Showing papers on "Light scattering published in 2008"

High contrast in vitro and in vivo photoluminescence bioimaging using near infrared to near infrared up-conversion in Tm3+ and Yb3+ doped fluoride nanophosphors.

Abstract: A new approach for photoluminescence imaging in vitro and in vivo has been shown utilizing near infrared to near infrared (NIR-to-NIR) up-conversion in nanophosphors. This NIR-to-NIR up-conversion process provides deeper light penetration into biological specimen and results in high contrast optical imaging due to absence of an autofluorescence background and decreased light scattering. Aqueous dispersible fluoride (NaYF4) nanocrystals (20−30 nm size) co-doped with the rare earth ions, Tm3+ and Yb3+, were synthesized and characterized by TEM, XRD, and photoluminescence (PL) spectroscopy. In vitro cellular uptake was shown by the PL microscopy visualizing the characteristic emission of Tm3+ at ∼800 nm excited with 975 nm. No apparent cytotoxicity was observed. Subsequent animal imaging studies were performed using Balb-c mice injected intravenously with up-converting nanophosphors, demonstrating the high contrast PL imaging in vivo.

Optical phase conjugation for turbidity suppression in biological samples.

Abstract: Elastic optical scattering, the dominant light-interaction process in biological tissues, prevents tissues from being transparent. Although scattering may appear stochastic, it is in fact deterministic in nature. We show that, despite experimental imperfections, optical phase conjugation (λ = 532 nm) can force a transmitted light field to retrace its trajectory through a biological target and recover the original light field. For a 0.69-mm-thick chicken breast tissue section, we can enhance point-source light return by a factor of ~5 x 10^3 and achieve a light transmission enhancement factor of 3.8 within a collection angle of 29°. Additionally, we find that the reconstruction's quality, measured by the width of the reconstructed point source, is independent of tissue thickness (up to a thickness of 0.69 mm). This phenomenon may be used to enhance light transmission through tissue, enable measurement of small tissue movements, and form the basis of new tissue imaging techniques.

A One-Step Homogeneous Immunoassay for Cancer Biomarker Detection Using Gold Nanoparticle Probes Coupled with Dynamic Light Scattering

Abstract: A one-step homogeneous immunoassay for the detection of a prostate cancer biomarker, free-PSA (prostate specific antigen), was developed using gold nanoparticle probes coupled with dynamic light scattering (DLS) measurements. A spherical gold nanoparticle with a core diameter around 37 nm and a gold nanorod with a dimension of 40 by 10 nm were first conjugated with two different primary anti-PSA antibodies and then used as optical probes for the immunoassay. In the presence of antigen f-PSA in solution, the nanoparticles and nanorods aggregate together into pairs and oligomers through the formation of a sandwich type antibody−antigen−antibody linkage. The relative ratio of nanoparticle-nanorod pairs and oligomers versus individual nanoparticles was quantitatively monitored by DLS measurement. A correlation can be established between this relative ratio and the amount of antigen in solution. The light scattering intensity of nanoparticles and nanoparticle oligomers is several orders of magnitude higher tha...

Design of light scattering in nanowire materials for photovoltaic applications

Abstract: We experimentally investigate the optical properties of layers of InP, Si, and GaP nanowires, relevant for applications in solar cells. The nanowires are strongly photonic, resulting in a significant coupling mismatch with incident light due to multiple scattering. We identify a design principle for the effective suppression of reflective losses, based on the ratio of the nondiffusive absorption and diffusive scattering lengths. Using this principle, we demonstrate successful suppression of the hemispherical diffuse reflectance of InP nanowires to below that of the corresponding transparent effective medium. The design of light scattering in nanowire materials is of large importance for optimization of the external efficiency of nanowire-based photovoltaic devices.

