Method of bundling rods so as to form an optical fiber preform

DOEpatents

Kliner, Dahv A. V. [San Ramon, CA; Koplow, Jeffery P [Washington, DC

2004-03-30

The present invention provides a simple method for fabricating fiber-optic glass preforms having complex refractive index configurations and/or dopant distributions in a radial direction with a high degree of accuracy and precision. The method teaches bundling together a plurality of glass rods of specific physical, chemical, or optical properties and wherein the rod bundle is fused in a manner that maintains the cross-sectional composition and refractive-index profiles established by the position of the rods.

Retrieval of spheroid particle size distribution from spectral extinction data in the independent mode using PCA approach

NASA Astrophysics Data System (ADS)

Tang, Hong; Lin, Jian-Zhong

2013-01-01

An improved anomalous diffraction approximation (ADA) method is presented for calculating the extinction efficiency of spheroids firstly. In this approach, the extinction efficiency of spheroid particles can be calculated with good accuracy and high efficiency in a wider size range by combining the Latimer method and the ADA theory, and this method can present a more general expression for calculating the extinction efficiency of spheroid particles with various complex refractive indices and aspect ratios. Meanwhile, the visible spectral extinction with varied spheroid particle size distributions and complex refractive indices is surveyed. Furthermore, a selection principle about the spectral extinction data is developed based on PCA (principle component analysis) of first derivative spectral extinction. By calculating the contribution rate of first derivative spectral extinction, the spectral extinction with more significant features can be selected as the input data, and those with less features is removed from the inversion data. In addition, we propose an improved Tikhonov iteration method to retrieve the spheroid particle size distributions in the independent mode. Simulation experiments indicate that the spheroid particle size distributions obtained with the proposed method coincide fairly well with the given distributions, and this inversion method provides a simple, reliable and efficient method to retrieve the spheroid particle size distributions from the spectral extinction data.

Simultaneous identification of the low-field-induced tiny variation of complex refractive index for anisotropic and opaque magnetic-fluid thin film by a stable heterodyne Mach-Zehnder interferometer.

PubMed

Hong, Chin-Yih; Chieh, Jen-Jie; Yang, Shieh-Yueh; Yang, Hong-Chang; Horng, Herng-Er

2009-10-10

We use a heterodyne Mach-Zehnder interferometer to simultaneously and simply measure the complex refractive index by only normal incidence on the specimen, instead of using a complicated measurement procedure or instrument that only measures the real or imaginary part of the complex refractive index. To study the tiny variation of the complex refractive index, the small complex refractive-index variation of a rare-concentration magnetic-fluid thin film, due to a weak field of less than 200 Oe, was processed by this interferometer. We also present the wavelength trend of the complex refractive index of magnetic fluids to verify the appearance of the slight change in a small wavelength range.

Retrieval of the aerosol size distribution in the complex anomalous diffraction approximation

NASA Astrophysics Data System (ADS)

Franssens, Ghislain R.

This contribution reports some recently achieved results in aerosol size distribution retrieval in the complex anomalous diffraction approximation (ADA) to MIE scattering theory. This approximation is valid for spherical particles that are large compared to the wavelength and have a refractive index close to 1. The ADA kernel is compared with the exact MIE kernel. Despite being a simple approximation, the ADA seems to have some practical value for the retrieval of the larger modes of tropospheric and lower stratospheric aerosols. The ADA has the advantage over MIE theory that an analytic inversion of the associated Fredholm integral equation becomes possible. In addition, spectral inversion in the ADA can be formulated as a well-posed problem. In this way, a new inverse formula was obtained, which allows the direct computation of the size distribution as an integral over the spectral extinction function. This formula is valid for particles that both scatter and absorb light and it also takes the spectral dispersion of the refractive index into account. Some details of the numerical implementation of the inverse formula are illustrated using a modified gamma test distribution. Special attention is given to the integration of spectrally truncated discrete extinction data with errors.

Scattering and Absorption Properties of Polydisperse Wavelength-sized Particles Covered with Much Smaller Grains

NASA Technical Reports Server (NTRS)

Dlugach, Jana M.; Mishchenko, Michael I.; Mackowski, Daniel W.

2012-01-01

Using the results of direct, numerically exact computer solutions of the Maxwell equations, we analyze scattering and absorption characteristics of polydisperse compound particles in the form of wavelength-sized spheres covered with a large number of much smaller spherical grains.The results pertain to the complex refractive indices1.55 + i0.0003,1.55 + i0.3, and 3 + i0.1. We show that the optical effects of dusting wavelength-sized hosts by microscopic grains can vary depending on the number and size of the grains as well as on the complex refractive index. Our computations also demonstrate the high efficiency of the new superposition T-matrix code developed for use on distributed memory computer clusters.

Nondestructive measurement of the refractive index distribution of a glass molded lens by two-wavelength wavefronts.

PubMed

Sugimoto, Tomohiro

2016-10-01

This paper presents a nondestructive and non-exact-index-matching method for measuring the refractive index distribution of a glass molded lens with high refractivity. The method measures two-wavelength wavefronts of a test lens immersed in a liquid with a refractive index dispersion different from that of the test lens and calculates the refractive index distribution by eliminating the refractive index distribution error caused by the shape error of the test lens. The estimated uncertainties of the refractive index distributions of test lenses with n_d≈1.77 and n_d≈1.85 were 1.9×10^-5  RMS and 2.4×10^-5  RMS, respectively. I validated the proposed method by evaluating the agreement between the estimated uncertainties and experimental values.

Complex refractive index of Martian dust - Wavelength dependence and composition

NASA Technical Reports Server (NTRS)

Pang, K.; Ajello, J. M.

1977-01-01

The size distribution and complex refractive index of Martian dust-cloud particles observed in 1971 with the Mariner 9 UV spectrometer are determined by matching the observed single-scattering albedo and phase function with Mie-scattering calculations for size distributions of spheres. Values of phase function times single-scattering albedo are presented for 12 wavelength intervals in the range from 190 to 350 nm, and best-fit values are obtained for the absorption index. It is found that the absorption index of the dust particles increases with decreasing wavelength from 350 to about 210 nm and then drops off shortward of 210 nm, with a structural shoulder occurring in the absorption spectrum between 240 and 250 nm. A search for a candidate material that can explain the strong UV absorption yields TiO2, whose anatase polymorph has an absorption spectrum matching that of the Martian dust. The TiO2 content of the dust particles is estimated to be a few percent or less.

Determination of effective complex refractive index of a turbid liquid with surface plasmon resonance phase detection.

PubMed

Yingying, Zhang; Jiancheng, Lai; Cheng, Yin; Zhenhua, Li

2009-03-01

The dependence of the surface plasmon resonance (SPR) phase difference curve on the complex refractive index of a sample in Kretschmann configuration is discussed comprehensively, based on which a new method is proposed to measure the complex refractive index of turbid liquid. A corresponding experiment setup was constructed to measure the SPR phase difference curve, and the complex refractive index of turbid liquid was determined. By using the setup, the complex refractive indices of Intralipid solutions with concentrations of 5%, 10%, 15%, and 20% are obtained to be 1.3377+0.0005 i, 1.3427+0.0028 i, 1.3476+0.0034 i, and 1.3496+0.0038 i, respectively. Furthermore, the error analysis indicates that the root-mean-square errors of both the real and the imaginary parts of the measured complex refractive index are less than 5x10(-5).

A new fabrication technique for complex refractive micro-optical systems

NASA Astrophysics Data System (ADS)

Tormen, Massimo; Carpentiero, Alessandro; Ferrari, Enrico; Cabrini, Stefano; Cojoc, Dan; Di Fabrizio, Enzo

2006-01-01

We present a new method that allows to fabricate structures with tightly controlled three-dimensional profiles in the 10 nm to 100 μm scale range. This consists of a sequence of lithographic steps such as Electron Beam (EB) or Focused Ion Beam (FIB) lithography, alternated with isotropic wet etching processes performed on a quartz substrate. Morphological characterization by SEM and AFM shows that 3D structures with very accurate shape control and nanometer scale surface roughness can be realized. Quartz templates have been employed as complex system of micromirrors after metal coating of the patterned surface or used as stamps in nanoimprint, hot embossing or casting processes to shape complex plastic elements. Compared to other 3D micro and nanostructuring methods, in which a hard material is directly "sculptured" by energetic beams, our technique requires a much less intensive use of expensive lithographic equipments, for comparable volumes of structured material, resulting in dramatic increase of throughput. Refractive micro-optical elements have been fabricated and characterized in transmission and reflection modes with white and monochromatic light. The elements produce a distribution of sharp focal spots and lines in the three dimensional space, opening the route for applications of image reconstruction based on refractive optics.

Retrieving the aerosol complex refractive index using PyMieScatt: A Mie computational package with visualization capabilities

NASA Astrophysics Data System (ADS)

Sumlin, Benjamin J.; Heinson, William R.; Chakrabarty, Rajan K.

2018-01-01

The complex refractive index m = n + ik of a particle is an intrinsic property which cannot be directly measured; it must be inferred from its extrinsic properties such as the scattering and absorption cross-sections. Bohren and Huffman called this approach "describing the dragon from its tracks", since the inversion of Lorenz-Mie theory equations is intractable without the use of computers. This article describes PyMieScatt, an open-source module for Python that contains functionality for solving the inverse problem for complex m using extensive optical and physical properties as input, and calculating regions where valid solutions may exist within the error bounds of laboratory measurements. Additionally, the module has comprehensive capabilities for studying homogeneous and coated single spheres, as well as ensembles of homogeneous spheres with user-defined size distributions, making it a complete tool for studying the optical behavior of spherical particles.

Refractive laser beam shaping by means of a functional differential equation based design approach.

PubMed

Duerr, Fabian; Thienpont, Hugo

2014-04-07

Many laser applications require specific irradiance distributions to ensure optimal performance. Geometric optical design methods based on numerical calculation of two plano-aspheric lenses have been thoroughly studied in the past. In this work, we present an alternative new design approach based on functional differential equations that allows direct calculation of the rotational symmetric lens profiles described by two-point Taylor polynomials. The formalism is used to design a Gaussian to flat-top irradiance beam shaping system but also to generate a more complex dark-hollow Gaussian (donut-like) irradiance distribution with zero intensity in the on-axis region. The presented ray tracing results confirm the high accuracy of both calculated solutions and emphasize the potential of this design approach for refractive beam shaping applications.

Determination of Atmospheric Aerosol Characteristics from the Polarization of Scattered Radiation

NASA Technical Reports Server (NTRS)

Harris, F. S., Jr.; McCormick, M. P.

1973-01-01

Aerosols affect the polarization of radiation in scattering, hence measured polarization can be used to infer the nature of the particles. Size distribution, particle shape, real and absorption parts of the complex refractive index affect the scattering. From Lorenz-Mie calculations of the 4-Stokes parameters as a function of scattering angle for various wavelengths the following polarization parameters were plotted: total intensity, intensity of polarization in plane of observation, intensity perpendicular to the plane of observation, polarization ratio, polarization (using all 4-Stokes parameters), plane of the polarization ellipse and its ellipticity. A six-component log-Gaussian size distribution model was used to study the effects of the nature of the polarization due to variations in the size distribution and complex refractive index. Though a rigorous inversion from measurements of scattering to detailed specification of aerosol characteristics is not possible, considerable information about the nature of the aerosols can be obtained. Only single scattering from aerosols was used in this paper. Also, the background due to Rayleigh gas scattering, the reduction of effects as a result of multiple scattering and polarization effects of possible ground background (airborne platforms) were not included.

On-chip integrated optofluidic complex refractive index sensing using silicon photonic crystal nanobeam cavities.

PubMed

Zhang, Xingwang; Zhou, Guangya; Shi, Peng; Du, Han; Lin, Tong; Teng, Jinghua; Chau, Fook Siong

2016-03-15

Complex refractive index sensing is proposed and experimentally demonstrated in optofluidic sensors based on silicon photonic crystal nanobeam cavities. The sensitivities are 58 and 139 nm/RIU, respectively, for the real part (n) and the imaginary part (κ) of the complex refractive index, and the corresponding detection limits are 1.8×10(-5) RIU for n and 4.1×10(-6) RIU for κ. Moreover, the capability of the complex refractive index sensing method to detect the concentration composition of the ternary mixture is demonstrated without the surface immobilization of functional groups, which is impossible to realize with the conventional refractive index sensing scheme.

Measurement of refractive index profile of non-symmetric, complex silica preforms with high refractive index differences

NASA Astrophysics Data System (ADS)

Probostova, Jana; Slanicka, Jiri; Mrazek, Jan; Podrazky, Ondrej; Benda, Adam; Peterka, Pavel

2016-04-01

Refractive index profile measurement is a key instrument for characterization of optical properties of preforms, which are used for drawing of high-quality optical fibers. Common industrial optical preform analyzers have been designed for measurement of simple symmetric structures such as step-index or graded-index preforms with refractive index close to the silica (n=1.457 at 633 nm). However, these conditions are usually far from more complex structures used in fiber lasers or in fiber sensor area. Preforms for the drawing of advanced optical fibers, such as Bragg, microstructure or photonic crystal fibers, are usually constituted from stacks with non-symmetric internal structure or composed of alternating layers with high refractive index contrasts. In this paper we present comparison of refractive index profile measurements of simple as well as complex structures with high refractive index differences simulating the Bragg structures. Commercial Photon Kinetics 2600 preform analyzer was used for the refractive index profile measurements. A set of concentrically arranged silica tubes was welded to form a complex preforms. Free space between the tubes was filled by immersion with varying refractive indices to simulate the Bragg structure. Up to three tubes were used for the analysis and the refractive indices of immersion were changed from 1.4 to 1.5. When refractive index of immersion was independently measured the structure of preform was defined. Profiles of these "known" structures were compared to measured data processed by originally proposed algorithm. The work provides an extension of issues of refractive index profile measurements in non-symmetric complex silica structures by a commercial preform analyzer and proposes more convenient methods of numeric data processing.

Moment expansion for ionospheric range error

NASA Technical Reports Server (NTRS)

Mallinckrodt, A.; Reich, R.; Parker, H.; Berbert, J.

1972-01-01

On a plane earth, the ionospheric or tropospheric range error depends only on the total refractivity content or zeroth moment of the refracting layer and the elevation angle. On a spherical earth, however, the dependence is more complex; so for more accurate results it has been necessary to resort to complex ray-tracing calculations. A simple, high-accuracy alternative to the ray-tracing calculation is presented. By appropriate expansion of the angular dependence in the ray-tracing integral in a power series in height, an expression is obtained for the range error in terms of a simple function of elevation angle, E, at the expansion height and of the mth moment of the refractivity, N, distribution about the expansion height. The rapidity of convergence is heavily dependent on the choice of expansion height. For expansion heights in the neighborhood of the centroid of the layer (300-490 km), the expansion to N = 2 (three terms) gives results accurate to about 0.4% at E = 10 deg. As an analytic tool, the expansion affords some insight on the influence of layer shape on range errors in special problems.

Experimental investigation on the infrared refraction and extinction properties of rock dust in tunneling face of coal mine.

PubMed

Wang, Wenzheng; Wang, Yanming; Shi, Guoqing

2015-12-10

Comprehensive experimental research on the fundamental optical properties of dust pollution in a coal mine is presented. Rock dust generated in a tunneling roadway was sampled and the spectral complex refractive index within an infrared range of 2.5-25 μm was obtained by Fourier transform infrared spectroscopy measurement and Kramers-Kronig relation. Experimental results were validated to be consistent with equivalent optical constants simulated by effective medium theory based on component analysis of x-ray fluorescence, which illustrates that the top three mineral components are SiO2 (62.06%), Al2O3 (21.26%), and Fe2O3 (4.27%). The complex refractive index and the spatial distribution tested by a filter dust and particle size analyzer were involved in the simulation of extinction properties of rock dust along the tunneling roadway solved by the discrete ordinates method and Mie scattering model. The compared results illustrate that transmission is obviously enhanced with the increase of height from the floor but weakened with increasing horizontal distance from the air duct.

Complex refractive index of Martian dust - Mariner 9 ultraviolet observations

NASA Technical Reports Server (NTRS)

Pang, K.; Ajello, J. M.; Hord, C. W.; Egan, W. G.

1976-01-01

Mariner 9 ultraviolet spectrometer observations of the 1971 dust clouds obscuring the surface of Mars have been analyzed by matching the observed dust phase function with Mie scattering calculations for size distributions of homogeneous and isotropic material. Preliminary results indicate an effective particle radius of not less than 0.2. The real component of the index of refraction is not less than 1.8 at both 268 and 305 nm; corresponding values for the imagery component are 0.02 and 0.01. These values are consistent with those found by Mead (1970) for the visible and near-visible wavelengths. The refractive index and the absorption coefficient increase rapidly with decreasing wavelength in going from the visible to the ultraviolet, indicating the presence of an ultraviolet absorption band which may shield organisms from ultraviolet irradiation.

Fermat's principle and the formal equivalence of local light-ray rotation and refraction at the interface between homogeneous media with a complex refractive index ratio.

PubMed

Sundar, Bhuvanesh; Hamilton, Alasdair C; Courtial, Johannes

2009-02-01

We derive a formal description of local light-ray rotation in terms of complex refractive indices. We show that Fermat's principle holds, and we derive an extended Snell's law. The change in the angle of a light ray with respect to the normal of a refractive index interface is described by the modulus of the refractive index ratio; the rotation around the interface normal is described by the argument of the refractive index ratio.

[Measurement and analysis on complex refraction indices of pear pollen in infrared band].

PubMed

Li, Le; Hu, Yi-hua; Gu, You-lin; Chen, Wei; Zhao, Yi-zheng; Chen, Shan-jing

2015-01-01

Pollen is an important part of bioaerosols, and its complex refractive index is a crucial parameter for study on optical characteristics and detection, identification of bioaerosols. The reflection spectra of pear pollen within the 2. 5 - 15µm waveband were measured by squash method. Based on the measured data, the complex refractive index of pear pollen within the wave-band of 2. 5 to 15 µm was calculated by using Kramers-Kroning (K-K) relation, and calculation deviation about incident angle and different reflectivities at high and low frequencies.were analyzed. The results indicate that 18 degrees angle of incidence and different reflectivities at high and low frequencies have little effect on the results, and it is practicable to calculate the complex refractive index of pollen based on its reflection spectral data. The data of complex refractive index of pollen have some reference value for optical characteristics of pollen, detection and identification of bioaerosols.

Acoustic computer tomographic pyrometry for two-dimensional measurement of gases taking into account the effect of refraction of sound wave paths

NASA Astrophysics Data System (ADS)

Lu, J.; Wakai, K.; Takahashi, S.; Shimizu, S.

2000-06-01

The algorithm which takes into account the effect of refraction of sound wave paths for acoustic computer tomography (CT) is developed. Incorporating the algorithm of refraction into ordinary CT algorithms which are based on Fourier transformation is very difficult. In this paper, the least-squares method, which is capable of considering the refraction effect, is employed to reconstruct the two-dimensional temperature distribution. The refraction effect is solved by writing a set of differential equations which is derived from Fermat's theorem and the calculus of variations. It is impossible to carry out refraction analysis and the reconstruction of temperature distribution simultaneously, so the problem is solved using the iteration method. The measurement field is assumed to take the shape of a circle and 16 speakers, also serving as the receivers, are set around it isometrically. The algorithm is checked through computer simulation with various kinds of temperature distributions. It is shown that the present method which takes into account the algorithm of the refraction effect can reconstruct temperature distributions with much greater accuracy than can methods which do not include the refraction effect.

Radiation characteristics and effective optical properties of dumbbell-shaped cyanobacterium Synechocystis sp.

NASA Astrophysics Data System (ADS)

Heng, Ri-Liang; Pilon, Laurent

2016-05-01

This study presents experimental measurements of the radiation characteristics of unicellular freshwater cyanobacterium Synechocystis sp. during their exponential growth in F medium. Their scattering phase function at 633 nm average spectral absorption and scattering cross-sections between 400 and 750 nm were measured. In addition, an inverse method was used for retrieving the spectral effective complex index of refraction of overlapping or touching bispheres and quadspheres from their absorption and scattering cross-sections. The inverse method combines a genetic algorithm and a forward model based on Lorenz-Mie theory, treating bispheres and quadspheres as projected area and volume-equivalent coated spheres. The inverse method was successfully validated with numerically predicted average absorption and scattering cross-sections of suspensions consisting of bispheres and quadspheres, with realistic size distributions, using the T-matrix method. It was able to retrieve the monomers' complex index of refraction with size parameter up to 11, relative refraction index less than 1.3, and absorption index less than 0.1. Then, the inverse method was applied to retrieve the effective spectral complex index of refraction of Synechocystis sp. approximated as randomly oriented aggregates consisting of two overlapping homogeneous spheres. Both the measured absorption cross-section and the retrieved absorption index featured peaks at 435 and 676 nm corresponding to chlorophyll a, a peak at 625 nm corresponding to phycocyanin, and a shoulder around 485 nm corresponding to carotenoids. These results can be used to optimize and control light transfer in photobioreactors. The inverse method and the equivalent coated sphere model could be applied to other optically soft particles of similar morphologies.

Mixed effects modelling for glass category estimation from glass refractive indices.

PubMed

Lucy, David; Zadora, Grzegorz

2011-10-10

520 Glass fragments were taken from 105 glass items. Each item was either a container, a window, or glass from an automobile. Each of these three classes of use are defined as glass categories. Refractive indexes were measured both before, and after a programme of re-annealing. Because the refractive index of each fragment could not in itself be observed before and after re-annealing, a model based approach was used to estimate the change in refractive index for each glass category. It was found that less complex estimation methods would be equivalent to the full model, and were subsequently used. The change in refractive index was then used to calculate a measure of the evidential value for each item belonging to each glass category. The distributions of refractive index change were considered for each glass category, and it was found that, possibly due to small samples, members of the normal family would not adequately model the refractive index changes within two of the use types considered here. Two alternative approaches to modelling the change in refractive index were used, one employed more established kernel density estimates, the other a newer approach called log-concave estimation. Either method when applied to the change in refractive index was found to give good estimates of glass category, however, on all performance metrics kernel density estimates were found to be slightly better than log-concave estimates, although the estimates from log-concave estimation prossessed properties which had some qualitative appeal not encapsulated in the selected measures of performance. These results and implications of these two methods of estimating probability densities for glass refractive indexes are discussed. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

Phenomenological model to fit complex permittivity data of water from radio to optical frequencies.

PubMed

Shubitidze, Fridon; Osterberg, Ulf

2007-04-01

A general factorized form of the dielectric function together with a fractional model-based parameter estimation method is used to provide an accurate analytical formula for the complex refractive index in water for the frequency range 10(8)-10(16)Hz . The analytical formula is derived using a combination of a microscopic frequency-dependent rational function for adjusting zeros and poles of the dielectric dispersion together with the macroscopic statistical Fermi-Dirac distribution to provide a description of both the real and imaginary parts of the complex permittivity for water. The Fermi-Dirac distribution allows us to model the dramatic reduction in the imaginary part of the permittivity in the visible window of the water spectrum.

First-Principle Study of the Optical Properties of Dilute-P GaN1-xPx Alloys.

PubMed

Borovac, Damir; Tan, Chee-Keong; Tansu, Nelson

2018-04-16

An investigation on the optical properties of dilute-P GaN 1-x P x alloys by First-Principle Density Functional Theory (DFT) methods is presented, for phosphorus (P) content varying from 0% up to 12.5%. Findings on the imaginary and real part of the dielectric function are analyzed and the results are compared with previously reported theoretical works on GaN. The complex refractive index, normal-incidence reflectivity and birefringence are presented and a difference in the refractive index in the visible regime between GaN and GaNP alloys of ~0.3 can be engineered by adding minute amounts of phosphorus, indicating strong potential for refractive index tunability. The optical properties of the GaN 1-x P x alloys indicate their strong potential for implementation in various III-nitride-based photonic waveguide applications and Distributed Bragg Reflectors (DBR).

Determination of refractive index, size, and concentration of nonabsorbing colloidal nanoparticles from measurements of the complex effective refractive index.

PubMed

Márquez-Islas, Roberto; Sánchez-Pérez, Celia; García-Valenzuela, Augusto

2014-02-01

We describe a method for obtaining the refractive index (RI), size, and concentration of nonabsorbing nanoparticles in suspension from relatively simple optical measurements. The method requires measuring the complex effective RI of two dilute suspensions of the particles in liquids of different refractive indices. We describe the theoretical basis of the proposed method and provide experimental results validating the procedure.

Results of a comprehensive atmospheric aerosol-radiation experiment in the southwestern United States. I - Size distribution, extinction optical depth and vertical profiles of aerosols suspended in the atmosphere. II - Radiation flux measurements and

NASA Technical Reports Server (NTRS)

Deluisi, J. J.; Furukawa, F. M.; Gillette, D. A.; Schuster, B. G.; Charlson, R. J.; Porch, W. M.; Fegley, R. W.; Herman, B. M.; Rabinoff, R. A.; Twitty, J. T.

1976-01-01

Results are reported for a field test that was aimed at acquiring a sufficient set of measurements of aerosol properties required as input for radiative-transfer calculations relevant to the earth's radiation balance. These measurements include aerosol extinction and size distributions, vertical profiles of aerosols, and radiation fluxes. Physically consistent, vertically inhomogeneous models of the aerosol characteristics of a turbid atmosphere over a desert and an agricultural region are constructed by using direct and indirect sampling techniques. These results are applied for a theoretical interpretation of airborne radiation-flux measurements. The absorption term of the complex refractive index of aerosols is estimated, a regional variation in the refractive index is noted, and the magnitude of solar-radiation absorption by aerosols and atmospheric molecules is determined.

Qualitative identification of food materials by complex refractive index mapping in the terahertz range.

PubMed

Shin, Hee Jun; Choi, Sung-Wook; Ok, Gyeongsik

2018-04-15

We investigated the feasibility of qualitative food analysis using complex refractive index mapping of food materials in the terahertz (THz) frequency range. We studied optical properties such as the refractive index and absorption coefficient of food materials, including insects as foreign substances, from 0.2 to 1.3 THz. Although some food materials had a complex composition, their refractive indices were approximated with effective medium values, and therefore, they could be discriminated on the complex refractive index map. To demonstrate food quality inspection with THz imaging, we obtained THz reflective images and time-of-flight imaging of hidden defects in a sugar and milk powder matrix by using time domain THz pulses. Our results indicate that foreign substances can be clearly classified and detected according to the optical parameters of the foods and insects by using THz pulses. Copyright © 2017. Published by Elsevier Ltd.

Computer simulation of schlieren images of rotationally symmetric plasma systems: a simple method.

PubMed

Noll, R; Haas, C R; Weikl, B; Herziger, G

1986-03-01

Schlieren techniques are commonly used methods for quantitative analysis of cylindrical or spherical index of refraction profiles. Many schlieren objects, however, are characterized by more complex geometries, so we have investigated the more general case of noncylindrical, rotationally symmetric distributions of index of refraction n(r,z). Assuming straight ray paths in the schlieren object we have calculated 2-D beam deviation profiles. It is shown that experimental schlieren images of the noncylindrical plasma generated by a plasma focus device can be simulated with these deviation profiles. The computer simulation allows a quantitative analysis of these schlieren images, which yields, for example, the plasma parameters, electron density, and electron density gradients.

Fabrication of refractive index distributions in polymer using a photochemical reaction

NASA Astrophysics Data System (ADS)

Kada, Takeshi; Obara, Atsushi; Watanabe, Toshiyuki; Miyata, Seizo; Liang, Chuan Xin; Machida, Hideaki; Kiso, Koichi

2000-01-01

We demonstrate that a photochemical reaction can create various distributions of refractive index in polymer. When the polymer containing a photochemically active material is irradiated by UV light, the photochemical reaction which breaks the π-conjugated system in the material and decreases its linear polarizability can reduce refractive index of the polymer. We prepared a PMMA film added DMAPN ((4-N,N-dimethylaminophenyl)-N'-phenylnitrone) with a rate of 23 wt % by use of spin coating. Electronic structural change of DMAPN and refractive indices of the film before and after UV irradiation were evaluated by UV absorption spectra and m-line method, respectively. The UV irradiation decreased λmax at 380 nm in the absorption spectra, which is attributed to nitrone, and the refractive indices exponentially with irradiation time. The change of refractive indices reached 0.028. The refractive index profile upon depth of the film was investigated by measuring refractive indices of stacked DMAPN/PMMA films. When UV with a power of 10.7 mW/cm2 irradiated upon three stacked DMAPN/PMMA films for 35 s, variation of the refractive index change showed a quadratic profile. The refractive index profile with various irradiation time can be accounted with the combination of the chemical kinetics with the steady state approximation and Lambert-Beer's law. Thus, the photochemical reaction can be used to control the refractive index distribution in polymer.

Three-dimensional refractive index and fluorescence tomography using structured illumination (Conference Presentation)

NASA Astrophysics Data System (ADS)

Park, GwangSik; Shin, SeungWoo; Kim, Kyoohyun; Park, YongKeun

2017-02-01

Optical diffraction tomography (ODT) has been an emerging optical technique for label-free imaging of three-dimensional (3-D) refractive index (RI) distribution of biological samples. ODT employs interferometric microscopy for measuring multiple holograms of samples with various incident angles, from which the Fourier diffraction theorem reconstructs the 3-D RI distribution of samples from retrieved complex optical fields. Since the RI value is linearly proportional to the protein concentration of biological samples where the proportional coefficient is called as refractive index increment (RII), reconstructed 3-D RI tomograms provide precise structural and biochemical information of individual biological samples. Because most proteins have similar RII value, however, ODT has limited molecular specificity, especially for imaging eukaryotic cells having various types of proteins and subcellular organelles. Here, we present an ODT system combined with structured illumination microscopy which can measure the 3-D RI distribution of biological samples as well as 3-D super-resolution fluorescent images in the same optical setup. A digital micromirror device (DMD) controls the incident angle of the illumination beam for tomogram reconstruction, and the same DMD modulates the structured illumination pattern of the excitation beam for super-resolution fluorescent imaging. We first validate the proposed method for simultaneous optical diffraction tomographic imaging and super-resolution fluorescent imaging of fluorescent beads. The proposed method is also exploited for various biological samples.

