Showing papers on "Light scattering published in 2000"

Light Scattering by Nonspherical Particles: Theory, Measurements, and Applications

Abstract: Almost all solid particles and very many liquid drops are not spherical. In addition, particles may have internal structure, both homogeneous and heterogeneous, and there may be agglomeration. It has long been recognized that the well-known Mie theory for homogeneous spheres, and similar theories for simple shapes such as the infinite cylinder, are not adequate representations of the scattering by more complex shapes and structures. There may be significant differences in the calculated phase function to that in reality, and a theory for homogeneous spheres will completely fail to predict polarization effects. In the absence of rigorous analytical solutions for particles of general shape and structure, recourse is made to numerical techniques. The development of powerful computers has enabled these calculations to be performed rapidly and accurately for a wide range of particle types and sizes. The growth in numerical techniques has been exponential. For these reasons this book has come at a very opportune time, and is a welcome review of a large field of expertise. Authors who are recognized masters review each subject, and all the major methods are covered. For completeness there are also sections dealing with examples of practical applications of the calculations to nature. The book opens with a foreword by the renowned H C van de Hulst, who provides an interesting historical review and perspective. An introductory section of three chapters follows, dealing with fundamental concepts and definitions. The first of these deals with scattering by single particles and moves on to multiple scattering and radiative transfer. The second chapter is concerned with methods for nonspherical particles. It briefly reviews the limited exact theories available and then covers numerical and approximate methods. Finally, there is a chapter covering the basic properties of the scattering matrix for small particles. Overall, this section provides a most welcome review and grounding in the necessary basics of the subject. The next two sections form the backbone of the book and are concerned with reviewing developments in numerical techniques. The first of these has chapters covering the method of separation of variables, the discrete dipole approximation, the T-matrix method and the finite difference time domain (FDTD) technique. The second section pursues inhomogeneous particles with refractive index profiles, heterogeneous particles with inclusions, multiple interacting particles and aggregates. At the end of this section is a chapter reviewing developments to date in the theory of scattering by statistically irregular particles. This is very welcome in light of the fact that the bulk of natural particles are not regular in the sense that their shapes can be predicted. The latter part of the book is the province of measurements and applications. Here it is slightly less satisfactory, being perhaps a little narrower in scope. Under measurements there is a description of one experimental method for the determination of the elements of the Stokes matrix and a description of one microwave facility for large scale modelling of particles. The final section is a review of applications. This is largely concerned with environmental situations, covering LIDAR and radiative transfer methods for studies of clouds, microwave measurements of precipitation, scattering in marine environments and interplanetary dust. The book ends with a short chapter of biological applications. These are all interesting and useful illustrative examples, but I wonder whether a wider view may have been appropriate. Applications in industrial situations come to mind. In summary this is a very worthwhile research publication. It is attractively presented and comprehensive. It will prove to be a most useful addition to the literature in the ever-expanding field of light scattering. A R Jones

Scattering of Electromagnetic Waves: Theories and Applications

Abstract: Introduction to Electromagnetic Scattering by a Single Particle. Basic Theory of Electromagnetic Scattering. Fundamentals of Random Scattering. Characteristics of Discrete Scatterers and Rough Surfaces. Scattering and Emission by Layered Media. Single Scattering and Applications. Radiative Transfer Theory. Solution Techniques of Radiative Transfer Theory. One-Dimensional Random Rough Surface Scattering. Index.

Dynamic Light Scattering Measurement of Nanometer Particles in Liquids

Abstract: Dynamic light scattering (DLS) techniques for studying sizes and shapes of nanoparticles in liquids are reviewed. In photon correlation spectroscopy (PCS), the time fluctuations in the intensity of light scattered by the particle dispersion are monitored. For dilute dispersions of spherical nanoparticles, the decay rate of the time autocorrelation function of these intensity fluctuations is used to directly measure the particle translational diffusion coefficient, which is in turn related to the particle hydrodynamic radius. For a spherical particle, the hydrodynamic radius is essentially the same as the geometric particle radius (including any possible solvation layers). PCS is one of the most commonly used methods for measuring radii of submicron size particles in liquid dispersions. Depolarized Fabry-Perot interferometry (FPI) is a less common dynamic light scattering technique that is applicable to optically anisotropic nanoparticles. In FPI the frequency broadening of laser light scattered by the particles is analyzed. This broadening is proportional to the particle rotational diffusion coefficient, which is in turn related to the particle dimensions. The translational diffusion coefficient measured by PCS and the rotational diffusion coefficient measured by depolarized FPI may be combined to obtain the dimensions of non-spherical particles. DLS studies of liquid dispersions of nanometer-sized oligonucleotides in a water-based buffer are used as examples.