Dark-field microscopy studies of single metal nanoparticles: understanding the factors that influence the linewidth of the localized surface plasmon resonance

Abstract: This article provides a review of our recent Rayleigh scattering measurements on single metal nanoparticles. Two different systems will be discussed in detail: gold nanorods with lengths between 30 and 80 nm, and widths between 8 and 30 nm; and hollow gold-silver nanocubes (termed nanoboxes or nanocages depending on their exact morphology) with edge lengths between 100 and 160 nm, and wall thicknesses of the order of 10 nm. The goal of this work is to understand how the linewidth of the localized surface plasmon resonance depends on the size, shape, and environment of the nanoparticles. Specifically, the relative contributions from bulk dephasing, electron-surface scattering, and radiation damping (energy loss via coupling to the radiation field) have been determined by examining particles with different dimensions. This separation is possible because the magnitude of the radiation damping effect is proportional to the particle volume, whereas, the electron-surface scattering contribution is inversely proportional to the dimensions. For the nanorods, radiation damping is the dominant effect for thick rods (widths greater than 20 nm), while electron-surface scattering is dominant for thin rods (widths less than 10 nm). Rods with widths in between these limits have narrow resonances-approaching the value determined by the bulk contribution. For nanoboxes and nanocages, both radiation damping and electron-surface scattering are significant at all sizes. This is because these materials have thin walls, but large edge lengths and, therefore, relatively large volumes. The effect of the environment on the localized surface plasmon resonance has also been studied for nanoboxes. Increasing the dielectric constant of the surroundings causes a red-shift and an increase in the linewidth of the plasmon band. The increase in linewidth is attributed to enhanced radiation damping.

Mapping the Plasmon Resonances of Metallic Nanoantennas

Abstract: We study the light scattering and surface plasmon resonances of Au nanorods that are commonly used as optical nanoantennas in analogy to dipole radio antennas for chemical and biodetection field-enhanced spectroscopies and scanned-probe microscopies. With the use of the boundary element method, we calculate the nanorod near-field and far-field response to show how the nanorod shape and dimensions determine its optical response. A full mapping of the size (length and radius) dependence for Au nanorods is obtained. The dipolar plasmon resonance wavelength I shows a nearly linear dependence on total rod length L out to the largest lengths that we study. However, L is always substantially less than I/2, indicating the difference between optical nanoantennas and long-wavelength traditional I/2 antennas. Although it is often assumed that the plasmon wavelength scales with the nanorod aspect ratio, we find that this scaling does not apply except in the extreme limit of very small, spherical nanoparticles. The plasmon response depends critically on both the rod length and radius. Large (500 nm) differences in resonance wavelength are found for structures with different sizes but with the same aspect ratio. In addition, the plasmon resonance deduced from the near-field enhancement can be significantly red-shifted due to retardation from the resonance in far-field scattering. Large differences in near-field and far-field response, together with the breakdown of the simple scaling law must be accounted for in the choice and design of metallic I/2 nanoantennas. We provide a general, practical map of the resonances for use in locating the desired response for gold nanoantennas.

Tutorial on diffuse light transport.

Abstract: A tutorial introduction to diffuse light transport is presented. The basic analytic equations of time-resolved, steady-state and modu- lated light transport are introduced. The perturbation method for han- dling slight heterogeneities in optical properties is outlined. The treat- ment of boundary conditions such as an air/tissue surface is described. Finite mesh-based numerical methods are introduced to calculate the diffuse light field in complex tissues with arbitrary boundaries. Appli- cations in tissue spectroscopy and imaging illustrate these theoretical and computational tools. © 2008 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2967535 This report is a tutorial introduction to diffuse light transport in biological tissues. Section 1 presents the basics of diffuse light transport, showing the simple equations for time- resolved, steady-state, and modulated light transport. The per- turbation method for handling slight heterogeneities in optical properties is introduced. The treatment of an air/tissue surface boundary condition is considered. Section 2 describes numeri- cal methods for simulating light transport in complex tissues. The goal of this work is to provide the novice in biomedical optics with an introduction to diffuse light transport, and the underpinnings of how basic approaches to solving light trans- port problems can be solved.