Complex refractive index of starch acetate used as a biodegradable pigment and filler of paper

NASA Astrophysics Data System (ADS)

Karvinen, Petri; Oksman, Antti; Silvennoinen, Raimo; Mikkonen, Hannu

2007-05-01

Complex refractive index of strongly depolarizing starch acetate is investigated as a function of bulk package density, which is compulsory parameter in analysis of light scattering from nanoscale starch acetate pigments and fillers. The measurements were made using a laser-goniometer and spectrophotometer to gain data for refractive index analysis according to the Brewster's law and Fresnel equations. The real part of refractive index was verified by microscopic immersion method.

Quantification of scaling exponents and dynamical complexity of microwave refractivity in a tropical climate

NASA Astrophysics Data System (ADS)

Fuwape, Ibiyinka A.; Ogunjo, Samuel T.

2016-12-01

Radio refractivity index is used to quantify the effect of atmospheric parameters in communication systems. Scaling and dynamical complexities of radio refractivity across different climatic zones of Nigeria have been studied. Scaling property of the radio refractivity across Nigeria was estimated from the Hurst Exponent obtained using two different scaling methods namely: The Rescaled Range (R/S) and the detrended fluctuation analysis(DFA). The delay vector variance (DVV), Largest Lyapunov Exponent (λ1) and Correlation Dimension (D2) methods were used to investigate nonlinearity and the results confirm the presence of deterministic nonlinear profile in the radio refractivity time series. The recurrence quantification analysis (RQA) was used to quantify the degree of chaoticity in the radio refractivity across the different climatic zones. RQA was found to be a good measure for identifying unique fingerprint and signature of chaotic time series data. Microwave radio refractivity was found to be persistent and chaotic in all the study locations. The dynamics of radio refractivity increases in complexity and chaoticity from the Coastal region towards the Sahelian climate. The design, development and deployment of robust and reliable microwave communication link in the region will be greatly affected by the chaotic nature of radio refractivity in the region.

Observation of a Saharan dust outbreaks in the frame of the Convective and Orographically-induced Precipitation Study

NASA Astrophysics Data System (ADS)

Di Girolamo, Paolo; Summa, Donato; Bhawar, Rohini; Di Iorio, Tatiana; Caccaini, Marco; Veselovskii, Igor; Kolgotin, Alexey

2009-03-01

The Raman lidar system BASIL was operational in Achern (Supersite R, Lat: 48.64° N, Long: 8.06° E, Elev.: 140 m) in the frame of the Convective and Orographically-induced Precipitation Study. BASIL operated continuously over a period of approx. 36 hours from 06:22 UTC on 1 August to 18:28 UTC on 2 August 2007, to cover IOPs 13 a-b. In this timeframe the signature of a severe Saharan dust outbreak episode was captured. An inversion algorithm was used to retrieve particle size distribution parameters, i.e., mean and effective radius, number, surface area, and volume concentration, and complex refractive index, as well as the parameters of a bimodal particle size distribution, from the multi-wavelength lidar data of particle backscattering and extinction. The inversion method employs Tikhonov's inversion with regularization. Size distribution parameters are estimated as a function of altitude at different times during the dust outbreak event. Retrieval results reveal the dominance in the upper dust layer of a coarse mode with radii 3-4 μm. Number density and volume concentration are in the range 100-800 cm-3 and 5-40 μm3/cm3, respectively, while real and imaginary part of the complex refractive index are in the range 1.41-1.53 and 0.003-0.014, respectively.

Plasma Parameters From Reentry Signal Attenuation

DOE PAGES

Statom, T. K.

2018-02-27

This study presents the application of a theoretically developed method that provides plasma parameter solution space information from measured RF attenuation that occurs during reentry. The purpose is to provide reentry plasma parameter information from the communication signal attenuation. The theoretical development centers around the attenuation and the complex index of refraction. The methodology uses an imaginary index of the refraction matching algorithm with a tolerance to find suitable solutions that satisfy the theory. The imaginary matching terms are then used to determine the real index of refraction resulting in the complex index of refraction. Then a filter is usedmore » to reject nonphysical solutions. Signal attenuation-based plasma parameter properties investigated include the complex index of refraction, plasma frequency, electron density, collision frequency, propagation constant, attenuation constant, phase constant, complex plasma conductivity, and electron mobility. RF plasma thickness attenuation is investigated and compared to the literature. Finally, similar plasma thickness for a specific signal attenuation can have different plasma properties.« less

Plasma Parameters From Reentry Signal Attenuation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Statom, T. K.

This study presents the application of a theoretically developed method that provides plasma parameter solution space information from measured RF attenuation that occurs during reentry. The purpose is to provide reentry plasma parameter information from the communication signal attenuation. The theoretical development centers around the attenuation and the complex index of refraction. The methodology uses an imaginary index of the refraction matching algorithm with a tolerance to find suitable solutions that satisfy the theory. The imaginary matching terms are then used to determine the real index of refraction resulting in the complex index of refraction. Then a filter is usedmore » to reject nonphysical solutions. Signal attenuation-based plasma parameter properties investigated include the complex index of refraction, plasma frequency, electron density, collision frequency, propagation constant, attenuation constant, phase constant, complex plasma conductivity, and electron mobility. RF plasma thickness attenuation is investigated and compared to the literature. Finally, similar plasma thickness for a specific signal attenuation can have different plasma properties.« less

Controlling plasma distributions as driving forces for ion migration during fs laser writing

NASA Astrophysics Data System (ADS)

Teddy Fernandez, Toney; Siegel, Jan; Hoyo, Jesus; Sotillo, Belen; Fernandez, Paloma; Solis, Javier

2015-04-01

The properties of structures written inside dielectrics with high repetition rate femtosecond lasers are known to depend strongly on the complex interplay of a large number of writing parameters. Recently, ion migration within the laser-excited volume has been identified as a powerful mechanism for changing the local element distribution and producing efficient optical waveguides. In this work it is shown that the transient plasma distribution induced during laser irradiation is a reliable monitor for predicting the final refractive index distribution of the waveguide caused by ion migration. By performing in situ plasma emission microscopy during the writing process inside a La-phosphate glass it is found that the long axis of the plasma distribution determines the axis of ion migration, being responsible for the local refractive index increase. This observation is also valid when strong positive or negative spherical aberration is induced, greatly deforming the focal volume and inverting the index profile. Even subtle changes in the writing conditions, such as an inversion of the writing direction (quill writing effect), show up in the form of a modified plasma distribution, which manifests as a modified index distribution. Finally, it is shown that the superior control over the waveguide properties employing the slit shaping technique is caused by the more confined plasma distribution produced. The underlying reasons for this unexpected result are discussed in terms of non-linear propagation and heat accumulation.

Modelling the bidirectional reflectance distribution function (BRDF) of seawater polluted by an oil film.

PubMed

Otremba, Zbigniew; Piskozub, Jacek

2004-04-19

The Bi-directional Reflectance Distribution Function (BRDF) of both clean seawaters and those polluted with oil film was determined using the Monte Carlo radiative transfer technique in which the spectrum of complex refractive index of Romashkino crude oil and the optical properties of case II water for chosen wavelengths was considered. The BRDF values were recorded for 1836 solid angular sectors of throughout the upper hemisphere. The visibility of areas polluted with oil observed from various directions and for various wavelengths is discussed.

Computational determination of refractive index distribution in the crystalline cones of the compound eye of Antarctic krill (Euphausia superba).

PubMed

Gál, József; Miyazaki, Taeko; Meyer-Rochow, Victor Benno

2007-01-21

In order to understand how a compound eye channels light to the retina and forms an image, one needs to know the refractive index distribution in the crystalline cones. Direct measurements of the refractive indices require sections of fresh, unfixed tissue and the use of an interference microscope, but frequently neither is available. Using the eye of the Antarctic krill Euphausia superba (the main food of baleen whales) we developed a computational method to predict a likely refractive index distribution non-invasively from sections of fixed material without the need of an interference microscope. We used a computer model of the eye and calculated the most realistic spatial distribution of the refractive index gradient in the crystalline cone that would enable the eye to produce a sharp image on the retina. The animals are known to see well and on the basis of our computations we predict that for the eyes of the adult a maximum refractive index of 1.45-1.50 in the centre of the cone yields a better angular sensitivity and light absorption in a target receptor of the retina than if N(max) were 1.55. In juveniles with a narrower spatial separation between dioptric structures and retina, however, an N(max) of 1.50-1.55 gives a superior result. Our method to determine the most likely refractive index distribution in the cone without the need of fresh material and an interference microscope could be useful in the study of other invertebrate eyes that are known to possess good resolving power, but for a variety of reasons are not suitable for or will not permit direct refractive index measurements of their dioptric tissues to be taken.

UV-Vis-IR spectral complex refractive indices and optical properties of brown carbon aerosol from biomass burning

NASA Astrophysics Data System (ADS)

Sumlin, Benjamin J.; Heinson, Yuli W.; Shetty, Nishit; Pandey, Apoorva; Pattison, Robert S.; Baker, Stephen; Hao, Wei Min; Chakrabarty, Rajan K.

2018-02-01

Constraining the complex refractive indices, optical properties and size of brown carbon (BrC) aerosols is a vital endeavor for improving climate models and satellite retrieval algorithms. Smoldering wildfires are the largest source of primary BrC, and fuel parameters such as moisture content, source depth, geographic origin, and fuel packing density could influence the properties of the emitted aerosol. We measured in situ spectral (375-1047 nm) optical properties of BrC aerosols emitted from smoldering combustion of Boreal and Indonesian peatlands across a range of these fuel parameters. Inverse Lorenz-Mie algorithms used these optical measurements along with simultaneously measured particle size distributions to retrieve the aerosol complex refractive indices (m = n + iκ). Our results show that the real part n is constrained between 1.5 and 1.7 with no obvious functionality in wavelength (λ), moisture content, source depth, or geographic origin. With increasing λ from 375 to 532 nm, κ decreased from 0.014 to 0.003, with corresponding increase in single scattering albedo (SSA) from 0.93 to 0.99. The spectral variability of κ follows the Kramers-Kronig dispersion relation for a damped harmonic oscillator. For λ ≥ 532 nm, both κ and SSA showed no spectral dependency. We discuss differences between this study and previous work. The imaginary part κ was sensitive to changes in FPD, and we hypothesize mechanisms that might help explain this observation.

Refractive index variance of cells and tissues measured by quantitative phase imaging.

PubMed

Shan, Mingguang; Kandel, Mikhail E; Popescu, Gabriel

2017-01-23

The refractive index distribution of cells and tissues governs their interaction with light and can report on morphological modifications associated with disease. Through intensity-based measurements, refractive index information can be extracted only via scattering models that approximate light propagation. As a result, current knowledge of refractive index distributions across various tissues and cell types remains limited. Here we use quantitative phase imaging and the statistical dispersion relation (SDR) to extract information about the refractive index variance in a variety of specimens. Due to the phase-resolved measurement in three-dimensions, our approach yields refractive index results without prior knowledge about the tissue thickness. With the recent progress in quantitative phase imaging systems, we anticipate that using SDR will become routine in assessing tissue optical properties.

Experimental Determination of Infrared Extinction Coefficients of Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Spann, J. F., Jr.; Abbas, M. M.

1998-01-01

This technique is based on irradiating a single isolated charged dust particle suspended in balance by an electric field, and measuring the scattered radiation as a function of angle. The observed scattered intensity profile at a specific wavelength obtained for a dust particle of known composition is compared with Mie theory calculations, and the variable parameters relating to the particle size and complex refractive index are adjusted for a best fit between the two profiles. This leads to a simultaneous determination of the particle radius, the complex refractive index, and the scattering and extinction coefficients. The results of these experiments can be utilized to examine the IRAS and DIRBE (Diffuse Infrared Background Experiment) infrared data sets in order to determine the dust particle physical characteristics and distributions by using infrared models and inversion techniques. This technique may also be employed for investigation of the rotational bursting phenomena whereby large size cosmic and interplanetary particles are believed to fragment into smaller dust particles.

Retrieval of Spatio-temporal Distributions of Particle Parameters from Multiwavelength Lidar Measurements Using the Linear Estimation Technique and Comparison with AERONET

NASA Technical Reports Server (NTRS)

Veselovskii, I.; Whiteman, D. N.; Korenskiy, M.; Kolgotin, A.; Dubovik, O.; Perez-Ramirez, D.; Suvorina, A.

2013-01-01

The results of the application of the linear estimation technique to multiwavelength Raman lidar measurements performed during the summer of 2011 in Greenbelt, MD, USA, are presented. We demonstrate that multiwavelength lidars are capable not only of providing vertical profiles of particle properties but also of revealing the spatio-temporal evolution of aerosol features. The nighttime 3 Beta + 1 alpha lidar measurements on 21 and 22 July were inverted to spatio-temporal distributions of particle microphysical parameters, such as volume, number density, effective radius and the complex refractive index. The particle volume and number density show strong variation during the night, while the effective radius remains approximately constant. The real part of the refractive index demonstrates a slight decreasing tendency in a region of enhanced extinction coefficient. The linear estimation retrievals are stable and provide time series of particle parameters as a function of height at 4 min resolution. AERONET observations are compared with multiwavelength lidar retrievals showing good agreement.

Self-Referenced Method for Estimating Refractive Index and Absolute Absorption of Loose Semiconductor Powders

DOE PAGES

Huang, Huafeng; Colabello, Diane M.; Sklute, Elizabeth C.; ...

2017-04-23

The absolute absorption coefficient, α(E), is a critical design parameter for devices using semiconductors for light harvesting associated with renewable energy production, both for classic technologies such as photovoltaics and for emerging technologies such as direct solar fuel production. While α(E) is well-known for many classic simple semiconductors used in photovoltaic applications, the absolute values of α(E) are typically unknown for the complex semiconductors being explored for solar fuel production due to the absence of single crystals or crystalline epitaxial films that are needed for conventional methods of determining α(E). In this work, a simple self-referenced method for estimating bothmore » the refractive indices, n(E), and absolute absorption coefficients, α(E), for loose powder samples using diffuse reflectance data is demonstrated. In this method, the sample refractive index can be deduced by refining n to maximize the agreement between the relative absorption spectrum calculated from bidirectional reflectance data (calculated through a Hapke transform which depends on n) and integrating sphere diffuse reflectance data (calculated through a Kubleka–Munk transform which does not depend on n). This new method can be quickly used to screen the suitability of emerging semiconductor systems for light-harvesting applications. The effectiveness of this approach is tested using the simple classic semiconductors Ge and Fe 2O 3 as well as the complex semiconductors La 2MoO 5 and La 4Mo 2O 11. The method is shown to work well for powders with a narrow size distribution (exemplified by Fe 2O 3) and to be ineffective for semiconductors with a broad size distribution (exemplified by Ge). As such, it provides a means for rapidly estimating the absolute optical properties of complex solids which are only available as loose powders.« less

Refractive, corneal and ocular residual astigmatism: distribution in a German population and age-dependency - the Gutenberg health study.

PubMed

Schuster, Alexander Karl-Georg; Pfeiffer, Norbert; Schulz, Andreas; Hoehn, René; Ponto, Katharina A; Wild, Philipp S; Blettner, Maria; Beutel, Manfred E; Lackner, Karl J; Münzel, Thomas; Mirshahi, Alireza

2017-12-01

Worldwide, the most frequent cause of visual impairment is uncorrected refractive error. This analysis focused on the distribution and associations of refractive, corneal and ocular residual astigmatism. As part of the Gutenberg Health study, a population-based cross-sectional study was conducted in the general population of Germany. A comprehensive ophthalmological examination including refraction, tonometry, and Scheimpflug imaging of the anterior cornea (Pachycam) was performed. In addition to the magnitude and type (with-the-rule, against-the-rule, oblique) of the refractive or corneal astigmatism, we calculated the vector components (J 0 , J 45 ) of both astigmatisms and calculated the ocular residual astigmatism. We performed multiple quantile regression analysis to evaluate the factors associated with refractive, corneal and ocular residual astigmatisms. A total of 13,558 subjects (49% female) with a mean age of 54.0 years (range 35-74 years) were included in this study. The prevalence of refractive astigmatism (>1.0D) was 13.0% in right eyes and 12.0% in left eyes, and 85% of these subjects wore spectacles. The distribution of refractive astigmatism showed a two-peak distribution with high astigmatism for with-the-rule and against-the-rule astigmatism. The associated factors were corneal curvature, age and sex for the different astigmatisms (p < 0.001). We analyzed the prevalence of different astigmatisms within a European population. We confirmed a shift with aging from with-the-rule to against-the-rule astigmatism to refractive and corneal astigmatism. Astigmatism has a large impact on visual perception; more than 85% of people with astigmatism over one diopter wore glasses for distance vision.

Global scale variability of the mineral dust longwave refractive index from laboratory chamber experiments: re‒evaluation of its direct radiative effect

NASA Astrophysics Data System (ADS)

Di Biagio, C.; Formenti, P.; Balkanski, Y.; Caponi, L.; Cazaunau, M.; Pangui, E.; Journet, E.; Nowak, S.; Caquineau, S.; Andreae, M. O.; Kandler, K.; Saeed, T.; Piketh, S.; Seibert, D.; Williams, E.; Boucher, O.; Doussin, J. F.

2017-12-01

New measurements of the longwave complex refractive index (LW CRI) of mineral dust and its global variability were obtained in situ in the 4.2 m3CESAM simulation chamber at LISA (Laboratoire Interuniversitaire des Systemes Atmospheriques) in Créteil, France. Aerosols generated by mechanical shaking from nineteen natural soils with contrasted mineralogical composition were suspended in the chamber, where their LW extinction spectra (2-16 μm), size distribution, and mineralogical composition were measured. The CRI of the dust aerosol was obtained by optical calculations based upon the measured extinction spectrum and size distribution. Laboratory results indicate that the LW refractive index of dust strongly varies with the source region of emission in link with the changes of its mineralogy. In the 2-16 μm spectral range, the imaginary refractive index (k) is between 0.001 and 0.92, and the real part (n) in the range 0.84-1.94. The strength of the dust absorption at 7 and 11.4 µm depends on the amount of calcite within the samples, while the absorption between 8 and 14 µm is determined by the relative abundance of quartz and clays. A linear relationship between the magnitude of k at 7, 9.2, and 11.4 µm and the mass concentration of calcite and quartz absorbing at these wavelengths was found, which suggests that predictive rules could be established to estimate the LW refractive index of dust in specific bands based on an assumed or predicted mineralogical composition. Our observations also suggest that the LW CRI of dust does not change as a result of the loss of coarse particles by gravitational settling, so that a constant value can be assumed close to sources and following transport. This unprecedented dataset of refractive indices was used as input into the LMDZORINCA model coupled with the RRTM radiative transfer module in order to re‒evaluate the direct dust LW radiative effect. This represents a first attempt to use regional‒dependent values of the LW refractive indices rather than generic values in models. Results from the simulations indicate that with these new refractive indices the LW direct effect of dust is significantly smaller compared to most of the already published results.

Small and large particle limits of single scattering albedo for homogeneous, spherical particles

NASA Astrophysics Data System (ADS)

Moosmüller, H.; Sorensen, C. M.

2018-01-01

The aerosol single scattering albedo (SSA) is the dominant intensive particle parameter determining aerosols direct radiative forcing. For homogeneous spherical particles and a complex refractive index independent of wavelength, the SSA is solely dependent on size parameter (ratio of particle circumference and wavelength) and complex refractive index of the particle. Here, we explore this dependency for the small and large particle limits with size parameters much smaller and much larger than one. We show that in the small particle limit of Rayleigh scattering, a novel, generalized size parameter can be introduced that unifies the SSA dependence on particle size parameter independent of complex refractive index. In the large particle limit, SSA decreases with increasing product of imaginary part of the refractive index and size parameter, another generalized parameter, until this product becomes about one, then stays fairly constant until the imaginary part of the refractive index becomes comparable with the real part minus one. Beyond this point, particles start to acquire metallic character and SSA quickly increases with the imaginary part of the refractive index and approaches one.

Nature and Nurture: the complex genetics of myopia and refractive error

PubMed Central

Wojciechowski, Robert

2010-01-01

The refractive errors, myopia and hyperopia, are optical defects of the visual system that can cause blurred vision. Uncorrected refractive errors are the most common causes of visual impairment worldwide. It is estimated that 2.5 billion people will be affected by myopia alone with in the next decade. Experimental, epidemiological and clinical research has shown that refractive development is influenced by both environmental and genetic factors. Animal models have demonstrated that eye growth and refractive maturation during infancy are tightly regulated by visually-guided mechanisms. Observational data in human populations provide compelling evidence that environmental influences and individual behavioral factors play crucial roles in myopia susceptibility. Nevertheless, the majority of the variance of refractive error within populations is thought to be due to hereditary factors. Genetic linkage studies have mapped two dozen loci, while association studies have implicated more than 25 different genes in refractive variation. Many of these genes are involved in common biological pathways known to mediate extracellular matrix composition and regulate connective tissue remodeling. Other associated genomic regions suggest novel mechanisms in the etiology of human myopia, such as mitochondrial-mediated cell death or photoreceptor-mediated visual signal transmission. Taken together, observational and experimental studies have revealed the complex nature of human refractive variation, which likely involves variants in several genes and functional pathways. Multiway interactions between genes and/or environmental factors may also be important in determining individual risks of myopia, and may help explain the complex pattern of refractive error in human populations. PMID:21155761

About complex refractive index of black Si

NASA Astrophysics Data System (ADS)

Pinčík, Emil; Brunner, Robert; Kobayashi, Hikaru; Mikula, Milan

2017-12-01

The paper deals with the complex refractive index in the IR light region of two types of samples (i) as prepared black silicon, and (ii) thermally oxidized black silicon (BSi) nano-crystalline specimens produced both by the surface structure chemical transfer method using catalytic Ag evaporated spots (as prepared sample) and by the catalytic Pt catalytic mesh (thermally oxidized sample). We present, compare, and discuss the values of the IR complex refractive index obtained by calculation using the Kramers-Krönig transformation. Results indicate that small differences between optical properties of as prepared black Si and thermally oxidized BSi are given by: (i) - oxidation procedure, (ii) - thickness of the formed black Si layer, mainly, not by utilization of different catalytic metals, and by iii) the different thickness. Contamination of the surface by different catalytic metals contributes almost equally to the calculated values of the corresponding complex refractive index.

Survey of Radar Refraction Error Corrections

DTIC Science & Technology

2016-11-01

ELECTRONIC TRAJECTORY MEASUREMENTS GROUP RCC 266-16 SURVEY OF RADAR REFRACTION ERROR CORRECTIONS DISTRIBUTION A: Approved for...DOCUMENT 266-16 SURVEY OF RADAR REFRACTION ERROR CORRECTIONS November 2016 Prepared by Electronic...This page intentionally left blank. Survey of Radar Refraction Error Corrections, RCC 266-16 iii Table of Contents Preface

Quantitative refractive index distribution of single cell by combining phase-shifting interferometry and AFM imaging.

PubMed

Zhang, Qinnan; Zhong, Liyun; Tang, Ping; Yuan, Yingjie; Liu, Shengde; Tian, Jindong; Lu, Xiaoxu

2017-05-31

Cell refractive index, an intrinsic optical parameter, is closely correlated with the intracellular mass and concentration. By combining optical phase-shifting interferometry (PSI) and atomic force microscope (AFM) imaging, we constructed a label free, non-invasive and quantitative refractive index of single cell measurement system, in which the accurate phase map of single cell was retrieved with PSI technique and the cell morphology with nanoscale resolution was achieved with AFM imaging. Based on the proposed AFM/PSI system, we achieved quantitative refractive index distributions of single red blood cell and Jurkat cell, respectively. Further, the quantitative change of refractive index distribution during Daunorubicin (DNR)-induced Jurkat cell apoptosis was presented, and then the content changes of intracellular biochemical components were achieved. Importantly, these results were consistent with Raman spectral analysis, indicating that the proposed PSI/AFM based refractive index system is likely to become a useful tool for intracellular biochemical components analysis measurement, and this will facilitate its application for revealing cell structure and pathological state from a new perspective.

Influence of refractive condition on retinal vasculature complexity in younger subjects.

PubMed

Azemin, Mohd Zulfaezal Che; Daud, Norsyazwani Mohamad; Ab Hamid, Fadilah; Zahari, Ilyanoon; Sapuan, Abdul Halim

2014-01-01

The aim of this study was to compare the retinal vasculature complexity between emmetropia, and myopia in younger subjects. A total of 82 patients (24.12 ± 1.25 years) with two types of refractive conditions, myopia and emmetropia were enrolled in this study. Refraction data were converted to spherical equivalent refraction. These retinal images (right eyes) were obtained from NAVIS Lite Image Filing System and the vasculature complexity was measured by fractal dimension (D f ), quantified using a computer software following a standardized protocol. There was a significant difference (P < 0.05) in the value of D f between emmetropic (1.5666 ± 0.0160) and myopic (1.5588 ± 0.0142) groups. A positive correlation (rho = 0.260, P < 0.05) between the D f and the spherical equivalent refraction was detected in this study. Using a linear model, it was estimated that 6.7% of the variation in D f could be explained by spherical equivalent refraction. This study provides valuable findings about the effect of moderate to high myopia on the fractal dimension of the retinal vasculature network. These results show that myopic refraction in younger subjects was associated with a decrease in D f , suggesting a loss of retinal vessel density with moderate to high myopia.

Human resources for refraction services in Central Nepal.

PubMed

Kandel, Himal; Murthy, G V S; Bascaran, Covadonga

2015-07-01

Uncorrected refractive error is a public health problem globally and in Nepal. Planning of refraction services is hampered by a paucity of data. This study was conducted to determine availability and distribution of human resources for refraction, their efficiency, the type and extent of their training; the current service provision of refraction services and the unmet need in human resources for refraction in Central Nepal. This was a descriptive cross-sectional study. All refraction facilities in the Central Region were identified through an Internet search and interviews of key informants from the professional bodies and parent organisations of primary eye centres. A stratified simple random sampling technique was used to select 50 per cent of refraction facilities. The selected facilities were visited for primary data collection. Face-to-face interviews were conducted with the managers and the refractionists available in the facilities using a semi-structured questionnaire. Data was collected in 29 centres. All the managers (n=29; response rate 100 per cent) and 50 refractionists (Response rate 65.8 per cent) were interviewed. Optometrists and ophthalmic assistants were the main providers of refraction services (n=70, 92.11 per cent). They were unevenly distributed across the region, highly concentrated around urban areas. The median number of refractions per refractionist per year was 3,600 (IQR: 2,400 - 6,000). Interviewed refractionists stated that clients' knowledge, attitude and practice related factors such as lack of awareness of the need for refraction services and/or availability of existing services were the major barriers to the output of refraction services. The total number of refractions carried out in the Central Region per year was 653,176. An additional 170 refractionists would be needed to meet the unmet need of 1,323,234 refractions. The study findings demand a major effort to develop appropriately trained personnel when planning refraction services in the Central Region and in Nepal as a whole. The equitable distribution of the refractionists, their community-outreach services and awareness raising activities should be emphasised. © 2015 The Authors. Clinical and Experimental Optometry © 2015 Optometry Australia.

Method of determining effects of heat-induced irregular refractive index on an optical system.

PubMed

Song, Xifa; Li, Lin; Huang, Yifan

2015-09-01

The effects of an irregular refractive index on optical performance are examined. A method was developed to express a lens's irregular refractive index distribution. An optical system and its mountings were modeled by a thermomechanical finite element (FE) program in the predicted operating temperature range, -45°C-50°C. FE outputs were elaborated using a MATLAB optimization routine; a nonlinear least squares algorithm was adopted to determine which gradient equation best fit each lens's refractive index distribution. The obtained gradient data were imported into Zemax for sequential ray-tracing analysis. The root mean square spot diameter, modulation transfer function, and diffraction ensquared energy were computed for an optical system under an irregular refractive index and under thermoelastic deformation. These properties are greatly reduced by the irregular refractive index effect, which is one-third to five-sevenths the size of the thermoelastic deformation effect. Thus, thermal analyses of optical systems should consider not only thermoelastic deformation but also refractive index irregularities caused by inhomogeneous temperature.

Extinction spectra of suspensions of microspheres: determination of the spectral refractive index and particle size distribution with nanometer accuracy.

PubMed

Gienger, Jonas; Bär, Markus; Neukammer, Jörg

2018-01-10

A method is presented to infer simultaneously the wavelength-dependent real refractive index (RI) of the material of microspheres and their size distribution from extinction measurements of particle suspensions. To derive the averaged spectral optical extinction cross section of the microspheres from such ensemble measurements, we determined the particle concentration by flow cytometry to an accuracy of typically 2% and adjusted the particle concentration to ensure that perturbations due to multiple scattering are negligible. For analysis of the extinction spectra, we employ Mie theory, a series-expansion representation of the refractive index and nonlinear numerical optimization. In contrast to other approaches, our method offers the advantage to simultaneously determine size, size distribution, and spectral refractive index of ensembles of microparticles including uncertainty estimation.