Rayleigh scattering in high-Q microspheres

Abstract: The Rayleigh scattering has to be largely suppressed in high-Q whispering-gallery modes in microspheres because of restrictions imposed on scattering angles by cavity confinement. Earlier estimates of the fundamental limit for the quality factor in fused-silica microspheres are revisited, and Q≃1012 is predicted in few-millimeter-size fused-silica spheres, if the surface hydration problem is ovecome. Particular effects of surface scattering losses are analyzed, and the manifestation of scattering in the form of intermode coupling is calculated. The predominant effect of counterpropagating mode coupling (intracavity backscattering) is analyzed in the presence of a mode-matched traveling-wave coupler. As much as 100% resonance reflection regime is shown to be feasible.

Enhanced light extraction in LEDs through the use of internal and external optical elements

Abstract: This invention describes new LEDs having light extraction structures (26) on or within the LED to increase its efficiency. The new light extraction structures (26) provide surfaces for reflecting, refracting or scattering light into directions that are more favorable for the light to escape into the package. The structures can be arrays of light extraction elements (42, 44, 46, 48, 50, 52) or disperser layers (112, 122, 134, 144, 152, 162). The light extraction elements can have many different shapes and are placed in many locations to increase the efficiency of the LED over conventional LEDs. The disperser layers provide scattering centers for light and can be placed in many locations as well. The new LEDs with arrays of light extraction elements are fabricated with standard processing techniques making them highly manufacturable at costs similar to standard LEDs. The new LEDs with disperser layers are manufactured using new methods and are also highly manufacturable.

Imaging superficial tissues with polarized light.

Abstract: Objective Polarized light can be used to obtain images of superficial tissue layers such as skin, and some example images are presented. This study presents a study of the transition of linearly polarized light into randomly polarized light during light propagation through tissues. Study Design/Materials and Methods The transition of polarization was studied in polystyrene microsphere solutions, in chicken muscle (breast) and liver, and in porcine muscle and skin. The transition is discussed in terms of a diffusion process characterized by an angular diffusivity (radians2/mean free path) for the change in angular orientation of linearly polarized light per unit optical path traveled by the light. Results Microsphere diffusivity increased from 0.031 to 0.800 for diameters decreasing from 6.04 μm to 0.306 μm, respectively. Tissue diffusivity varied from a very low value (0.0004) for chicken liver to an intermediate value (0.055) for chicken and porcine muscle to a very high value (0.78) for pig skin. Conclusion The results are consistent with the hypothesis that birefringent tissues randomize linearly polarized light more rapidly than nonbirefringent tissues. The results suggest that polarized light imaging of skin yields images based only on photons backscattered from the superficial epidermal and initial papillary dermis because the birefringent dermal collagen rapidly randomizes polarized light. This anatomic region of the skin is where cancer commonly arises. Lasers Surg. Med. 26:119–129, 2000. © 2000 Wiley-Liss, Inc.

Spectroscopy of single metallic nanoparticles using total internal reflection microscopy

Abstract: We have developed a simple, fast, and flexible technique to measure optical scattering spectra of individual metallic nanoparticles. The particles are placed in an evanescent field produced by total internal reflection of light from a halogen lamp in a glass prism. The light scattered by individual particles is collected using a conventional microscope and is spectrally analyzed by a nitrogen-cooled charge-coupled-device array coupled to a spectrometer. This technique is employed to measure the effect of particle diameter on the dephasing time of the particle plasmon resonance in gold nanoparticles. We also demonstrate the use of this technique for measurements in liquids, which is important for the potential application of particle plasmons in chemical or biological nanosensors.

Particle Characterization: Light Scattering Methods

Abstract: Preface. Acknowledgements. 1. Particle Characterization - An Overview. 2. Light Scattering - The Background Information. 3. Laser Diffraction - Sizing from Nanometers to Millimeters. 4. Optical Particle Counting - Counting and Sizing. 5. Photon Correlation Spectroscopy - Submicron Particle Characterization. 6. Electrophoretic Light Scattering - Zeta Potential Measurement. Appendices. Author Index. Subject Index.

Fractal-like Aggregates: Relation between Morphology and Physical Properties.

