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Light Propagation (light + propagation)

Distribution by Scientific Domains

Physics and Astronomy	44%
Chemistry	22%

Selected Abstracts

Light propagation in multi-step index optical fibres

LASER & PHOTONICS REVIEWS, Issue 3 2008
J. Zubia
Abstract This paper reviews the theoretical analysis of light propagation we have carried out on multimode multi-step index (MSI) optical fibres. Starting from the Eikonal equation, we derive the analytical expressions that allow calculating the ray trajectories inside these fibres. We also analyse the effects of leaky rays on the transmission properties of MSI fibres. For this purpose, a single analytical expression for the evaluation of the ray power transmission coefficient is calculated. Afterwards, we investigate the effects of extrinsic and intrinsic coupling losses on the performance of MSI fibres, providing analytical expressions to calculate the coupling loss and, also, determining the most critical parameters. Finally, we carry out a comprehensive numerical analysis of the fibre bandwidth under different source configurations. [source]

Light propagation and scattering in porous silicon nanocomposite waveguides

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2005
P. Pirasteh
Abstract Planar waveguides have been achieved from oxidised porous silicon layers (OPS) which have been impregnated by solvents, Congo Red (CR) dye and poly(p-phenylene vinylene) (PPV) polymer. Optical loss has been investigated by a simple technique based on surface optical scattering measurements. Optical loss has been studied as a function of the wavelength, impregnation type and CR concentration. The main sources of attenuation, such as absorption, scattering from interface roughness, scattering from nano- crystallites and modification of the refractive indexes after filling are discussed. Optical loss measured at 0.633 µm is about 1.8 dB/cm for the OPS waveguides The optical loss decreases with wavelength. Otherwise, the optical loss increases with the concentration of Congo Red dye which is absorbent at this wavelength. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Light propagation in a coupled waveguide-triple quantum well structure

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008
M. Yamaguchi
Abstract The light propagation in a waveguide which was weakly coupled to a quantum well (QW) structure was studied to demonstrate the detectability of the electronic states in the small area of QW. The small area of QW was made with a GaAs/AlGaAs asymmetric triple QW. Since the electronic states in the triple QW were easily controlled by an electric field which was induced by an optical injection, we observed the optical spectra obtained from the waveguide under the various intensities of optical injection. The spectral change was observed around the characteristic wavelengths of the QW. In order to verify the observed spectral change, we measured the optical spectra of the traveling wave in a sample whose QW surface has been etched off. By comparing the results, we interpreted that the spectral change is due to the reconstruction of the electronic states in the small area of QW due to the optically excited carriers. This proves the detection of small electronic state changes in the small area of QW with the traveling light in the waveguide. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Empirical preprocessing methods and their impact on NIR calibrations: a simulation study

JOURNAL OF CHEMOMETRICS, Issue 2 2005
S. N. Thennadil
Abstract The extraction of chemical information from dense particulate suspensions, such as industrial slurries and biological suspensions, using near-infrared (NIR) spectroscopic measurements is complicated by sample-to-sample path length variations due to light scattering. Empirical preprocessing techniques such as multiplicative scatter correction (MSC), extended MSC and derivatives have been applied to remove these effects and in some cases have shown promise. While the performance of these techniques and other related approaches is known to depend on the nature and extent of the variations and on the measurement configuration, detailed investigations into the efficacy of these approaches under various conditions have not been previously undertaken. The main obstacle to carrying out such investigations has been the lack of, and the difficulty in obtaining, an accurate and comprehensive experimental data set. In this work, simulations that generate ,actual' measurements were carried out to obtain ,experimental' spectroscopic data on particulate systems. This was achieved by solving the exact transport equation for light propagation. A model system comprising four chemical components with one consisting of spherical submicron particles was considered. Total diffuse transmittance and reflectance data generated through simulations for moderate particle concentrations were used as the basis for examining the effect of particle size variations and measurement configurations on the efficacy of a number of preprocessing techniques in enhancing the performance of partial least squares (PLS) models for predicting the concentration of one of the non-scattering chemical species. Additionally, a form of extended multiplicative signal correction based on considerations arising from fundamental light scattering theory is proposed and found to perform better than the other techniques for the cases considered in the study. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Measurement of low-dose active pharmaceutical ingredient in a pharmaceutical blend using frequency-domain photon migration