The absorption Ångström exponent of black carbon: from numerical aspects

NASA Astrophysics Data System (ADS)

Liu, Chao; Eddy Chung, Chul; Yin, Yan; Schnaiter, Martin

2018-05-01

The absorption Ångström exponent (AAE) is an important aerosol optical parameter used for aerosol characterization and apportionment studies. The AAE of black carbon (BC) particles is widely accepted to be 1.0, although observational estimates give quite a wide range of 0.6-1.3. With considerable uncertainties related to observations, a numerical study is a powerful method, if not the only one, to provide a better and more accurate understanding on BC AAE. This study calculates BC AAE using realistic particle geometries based on fractal aggregate and an accurate numerical optical model (namely the multiple-sphere T-matrix method), and considers bulk properties of an ensemble of BC particles following lognormal size distributions. At odds with the expectations, BC AAE is not 1.0, even when BC is assumed to have small sizes and a wavelength-independent refractive index. With a wavelength-independent refractive index, the AAE of fresh BC is approximately 1.05 and relatively insensitive to particle size. For BC with geometric mean diameters larger than 0.12 µm, BC AAE becomes smaller when BC particles are aged (compact structures or coated by other non-absorptive materials). For coated BC, we prescribe the coating fraction variation based on a laboratory study, where smaller BC cores are shown to develop larger coating fractions than those of bigger BC cores. For both compact and coated BC, the AAE is highly sensitive to particle size distribution, ranging from approximately 0.8 to even over 1.4 with wavelength-independent refractive index. When the refractive index is allowed to vary with wavelength, a feature with observational backing, the BC AAE may show an even wider range. For different BC morphologies, we derive simple empirical equations on BC AAE based on our numerical results, which can serve as a guide for the response of BC AAE to BC size and refractive index. Due to its complex influences, the effects of BC geometry is better to be discussed at certain BC properties, i.e., known size and refractive index.

Unobstructed particle image velocimetry measurements within an axial turbo-pump using liquid and blades with matched refractive indices

NASA Astrophysics Data System (ADS)

Uzol, O.; Chow, Y.-C.; Katz, J.; Meneveau, C.

2002-08-01

Performing PIV measurements within complex turbomachinery with multiple blade rows is difficult due to the optical obstruction to the illuminating sheet and to the camera caused by the blades. This paper introduces a refractive index matched facility that overcomes this problem. The rotor and stator blades are made of transparent acrylic, and the working fluid has the same optical refractive index as the blades. A 64% by weight solution of sodium iodide in water is used for this purpose. This liquid has a kinematic viscosity of about 1.1×10-6 m2/s, which is almost the same as that of water enabling operation at high Reynolds numbers. Issues related to operating with this fluid such as chemical stability, variations in transmittance and solutions to these problems are discussed. This setup allows full optical access to the entire rotor and stator passages both to the laser sheet and the camera. The experiments are conducted at different streamwise locations covering the entire flow fields around the rotor, the stator, the gap between them, and the wakes behind. Vector maps of the instantaneous and phase-averaged flow fields as well as the distribution of turbulent kinetic energy are obtained. Measurements at different magnifications enable us to obtain an overview of the flow structure, as well as detailed velocity distributions in the boundary layers and in the wakes.

Effect of Index of Refraction on Radiation Characteristics in a Heated Absorbing, Emitting, and Scattering Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1992-01-01

The effect of the index of refraction on the temperature distribution and radiative heat flux in semitransparent materials, such as some ceramics, is investigated analytically. In the case considered here, a plane layer of a ceramic material is subjected to external radiative heating incident on each of its surfaces; the material emits, absorbs, and isotropically scatters radiation. It is shown that, for radiative equilibrium in a gray layer with diffuse interfaces, the temperature distribution and radiative heat flux for any index of refraction can be obtained in a simple manner from the results for an index of refraction of unity.

Calculations of atmospheric refraction for spacecraft remote-sensing applications

NASA Technical Reports Server (NTRS)

Chu, W. P.

1983-01-01

Analytical solutions to the refraction integrals appropriate for ray trajectories along slant paths through the atmosphere are derived in this paper. This type of geometry is commonly encountered in remote-sensing applications utilizing an occultation technique. The solutions are obtained by evaluating higher-order terms from expansion of the refraction integral and are dependent on the vertical temperature distributions. Refraction parameters such as total refraction angles, air masses, and path lengths can be accurately computed. It is also shown that the method can be used for computing refraction parameters in astronomical refraction geometry for large zenith angles.

Modified Kramers-Kronig relations and sum rules for meromorphic total refractive index

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peiponen, Kai-Erik; Saarinen, Jarkko J.; Vartiainen, Erik M.

2003-08-01

Modified Kramers-Kronig relations and corresponding sum rules are shown to hold for the total refractive index that can be presented as a sum of complex linear and nonlinear refractive indices, respectively. It is suggested that a self-action process, involving the degenerate third-order nonlinear susceptibility, can yield a negative total refractive index at some spectral range.

FIBER AND INTEGRATED OPTICS: Use of the offset method in an analysis of a non-Gaussian field distribution in single-mode fiber waveguides

NASA Astrophysics Data System (ADS)

Belov, A. V.; Kurkov, Andrei S.; Chikolini, A. V.

1990-08-01

An offset method is modified to allow an analysis of the distribution of fields in a single-mode fiber waveguide without recourse to the Gaussian approximation. A new approximation for the field is obtained for fiber waveguides with a step refractive index profile and a special analysis employing the Hankel transformation is applied to waveguides with a distributed refractive index. The field distributions determined by this method are compared with the corresponding distributions calculated from the refractive index of a preform from which the fibers are drawn. It is shown that these new approaches can be used to determine the dimensions of a mode spot defined in different ways and to forecast the dispersion characteristics of single-mode fiber waveguides.

Crystalline lens and refractive development.

PubMed

Iribarren, Rafael

2015-07-01

Individual refractive errors usually change along lifespan. Most children are hyperopic in early life. This hyperopia is usually lost during growth years, leading to emmetropia in adults, but myopia also develops in children during school years or during early adult life. Those subjects who remain emmetropic are prone to have hyperopic shifts in middle life. And even later, at older ages, myopic shifts are developed with nuclear cataract. The eye grows from 15 mm in premature newborns to approximately 24 mm in early adult years, but, in most cases, refractions are maintained stable in a clustered distribution. This growth in axial length would represent a refractive change of more than 40 diopters, which is compensated by changes in corneal and lens powers. The process which maintains the balance between the ocular components of refraction during growth is still under study. As the lens power cannot be measured in vivo, but can only be calculated based on the other ocular components, there have not been many studies of lens power in humans. Yet, recent studies have confirmed that the lens loses power during growth in children, and that hyperopic and myopic shifts in adulthood may be also produced by changes in the lens. These studies in children and adults give a picture of the changing power of the lens along lifespan. Other recent studies about the growth of the lens and the complexity of its internal structure give clues about how these changes in lens power are produced along life. Copyright © 2015 Elsevier Ltd. All rights reserved.

Low-refractive-index dye-aggregate films with small absorption based on anomalous dispersion.

PubMed

Wakamatsu, Takashi; Watanabe, Keita; Saito, Kazuhiro

2005-02-20

Complex-refractive-index spectra of Squarylium (SQ) dye-aggregate films deposited upon metal films have been investigated by measurements of properties of the films including absorption spectra (AS) and attenuated total reflection. Complex refractive indices are estimated by Kramers-Kronig analysis for the AS and by a theoretical curve-fitting analysis for attenuated total reflection. The dye-aggregate films exhibited an absorption that was blueshifted from that of a monomer, as a result of the H-aggregate formation of SQ molecules, and had a changing refractive index with anomalous dispersion about the H-absorption band. From both measurements of the SQ films it was found that there is a region of low absorption in the short-wavelength side of the absorption band and that the refractive index there is lower than that of glass.

Low-refractive-index dye-aggregate films with small absorption based on anomalous dispersion

NASA Astrophysics Data System (ADS)

Wakamatsu, Takashi; Watanabe, Keita; Saito, Kazuhiro

2005-02-01

Complex-refractive-index spectra of Squarylium (SQ) dye-aggregate films deposited upon metal films have been investigated by measurements of properties of the films including absorption spectra (AS) and attenuated total reflection. Complex refractive indices are estimated by Kramers-Kronig analysis for the AS and by a theoretical curve-fitting analysis for attenuated total reflection. The dye-aggregate films exhibited an absorption that was blueshifted from that of a monomer, as a result of the H-aggregate formation of SQ molecules, and had a changing refractive index with anomalous dispersion about the H-absorption band. From both measurements of the SQ films it was found that there is a region of low absorption in the short-wavelength side of the absorption band and that the refractive index there is lower than that of glass.

Ultraviolet refractometry using field-based light scattering spectroscopy

PubMed Central

Fu, Dan; Choi, Wonshik; Sung, Yongjin; Oh, Seungeun; Yaqoob, Zahid; Park, YongKeun; Dasari, Ramachandra R.; Feld, Michael S.

2010-01-01

Accurate refractive index measurement in the deep ultraviolet (UV) range is important for the separate quantification of biomolecules such as proteins and DNA in biology. This task is demanding and has not been fully exploited so far. Here we report a new method of measuring refractive index using field-based light scattering spectroscopy, which is applicable to any wavelength range and suitable for both solutions and homogenous objects with well-defined shape such as microspheres. The angular scattering distribution of single microspheres immersed in homogeneous media is measured over the wavelength range 260 to 315 nm using quantitative phase microscopy. By least square fitting the observed scattering distribution with Mie scattering theory, the refractive index of either the sphere or the immersion medium can be determined provided that one is known a priori. Using this method, we have measured the refractive index dispersion of SiO2 spheres and bovine serum albumin (BSA) solutions in the deep UV region. Specific refractive index increments of BSA are also extracted. Typical accuracy of the present refractive index technique is ≤0.003. The precision of refractive index measurements is ≤0.002 and that of specific refractive index increment determination is ≤0.01 mL/g. PMID:20372622

Electrical modulation of the complex refractive index in mid-infrared quantum cascade lasers.

PubMed

Teissier, J; Laurent, S; Manquest, C; Sirtori, C; Bousseksou, A; Coudevylle, J R; Colombelli, R; Beaudoin, G; Sagnes, I

2012-01-16

We have demonstrated an integrated three terminal device for the modulation of the complex refractive index of a distributed feedback quantum cascade laser (QCL). The device comprises an active region to produce optical gain vertically stacked with a control region made of asymmetric coupled quantum wells (ACQW). The optical mode, centered on the gain region, has a small overlap also with the control region. Owing to the three terminals an electrical bias can be applied independently on both regions: on the laser for producing optical gain and on the ACQW for tuning the energy of the intersubband transition. This allows the control of the optical losses at the laser frequency as the absorption peak associated to the intersubband transition can be electrically brought in and out the laser transition. By using this function a laser modulation depth of about 400 mW can be achieved by injecting less than 1 mW in the control region. This is four orders of magnitude less than the electrical power needed using direct current modulation and set the basis for the realisation of electrical to optical transducers.

O the Determination of the Complex Refractive Index of Powdered Materials in the 9 TO 11 Micrometer Spectral Region Utilizing AN Attenuated Total Reflectance Technique.

NASA Astrophysics Data System (ADS)

Gillespie, James Bryce

1982-03-01

A specific method of determining the complex refractive index of powdered materials using attenuated total reflectance (ATR) spectroscopy was investigated. A very precise laser/goniometric ATR system was assembled and applied to powdered samples of carbon blacks, graphite, kaolin clay, quartz, calcite, and sodalime glass beads. The reflectivity data fell into two categories: (1) data representative of a medium having a unique effective refractive index and (2) data representative of a scattering medium having no unique refractive index. Data of the first kind were obtained from all the carbon black, graphite, and kaolin clay samples. The Fahrenfort-Visser solution of the Fresnel equations was applied to the goniometric reflectivity data for these samples to obtain the complex refractive index of these effective media. The complex refractive index obtained in this manner is not that of the bulk material but is instead a value which may be related to the bulk material value through some refractive index mixing rule. A systematic experiment using carbon black of particle size 0.0106 mm diameter was conducted to determine the applicability of several mixture rules for the volume packing fraction range of .2 to .6 which is most often encountered. The Bruggemann effective medium theory produced credible results while the Lorentz-Lorenz rule and the empirical Biot-Arago rule were invalid in this volume packing region. The Bruggemann rule was applied to lampblack, Mogul-L carbon black, graphite, and kaolin clay to obtain the complex refractive indices of these materials from the ATR spectroscopy data. Goniometric reflectivity data representative of an inhomogeneous scattering medium were obtained from all the powdered quartz, powdered calcite, and sodalime glass beads samples. These samples all contained particles with diameters nearly as large as the wavelength. These data demonstrate that the ATR technique, coupled with an effective medium analysis, may be used to obtain optical constants of powdered materials only when the particles are small compared to the wavelength.

An efficient method for the calculation of mean extinction. I - The analyticity of the complex extinction efficiency of homogeneous spheres

NASA Astrophysics Data System (ADS)

Xing, Zhang-Fan; Greenberg, J. M.

1992-11-01

Results of an investigation of the analyticity of the complex extinction efficiency Q-tilde(ext) in different parameter domains are presented. In the size parameter domain, x = omega(a/c), numerical Hilbert transforms are used to study the analyticity properties of Q-tilde(ext) for homogeneous spheres. Q-tilde(ext) is found to be analytic in the entire lower complex x-tilde-plane when the refractive index, m, is fixed as a real constant (pure scattering) or infinity (perfect conductor); poles, however, appear in the left side of the lower complex x-tilde-plane as m becomes complex. The computation of the mean extinction produced by an extended size distribution of particles may be conveniently and accurately approximated using only a few values of the complex extinction evaluated in the complex plane.

Using a laser source to measure the refractive index of glass beads and Debye theory analysis.

PubMed

Li, Shui-Yan; Qin, Shuang; Li, Da-Hai; Wang, Qiong-Hua

2015-11-20

Using a monochromatic laser beam to illuminate a homogeneous glass bead, some rainbows will appear around it. This paper concentrates on the study of the scattering intensity distribution and the method of measuring the refractive index for glass beads based on the Debye theory. It is found that the first rainbow due to the scattering superposition of backward light of the low-refractive-index glass beads can be explained approximately with the diffraction, the external reflection plus the one internal reflection, while the second rainbow of high-refractive-index glass beads is due to the contribution from the diffraction, the external reflection, the direct transmission, and the two internal reflections. The scattering intensity distribution is affected by the refractive index, the radius of the glass bead, and the incident beam width. The effects of the refractive index and the glass bead size on the first and second minimum deviation angle position are analyzed in this paper. The results of the measurements agree very well with the specifications.

The estimation of lower refractivity uncertainty from radar sea clutter using the Bayesian—MCMC method

NASA Astrophysics Data System (ADS)

Sheng, Zheng

2013-02-01

The estimation of lower atmospheric refractivity from radar sea clutter (RFC) is a complicated nonlinear optimization problem. This paper deals with the RFC problem in a Bayesian framework. It uses the unbiased Markov Chain Monte Carlo (MCMC) sampling technique, which can provide accurate posterior probability distributions of the estimated refractivity parameters by using an electromagnetic split-step fast Fourier transform terrain parabolic equation propagation model within a Bayesian inversion framework. In contrast to the global optimization algorithm, the Bayesian—MCMC can obtain not only the approximate solutions, but also the probability distributions of the solutions, that is, uncertainty analyses of solutions. The Bayesian—MCMC algorithm is implemented on the simulation radar sea-clutter data and the real radar sea-clutter data. Reference data are assumed to be simulation data and refractivity profiles are obtained using a helicopter. The inversion algorithm is assessed (i) by comparing the estimated refractivity profiles from the assumed simulation and the helicopter sounding data; (ii) the one-dimensional (1D) and two-dimensional (2D) posterior probability distribution of solutions.

Change in human lens dimensions, lens refractive index distribution and ciliary body ring diameter with accommodation.

PubMed

Khan, Adnan; Pope, James M; Verkicharla, Pavan K; Suheimat, Marwan; Atchison, David A

2018-03-01

We investigated changes in ciliary body ring diameter, lens dimensions and lens refractive index distributions with accommodation in young adults. A 3T clinical magnetic resonance imaging scanner imaged right eyes of 38 18-29 year old participants using a multiple spin echo sequence to determine accommodation-induced changes along lens axial and equatorial directions. Accommodation stimuli were approximately 1 D and 5 D. With accommodation, ciliary body ring diameter, and equatorial lens diameter decreased (-0.43 ± 0.31 mm and -0.30 ± 0.23 mm, respectively), and axial lens thickness increased ( + 0.34 ± 0.16 mm). Lens shape changes cause redistribution of the lens internal structure, leading to change in refractive index distribution profiles. With accommodation, in the axial direction refractive index profiles became flatter in the center and steeper near the periphery of the lens, while in the equatorial direction they became steeper in the center and flatter in the periphery. The results suggest that the anatomical accuracy of lens optical models can be improved by accounting for changes in the refractive index profile during accommodation.

Application of stochastic particle swarm optimization algorithm to determine the graded refractive index distribution in participating media

NASA Astrophysics Data System (ADS)

Wei, Lin-Yang; Qi, Hong; Ren, Ya-Tao; Ruan, Li-Ming

2016-11-01

Inverse estimation of the refractive index distribution in one-dimensional participating media with graded refractive index (GRI) is investigated. The forward radiative transfer problem is solved by the Chebyshev collocation spectral method. The stochastic particle swarm optimization (SPSO) algorithm is employed to retrieve three kinds of GRI distribution, i.e. the linear, sinusoidal and quadratic GRI distribution. The retrieval accuracy of GRI distribution with different wall emissivity, optical thickness, absorption coefficients and scattering coefficients are discussed thoroughly. To improve the retrieval accuracy of quadratic GRI distribution, a double-layer model is proposed to supply more measurement information. The influence of measurement errors upon the precision of estimated results is also investigated. Considering the GRI distribution is unknown beforehand in practice, a quadratic function is employed to retrieve the linear GRI by SPSO algorithm. All the results show that the SPSO algorithm is applicable to retrieve different GRI distributions in participating media accurately even with noisy data.

A Wind Dependent Desert Aerosol Model: Radiative Properties

DTIC Science & Technology

1988-04-19

Source Regions and Transport Characteristics 5 2.2 Size Distributions 6 2.3 Composition 8 2.4 Effects of Wind 10 2.5 Indices of Refraction 12 2.5.1 An...Hematite Concentrations of 0, 5, and 10 %, (a) O-Ray and (b) E-Ray 44 8 . Imaginary Part of the Index of Refraction for Sand Having Hematite...rarbonaceous Material 31 8 . Indices of Refraction "or Ammonium Sulfate 32 9. Indices of Refraction for the 0-Ray of Quartz 35 10 . Indices of Refraction for the

Analytical inversions in remote sensing of particle size distributions. IV - Comparison of Fymat and Box-McKellar solutions in the anomalous diffraction approximation

NASA Technical Reports Server (NTRS)

Fymat, A. L.; Smith, C. B.

1979-01-01

It is shown that the inverse analytical solutions, provided separately by Fymat and Box-McKellar, for reconstructing particle size distributions from remote spectral transmission measurements under the anomalous diffraction approximation can be derived using a cosine and a sine transform, respectively. Sufficient conditions of validity of the two formulas are established. Their comparison shows that the former solution is preferable to the latter in that it requires less a priori information (knowledge of the particle number density is not needed) and has wider applicability. For gamma-type distributions, and either a real or a complex refractive index, explicit expressions are provided for retrieving the distribution parameters; such expressions are, interestingly, proportional to the geometric area of the polydispersion.

Measurement of the complex refractive index and complex dielectric permittivity of T.P.S. Space Shuttle tile materials at millimeter wavelengths

NASA Technical Reports Server (NTRS)

Afsar, Mohammed Nurul; Chi, Hua; Li, Xiaohui

1990-01-01

Complex refractive index and dielectric permittivity studies of presently used Space Shuttle tile materials at millimeter wavelengths reveal these tiles to exhibit similar absorption characteristics to those of fused silica materials. This absorption is mainly related to the water content in the specimen. A strong birefringence is observed at least in one of these fibrous refractory composite materials.

[Modeling and Simulation of Spectral Polarimetric BRDF].

PubMed

Ling, Jin-jiang; Li, Gang; Zhang, Ren-bin; Tang, Qian; Ye, Qiu

2016-01-01

Under the conditions of the polarized light, The reflective surface of the object is affected by many factors, refractive index, surface roughness, and so the angle of incidence. For the rough surface in the different wavelengths of light exhibit different reflection characteristics of polarization, a spectral polarimetric BRDF based on Kirchhof theory is proposee. The spectral model of complex refraction index is combined with refraction index and extinction coefficient spectral model which were got by using the known complex refraction index at different value. Then get the spectral model of surface roughness derived from the classical surface roughness measuring method combined with the Fresnel reflection function. Take the spectral model of refraction index and roughness into the BRDF model, then the spectral polarimetirc BRDF model is proposed. Compare the simulation results of the refractive index varies with wavelength, roughness is constant, the refraction index and roughness both vary with wavelength and origin model with other papers, it shows that, the spectral polarimetric BRDF model can show the polarization characteristics of the surface accurately, and can provide a reliable basis for the application of polarization remote sensing, and other aspects of the classification of substances.

Simultaneous reconstruction of 3D refractive index, temperature, and intensity distribution of combustion flame by double computed tomography technologies based on spatial phase-shifting method

NASA Astrophysics Data System (ADS)

Guo, Zhenyan; Song, Yang; Yuan, Qun; Wulan, Tuya; Chen, Lei

2017-06-01

In this paper, a transient multi-parameter three-dimensional (3D) reconstruction method is proposed to diagnose and visualize a combustion flow field. Emission and transmission tomography based on spatial phase-shifted technology are combined to reconstruct, simultaneously, the various physical parameter distributions of a propane flame. Two cameras triggered by the internal trigger mode capture the projection information of the emission and moiré tomography, respectively. A two-step spatial phase-shifting method is applied to extract the phase distribution in the moiré fringes. By using the filtered back-projection algorithm, we reconstruct the 3D refractive-index distribution of the combustion flow field. Finally, the 3D temperature distribution of the flame is obtained from the refractive index distribution using the Gladstone-Dale equation. Meanwhile, the 3D intensity distribution is reconstructed based on the radiation projections from the emission tomography. Therefore, the structure and edge information of the propane flame are well visualized.

Dark solitons at nonlinear interfaces.

PubMed

Sánchez-Curto, Julio; Chamorro-Posada, Pedro; McDonald, Graham S

2010-05-01

The refraction of dark solitons at a planar boundary separating two defocusing Kerr media is simulated and analyzed, for the first time (to our knowledge). Analysis is based on the nonlinear Helmholtz equation and is thus valid for any angle of incidence. A new law, governing refraction of black solitons, is combined with one describing bright soliton refraction to yield a generalized Snell's law whose validity is verified numerically. The complexity of gray soliton refraction is also analyzed, and illustrated by a change from external to internal refraction on varying the soliton contrast parameter.

Retrieval of the scattering and microphysical properties of aerosols from ground-based optical measurements including polarization. I. Method.

PubMed

Vermeulen, A; Devaux, C; Herman, M

2000-11-20

A method has been developed for retrieving the scattering and microphysical properties of atmospheric aerosol from measurements of solar transmission, aureole, and angular distribution of the scattered and polarized sky light in the solar principal plane. Numerical simulations of measurements have been used to investigate the feasibility of the method and to test the algorithm's performance. It is shown that the absorption and scattering properties of an aerosol, i.e., the single-scattering albedo, the phase function, and the polarization for single scattering of incident unpolarized light, can be obtained by use of radiative transfer calculations to correct the values of scattered radiance and polarized radiance for multiple scattering, Rayleigh scattering, and the influence of ground. The method requires only measurement of the aerosol's optical thickness and an estimate of the ground's reflectance and does not need any specific assumption about properties of the aerosol. The accuracy of the retrieved phase function and polarization of the aerosols is examined at near-infrared wavelengths (e.g., 0.870 mum). The aerosol's microphysical properties (size distribution and complex refractive index) are derived in a second step. The real part of the refractive index is a strong function of the polarization, whereas the imaginary part is strongly dependent on the sky's radiance and the retrieved single-scattering albedo. It is demonstrated that inclusion of polarization data yields the real part of the refractive index.

Quantitative measurement of binary liquid distributions using multiple-tracer x-ray fluorescence and radiography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halls, Benjamin R.; Meyer, Terrence R.; Kastengren, Alan L.

2015-01-01

The complex geometry and large index-of-refraction gradients that occur near the point of impingement of binary liquid jets present a challenging environment for optical interrogation. A simultaneous quadruple-tracer x-ray fluorescence and line-of-sight radiography technique is proposed as a means of distinguishing and quantifying individual liquid component distributions prior to, during, and after jet impact. Two different pairs of fluorescence tracers are seeded into each liquid stream to maximize their attenuation ratio for reabsorption correction and differentiation of the two fluids during mixing. This approach for instantaneous correction of x-ray fluorescence reabsorption is compared with a more time-intensive approach of usingmore » stereographic reconstruction of x-ray attenuation along multiple lines of sight. The proposed methodology addresses the need for a quantitative measurement technique capable of interrogating optically complex, near-field liquid distributions in many mixing systems of practical interest involving two or more liquid streams.« less

Quantitative measurement of binary liquid distributions using multiple-tracer x-ray fluorescence and radiography

DOE PAGES

Halls, Benjamin R.; Meyer, Terrence R.; Kastengren, Alan L.

2015-01-23

The complex geometry and large index-of-refraction gradients that occur near the point of impingement of binary liquid jets present a challenging environment for optical interrogation. A simultaneous quadruple-tracer x-ray fluorescence and line-of-sight radiography technique is proposed as a means of distinguishing and quantifying individual liquid component distributions prior to, during, and after jet impact. Two different pairs of fluorescence tracers are seeded into each liquid stream to maximize their attenuation ratio for reabsorption correction and differentiation of the two fluids during mixing. This approach for instantaneous correction of x-ray fluorescence reabsorption is compared with a more time-intensive approach of usingmore » stereographic reconstruction of x-ray attenuation along multiple lines of sight. The proposed methodology addresses the need for a quantitative measurement technique capable of interrogating optically complex, near-field liquid distributions in many mixing systems of practical interest involving two or more liquid streams.« less

Dependent scattering and absorption by densely packed discrete spherical particles: Effects of complex refractive index

NASA Astrophysics Data System (ADS)

Ma, L. X.; Tan, J. Y.; Zhao, J. M.; Wang, F. Q.; Wang, C. A.; Wang, Y. Y.

2017-07-01

Due to the dependent scattering and absorption effects, the radiative transfer equation (RTE) may not be suitable for dealing with radiative transfer in dense discrete random media. This paper continues previous research on multiple and dependent scattering in densely packed discrete particle systems, and puts emphasis on the effects of particle complex refractive index. The Mueller matrix elements of the scattering system with different complex refractive indexes are obtained by both electromagnetic method and radiative transfer method. The Maxwell equations are directly solved based on the superposition T-matrix method, while the RTE is solved by the Monte Carlo method combined with the hard sphere model in the Percus-Yevick approximation (HSPYA) to consider the dependent scattering effects. The results show that for densely packed discrete random media composed of medium size parameter particles (equals 6.964 in this study), the demarcation line between independent and dependent scattering has remarkable connections with the particle complex refractive index. With the particle volume fraction increase to a certain value, densely packed discrete particles with higher refractive index contrasts between the particles and host medium and higher particle absorption indexes are more likely to show stronger dependent characteristics. Due to the failure of the extended Rayleigh-Debye scattering condition, the HSPYA has weak effect on the dependent scattering correction at large phase shift parameters.

Method of analysis of polymerizable monomeric species in a complex mixture

DOEpatents

Hermes, Robert E

2014-03-18

Method of selective quantitation of a polymerizable monomeric species in a well spacer fluid, said method comprising the steps of adding at least one solvent having a refractive index of less than about 1.33 to a sample of the complex mixture to produce a solvent phase, and measuring the refractive index of the solvent phase.

Imaging the environment of green fluorescent protein.