Strong spectral variation of biomass smoke light absorption and single scattering albedo observed with a novel dual-wavelength photoacoustic instrument

Abstract: [1] A dual-wavelength photoacoustic instrument operating at 405 and 870 nm was used during the 2006 Fire Lab at Missoula Experiment to measure light scattering and absorption by smoke from the combustion of a variety of biomass fuels. Simultaneous measurements of aerosol light scattering by reciprocal nephelometry within the instrument's acoustic resonator accompany photoacoustic aerosol light absorption measurements. Single scattering albedo values at 405 nm ranging from 0.37 to 0.95 were measured for different fuel types, and the spectral dependence of absorption was quantified using the Angstrom exponent of absorption. An absorption Angstrom exponent near unity is commonly observed for motor vehicle emission-generated black carbon aerosol. For biomass smoke, Angstrom exponents as high as 3.5 were found in association with smoke having single scattering albedo near unity. The measurements strongly suggest that light-absorbing organic material is present in wood smoke. A second single-wavelength photoacoustic instrument with reciprocal nephelometry was used to quantify aerosol scattering and absorption at 532 nm. Absorption Angstrom exponents calculated using 532 and 870 nm data were as large as 2.5 for smoke with single scattering albedos near unity. The spectral variation in optical properties provides insight into the differentiation of aerosols from mobile or industrial sources versus those from biomass burning. Optical properties of biomass smokes could be classified by general fuel type such as flowering shrubs versus pine needle litter.

Underwater Wireless Optical Communication Channel Modeling and Performance Evaluation using Vector Radiative Transfer Theory

Abstract: This paper presents the modeling of an underwater wireless optical communication channel using the vector radiative transfer theory. The vector radiative transfer equation captures the multiple scattering nature of natural water, and also includes the polarization behavior of light. Light propagation in an underwater environment encounters scattering effect creating dispersion which introduces inter-symbol-interference to the data communication. The attenuation effect further reduces the signal to noise ratio. Both scattering and absorption have adverse effects on underwater data communication. Using a channel model based on radiative transfer theory, we can quantify the scattering effect as a function of distance and bit rate by numerical Monte Carlo simulations. We also investigate the polarization behavior of light in the underwater environment, showing the significance of the cross-polarization component when the light encounters more scattering.

Light Scattering by Systems of Particles

Abstract: Light Scattering by Systems of Particles comprehensively develops the theory of the null-field method, while covering almost all aspects and current applications The Null-field Method with Discrete Sources is an extension of the Null-field Method (also called T-Matrix Method) to compute light scattering by arbitrarily shaped dielectric particles It also incorporates FORTRAN programs and exemplary simulation results that demonstrate all aspects of the latest developments of the method The FORTRAN source programs included on the enclosed CD exemplify the wide range of application of the T-matrix method Worked examples of the application of the FORTRAN programs show readers how to adapt or modify the programs for his specific application

Mueller matrix decomposition for extraction of individual polarization parameters from complex turbid media exhibiting multiple scattering, optical activity, and linear birefringence

Abstract: Linear birefringence and optical activity are two common optical polarization effects present in biological tissue, and determi- nation of these properties has useful biomedical applications. How- ever, measurement and unique interpretation of these parameters in tissue is hindered by strong multiple scattering effects and by the fact that these and other polarization effects are often present simulta- neously. We have investigated the efficacy of a Mueller matrix decom- position methodology to extract the individual intrinsic polarimetry characteristics linear retardance and optical rotation , in particu- lar from a multiply scattering medium exhibiting simultaneous linear birefringence and optical activity. In the experimental studies, a pho- toelastic modulation polarimeter was used to record Mueller matrices from polyacrylamide phantoms having strain-induced birefringence, sucrose-induced optical activity, and polystyrene microspheres- induced scattering. Decomposition of the Mueller matrices recorded in the forward detection geometry from these phantoms with con- trolled polarization properties yielded reasonable estimates for and parameters. The confounding effects of scattering, the propagation path of multiple scattered photons, and detection geometry on the estimated values for and were further investigated using polarization-sensitive Monte Carlo simulations. The results show that in the forward detection geometry, the effects of scattering induced linear retardance and diattenuation are weak, and the decomposition of the Mueller matrix can retrieve the intrinsic values for and with reasonable accuracy. The ability of this approach to extract the indi- vidual intrinsic polarimetry characteristics should prove valuable in diagnostic photomedicine, for example, in quantifying the small opti- cal rotations due to the presence of glucose in tissue and for monitor- ing changes in tissue birefringence as a signature of tissue abnormality. © 2008 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2960934