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2004
Tianshu Pan
Abstract Frequency-domain photon migration (FDPM) measurements of time-dependent light propagation are conducted to provide the powder absorbance for quantitative prediction of terazosin as the active pharmaceutical ingredient (API) in a low-dose (0.72 wt %) oral tablet formulation. Calibration of the FDPM-derived powder absorbance at discrete wavelengths of 514, 650, 687, and 785 nm was performed for API contents ranging between 0 and 1.5 wt % in mixtures showing maximum sensitivity at 650 nm. The relative standard deviation (RSD) of FDPM absorption coefficient measurement at 650 nm in a well-mixed 1.08 wt % terazosin blend was <1.6%, of which no more than 0.12% arose from FDPM instrumental error and the remainder was attributable to the complete-random-mixture model. The applicability of FDPM as an on-line sensor for powder-blending operations was further evaluated by analyzing grab samples taken directly from five locations of a 2-cu-ft Gallay blender at intervals of 5 min within the blending process. FDPM results indicate that homogeneity was largely achieved in the first 10 min, during which the RSD of API content across five sampling locations decreased from 27% to 8%, and the RSD decreased to 5% after 25 min of blending. Evolution of homogeneity within the blending process assessed through FDPM measurements was fit to the first-order model of particle blending further evidencing applicability for monitoring powder-blending processes. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:635,645, 2004 [source]

Light propagation in multi-step index optical fibres

Optical properties of thin-film silicon solar cells with grating couplers

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2006
C. Haase
Abstract The effect of grating couplers on the optical properties of silicon thin-film solar cells was studied by a comparison of experimental results with numerical simulations. The thin-film solar cells studied are based on microcrystalline silicon (,c-Si:H) absorber layers of thickness in the micrometer range. To investigate the light propagation in these cells, especially in the red wavelength region, three-dimensional power loss profiles are simulated. The influence of different grating parametres,such as period size, groove height, and shape of the grating,was studied to gain more insight into the light propagation within thin-film silicon solar cells and to determine an optimized light trapping scheme. The effect of the TCO front and TCO back side layer thickness was investigated. The calculated quantum efficiencies and short-circuit current densities are in good agreement with the experimental data. The simulations predict further optimization criteria. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Experimental testing of a random medium optical model of porous silicon for photovoltaic applications

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 1 2001
A. A. Abouelsaood
We have developed a model for light propagation in porous silicon (PS) based on the theory of wave propagation in random media. The low porosity case is considered, with silicon being the host material assuming randomly distributed spherical voids as scattering particles. The specular and the diffuse part of the light could be determined and treated separately. The model is applied to the case in which porous silicon would be used as a diffuse back reflector in a thin-film crystalline silicon solar cell realized in an ultrathin (1,3,,m) epitaxially grown Si layer on PS. Three,layer structures (epi/PS/Si) have been fabricated by atmospheric pressure chemical vapor deposition (APCVD) of 150,1000 nm epitaxial silicon layers on silicon wafers of which 150,450 nm of the surface has been electrochemically etched. An excellent agreement is found between the experimentally measured reflection data in the 400,1000 nm wavelength range and those calculated using the proposed model. The values of the layer thickness agree, within a reasonable experimental error, with those obtained independently by cross,sectional transmission electron microscopy (XTEM) analysis. This provides an experimental verification of the random,medium approach to porous silicon in the low porosity case. The analysis shows that the epitaxial growth process has led to appreciable porosity decrease of an initially high,porosity layer from about 60% to 20,30%. Copyright © 2001 John Wiley & Sons, Ltd. [source]

3124: Algorithms and instrumentation for quantified retinal oximetry in a snapshot

ACTA OPHTHALMOLOGICA, Issue 2010
AR HARVEY
Purpose To develop an instrument and techniques for useful absolute and relative clinical oximetry of the retina. Methods A novel snapshot multispectral imaging system has been optimised for retinal oximetry. Eight monochromatic images of the retina are recorded with a field of view of 24 degrees. Algorithms calculate the absorption of light at each point along delineated blood vessels and for each of the eight wavebands. Data inversion using an analytical model for light propagation enables oximetry at along the blood vessels. Spectral inversion has been refined using ray tracing and Monte Carlo modelling of light propagation using a realistic phantom eye. Results A comparison of Monte Carlo modelling of light propagation in the phantom retina with recorded images for blood of various oxygenations indicates the influence of several unknowns, including scatter from optical surfaces within the ophthalmoscope and eye, the geometry of the blood vessels and eye, the optical constants of the ocular media and the complexity of light propagation in the retinal structure. Relative oximetry within the retina is possible with repeatability of about 1% in the phantom and 5% in a real eye but the influence of various systematic effects can introduce systematic differences between actual and calculated oxygenation that can significantly exceed these values. Conclusion Although oximetry using only a very small number of spectral bands is possible, this is prone to systematic errors that can effect both absolute and relative oximetry. The ability to record eight spectral images in a single snapshot offers promise to provide an enhanced clinically useful and validated oximetry technique. [source]