PubMed Central

Suhling, Klaus; Siegel, Jan; Phillips, David; French, Paul M W; Lévêque-Fort, Sandrine; Webb, Stephen E D; Davis, Daniel M

2002-01-01

An emerging theme in cell biology is that cell surface receptors need to be considered as part of supramolecular complexes of proteins and lipids facilitating specific receptor conformations and distinct distributions, e.g., at the immunological synapse. Thus, a new goal is to develop bioimaging that not only locates proteins in live cells but can also probe their environment. Such a technique is demonstrated here using fluorescence lifetime imaging of green fluorescent protein (GFP). We first show, by time-correlated single-photon counting, that the fluorescence decay of GFP depends on the local refractive index. This is in agreement with the Strickler Berg formula, relating the Einstein A and B coefficients for absorption and spontaneous emission in molecules. We then quantitatively image, by wide-field time-gated fluorescence lifetime imaging, the refractive index of the environment of GFP. This novel approach paves the way for imaging the biophysical environment of specific GFP-tagged proteins in live cells. PMID:12496126

Refractive Status and Prevalence of Refractive Errors in Suburban School-age Children

PubMed Central

Pi, Lian-Hong; Chen, Lin; Liu, Qin; Ke, Ning; Fang, Jing; Zhang, Shu; Xiao, Jun; Ye, Wei-Jiang; Xiong, Yan; Shi, Hui; Yin, Zheng-Qin

2010-01-01

Objective: This study investigated the distribution pattern of refractive status and prevalence of refractive errors in school-age children in Western China to determine the possible environmental factors. Methods: A random sampling strategy in geographically defined clusters was used to identify children aged 6-15 years in Yongchuan, a socio-economically representative area in Western China. We carried out a door-to-door survey and actual eye examinations, including visual acuity measurements, stereopsis examination, anterior segment and eyeball movements, fundus examinations, and cycloplegic retinoscopy with 1% cyclopentolate. Results: A total of 3469 children living in 2552 households were selected, and 3070 were examined. The distributions of refractive status were positively-skewed for 6-8-year-olds, and negatively-skewed for 9-12 and 13-15-year-olds. The prevalence of hyperopia (≥+2.00 D spherical equivalent [SE]), myopia (≤-0.50 D SE), and astigmatism (≥1.00 diopter of cylinder [DC]) were 3.26%, 13.75%, and 3.75%, respectively. As children's ages increased, the prevalence rate of hyperopia decreased (P<0.001) and that of myopia increased significantly (P<0.001). Children in academically challenging schools had a higher risk of myopia (P<0.001) and astigmatism (≥1.00DC, P =0.04) than those in regular schools. Conclusion: The distribution of refractive status changes gradually from positively-skewed to negatively-skewed distributions as age increases, with 9-year-old being the critical age for the changes. Environmental factors and study intensity influence the occurrence and development of myopia. PMID:20975844

Change in human lens dimensions, lens refractive index distribution and ciliary body ring diameter with accommodation

PubMed Central

Khan, Adnan; Pope, James M.; Verkicharla, Pavan K.; Suheimat, Marwan; Atchison, David A.

2018-01-01

We investigated changes in ciliary body ring diameter, lens dimensions and lens refractive index distributions with accommodation in young adults. A 3T clinical magnetic resonance imaging scanner imaged right eyes of 38 18-29 year old participants using a multiple spin echo sequence to determine accommodation-induced changes along lens axial and equatorial directions. Accommodation stimuli were approximately 1 D and 5 D. With accommodation, ciliary body ring diameter, and equatorial lens diameter decreased (–0.43 ± 0.31 mm and –0.30 ± 0.23 mm, respectively), and axial lens thickness increased ( + 0.34 ± 0.16 mm). Lens shape changes cause redistribution of the lens internal structure, leading to change in refractive index distribution profiles. With accommodation, in the axial direction refractive index profiles became flatter in the center and steeper near the periphery of the lens, while in the equatorial direction they became steeper in the center and flatter in the periphery. The results suggest that the anatomical accuracy of lens optical models can be improved by accounting for changes in the refractive index profile during accommodation. PMID:29541520

Characteristics of Refractive Errors in a Population of Adults in the Central Region of Poland.

PubMed

Nowak, Michal S; Jurowski, Piotr; Grzybowski, Andrzej; Smigielski, Janusz

2018-01-08

Background : To investigate the distribution of refractive errors and their characteristics in older adults from a Polish population. Methods : The study design was a cross-sectional study. A total of 1107 men and women were interviewed and underwent detailed ophthalmic examinations, 998 subjects underwent refraction. Myopia was defined as spherical equivalent (SER) refraction ≤-0.5 dioptres (D) and hyperopia was defined as SER ≥+0.5 dioptres (D). Results : Among those who were refracted the distribution of myopia and hyperopia was 24.1% (95% CI 21.4-26.7) and 37.5% (95% CI 34.5-40.5), respectively. Myopia decreased from 28.7% in subjects aged 35-59 years to 19.3% in those aged 60 years or older and hyperopia increased from 21.8% at 35-59 years of age to 53.3% in subjects aged ≥60 years. Multiple regression analysis showed decreasing age (OR 0.98, 95% CI 0.96-1.00), female gender (OR 1.87, 95% CI 1.18-2.95) and presence of cataract (OR 2.40, 95% CI 1.24-4.63) were independent risk factors associated with myopia. Conclusions : The distribution of refractive errors found in our study is similar to those reported in other Caucasian populations and differs from Asian populations. Myopia was positively associated with younger age, female gender and presence of cataract.

Epidemiology of myopia

PubMed Central

Foster, P J; Jiang, Y

2014-01-01

Myopia is one of the most prevalent disorders of the eye. Higher myopia is associated with comorbidities that increase risks of severe and irreversible loss of vision, such as retinal detachment, subretinal neovascularization, dense cataract, and glaucoma. In recent years, reports from population-based prevalence studies carried out in various geographical areas now give a clear picture of the current distribution of refractive error. The scarcity of data from well-designed longitudinal cohort studies is still yet to be addressed. These studies have confirmed the previous data indicating that prevalence of refractive error varies according to ethnicity and geographic regions, and also point to an increase in myopia prevalence over the past half-century. The problem is particularly pronounced in affluent, industrialised areas of East Asia. Environmental risk factors for myopia related to socioeconomic status and lifestyle have been identified. The past decade has seen a greater understanding of the molecular biological mechanisms that determine refractive error, giving further support to the belief that myopia is the result of a complex interaction between genetic predisposition and environmental exposures. This review summarizes data on the prevalence, incidence, progression, associations, risk factors, and impact from recent epidemiological studies on myopia. PMID:24406412

Interpretation of a seismic refraction profile across the Roosevelt Hot Springs, Utah and vicinity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gertson, R.C.; Smith, R.B.

1979-03-01

In April 1977, a seismic refraction profile was recorded across the Milford Valley, the Roosevelt Hot Springs KGRA, and the northern Mineral Mountains in southwestern Utah. Seven shot points were used to provide multiple subsurface seismic refraction coverage along the 30 km east-west profile line. Since an inspection of power spectrums revealed large components of 60 Hz noise on some traces, computer routines were used to low-pass filter all seismograms. Amplitude information was utilized by normalizing all traces that recorded the same blast. Subsurface structural modeling was conducted by means of first arrival P-wave delay-time analysis and ray tracing. Herglotz-Wiechertmore » travel-time inversion was used for the velocity-depth distribution in the Mineral Mountains. The interpretation of the P-wave travel-times suggests that the Milford Valley fill consists of two units with a total thickness of at least 1.8 km. In the vicinity of the Roosevelt KGRA, a thin low velocity alluvial layer covers a basement igneous complex with a velocity of 5.2 km/s. Granite velocities between 3.3 km/s and 4.0 km/s were calculated from the travel-times in the Mineral Mountains.« less

Relative Proportion Of Different Types Of Refractive Errors In Subjects Seeking Laser Vision Correction.

PubMed

Althomali, Talal A

2018-01-01

Refractive errors are a form of optical defect affecting more than 2.3 billion people worldwide. As refractive errors are a major contributor of mild to moderate vision impairment, assessment of their relative proportion would be helpful in the strategic planning of health programs. To determine the pattern of the relative proportion of types of refractive errors among the adult candidates seeking laser assisted refractive correction in a private clinic setting in Saudi Arabia. The clinical charts of 687 patients (1374 eyes) with mean age 27.6 ± 7.5 years who desired laser vision correction and underwent a pre-LASIK work-up were reviewed retrospectively. Refractive errors were classified as myopia, hyperopia and astigmatism. Manifest refraction spherical equivalent (MRSE) was applied to define refractive errors. Distribution percentage of different types of refractive errors; myopia, hyperopia and astigmatism. The mean spherical equivalent for 1374 eyes was -3.11 ± 2.88 D. Of the total 1374 eyes, 91.8% (n = 1262) eyes had myopia, 4.7% (n = 65) eyes had hyperopia and 3.4% (n = 47) had emmetropia with astigmatism. Distribution percentage of astigmatism (cylinder error of ≥ 0.50 D) was 78.5% (1078/1374 eyes); of which % 69.1% (994/1374) had low to moderate astigmatism and 9.4% (129/1374) had high astigmatism. Of the adult candidates seeking laser refractive correction in a private setting in Saudi Arabia, myopia represented greatest burden with more than 90% myopic eyes, compared to hyperopia in nearly 5% eyes. Astigmatism was present in more than 78% eyes.

Rapid Inversion of Angular Deflection Data for Certain Axisymmetric Refractive Index Distributions

NASA Technical Reports Server (NTRS)

Rubinstein, R.; Greenberg, P. S.

1994-01-01

Certain functions useful for representing axisymmetric refractive-index distributions are shown to have exact solutions for Abel transformation of the resulting angular deflection data. An advantage of this procedure over direct numerical Abel inversion is that least-squares curve fitting is a smoothing process that reduces the noise sensitivity of the computation

Gradients of refractive index in the crystalline lens and transient changes in refraction among patients with diabetes.

PubMed

Charman, W Neil; Adnan; Atchison, David A

2012-12-01

Transient hyperopic refractive shifts occur on a timescale of weeks in some patients after initiation of therapy for hyperglycemia, and are usually followed by recovery to the original refraction. Possible lenticular origin of these changes is considered in terms of a paraxial gradient index model. Assuming that the lens thickness and curvatures remain unchanged, as observed in practice, it appears possible to account for initial hyperopic refractive shifts of up to a few diopters by reduction in refractive index near the lens center and alteration in the rate of change between center and surface, so that most of the index change occurs closer to the lens surface. Restoration of the original refraction depends on further change in the refractive index distribution with more gradual changes in refractive index from the lens center to its surface. Modeling limitations are discussed.

Gradients of refractive index in the crystalline lens and transient changes in refraction among patients with diabetes

PubMed Central

Charman, W. Neil; Adnan; Atchison, David A.

2012-01-01

Transient hyperopic refractive shifts occur on a timescale of weeks in some patients after initiation of therapy for hyperglycemia, and are usually followed by recovery to the original refraction. Possible lenticular origin of these changes is considered in terms of a paraxial gradient index model. Assuming that the lens thickness and curvatures remain unchanged, as observed in practice, it appears possible to account for initial hyperopic refractive shifts of up to a few diopters by reduction in refractive index near the lens center and alteration in the rate of change between center and surface, so that most of the index change occurs closer to the lens surface. Restoration of the original refraction depends on further change in the refractive index distribution with more gradual changes in refractive index from the lens center to its surface. Modeling limitations are discussed. PMID:23243557

Complex refractive index of normal and malignant human colorectal tissue in the visible and near-infrared.

PubMed

Giannios, Panagiotis; Koutsoumpos, Spyridon; Toutouzas, Konstantinos G; Matiatou, Maria; Zografos, George C; Moutzouris, Konstantinos

2017-02-01

A multi-wavelength prism coupling refractometer is utilized to measure the angular reflectance of freshly excised human intestinal tissue specimens. Based on reflectance data, the real and imaginary part of the refractive index is calculated via Fresnel analysis for three visible (blue, green, red) and two near-infrared (963 nm and 1551 nm) wavelengths. Averaged values of the complex refractive index and corresponding Cauchy dispersion fits are given for the mucosa, submucosa and serosa layers of the colorectal wall at the normal state. The refractive constants of tumorous and normal mucosa are then cross-compared for the indicative cases of one patient diagnosed with a benign polyp and three patients diagnosed with adenocarcinomas of different phenotype. Significant index contrast exists between the normal and diseased states, indicating the potential use of refractive index as a marker of colorectal dysplasia. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

[Correction of light refraction and reflection in medical transmission optical tomography].

PubMed

Tereshchenko, S A; Potapov, D A

2002-01-01

The effects of light refraction and reflection on the quality of image reconstruction in medical transmission optical tomography of high-scattering media are considered. It has been first noted that light refraction not only distorts the geometric scheme of measurements, but may lead to the appearance of object areas that cannot be scanned. Some ways of decreasing the effect of refraction on the reconstruction of spatial distribution of the extinction coefficient are stated.

Ultraviolet complex refractive index of Martian dust Laboratory measurements of terrestrial analogs

NASA Technical Reports Server (NTRS)

Egan, W. G.; Hilgeman, T.; Pang, K.

1975-01-01

The optical complex index of refraction of four candidate Martian surface materials has been determined between 0.185 and 0.4 microns using a modified Kubelka-Munk scattering theory. The cadidate materials were limonite, andesite, montmorillonite, and basalt. The effect of scattering has been removed from the results. Also presented are diffuse reflection and transmission data on these samples.

Effect of Index of Refraction on Radiation Characteristics in a Heated Absorbing, Emitting, and Scattering Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1992-01-01

The index of refraction can considerably influence the temperature distribution and radiative heat flow in semitransparent materials such as some ceramics. For external radiant heating, the refractive index influences the amount of energy transmitted into the interior of the material. Emission within a material depends on the square of its refractive index, and hence this emission can be many times that for a biackbody radiating into a vacuum. Since radiation exiting through an interface into a vacuum cannot exceed that of a blackbody, there is extensive reflection at the internal surface of an interface, mostly by total internal reflection. This redistributes energy within the layer and tends to make its temperature distribution more uniform. The purpose of the present analysis is to show that, for radiative equilibrium in a gray layer with diffuse interfaces, the temperature distribution and radiative heat flux for any index of refraction can be obtained very simply from the results for an index of refraction of unity. For the situation studied here, the layer is subjected to external radiative heating incident on each of its surfaces. The material emits, absorbs, and isotropically scatters radiation. For simplicity the index of refraction is unity in the medium surrounding the layer. The surfaces of the layer are assumed diffuse. This is probably a reasonable approximation for a ceramic layer that has not been polished. When transmitted radiation or radiation emitted from the interior reaches the inner surface of an interface, the radiation is diffused and some of it thereby placed into angular directions for which there is total internal reflection. This provides a trapping effect for retaining energy within the layer and tends to equalize its temperature distribution. An analysis of temperature distributions in absorbing-emitting layers, including index of refraction effects, was developed by Gardon (1958) to predict cooling and heat treating of glass plates. The interfaces were optically smooth; the resulting specular reflections were computed from the Fresnel reflection laws. This provides a somewhat different behavior than for diffuse interfaces. A similar application was for heating that occurs in a window of a re-entry vehicle (Fowle et al., 1969). A number of recent papers (Rokhsaz and Dougherty, 1989; Ping and Lallemand, 1989; Crosbie and Shieh, 1990) further examined the effects of Fresnel boundary reflections and nonunity refractive index. Other examples of analyses of both steady and transient heat transfer to single or multiple plane layers (Amlin and Korpela, 1979; Tarshis et al., 1969) have used diffuse assumptions at the interfaces as in the present study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Huafeng; Colabello, Diane M.; Sklute, Elizabeth C.

The absolute absorption coefficient, α(E), is a critical design parameter for devices using semiconductors for light harvesting associated with renewable energy production, both for classic technologies such as photovoltaics and for emerging technologies such as direct solar fuel production. While α(E) is well-known for many classic simple semiconductors used in photovoltaic applications, the absolute values of α(E) are typically unknown for the complex semiconductors being explored for solar fuel production due to the absence of single crystals or crystalline epitaxial films that are needed for conventional methods of determining α(E). In this work, a simple self-referenced method for estimating bothmore » the refractive indices, n(E), and absolute absorption coefficients, α(E), for loose powder samples using diffuse reflectance data is demonstrated. In this method, the sample refractive index can be deduced by refining n to maximize the agreement between the relative absorption spectrum calculated from bidirectional reflectance data (calculated through a Hapke transform which depends on n) and integrating sphere diffuse reflectance data (calculated through a Kubleka–Munk transform which does not depend on n). This new method can be quickly used to screen the suitability of emerging semiconductor systems for light-harvesting applications. The effectiveness of this approach is tested using the simple classic semiconductors Ge and Fe 2O 3 as well as the complex semiconductors La 2MoO 5 and La 4Mo 2O 11. The method is shown to work well for powders with a narrow size distribution (exemplified by Fe 2O 3) and to be ineffective for semiconductors with a broad size distribution (exemplified by Ge). As such, it provides a means for rapidly estimating the absolute optical properties of complex solids which are only available as loose powders.« less

Microwave Properties of Ice-Phase Hydrometeors for Radar and Radiometers: Sensitivity to Model Assumptions

NASA Technical Reports Server (NTRS)

Johnson, Benjamin T.; Petty, Grant W.; Skofronick-Jackson, Gail

2012-01-01

A simplied framework is presented for assessing the qualitative sensitivities of computed microwave properties, satellite brightness temperatures, and radar reflectivities to assumptions concerning the physical properties of ice-phase hydrometeors. Properties considered included the shape parameter of a gamma size distribution andthe melted-equivalent mass median diameter D0, the particle density, dielectric mixing formula, and the choice of complex index of refraction for ice. We examine these properties at selected radiometer frequencies of 18.7, 36.5, 89.0, and 150.0 GHz; and radar frequencies at 2.8, 13.4, 35.6, and 94.0 GHz consistent with existing and planned remote sensing instruments. Passive and active microwave observables of ice particles arefound to be extremely sensitive to the melted-equivalent mass median diameter D0 ofthe size distribution. Similar large sensitivities are found for variations in the ice vol-ume fraction whenever the geometric mass median diameter exceeds approximately 1/8th of the wavelength. At 94 GHz the two-way path integrated attenuation is potentially large for dense compact particles. The distribution parameter mu has a relatively weak effect on any observable: less than 1-2 K in brightness temperature and up to 2.7 dB difference in the effective radar reflectivity. Reversal of the roles of ice and air in the MaxwellGarnett dielectric mixing formula leads to a signicant change in both microwave brightness temperature (10 K) and radar reflectivity (2 dB). The choice of Warren (1984) or Warren and Brandt (2008) for the complex index of refraction of ice can produce a 3%-4% change in the brightness temperature depression.

Rigorous theoretical framework for particle sizing in turbid colloids using light refraction.

PubMed

García-Valenzuela, Augusto; Barrera, Rubén G; Gutierrez-Reyes, Edahí

2008-11-24

Using a non-local effective-medium approach, we analyze the refraction of light in a colloidal medium. We discuss the theoretical grounds and all the necessary precautions to design and perform experiments to measure the effective refractive index in dilute colloids. As an application, we show that it is possible to retrieve the size of small dielectric particles in a colloid by measuring the complex effective refractive index and the volume fraction occupied by the particles.

Atmospheric refraction effects on baseline error in satellite laser ranging systems

NASA Technical Reports Server (NTRS)

Im, K. E.; Gardner, C. S.

1982-01-01

Because of the mathematical complexities involved in exact analyses of baseline errors, it is not easy to isolate atmospheric refraction effects; however, by making certain simplifying assumptions about the ranging system geometry, relatively simple expressions can be derived which relate the baseline errors directly to the refraction errors. The results indicate that even in the absence of other errors, the baseline error for intercontinental baselines can be more than an order of magnitude larger than the refraction error.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, expressions provide the temperature distribution and heat flow for a diffusing medium with a continually varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Non-uniform refractive index field measurement based on light field imaging technique

NASA Astrophysics Data System (ADS)

Du, Xiaokun; Zhang, Yumin; Zhou, Mengjie; Xu, Dong

2018-02-01

In this paper, a method for measuring the non-uniform refractive index field based on the light field imaging technique is proposed. First, the light field camera is used to collect the four-dimensional light field data, and then the light field data is decoded according to the light field imaging principle to obtain image sequences with different acquisition angles of the refractive index field. Subsequently PIV (Particle Image Velocimetry) technique is used to extract ray offset of each image. Finally, the distribution of non-uniform refractive index field can be calculated by inversing the deflection of light rays. Compared with traditional optical methods which require multiple optical detectors from multiple angles to synchronously collect data, the method proposed in this paper only needs a light field camera and shoot once. The effectiveness of the method has been verified by the experiment which quantitatively measures the distribution of the refractive index field above the flame of the alcohol lamp.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, the analytical expressions provide the temperature distribution and heat flow for a diffusing medium with a continuously varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Response to Comment on "Is the nuclear refractive index lower than cytoplasm? Validation of phase measurements and implications for light scattering technologies": A Comment on "How a phase image of a cell with nucleus refractive index smaller than that of the cytoplasm should look like?", e201800033.

PubMed

Steelman, Zachary A; Eldridge, Will J; Wax, Adam

2018-06-01

Recently, Maxim A. Yurkin commented on our paper "Is the nuclear refractive index lower than cytoplasm? Validation of phase measurements and implications for light scattering technologies" as well as on a complementary study "Cell nuclei have lower refractive index and mass density than cytoplasm" from Schürmann et al. In his comment, Yurkin concluded that quantitative phase images of cells with nuclei that are less optically dense than the cytoplasm must exhibit a characteristic concavity, the absence of which is evidence against our conclusion of a less-dense nucleus. In this response, we suggest that Yurkin's conclusion is reached through an oversimplification of the spatial refractive index distribution within cells, which does not account for high index inclusions such as the nucleolus. We further cite recent studies in 3-dimensional refractive index imaging, in which the preponderance of studies supports our conclusion. Finally, we comment on the current state of knowledge regarding subcellular refractive index distributions in living cells. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The investigation of advanced remote sensing techniques for the measurement of aerosol characteristics

NASA Technical Reports Server (NTRS)

Deepak, A.; Becher, J.

1979-01-01

Advanced remote sensing techniques and inversion methods for the measurement of characteristics of aerosol and gaseous species in the atmosphere were investigated. Of particular interest were the physical and chemical properties of aerosols, such as their size distribution, number concentration, and complex refractive index, and the vertical distribution of these properties on a local as well as global scale. Remote sensing techniques for monitoring of tropospheric aerosols were developed as well as satellite monitoring of upper tropospheric and stratospheric aerosols. Computer programs were developed for solving multiple scattering and radiative transfer problems, as well as inversion/retrieval problems. A necessary aspect of these efforts was to develop models of aerosol properties.

Cavity-enhanced measurements for determining dielectric-membrane thickness and complex index of refraction.

PubMed

Stambaugh, Corey; Durand, Mathieu; Kemiktarak, Utku; Lawall, John

2014-08-01

The material properties of silicon nitride (SiN) play an important role in the performance of SiN membranes used in optomechanical applications. An optimum design of a subwavelength high-contrast grating requires accurate knowledge of the membrane thickness and index of refraction, and its performance is ultimately limited by material absorption. Here we describe a cavity-enhanced method to measure the thickness and complex index of refraction of dielectric membranes with small, but nonzero, absorption coefficients. By determining Brewster's angle and an angle at which reflection is minimized by means of destructive interference, both the real part of the index of refraction and the sample thickness can be measured. A comparison of the losses in the empty cavity and the cavity containing the dielectric sample provides a measurement of the absorption.

Two-step recording of visible holographic elements in photo-thermo-refractive glass

NASA Astrophysics Data System (ADS)

Kompan, Fedor; Divliansky, Ivan; Smirnov, Vadim; Glebov, Leonid B.

2018-02-01

Photo-thermo-refractive (PTR) glass) is a photosensitive silicate glass doped with Ce3+ where a permanent refractive index decrement is produced by UV exposure followed by thermal development. This material provides high efficiency and low losses combined with high thermal, ionizing and laser tolerance of holographic optical elements (HOEs). This is why PTR glass is widely used for holographic recording of volume Bragg gratings (trivial holograms produced by interference of two collimated beams) and phase plates operating in near UV, visible, and near IR spectral regions. It would be very beneficial though to record also complex HOEs (lenses and curved mirrors) for those spectral regions. However, PTR is not sensitive to visible or IR radiation and therefore does not allow the recording of nonplanar holograms for these regions. The present paper describes a technique for recording complex HOEs using visible radiation in Ce3+ doped PTR glass. This two-step technique includes a blank exposure to UV radiation followed by structured exposure to a visible beam. It was found that the second exposure decreases the refractive index decrement induced in the UV exposed glass after thermal development. This means that areas, which underwent double exposure, have refractive index lower than in unexposed areas but higher than in just UV exposed ones. Thus, this technique provides refractive index increment after visible irradiation of UV exposed PTR glass. Using this approach, complex holograms (curved mirrors and lenses) operating in the visible region, were recorded in PTR glass.

Significant Axial Elongation with Minimal Change in Refraction in 3- to 6-Year-Old Chinese Preschoolers: The Shenzhen Kindergarten Eye Study.

PubMed

Guo, Xinxing; Fu, Min; Ding, Xiaohu; Morgan, Ian G; Zeng, Yangfa; He, Mingguang

2017-12-01

To document the distribution of ocular biometry and to evaluate its associations with refraction in a group of Chinese preschoolers. Population-based cross-sectional study. A total of 1133 preschoolers 3 to 6 years of age from 8 representative kindergartens. Biometric measurements including axial length (AL), anterior chamber depth (ACD), and corneal radius of curvature (CR) were obtained from partial-coherence laser interferometry (IOL Master; Carl Zeiss Meditec, Oberkochen, Germany) before cycloplegia. Lens power (LP) and AL-to-CR ratio were calculated. Cycloplegic refraction (3 drops of 1% cyclopentolate) was measured using an autorefractor (KR8800; Topcon Corp., Tokyo, Japan), and spherical equivalent refraction (SER) was calculated. Biometric and refractive parameters were assessed as a function of age and gender. Multiple regression analysis was performed to explore the associations between refraction and ocular biometry. Ocular biometric distributions and their relationships to refraction. Among the 1127 children (99.5%) with successful cycloplegic refraction, mean SER was 1.37±0.63 diopters (D). Prevalence of myopia increased from 0% at 3 years of age to 3.7% (95% confidence interval, 1.0%-6.5%) at 6 years of age. Biometric parameters followed Gaussian distributions with means of 22.39±0.68 mm for AL, 7.79±0.25 mm for CR, and 24.61±1.42 D for calculated LP; and non-Gaussian distributions with means of 3.34±0.24 mm for ACD and 2.88±0.06 for AL-to-CR ratio. Axial length, ACD, and AL-to-CR ratio increased from 3 to 6 years of age, CR remained stable, whereas LP declined. Overall, SER declined slightly. For the SER variance, AL explained 18.6% and AL-to-CR ratio explained 39.8%, whereas AL, CR, and LP accounted for 80.0% after adjusting for age and gender. Young Chinese children are predominantly mildly hyperopic, with a low prevalence of myopia by the age of 6 years. An increase of 1 mm in AL was associated with only 0.45 D of myopic change. Decreases in LP reduce the myopic shifts that normally would be associated with increases in AL, and thus play a key role in refractive development in this age group. Copyright © 2017 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.

Capturing Characteristics of Atmospheric Refractivity Using Observations and Modeling Approaches

DTIC Science & Technology

2015-06-01

Approved for public release; distribution is unlimited 12b. DISTRIBUTION CODE 13. ABSTRACT (maximum 200 words) Electromagnetic wave...INTENTIONALLY LEFT BLANK v ABSTRACT Electromagnetic wave propagation is sensitive to gradients of refractivity derived from atmospheric temperature...evaporation duct profiles is then run through AREPS to calculate the propagation loss of EM energy along the path of varying geometric and transmitter setups

Relative Proportion Of Different Types Of Refractive Errors In Subjects Seeking Laser Vision Correction

PubMed Central

Althomali, Talal A.

2018-01-01

Background: Refractive errors are a form of optical defect affecting more than 2.3 billion people worldwide. As refractive errors are a major contributor of mild to moderate vision impairment, assessment of their relative proportion would be helpful in the strategic planning of health programs. Purpose: To determine the pattern of the relative proportion of types of refractive errors among the adult candidates seeking laser assisted refractive correction in a private clinic setting in Saudi Arabia. Methods: The clinical charts of 687 patients (1374 eyes) with mean age 27.6 ± 7.5 years who desired laser vision correction and underwent a pre-LASIK work-up were reviewed retrospectively. Refractive errors were classified as myopia, hyperopia and astigmatism. Manifest refraction spherical equivalent (MRSE) was applied to define refractive errors. Outcome Measures: Distribution percentage of different types of refractive errors; myopia, hyperopia and astigmatism. Results: The mean spherical equivalent for 1374 eyes was -3.11 ± 2.88 D. Of the total 1374 eyes, 91.8% (n = 1262) eyes had myopia, 4.7% (n = 65) eyes had hyperopia and 3.4% (n = 47) had emmetropia with astigmatism. Distribution percentage of astigmatism (cylinder error of ≥ 0.50 D) was 78.5% (1078/1374 eyes); of which % 69.1% (994/1374) had low to moderate astigmatism and 9.4% (129/1374) had high astigmatism. Conclusion and Relevance: Of the adult candidates seeking laser refractive correction in a private setting in Saudi Arabia, myopia represented greatest burden with more than 90% myopic eyes, compared to hyperopia in nearly 5% eyes. Astigmatism was present in more than 78% eyes. PMID:29872484

Vacuum birefringence in strong magnetic fields: (II) Complex refractive index from the lowest Landau level

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hattori, Koichi, E-mail: khattori@yonsei.ac.kr; Itakura, Kazunori, E-mail: kazunori.itakura@kek.jp; Department of Particle and Nuclear Studies, Graduate University for Advanced Studies

2013-07-15

We compute the refractive indices of a photon propagating in strong magnetic fields on the basis of the analytic representation of the vacuum polarization tensor obtained in our previous paper. When the external magnetic field is strong enough for the fermion one-loop diagram of the polarization tensor to be approximated by the lowest Landau level, the propagating mode in parallel to the magnetic field is subject to modification: The refractive index deviates from unity and can be very large, and when the photon energy is large enough, the refractive index acquires an imaginary part indicating decay of a photon intomore » a fermion–antifermion pair. We study dependences of the refractive index on the propagating angle and the magnetic-field strength. It is also emphasized that a self-consistent treatment of the equation which defines the refractive index is indispensable for accurate description of the refractive index. This self-consistent treatment physically corresponds to consistently including the effects of back reactions of the distorted Dirac sea in response to the incident photon. -- Highlights: •Vacuum birefringence and photon decay are described by the complex refractive index. •Resummed photon vacuum polarization tensor in the lowest Landau level is used. •Back reactions from the distorted Dirac sea are self-consistently taken into account. •Self-consistent treatment drastically changes structure in photon energy dependence. •Dependences on photon propagation angle and magnetic-field strength are presented.« less

Subjective method of refractometry and depth of focus

PubMed Central

Sergienko, Nikolai M.; Gromova, Anastasia; Sergienko, Nikolai

2012-01-01

Purpose To study the impact of the depth of focus on subjective refraction and distribution of myopic and hyperopic refractions. Methods A total of 450 eyes of 305 subjects in the age range of 23–34 years were recruited for the study. A distribution of refractions was examined using a traditional method of the subjective refractometry on the basis of point-like posterior focus notion. Correction of the results was made on the assumption that the emmetropic eye retains high visual acuity when applying convex lenses with values which are fewer or equal to the depth of focus values. The following values of the depth of focus were used: ±0.55 D, ±0.35 D and ±0.2 D for visual acuity 1.0, 1.5 and 2.0, respectively. Results Application of the traditional method of refractometry produced the following occurrence of refractions: hypermetropia 59.3%, myopia 22% and emmetropia 18.7%. After correction of the initial results of values of the depth of focus the distribution of refractions was as follows: hypermetropia 12.7%, myopia 22% and emmetropia 65.3%. Conclusion The traditional method of subjective refractometry with application of trial lenses was developed on the basis of data of large optical aberrations and significant depth of focus which values should be taken into account during interpretation of results of subjective refractometry. Our data regarding to prevalence of emmetropic refraction falls in line with basic science provisions in respect of the physiology of the eye.