Demixing light paths inside disordered metamaterials

Abstract: We experimentally demonstrate the first method to focus light inside disordered photonic metamaterials. In such materials, scattering prevents light from forming a geometric focus. Instead of geometric optics, we used multi-path interference to make the scattering process itself concentrate light on a fluorescent nanoscale probe at the target position. Our method uses the fact that the disorder in a solid material is fixed in time. Therefore, even disordered light scattering is deterministic. Measurements of the probes fluorescence provided the information needed to construct a specific linear combination of hundreds of incident waves, which interfere constructively at the probe.

Soft-Matter Characterization

Abstract: Progress in basic soft matter research is driven largely by the experimental techniques available. Much of the work is concerned with understanding them at the microscopic level, especially at the nanometer length scales that give soft matter studies a wide overlap with nanotechnology. This 2 volume reference work, split into 4 parts, presents detailed discussions of many of the major techniques commonly used as well as some of those in current development for studying and manipulating soft matter. The articles are intended to be accessible to the interdisciplinary audience (at the graduate student level and above) that is or will be engaged in soft matter studies or those in other disciplines who wish to view some of the research methods in this fascinating field. Part 1 contains articles with a largely (but, in most cases, not exclusively) theoretical content and/or that cover material relevant to more than one of the techniques covered in subsequent volumes. It includes an introductory chapter on some of the time and space-time correlation functions that are extensively employed in other articles in the series, a comprehensive treatment of integrated intensity (static) light scattering from macromolecular solutions, as well as articles on small angle scattering from micelles and scattering from brush copolymers. A chapter on block copolymers reviews the theory (random phase approximation) of these systems, and surveys experiments on them (including static and dynamic light scattering, small-angle x-ray and neutron scattering as well as neutron spin echo (NSE) experiments). This chapter describes block copolymer behavior in the "disordered phase" and also their self-organization. The volume concludes with a review of the theory and computer simulations of polyelectrolyte solutions. Part 2 contains material on dynamic light scattering, light scattering in shear fields and the related techniques of fluorescence recovery after photo bleaching (also called fluorescence photo bleaching recovery to avoid the unappealing acronym of the usual name), fluorescence fluctuation spectroscopy, and forced Rayleigh scattering. Volume 11 concludes with an extensive treatment of light scattering from dispersions of polysaccharides. Part 3 presents articles devoted to the use of x-rays and neutrons to study soft matter systems. It contains survey articles on both neutron and x-ray methods and more detailed articles on the study of specific systems- gels, melts, surfaces, polyelectrolytes, proteins, nucleic acids, block copolymers. It includes an article on the emerging x-ray photon correlation technique, the x-ray analogue to dynamic light scattering (photon correlation spectroscopy). Part 4 describes direct imaging techniques and methods for manipulating soft matter systems. It includes discussions of electron microscopy techniques, atomic force microscopy, single molecule microscopy, optical tweezers (with applications to the study of DNA, myosin motors, etc.), visualizing molecules at interfaces, advances in high contrast optical microscopy (with applications to imaging giant vesicles and motile cells), and methods for synthesizing and atomic force microscopy imaging of novel highly branched polymers.. Soft matter research is, like most modern scientific work, an international endeavor. This is reflected by the contributions to these volumes by leaders in the field from laboratories in nine different counties. An important contribution to the international flavor of the field comes, in particular, from x-ray and neutron experiments that commonly involve the use of a few large facilities that are multinational in their staff and user base.

