Showing papers in "Applied Optics in 2001"
TL;DR: A compact image-capturing system called TOMBO (an acronym for thin observation module by bound optics) is presented in which the compound-eye imaging system is utilized to achieve a thin optical configuration.
Abstract: A compact image-capturing system called TOMBO (an acronym for thin observation module by bound optics) is presented in which the compound-eye imaging system is utilized to achieve a thin optical configuration. The captured multiple images are processed to retrieve the image of the target object. For image retrieval, two kinds of processing method are considered: image sampling and backprojection. Computer simulations and preliminary experiments were executed on an evaluation system to verify the principles of the system and to clarify the issues related to its implementation.
636 citations
TL;DR: The method of cumulants is a standard technique used to analyze dynamic light-scattering data measured for polydisperse samples that does not permit independent determination of the long-time baseline of the intensity correlation function and can lead to inconsistent results when different numbers of data points are included in the fit.
Abstract: The method of cumulants is a standard technique used to analyze dynamic light-scattering data measured for polydisperse samples. These data, from an intensity–intensity autocorrelation function of the scattered light, can be described in terms of a distribution of decay rates. The method of cumulants provides information about the cumulants and the moments of this distribution. However, the method does not permit independent determination of the long-time baseline of the intensity correlation function and can lead to inconsistent results when different numbers of data points are included in the fit. The method is reformulated in terms of the moments about the mean to permit more robust and satisfactory fits. The different versions of the method are compared by analysis of the data for polydisperse-vesicle samples.
520 citations
TL;DR: A photonic device based on a high-finesse, whispering-gallery-mode disk resonator that can be used for the detection of biological pathogens and formulas are presented that allow the sensitivity of the device to be quantified and that show that, under optimum conditions, as few as 100 molecules can be detected.
Abstract: We describe a photonic device based on a high-finesse, whispering-gallery-mode disk resonator that can be used for the detection of biological pathogens. This device operates by means of monitoring the change in transfer characteristics of the disk resonator when biological materials fall onto its active area. High sensitivity is achieved because the light wave interacts many times with each pathogen as a consequence of the resonant recirculation of light within the disk structure. Specificity of the detected substance can be achieved when a layer of antibodies or other binding material is deposited onto the active area of the resonator. Formulas are presented that allow the sensitivity of the device to be quantified and that show that, under optimum conditions, as few as 100 molecules can be detected.
451 citations
TL;DR: The Tropospheric Emission Spectrometer (TES) is an imaging infrared Fourier-transform spectrometer scheduled to be launched into polar Sun-synchronous orbit aboard the Earth Observing System's Aura satellite in June 2003 as mentioned in this paper.
Abstract: The Tropospheric Emission Spectrometer (TES) is an imaging infrared Fourier-transform spectrometer scheduled to be launched into polar Sun-synchronous orbit aboard the Earth Observing System’s Aura satellite in June 2003. The primary objective of the TES is to make global three-dimensional measurements of tropospheric ozone and of the physical–chemical factors that control its formation, destruction, and distribution. Such an ambitious goal requires a highly sophisticated cryogenic instrument operating over a wide frequency range, which, in turn, demands state-of-the-art infrared detector arrays. In addition, the measurements require an instrument that can operate in both nadir and limb-sounding modes with a precision pointing system. The way in which these mission objectives flow down to the specific science and measurement requirements and in turn are implemented in the flight hardware are described. A brief overview of the data analysis approach is provided.
368 citations
TL;DR: This work discusses image formation in phase-shifting digital holography by developing an analytical formulation based on the Fresnel-Kirchhoff diffraction theory that is derived for general configurations in which a spherical reference is employed.
Abstract: We discuss image formation in phase-shifting digital holography by developing an analytical formulation based on the Fresnel-Kirchhoff diffraction theory. Image-plane position and imaging magnification are derived for general configurations in which a spherical reference is employed. The influences of discrete sampling of the resulting interference patterns by a CCD and numerical reconstruction on qualities of point images are investigated. Dependence of the point images on the ratio of the minimum fringe spacing to pixel pitch of the CCD is numerically analyzed. Two-point resolution and magnification are also investigated as a function of pixel numbers by a simulation using a one-dimensional model. In experiments magnified images of biological objects and a resolution target were reconstructed with the same quality as by conventional microscopy.