Characteristics of Refractive Errors in a Population of Adults in the Central Region of Poland

PubMed Central

Jurowski, Piotr; Grzybowski, Andrzej; Smigielski, Janusz

2018-01-01

Background: To investigate the distribution of refractive errors and their characteristics in older adults from a Polish population. Methods: The study design was a cross-sectional study. A total of 1107 men and women were interviewed and underwent detailed ophthalmic examinations, 998 subjects underwent refraction. Myopia was defined as spherical equivalent (SER) refraction ≤−0.5 dioptres (D) and hyperopia was defined as SER ≥+0.5 dioptres (D). Results: Among those who were refracted the distribution of myopia and hyperopia was 24.1% (95% CI 21.4–26.7) and 37.5% (95% CI 34.5–40.5), respectively. Myopia decreased from 28.7% in subjects aged 35–59 years to 19.3% in those aged 60 years or older and hyperopia increased from 21.8% at 35–59 years of age to 53.3% in subjects aged ≥60 years. Multiple regression analysis showed decreasing age (OR 0.98, 95% CI 0.96–1.00), female gender (OR 1.87, 95% CI 1.18–2.95) and presence of cataract (OR 2.40, 95% CI 1.24–4.63) were independent risk factors associated with myopia. Conclusions: The distribution of refractive errors found in our study is similar to those reported in other Caucasian populations and differs from Asian populations. Myopia was positively associated with younger age, female gender and presence of cataract. PMID:29316688

Determination of the refractive index of dehydrated cells by means of digital holographic microscopy

NASA Astrophysics Data System (ADS)

Belashov, A. V.; Zhikhoreva, A. A.; Bespalov, V. G.; Vasyutinskii, O. S.; Zhilinskaya, N. T.; Novik, V. I.; Semenova, I. V.

2017-10-01

Spatial distributions of the integral refractive index in dehydrated cells of human oral cavity epithelium are obtained by means of digital holographic microscopy, and mean refractive index of the cells is determined. The statistical analysis of the data obtained is carried out, and absolute errors of the method are estimated for different experimental conditions.

Retrieval of Aerosol Microphysical Properties from AERONET Photo-Polarimetric Measurements. 2: A New Research Algorithm and Case Demonstration

NASA Technical Reports Server (NTRS)

Xu, Xiaoguang; Wang, Jun; Zeng, Jing; Spurr, Robert; Liu, Xiong; Dubovik, Oleg; Li, Li; Li, Zhengqiang; Mishchenko, Michael I.; Siniuk, Aliaksandr;

Analysis of interferograms of refractive index inhomogeneities produced in optical materials

NASA Astrophysics Data System (ADS)

Tarjányi, N.

2014-12-01

Optical homogeneity of materials intended for optical applications is one of the criterions which decide on an appropriate application method for the material. The existence of a refractive index inhomogeneity inside a material may disqualify it from utilization or by contrary, provide an advantage. For observation of a refractive index inhomogeneity, even a weak one, it is convenient to use any of interferometric methods. They are very sensitive and provide information on spatial distribution of the refractive index, immediately. One can use them also in case when the inhomogeneity evolves in time, usually due to action of some external fields. Then, the stream of interferograms provides a dynamic evolution of a spatial distribution of the inhomogeneity. In the contribution, there are presented results of the analysis of interferograms obtained by observing the creation of a refractive index inhomogeneity due to illumination of thin layers of a polyvinyl-alcohol/acrylamide photopolymer and a plate of photorefractive crystal, lithium niobate, by light and a refractive index inhomogeneity originated at the boundary of two layers of polydimethylsiloxane. The obtained dependences can be used for studying of the mechanisms responsible for the inhomogeneity creation, designing various technical applications or for diagnostics of fabricated components.

Evaluation of a flow cytometry method to determine size and real refractive index distributions in natural marine particle populations.

PubMed

Agagliate, Jacopo; Röttgers, Rüdiger; Twardowski, Michael S; McKee, David

2018-03-01

A flow cytometric (FC) method was developed to retrieve particle size distributions (PSDs) and real refractive index (n r ) information in natural waters. Geometry and signal response of the sensors within the flow cytometer (CytoSense, CytoBuoy b.v., Netherlands) were characterized to form a scattering inversion model based on Mie theory. The procedure produced a mesh of diameter and n r isolines where each particle is assigned the diameter and n r values of the closest node, producing PSDs and particle real refractive index distributions. The method was validated using polystyrene bead standards of known diameter and polydisperse suspensions of oil with known n r , and subsequently applied to natural samples collected across a broad range of UK shelf seas. FC PSDs were compared with independent PSDs produced from data of two LISST-100X instruments (type B and type C). PSD slopes and features were found to be consistent between the FC and the two LISST-100X instruments, but LISST concentrations were found in disagreement with FC concentrations and with each other. FC n r values were found to agree with expected refractive index values of typical marine particle components across all samples considered. The determination of particle size and refractive index distributions enabled by the FC method has potential to facilitate identification of the contribution of individual subpopulations to the bulk inherent optical properties and biogeochemical properties of the particle population.

Evaluation of internal refraction with the optical path difference scan.

PubMed

Muftuoglu, Orkun; Erdem, Uzeyir

2008-01-01

To evaluate internal refraction and its relation to other optical properties of the eye across a large range of refractive errors, which can provide useful information for the assessment and design of intraocular lenses and corneal ablation patterns. Cohort study. Three hundred ninety-four eyes of 197 healthy subjects with a mean age of 27+/-7 years (range, 18-42). All eyes underwent optical path difference scans to evaluate corneal topography, whole and internal ocular refraction (determined by the subtraction of corneal refraction from whole ocular refraction), and total and higher-order aberrations (HOAs) were assessed. After the conversion of any spherocylindrical refractive errors to vectorial data (sphere equivalent, blurring strength; cylinder, J(0) [power of Jackson cross cylinder at 90 degrees and 180 degrees] and J45 [power of Jackson cross cylinder at 45 degrees and 135 degrees]), the distribution of internal refraction among refraction groups (high myopes, low to moderate myopes, hyperopes, mixed astigmats, and emmetropes) and relationships between internal refraction, corneal refraction, and wavefront aberrations were analyzed. The compensation relation and its rate between corneal and internal astigmatism was assessed by the compensation factor (CF). Whole ocular power and astigmatism, corneal power and astigmatism, internal power and astigmatism, CF for astigmatic data, location of the highest internal refraction zone, and wavefront aberrations. The highest refraction zone was mostly (90%) located in the center in myopes, whereas it was located at the nasal side (71%) in hyperopes. There was a significant correlation between whole ocular and internal powers (P<0.01), but no correlation was observed between corneal and internal powers (P>0.05). Internal astigmatism was mostly against the rule. The mean CF J(0) was 0.63+/-3.78 and CF J(45) was 0.57+/-2.47. The magnitude of the internal astigmatism under the 3-mm zone was correlated with the magnitude of corneal astigmatism (P<0.05). The distribution of astigmatic CF differed among refraction groups. There were significant correlations between internal power and spherical aberration (P<0.05) and internal cylinder under the 5-mm zone and HOAs (P<0.001). There is a remarkable tilt in internal refraction in hyperopes. Although there is a tendency of undercompensation of the corneal astigmatism by internal astigmatism in the entire group of eyes, the compensation differs among refraction groups.

Estimation and evaluation of COSMIC radio occultation excess phase using undifferenced measurements

NASA Astrophysics Data System (ADS)

Xia, Pengfei; Ye, Shirong; Jiang, Kecai; Chen, Dezhong

2017-05-01

In the GPS radio occultation technique, the atmospheric excess phase (AEP) can be used to derive the refractivity, which is an important quantity in numerical weather prediction. The AEP is conventionally estimated based on GPS double-difference or single-difference techniques. These two techniques, however, rely on the reference data in the data processing, increasing the complexity of computation. In this study, an undifferenced (ND) processing strategy is proposed to estimate the AEP. To begin with, we use PANDA (Positioning and Navigation Data Analyst) software to perform the precise orbit determination (POD) for the purpose of acquiring the position and velocity of the mass centre of the COSMIC (The Constellation Observing System for Meteorology, Ionosphere and Climate) satellites and the corresponding receiver clock offset. The bending angles, refractivity and dry temperature profiles are derived from the estimated AEP using Radio Occultation Processing Package (ROPP) software. The ND method is validated by the COSMIC products in typical rising and setting occultation events. Results indicate that rms (root mean square) errors of relative refractivity differences between undifferenced and atmospheric profiles (atmPrf) provided by UCAR/CDAAC (University Corporation for Atmospheric Research/COSMIC Data Analysis and Archive Centre) are better than 4 and 3 % in rising and setting occultation events respectively. In addition, we also compare the relative refractivity bias between ND-derived methods and atmPrf profiles of globally distributed 200 COSMIC occultation events on 12 December 2013. The statistical results indicate that the average rms relative refractivity deviation between ND-derived and COSMIC profiles is better than 2 % in the rising occultation event and better than 1.7 % in the setting occultation event. Moreover, the observed COSMIC refractivity profiles from ND processing strategy are further validated using European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data, and the results indicate that the undifferenced method reduces the noise level on the excess phase paths in the lower troposphere compared to the single-difference processing strategy.

Numerical simulations of negative-index refraction in wedge-shaped metamaterials.

PubMed

Dong, Z G; Zhu, S N; Liu, H; Zhu, J; Cao, W

2005-07-01

A wedge-shaped structure made of split-ring resonators (SRR) and wires is numerically simulated to evaluate its refraction behavior. Four frequency bands, namely, the stop band, left-handed band, ultralow-index band, and positive-index band, are distinguished according to the refracted field distributions. Negative phase velocity inside the wedge is demonstrated in the left-handed band and the Snell's Law is conformed in terms of its refraction behaviors in different frequency bands. Our results confirmed that negative index of refraction indeed exists in such a composite metamaterial and also provided a convincing support to the results of previous Snell's Law experiments.

Improved identification of the solution space of aerosol microphysical properties derived from the inversion of profiles of lidar optical data, part 1: theory.

PubMed

Kolgotin, Alexei; Müller, Detlef; Chemyakin, Eduard; Romanov, Anton

2016-12-01

Multiwavelength Raman/high spectral resolution lidars that measure backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm can be used for the retrieval of particle microphysical parameters, such as effective and mean radius, number, surface-area and volume concentrations, and complex refractive index, from inversion algorithms. In this study, we carry out a correlation analysis in order to investigate the degree of dependence that may exist between the optical data taken with lidar and the underlying microphysical parameters. We also investigate if the correlation properties identified in our study can be used as a priori or a posteriori constraints for our inversion scheme so that the inversion results can be improved. We made the simplifying assumption of error-free optical data in order to find out what correlations exist in the best case situation. Clearly, for practical applications, erroneous data need to be considered too. On the basis of simulations with synthetic optical data, we find the following results, which hold true for arbitrary particle size distributions, i.e., regardless of the modality or the shape of the size distribution function: surface-area concentrations and extinction coefficients are linearly correlated with a correlation coefficient above 0.99. We also find a correlation coefficient above 0.99 for the extinction coefficient versus (1) the ratio of the volume concentration to effective radius and (2) the product of the number concentration times the sum of the squares of the mean radius and standard deviation of the investigated particle size distributions. Besides that, we find that for particles of any mode fraction of the particle size distribution, the complex refractive index is uniquely defined by extinction- and backscatter-related Ångström exponents, lidar ratios at two wavelengths, and an effective radius.

On the Distribution of Protein Refractive Index Increments

PubMed Central

Zhao, Huaying; Brown, Patrick H.; Schuck, Peter

2011-01-01

The protein refractive index increment, dn/dc, is an important parameter underlying the concentration determination and the biophysical characterization of proteins and protein complexes in many techniques. In this study, we examine the widely used assumption that most proteins have dn/dc values in a very narrow range, and reappraise the prediction of dn/dc of unmodified proteins based on their amino acid composition. Applying this approach in large scale to the entire set of known and predicted human proteins, we obtain, for the first time, to our knowledge, an estimate of the full distribution of protein dn/dc values. The distribution is close to Gaussian with a mean of 0.190 ml/g (for unmodified proteins at 589 nm) and a standard deviation of 0.003 ml/g. However, small proteins <10 kDa exhibit a larger spread, and almost 3000 proteins have values deviating by more than two standard deviations from the mean. Due to the widespread availability of protein sequences and the potential for outliers, the compositional prediction should be convenient and provide greater accuracy than an average consensus value for all proteins. We discuss how this approach should be particularly valuable for certain protein classes where a high dn/dc is coincidental to structural features, or may be functionally relevant such as in proteins of the eye. PMID:21539801

On the distribution of protein refractive index increments.

PubMed

Zhao, Huaying; Brown, Patrick H; Schuck, Peter

2011-05-04

The protein refractive index increment, dn/dc, is an important parameter underlying the concentration determination and the biophysical characterization of proteins and protein complexes in many techniques. In this study, we examine the widely used assumption that most proteins have dn/dc values in a very narrow range, and reappraise the prediction of dn/dc of unmodified proteins based on their amino acid composition. Applying this approach in large scale to the entire set of known and predicted human proteins, we obtain, for the first time, to our knowledge, an estimate of the full distribution of protein dn/dc values. The distribution is close to Gaussian with a mean of 0.190 ml/g (for unmodified proteins at 589 nm) and a standard deviation of 0.003 ml/g. However, small proteins <10 kDa exhibit a larger spread, and almost 3000 proteins have values deviating by more than two standard deviations from the mean. Due to the widespread availability of protein sequences and the potential for outliers, the compositional prediction should be convenient and provide greater accuracy than an average consensus value for all proteins. We discuss how this approach should be particularly valuable for certain protein classes where a high dn/dc is coincidental to structural features, or may be functionally relevant such as in proteins of the eye. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Waveguide-based optical chemical sensor

DOEpatents

Grace, Karen M [Ranchos de Taos, NM; Swanson, Basil I [Los Alamos, NM; Honkanen, Seppo [Tucson, AZ

2007-03-13

The invention provides an apparatus and method for highly selective and sensitive chemical sensing. Two modes of laser light are transmitted through a waveguide, refracted by a thin film host reagent coating on the waveguide, and analyzed in a phase sensitive detector for changes in effective refractive index. Sensor specificity is based on the particular species selective thin films of host reagents which are attached to the surface of the planar optical waveguide. The thin film of host reagents refracts laser light at different refractive indices according to what species are forming inclusion complexes with the host reagents.

Negative refractive index, perfect lenses and checkerboards: Trapping and imaging effects in folded optical spaces

NASA Astrophysics Data System (ADS)

Guenneau, Sébastien; Ramakrishna, S. Anantha

2009-06-01

Newly discovered metamaterials have opened new vistas for better control of light via negative refraction, whereby light refracts in the "wrong" manner. These are dielectric and metallic composite materials structured at subwavelength lengthscales. Their building blocks consist of local resonators such as conducting thin bars and split rings driving the material parameters such as the dielectric permittivity and magnetic permeability to negative (complex) values. Combined together, these structural elements can bring about a (complex valued) negative effective refractive index for the Snell-Descartes law and result in negative refraction of radiation. Negative refractive index materials can support a host of surface plasmon states for both polarizations of light. This makes possible unique effects such as imaging with subwavelength image resolution through the Pendry-Veselago slab lens. Other geometries have also been investigated, such as cylindrical or spherical lenses that enable a magnification of images with subwavelength resolution. Superlenses of three-fold (equilateral triangle), four-fold (square) and six-fold (hexagonal) geometry allow for multiple images, respectively two, three, and five. Generalization to rectangular and triangular checkerboards consisting of alternating cells of positive and negative refractive index represents a very singular situation in which the density of modes diverges at the corners, with an infinity of images. Sine-cosecant anisotropic heterogeneous square and triangular checkerboards can be respectively mapped onto three-dimensional cubic and icosahedral corner lenses consisting of alternating positive and negative refractive regions. All such systems with corners between negative and positive refractive media display very singular behavior with the local density of states becoming infinitely large at the corner, in the limit of no dissipation. We investigate all of these, using the unifying viewpoint of transformation optics. To cite this article: S. Guenneau, S.A. Ramakrishna, C. R. Physique 10 (2009).

Refractive-index measurement and inverse correction using optical coherence tomography.

PubMed

Stritzel, Jenny; Rahlves, Maik; Roth, Bernhard

2015-12-01

We describe a novel technique for determination of the refractive index of hard biological tissue as well as nonopaque technical samples based on optical coherence tomography (OCT). Our method relies on an inverse refractive-index correction (I-RIC), which matches a measured feature geometry distorted due to refractive-index boundaries to its real geometry. For known feature geometry, the refractive index can be determined with high precision from the best match between the distorted and corrected images. We provide experimental data for refractive-index measurements on a polymethylmethacrylate (PMMA) and on an ex vivo porcine cranial-bone, which are compared to reference measurements and previously published data. Our method is potentially capable of in vivo measurements on rigid biological tissue such as bone as, for example, is required to improve guidance in robot-aided surgical interventions and also for retrieving complex refractive-index profiles of compound materials.

Bioinspired adaptive gradient refractive index distribution lens

NASA Astrophysics Data System (ADS)

Yin, Kezhen; Lai, Chuan-Yar; Wang, Jia; Ji, Shanzuo; Aldridge, James; Feng, Jingxing; Olah, Andrew; Baer, Eric; Ponting, Michael

2018-02-01

Inspired by the soft, deformable human eye lens, a synthetic polymer gradient refractive index distribution (GRIN) lens with an adaptive geometry and focal power has been demonstrated via multilayer coextrusion and thermoforming of nanolayered elastomeric polymer films. A set of 30 polymer nanolayered films comprised of two thermoplastic polyurethanes having a refractive index difference of 0.05 were coextruded via forced-assembly technique. The set of 30 nanolayered polymer films exhibited transmission near 90% with each film varying in refractive index by 0.0017. An adaptive GRIN lens was fabricated from a laminated stack of the variable refractive index films with a 0.05 spherical GRIN. This lens was subsequently deformed by mechanical ring compression of the lens. Variation in the optical properties of the deformable GRIN lens was determined, including 20% variation in focal length and reduced spherical aberration. These properties were measured and compared to simulated results by placido-cone topography and ANSYS methods. The demonstration of a solid-state, dynamic focal length, GRIN lens with improved aberration correction was discussed relative to the potential future use in implantable devices.

Micrometer-scale particle sizing by laser diffraction: critical impact of the imaginary component of refractive index.

PubMed

Beekman, Alice; Shan, Daxian; Ali, Alana; Dai, Weiguo; Ward-Smith, Stephen; Goldenberg, Merrill

2005-04-01

This study evaluated the effect of the imaginary component of the refractive index on laser diffraction particle size data for pharmaceutical samples. Excipient particles 1-5 microm in diameter (irregular morphology) were measured by laser diffraction. Optical parameters were obtained and verified based on comparison of calculated vs. actual particle volume fraction. Inappropriate imaginary components of the refractive index can lead to inaccurate results, including false peaks in the size distribution. For laser diffraction measurements, obtaining appropriate or "effective" imaginary components of the refractive index was not always straightforward. When the recommended criteria such as the concentration match and the fit of the scattering data gave similar results for very different calculated size distributions, a supplemental technique, microscopy with image analysis, was used to decide between the alternatives. Use of effective optical parameters produced a good match between laser diffraction data and microscopy/image analysis data. The imaginary component of the refractive index can have a major impact on particle size results calculated from laser diffraction data. When performed properly, laser diffraction and microscopy with image analysis can yield comparable results.

FIBER AND INTEGRATED OPTICS: Detection of the optical anisotropy in KTP:Rb waveguides

NASA Astrophysics Data System (ADS)

Buritskiĭ, K. S.; Dianov, Evgenii M.; Maslov, Vladislav A.; Chernykh, V. A.; Shcherbakov, E. A.

1990-10-01

The optical characteristics of channel waveguides made of rubidium-activated potassium titanyl phosphate (KTP:Rb) were determined. The refractive index increment of such waveguides was found to exhibit a considerable anisotropy: Δnx / Δnz approx 2. A deviation of the distribution of the refractive index in a channel waveguide from the model distribution was observed for ion-exchange times in excess of 1 h.

Improved algorithm of ray tracing in ICF cryogenic targets

NASA Astrophysics Data System (ADS)

Zhang, Rui; Yang, Yongying; Ling, Tong; Jiang, Jiabin

2016-10-01

The high precision ray tracing inside inertial confinement fusion (ICF) cryogenic targets plays an important role in the reconstruction of the three-dimensional density distribution by algebraic reconstruction technique (ART) algorithm. The traditional Runge-Kutta methods, which is restricted by the precision of the grid division and the step size of ray tracing, cannot make an accurate calculation in the case of refractive index saltation. In this paper, we propose an improved algorithm of ray tracing based on the Runge-Kutta methods and Snell's law of refraction to achieve high tracing precision. On the boundary of refractive index, we apply Snell's law of refraction and contact point search algorithm to ensure accuracy of the simulation. Inside the cryogenic target, the combination of the Runge-Kutta methods and self-adaptive step algorithm are employed for computation. The original refractive index data, which is used to mesh the target, can be obtained by experimental measurement or priori refractive index distribution function. A finite differential method is performed to calculate the refractive index gradient of mesh nodes, and the distance weighted average interpolation methods is utilized to obtain refractive index and gradient of each point in space. In the simulation, we take ideal ICF target, Luneberg lens and Graded index rod as simulation model to calculate the spot diagram and wavefront map. Compared the simulation results to Zemax, it manifests that the improved algorithm of ray tracing based on the fourth-order Runge-Kutta methods and Snell's law of refraction exhibits high accuracy. The relative error of the spot diagram is 0.2%, and the peak-to-valley (PV) error and the root-mean-square (RMS) error of the wavefront map is less than λ/35 and λ/100, correspondingly.

Extended bidirectional reflectance distribution function for polarized light scattering from subsurface defects under a smooth surface.

PubMed

Shen, Jian; Deng, Degang; Kong, Weijin; Liu, Shijie; Shen, Zicai; Wei, Chaoyang; He, Hongbo; Shao, Jianda; Fan, Zhengxiu

2006-11-01

By introducing the scattering probability of a subsurface defect (SSD) and statistical distribution functions of SSD radius, refractive index, and position, we derive an extended bidirectional reflectance distribution function (BRDF) from the Jones scattering matrix. This function is applicable to the calculation for comparison with measurement of polarized light-scattering resulting from a SSD. A numerical calculation of the extended BRDF for the case of p-polarized incident light was performed by means of the Monte Carlo method. Our numerical results indicate that the extended BRDF strongly depends on the light incidence angle, the light scattering angle, and the out-of-plane azimuth angle. We observe a 180 degrees symmetry with respect to the azimuth angle. We further investigate the influence of the SSD density, the substrate refractive index, and the statistical distributions of the SSD radius and refractive index on the extended BRDF. For transparent substrates, we also find the dependence of the extended BRDF on the SSD positions.

Very low-refractive-index optical thin films consisting of an array of SiO2 nanorods

NASA Astrophysics Data System (ADS)

Xi, J.-Q.; Kim, Jong Kyu; Schubert, E. F.; Ye, Dexian; Lu, T.-M.; Lin, Shawn-Yu; Juneja, Jasbir S.

2006-03-01

The refractive-index contrast in dielectric multilayer structures, optical resonators, and photonic crystals is an important figure of merit that creates a strong demand for high-quality thin films with a low refractive index. A SiO2 nanorod layer with low refractive index of n=1.08, to our knowledge the lowest ever reported in thin-film materials, is grown by oblique-angle electron-beam deposition of SiO2. A single-pair distributed Bragg reflector employing a SiO2 nanorod layer is demonstrated to have enhanced reflectivity, showing the great potential of low-refractive-index films for applications in photonic structures and devices.

Refractive error characteristics of early and advanced presbyopic individuals.

DOT National Transportation Integrated Search

1977-07-01

The frequency and distribution of ocular refractive errors among middle-aged and older people were obtained from a nonclinical population holding a variety of blue-collar, clerical, and technical jobs. The 422 individuals ranged in age from 35 to 69 ...

Modeling of particle radiative properties in coal combustion depending on burnout

NASA Astrophysics Data System (ADS)

Gronarz, Tim; Habermehl, Martin; Kneer, Reinhold

2017-04-01

In the present study, absorption and scattering efficiencies as well as the scattering phase function of a cloud of coal particles are described as function of the particle combustion progress. Mie theory for coated particles is applied as mathematical model. The scattering and absorption properties are determined by several parameters: size distribution, spectral distribution of incident radiation and spectral index of refraction of the particles. A study to determine the influence of each parameter is performed, finding that the largest effect is due to the refractive index, followed by the effect of size distribution. The influence of the incident radiation profile is negligible. As a part of this study, the possibility of applying a constant index of refraction is investigated. Finally, scattering and absorption efficiencies as well as the phase function are presented as a function of burnout with the presented model and the results are discussed.

Study on the refractive errors of school going children of Pokhara city in Nepal.

PubMed

Niroula, D R; Saha, C G

Refractive errors are the one of the most common visual disorders found worldwide in school going children and also it is one of the causes of blindness. It can easily be prevented, if timely proper measures are taken. In Kathmandu valley and Mechi Zone of Nepal, the distribution of refractive errors was found to be very high. No records are available from the Western part of Nepal. Considering the importance of the refractive errors the present study had been undertaken in Pokhara city. 964 subjects (474 boys, 490 girls) were selected between age groups 10 to 19 years from 6 schools representing different region of Pokhara. After Preliminary examination: on acuity of vision with Snellen's and Jaeger's charts, the subjects were referred to the Manipal Teaching Hospital, Pokhara for confirmation of the refractive errors. Sixty two schools children (6.43%), out of 964 had refractive errors. The myopia was found to be most common (4.05%). The refractive errors were found more in Private school children (9.29%) than Government school children (4.23%), which is statistically significant (P < 0.05). More boys (7.59%) were found to have suffered from refractive errors than girls (5.31%). Further, children with vegetarian diet (10.52%) had greater number of refractive errors than non-vegetarian diet children (6.17%). In the present study, percentage distribution of myopia was found to be higher (4.05%) than the hyperopia (1.24%) and astigmatism (1.14%). Interestingly, in the present study the refractive errors were found significantly higher in Private schools children than Government schools because the children who read in Private schools have higher socioeconomic status; spend more time in home work, watching Television and Computer as compared to government schools children. These near activities of the eyes causes stress on eyes of the children and might be one of the causes of developing myopia.

Retrospective analysis of refractive errors in children with vision impairment.

PubMed

Du, Jojo W; Schmid, Katrina L; Bevan, Jennifer D; Frater, Karen M; Ollett, Rhondelle; Hein, Bronwyn

2005-09-01

Emmetropization is the reduction in neonatal refractive errors that occurs after birth. Ocular disease may affect this process. We aimed to determine the relative frequency of ocular conditions causing vision impairment in the pediatric population and characterize the refractive anomalies present. We also compared the causes of vision impairment in children today to those between 1974 and 1981. Causes of vision impairment and refractive data of 872 children attending a pediatric low-vision clinic from 1985 to 2002 were retrospectively collated. As a result of associated impairments, refractive data were not available for 59 children. An analysis was made of the causes of vision impairment, the distribution of refractive errors in children with vision impairment, and the average type of refractive error for the most commonly seen conditions. We found that cortical or cerebral vision impairment (CVI) was the most common condition causing vision impairment, accounting for 27.6% of cases. This was followed by albinism (10.6%), retinopathy of prematurity (ROP; 7.0%), optic atrophy (6.2%), and optic nerve hypoplasia (5.3%). Vision impairment was associated with ametropia; fewer than 25% of the children had refractive errors < or = +/-1 D. The refractive error frequency plots (for 0 to 2-, 6 to 8-, and 12 to 14-year age bands) had a Gaussian distribution indicating that the emmetropization process was abnormal. The mean spherical equivalent refractive error of the children (n = 813) was +0.78 +/- 6.00 D with 0.94 +/- 1.24 D of astigmatism and 0.92 +/- 2.15 D of anisometropia. Most conditions causing vision impairment such as albinism were associated with low amounts of hyperopia. Moderate myopia was observed in children with ROP. The relative frequency of ocular conditions causing vision impairment in children has changed since the 1970s. Children with vision impairment often have an associated ametropia suggesting that the emmetropization system is also impaired.