Characterization of the Beam-Spread Function for Underwater Wireless Optical Communications Links

Abstract: Optical links are currently being considered for high-bandwidth underwater communications at short ranges (<100 m). To predict the performance of these links, a firm understanding of how the inherent optical properties of water affect the encoded optical signal is needed. Of particular interest is the impact of scattering due to particulates. Typically, the link loss is computed using the beam attenuation coefficient, which describes the attenuation of nonscattered light due to absorption and scattering. This approach is insufficient, as it neglects the contribution of scattered light to the total received signal. Given the dynamic nature of underwater platforms, as well as the dynamic nature of the environment itself, knowledge of the angular dependence of forward-scattered light is imperative for determining pointing and tracking requirements as well as overall signal to noise. In this work, the theory necessary to describe spatial spreading of an optical beam in the presence of scattering agents underwater is reviewed. This theory is then applied to a performance prediction model that is validated via laboratory experiments. Finally, the model is used to study the impact of spatial spreading on an underwater optical link.

Estimating and correcting mie scattering in synchrotron-based microscopic fourier transform infrared spectra by extended multiplicative signal correction.

Abstract: We present an approach for estimating and correcting Mie scattering occurring in infrared spectra of single cells, at diffraction limited probe size, as in synchrotron based microscopy. The Mie scattering is modeled by extended multiplicative signal correction (EMSC) and subtracted from the vibrational absorption. Because the Mie scattering depends non-linearly on α, the product of the radius and the refractive index of the medium/sphere causing it, a new method was developed for estimating the Mie scattering by EMSC for unknown radius and refractive index of the Mie scatterer. The theoretically expected Mie contributions for a range of different α values were computed according to the formulae developed by Van de Hulst (1957). The many simulated spectra were then summarized by a six-dimensional subspace model by principal component analysis (PCA). This subspace model was used in EMSC to estimate and correct for Mie scattering, as well as other additive and multiplicative interference effects. The approach was applied to a set of Fourier transform infrared (FT-IR) absorbance spectra measured for individual lung cancer cells in order to remove unwanted interferences and to estimate ranges of important α values for each spectrum. The results indicate that several cell components may contribute to the Mie scattering.

Low R_v from circumstellar dust around supernovae

Abstract: The effective extinction law for supernovae surrounded by circumstellar dust is examined by Monte-Carlo simulations. Grains with light scattering properties as for interstellar dust in the Milky-Way (MW) or the Large Magellanic Clouds (LMC), but surrounding the explosion site would cause a semi-diffusive propagation of light up to the edge of the dust shell. Multiple scattering of photons predominantly attenuates photons with shorter wavelengths, thus steepening the effective extinction law as compared to the case of single scattering in the interstellar medium. Our simulations yield typical values for the total to selective extinction ratio $R_V\sim 1.5-2.5$, as seen in recent studies of Type Ia supernova colors, with further stiffening differential extinction toward the near-UV.

Light scattering by random shaped particles and consequences on measuring suspended sediments by laser diffraction

Abstract: [1] We present new observational data on small-angle light scattering properties of natural, random shaped particles, as contrasted with spherical particles. The interest in this ‘‘shape effect’’ on scattering arises from the need for a suitable kernel matrix for use in the laser diffraction method (LD) of particle sizing. LD is now used broadly for measuring size distribution of suspended marine particles. LD involves the measurement of small-angle forward scattering at multiple angles. This data is inverted using the kernel matrix to produce size distribution. In the absence of a suitable matrix for random shaped particles, past practice has been to use a model based on Mie theory, applicable strictly only to homogeneous spheres. The present work replaces Mie theory with empirical data. The work was motivated in part by anomalous field observations of size distribution and settling velocity distributions reported in literature. We show that a kernel matrix for random shaped particles results in improved interpretation of field multiangle scattering observations. In particular, a rising edge at the fine particle end of the size spectrum is shown to be associated with shape effects.