367 citations
TL;DR: An approach to modeling the ocean's inherent optical properties (IOPs) that permits extensive analyses of IOPs as the detailed composition of suspended particulate matter is varied in a controlled manner is described.
Abstract: We describe an approach to modeling the ocean's inherent optical properties (IOPs) that permits extensive analyses of IOPs as the detailed composition of suspended particulate matter is varied in a controlled manner. Example simulations of the IOP model, which includes 18 planktonic components covering a size range from submicrometer viruses and heterotrophic bacteria to microplanktonic species of 30-mum cell diameter, are discussed. Input data to the model include the spectral optical cross sections on a per particle basis and the particle-number concentration for each individual component. This approach represents a significant departure from traditional IOP and bio-optical models in which the composition of seawater is described in terms of a few components only or chlorophyll concentration alone. The simulations illustrate how the separation and understanding of the effects of various types of particle present within a water body can be achieved. In an example simulation representing an oligotrophic water body with a chlorophyll a concentration of 0.18 mg m(-3), the planktonic microorganisms altogether are the dominant particulate component in the process of light absorption, but their relative contribution to light scattering is smaller than that of nonliving particles. A series of simulations of water bodies with the same chlorophyll a concentration but dominated by different phytoplankton species shows that composition of the planktonic community is an important source of optical variability in the ocean.
357 citations
TL;DR: This method introduces a single-mode continuous-wave laser into the cavity by use of an off-axis cavity alignment geometry to eliminate systematically the resonances commonly associated with optical cavities, while preserving the absorption signal amplifying properties of such cavities.
Abstract: A simple and easy to use method that allows high-finesse optical cavities to be used as absorption cells for spectroscopic purposes is presented. This method introduces a single-mode continuous-wave laser into the cavity by use of an off-axis cavity alignment geometry to eliminate systematically the resonances commonly associated with optical cavities, while preserving the absorption signal amplifying properties of such cavities. This considerably reduces the complexity of the apparatus compared with other high-resolution cavity-based absorption methods. Application of this technique in conjunction with either cavity ringdown spectroscopy or integrated cavity output spectroscopy produced absorption sensitivities of 1.5 x 10(-9) cm(-1) Hz(-1/2) and 1.8 x 10(-10) cm(-1) Hz(-1/2), respectively.
339 citations
TL;DR: Computational results demonstrate that an absorbing medium significantly affects the scattering of light by a sphere and derives absorption and scattering efficiencies by using the near field at the surface of the particle.
Abstract: Analytic equations are developed for the single-scattering properties of a spherical particle embedded in an absorbing medium, which include absorption, scattering, extinction efficiencies, the scattering phase function, and the asymmetry factor. We derive absorption and scattering efficiencies by using the near field at the surface of the particle, which avoids difficulty in obtaining the extinction based on the optical theorem when the far field is used. Computational results demonstrate that an absorbing medium significantly affects the scattering of light by a sphere.
310 citations
TL;DR: There are two reasons for the tight correlation between observed scattering near 120 degrees and the backscattering coefficient reported by Oishi, namely, that the shape of the VSF of particles does not vary much near that angle for particle assemblages of differing optical properties and size.
Abstract: We revisit the problem of computing the backscattering coefficient based on the measurement of scattering at one angle in the back direction. Our approach uses theory and new observations of the volume scattering function (VSF) to evaluate the choice of angle used to estimate bb. We add to previous studies by explicitly treating the molecular backscattering of water (bbw) and its contribution to the VSF shape and to bb. We find that there are two reasons for the tight correlation between observed scattering near 120° and the backscattering coefficient reported by Oishi [Appl. Opt.29, 4658, (1990)], namely, that (1) the shape of the VSF of particles (normalized to the backscattering) does not vary much near that angle for particle assemblages of differing optical properties and size, and (2) the ratio of the VSF to the backscattering is not sensitive to the contribution by water near this angle. We provide a method to correct for the water contribution to backscattering when single-angle measurements are used in the back direction (for angles spanning from near 90° to 160°) that should provide improved estimates of the backscattering coefficient.