Rigorous Electromagnetic Analysis of the Focusing Action of Refractive Cylindrical Microlens

NASA Astrophysics Data System (ADS)

Liu, Juan; Gu, Ben-Yuan; Dong, Bi-Zhen; Yang, Guo-Zhen

The focusing action of refractive cylindrical microlens is investigated based on the rigorous electromagnetic theory with the use of the boundary element method. The focusing behaviors of these refractive microlenses with continuous and multilevel surface-envelope are characterized in terms of total electric-field patterns, the electric-field intensity distributions on the focal plane, and their diffractive efficiencies at the focal spots. The obtained results are also compared with the ones obtained by Kirchhoff's scalar diffraction theory. The present numerical and graphical results may provide useful information for the analysis and design of refractive elements in micro-optics.

Estimation of atmospheric columnar organic matter (OM) mass concentration from remote sensing measurements of aerosol spectral refractive indices

NASA Astrophysics Data System (ADS)

Zhang, Ying; Li, Zhengqiang; Sun, Yele; Lv, Yang; Xie, Yisong

2018-04-01

Aerosols have adverse effects on human health and air quality, changing Earth's energy balance and lead to climate change. The components of aerosol are important because of the different spectral characteristics. Based on the low hygroscopic and high scattering properties of organic matter (OM) in fine modal atmospheric aerosols, we develop an inversion algorithm using remote sensing to obtain aerosol components including black carbon (BC), organic matter (OM), ammonium nitrate-like (AN), dust-like (DU) components and aerosol water content (AW). In the algorithm, the microphysical characteristics (i.e. volume distribution and complex refractive index) of particulates are preliminarily separated to fine and coarse modes, and then aerosol components are retrieved using bimodal parameters. We execute the algorithm using remote sensing measurements of sun-sky radiometer at AERONET site (Beijing RADI) in a period from October of 2014 to January of 2015. The results show a reasonable distribution of aerosol components and a good fit for spectral feature calculations. The mean OM mass concentration in atmospheric column is account for 14.93% of the total and 56.34% of dry and fine-mode aerosol, being a fairly good correlation (R = 0.56) with the in situ observations near the surface layer.

Computational diffraction tomographic microscopy with transport of intensity equation using a light-emitting diode array

NASA Astrophysics Data System (ADS)

Li, Jiaji; Chen, Qian; Zhang, Jialin; Zuo, Chao

2017-10-01

Optical diffraction tomography (ODT) is an effective label-free technique for quantitatively refractive index imaging, which enables long-term monitoring of the internal three-dimensional (3D) structures and molecular composition of biological cells with minimal perturbation. However, existing optical tomographic methods generally rely on interferometric configuration for phase measurement and sophisticated mechanical systems for sample rotation or beam scanning. Thereby, the measurement is suspect to phase error coming from the coherent speckle, environmental vibrations, and mechanical error during data acquisition process. To overcome these limitations, we present a new ODT technique based on non-interferometric phase retrieval and programmable illumination emitting from a light-emitting diode (LED) array. The experimental system is built based on a traditional bright field microscope, with the light source replaced by a programmable LED array, which provides angle-variable quasi-monochromatic illumination with an angular coverage of +/-37 degrees in both x and y directions (corresponding to an illumination numerical aperture of ˜ 0.6). Transport of intensity equation (TIE) is utilized to recover the phase at different illumination angles, and the refractive index distribution is reconstructed based on the ODT framework under first Rytov approximation. The missing-cone problem in ODT is addressed by using the iterative non-negative constraint algorithm, and the misalignment of the LED array is further numerically corrected to improve the accuracy of refractive index quantification. Experiments on polystyrene beads and thick biological specimens show that the proposed approach allows accurate refractive index reconstruction while greatly reduced the system complexity and environmental sensitivity compared to conventional interferometric ODT approaches.

Optical diffraction tomography microscopy with transport of intensity equation using a light-emitting diode array

NASA Astrophysics Data System (ADS)

Li, Jiaji; Chen, Qian; Zhang, Jialin; Zhang, Zhao; Zhang, Yan; Zuo, Chao

2017-08-01

Optical diffraction tomography (ODT) is an effective label-free technique for quantitatively refractive index imaging, which enables long-term monitoring of the internal three-dimensional (3D) structures and molecular composition of biological cells with minimal perturbation. However, existing optical tomographic methods generally rely on interferometric configuration for phase measurement and sophisticated mechanical systems for sample rotation or beam scanning. Thereby, the measurement is suspect to phase error coming from the coherent speckle, environmental vibrations, and mechanical error during data acquisition process. To overcome these limitations, we present a new ODT technique based on non-interferometric phase retrieval and programmable illumination emitting from a light-emitting diode (LED) array. The experimental system is built based on a traditional bright field microscope, with the light source replaced by a programmable LED array, which provides angle-variable quasi-monochromatic illumination with an angular coverage of ±37 degrees in both x and y directions (corresponding to an illumination numerical aperture of ∼0.6). Transport of intensity equation (TIE) is utilized to recover the phase at different illumination angles, and the refractive index distribution is reconstructed based on the ODT framework under first Rytov approximation. The missing-cone problem in ODT is addressed by using the iterative non-negative constraint algorithm, and the misalignment of the LED array is further numerically corrected to improve the accuracy of refractive index quantification. Experiments on polystyrene beads and thick biological specimens show that the proposed approach allows accurate refractive index reconstruction while greatly reduced the system complexity and environmental sensitivity compared to conventional interferometric ODT approaches.

Numerical simulation and comparison of nonlinear self-focusing based on iteration and ray tracing

NASA Astrophysics Data System (ADS)

Li, Xiaotong; Chen, Hao; Wang, Weiwei; Ruan, Wangchao; Zhang, Luwei; Cen, Zhaofeng

2017-05-01

Self-focusing is observed in nonlinear materials owing to the interaction between laser and matter when laser beam propagates. Some of numerical simulation strategies such as the beam propagation method (BPM) based on nonlinear Schrödinger equation and ray tracing method based on Fermat's principle have applied to simulate the self-focusing process. In this paper we present an iteration nonlinear ray tracing method in that the nonlinear material is also cut into massive slices just like the existing approaches, but instead of paraxial approximation and split-step Fourier transform, a large quantity of sampled real rays are traced step by step through the system with changing refractive index and laser intensity by iteration. In this process a smooth treatment is employed to generate a laser density distribution at each slice to decrease the error caused by the under-sampling. The characteristics of this method is that the nonlinear refractive indices of the points on current slice are calculated by iteration so as to solve the problem of unknown parameters in the material caused by the causal relationship between laser intensity and nonlinear refractive index. Compared with the beam propagation method, this algorithm is more suitable for engineering application with lower time complexity, and has the calculation capacity for numerical simulation of self-focusing process in the systems including both of linear and nonlinear optical media. If the sampled rays are traced with their complex amplitudes and light paths or phases, it will be possible to simulate the superposition effects of different beam. At the end of the paper, the advantages and disadvantages of this algorithm are discussed.

Measuring the Refractive Index of Highly Crystalline Monolayer MoS2 with High Confidence

PubMed Central

Zhang, Hui; Ma, Yaoguang; Wan, Yi; Rong, Xin; Xie, Ziang; Wang, Wei; Dai, Lun

2015-01-01

Monolayer molybdenum disulphide (MoS2) has attracted much attention, due to its attractive properties, such as two-dimensional properties, direct bandgap, valley-selective circular dichroism, and valley Hall effect. However, some of its fundamental physical parameters, e.g. refractive index, have not been studied in detail because of measurement difficulties. In this work, we have synthesized highly crystalline monolayer MoS2 on SiO2/Si substrates via chemical vapor deposition (CVD) method and devised a method to measure their optical contrast spectra. Using these contrast spectra, we extracted the complex refractive index spectrum of monolayer MoS2 in the wavelength range of 400 nm to 750 nm. We have analyzed the pronounced difference between the obtained complex refractive index spectrum and that of bulk MoS2. The method presented here is effective for two-dimensional materials of small size. Furthermore, we have calculated the color contour plots of the contrast as a function of both SiO2 thickness and incident light wavelength for monolayer MoS2 using the obtained refractive index spectrum. These plots are useful for both fundamental study and device application. PMID:25676089

Measuring the refractive index of highly crystalline monolayer MoS2 with high confidence.

PubMed

Zhang, Hui; Ma, Yaoguang; Wan, Yi; Rong, Xin; Xie, Ziang; Wang, Wei; Dai, Lun

2015-02-13

Monolayer molybdenum disulphide (MoS2) has attracted much attention, due to its attractive properties, such as two-dimensional properties, direct bandgap, valley-selective circular dichroism, and valley Hall effect. However, some of its fundamental physical parameters, e.g. refractive index, have not been studied in detail because of measurement difficulties. In this work, we have synthesized highly crystalline monolayer MoS2 on SiO2/Si substrates via chemical vapor deposition (CVD) method and devised a method to measure their optical contrast spectra. Using these contrast spectra, we extracted the complex refractive index spectrum of monolayer MoS2 in the wavelength range of 400 nm to 750 nm. We have analyzed the pronounced difference between the obtained complex refractive index spectrum and that of bulk MoS2. The method presented here is effective for two-dimensional materials of small size. Furthermore, we have calculated the color contour plots of the contrast as a function of both SiO2 thickness and incident light wavelength for monolayer MoS2 using the obtained refractive index spectrum. These plots are useful for both fundamental study and device application.

Measuring the Refractive Index of Highly Crystalline Monolayer MoS2 with High Confidence

NASA Astrophysics Data System (ADS)

Zhang, Hui; Ma, Yaoguang; Wan, Yi; Rong, Xin; Xie, Ziang; Wang, Wei; Dai, Lun

2015-02-01

Monolayer molybdenum disulphide (MoS2) has attracted much attention, due to its attractive properties, such as two-dimensional properties, direct bandgap, valley-selective circular dichroism, and valley Hall effect. However, some of its fundamental physical parameters, e.g. refractive index, have not been studied in detail because of measurement difficulties. In this work, we have synthesized highly crystalline monolayer MoS2 on SiO2/Si substrates via chemical vapor deposition (CVD) method and devised a method to measure their optical contrast spectra. Using these contrast spectra, we extracted the complex refractive index spectrum of monolayer MoS2 in the wavelength range of 400 nm to 750 nm. We have analyzed the pronounced difference between the obtained complex refractive index spectrum and that of bulk MoS2. The method presented here is effective for two-dimensional materials of small size. Furthermore, we have calculated the color contour plots of the contrast as a function of both SiO2 thickness and incident light wavelength for monolayer MoS2 using the obtained refractive index spectrum. These plots are useful for both fundamental study and device application.

The application of terahertz pulsed imaging in characterising density distribution of roll-compacted ribbons.

PubMed

Zhang, Jianyi; Pei, Chunlei; Schiano, Serena; Heaps, David; Wu, Chuan-Yu

2016-09-01

Roll compaction is a commonly used dry granulation process in pharmaceutical, fine chemical and agrochemical industries for materials sensitive to heat or moisture. The ribbon density distribution plays an important role in controlling properties of granules (e.g. granule size distribution, porosity and strength). Accurate characterisation of ribbon density distribution is critical in process control and quality assurance. The terahertz imaging system has a great application potential in achieving this as the terahertz radiation has the ability to penetrate most of the pharmaceutical excipients and the refractive index reflects variations in density and chemical compositions. The aim of this study is to explore whether terahertz pulse imaging is a feasible technique for quantifying ribbon density distribution. Ribbons were made of two grades of microcrystalline cellulose (MCC), Avicel PH102 and DG, using a roll compactor at various process conditions and the ribbon density variation was investigated using terahertz imaging and section methods. The density variations obtained from both methods were compared to explore the reliability and accuracy of the terahertz imaging system. An average refractive index is calculated from the refractive index values in the frequency range between 0.5 and 1.5THz. It is shown that the refractive index gradually decreases from the middle of the ribbon towards to the edges. Variations of density distribution across the width of the ribbons are also obtained using both the section method and the terahertz imaging system. It is found that the terahertz imaging results are in excellent agreement with that obtained using the section method, demonstrating that terahertz imaging is a feasible and rapid tool to characterise ribbon density distributions. Copyright © 2016 Elsevier B.V. All rights reserved.

Reflection and Refraction of Light in Absorbing Media

NASA Astrophysics Data System (ADS)

Katsumata, Koichi; Sasaki, Shosuke

2018-05-01

The results of a rigorous calculation of optical phenomena in absorbing media based on Maxwell's equations are reported. In the case of an absorbing dielectric, we assume a complex dielectric constant. We find an expression for the angle of refraction as a function of the incident angle and the real and imaginary parts of the complex dielectric constant, all of which are real. The amplitudes of the reflected and transmitted waves are calculated on the same footing. These amplitudes are shown to be complex, from which we deduce the magnitude and phase change of the reflection and transmission coefficients. The same argument applies to an absorbing magnetic material if we replace the complex dielectric constant by a complex magnetic permeability.

Velocimetry with refractive index matching for complex flow configurations, phase 1

NASA Technical Reports Server (NTRS)

Thompson, B. E.; Vafidis, C.; Whitelaw, J. H.

1987-01-01

The feasibility of obtaining detailed velocity field measurements in large Reynolds number flow of the Space Shuttle Main Engine (SSME) main injector bowl was demonstrated using laser velocimetry and the developed refractive-index-matching technique. An experimental system to provide appropriate flow rates and temperature control of refractive-index-matching fluid was designed and tested. Test results are presented to establish the feasibility of obtaining accurate velocity measurements that map the entire field including the flow through the LOX post bundles: sample mean velocity, turbulence intensity, and spectral results are presented. The results indicate that a suitable fluid and control system is feasible for the representation of complex rocket-engine configurations and that measurements of velocity characteristics can be obtained without the optical access restrictions normally associated with laser velocimetry. The refractive-index-matching technique considered needs to be further developed and extended to represent other rocket-engine flows where current methods either cannot measure with adequate accuracy or they fail.

The distribution of refractive errors among children attending Lumbini Eye Institute, Nepal.

PubMed

Rai, S; Thapa, H B; Sharma, M K; Dhakhwa, K; Karki, R

2012-01-01

Uncorrected refractive error is an important cause of childhood blindness and visual impairment. To describe the patterns of refractive errors among children attending the outpatient clinic at the Department of Pediatric Ophthalmology, Lumbini Eye Institute, Bhairahawa, Nepal. Records of 133 children with refractive errors aged 5 - 15 years from both the urban and rural areas of Nepal and the adjacent territory of India attending the hospital between September and November 2010 were examined for patterns of refractive errors. The SPSS statistical software was used to perform data analysis. The commonest type of refractive error among the children was astigmatism (47 %) followed by myopia (34 %) and hyperopia (15 %). The refractive error was more prevalent among children of both the genders of age group 11-15 years as compared to their younger counterparts (RR = 1.22, 95 % CI = 0.66 - 2.25). The refractive error was more common (70 %) in the rural than the urban children (26 %). The rural females had a higher (38 %) prevalence of myopia than urban females (18 %). Among the children with refractive errors, only 57 % were using spectacles at the initial presentation. Astigmatism is the commonest type of refractive error among the children of age 5 - 15 years followed by hypermetropia and myopia. Refractive error remains uncorrected in a significant number of children. © NEPjOPH.

Gradient polymer network liquid crystal with a large refractive index change.

PubMed

Ren, Hongwen; Xu, Su; Wu, Shin-Tson

2012-11-19

A simple approach for preparing gradient polymer network liquid crystal (PNLC) with a large refractive index change is demonstrated. To control the effective refractive index at a given cell position, we applied a voltage to a homogeneous cell containing LC/diacrylate monomer mixture to generate the desired tilt angle and then stabilize the LC orientation with UV-induced polymer network. By varying the applied voltage along with the cells' movement, a PNLC with a gradient refractive index distribution is obtained. In comparison with conventional approaches using patterned photomask or electrode, our method offers following advantages: large refractive index change, freedom to design specific index profile, and large panel capability. Potential applications include tunable-focus lenses, prism gratings, phase modulators, and other adaptive photonic devices.

Electrically tunable negative refraction in core/shell-structured nanorod fluids.

PubMed

Su, Zhaoxian; Yin, Jianbo; Guan, Yanqing; Zhao, Xiaopeng

2014-10-21

We theoretically investigate optical refraction behavior in a fluid system which contains silica-coated gold nanorods dispersed in silicone oil under an external electric field. Because of the formation of a chain-like or lattice-like structure of dispersed nanorods along the electric field, the fluid shows a hyperbolic equifrequency contour characteristic and, as a result, all-angle broadband optical negative refraction for transverse magnetic wave propagation can be realized. We calculate the effective permittivity tensor of the fluid and verify the analysis using finite element simulations. We also find that the negative refractive index can vary with the electric field strength and external field distribution. Under a non-uniform external field, the gradient refraction behavior can be realized.

Logarithm conformal mapping brings the cloaking effect

PubMed Central

Xu, Lin; Chen, Huanyang

2014-01-01

Over the past years, invisibility cloaks have been extensively discussed since transformation optics emerges. Generally, the electromagnetic parameters of invisibility cloaks are complicated tensors, yet difficult to realize. As a special method of transformation optics, conformal mapping helps us design invisibility cloak with isotropic materials of a refractive index distribution. However, for all proposed isotropic cloaks, the refractive index range is at such a breadth that challenges current experimental fabrication. In this work, we propose two new kinds of logarithm conformal mappings for invisible device designs. For one of the mappings, the refractive index distribution of conformal cloak varies from 0 to 9.839, which is more feasible for future implementation. Numerical simulations by using finite element method are performed to confirm the theoretical analysis. PMID:25359138

Objective assessment of the effect of pupil size upon the power distribution of multifocal contact lenses.

PubMed

Papadatou, Eleni; Del Águila-Carrasco, Antonio J; Esteve-Taboada, José J; Madrid-Costa, David; Cerviño-Expósito, Alejandro

2017-01-01

To analytically assess the effect of pupil size upon the refractive power distributions of different designs of multifocal contact lenses. Two multifocal contact lenses of center-near design and one multifocal contact lens of center-distance design were used in this study. Their power profiles were measured using the NIMO TR1504 device (LAMBDA-X, Belgium). Based on their power profiles, the power distribution was assessed as a function of pupil size. For the high addition lenses, the resulting refractive power as a function of viewing distance (far, intermediate, and near) and pupil size was also analyzed. The power distribution of the lenses was affected by pupil size differently. One of the lenses showed a significant spread in refractive power distribution, from about -3 D to 0 D. Generally, the power distribution of the lenses expanded as the pupil diameter became greater. The surface of the lens dedicated for each distance varied substantially with the design of the lens. In an experimental basis, our results show how the lenses power distribution is affected by the pupil size and underlined the necessity of careful evaluation of the patient's visual needs and the optical properties of a multifocal contact lens for achieving the optimal visual outcome.

Interference in astronomical speckle patterns

NASA Technical Reports Server (NTRS)

Breckinridge, J. B.

1976-01-01

Astronomical speckle patterns are examined in an atmospheric-optics context in order to determine what kind of image quality is to be expected from several different imaging techniques. The model used to describe the instantaneous complex field distribution across the pupil of a large telescope regards the pupil as a deep phase grating with a periodicity given by the size of the cell of uniform phase or the refractive index structure function. This model is used along with an empirical formula derived purely from the physical appearance of the speckle patterns to discuss the orders of interference in astronomical speckle patterns.

Airborne Laser Polar Nephelometer

NASA Technical Reports Server (NTRS)

Grams, Gerald W.

1973-01-01

A polar nephelometer has been developed at NCAR to measure the angular variation of the intensity of light scattered by air molecules and particles. The system has been designed for airborne measurements using outside air ducted through a 5-cm diameter airflow tube; the sample volume is that which is common to the intersection of a collimated source beam and the detector field of view within the airflow tube. The source is a linearly polarized helium-neon laser beam. The optical system defines a collimated field-of-view (0.5deg half-angle) through a series of diaphragms located behind a I72-mm focal length objective lens. A photomultiplier tube is located immediately behind an aperture in the focal plane of the objective lens. The laser beam is mechanically chopped (on-off) at a rate of 5 Hz; a two-channel pulse counter, synchronized to the laser output, measures the photomultiplier pulse rate with the light beam both on and off. The difference in these measured pulse rates is directly proportional to the intensity of the scattered light from the volume common to the intersection of the laser beam and the detector field-of-view. Measurements can be made at scattering angles from 15deg to 165deg with reference to the direction of propagation of the light beam. Intermediate angles are obtained by selecting the angular increments desired between these extreme angles (any multiple of 0.1deg can be selected for the angular increment; 5deg is used in normal operation). Pulses provided by digital circuits control a stepping motor which sequentially rotates the detector by pre-selected angular increments. The synchronous photon-counting system automatically begins measurement of the scattered-light intensity immediately after the rotation to a new angle has been completed. The instrument has been flown on the NASA Convair 990 airborne laboratory to obtain data on the complex index of refraction of atmospheric aerosols. A particle impaction device is operated simultaneously to collect particles from the same airflow tube used to make the scattered-light measurements. A size distribution function is obtained by analysis of the particles collected by the impaction device. Calculated values of the angular variation of the scattered-light intensity are obtained by applying Mie scattering theory to the observed size distribution function and assuming different values of the complex index of refraction of the particles. The calculated values are then compared with data on the actual variation of the scattered-light intensity obtained with the polar nephelometer. The most probable value of the complex refractive index is that which provides the best fit between the experimental light scattering data and the parameters calculated from the observed size distribution function.

Sound transmission through an acoustic porous metasurface with periodic structures

NASA Astrophysics Data System (ADS)

Fang, Yi; Zhang, Xin; Zhou, Jie

2017-04-01

We report an analytical, numerical, and experimental study of sound transmission through a metasurface fabricated by porous materials, detailing systematically the factors that influence acoustic properties. The design of the metasurface is composed of four elements with varying properties, which are aligned in a periodic manner. The structures are carefully designed to form a uniform phase shift profile in one period. It is able to refract an incidence wave in an anomalous yet controllable way. A good agreement of refraction behavior between simulated and experimental results is achieved by the study. Furthermore, we systemically summarize the relationships between the refraction and the incidence angles for structures with various ratios of wavelengths and period lengths. Remarkably, the study proves that the propagation directions and the number of refracted waves are only affected by period lengths at a specified frequency. The phase shift profile only has an influence on energy distribution in the refraction region. The study suggests that a careful design of phase shift profile plays an important role in controlling sound energy distribution of the periodic structure, which is vital for applying this kind of porous metasurface in sound absorption and isolation in the future.

On the refractive index of sodium iodide solutions for index matching in PIV

NASA Astrophysics Data System (ADS)

Bai, Kunlun; Katz, Joseph

2014-04-01

Refractive index matching has become a popular technique for facilitating applications of modern optical diagnostic techniques, such as particle image velocimetry, in complex systems. By matching the refractive index of solid boundaries with that of the liquid, unobstructed optical paths can be achieved for illumination and image acquisition. In this research note, we extend previously provided data for the refractive index of aqueous solutions of sodium iodide (NaI) for concentrations reaching the temperature-dependent solubility limit. Results are fitted onto a quadratic empirical expression relating the concentration to the refractive index. Temperature effects are also measured. The present range of indices, 1.333-1.51, covers that of typical transparent solids, from silicone elastomers to several recently introduced materials that could be manufactured using rapid prototyping. We also review briefly previous measurements of the refractive index, viscosity, and density of NaI solutions, as well as prior research that has utilized this fluid.

Visible to near-infrared refractive properties of freshly-excised human-liver tissues: marking hepatic malignancies

PubMed Central

Giannios, Panagiotis; Toutouzas, Konstantinos G.; Matiatou, Maria; Stasinos, Konstantinos; Konstadoulakis, Manousos M.; Zografos, George C.; Moutzouris, Konstantinos

2016-01-01

The refractive index is an optical constant that plays a significant role in the description of light-matter interactions. When it comes to biological media, refraction is understudied despite recent advances in the field of bio-optics. In the present article, we report on the measurement of the refractive properties of freshly excised healthy and cancerous human liver samples, by use of a prism-coupling technique covering the visible and near-infrared spectral range. Novel data on the wavelength-dependent complex refractive index of human liver tissues are presented. The magnitude of the real and imaginary part of the refractive index is correlated with hepatic pathology. Notably, the real index contrast is pointed out as a marker of discrimination between normal liver tissue and hepatic metastases. In view of the current progress in optical biosensor technologies, our findings may be exploited for the development of novel surgical and endoscopic tools. PMID:27297034

Resident and young physician experience with complex cataract surgery and new cataract and refractive technology: Results of the ASCRS 2016 Young Eye Surgeons survey.

PubMed

Schallhorn, Julie M; Ciralsky, Jessica B; Yeu, Elizabeth

2017-05-01

A survey was offered to attendees of the 2016 annual meeting of the American Society of Cataract and Refractive Surgery (ASCRS) as well as online to ASCRS members. Of the 429 self-identified surgeons in training or those with fewer than 5 years in practice, 83% had performed complex cataract surgery using iris expansion devices or capsular tension rings (63%) and 70% had implanted a toric intraocular lens (IOL). A minority of respondents had performed laser-assisted cataract surgery (27%) or implanted presbyopia-correcting IOLs (39%), and only half (50%) had performed laser vision correction (LVC). Comfort with complex cataract and IOL procedures improved with increasing number of cases performed until greater than 10 cases. From this we can conclude that young surgeons have adequate exposure to complex cataracts but lack experience in refractive surgery and new IOL technology. Reported surgeon confidence improved with increased experience and exposure. Copyright © 2017 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Femtosecond laser-induced inverted microstructures inside glasses by tuning refractive index of objective's immersion liquid.

PubMed

Luo, Fangfang; Song, Juan; Hu, Xiao; Sun, Haiyi; Lin, Geng; Pan, Huaihai; Cheng, Ya; Liu, Li; Qiu, Jianrong; Zhao, Quanzhong; Xu, Zhizhan

2011-06-01

We report the formation of inverted microstructures inside glasses after femtosecond laser irradiation by tuning the refractive index contrast between the immersion liquid and the glass sample. By using water as well as 1-bromonaphthalene as immersion liquids, microstructures with similar shape but opposite directions are induced after femtosecond laser irradiation. Interestingly, the elemental distribution in the induced structures is also inverted. The simulation of laser intensity distribution along the laser propagation direction indicates that the interfacial spherical aberration effect is responsible for the inversion of microstructures and elemental distribution. © 2011 Optical Society of America

INVOLVEMENT OF MULTIPLE MOLECULAR PATHWAYS IN THE GENETICS OF OCULAR REFRACTION AND MYOPIA.

PubMed

Wojciechowski, Robert; Cheng, Ching-Yu

2018-01-01

The prevalence of myopia has increased dramatically worldwide within the last three decades. Recent studies have shown that refractive development is influenced by environmental, behavioral, and inherited factors. This review aims to analyze recent progress in the genetics of refractive error and myopia. A comprehensive literature search of PubMed and OMIM was conducted to identify relevant articles in the genetics of refractive error. Genome-wide association and sequencing studies have increased our understanding of the genetics involved in refractive error. These studies have identified interesting candidate genes. All genetic loci discovered to date indicate that refractive development is a heterogeneous process mediated by a number of overlapping biological processes. The exact mechanisms by which these biological networks regulate eye growth are poorly understood. Although several individual genes and/or molecular pathways have been investigated in animal models, a systematic network-based approach in modeling human refractive development is necessary to understand the complex interplay between genes and environment in refractive error. New biomedical technologies and better-designed studies will continue to refine our understanding of the genetics and molecular pathways of refractive error, and may lead to preventative and therapeutic measures to combat the myopia epidemic.

Refractive Index and Scattering Effects on Radiative Behavior of a Semitransparent Layer

NASA Technical Reports Server (NTRS)

Spuckler, C. M.; Siegel, R.

1993-01-01

Heat transfer characteristics are analyzed for a plane layer of semitransparent material with refractive index not less than 1. Energy transfer in the material is by conduction, emission, absorption, and isotropic scattering. Each side of the layer is heated by radiation and convection. For a refractive index larger than unity, there is internal reflection of some of the energy within the layer. This, coupled with scattering, has a substantial effect on distributing energy across the layer and altering the temperature distribution from when the refractive index is unity. The effect of scattering is examined by comparisons with results from an earlier paper for an absorbing layer. Results are given for a gray medium with a scattering albedo up to 0.999, and for a two-band spectral variation of the albedo with one band having low absorption. Radiant energy leaving the surface as a result of emission and scattering was examined to determine if it could be used to accurately indicate the surface temperature.

Experimental investigation of gas flow rate and electric field effect on refractive index and electron density distribution of cold atmospheric pressure-plasma by optical method, Moiré deflectometry

NASA Astrophysics Data System (ADS)

Khanzadeh, Mohammad; Jamal, Fatemeh; Shariat, Mahdi

2018-04-01

Nowadays, cold atmospheric-pressure (CAP) helium plasma jets are widely used in material processing devices in various industries. Researchers often use indirect and spectrometric methods for measuring the plasma parameters which are very expensive. In this paper, for the first time, characterization of CAP, i.e., finding its parameters such as refractive index and electron density distribution, was carried out using an optical method, Moiré deflectometry. This method is a wave front analysis technique based on geometric optics. The advantages of this method are simplicity, high accuracy, and low cost along with the non-contact, non-destructive, and direct measurement of CAP parameters. This method demonstrates that as the helium gas flow rate decreases, the refractive index increases. Also, we must note that the refractive index is larger in the gas flow consisting of different flow rates of plasma comparing with the gas flow without the plasma.

