Showing papers on "Light scattering published in 1990"
TL;DR: In this article, a simple theory of diffusing wave spectroscopy (DWS) based on the diffusion approximation for the transport of light is developed to calculate the temporal electric field autocorrelation functions of multiply scattered light.
Abstract: Dynamic light scattering is extended to optically thick (opaque) media which exhibit a very high degree of multiple scattering This new technique, called diffusing-wave spectroscopy (DWS), exploits the diffusive nature of the transport of light in strongly scattering media to relate the temporal fluctuations of the multiply scattered light to the motion of the scatterers A simple theory of DWS, based on the diffusion approximation for the transport of light, is developed to calculate the temporal electric field autocorrelation functions of the multiply scattered light Two important scattering geometries are treated : transmission and backscattering The theory is compared to experimental measurements of Brownian motion of submicron-diameter polystyrene spheres in aqueous suspension The agreement between theory and experiment is excellent The limitations of the photon diffusion approximation and the polarization dependence of the autocorrelation functions are discussed for the backscattering measurements The effects of absorption of light and particle polydispersity are also incorporated into the theory and verified experimentally It is also shown how DWS can be used to obtain information about the mean size of the particles which scatter light
266 citations
TL;DR: Anisotropic gels were produced by photopolymerization of an oriented liquid-crystalline (LC) mixture containing LC diacrylates and conventional LC molecules as mentioned in this paper.
Abstract: Anisotropic gels were produced by photopolymerization of an oriented liquid‐crystalline (LC) mixture containing LC diacrylates and conventional LC molecules. Gels produced in this way were clear and did not give rise to excess scattering of light. Upon application of an electric field across the gel, the system turned translucent. Light scattered by the gel was found to be highly dependent on the direction of polarization and wavelength of the incident light.
265 citations
TL;DR: Angle- and time-resolved studies are presented for an ultrafast laser pulse propagating through a slab of random media in the intermediate scattering regime, where a coherent (ballistic) component coexists with a incoherent (diffusive) component in the forward-scattered light.
Abstract: Angle- and time-resolved studies are presented for an ultrafast laser pulse propagating through a slab of random media in the intermediate scattering regime, where a coherent (ballistic) component coexists with a incoherent (diffusive) component in the forward-scattered light. The incoherent component can be approximated by diffusion theory when the thickness of the slab is greater than 10 transport mean free paths. The theoretical results from the two-frequency coherence function in the Rytov approximation are in qualitative but not quantitative agreement with the experimental results.
234 citations
TL;DR: The basic principles relating the intensity of scattered light to underlying molecular structure were established by Lord Rayleigh in his classic 1871 paper explaining why the sky appears to be blue as mentioned in this paper.
Abstract: Light scattering has long been used to probe properties of bulk matter. In transparent media such as air or clear water, measurements can be analyzed easily and remote sensing can be done over great distances. The basic principles relating the intensity of scattered light to underlying molecular structure were established by Lord Rayleigh in his classic 1871 paper explaining why the sky appears to be blue.
226 citations
TL;DR: In this article, the problem of scattering of optical or electromagnetic waves from a family of irregular rough surfaces characterized by band-limited fractal functions was considered and a unified and realistic method for examining rough surfaces without the use of random or periodic functions was proposed.
Abstract: We consider the problem of scattering of optical or electromagnetic waves from a family of irregular rough surfaces characterized by band-limited fractal functions. This method provides a unified and realistic method for examining rough surfaces without the use of random or periodic functions. We relate the angular distribution and the amount of energy in the specularly scattered field to the fractal characteristics of the surfaces by finding their analytical expressions under the Kirchhoff limit and calculating the scattering patterns.
170 citations
01 Jun 1990
TL;DR: In this paper, the structure of fractal colloid aggregates formed in both the diffusion-and the reaction-limited regimes is studied by static light scattering experiments, and the crossover region of the structure factor of the clusters is measured.
