Showing papers on "Light scattering published in 1999"
TL;DR: In this paper, the first observation of random laser action with coherent feedback in semiconductor powder was reported and the dependence of the lasing threshold intensity on the excitation volume agrees with the random laser theory.
Abstract: We report the first observation of random laser action with coherent feedback in semiconductor powder. Since the scattering mean free path is less than the emission wavelength, recurrent light scattering arises and provides coherent feedback for lasing. Discrete lasing modes have been observed above the threshold. The dependence of the lasing threshold intensity on the excitation volume agrees with the random laser theory. Laser emission from the powder could be observed in all directions. This observation also provides direct evidence for the existence of recurrent scattering of light.
1,441 citations
TL;DR: In this paper, a calibration of a recently developed filter-based instrument for continuous measurement of light absorption (model PSAP, Radiance Research, Seattle, WA) that has been incorporated in several measurement programs is presented.
Abstract: Data on light absorption by atmospheric particles are scarce relative to the need for global characterization. Most of the existing data come from methods that measure the change in light transmission through a filter on which particles are collected. We present a calibration of a recently developed filter-based instrument for continuous measurement of light absorption (model PSAP, Radiance Research, Seattle, WA) that has been incorporated in several measurement programs. This calibration uses a reference absorption determined as the difference between light extinction and light scattering by unaltered (suspended) particles. In addition, we perform the same calibration for two other common filter-based methods: an Integrating Plate and the Hybrid Integrating Plate System. For each method, we assess the responses to both particulate light scattering and particulate light absorption. We find that each of the instruments exhibits a significant response to nonabsorbing aerosols and overestimates absorption at...
936 citations
TL;DR: In this paper, a precise treatment of the diffuse intensity is derived which automatically includes the effects of boundary layers, and effects such as the enhanced backscatter cone and imaging of objects in opaque media are also discussed.
Abstract: important corrections are presented. These corrections are calculated with the radiative transfer or Schwarzschild-Milne equation, which describes intensity transport at the ‘‘mesoscopic’’ level and is derived from the ‘‘microscopic’’ wave equation. A precise treatment of the diffuse intensity is derived which automatically includes the effects of boundary layers. Effects such as the enhanced backscatter cone and imaging of objects in opaque media are also discussed within this framework. This approach is extended to mesoscopic correlations between multiple scattered intensities that arise when scattering is strong. These correlations arise from the underlying wave character. The derivation of correlation functions and intensity distribution functions is given and experimental data are discussed. Although the focus is on light scattering, the theory is also applicable to microwaves, sound waves, and noninteracting electrons. [S0034-6861(99)00601-7]
615 citations
TL;DR: In this article, a-Si/a-Si stacked solar cells were realized with initial efficiencies exceeding 10% in the long wavelength range, demonstrating an effective light trapping capability.
559 citations
TL;DR: In this paper, an overview of recent tests of the mode-coupling theory for the evolution of structural relaxation in glass-forming liquids is given, focusing on comparisons between the leading-order asymptotic formulae derived for the dynamics near glass transition singularities and the results of neutron scattering, depolarized light scattering, impulsive stimulated light scattering and dielectric-loss spectroscopy for conventional liquids.
Abstract: An overview is given of recent tests of the mode-coupling theory for the evolution of structural relaxation in glass-forming liquids. Emphasis is put on comparisons between the leading-order asymptotic formulae derived for the dynamics near glass transition singularities and the results of neutron scattering, depolarized light scattering, impulsive stimulated light scattering and dielectric-loss spectroscopy for conventional liquids. The tests based on photon-correlation spectroscopy results for the glassy dynamics of colloids and the findings of molecular dynamics simulations for model systems are also considered.
553 citations
TL;DR: Optical-property values for human skull, white matter, scar tissue, optic nerve, and tumors are reported that show distinct absorption and scattering differences between structures and a dependence on the phase-function parameter gamma.