Abstract: A number of modern technological applications require a detailed calculation of the physical properties of aggregated aerosol particles. For example, in probing soot aerosols by the method called laser-induced incandescence (LII), the soot clusters are suddenly heated by a short, powerful laser pulse and then cool down to the temperature of the carrier gas. LII sizing is based on rigorous calculation of the soot aggregate heat-up and cooling and involves prediction of laser light absorption and energy and mass transfer between aggregated particles and the ambient gas. This paper describes results of numerical simulations of the mass or energy transfer between the gas and fractal-like aggregates of N spherical particles in either the free-molecular or continuum regime, as well as the light scattering properties of random fractal-like aggregates, based on Rayleigh–Debye–Gans (RDG) theory. The aggregate geometries are generated numerically using specially developed algorithms allowing “tuning” of the fractal dimension and prefactor values. Our results are presented in the form of easily applicable scaling laws, with special attention paid to relations between the aggregate gyration radius and the effective radius describing various transport processes between the aggregates and the carrier gas.

Organic light-emitting device with an ordered monolayer of silica microspheres as a scattering medium

Abstract: Periodic dielectric structures, consisting of hexagonally closed-packed arrays of silica microspheres with the diameter of 550 nm, were incorporated into organic light-emitting devices with a conventional two-layer structure made with vacuum-sublimation The arrays acted as a two-dimensional diffraction lattice which behaved as a light scattering medium for the light propagated in waveguiding modes within the device Strongly scattered light emission through the front surface of the devices was observed An increase in the device coupling-out factor for electroluminescent efficiency by using the scattering structure is demonstrated

Parameterization of the scattering and absorption properties of individual ice crystals

Abstract: We present parameterizations of the single-scattering properties for individual ice crystals of various habits based on the results computed from the accurate light scattering calculations. The projected area, volume, and single-scattering properties of ice crystals with various shapes and sizes are computed for 56 narrow spectral bands covering 0.2–5 μm. The ice crystal habits considered in this study are hexagonal plates, solid and hollow columns, planar and spatial bullet rosettes, and aggregates that are commonly observed in cirrus clouds. Using the observational relationships between the aspect ratios and the sizes of ice crystals, we can define the three-dimensional structure of these ice crystal habits with respect to their maximum dimensions for light scattering calculations. The volume and projected area of ice crystals, expressed in terms of the diameters of the corresponding equivalent spheres, are first parameterized by employing the ice crystal maximum dimensions. Further, various analytical expressions as functions of the effective dimensions of ice crystals have been developed to parameterize the extinction and absorption efficiencies, asymmetry factor, and the truncation of the forward peak energy in the phase function. The present parameterization scheme provides an efficient approach to obtain the basic scattering and absorption properties of nonspherical ice crystals.

Broad bandwidth frequency domain instrument for quantitative tissue optical spectroscopy

Abstract: Near-infrared (NIR) optical properties of turbid media, eg, tissue, can be accurately quantified noninvasively using methods based on diffuse reflectance or transmittance, such as frequency domain photon migration (FDPM) Factors which govern the accuracy and sensitivity of FDPM-measured optical properties include instrument performance, the light propagation model, and fitting algorithms used to calculate optical properties from measured data In this article, we characterize instrument, model, and fitting uncertaintics of an FDPM system designed for clinical use and investigate how each of these factors affects the quantification of NIR absorption (μa) and reduced scattering (μs′) parameters in tissue phantoms The instrument is based on a 500 MHz, multiwavelength platform that sweeps through 201 discrete frequencies in as little as 675 ms Phase and amplitude of intensity modulated light launched into tissue, ie, diffuse photon density waves (PDW), are measured with an accuracy of ±030° and ±35%,

Optical modeling of a-Si:H solar cells with rough interfaces: Effect of back contact and interface roughness

Abstract: An approach to study the optical behavior of hydrogenated amorphous silicon solar cells with rough interfaces using computer modeling is presented. In this approach the descriptive haze parameters of a light scattering interface are related to the root mean square roughness of the interface. Using this approach we investigated the effect of front window contact roughness and back contact material on the optical properties of a single junction a-Si:H superstrate solar cell. The simulation results for a-Si:H solar cells with SnO2:F as a front contact and ideal Ag, ZnO/Ag, and Al/Ag as a back contact are shown. For cells with an absorber layer thickness of 150–600 nm the simulations demonstrate that the gain in photogenerated current density due to the use of a textured superstrate is around 2.3 mA cm−2 in comparison to solar cells with flat interfaces. The effect of the front and back contact roughness on the external quantum efficiency (QE) of the solar cell for different parts of the light spectrum was de...