The New Zealand cataract and refractive surgery survey 1997/1998.

PubMed

Elder, M; Tarr, K; Leaming, D

2000-04-01

This study documents the current practice for cataract and refractive surgery in New Zealand. A postal questionnaire was distributed in late 1997 to all consultant members of the Ophthalmological Society of New Zealand that were resident in the country at that time. Most questions were identical to the 1997 survey of the American Society of Cataract and Refraction Surgeons (ASCRS) to enable a comparison. There were 98 returns from 101 surveys distributed. Of the returns, 72 performed cataract surgery, 23 performed PRK and 11 performed LASIK. ASCRS members did more refractive surgery than did New Zealanders: 28 versus 1% of 1-5 RK per month, 7 versus 1% of 1-2 clear lens extractions per month and 85 versus 51% had access to an excimer laser. For cataract surgery, ASCRS members used more topical anaesthesia (30 vs 5.5%), used no sutures more often (73 vs 51%), used more preoperative antibiotics (76 vs 26%) and used fewer injections of antibiotic/steroids (38 vs 61%). Otherwise the two groups were broadly similar.

Visual Survey of Infantry Troops. Part 1. Visual Acuity, Refractive Status, Interpupillary Distance and Visual Skills

DTIC Science & Technology

1989-06-01

letters on one line and several letters on the next line, there is no accurate way to credit these extra letters for statistical analysis. The decimal and...contains the descriptive statistics of the objective refractive error components of infantrymen. Figures 8-11 show the frequency distributions for sphere...equivalents. Nonspectacle wearers Table 12 contains the idescriptive statistics for non- spectacle wearers. Based or these refractive error data, about 30

Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer

NASA Astrophysics Data System (ADS)

Hessler, Steffen; Rosenberger, Manuel; Schmauss, Bernhard; Hellmann, Ralf

2018-01-01

In this paper we precisely determine laser-induced refractive index profiles created in cyclic olefin copolymer Topas 6017 employing a sophisticated phase shifting Mach-Zehnder interferometry approach. Beyond the usual one-dimensional modification depth measurement we highlight that for straight waveguide structures also a two-dimensional refractive index distribution can be directly obtained providing full information of a waveguide's exact cross section and its gradient refractive index contrast. Deployed as direct data input in optical waveguide simulation, the evaluated 2D refractive index profiles permit a detailed calculation of the waveguides' actual mode profiles. Furthermore, conventional one-dimensional interferometric measurements for refractive index depth profiles with varying total imposed laser fluence of a 248 nm KrF excimer laser are included to investigate the effect on refractive index modification depth. Maximum surface refractive index increase turns out to attain up to 1.86 ·10-3 enabling laser-written optical waveguide channels. Additionally, a comprehensive optical material characterization in terms of dispersion, thermo-optic coefficient and absorption measurement of unmodified and UV-modified Topas 6017 is carried out.

Average value of the shape and direction factor in the equation of refractive index

NASA Astrophysics Data System (ADS)

Zhang, Tao

2017-10-01

The theoretical calculation of the refractive indices is of great significance for the developments of new optical materials. The calculation method of refractive index, which was deduced from the electron-cloud-conductor model, contains the shape and direction factor 〈g〉. 〈g〉 affects the electromagnetic-induction energy absorbed by the electron clouds, thereby influencing the refractive indices. It is not yet known how to calculate 〈g〉 value of non-spherical electron clouds. In this paper, 〈g〉 value is derived by imaginatively dividing the electron cloud into numerous little volume elements and then regrouping them. This paper proves that 〈g〉 = 2/3 when molecules’ spatial orientations distribute randomly. The calculations of the refractive indices of several substances validate this equation. This result will help to promote the application of the calculation method of refractive index.

Power-controlled transition from standard to negative refraction in reorientational soft matter.

PubMed

Piccardi, Armando; Alberucci, Alessandro; Kravets, Nina; Buchnev, Oleksandr; Assanto, Gaetano

2014-11-25

Refraction at a dielectric interface can take an anomalous character in anisotropic crystals, when light is negatively refracted with incident and refracted beams emerging on the same side of the interface normal. In soft matter subject to reorientation, such as nematic liquid crystals, the nonlinear interaction with light allows tuning of the optical properties. We demonstrate that in such material a beam of light can experience either positive or negative refraction depending on input power, as it can alter the spatial distribution of the optic axis and, in turn, the direction of the energy flow when traveling across an interface. Moreover, the nonlinear optical response yields beam self-focusing and spatial localization into a self-confined solitary wave through the formation of a graded-index waveguide, linking the refractive transition to power-driven readdressing of copolarized guided-wave signals, with a number of output ports not limited by diffraction.

Theoretical study of polarization insensitivity of carrier-induced refractive index change of multiple quantum well.

PubMed

Miao, Qingyuan; Zhou, Qunjie; Cui, Jun; He, Ping-An; Huang, Dexiu

2014-12-29

Characteristics of polarization insensitivity of carrier-induced refractive index change of 1.55 μm tensile-strained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensile-strained MQW is expected to achieve polarization insensitivity of carrier-induced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10^-3). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility.

Dispersion dependence of second-order refractive index and complex third-order optical susceptibility in oxide glasses

NASA Astrophysics Data System (ADS)

Abdel Wahab, F. A.; El-Diasty, Fouad; Abdel-Baki, Manal

2009-10-01

A method correlates Fresnel-based spectrophotometric measurements and Lorentz dispersion theory is presented to study the dispersion of nonlinear optical parameters in particularly oxide glasses in a very wide range of angular frequency. The second-order refractive index and third-order optical susceptibility of Cr-doped glasses are determined from linear refractive index. Furthermore, both real and imaginary components of the complex susceptibility are carried out. The study reveals the importance of determining the dispersion of nonlinear absorption (two-photon absorption coefficient) to find the maximum resonant and nonresonant susceptibilities of investigated glasses. The present method is applied on Cr-doped lithium aluminum silicate (LAS) glasses due to their semiconductor-like behavior and also to their application in laser industry.

Tomographic reconstruction of melanin structures of optical coherence tomography via the finite-difference time-domain simulation

NASA Astrophysics Data System (ADS)

Huang, Shi-Hao; Wang, Shiang-Jiu; Tseng, Snow H.

2015-03-01

Optical coherence tomography (OCT) provides high resolution, cross-sectional image of internal microstructure of biological tissue. We use the Finite-Difference Time-Domain method (FDTD) to analyze the data acquired by OCT, which can help us reconstruct the refractive index of the biological tissue. We calculate the refractive index tomography and try to match the simulation with the data acquired by OCT. Specifically, we try to reconstruct the structure of melanin, which has complex refractive indices and is the key component of human pigment system. The results indicate that better reconstruction can be achieved for homogenous sample, whereas the reconstruction is degraded for samples with fine structure or with complex interface. Simulation reconstruction shows structures of the Melanin that may be useful for biomedical optics applications.

Density functional theory calculation of refractive indices of liquid-forming silicon oil compounds

NASA Astrophysics Data System (ADS)

Lee, Sanghun; Park, Sung Soo; Hagelberg, Frank

2012-02-01

A combination of quantum chemical calculation and molecular dynamics simulation is applied to compute refractive indices of liquid-forming silicon oils. The densities of these species are obtained from molecular dynamics simulations based on the NPT ensemble while the molecular polarizabilities are evaluated by density functional theory. This procedure is shown to yield results well compatible with available experimental data, suggesting that it represents a robust and economic route for determining the refractive indices of liquid-forming organic complexes containing silicon.

Model function to calculate the refractive index of native hemoglobin in the wavelength range of 250-1100 nm dependent on concentration.

PubMed

Friebel, Moritz; Meinke, Martina

2006-04-20

The real part of the complex refractive index of oxygenated native hemoglobin solutions dependent on concentration was determined in the wavelength range 250 to 1100 nm by Fresnel reflectance measurements. The hemoglobin solution was produced by physical hemolysis of human erythrocytes followed by ultracentrifugation and filtration. A model function is presented for calculating the refractive index of hemoglobin solutions depending on concentration in the wavelength range 250 to 1100 nm.

Optical Refraction in Silver: Counterposition, Negative Phase Velocity and Orthogonal Phase Velocity

ERIC Educational Resources Information Center

Naqvi, Qaisar A.; Mackay, Tom G.; Lakhtakia, Akhlesh

2011-01-01

Complex behaviour associated with metamaterials can arise even in commonplace isotropic dielectric materials. We demonstrate how silver, for example, can support negative phase velocity and counterposition, but not negative refraction, at optical frequencies. The transition from positive to negative phase velocity is not accompanied by remarkable…

Generalized ray tracing method for the calculation of the peripheral refraction induced by an ophthalmic lens

NASA Astrophysics Data System (ADS)

Rojo, Pilar; Royo, Santiago; Caum, Jesus; Ramírez, Jorge; Madariaga, Ines

2015-02-01

Peripheral refraction, the refractive error present outside the main direction of gaze, has lately attracted interest due to its alleged relationship with the progression of myopia. The ray tracing procedures involved in its calculation need to follow an approach different from those used in conventional ophthalmic lens design, where refractive errors are compensated only in the main direction of gaze. We present a methodology for the evaluation of the peripheral refractive error in ophthalmic lenses, adapting the conventional generalized ray tracing approach to the requirements of the evaluation of peripheral refraction. The nodal point of the eye and a retinal conjugate surface will be used to evaluate the three-dimensional distribution of refractive error around the fovea. The proposed approach enables us to calculate the three-dimensional peripheral refraction induced by any ophthalmic lens at any direction of gaze and to personalize the lens design to the requirements of the user. The complete evaluation process for a given user prescribed with a -5.76D ophthalmic lens for foveal vision is detailed, and comparative results obtained when the geometry of the lens is modified and when the central refractive error is over- or undercorrected. The methodology is also applied for an emmetropic eye to show its application for refractive errors other than myopia.

Modeling cometary photopolarimetric characteristics with Sh-matrix method

NASA Astrophysics Data System (ADS)

Kolokolova, L.; Petrov, D.

2017-12-01

Cometary dust is dominated by particles of complex shape and structure, which are often considered as fractal aggregates. Rigorous modeling of light scattering by such particles, even using parallelized codes and NASA supercomputer resources, is very computer time and memory consuming. We are presenting a new approach to modeling cometary dust that is based on the Sh-matrix technique (e.g., Petrov et al., JQSRT, 112, 2012). This method is based on the T-matrix technique (e.g., Mishchenko et al., JQSRT, 55, 1996) and was developed after it had been found that the shape-dependent factors could be separated from the size- and refractive-index-dependent factors and presented as a shape matrix, or Sh-matrix. Size and refractive index dependences are incorporated through analytical operations on the Sh-matrix to produce the elements of T-matrix. Sh-matrix method keeps all advantages of the T-matrix method, including analytical averaging over particle orientation. Moreover, the surface integrals describing the Sh-matrix elements themselves can be solvable analytically for particles of any shape. This makes Sh-matrix approach an effective technique to simulate light scattering by particles of complex shape and surface structure. In this paper, we present cometary dust as an ensemble of Gaussian random particles. The shape of these particles is described by a log-normal distribution of their radius length and direction (Muinonen, EMP, 72, 1996). Changing one of the parameters of this distribution, the correlation angle, from 0 to 90 deg., we can model a variety of particles from spheres to particles of a random complex shape. We survey the angular and spectral dependencies of intensity and polarization resulted from light scattering by such particles, studying how they depend on the particle shape, size, and composition (including porous particles to simulate aggregates) to find the best fit to the cometary observations.

An Accurate Analytic Approximation for Light Scattering by Non-absorbing Spherical Aerosol Particles

NASA Astrophysics Data System (ADS)

Lewis, E. R.

2017-12-01

The scattering of light by particles in the atmosphere is a ubiquitous and important phenomenon, with applications to numerous fields of science and technology. The problem of scattering of electromagnetic radiation by a uniform spherical particle can be solved by the method of Mie and Debye as a series of terms depending on the size parameter, x=2πr/λ, and the complex index of refraction, m. However, this solution does not provide insight into the dependence of the scattering on the radius of the particle, the wavelength, or the index of refraction, or how the scattering varies with relative humidity. Van de Hulst demonstrated that the scattering efficiency (the scattering cross section divided by the geometric cross section) of a non-absorbing sphere, over a wide range of particle sizes of atmospheric importance, depends not on x and m separately, but on the quantity 2x(m-1); this is the basis for the anomalous diffraction approximation. Here an analytic approximation for the scattering efficiency of a non-absorbing spherical particle is presented in terms of this new quantity that is accurate over a wide range of particle sizes of atmospheric importance and which readily displays the dependences of the scattering efficiency on particle radius, index of refraction, and wavelength. For an aerosol for which the particle size distribution is parameterized as a gamma function, this approximation also yields analytical results for the scattering coefficient and for the Ångström exponent, with the dependences of scattering properties on wavelength and index of refraction clearly displayed. This approximation provides insight into the dependence of light scattering properties on factors such as relative humidity, readily enables conversion of scattering from one index of refraction to another, and demonstrates the conditions under which the aerosol index (the product of the aerosol optical depth and the Ångström exponent) is a useful proxy for the number of cloud condensation nuclei.

Remote sensing of soot carbon - Part 1: Distinguishing different absorbing aerosol species

NASA Astrophysics Data System (ADS)

Schuster, G. L.; Dubovik, O.; Arola, A.

2016-02-01

We describe a method of using the Aerosol Robotic Network (AERONET) size distributions and complex refractive indices to retrieve the relative proportion of carbonaceous aerosols and free iron minerals (hematite and goethite). We assume that soot carbon has a spectrally flat refractive index and enhanced imaginary indices at the 440 nm wavelength are caused by brown carbon or hematite. Carbonaceous aerosols can be separated from dust in imaginary refractive index space because 95 % of biomass burning aerosols have imaginary indices greater than 0.0042 at the 675-1020 nm wavelengths, and 95 % of dust has imaginary refractive indices of less than 0.0042 at those wavelengths. However, mixtures of these two types of particles can not be unambiguously partitioned on the basis of optical properties alone, so we also separate these particles by size. Regional and seasonal results are consistent with expectations. Monthly climatologies of fine mode soot carbon are less than 1.0 % by volume for West Africa and the Middle East, but the southern African and South American biomass burning sites have peak values of 3.0 and 1.7 %. Monthly averaged fine mode brown carbon volume fractions have a peak value of 5.8 % for West Africa, 2.1 % for the Middle East, 3.7 % for southern Africa, and 5.7 % for South America. Monthly climatologies of free iron volume fractions show little seasonal variability, and range from about 1.1 to 1.7 % for coarse mode aerosols in all four study regions. Finally, our sensitivity study indicates that the soot carbon retrieval is not sensitive to the component refractive indices or densities assumed for carbonaceous and free iron aerosols, and the retrieval differs by only 15.4 % when these parameters are altered from our chosen baseline values. The total uncertainty of retrieving soot carbon mass is ˜ 50 % (when uncertainty in the AERONET product and mixing state is included in the analysis).

TE modes of UV-laser generated waveguides in a planar polymer chip of parabolic refractive index profile

NASA Astrophysics Data System (ADS)

Shams El-Din, M. A.

2018-04-01

The UV-laser lithographic method is used for the preparation of Polymeric integrated-optical waveguides in a planar polymer chip. The waveguide samples are irradiated by an excimer laser of wavelength 248 nm with different doses and with the same fluencies. The refractive index depth profile for the waveguides, in the first zone is found to have a parabolic shape and Gaussian shape in the second one that can be determined by Mach-Zehnder interferometer. Both the mode field distribution and the effective mode indices for the first zone only are determined by making use of the theoretical mode and the experimental data. It is found that the model field distribution is strongly dependent on the refractive indices for each zone.

Genome-Wide Meta-Analysis of Myopia and Hyperopia Provides Evidence for Replication of 11 Loci

PubMed Central

Simpson, Claire L.; Wojciechowski, Robert; Oexle, Konrad; Murgia, Federico; Portas, Laura; Li, Xiaohui; Verhoeven, Virginie J. M.; Vitart, Veronique; Schache, Maria; Hosseini, S. Mohsen; Hysi, Pirro G.; Raffel, Leslie J.; Cotch, Mary Frances; Chew, Emily; Klein, Barbara E. K.; Klein, Ronald; Wong, Tien Yin; van Duijn, Cornelia M.; Mitchell, Paul; Saw, Seang Mei; Fossarello, Maurizio; Wang, Jie Jin; Polašek, Ozren; Campbell, Harry; Rudan, Igor; Oostra, Ben A.; Uitterlinden, André G.; Hofman, Albert; Rivadeneira, Fernando; Amin, Najaf; Karssen, Lennart C.; Vingerling, Johannes R.; Döring, Angela; Bettecken, Thomas; Bencic, Goran; Gieger, Christian; Wichmann, H.-Erich; Wilson, James F.; Venturini, Cristina; Fleck, Brian; Cumberland, Phillippa M.; Rahi, Jugnoo S.; Hammond, Chris J.; Hayward, Caroline; Wright, Alan F.; Paterson, Andrew D.; Baird, Paul N.; Klaver, Caroline C. W.; Rotter, Jerome I.; Pirastu, Mario; Meitinger, Thomas; Bailey-Wilson, Joan E.; Stambolian, Dwight

2014-01-01

Refractive error (RE) is a complex, multifactorial disorder characterized by a mismatch between the optical power of the eye and its axial length that causes object images to be focused off the retina. The two major subtypes of RE are myopia (nearsightedness) and hyperopia (farsightedness), which represent opposite ends of the distribution of the quantitative measure of spherical refraction. We performed a fixed effects meta-analysis of genome-wide association results of myopia and hyperopia from 9 studies of European-derived populations: AREDS, KORA, FES, OGP-Talana, MESA, RSI, RSII, RSIII and ERF. One genome-wide significant region was observed for myopia, corresponding to a previously identified myopia locus on 8q12 (p = 1.25×10−8), which has been reported by Kiefer et al. as significantly associated with myopia age at onset and Verhoeven et al. as significantly associated to mean spherical-equivalent (MSE) refractive error. We observed two genome-wide significant associations with hyperopia. These regions overlapped with loci on 15q14 (minimum p value = 9.11×10−11) and 8q12 (minimum p value 1.82×10−11) previously reported for MSE and myopia age at onset. We also used an intermarker linkage- disequilibrium-based method for calculating the effective number of tests in targeted regional replication analyses. We analyzed myopia (which represents the closest phenotype in our data to the one used by Kiefer et al.) and showed replication of 10 additional loci associated with myopia previously reported by Kiefer et al. This is the first replication of these loci using myopia as the trait under analysis. “Replication-level” association was also seen between hyperopia and 12 of Kiefer et al.'s published loci. For the loci that show evidence of association to both myopia and hyperopia, the estimated effect of the risk alleles were in opposite directions for the two traits. This suggests that these loci are important contributors to variation of refractive error across the distribution. PMID:25233373

Genome-wide meta-analysis of myopia and hyperopia provides evidence for replication of 11 loci.

PubMed

Simpson, Claire L; Wojciechowski, Robert; Oexle, Konrad; Murgia, Federico; Portas, Laura; Li, Xiaohui; Verhoeven, Virginie J M; Vitart, Veronique; Schache, Maria; Hosseini, S Mohsen; Hysi, Pirro G; Raffel, Leslie J; Cotch, Mary Frances; Chew, Emily; Klein, Barbara E K; Klein, Ronald; Wong, Tien Yin; van Duijn, Cornelia M; Mitchell, Paul; Saw, Seang Mei; Fossarello, Maurizio; Wang, Jie Jin; Polašek, Ozren; Campbell, Harry; Rudan, Igor; Oostra, Ben A; Uitterlinden, André G; Hofman, Albert; Rivadeneira, Fernando; Amin, Najaf; Karssen, Lennart C; Vingerling, Johannes R; Döring, Angela; Bettecken, Thomas; Bencic, Goran; Gieger, Christian; Wichmann, H-Erich; Wilson, James F; Venturini, Cristina; Fleck, Brian; Cumberland, Phillippa M; Rahi, Jugnoo S; Hammond, Chris J; Hayward, Caroline; Wright, Alan F; Paterson, Andrew D; Baird, Paul N; Klaver, Caroline C W; Rotter, Jerome I; Pirastu, Mario; Meitinger, Thomas; Bailey-Wilson, Joan E; Stambolian, Dwight

2014-01-01

Refractive error (RE) is a complex, multifactorial disorder characterized by a mismatch between the optical power of the eye and its axial length that causes object images to be focused off the retina. The two major subtypes of RE are myopia (nearsightedness) and hyperopia (farsightedness), which represent opposite ends of the distribution of the quantitative measure of spherical refraction. We performed a fixed effects meta-analysis of genome-wide association results of myopia and hyperopia from 9 studies of European-derived populations: AREDS, KORA, FES, OGP-Talana, MESA, RSI, RSII, RSIII and ERF. One genome-wide significant region was observed for myopia, corresponding to a previously identified myopia locus on 8q12 (p = 1.25×10(-8)), which has been reported by Kiefer et al. as significantly associated with myopia age at onset and Verhoeven et al. as significantly associated to mean spherical-equivalent (MSE) refractive error. We observed two genome-wide significant associations with hyperopia. These regions overlapped with loci on 15q14 (minimum p value = 9.11×10(-11)) and 8q12 (minimum p value 1.82×10(-11)) previously reported for MSE and myopia age at onset. We also used an intermarker linkage- disequilibrium-based method for calculating the effective number of tests in targeted regional replication analyses. We analyzed myopia (which represents the closest phenotype in our data to the one used by Kiefer et al.) and showed replication of 10 additional loci associated with myopia previously reported by Kiefer et al. This is the first replication of these loci using myopia as the trait under analysis. "Replication-level" association was also seen between hyperopia and 12 of Kiefer et al.'s published loci. For the loci that show evidence of association to both myopia and hyperopia, the estimated effect of the risk alleles were in opposite directions for the two traits. This suggests that these loci are important contributors to variation of refractive error across the distribution.

A discussion on validity of the diffusion theory by Monte Carlo method

NASA Astrophysics Data System (ADS)

Peng, Dong-qing; Li, Hui; Xie, Shusen

2008-12-01

Diffusion theory was widely used as a basis of the experiments and methods in determining the optical properties of biological tissues. A simple analytical solution could be obtained easily from the diffusion equation after a series of approximations. Thus, a misinterpret of analytical solution would be made: while the effective attenuation coefficient of several semi-infinite bio-tissues were the same, the distribution of light fluence in the tissues would be the same. In order to assess the validity of knowledge above, depth resolved internal fluence of several semi-infinite biological tissues which have the same effective attenuation coefficient were simulated with wide collimated beam in the paper by using Monte Carlo method in different condition. Also, the influence of bio-tissue refractive index on the distribution of light fluence was discussed in detail. Our results showed that, when the refractive index of several bio-tissues which had the same effective attenuation coefficient were the same, the depth resolved internal fluence would be the same; otherwise, the depth resolved internal fluence would be not the same. The change of refractive index of tissue would have affection on the light depth distribution in tissue. Therefore, the refractive index is an important optical property of tissue, and should be taken in account while using the diffusion approximation theory.

Enlightening intracellular complexity of living cells with quantitative phase microscopy

NASA Astrophysics Data System (ADS)

Martinez Torres, C.; Laperrousaz, B.; Berguiga, L.; Boyer Provera, E.; Elezgaray, J.; Nicolini, F. E.; Maguer-Satta, V.; Arneodo, A.; Argoul, F.

2016-03-01

The internal distribution of refractive indices (RIs) of a living cell is much more complex than usually admitted in multi-shell models. The reconstruction of RI maps from single phase images has rarely been achieved for several reasons: (i) we still have very little knowledge of the impact of internal macromolecular complexes on the local RI and (ii) phase changes produced by light propagation through the sample are mixed with diffraction effects by internal cell bodies. We propose the implementation a 2D wavelet-based contour chain detection method to distinguish internal boundaries thanks to their greatest optical path difference gradients. These contour chains correspond to the highest image phase contrast and follow the local RI inhomogeneities linked to the intracellular structural intricacy. Their statistics and spatial distribution are morphological indicators for distinguishing cells of different origins and to follow their transformation in pathologic situations. We use this method to compare non adherent blood cells from primary and laboratory culture origins, in healthy and pathological situations (chronic myelogenous leukaemia). In a second part of this presentation, we concentrate on the temporal dynamics of the phase contour chains and we discuss the spectral decomposition of their dynamics in both health and disease.

Measurement of the refractive index of hemoglobin solutions for a continuous spectral region

PubMed Central

Wang, Jin; Deng, Zhichao; Wang, Xiaowan; Ye, Qing; Zhou, Wenyuan; Mei, Jianchun; Zhang, Chunping; Tian, Jianguo

2015-01-01

Determination of the refractive index of hemoglobin solutions over a wide wavelength range remains challenging. A famous detour approach is the Kramers-Kronig (KK) analysis which can resolve the real part of complex refractive index from the imaginary part. However, KK analysis is limited by the contradiction between the requirement of semi-infinite frequency range and limited measured range. In this paper, based on the Multi-curve fitting method (MFM), continuous refractive index dispersion (CRID) of oxygenated and deoxygenated hemoglobin solutions are measured using a homemade symmetrical arm-linked apparatus in the continuous wavelength range with spectral resolution of about 0.259nm. A novel method to obtain the CRID is proposed. PMID:26203379

The light wave flow effect in a plane-parallel layer with a quasi-zero refractive index under the action of bounded light beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gadomsky, O. N., E-mail: gadomsky@mail.ru; Shchukarev, I. A., E-mail: blacxpress@gmail.com

2016-08-15

It is shown that external optical radiation in the 450–1200 nm range can be efficiently transformed under the action of bounded light beams to a surface wave that propagates along the external and internal boundaries of a plane-parallel layer with a quasi-zero refractive index. Reflection regimes with complex and real angles of refraction in the layer are considered. The layer with a quasi-zero refractive index in this boundary problem is located on a highly reflective metal substrate; it is shown that the uniform low reflection of light is achieved in the wavelength range under study.

Photoacoustic measurement of refractive index of dye solutions and myoglobin for biosensing applications

PubMed Central

Goldschmidt, Benjamin S.; Mehta, Smit; Mosley, Jeff; Walter, Chris; Whiteside, Paul J. D.; Hunt, Heather K.; Viator, John A.

2013-01-01

Current methods of determining the refractive index of chemicals and materials, such as ellipsometry and reflectometry, are limited by their inability to analyze highly absorbing or highly transparent materials, as well as the required prior knowledge of the sample thickness and estimated refractive index. Here, we present a method of determining the refractive index of solutions using the photoacoustic effect. We show that a photoacoustic refractometer can analyze highly absorbing dye samples to within 0.006 refractive index units of a handheld optical refractometer. Further, we use myoglobin, an early non-invasive biomarker for malignant hyperthermia, as a proof of concept that this technique is applicable for use as a medical diagnostic. Comparison of the speed, cost, simplicity, and accuracy of the techniques shows that this photoacoustic method is well-suited for optically complex systems. PMID:24298407

LETTER TO THE EDITOR: Free-response operator characteristic models for visual search

NASA Astrophysics Data System (ADS)

Hutchinson, T. P.

2007-05-01

Computed tomography of diffraction enhanced imaging (DEI-CT) is a novel x-ray phase-contrast computed tomography which is applied to inspect weakly absorbing low-Z samples. Refraction-angle images which are extracted from a series of raw DEI images measured in different positions of the rocking curve of the analyser can be regarded as projections of DEI-CT. Based on them, the distribution of refractive index decrement in the sample can be reconstructed according to the principles of CT. How to combine extraction methods and reconstruction algorithms to obtain the most accurate reconstructed results is investigated in detail in this paper. Two kinds of comparison, the comparison of different extraction methods and the comparison between 'two-step' algorithms and the Hilbert filtered backprojection (HFBP) algorithm, draw the conclusion that the HFBP algorithm based on the maximum refraction-angle (MRA) method may be the best combination at present. Though all current extraction methods including the MRA method are approximate methods and cannot calculate very large refraction-angle values, the HFBP algorithm based on the MRA method is able to provide quite acceptable estimations of the distribution of refractive index decrement of the sample. The conclusion is proved by the experimental results at the Beijing Synchrotron Radiation Facility.

Measurement of the optical properties of a transparent, conductive carbon nanotube film using spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Kuwahara, Masashi; Kim, Yeji; Azumi, Reiko

2015-07-01

We have measured the complex refractive indices of a transparent, conductive carbon nanotube film by spectroscopic ellipsometry at wavelengths of 300-1700 nm (this includes the visible range). The film was produced on a quartz substrate by the doctor-blade method using single-walled carbon nanotube-polymer ink. The imaginary part of the complex refractive index of the film was found to be lower than 0.09 over the entire wavelength range. This film has a large advantage as a transparent, flexible, and conductive material.

A clinic-based study of refractive errors, strabismus, and amblyopia in pediatric age-group.