Abstract: Local and superficial near-infrared (NIR) optical-property characterization of turbid biological tissues can be achieved by measurement of spatially resolved diffuse reflectance at small source-detector separations (<1.4 mm). However, in these conditions the inverse problem, i.e., calculation of localized absorption and the reduced scattering coefficients, is necessarily sensitive to the scattering phase function. This effect can be minimized if a new parameter of the phase function gamma, which depends on the first and the second moments of the phase function, is known. If gamma is unknown, an estimation of this parameter can be obtained by the measurement, but the uncertainty of the absorption coefficient is increased. A spatially resolved reflectance probe employing multiple detector fibers (0.3-1.4 mm from the source) is described. Monte Carlo simulations are used to determine gamma, the reduced scattering and absorption coefficients from reflectance data. Probe performance is assessed by measurements on phantoms, the optical properties of which were measured by other techniques [frequency domain photon migration (FDPM) and spatially resolved transmittance]. Our results show that changes in the absorption coefficient, the reduced scattering coefficient, and gamma can be measured to within +/-0.005 mm(-1), +/-0.05 mm(-1), and +/-0.2, respectively. In vivo measurements performed intraoperatively on a human skull and brain are reported for four NIR wavelengths (674, 811, 849, 956 nm) when the spatially resolved probe and FDPM are used. The spatially resolved probe shows optimum measurement sensitivity in the measurement volume immediately beneath the probe (typically 1 mm(3) in tissues), whereas FDPM typically samples larger regions of tissues. Optical-property values for human skull, white matter, scar tissue, optic nerve, and tumors are reported that show distinct absorption and scattering differences between structures and a dependence on the phase-function parameter gamma.
463 citations
TL;DR: In this paper, an in situ method of probing the structure of living epithelial cells, based on light scattering spectroscopy with polarized light, was proposed, which makes it possible to distinguish between single backscattering from uppermost epithelium cells and multiply scattered light.
Abstract: We report an in situ method of probing the structure of living epithelial cells, based on light scattering spectroscopy with polarized light. The method makes it possible to distinguish between single backscattering from uppermost epithelial cells and multiply scattered light. The spectrum of the single backscattering component can be further analyzed to provide histological information about the epithelial cells such as the size distribution of the cell nuclei and their refractive index. These are valuable quantities' to detect and diagnose precancerous changes in human tissues.
450 citations
TL;DR: Polarization-sensitive optical coherence tomography (PS-OCT) was used to characterize completely the polarization state of light backscattered from turbid media as discussed by the authors, which has potentially useful applications in biomedical optics by imaging simultaneously the structural properties of turbid biological materials.
Abstract: Polarization-sensitive optical coherence tomography (PS-OCT) was used to characterize completely the polarization state of light backscattered from turbid media. Using a low-coherence light source, one can determine the Stokes parameters of backscattered light as a function of optical path in turbid media. To demonstrate the application of this technique we determined the birefringence and the optical axis in fibrous tissue (rodent muscle) and in vivo rodent skin. PS-OCT has potentially useful applications in biomedical optics by imaging simultaneously the structural properties of turbid biological materials and their effects on the polarization state of backscattered light. This method may also find applications in material science for investigation of polarization properties (e.g., birefringence) in opaque media such as ceramics and crystals.
409 citations
TL;DR: Rayleigh scattering off a Bose-Einstein condensate was studied and resulted in the observation of highly directional scattering of light and atoms by a single off-resonant laser beam.
Abstract: Rayleigh scattering off a Bose-Einstein condensate was studied. Exposing an elongated condensate to a single off-resonant laser beam resulted in the observation of highly directional scattering of light and atoms. This collective light scattering is caused by the coherent center-of-mass motion of the atoms in the condensate. A directional beam of recoiling atoms was built up by matter wave amplification.
402 citations
TL;DR: FDTD and experimental results indicate that scattering properties are strongly influenced by cellular biochemical and morphological structure.
Abstract: We have examined the light-scattering properties of inhomogeneous biological cells through a combination of theoretical simulations and goniometric measurements. A finite-difference time-domain (FDTD) technique was used to compute intensity as a function of scattering angle for cells containing multiple organelles and spatially varying index of refraction profiles. An automated goniometer was constructed to measure the scattering properties of dilute cell suspensions. Measurements compared favorably with FDTD predictions. FDTD and experimental results indicate that scattering properties are strongly influenced by cellular biochemical and morphological structure.
TL;DR: In this paper, the structure factor of a Bose-Einstein condensate in the phonon regime was measured using small-angle light scattering, revealing the presence of correlated pair excitations and quantum depletion.
Abstract: Stimulated small-angle light scattering was used to measure the structure factor of a Bose-Einstein condensate in the phonon regime. The excitation strength for phonons was found to be significantly reduced from that of free particles, revealing the presence of correlated pair excitations and quantum depletion in the condensate. The Bragg resonance line strength and line shift agreed with predictions for the homogeneous Bose gas using a local density approximation.