Abstract: The structure of fractal colloid aggregates formed in both the diffusion- and the reaction-limited regimes is studied by static light scattering experiments. The crossover region of the structure factor of the clusters is measured, and the effects of the finite extent of the fractal structure on the scattering are investigated. The polydispersity of the cluster mass distribution markedly changes the shape of the measured scattering intensity. A form for the structure factor obtained from computer-generated clusters is found to describe the colloidal aggregates very well, for both regimes. Other available models for the crossover region are also discussed. In addition, the effects of the optical plasma resonance in the case of metallic colloids and the effects of cluster restructuring on the static scattering are discussed.
167 citations
TL;DR: Measurements, and comparisons with theory, of the transport mean free path and the width of the coherent backscattering cone demonstrate the validity of the diffusion approximation of light in correlated suspensions.
Abstract: The effects of short-range interparticle correlations on the multiple scattering of light in colloidal suspensions are studied. Our measurements, and comparisons with theory, of the transport mean free path and the width of the coherent backscattering cone demonstrate the validity of the diffusion approximation of light in correlated suspensions. Dynamic multiple-light-scattering measurements allow determination of the short-time self-diffusion constant of the spheres. The data agree with hydrodynamic theory up to 45% volume fraction with no adjustable parameters.
164 citations
TL;DR: In this paper, the Stokes parameters of the average scattered light from two-dimensional rough surfaces show the presence of an unpolarized component, which lends support to the multiply scattering ray model.
Abstract: An experimental study of backscatter enhancement from rough surfaces is presented. The Stokes parameters of the average scattered light from two-dimensional rough surfaces show the presence of an unpolarized component, which lends support to the multiply scattering ray model. Experimental data from one-dimensional rough surfaces are compared with numerical calculation.
TL;DR: In this paper, a numerical method based on an integral representation of Maxwell's equations is used to calculate scattering properties of model porous aggregates of small particles, and the validity of the Maxwell-Garnett effective medium theory is shown for certain cases where the individual particles in the aggregate satisfy the Rayleigh size conditions.
Abstract: A numerical method, based on an integral representation of Maxwell's equations, is used to calculate scattering properties of model porous aggregates of small particles. It is shown that increasing porosity can lead to enhanced absorption and emission of radiation and a lower albedo. One application is to show how strongly the 9.7-micron emission feature of a piece of astronomical silicate matter depends on its porosity. The integral method is compared with the well-known coupled dipole approach for the case of a solid sphere. The validity of the Maxwell-Garnett effective medium theory is shown for certain cases where the individual particles in the aggregate satisfy the Rayleigh size conditions. 27 refs.
01 Jun 1990
TL;DR: The effects of thermal coagulation on the macroscopic optical transport parameters that govern the distribution of light in tissues were studied in this paper, where the optical absorption coefficients and reduced scattering coefficients were deduced from measurements of total transmission and total reflectance of HeNe laser radiation.
Abstract: The effects of thermal coagulation on the macroscopic optical transport parameters that govern the
distribution of light in tissues were studied. The optical absorption coefficients, pa, and the
reduced scattering coefficients, j.ts (1-g), were deduced from measurements of total transmission
and total reflectance of HeNe laser radiation ( = 633 and 594 nm) directed to thin slices of dog
myocardium heated in vitro. The first optical changes were detected at 45°and, at temperatures
above 65°, there was a 2-fold increase in absorption and a 7-fold increase in scattering.
Transmission electron microscopy of laser-induced thermally coagulated lesions in rat
myocardium (cw argon ion, = 514 nm) revealed ultrastructural alterations that were considered
responsible for the increased scattering based on Mie theory. These microscopic alterations
included disruption of mitochondria to form aggregates of electron dense granules and granular
transformation of thermally coagulated proteins of the sarcomeres and cytoplasm. Our preliminary
analyses suggest that the mitochondrial granules and the protein granules contribute to the
increased scattering oflight in thermally coagulated myocardium.
01 Sep 1990
TL;DR: A new two pass approach based on a variation of backward ray tracing backward beam tracing, which has the capability of rendering complex, hitherto unattainable, specular to diffuse phenomenon and its easy insertion into standard renderers is presented.
Abstract: A new two pass approach is presented based on a variation of backward ray tracing backward beam tracing. Advantages include its capability of rendering complex, hitherto unattainable, specular to diffuse phenomenon and its easy insertion into standard renderers. The algorithm is applied to aspects of the interaction of light with water. Within this context a variety of first generation effects, including shadowing and light scattering, are both rendered and animated. Results taken from the treatment of caustics within classical optics are included as they provide valuable insights into the precise nature of specular to diffuse transfer.
