light waves can be disregarded. Recurrent events are events in which a wave is scattered more than once by the same scatterer. The neglect of recurrent scattering will be referred to as the self-avoiding multiple scattering (SAMS) approximation, and is valid in the weak scattering limit. However, for strong scattering recurrent events can become important. They could play a role in strong localization of light. In order to find evidence for the existence of recurrent scattering we studied coherent backscattering or weak localization of light. Coherent backscattering manifests itself in the form of an enhancement of the intensity in the back direction for the light scattered from a disordered sample. This enhancement originates from constructive interference between multiply scattered amplitudes and their time reversed counterparts. Moving away from the exact backscattering direction, phase differences develop that average out this interference effect. The result is a “cone” of enhanced backscattering on top of the diffuse background, which has a width of the order of sk,d 21 where , is the (transport) mean free path of the light in

Green function for multilayers: Light scattering in planar cavities.

Abstract: A compact and transparent plane-wave expansion of the complete Green function for an absorbing multilayered system is derived. The plane-wave solutions involved match, in the appropriate limit, the space-mode functions recently employed for quantization of the radiation field in a planar cavity and make this Green function particularly convenient for consideration of optical processes in realistic cavities and multilayers in general. This is illustrated by considering classically light scattering on a molecule in a planar cavity. It is demonstrated that the cross sections derived, besides generally describing light scattering on molecules embedded in a multilayer, correctly reproduce the effects of field confinement on light scattering in a planar cavity as predicted recently by the quantum-mechanical theory of Cairo et al. [Phys. Rev. Lett. 70, 1413 (1993)]. It is also pointed out that scattering into waves guided by the cavity lossy (metallic) mirrors may become an effective process in low-order microcavities. As a by product, a classical approach to spontaneous emission in absorbing planar cavities emerges from these considerations.

Light scattering by hexagonal ice crystals: comparison of finite-difference time domain and geometric optics models

Abstract: We have developed a finite-difference time domain (FDTD) method and a novel geometric ray-tracing model for the calculation of light scattering by hexagonal ice crystals. In the FDTD method we use a staggered Cartesian grid with the implementation of an efficient absorbing boundary condition for the truncation of the computation domain. We introduce the Maxwell–Garnett rule to compute the mean values of the dielectric constant at grid points to reduce the inaccuracy produced by the staircasing approximation. The phase matrix elements and the scattering efficiencies for the scattering of visible light by two-dimensional long circular ice cylinders match closely those computed from the exact solution for size parameters as large as 60, with maximum differences less than 5%. In the new ray-tracing model we invoke the principle of geometric optics to evaluate the reflection and the refraction of localized waves, from which the electric and magnetic fields at the particle surface (near field) can be computed. Based on the equivalence theorem, the near field can subsequently be transformed to the far field, in which the phase interferences are fully accounted for. The phase functions and the scattering efficiencies for hexagonal ice crystals computed from the new geometric ray-tracing method compare reasonably well with the FDTD results for size parameters larger than approximately 20. When absorption is involved in geometric ray tracing, the adjusted real and imaginary refractive indices and Fresnel formulas are derived for practical applications based on the fundamental wave theory.

Electromagnetic scattering from a multilayered sphere located in an arbitrary beam

Abstract: A solution is given for the problem of scattering of an arbitrary shaped beam by a multilayered sphere. Starting from Bromwich potentials and using the appropriate boundary conditions, we give expressions for the external and the internal fields. It is shown that the scattering coefficients can be generated from those established for a plane-wave illumination. Some numerical results that describe the scattering patterns and the radiation-pressure behavior when an incident Gaussian beam or a plane wave impinges on a multilayered sphere are presented.

Concept of polarization entropy in optical scattering

Abstract: We consider the application of the general theory of unitary matrices to problems of wave scattering involving polarized waves. Haying outlined useful parameterizations of the low dimensional groups associated with these unitary matrices, we develop a general processing strategy, which we suggest has application in the extraction of physical information from a range of scattering matrices in optics. Examples are presented of applying the unitary matrix structure to problems of single and multiple scattering from a cloud of random particles. The techniques are best suited to characterization of depolarizing systems, where the scattered waves undergo a change of degree as well as polarization state. The degree of disorder of the system is then quantified by a scalar, the polarimetric entropy, defined from the eigenvalues of a scattering matrix that ranges from 0 for systems with zero scattering to 1 for perfect depolarizers. Further, we show that the unitary matrix parameterization can be used to extract important system information from the eigenvectors of this matrix.