Abstract: Electromagnetic band structure can produce either an enhancement or a suppression of spontaneous emission from two-dimensional (2-D) photonic crystal thin films. We believe that such effects might be important for light emitting diodes. Our experiments were based on thin-film InGaAs-InP 2-D photonic crystals at ambient temperature, but the concepts would apply equally to InGaN thin films, for example. We show that the magnitude of Purcell enhancement factor, F/sub p//spl sim/2, for spatially extended band modes, is similar to that for a tiny mode in a three dimensional (3-D) nanocavity. Nonetheless, light extraction enhancement that arises from Zone folding or Bragg scattering of the photonic bands is probably the more important effect, and an external quantum efficiency >50% is possible. Angle resolved photoluminescence from inside the photonic crystal gives a direct spectral readout of the internal 2-D photonic band dispersion. The tradeoffs for employing various photonic crystal structures in high efficiency light-emitting diodes are analyzed.
TL;DR: In this paper, the authors studied the thermoreversible gelation of methylcellulose in aqueous solution by static and dynamic light scattering (DLS), small-angle neutron scattering (SANS), and rheology.
Abstract: The thermoreversible gelation of methylcellulose in aqueous solution has been studied by static and dynamic light scattering (DLS), small-angle neutron scattering (SANS), and rheology. At 20 °C, dilute solution light scattering establishes the molecular weight, second virial coefficient, radius of gyration, and hydrodynamic radius of the polymer. Semidilute solutions exhibit two relaxation modes in DLS, one reflecting cooperative diffusion and the other attributable to pregel clusters. Rheological measurements in this regime also suggest a weak supermolecular association. The gelation of semidilute solutions proceeds in two stages with increasing temperature above 20 °C, consistent with previous reports. The first stage is attributable to clustering of chains, driven by hydrophobic association, and extends up to approximately 50 °C. This process is accompanied by an increase in the low-frequency dynamic elastic modulus, G‘, and an increase in both light and neutron scattered intensity. The DLS properties ...
TL;DR: In this paper, a model is presented that estimates the enhancement of optical absorption that can be obtained from light scattering in the porous nanocrystalline films used in these cells and from reflection at the back electrode.
TL;DR: In this article, a parametric model for radar scattering as a function of frequency and aspect angle is presented for analysis of synthetic aperture radar measurements and an image domain estimation algorithm is applied to two measured data examples.
Abstract: We present a parametric model for radar scattering as a function of frequency and aspect angle. The model is used for analysis of synthetic aperture radar measurements. The estimated parameters provide a concise, physically relevant description of measured scattering for use in target recognition, data compression and scattering studies. The scattering model and an image domain estimation algorithm are applied to two measured data examples.
TL;DR: Flow cytometry of fluorescently labeled and unlabeled latex particles is demonstrated on a microfabricated device and the results are found to be within experimental error of the expected ratios.
Abstract: Flow cytometry of fluorescently labeled and unlabeled latex particles is demonstrated on a microfabricated device. The latex particles were detected and counted using laser light scattering and fluorescence coincidence measurements. Sample confinement was accomplished using electrokinetic focusing at a cross intersection, and detection occurred 50 μm downstream from the intersection. Particles with diameters of 1 and 2 μm were analyzed and distinguished from each other based on their light scattering intensity and fluorescence. A maximum sample throughput of 34 particles/s was achieved. Sample mixtures with varying proportions of fluorescently labeled and unlabeled particles were also analyzed and found to be within experimental error of the expected ratios.
TL;DR: In this paper, the authors combine extinction and Resonance Light Scattering (RLS) measurements on the same samples of acidified tetrakis(4-sulfonatophenyl)porphine (H4TPPS).
Abstract: Resonance light scattering (RLS) on supramolecular assemblies of chromophores is a sensitive and selective method to extract size and shape information, but the interpretation of the data is complicated by the large amount of absorption present. By combining extinction and RLS measurements on the same samples of acidified tetrakis(4-sulfonatophenyl)porphine (H4TPPS), a technique is described whereby the scattering spectrum can be “corrected” for absorption. An additional benefit of this analysis is that the spectrum obtained for these solutions on a spectrophotometer, which is really an extinction spectrum, can be parsed into its absorption and scattering components. The results demonstrate that scattering contributes significantly to the aggregate peak in the extinction spectrum. Knowledge of the absorption and scattering components allows an estimation of the average aggregation number to be made, which for these solutions is on the order of 105−106. In addition, static and dynamic light scattering meas...
TL;DR: In this paper, metal nanoshells are used for the controllable redirection of electromagnetic radiation via careful engineering of their multilayer structures, which can focus, redirect, or split the incident light with subwavelength precision.