TL;DR: In this paper, the authors used a simple, inexpensive HeNe laser and a video camera to measure light scattering intensity and location in an SiO2 sputtering process used in semiconductor manufacturing under actual process conditions in a class 10 cleanroom.
Abstract: Using a simple, inexpensive HeNe laser and a video camera to measure light scattering intensity and location, particulate contamination in an SiO2 sputtering process used in semiconductor manufacturing has been studied under actual process conditions in a class 10 cleanroom. Particulates were observed during all aspects of the sputtering process. It was seen that portions of the process which resulted in mechanical stress on the tool walls produced the greatest flux of particles inside the tool. However, the sputtering step was the major contributor to contamination in this chemically simple process, because of its long duration and the stress‐inducing nature of the plasma. The contamination level in this plasma is estimated to exceed the cleanroom ambient by three orders of magnitude. As in other process plasmas, the particles were suspended at the sheath/plasma boundary. It is argued that a relatively weak electrostatic field is required for gravitational counterbalance of these highly charged particles...
TL;DR: In this article, the authors derived temporal autocorrelation functions for multiply scattered light, taking into account particle displacements arising from deterministic shear flow and random Brownian motion.
Abstract: We present a new technique for measuring velocity gradients for laminar shear flow, using dynamic light scattering in the strongly multiple-scattering regime. We derive temporal autocorrelation functions for multiply scattered light, taking into account particle displacements arising from deterministic shear flow and random Brownian motion. The laminar shear flow and Brownian motion are characterized by the relaxation rates τS−1=Γ¯k0l*/30 and τB−1 = Dk02, respectively, where Γ¯ is the mean shear rate of the scatterers, k0 = 2πn/λ is the wave number in the scattering medium, l* is the transport mean free path of the photons, and D is the diffusion coefficient of the scatterers. We obtain excellent agreement between theory and experiment over a wide range of shear rates, 0.5sec−1<Γ¯<200sec−1. In addition, the autocorrelation function for forward scattering is independent of the scattering properties of the medium and depends only on the mean shear rate and sample thickness when τS is much less than τB. Thus the mean shear rate can be simply determined by a single measurement.
TL;DR: In this article, the mean real aerosol refractive index is estimated based on aerosol chemical composition and the partial molar refraction approach, assuming all chemical constituents are homogeneously distributed throughout the aerosol phase.
Abstract: The ambient aerosol of the polluted troposphere is a complex mixture of water, electrolytes, ionic solids, metal oxides and glasses, and carbonaceous material. Prediction of the refractive indexes of these inhomogeneous mixtures can be a formidable task. Contained within this paper is the necessary parameterization to estimate the mean real aerosol refractive index based on aerosol chemical composition and the partial molar refraction approach. This approach assumes all chemical constituents are homogeneously distributed throughout the aerosol phase. Consistency of the data is discussed, and this approach is verified by prediction of refractive indexes of NaOH-Si-O{sub 2}-H{sub 2}O mixtures. Finally, aerosol chemical composition data from the Los Angeles Basin are used to predict mean real aerosol refractive indexes. These values are compared to urban aerosol refractive indexes calculated via other techniques (light scattering).
TL;DR: A numerically stable and accurate algorithm for computation of the internal radiative properties, as well as the overall scattering and extinction of a stratified sphere having an arbitrary number of layers is developed.
Abstract: Series expressions for the radially dependent absorption cross section and angle-averaged absorption heat source function within a stratified sphere are presented A numerically stable and accurate algorithm for computation of the internal radiative properties, as well as the overall scattering and extinction of a stratified sphere having an arbitrary number of layers is developed The results allow for direct estimation of the degree of penetration and intensity of radiative heating in radially inhomogeneous spherical particles, and also provide an estimate of the thermal emission coefficient of particles having a radial temperature distribution
TL;DR: In this article, the authors measured light scattering time correlation functions from dilute solutions of linear, monodisperse DNA restriction fragments, ranging in size from 367 to 2311 base pairs (molecular weight from 0.24 to 1.5 million), were measured at 20°C, in 100 mM NaCl, 10 mM Tris-HCl, and 1 mM EDTA.