Nobel Lecture: From spin waves to giant magnetoresistance and beyond *

Abstract: The “Institute for Magnetism” within the department for solid-state physics at the research center in Julich, Germany, which I joined in 1972, was founded in 1971 by Professor W. Zinn. The main research topic was the exploration of the model magnetic semiconductors EuO and EuS with Curie temperatures Tc=60 K and Tc =17 K, respectively. As I had been working with light scattering LS techniques before I came to Julich, I was very much interested in the observation of spin waves in magnetic materials by means of LS. LS can be performed with grating spectrometers, which is called Raman spectroscopy, and alternatively by Brillouin light scattering BLS spectroscopy. In the latter case, a Fabry-Perot FP interferometer is used for the frequency analysis of the scattered light see righthand side of Fig. 1 . The central part consists of two FP mirrors whose distance is scanned during operation. BLS spectroscopy is used when the frequency shift of the scattered light is small below 100 GHz , as expected for spin waves in ferromagnets. In the early 1970s, an interesting instrumental development took place in BLS, namely, the invention of the multipass operation, and later, the combination of two multipass interferometers in tandem. The inventor was Dr. J. A. Sandercock in Zurich. Since we had the opportunity to install a new laboratory, we decided in favor of BLS, initially using a single three-pass instrument as displayed on the righthand side of Fig. 1. With this, we started investigating spin waves in EuO. We indeed were able to find and identify the expected spin waves as shown by the peaks in Fig. 1 marked green . Different intensities on the Stokes S and antiStokes aS side were known from other work to be due to the magneto-optic interaction of light with the spin waves. The peaks marked red remained a puzzle for some time until good luck came to help us. Good luck in this case was a breakdown of the system, a repair and unintentional interchange of the leads when reconnecting the magnet to the power supply. To our surprise S and aS side were now reversed. To understand what this means, one has to know that classically S and aS scattering is related to the propagation direction of the observed mode, which is opposite for the two cases. This can be understood from the corresponding Doppler shift, which is to higher frequencies when the wave travels towards the observer and down when away from him. The position of the observer here would be the same as of the viewer in Fig. 1. The appearance of the red peak in the spectra on only either the S or the aS side can be explained by an unidirectional propagation of the corresponding spin wave along the surface of the sample. It can be reversed by reversing B0 and M. The unidirectional behavior of the wave can be understood on the basis of symmetry. For this, one has to know that axial vectors which appear in nature, such as B and M on the left-hand side of Fig. 1, reverse their sign under time inversion and so does the sense of the propagation of the surface wave as indicated. The upper and lower parts of Fig. 1, on the left-hand side therefore are linked by time inversion symmetry, which is valid without damping. Hence, the unidirectional behavior reflects the symmetry of the underlying system. Finally, the observed wave could be identified as the DamonEshbach DE surface mode known from theory and from microwave experiments. From the magnetic parameters of EuO, one predicts in the present case that the penetration depth of the DE mode will be a few 100 A. Sample thickness d is of the order of mm. Therefore, for the present purpose, EuO is opaque. In this case, the wave traveling on the backside of the sample in the opposite direction to the wave on the front side cannot be seen in this experiment. BLS is then either S or aS but not both at the same time. Due to all of these unique features, the results of Fig. 1 have also been chosen as examples for current research in magnetism in a textbook on “Solid State Physics” Ibach and Luth, 1995, p. 186 .

Photonic-Plasmonic Scattering Resonances in Deterministic Aperiodic Structures

Abstract: In this paper, we combine experimental dark-field scattering spectroscopy and accurate electrodynamics calculations to investigate the scattering properties of two-dimensional plasmonic lattices based on the concept of aperiodic order. In particular, by discussing visible light scattering from periodic, Fibonacci, Thue-Morse and Rudin-Shapiro lattices fabricated by electron-beam lithography on transparent quartz substrates, we demonstrate that deterministic aperiodic Au nanoparticle arrays give rise to broad plasmonic resonances spanning the entire visible spectrum. In addition, we show that far-field diffractive coupling is responsible for the formation of characteristic photonic-plasmonic scattering modes in aperiodic arrays of metal nanoparticles. Accurate scattering simulations based on the generalized Mie theory approach support our experimental results. The possibility of engineering complex metal nanoparticle arrays with distinctive plasmonic resonances extending across the entire visible spectrum can have a significant impact on the design and fabrication of novel nanodevices based on broadband plasmonic enhancement.