Abstract: Metal nanoshells are nanoscale optical components that allow for the controllable redirection of electromagnetic radiation via careful engineering of their multilayer structures. By varying the core size and shell thickness of these nanoparticles, nanoscale “antennas” are constructed that can be selectively driven into a dipolar or quadrupolar oscillation pattern. With scattering cross sections many times larger than their physical cross section, these antennas efficiently couple to the incident electromagnetic wave. These structures can focus, redirect, or split the incident light with subwavelength precision, and may find useful applications in the remote coupling of electromagnetic signals into nanoscale machines or devices.
TL;DR: In this article, the authors review the status of elastic light scattering, focusing on recent developments, rather than being over-repetitive of earlier reviews, but considerable background is included with the aim of making the paper self-contained.
TL;DR: The structure and internal dynamics of β-lactoglobulin aggregates formed after heat-induced denaturation at pH 2 and different ionic strengths were investigated using light, neutron, and X-ray scattering as discussed by the authors.
Abstract: The structure and internal dynamics of β-lactoglobulin aggregates formed after heat-induced denaturation at pH 2 and different ionic strengths were investigated using light, neutron, and X-ray scattering. Polydisperse aggregates are formed with a rigid rodlike local structure with mass per unit length close to that of a string of β-lactoglobulin monomers but with a somewhat larger diameter. The persistence length decreases with increasing ionic strength from more than 600 nm at 0.013 M to 38 nm at 0.1 M. At ionic strengths of 0.1 and 0.2 M, a self-similar structure with fractal dimensions of 1.8 and 2.0 is seen by using light scattering. The concentration dependence of the static structure factor and the internal dynamics are close to those of flexible linear chains. In contrast, a rigid behavior is observed at lower ionic strength (0.03 and 0.013 M). The persistence length of aggregates formed at 0.013 M is reduced after dilution in 0.1 and 0.2 M ionic strength solvents but remains larger than that of ag...
TL;DR: In this article, a multi-tau software correlator was used to measure dynamic light scattering at many angles simultaneously, from 0.07° to 5.1°, in order to cover the wide spectrum of decay times associated with the large range of accessible angles, where the correlator channel spacing is quasilogarithmic rather than linear.
Abstract: We use a charge coupled device (CCD) camera and a multi-tau software correlator to measure dynamic light scattering (DLS) at many angles simultaneously, from 0.07° to 5.1°. Real-time autocorrelation functions are calculated by averaging both over time and over CCD pixels, each corresponding to a different coherence area. In order to cover the wide spectrum of decay times associated with the large range of accessible angles, we adopt the multitau scheme, where the correlator channel spacing is quasilogarithmic rather than linear. A detailed analysis is presented of the effects of dark noise, stray light, and finite pixel area, and methods to correct the data for these effects are developed, making a CCD camera a viable alternative for a DLS detector. We test the apparatus on a dilute suspension of colloidal particles. Very good agreement is found between the particle radius derived from the CCD data, and that obtained with a conventional DLS setup.
TL;DR: In this paper, the size of a single droplet is continuously measured by analyzing the angle-resolved light scattering pattern of the droplets with classical Mie theory, and the freezing process is detected by a pronounced increase in the depolarization of the scattered light.
Abstract: Homogeneous nucleation rates are determined for micrometer sized water droplets levitated inside an electrodynamic Paul-trap. The size of a single droplet is continuously measured by analyzing the angle-resolved light scattering pattern of the droplets with classical Mie theory. The freezing process is detected by a pronounced increase in the depolarization of the scattered light. By statistical analysis of the freezing process of some thousand individual droplets, we obtained the homogeneous nucleation rate of water between 236 and 237 K. The values are in agreement with former expansion cloud chamber measurements but could be determined with considerably higher precision. The measurements are discussed in the light of classical nucleation theory in order to obtain the size and the formation energy of the critical nucleus.
TL;DR: A three-dimensional finite-difference time-domain program has been developed to provide a numerical solution for light scattering by nonspherical dielectric particles using the perfectly matched layer absorbing boundary condition (ABC) to truncate the computational domain.
Abstract: A three-dimensional finite-difference time-domain (FDTD) program has been developed to provide a numerical solution for light scattering by nonspherical dielectric particles. The perfectly matched layer (PML) absorbing boundary condition (ABC) is used to truncate the computational domain. As a result of using the PML ABC, the present FDTD program requires much less computer memory and CPU time than those that use traditional truncation techniques. For spheres with particle-size parameters as large as 40, the extinction and absorption efficiencies from the present FDTD program match the Mie results closely, with differences of less than ∼1%. The difference in the scattering phase function is typically smaller than ∼5%. The FDTD program has also been checked by use of the exact solution for light scattering by a pair of spheres in contact. Finally, applications of the PML FDTD to hexagonal particles and to spheres aggregated into tetrahedral structures are presented.