284 citations
TL;DR: Experimental evidence is presented demonstrating the validity of a photon-migration-based picture-based approach for extracting the intrinsic fluorescence for a wide range of scatterer and absorber concentrations in tissue models, ex vivo and in vivo tissues.
Abstract: The fluorescence from a turbid medium such as biologic tissue contains information about scattering and absorption, as well as the intrinsic fluorescence, i.e., the fluorescence from an optically thin sample of pure fluorophores. The interplay of scattering and absorption can result in severe distortion of the intrinsic spectral features. These distortions can be removed by use of a photon-migration-based picture and information from simultaneously acquired fluorescence and reflectance spectra. We present experimental evidence demonstrating the validity of such an approach for extracting the intrinsic fluorescence for a wide range of scatterer and absorber concentrations in tissue models, ex vivo and in vivo tissues. We show that variations in line shape and intensity in intrinsic tissue fluorescence are significantly reduced compared with the corresponding measured fluorescence.
258 citations
TL;DR: The experimental technique is described, measurements that complement the results of light scattering are described, and the structure and the dynamics of colloidal gels, glasses, and binary fluids are characterized in qualitatively new ways.
Abstract: Confocal microscopy is used in the study of colloidal gels, glasses, and binary fluids. We measure the three-dimensional positions of colloidal particles with a precision of approximately 50 nm ~a small fraction of each particle’s radius! and with a time resolution sufficient for tracking the thermal motions of several thousand particles at once. This information allows us to characterize the structure and the dynamics of these materials in qualitatively new ways, for example, by quantifying the topology of chains and clusters of particles as well as by measuring the spatial correlations between particles with high mobilities. We describe our experimental technique and describe measurements that complement the results of light scattering. © 2001 Optical Society of America OCIS codes: 110.2960, 110.0180, 180.1790.
TL;DR: The model to provide a good fit for the range of parameters most often encountered in the ocean, and it is found that the particulate attenuation spectrum, c(p)(lambda), is well described by a hyperbolic relation to the wavelength c( p) ?
Abstract: The link between the spectral shape of the beam attenuation spectrum and the
shape of the particle size distribution (PSD) of oceanic particles is revisited to
evaluate the extent to which one can be predicted from the other. Assuming a
hyperbolic (power-law) PSD, N(D) ∝ D-ξ, past studies have found for an
infinite distribution of nonabsorbing spheres with a constant index of refraction
that the attenuation spectrum is hyperbolic and that the attenuation spectral slope
γ is related to the PSD slope ξ by ξ = γ + 3. Here we add a correction to this model
because of the finite size of the biggest particle in the population. This inversion
model is given by ξ = γ + 3 - 0.5 exp(-6γ). In most oceanic observations ξ > 3,
and the deviation between these two models is negligible. To test the robustness of
this inversion, we perturbed its assumptions by allowing for populations of
particles that are nonspherical, or absorbing, or with an index of refraction that
changes with wavelength. We found the model to provide a good fit for the range of
parameters most often encountered in the ocean. In addition, we found that the
particulate attenuation spectrum, cp(λ), is well described by a
hyperbolic relation to the wavelength cp ∝ λ-γ throughout the
range of the investigated parameters, even when the inversion model does not apply.
This implies that knowledge of the particulate attenuation at two visible
wavelengths could provide, to a high degree of accuracy, the particulate attenuation
at other wavelengths in the visible spectrum.
TL;DR: The artificial resonances of dielectric optical cavities can be used to enhance the detection sensitivity of evanescent-wave optical fluorescence biosensors to the binding of a labeled analyte with a biospecific monolayer.