A simple light scattering method to assay magnetism in Magnetospirillum gryphiswaldense

Abstract: A simple optical method was developed for assaying cellular magnetism in culture samples of magnetic spirilla. Cells are aligned parallel to the field lines in a magnetic field, resulting in a change in light scattering. The ratio of scattering intensities at different angles of magnetic field relative to the light beam (Cmag) is used to characterize the average magnetic orientation of the cells. Cmag was found to be well correlated with the average number of particles in different magnetic cell populations. Thus, estimations of magnetosome content can be made using magnetically induced differential light scattering. The method provides a fast and sensitive tool for monitoring the magnetite formation in growing cultures of Magnetospirillum gryphiswaldense.

Polymer stabilized liquid crystalline light modulating device and material

Abstract: A new liquid crystalline light modulating cell and material are characterized by liquid crystalline light modulating material of liquid crystal and polymer, the liquid crystal being a chiral nematic liquid crystal having positive dielectric anisotropy and including chiral material in an amount effective to form focal conic and twisted planar textures, the polymer being distributed in phase separated domains in the liquid crystal cell in an amount that stabilizes the focal conic and twisted planar textures in the absence of a field and permits the liquid crystal to change textures upon the application of a field. In one embodiment, the material is light scattering in a field-OFF condition and optically clear in a field-ON condition, while in another embodiment, the material is optically clear in a field-OFF condition and light scattering in a field-ON condition. In still another embodiment, the material exhibits stability at zero field in a colored, light reflecting state, a light scattering state and multiple stable reflecting state therebetween, as well as being optically clear in the presence of a field.

Relationship between optical transparency and nanostructural features of silica aerogels

Abstract: Silica aerogels are considered to be of great promise for use in transparent thermal insulation systems in solar architecture. The optical transparency of these highly porous materials is influenced by the reaction parameters upon preparation and the precursor used. Previously it was shown that the specific extinction due to bulk scattering decreases both with increasing macroscopic density and increasing pH-value of the sol-gel starting solution. Recently, it was also found that within the measurement accuracy the light scattering intensity of the aerogel bulk equals the extrapolated small-angle X-ray scattering intensity towards scattering angle zero if both types of measurement are performed with respect to an absolute scale. In the meantime, ultra small-angle X-ray scattering measurements have been performed in order to close the gap in momentum space between light and conventional small-angle X-ray scattering. As a result it can be stated that the nearly isotropic (Rayleigh) scattering is caused by the same nanostructural inhomogeneities of the aerogel network which lead to the characteristic small-angle scattering pattern. As a consequence, the amount of isotropically scattered light and thus the optical extinction can be directly related to a quantity called the correlation volume. For a variety of silica aerogels, it is shown how the latter depends on the nanostructural features of the gel network, such as average particle size, interparticle arrangement, pore diameter and an ordering parameter, which accounts for concentration effects.

Propagation of Light through Human Dental Enamel and Dentine

Abstract: Techniques based on transillumination of teeth with visible light will be a valuable aid in caries diagnosis, if a higher sensitivity than that of the present Foti method is achieved. Therefore, a better understanding of light propagation through teeth is required, and hence it is useful to investigate the propagation of light through sound dental material. In this study the intensities emanating from the surfaces of enamel and dentine bars were measured when these bars were illuminated using a fibre rod transporting the light from a HeNe laser (lambda = 633 nm) as a light source. From the measured intensities, the radiant fluxes emanating from the surfaces were calculated. To account for a directional dependence of these fluxes, optical anisotropy in dental material was investigated by comparing the transmitted light intensity in a direction perpendicular and parallel to the approximal surface of the tooth from which the sample was cut. The mean ratio of the transmitted intensities in perpendicular and parallel direction was 0.86 +/- 0.06 for enamel and 2.88 +/- 0.43 for dentine. In addition, for enamel the asymmetry parameter, g, was estimated. The averaged value was g = 0.68 +/- 0.09. It was concluded that for dentine the optical anisotropy as measured supports the idea that tubules are the predominant cause of scattering in dentine. For enamel the results indicate that the hydroxyapatite crystals contribute significantly to scattering and that the influence of the prism structure on the light propagation is small.

Spinodals in a Polymer-Dispersed Liquid-Crystal

Abstract: Thermodynamic phase equilibria of a polymer dispersed liquid crystal (PDLC) consisting of monomeric liquid crystals and a polymer have been investigated theoretically and experimentally. The equilibrium limits of phase separation as well as phase transition of a PDLC system were calculated by taking into consideration the Flory–Huggins (FH) theory for the free energy of mixing of isotropic phases in conjunction with the Maier–Saupe (MS) theory for phase transition of a nematic liquid crystal. The correspondence between the Landau–de Gennes expansion and the Maier–Saupe theory was found and the coefficients were evaluated. The calculation based on the combined FH‐MS theory predicted a spinodal line within the coexistence of the nematic–isotropic region in addition to the conventional liquid–liquid spinodals. The cloud point phase diagram was determined by means of polarized optical microscopy and light scattering for a polybenzyl methacrylate/E7 (PBMA/E7) PDLC system. The calculated phase diagrams were tes...