Abstract: Dynamic light scattering time correlation functions from dilute solutions of linear, monodisperse DNA restriction fragments, ranging in size from 367 to 2311 base pairs (molecular weight from 0.24 to 1.5 million), were measured at 20°C, in 100 mM NaCl, 10 mM Tris-HCl, and 1 mM EDTA (pH 8). The correlation functions were analyzed by using CONTIN, a constrained inverse Laplace transform program. At scattering angles of 16 and 22°, the correlation functions are consistent with single exponential decays representing the translational motion of the DNAs
TL;DR: In the direct problem, the angular distribution of the scattered light calculated from the profile is shown to agree with the measured one and the rms roughness and the autocorrelation function are found by a least-squares fit to the measured angular distribution.
Abstract: Calculations are performed to relate the stylus profile of a one-dimensionally rough surface to the angular distribution of the light scattered by such a surface. In the direct problem, the angular distribution of the scattered light calculated from the profile is shown to agree with the measured one. In the inverse problem, the rms roughness and the autocorrelation function are found by a least-squares fit to the measured angular distribution. For the smoother surfaces, the rms roughness is mostly determined by the ratio between the power of the specular beam and the total power of the scattered light; the computed values are proportional to those calculated directly from the stylus profiles. The values of the parameters obtained by the least-squares fit are affected by a variety of errors and agree only partially with those obtained from the stylus profile.
01 Jan 1990
Book•
01 Jan 1990
TL;DR: In this article, the authors describe the physical optics of enhanced backscattering and surface scattering, including surface impedance boundary conditions, and the use of the Calderon projectors and the capacity operators in scattering.
Abstract: Part I: Volume Scattering. Experimental and theoretical studies on enhanced hackscattering from scatterers and rough surfaces (A. Ishimaru). Multiple scattering in dynamic systems (I. Freund). Dynamics of Brownian particles from strongly multiple light scattering (P.E. Wolf, G. Maret). Multiple scattering in dense media (P. Bruscaglioni, G. Zaccanti). Role of the inner scale of atmospheric turbulence in optical propagation and methods to measure it (A. Consortini). Diffraction tomography: Potentials and problems (L.-J. Gelius, J.J. Stamnes). The physical optics of enhanced backscattering (E. Jakeman). Part II: Surface Scattering. Scattering experiments with smoothly varying random rough surfaces and their interpretation (E.R. Mendez, K.A. O'Donnell). Measurements of angular scattering by randomly rough metal and dielectric surfaces (J.C. Dainty, M.-J. Kim, A.J. Sant). Backscattering effects in the elastic scattering of p-polarized light from a large amplitude random grating (A.A. Maradudin, E.R. Mendez, T. Michel). Electromagnetic scattering from very rough random surfaces and its connections with blazes from reflection gratings (M. Nieto-Vesperinas, J.M. Soto-Crespo). Rigorous solution of problems of scattering by large size objects (D. Maystre, M. Saillard). The method of smoothing applied to random volume and surface scattering (G.S. Brown). Scattering of EM waves from particles with random rough surfaces (R. Schiffer). Surface impedance boundary conditions used to study light scattering from metallic surfaces (R.A. Depine). The use of the Calderon projectors and the capacity operators in scattering (M. Cessenat). Part III. Non-linear Interactions. Gratings as electromagnetic field amplifiers for second harmonic generation (R. Reinisch, M. Neviere). Intrinsic instabilities of laser-irradiated surfaces (J.E. Sipe, H.M. van Driel). Brillouin scattering from thin films (G.I. Stegeman et al.) Author Index. Subject Index.
TL;DR: In this paper, the structure and dynamics of dilute Laponite RD sols were studied by static and dynamic light scattering, and collective diffusion coefficients were determined by slope analysis of the autocorrelation functions.
TL;DR: The authors determined a partir des resultats de DLS des distributions de temps de relaxation for des solutions de tres diluees a semidiluees de PS dans le cyclohexane.