High-refractive-index TiO2-nanoparticle-loaded encapsulants for light-emitting diodes

Abstract: A high-refractive-index (high-n) encapsulant is highly desirable because it can result in enhancement of light-extraction efficiency from high-n semiconductor light-emitting diode (LED) chips. A uniform dispersion of TiO2 nanoparticles in epoxy for LED encapsulation is demonstrated for surfactant-coated TiO2 nanoparticles by drying, mixing with a solvent, refluxing, centrifuging, and mixing with epoxy. The refractive index of surfactant-coated TiO2-nanoparticle-loaded epoxy is 1.67 at 500nm, significantly higher than that of conventional epoxy (n=1.53). Theoretical analysis of optical scattering in nanoparticle-loaded encapsulants reveals that the diameter of nanoparticles and the volume loading fraction of nanoparticles are of critical importance for optical scattering. Quasispecular transparency of the encapsulant film can be achieved if the thickness of the film is kept below the optical scattering length. A graded-refractive-index multilayer encapsulation structure with the thickness of each layer bei...

Application of structured illumination for multiple scattering suppression in planar laser imaging of dense sprays.

Abstract: A novel approach to reduce the multiple light scattering contribution in planar laser images of atomizing sprays is reported. This new technique, named Structured Laser Illumination Planar Imaging (SLIPI), has been demonstrated in the dense region of a hollow-cone water spray generated in ambient air at 50 bars injection pressure. The idea is based on using an incident laser sheet which is spatially modulated along the vertical direction. By properly shifting the spatial phase of the modulation and using post-processing of the successive recorded images, the blurring effects from multiple light scattering can be mitigated. Since hollow-cone sprays have a known inner structure in the central region, the efficiency of the method could be evaluated. We demonstrate, for the case of averaged images, that an unwanted contribution of 44% of the detected light intensity can be removed. The suppression of this diffuse light enables an increase from 55% to 80% in image contrast. Such an improvement allows a more accurate description of the near-field region and of the spray interior. The possibility of extracting instantaneous flow motion is also shown, here, for a dilute flow of water droplets. These results indicate promising applications of the technique to denser two-phase flows such as air-blast atomizer and diesel sprays.

Fourier transform light scattering of inhomogeneous and dynamic structures.

Abstract: Fourier transform light scattering (FTLS) is a novel experimental approach that combines optical microscopy, holography, and light scattering for studying inhomogeneous and dynamic media. In FTLS the optical phase and amplitude of a coherent image field are quantified and propagated numerically to the scattering plane. Because it detects all the scattered angles (spatial frequencies) simultaneously in each point of the image, FTLS can be regarded as the spatial equivalent of Fourier transform infrared spectroscopy, where all the temporal frequencies are detected at each moment in time.

Nanoparticle-induced light scattering for improved performance of quantum-well solar cells

Abstract: We report on the improved performance of InP∕InGaAsP quantum-well waveguide solar cells via light scattering from deposited dielectric or metal nanoparticles. The integration of metal or dielectric nanoparticles above the quantum-well solar cell device is shown to couple normally incident light into lateral optical propagation paths, with optical confinement provided by the refractive index contrast between the quantum-well layers and surrounding material. With minimal optimization, short-circuit current density increases of 12.9% and 7.3% and power conversion efficiency increases of 17% and 1% are observed for silica and Au nanoparticles, respectively.

Electroluminescent device having improved light output

Abstract: An electroluminescent device including a transparent substrate, a securing layer, a light scattering layer, an electroluminescent unit including a transparent electrode layer, a light emitting element including at least one light emitting layer, and a reflecting electrode layer in that order, wherein the light scattering layer includes one monolayer of inorganic particles having an index of refraction larger than that of the light emitting layer and wherein the securing layer holds the inorganic particles in the light scattering layer.