Light scattering from cells: the contribution of the nucleus and the effects of proliferative status

Abstract: As part of our ongoing efforts to understand the fundamental nature of light scattering from cells and tissues, we present data on elastic light scattering from isolated mammalian tumor cells and nuclei. The contribution of scattering from internal structures and in particular from the nuclei was compared to scattering from whole cells. Roughly 55% of the elastic light scattering at high-angles (> 40 degrees) comes from intracellular structures. An upper limit of 40% on the fractional contribution of nuclei to scattering from cells in tissue was determined. Using cell suspensions isolated from monolayer cultures at different stages of growth, we have also found that scattering at angles greater than about 110 degrees was correlated with the DNA content of the cells. Based on model calculations and the relative size difference of nuclei from cells in different stages of growth, we argue that this difference in scattering results from changes in the internal structures of the nucleus. This interpretation is consistent with our estimate of 0.2 micron as the mean size of the scattering centers in cells. Additionally, we find that while scattering from the nucleus accounts for a majority of internal scattering, a significant portion must result from scattering off of cytoplasmic structures such as mitochondria.

Communication through a diffusive medium: coherence and capacity

Abstract: Coherent wave propagation in disordered media gives rise to many fascinating phenomena as diverse as universal conductance fluctuations in mesoscopic metals and speckle patterns in light scattering. Here, the theory of electromagnetic wave propagation in diffusive media is combined with information theory to show how interference affects the information transmission rate between antenna arrays. Nontrivial dependencies of the information capacity on the nature of the antenna arrays are found, such as the dimensionality of the arrays and their direction with respect to the local scattering medium. This approach provides a physical picture for understanding the importance of scattering in the transfer of information through wireless communications.

Optical absorption and light scattering in microcrystalline silicon thin films and solar cells

Abstract: Optical characterization methods were applied to a series of microcrystalline silicon thin films and solar cells deposited by the very high frequency glow discharge technique. Bulk and surface light scattering effects were analyzed. A detailed theory for evaluation of the optical absorption coefficient α from transmittance, reflectance and absorptance (with the help of constant photocurrent method) measurements in a broad spectral region is presented for the case of surface and bulk light scattering. The spectral dependence of α is interpreted in terms of defect density, disorder, crystalline/amorphous fraction and material morphology. The enhanced light absorption in microcrystalline silicon films and solar cells is mainly due to a longer optical path as the result of an efficient diffuse light scattering at the textured film surface. This light scattering effect is a key characteristic of efficient thin-film-silicon solar cells.

Organic electroluminescent devices with enhanced light extraction

Abstract: An organic light emitting diode containing a first electrode, a second electrode, at least one organic light emitting layer, and an output coupler which reduces a Fresnel loss is provided. The index of refraction of the output coupler is matched to that of the adjacent layer of the device. The output coupler may be a dimpled transparent material or a composite layer containing light scattering particles to also reduce a critical angle loss.

Solid state illumination system containing a light emitting diode, a light scattering material and a luminescent material

Abstract: A lamp containing a radiation source, a luminescent material and a radiation scattering material located between the radiation source and the luminescent material is provided. The lamp may be a white emitting lamp. The radiation source may be a blue emitting LED. The luminescent material may be a yellow emitting phosphor or dye. The radiation scattering material may be ceramic particles, such as TiO 2 particles, in a carrier medium, such as glass, epoxy or silicone.

Nonionic Micelles near the Critical Point: Micellar Growth and Attractive Interaction†

Abstract: We report on a series of SANS experiments on the structure of binary water−nonionic surfactant systems accompanied by complementary ultralow shear experiments and depolarized light scattering. The analysis gives a clear picture of the temperature dependence of aqueous solutions of nonionic surfactants of the n-alkyl polyglycol ether type (CiEj) when approaching the cloud point curve. The series is based on temperature variations from 3 °C up to a temperature of about 1.5 K below the critical point Tc and concentration variations around the critical concentration cc by a factor of 3−9. Six different surfactants were studied, changing the alkyl chain length i as well as the number of ethylene oxide groups j. Excluded volume effects were taken into account in the evaluation procedure by a generalized indirect Fourier transformation procedure recently developed for the evaluation of scattering data from semidilute and dense systems. The bottom line is that all systems examined show a sphere-to-rod transition,...