Abstract: Determination a partir des resultats de DLS des distributions de temps de relaxation pour des solutions de tres diluees a semidiluees de PS dans le cyclohexane. les resultats pour les solutions semidiluees sont en accord partiel avec une theorie developpee par Brochard et De Gennes. La DLS est une methode d'etude possible de la viscoelasticite de solutions semidiluees de polymere
TL;DR: In this article, the structure of the discrete-dipole approximation is investigated, and the matrix formed by this approximation is identified to be a symmetric, block-Toeplitz matrix.
Abstract: The discrete-dipole approximation is used to study the problem of light scattering by homogeneous rectangular particles. The structure of the discrete-dipole approximation is investigated, and the matrix formed by this approximation is identified to be a symmetric, block-Toeplitz matrix. Special properties of block-Toeplitz arrays are explored, and an efficient algorithm to solve the dipole scattering problem is provided. Timings for conjugate gradient, Linpack, and block-Toeplitz solvers are given; the results indicate the advantages of the block-Toeplitz algorithm. A practical test of the algorithm was performed on a system of 1400 dipoles, which corresponds to direct inversion of an 8400 × 8400 real matrix. A short discussion of the limitations of the discrete-dipole approximation is provided, and some results for cubes and parallelepipeds are given. We briefly consider how the algorithm may be improved further.
TL;DR: In this article, the effect of dilution with carbon tetrachloride on crude oil spectra is determined for asphaltic crude oils and these results are contrasted with similar measurements on crude oils with an immiscible wax phase.
Abstract: The question of the relative magnitudes of light absorption and scattering by asphaltene particles in crude oils is addressed for the near-infrared spectral range. The effect of dilution with carbon tetrachloride on crude oil spectra is determined for asphaltic crude oils and these results are contrasted with similar measurements on crude oils with an immiscible wax phase. This comparison implies the dominance of absorption over scattering for asphaltic crude oils while scattering and absorption are found to be significant for waxy crude oils. Separation of crude oils into asphaltenes and maltenes allows for measurement of the absorption of individual crude oil components. The comparison of the original and composite spectra clearly shows that absorption dominates over scattering in the near-IR region. The functional forms expected for absorption and scattering are examined and found to be consistent with the experimental data.
TL;DR: In this article, the authors used laser light scattering, with the aid of Mie's scattering theory, to investigate bubble nucleation in concentrated polymer solutions and determined the critical bubble size by obtaining a one-to-one correspondence between the extrema of the experimental and theoretical scattering curves.
Abstract: Laser light scattering, with the aid of Mie's scattering theory, was used to investigate bubble nucleation in concentrated polymer solutions. Solutions with 40, 50 and 60 wt % polystyrene in toluene were used. A test solution in a high-pressure optical cell made of strain-free quartz was heated to a predetermined temperature under pressure. Upon release of the pressure in the cell, both scattered and transmitted light fluxes were measured with photomultipliers, and the variation of system pressure with time was measured using a piezoelectric pressure transducer. The measurement of the light scattering flux and control of the experiment were performed by means of a microcomputer with a general-purpose data acquisition interface. Data reduction was done using the same microcomputer. The critical bubble size was determined by obtaining a one-to-one correspondence between the extrema of the experimental and theoretical scattering curves. While the Mie scattering theory is for monodisperse particles, the experimental scattering curves indicated that the bubbles had a distribution of sizes. Therefore, the log-normal distribution function was used to represent the size distribution; and theoretical scattering curves were computed by varying the breadth parameter in the log-normal distribution function, until we had a one-to-one correspondence between the extrema of the experimental and theoretical scattering curves. In this way, we were able to determine (a) the size distribution of bubbles in the optical cell, (b) the critical bubble size, (c) the total number of bubbles nucleated, and (d) the critical pressure for bubble nucleation, as functions of temperature, the initial equilibrium pressure in the optical cell, and the concentration of the polymer solution.
TL;DR: In this article, a simple relationship between the number of fringes per degree and the size of the scattering drop was presented, and the possibility of measuring the drop size through visualization of the fringe pattern was demonstrated.
Abstract: The intensity angular pattern of the light scattered by a drop at a scattering angle of ca. 90 o is related to the size of the scattering drop. A simple relationship between the number of fringes per degree and the size is presented. The possibility of measuring the drop size through visualization of the fringe pattern is demonstrated