Patent•
19 Jul 1999
TL;DR: In this paper, the authors proposed a theoretical formula of Φ which represents a ratio of changes of optical densities of tissue measured with two wavelengths are not dependent on the wavelength and calculated an oxygen saturation by substituting Φ measured into simultaneous equations.
Abstract: Irradiating device 3 of a pulse oximeter includes a scattering plate 6. Scattering light is projected into a living tissue. The diameter of the incident area is sufficiently large compared with that of a light receiving area or vice versa. Therefore, tissue terms in a theoretical formula of Φ which represents a ratio of changes of optical densities of tissue measured with two wavelengths are not dependent on the wavelength. The digital processor 10 calculates an oxygen saturation by substituting Φ measured into simultaneous equations.
TL;DR: In this article, a combination of light scattering at a textured top surface and reflection on a backside mirror was proposed to achieve 22% external quantum efficiency of nonresonant cavity (NRC) light-emitting diodes.
Abstract: The external quantum efficiency of light-emitting diodes (LEDs) is usually limited by total internal reflection at the semiconductor–air interface. This problem can be overcome by a combination of light scattering at a textured top surface and reflection on a backside mirror. With this design, we achieve 22% external quantum efficiency. One of the main loss mechanisms in such nonresonant cavity (NRC) light-emitting diodes is coupling into an internal waveguide. Texturing the surface of this waveguide allows the partial extraction of the confined light. In this way, we demonstrate an increase in the external quantum efficiency of NRC-LEDs to 31%.
TL;DR: In this article, the scattering matrix method was applied to the analysis of finite two-dimensional photonic crystals and lightwave devices, and the light propagation in defect waveguides with abrupt bends, a branch and a directional coupler was demonstrated by this method.
Abstract: The scattering matrix method was applied to the analysis of finite two-dimensional photonic crystals and lightwave devices. Results indicated that 1) the light transmission at the photonic band gap (PBG) is suppressed to less than -30 dB in the densely packed and honeycomb crystals, both of which are composed of only four rows of unit cells of semiconductor columns and 2) this PBG effect is weakened to half when the nonuniformity from 10 to 30% is brought to the diameter of columns. Also, the light propagation in defect waveguides with abrupt bends, a branch and a directional coupler was demonstrated by this method. It was found that the coupling loss at the input end of the waveguide is drastically changed by the shape of the input end. The reflection loss at 600 bends was estimated to be less than 1 dB, and the excess loss at an abrupt Y-branch was estimated to be 0-4.6 dB, depending on the frequency of the input wave. The demultiplexing and power dividing functions were expected in a directional coupler with a submicron coupling length, which is considered to be due to antiguide characteristics of the waveguides.
TL;DR: A photo-assisted electrochemical etching technique to fabricate macropores in single-crystalline gallium phosphide with variable porosity with the highest scattering efficiency for visible light has been developed.
Abstract: A photo-assisted electrochemical etching technique to fabricate macropores in single-crystalline gallium phosphide (GaP) with variable porosity has been developed. Scanning electron microscopy and x-ray diffraction experiments confirm that the material consists of three-dimensional, interconnected random networks with pore sizes of about 150 nanometers. Optical transmission measurements demonstrate that the nonabsorbing disordered structures strongly scatter light. The photonic strength is controlled by filling the pores with liquids of different refractive indices. Macroporous gallium phosphide filled with air has the highest scattering efficiency for visible light.
TL;DR: In this article, the angular distribution of photoelectrons in isotropic solid state materials is interpreted in terms of the light scattering which peaks in the plane of light polarization is observed in glass pumped by intense laser radiation.
Abstract: Light scattering which peaks in the plane of light polarization is observed in glass pumped by intense laser radiation. The phenomenon is interpreted in terms of the angular distribution of photoelectrons in isotropic solid state materials.
TL;DR: It is shown that the intensity of the light scattered by the tungsten tip of an apertureless scanning near-field optical microscope is 2 orders of magnitude higher when the incident light is p polarized than when it is s polarized.
Abstract: Strong electric-field enhancements at the apex of a tungsten tip illuminated by an external light source were recently predicted theoretically. We present an experimental study of the dependence of this effect on the polarization angle of the incident light. It is shown that the intensity of the light scattered by the tungsten tip of an apertureless scanning near-field optical microscope is 2 orders of magnitude higher when the incident light is p polarized than when it is s polarized. This experimental result is in good agreement with theoretical predictions and provides an easy way to test the quality of the tips.