Abstract: We show that the artificial resonances of dielectric optical cavities can be used to enhance the detection sensitivity of evanescent-wave optical fluorescence biosensors to the binding of a labeled analyte with a biospecific monolayer. Resonant coupling of power into the optical cavity allows for efficient use of the long photon lifetimes (or equivalently, the high internal power) of the high-Q whispering gallery modes to increase the probability of photon absorption into the fluorophore, thereby enhancing fluorescence emission. A method to compare the intrinsic sensitivity between resonant cavity and waveguide formats is also developed. Using realistic estimates for dielectric cylindrical cavities in both bulk and integrated configurations, we can expect sensitivity enhancement by at least an order of magnitude over standard waveguide evanescent sensors of equivalent sensing geometries. In addition, the required sample volume can be reduced significantly. The cylindrical cavity format is compatible with a large variety of sensing modalities such as immunoassay and molecular diagnostic assay.
TL;DR: It is shown that, although sun glint contamination has a minor effect on retrieving ocean color products, the effect on retrieved atmospheric products, e.g., aerosol optical thickness, is significant and the derived ocean and atmospheric products are improved.
Abstract: For remote sensing of the ocean and atmosphere optical properties, the measurement of radiances affected by sun glint has to be avoided and/or masked out. There are usually no meaningful retrievals in regions significantly contaminated by sun glint. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) is capable of operationally tilting the sensor 20 degrees away from nadir to minimize sun glint contamination. The sun glint mask is computed from the Cox and Munk model [J. Opt. Soc. Am. 44, 838-850 (1954)] and applied to the SeaWiFS data. However, sun glint is still a factor near the subsolar point. We present results that demonstrate the effect of sun glint contamination on retrievals of ocean bio-optical and atmospheric products. We show that, although sun glint contamination has a minor effect on retrieved ocean color products, the effect on retrieved atmospheric products, e.g., aerosol optical thickness, is significant. We describe a sun glint correction scheme implemented in the SeaWiFS data-processing system and compare the results with and without sun glint correction. With sun glint correction the derived ocean and atmospheric products are improved. Also, the sun glint masked area can be reduced and therefore can increase significantly the coverage area near the subsolar point.
TL;DR: It is shown that one can exploit the spectral curvature information in the measured optical depth to permit a direct estimation of a fine-mode (submicrometer) Angström exponent (alpha(f)) as well as the optical fraction of fine- mode particles (eta).
Abstract: The classical Angstrom exponent is an operationally robust
optical parameter that contains size information on all optically
active aerosols in the field of view of a sunphotometer. Assuming
that the optical effects of a typical (radius) size distribution
can be approximated by separate submicrometer and supermicrometer
components, we show that one can exploit the spectral curvature
information in the measured optical depth to permit a direct estimation
of a fine-mode (submicrometer) Angstrom exponent
(αf) as well as the optical
fraction of fine-mode particles (η). Simple expressions that
enable the estimation of these parameters are presented and tested by
use of simulations and measurements.
TL;DR: The system is capable of imaging test microstructures with high resolution at sufficient working distances to permit good illumination of samples and achieves high imaging capacity and exhibits properties that are favorable for micromeasurement.
Abstract: We propose an in-line digital microscopic holography system for testing of microstructures. With the incorporation of a long-distance microscope with digital holography, the system is capable of imaging test microstructures with high resolution at sufficient working distances to permit good illumination of samples. The system, which was developed in an in-line configuration, achieves high imaging capacity and exhibits properties that are favorable for micromeasurement. We demonstrate the performance of the system with experiments to determine the displacement of a silicon microcantilever and with investigations of the microscopic resolution capability.
TL;DR: A VCSEL-based sensor for oxygen gas temperature distributions that exhibits a fast time response and can be adapted to probe a variety of species over a range of temperatures and pressures, it shows promise for industrial application.
Abstract: Line-of-sight diode-laser absorption techniques have been extended to enable temperature measurements in nonuniform-property flows. The sensing strategy for such flows exploits the broad wavelength-scanning abilities (>1.7 nm approximately 30 cm(-1)) of a vertical cavity surface-emitting laser (VCSEL) to interrogate multiple absorption transitions along a single line of sight. To demonstrate the strategy, a VCSEL-based sensor for oxygen gas temperature distributions was developed. A VCSEL beam was directed through paths containing atmospheric-pressure air with known (and relatively simple) temperature distributions in the 200-700 K range. The VCSEL was scanned over ten transitions in the R branch of the oxygen A band near 760 nm and optionally over six transitions in the P branch. Temperature distribution information can be inferred from these scans because the line strength of each probed transition has a unique temperature dependence; the measurement accuracy and resolution depend on the details of this temperature dependence and on the total number of lines scanned. The performance of the sensing strategy can be optimized and predicted theoretically. Because the sensor exhibits a fast time response (~30 ms) and can be adapted to probe a variety of species over a range of temperatures and pressures, it shows promise for industrial application.