Colloidal crystals made of poly( N -isopropylacrylamide) microgel particles

Abstract: Poly (N-isopropylacrylamide) microgel particles are found to form colloidal crystals similar to those occurring in typical hard-sphere colloids like poly(methylmethacrylate) beads. Samples made of particles with different crosslinker concentrations are investigated and their deswelling ratio is determined using dynamic light scattering. Small-angle neutron scattering data are also presented and analysed in terms of a face-centred-cubic crystal structure. The characteristic length, a, of the elementary cell is found to be 535 +/- 16 and 495 +/- 15 nm for the two systems investigated. This leads to particle radii of 189 +/- 6 and 175 +/- 5 nm, respectively. These values compare well to the radii determined using several different methods.

Novel Branching Topology in Polyethylenes As Revealed by Light Scattering and 13C NMR

Abstract: A group of polyethylenes synthesized using palladium α-diimine catalysts were studied using 13C NMR spectroscopy, intensity light scattering, dynamic light scattering, and viscometry. These catalysts are known to produce branched polyethylenes without α-olefin comonomers. The series of polymers studied were synthesized under conditions of varying ethylene pressure. The polymers are highly branched and completely amorphous and are thus soluble in common organic solvents at ambient temperatures. Light scattering determinations of the root-mean-square radius of gyration (Rg) and the molecular weight M of fractions eluting from a size exclusion chromatograph demonstrated that, at a given M, Rg decreased as ethylene pressure decreased. The hydrodynamic parametersthe Stokes radius (RH) from dynamic light scattering and the intrinsic viscosity ([η])also decreased. The change in Rg at a constant M results from the change in branching topology for the polymers synthesized at different ethylene pressures. The param...

Metropolis Light Transport for Participating Media

Abstract: In this paper we show how Metropolis Light Transport can be extended both in the underlying theoretical framework and the algorithmic implementation to incorporate volumetric scattering. We present a generalization of the path integral formulation that handles anisotropic scattering in non-homogeneous media. Based on this framework we introduce a new mutation strategy that is specifically designed for participating media. Our algorithm includes effects such as volume caustics and multiple volume scattering, is not restricted to certain classes of geometry and scattering models and has minimal memory requirements. Furthermore, it is unbiased and robust, in the sense that it produces satisfactory results for a wide range of input scenes and lighting situations within acceptable time bounds.

Effect of Particle Size of Chemical Mechanical Polishing Slurries for Enhanced Polishing with Minimal Defects

Abstract: In this study the effects of oversize particle contamination in chemical mechanical polishing (CMP) slurries were investigated on the silica CMP process The limits of light scattering technique were established in detecting coarse particles in a commercial silica CMP slurry using two different methods The detection limits were set by observing the shift in particle size distribution curve or by the appearance of an additional peak in the particle size distribution curve of the baseline slurry when a known amount of coarser particles were added to it Simultaneously, polishing tests were conducted by spiking the base slurry with coarser sol‐gel silica particles at the established detection limits It was observed that the contamination of larger particles not only created surface damage but also changed the material removal rate The mechanism of polishing in the presence of larger size particles is discussed as a function of particle size and concentration © 2000 The Electrochemical Society All rights reserved

Zeolite Growth by Addition of Subcolloidal Particles: Modeling and Experimental Validation

Abstract: Seeded growth of tetrapropylammonium (TPA)-silicalite-1 is studied using simulations and dynamic light scattering, atomic force microscopy, and transmission electron microscopy experiments. The effects of the total silica concentration, temperature, and total seed concentration are examined. When the composition of silica in solution is above a critical value, growth is observed. In such a case, the size of the seeds increases linearly with time, with a growth rate that is not significantly affected by the total silica concentration. Growth appears to be activated with an activation energy of 90 kJ/mol for a range of seed concentrations. Transmission electron microscopy and dynamic light scattering indicate the presence of subcolloidal particles. Simulations of the growth of a static particle in a suspension of subcolloidal particles are carried out. Good agreement with experimental results regarding the growth rate and the apparent activation energy is possible by considering DerjaguinLandau-Verwey-Overbeek (DLVO) interactions with electrostatic repulsion described with a constant surface charge model. The type of interaction was also verified with atomic force microscopy force measurements between a silicalite surface and a glass sphere. By use of these types of interactions, it is also possible to explain the stability of the seeded suspension and show that only a relatively narrow size distribution of growth precursors participate in the growth of the seeds. Our results support the possibility that under the conditions studied, growth of silicalite seeds proceeds by a mechanism with the rate-limiting step being the addition of subcolloidal particles.