TL;DR: Two methods of displaying autostereoscopic three-dimensional images by integral photography are described and compared from the viewpoints of lateral resolution, depth resolution, and viewing angle.
Abstract: We describe and compare two methods of displaying autostereoscopic three-dimensional images by integral photography. One method is to display the image in front of the lens array, and the other method is to display the image behind the lens array. We compare and discuss these two methods from the viewpoints of lateral resolution, depth resolution, and viewing angle. We also discuss the effect of the optical parameter difference in the pickup and display.
TL;DR: Drag force measurements and atomic force microscope scans demonstrate that, when added to a MR fluid, nonmagnetic abrasives are driven toward the workpiece surface because of the gradient in the magnetic field and hence become responsible for material removal.
Abstract: Recent advances in the study of the magnetorheological finishing (MRF) have allowed for the characterization of the dynamic yield stress of the magnetorheological (MR) fluid, as well as the nanohardness (H(nano)) of the carbonyl iron (CI) used in MRF. Knowledge of these properties has allowed for a more complete study of the mechanisms of material removal in MRF. Material removal experiments show that the nanohardness of CI is important in MRF with nonaqueous MR fluids with no nonmagnetic abrasives, but is relatively unimportant in aqueous MR fluids or when nonmagnetic abrasives are present. The hydrated layer created by the chemical effects of water is shown to change the way material is removed by hard CI as the MR fluid transitions from a nonaqueous MR fluid to an aqueous MR fluid. Drag force measurements and atomic force microscope scans demonstrate that, when added to a MR fluid, nonmagnetic abrasives (cerium oxide, aluminum oxide, and diamond) are driven toward the workpiece surface because of the gradient in the magnetic field and hence become responsible for material removal. Removal rates increase with the addition of these polishing abrasives. The relative increase depends on the amount and type of abrasive used.
TL;DR: Simulations, performed with a two-dimensional finite-difference time-domain technique with a perfectly matched layer absorbing boundary condition, showed the ability to filter an incident pulse into six spectral channels with a FWHM of 2 nm.
Abstract: A multichannel wavelength-division-multiplexing system consisting of a two-dimensional photonic crystal is proposed. The system consists of two parts, a waveguiding element, realized by defects in a photonic crystal, and frequency-selective elements, realized by photonic crystal microcavities. Simulations, performed with a two-dimensional finite-difference time-domain technique with a perfectly matched layer absorbing boundary condition, showed the ability to filter an incident pulse into six spectral channels with a FWHM of 2 nm.
TL;DR: A spectroscopic gas sensor for nitric oxide (NO) detection based on a cavity ringdown technique was designed and evaluated and future improvements are discussed that would allow quantification of NO in human breath.
Abstract: A spectroscopic gas sensor for nitric oxide (NO) detection based on a cavity ringdown technique was designed and evaluated. A cw quantum-cascade distributed-feedback laser operating at 5.2 mum was used as a tunable single-frequency light source. Both laser-frequency tuning and abrupt interruptions of the laser radiation were performed through manipulation of the laser current. A single ringdown event sensitivity to absorption of 2.2 x 10(-8) cm(-1) was achieved. Measurements of parts per billion (ppb) NO concentrations in N(2) with a 0.7-ppb standard error for a data collection time of 8 s have been performed. Future improvements are discussed that would allow quantification of NO in human breath.
TL;DR: Measurement of optical transport parameters of normal and malignant (ductal carcinoma) human breast tissue and the Mie equivalent average radius of tissue scatterers is estimated to be larger in malignant tissue than in normal tissue.
Abstract: We report measurement of optical transport parameters of normal and malignant (ductal carcinoma) human breast tissue. A spatially resolved steady-state diffuse reflectance technique was used for measurement of the reduced scattering coefficient (mu(s)?) and the absorption coefficient (mu(a)) of the tissue. The anisotropy parameter of scattering (g) was estimated by goniophotometric measurements of the scattering phase function. The values of mu(s)? and mu(a) for malignant breast tissue were observed to be larger than those for normal breast tissue over the wavelength region investigated (450-650 nm). Further, by using both the diffuse reflectance and the goniophotometric measurements, we estimated the Mie equivalent average radius of tissue scatterers to be larger in malignant tissue than in normal tissue.
TL;DR: A technique for improved carrier generation by eliminating the instability of a mechanical device in favor of an electro-optical phase modulator in the reference arm of an optical coherence tomography system achieves stable and reproducible interference fringe generation and permits phase-resolved digital data processing.
Abstract: We present a technique for improved carrier generation by eliminating the instability of a mechanical device in favor of an electro-optical phase modulator in the reference arm of an optical coherence tomography system. A greater than threefold reduction in the phase variance between consecutive A-line scans at a repetition rate of 1 kHz was achieved. Stable and reproducible interference fringe generation permits phase-resolved digital data processing. A correction algorithm was applied to the interferometric signal to compensate for the departure of the source spectrum from an ideal Gaussian shape, resulting in up to 8-dB sidelobe suppression at the expense of a 1-dB increase in the noise floor. In addition, we could eliminate completely the broadening effect of group-delay dispersion on the coherence function by introducing a quadratic phase shift in the Fourier domain of the interferometric signal.
TL;DR: A best fit to water and chlorophyll absorption line shapes and to Mie theory permitted the estimation of water andchlorophyll content and the average size of scattering centers in the bulk of intact fruits.
Abstract: Time-resolved reflectance spectroscopy can be used to assess nondestructively the bulk (rather than the superficial) optical properties of highly diffusive media. A fully automated system for time-resolved reflectance spectroscopy was used to evaluate the absorption and the transport scattering spectra of fruits in the red and the near-infrared regions. In particular, data were collected in the range 650-1000 nm from three varieties of apples and from peaches, kiwifruits, and tomatoes. The absorption spectra were usually dominated by the water peak near 970 nm, whereas chlorophyll was detected at 675 nm. For all species the scattering decreased progressively with increasing wavelength. A best fit to water and chlorophyll absorption line shapes and to Mie theory permitted the estimation of water and chlorophyll content and the average size of scattering centers in the bulk of intact fruits.
TL;DR: It is shown that it is possible to improve the linearity and fringe accuracy of certain standard interferometers by a modification of the Fourier filter, and a dual CPI system is proposed for the unambiguous mapping of phase to intensity over the complete input phase range.
Abstract: We have developed an analytical model for the design and optimization of common-path interferometers (CPI's) based on spatial filtering. We describe the mathematical analysis in detail and show how its application to the optimization of a range of different CPI's results in the development of a graphical framework to characterize quantitatively CPI performance. A detailed analytical treatment of the effect of curvature in the synthetic reference wave is undertaken. We show that it is possible to improve the linearity and fringe accuracy of certain standard interferometers by a modification of the Fourier filter, and we propose and analyze a dual CPI system for the unambiguous mapping of phase to intensity over the complete input phase range.
TL;DR: A 32-channel time-resolved imaging device for medical optical tomography has been employed to evaluate a scheme for imaging the human female breast and the reconstruction procedure has been tested on a conical phantom with tissue-equivalent optical properties.
Abstract: A 32-channel time-resolved imaging device for medical optical tomography has been employed to evaluate a scheme for imaging the human female breast. The fully automated instrument and the reconstruction procedure have been tested on a conical phantom with tissue-equivalent optical properties. The imaging protocol has been designed to obviate compression of the breast and the need for coupling fluids. Images are generated from experimental data with an iterative reconstruction algorithm that employs a three-dimensional (3D) finite-element diffusion-based forward model. Embedded regions with twice the background optical properties are revealed in separate 3D absorption and scattering images of the phantom. The implications for 3D time-resolved optical tomography of the breast are discussed.
TL;DR: The multiple scattering of light by aqueous foams is systematically studied as a function of wavelength, bubble size, and liquid fraction and the transport mean free path is found to be proportional to the bubble diameter and the reciprocal of the square root of liquid fraction.
Abstract: The multiple scattering of light by aqueous foams is systematically studied as a function of wavelength, bubble size, and liquid fraction. Results are analyzed in terms of the transport mean free path of the photons and an extrapolation length ratio for the diffuse photon concentration field. The wavelength dependence is minimal and may be attributed entirely to the wavelength dependence of the refractive index of water rather than thin-film interference effects. The transport mean free path is found to be proportional to the bubble diameter and the reciprocal of the square root of liquid fraction. The extrapolation length ratio varies almost linearly with liquid fraction between the values for water-glass-air and air-glass-air interfaces.
TL;DR: This work has calculated an effective Mueller matrix that, when operating on any incident state of light, will yield the output state and compared the results for several simple two-layer turbid systems separated by a dielectric interface.
Abstract: For single scattering in a turbid medium, the Mueller matrix is the 4 x 4 matrix that multiplies the incident Stokes vector to yield the scattered Stokes vector. This matrix contains all the information that can be obtained from an elastic-scattering system. We have extended this concept to the multiple-scattering domain where we can define an effective Mueller matrix that, when operating on any incident state of light, will yield the output state. We have calculated this matrix using two completely different computational methods and compared the results for several simple two-layer turbid systems separated by a dielectric interface. We have shown that both methods give reliable results and therefore can be used to accurately predict the scattering properties of turbid media.
TL;DR: A simple method of manufacturing micrometer-sized polymer elements at the extremity of both single-mode and multimode optical fibers is reported and it is shown that the tip geometry can be adjusted by the variation of basic parameters such as the geometry of the deposited drop and the conditions of drop illumination.
Abstract: A simple method of manufacturing micrometer-sized polymer elements at the extremity of both single-mode and multimode optical fibers is reported. The procedure consists of depositing a drop of a liquid photopolymerizable formulation on a cleaved fiber and using the light that emerges from the fiber to induce the polymerization process. After exposure and rinsing a polymer tip is firmly attached to the fiber as an extension of the fiber core. It is shown that the tip geometry can be adjusted by the variation of basic parameters such as the geometry of the deposited drop and the conditions of drop illumination. When this process is applied to a multimode fiber three-dimensional molds of the fiber’s linearly polarized modes can be obtained. The process of polymer-tip formation was simulated by a numerical calculation that consisted of an iterative beam-propagation method in a medium whose refractive index is time varying. It is shown that this process is based on the gradual growth, just above the fiber core, of an optical waveguide in the liquid formulation. Experimental data concerning two potential uses of the tipped fibers are presented.
TL;DR: A specially developed method is proposed to retrieve the particle volume distribution, the mean refractive index, and other important physical parameters, e.g., the effective radius, volume, surface area, and number concentrations of tropospheric and stratospheric aerosols from optical data by use of multiple wavelengths.
Abstract: A specially developed method is proposed to retrieve the particle volume distribution, the mean refractive index, and other important physical parameters, e.g., the effective radius, volume, surface area, and number concentrations of tropospheric and stratospheric aerosols, from optical data by use of multiple wavelengths. This algorithm requires neither a priori knowledge of the analytical shape of the distribution nor an initial guess of the distribution. As a result, even bimodal and multimodal distributions can be retrieved without any advance knowledge of the number of modes. The nonlinear ill-posed inversion is achieved by means of a hybrid method combining regularization by discretization, variable higher-order B-spline functions and a truncated singular-value decomposition. The method can be used to handle different lidar devices that work with various values and numbers of wavelengths. It is shown, to my knowledge for the first time, that only one extinction and three backscatter coefficients are sufficient for the solution. Moreover, measurement errors up to 20% are allowed. This result could be achieved by a judicious fusion of different properties of three suitable regularization parameters. Finally, numerical results with an additional unknown refractive index show the possibility of successfully recovering both unknowns simultaneously from the lidar data: the aerosol volume distribution and the refractive index.