PubMed

Al-Tamimi, Elham R; Shakeel, Ayisha; Yassin, Sanaa A; Ali, Syed I; Khan, Umar A

2015-01-01

The purpose of this cross-sectional observational study was to determine the distribution and patterns of refractive errors, strabismus, and amblyopia in children seen at a pediatric eye care. The study was conducted in a Private Hospital in Dammam, Kingdom of Saudi Arabia, from March to July 2013. During this period, a total of 1350 children, aged 1-15 years were seen at this Center's Pediatric Ophthalmology Unit. All the children underwent complete ophthalmic examination with cycloplegic refraction. Refractive errors accounted for 44.4% of the cases, the predominant refractive error being hypermetropia which represented 83%. Strabismus and amblyopia were present in 38% and 9.1% of children, respectively. In this clinic-based study, the focus was on the frequency of refractive errors, strabismus, and amblyopia which were considerably high. Hypermetropia was the predominant refractive error in contrast to other studies in which myopia was more common. This could be attributed to the criteria for sample selection since it was clinic-based rather than a population-based study. However, it is important to promote public education on the significance of early detection of refractive errors, and have periodic screening in schools.

Assessment of refractive index of pigments by Gaussian fitting of light backscattering data in context of the liquid immersion method.

PubMed

Niskanen, Ilpo; Peiponen, Kai-Erik; Räty, Jukka

2010-05-01

Using a multifunction spectrophotometer, the refractive index of a pigment can be estimated by measuring the backscattering of light from the pigment in immersion liquids having slightly different refractive indices. A simple theoretical Gaussian function model related to the optical path distribution is introduced that makes it possible to describe quantitatively the backscattering signal from transparent pigments using a set of only a few immersion liquids. With the aid of the data fitting by a Gaussian function, the measurement time of the refractive index of the pigment can be reduced. The backscattering measurement technique is suggested to be useful in industrial measurement environments of pigments.

A pitfall in shallow shear-wave refraction surveying

USGS Publications Warehouse

Xia, J.; Miller, R.D.; Park, C.B.; Wightman, E.; Nigbor, R.

2002-01-01

The shallow shear-wave refraction method works successfully in an area with a series of horizontal layers. However, complex near-surface geology may not fit into the assumption of a series of horizontal layers. That a plane SH-wave undergoes wave-type conversion along an interface in an area of nonhorizontal layers is theoretically inevitable. One real example shows that the shallow shear-wave refraction method provides velocities of a converted wave rather than an SH- wave. Moreover, it is impossible to identify the converted wave by refraction data itself. As most geophysical engineering firms have limited resources, an additional P-wave refraction survey is necessary to verify if velocities calculated from a shear-wave refraction survey are velocities of converted waves. The alternative at this time may be the surface wave method, which can provide reliable S-wave velocities, even in an area of velocity inversion (a higher velocity layer underlain by a lower velocity layer). ?? 2002 Elsevier Science B.V. All rights reserved.

Frequency and Distribution of Refractive Error in Adult Life: Methodology and Findings of the UK Biobank Study

PubMed Central

Cumberland, Phillippa M.; Bao, Yanchun; Hysi, Pirro G.; Foster, Paul J.; Hammond, Christopher J.; Rahi, Jugnoo S.

2015-01-01

Purpose To report the methodology and findings of a large scale investigation of burden and distribution of refractive error, from a contemporary and ethnically diverse study of health and disease in adults, in the UK. Methods U K Biobank, a unique contemporary resource for the study of health and disease, recruited more than half a million people aged 40–69 years. A subsample of 107,452 subjects undertook an enhanced ophthalmic examination which provided autorefraction data (a measure of refractive error). Refractive error status was categorised using the mean spherical equivalent refraction measure. Information on socio-demographic factors (age, gender, ethnicity, educational qualifications and accommodation tenure) was reported at the time of recruitment by questionnaire and face-to-face interview. Results Fifty four percent of participants aged 40–69 years had refractive error. Specifically 27% had myopia (4% high myopia), which was more common amongst younger people, those of higher socio-economic status, higher educational attainment, or of White or Chinese ethnicity. The frequency of hypermetropia increased with age (7% at 40–44 years increasing to 46% at 65–69 years), was higher in women and its severity was associated with ethnicity (moderate or high hypermetropia at least 30% less likely in non-White ethnic groups compared to White). Conclusions Refractive error is a significant public health issue for the UK and this study provides contemporary data on adults for planning services, health economic modelling and monitoring of secular trends. Further investigation of risk factors is necessary to inform strategies for prevention. There is scope to do this through the planned longitudinal extension of the UK Biobank study. PMID:26430771

Integrated dual-tomography for refractive index analysis of free-floating single living cell with isotropic superresolution.

PubMed

B, Vinoth; Lai, Xin-Ji; Lin, Yu-Chih; Tu, Han-Yen; Cheng, Chau-Jern

2018-04-13

Digital holographic microtomography is a promising technique for three-dimensional (3D) measurement of the refractive index (RI) profiles of biological specimens. Measurement of the RI distribution of a free-floating single living cell with an isotropic superresolution had not previously been accomplished. To the best of our knowledge, this is the first study focusing on the development of an integrated dual-tomographic (IDT) imaging system for RI measurement of an unlabelled free-floating single living cell with an isotropic superresolution by combining the spatial frequencies of full-angle specimen rotation with those of beam rotation. A novel 'UFO' (unidentified flying object) like shaped coherent transfer function is obtained. The IDT imaging system does not require any complex image-processing algorithm for 3D reconstruction. The working principle was successfully demonstrated and a 3D RI profile of a single living cell, Candida rugosa, was obtained with an isotropic superresolution. This technology is expected to set a benchmark for free-floating single live sample measurements without labeling or any special sample preparations for the experiments.

3D refractive index measurements of special optical fibers

NASA Astrophysics Data System (ADS)

Yan, Cheng; Huang, Su-Juan; Miao, Zhuang; Chang, Zheng; Zeng, Jun-Zhang; Wang, Ting-Yun

2016-09-01

A digital holographic microscopic chromatography-based approach with considerably improved accuracy, simplified configuration and performance stability is proposed to measure three dimensional refractive index of special optical fibers. Based on the approach, a measurement system is established incorporating a modified Mach-Zehnder interferometer and lab-developed supporting software for data processing. In the system, a phase projection distribution of an optical fiber is utilized to obtain an optimal digital hologram recorded by a CCD, and then an angular spectrum theory-based algorithm is adopted to extract the phase distribution information of an object wave. The rotation of the optic fiber enables the experimental measurements of multi-angle phase information. Based on the filtered back projection algorithm, a 3D refraction index of the optical fiber is thus obtained at high accuracy. To evaluate the proposed approach, both PANDA fibers and special elliptical optical fiber are considered in the system. The results measured in PANDA fibers agree well with those measured using S14 Refractive Index Profiler, which is, however, not suitable for measuring the property of a special elliptical fiber.

Dependence of columnar aerosol size distribution, optical properties, and chemical components on regional transport in Beijing

NASA Astrophysics Data System (ADS)

Wang, Shuo; Zhao, Weixiong; Xu, Xuezhe; Fang, Bo; Zhang, Qilei; Qian, Xiaodong; Zhang, Weijun; Chen, Weidong; Pu, Wei; Wang, Xin

2017-11-01

Seasonal dependence of the columnar aerosol optical and chemical properties on regional transport in Beijing over 10 years (from January 2005 to December 2014) were analyzed by using the ground-based remote sensing combined with backward trajectory analysis. Daily air mass backward trajectories terminated in Beijing were computed with HYSPLIT-4 model and were categorized into five clusters. The columnar mass concentrations of black carbon (BC), brown carbon (BrC), dust (DU), aerosol water content (AW), and ammonium sulfate like aerosol (AS) of each cluster were retrieved from the optical data obtained from the Aerosol Robotic NETwork (AERONET) with five-component model. It was found that the columnar aerosol properties in different seasons were changed, and they were related to the air mass origins. In spring, aerosol was dominated by coarse particles. Summer was characterized by higher single scattering albedo (SSA), lower real part of complex refractive index (n), and obvious hygroscopic growth due to humid air from the south. During autumn and winter, there was an observable increase in absorption aerosol optical thickness (AAOT) and the imaginary part of complex refraction (k), with high levels of retrieved BC and BrC. However, concentrations of BC showed less dependence on the clusters during the two seasons owing to the widely spread coal heating in north China.

Broadband metamaterial lens antennas with special properties by controlling both refractive-index distribution and feed directivity

NASA Astrophysics Data System (ADS)

Ma, Qian; Shi, Chuan Bo; Chen, Tian Yi; Qing Qi, Mei; Li, Yun Bo; Cui, Tie Jun

2018-04-01

A new method is proposed to design gradient refractive-index metamaterial lens antennas by optimizing both the refractive-index distribution of the lens and the feed directivity. Comparing to the conventional design methods, source optimization provides a new degree of freedom to control aperture fields effectively. To demonstrate this method, two lenses with special properties based on this method are designed, to emit high-efficiency plane waves and fan-shaped beams, respectively. Both lenses have good performance and wide frequency band from 12 to 18 GHz, verifying the validity of the proposed method. The plane-wave emitting lens realized a high aperture efficiency of 75%, and the fan-beam lens achieved a high gain of 15 dB over board bandwidth. The experimental results have good agreement with the design targets and full-wave simulations.

Two-dimensional simulation of holographic data storage medium for multiplexed recording.

PubMed

Toishi, Mitsuru; Takeda, Takahiro; Tanaka, Kenji; Tanaka, Tomiji; Fukumoto, Atsushi; Watanabe, Kenjiro

2008-02-18

In this paper, we propose a new analysis model for photopolymer recording processes that calculate the two-dimensional refractive index distribution of multiplexed holograms. For the simulation of the photopolymer medium, time evolution of monomer diffusion and polymerization need to be calculated simultaneously. The distribution of the refractive index inside the medium is induced by these processes. By evaluating the refractive index pattern on each layer, the diffraction beams from the multiplexed hologram can be read out by beam propagation method (BPM). This is the first paper to determine the diffraction beam from a multiplexed hologram in a simulated photopolymer medium process. We analyze the time response of the multiplexed hologram recording processes in the photopolymer, and estimate the degradation of diffraction efficiency with multiplexed recording. This work can greatly contribute to understanding the process of hologram recording.

Single-photon test of hyper-complex quantum theories using a metamaterial.

PubMed

Procopio, Lorenzo M; Rozema, Lee A; Wong, Zi Jing; Hamel, Deny R; O'Brien, Kevin; Zhang, Xiang; Dakić, Borivoje; Walther, Philip

2017-04-21

In standard quantum mechanics, complex numbers are used to describe the wavefunction. Although this has so far proven sufficient to predict experimental results, there is no theoretical reason to choose them over real numbers or generalizations of complex numbers, that is, hyper-complex numbers. Experiments performed to date have proven that real numbers are insufficient, but the need for hyper-complex numbers remains an open question. Here we experimentally probe hyper-complex quantum theories, studying one of their deviations from complex quantum theory: the non-commutativity of phases. We do so by passing single photons through a Sagnac interferometer containing both a metamaterial with a negative refractive index, and a positive phase shifter. To accomplish this we engineered a fishnet metamaterial to have a negative refractive index at 780 nm. We show that the metamaterial phase commutes with other phases with high precision, allowing us to place limits on a particular prediction of hyper-complex quantum theories.

Single-photon test of hyper-complex quantum theories using a metamaterial

DOE Office of Scientific and Technical Information (OSTI.GOV)

Procopio, Lorenzo M.; Rozema, Lee A.; Wong, Zi Jing

In standard quantum mechanics, complex numbers are used to describe the wavefunction. Although this has so far proven sufficient to predict experimental results, there is no theoretical reason to choose them over real numbers or generalizations of complex numbers, that is, hyper-complex numbers. Experiments performed to date have proven that real numbers are insufficient, but the need for hyper-complex numbers remains an open question. Here we experimentally probe hyper-complex quantum theories, studying one of their deviations from complex quantum theory: the non-commutativity of phases. We do so by passing single photons through a Sagnac interferometer containing both a metamaterial withmore » a negative refractive index, and a positive phase shifter. In order to accomplish this we engineered a fishnet metamaterial to have a negative refractive index at 780 nm. Here, we show that the metamaterial phase commutes with other phases with high precision, allowing us to place limits on a particular prediction of hyper-complex quantum theories.« less

Single-photon test of hyper-complex quantum theories using a metamaterial

DOE PAGES

Procopio, Lorenzo M.; Rozema, Lee A.; Wong, Zi Jing; ...

2017-04-21

In standard quantum mechanics, complex numbers are used to describe the wavefunction. Although this has so far proven sufficient to predict experimental results, there is no theoretical reason to choose them over real numbers or generalizations of complex numbers, that is, hyper-complex numbers. Experiments performed to date have proven that real numbers are insufficient, but the need for hyper-complex numbers remains an open question. Here we experimentally probe hyper-complex quantum theories, studying one of their deviations from complex quantum theory: the non-commutativity of phases. We do so by passing single photons through a Sagnac interferometer containing both a metamaterial withmore » a negative refractive index, and a positive phase shifter. In order to accomplish this we engineered a fishnet metamaterial to have a negative refractive index at 780 nm. Here, we show that the metamaterial phase commutes with other phases with high precision, allowing us to place limits on a particular prediction of hyper-complex quantum theories.« less

Single-photon test of hyper-complex quantum theories using a metamaterial

PubMed Central

Procopio, Lorenzo M.; Rozema, Lee A.; Wong, Zi Jing; Hamel, Deny R.; O'Brien, Kevin; Zhang, Xiang; Dakić, Borivoje; Walther, Philip

2017-01-01

In standard quantum mechanics, complex numbers are used to describe the wavefunction. Although this has so far proven sufficient to predict experimental results, there is no theoretical reason to choose them over real numbers or generalizations of complex numbers, that is, hyper-complex numbers. Experiments performed to date have proven that real numbers are insufficient, but the need for hyper-complex numbers remains an open question. Here we experimentally probe hyper-complex quantum theories, studying one of their deviations from complex quantum theory: the non-commutativity of phases. We do so by passing single photons through a Sagnac interferometer containing both a metamaterial with a negative refractive index, and a positive phase shifter. To accomplish this we engineered a fishnet metamaterial to have a negative refractive index at 780 nm. We show that the metamaterial phase commutes with other phases with high precision, allowing us to place limits on a particular prediction of hyper-complex quantum theories. PMID:28429711

Accurate in situ measurement of complex refractive index and particle size in intralipid emulsions

NASA Astrophysics Data System (ADS)

Dong, Miao L.; Goyal, Kashika G.; Worth, Bradley W.; Makkar, Sorab S.; Calhoun, William R.; Bali, Lalit M.; Bali, Samir

2013-08-01

A first accurate measurement of the complex refractive index in an intralipid emulsion is demonstrated, and thereby the average scatterer particle size using standard Mie scattering calculations is extracted. Our method is based on measurement and modeling of the reflectance of a divergent laser beam from the sample surface. In the absence of any definitive reference data for the complex refractive index or particle size in highly turbid intralipid emulsions, we base our claim of accuracy on the fact that our work offers several critically important advantages over previously reported attempts. First, our measurements are in situ in the sense that they do not require any sample dilution, thus eliminating dilution errors. Second, our theoretical model does not employ any fitting parameters other than the two quantities we seek to determine, i.e., the real and imaginary parts of the refractive index, thus eliminating ambiguities arising from multiple extraneous fitting parameters. Third, we fit the entire reflectance-versus-incident-angle data curve instead of focusing on only the critical angle region, which is just a small subset of the data. Finally, despite our use of highly scattering opaque samples, our experiment uniquely satisfies a key assumption behind the Mie scattering formalism, namely, no multiple scattering occurs. Further proof of our method's validity is given by the fact that our measured particle size finds good agreement with the value obtained by dynamic light scattering.

Accurate in situ measurement of complex refractive index and particle size in intralipid emulsions.

PubMed

Dong, Miao L; Goyal, Kashika G; Worth, Bradley W; Makkar, Sorab S; Calhoun, William R; Bali, Lalit M; Bali, Samir

2013-08-01

A first accurate measurement of the complex refractive index in an intralipid emulsion is demonstrated, and thereby the average scatterer particle size using standard Mie scattering calculations is extracted. Our method is based on measurement and modeling of the reflectance of a divergent laser beam from the sample surface. In the absence of any definitive reference data for the complex refractive index or particle size in highly turbid intralipid emulsions, we base our claim of accuracy on the fact that our work offers several critically important advantages over previously reported attempts. First, our measurements are in situ in the sense that they do not require any sample dilution, thus eliminating dilution errors. Second, our theoretical model does not employ any fitting parameters other than the two quantities we seek to determine, i.e., the real and imaginary parts of the refractive index, thus eliminating ambiguities arising from multiple extraneous fitting parameters. Third, we fit the entire reflectance-versus-incident-angle data curve instead of focusing on only the critical angle region, which is just a small subset of the data. Finally, despite our use of highly scattering opaque samples, our experiment uniquely satisfies a key assumption behind the Mie scattering formalism, namely, no multiple scattering occurs. Further proof of our method's validity is given by the fact that our measured particle size finds good agreement with the value obtained by dynamic light scattering.

The complex refractive index of atmospheric and model humic-like substances (HULIS) retrieved by a cavity ring down aerosol spectrometer (CRD-AS).

PubMed

Dinar, E; Riziq, A Abo; Spindler, C; Erlick, C; Kiss, G; Rudich, Y

2008-01-01

Atmospheric aerosols absorb and reflect solar radiation causing surface cooling and heating of the atmosphere. The interaction between aerosols and radiation depends on their complex index of refraction, which is related to the particles' chemical composition. The contribution of light absorbing organic compounds, such as HUmic-LIke Substances (HULIS) to aerosol scattering and absorption is among the largest uncertainties in assessing the direct effect of aerosols on climate. Using a Cavity Ring Down Aerosol Spectrometer (CRD-AS), the complex index of refraction of aerosols containing HULIS extracted from pollution, smoke, and rural continental aerosols, and molecular weight-fractionated fulvic acid was measured at 390 nm and 532 nm. The imaginary part of the refractive index (absorption) substantially increases towards the UV range with increasing molecular weight and aromaticity. At both wavelengths, HULIS extracted from pollution and smoke particles absorb more than HULIS from the rural aerosol. Sensitivity calculations for a pollution-type aerosol containing ammonium sulfate, organic carbon (HULIS), and soot suggests that accounting for absorption by HULIS leads in most cases to a significant decrease in the single scattering albedo and to a significant increase in aerosol radiative forcing efficiency, towards more atmospheric absorption and heating. This indicates that HULIS in biomass smoke and pollution aerosols, in addition to black carbon, can contribute significantly to light absorption in the ultraviolet and visible spectral regions.

Nonlinear refraction at the absorption edge in InAs.

PubMed

Poole, C D; Garmire, E

1984-08-01

The results of measurements of nonlinear refraction at the absorption edge in InAs between 68 and 90 K taken with an HF laser are compared with those of a band-gap resonant model in which the contribution of the light-hole band is included and found to account for more than 40% of the observed nonlinear refraction. A generalized expression for the nonlinear index is derived by using the complete Fermi-Dirac distribution function. Good agreement between theory and experiment is obtained, with no free parameters.

FIBER OPTICS: Ray invariants and wave equations for transverse modes in three-dimensional graded-index waveguides

NASA Astrophysics Data System (ADS)

Voevodin, V. G.; Morozov, A. N.; Stepanov, V. E.

1992-09-01

A theory of the second ray invariant is proposed using the theory of plane Frenet curves. Its existence requires that the coordinate dependence of the refractive index in the waveguide cross section should satisfy the regularity condition: curves of equal refractive index differ only by an amount which can be obtained using an isotropic scaling transformation. The theoretical conclusions are illustrated using the example of waveguides having the generalized refractive index distribution n ( r ) = n [ (x/ a) + (y/ b)q].

Light-driven liquid microlenses

NASA Astrophysics Data System (ADS)

Angelini, A.; Pirani, F.; Frascella, F.; Ricciardi, S.; Descrovi, E.

2017-02-01

We propose a liquid polymeric compound based on photo-responsive azo-polymers to be used as light-activated optical element with tunable and reversible functionalities. The interaction of a laser beam locally modifies the liquid density thus producing a refractive index gradient. The laser induced refractive index profiles are observed along the optical axis of the microscope to evaluate the total phase shift induced and along the orthogonal direction to provide the axial distribution of the refractive index variation. The focusing and imaging properties of the liquid lenses as functions of the light intensity are illustrated.

Bayesian assessment of uncertainty in aerosol size distributions and index of refraction retrieved from multiwavelength lidar measurements.

PubMed

Herman, Benjamin R; Gross, Barry; Moshary, Fred; Ahmed, Samir

2008-04-01

We investigate the assessment of uncertainty in the inference of aerosol size distributions from backscatter and extinction measurements that can be obtained from a modern elastic/Raman lidar system with a Nd:YAG laser transmitter. To calculate the uncertainty, an analytic formula for the correlated probability density function (PDF) describing the error for an optical coefficient ratio is derived based on a normally distributed fractional error in the optical coefficients. Assuming a monomodal lognormal particle size distribution of spherical, homogeneous particles with a known index of refraction, we compare the assessment of uncertainty using a more conventional forward Monte Carlo method with that obtained from a Bayesian posterior PDF assuming a uniform prior PDF and show that substantial differences between the two methods exist. In addition, we use the posterior PDF formalism, which was extended to include an unknown refractive index, to find credible sets for a variety of optical measurement scenarios. We find the uncertainty is greatly reduced with the addition of suitable extinction measurements in contrast to the inclusion of extra backscatter coefficients, which we show to have a minimal effect and strengthens similar observations based on numerical regularization methods.

Helping secondary school students develop a conceptual understanding of refraction

NASA Astrophysics Data System (ADS)

Ashmann, Scott; Anderson, Charles W.; Boeckman, Heather

2016-07-01

Using real-world examples, ray diagrams, and a cognitive apprenticeship cycle, this paper focuses on developing students’ conceptual (not mathematical) understanding of refraction. Refraction can be a difficult concept for students to comprehend if they do not have well-designed opportunities to practice explaining situations where reflection and refraction occur. The use of ray diagrams can be useful in (a) the teacher modelling a correct explanation to a situation where refraction occurs and (b) for students to create as they practice other examples. This paper includes eight examples of increasing complexity that use a cognitive apprenticeship cycle approach to scaffold student learning. The first examples (rock fish, floating penny) are shown and a solution is modeled using a ray diagram. Three more examples (bent pencil, dropping an item in water, sunrise/sunset) are presented for students to practice, with each becoming more sophisticated. Three assessment exercises are then provided (two dots, three coins, broken tube).

Nature versus nurture: A systematic approach to elucidate gene-environment interactions in the development of myopic refractive errors.

PubMed

Miraldi Utz, Virginia

2017-01-01

Myopia is the most common eye disorder and major cause of visual impairment worldwide. As the incidence of myopia continues to rise, the need to further understand the complex roles of molecular and environmental factors controlling variation in refractive error is of increasing importance. Tkatchenko and colleagues applied a systematic approach using a combination of gene set enrichment analysis, genome-wide association studies, and functional analysis of a murine model to identify a myopia susceptibility gene, APLP2. Differential expression of refractive error was associated with time spent reading for those with low frequency variants in this gene. This provides support for the longstanding hypothesis of gene-environment interactions in refractive error development.

Data-driven layer-stripping strategy in 3-D joint refraction and reflection travel-time tomography with TOMO3D

NASA Astrophysics Data System (ADS)

Meléndez, Adrià; Korenaga, Jun; Sallarès, Valentí; Miniussi, Alain; Ranero, César

2015-04-01

We present a new 3-D travel-time tomography code (TOMO3D) for the modelling of active-source seismic data that uses the arrival times of both refracted and reflected seismic phases to derive the propagation velocity distribution and the geometry of reflecting boundaries in the subsurface. The combination of refracted and reflected data provides a denser coverage of the study area. Moreover, because refractions only depend on the velocity parameters, they contribute to the mitigation of the negative effect of the ambiguity between layer thickness and propagation velocity that is intrinsic to the reflections that define these boundaries. This code is based on its renowned 2-D version TOMO2D from which it inherited the methods to solve the forward and inverse problems. The forward travel-time calculations are conducted using a hybrid ray-tracing technique combining the graph or shortest path method and the bending method. The LSQR algorithm is used to perform the iterative inversion of travel-time residuals to update the initial velocity and depth models. In order to cope with the increased computational demand due to the incorporation of the third dimension, the forward problem solver, which takes by far most of the run time (~90%), has been parallelised with a combination of MP and MPI standards. This parallelisation distributes the ray-tracing and travel-time calculations among the available computational resources, allowing the user to set the number of nodes, processors and cores to be used. The code's performance was evaluated with a complex synthetic case simulating a subduction zone. The objective is to retrieve the velocity distribution of both upper and lower plates and the geometry of the interplate and Moho boundaries. Our tomography method is designed to deal with a single reflector per inversion, and we show that a data-driven layer-stripping strategy allows to successfully recover several reflectors in successive inversions. This strategy consists in building the final velocity model layer by layer, sequentially extending it down with each inversion of a new, deeper reflector. One advantage of layer stripping is that it allows us to introduce and keep strong velocity contrasts associated to geological discontinuities that would otherwise be smoothened. Another advantage is that it poses simpler inverse problems at each step, facilitating the minimisation of travel-time residuals and ensuring a good control on each partial model before adding new data corresponding to deeper layers. Finally, we discuss the parallel performance of the code in this particular synthetic case.

A Refractive Index Sensor Based on the Resonant Coupling to Cladding Modes in a Fiber Loop

PubMed Central

Reyes, Mauricio; Monzón-Hernández, David; Martínez-Ríos, Alejandro; Silvestre, Enrique; Díez, Antonio; Cruz, José Luis; Andrés, Miguel V.

2013-01-01

We report an easy-to-build, compact, and low-cost optical fiber refractive index sensor. It consists of a single fiber loop whose transmission spectra exhibit a series of notches produced by the resonant coupling between the fundamental mode and the cladding modes in a uniformly bent fiber. The wavelength of the notches, distributed in a wavelength span from 1,400 to 1,700 nm, can be tuned by adjusting the diameter of the fiber loop and are sensitive to refractive index changes of the external medium. Sensitivities of 170 and 800 nm per refractive index unit for water solutions and for the refractive index interval 1.40–1.442, respectively, are demonstrated. We estimate a long range resolution of 3 × 10−4 and a short range resolution of 2 × 10−5 for water solutions. PMID:23979478

Refractive errors in a Brazilian population: age and sex distribution.

PubMed

Ferraz, Fabio H; Corrente, José E; Opromolla, Paula; Padovani, Carlos Roberto; Schellini, Silvana A

2015-01-01

To determine the prevalence of refractive errors and their distribution according to age and sex in a Brazilian population. This population-based cross-sectional study involved 7654 Brazilian inhabitants of nine municipalities of Sao Paulo State, Brazil, between March 2004 and July 2005. Participants aged >1 year were selected using a random, stratified, household cluster sampling technique, excluding individuals with previous refractive or cataract surgery. Myopia was defined as spherical equivalent (SE) ≤-0.5D, high myopia as SE ≤-3.0D, hyperopia as SE ≥+0.5D, high hyperopia as SE ≥+3D, astigmatism as ≤-0.5DC and anisometropia as ≥1.0D difference between eyes. Age, sex, complaints and a comprehensive eye examination including cycloplegic refraction test were collected and analysed using descriptive analysis, univariate and multivariate methods. The prevalence of astigmatism was 59.7%, hyperopia 33.8% and myopia was 25.3%. Astigmatism had a progressive increase with age. With-the-rule (WTR) axes of astigmatism were more frequently observed in the young participants and the against-the-rule (ATR) axes were more frequent in the older subjects. The onset of myopia occurred more frequently between the 2nd and 3rd decades of life. Anisometropia showed a prevalence of 13.2% (95% CI 12.4-13.9; p < 0.001). There was an association between age and all types of refractive error and hyperopia was also associated with sex. Hyperopia was associated with WTR axes (odds ratio 0.73; 95% CI: 0.6-0.8; p < 0.001) and myopia with ATR axes (odds ratio 0.66; 95% CI: 0.6-0.8; p < 0.001). Astigmatism was the most prevalent refractive error in a Brazilian population. There was a strong relationship between age and all refractive errors and between hyperopia and sex. WTR astigmatism was more frequently associated with hyperopia and ATR astigmatism with myopia. The vast majority of participants had low-grade refractive error, which favours planning aimed at correction of refractive error in the population. © 2014 The Authors Ophthalmic & Physiological Optics © 2014 The College of Optometrists.

Emission Properties of Fluorescent Nanoparticles Determined by Their Optical Environment

PubMed Central

Chung, Kelvin; Tomljenovic-Hanic, Snjezana

2015-01-01

The emission rate of a radiating dipole within a nanoparticle is crucially dependent on its surrounding refractive index environment. In this manuscript, we present numerical results on how the emission rates are affected for nanoparticles in a homogenous and substrate environment. These results are general, applicable to any refractive index distribution and emitter. PMID:28347043

Refractivity variations and propagation at Ultra High Frequency

NASA Astrophysics Data System (ADS)

Alam, I.; Najam-Ul-Islam, M.; Mujahid, U.; Shah, S. A. A.; Ul Haq, Rizwan

Present framework is established to deal with the refractivity variations normally affected the radio waves propagation at different frequencies, ranges and different environments. To deal such kind of effects, many researchers proposed several methodologies. One method is to use the parameters from meteorology to investigate these effects of variations in refractivity on propagation. These variations are region specific and we have selected a region of one kilometer height over the English Channel. We have constructed different modified refractivity profiles based on the local meteorological data. We have recorded more than 48 million received signal strength from a communication links of 50 km operating at 2015 MHz in the Ultra High Frequency band giving path loss between transmitting and receiving stations of the experimental setup. We have used parabolic wave equation method to simulate an hourly value of signal strength and compared the obtained simulated loss to the experimental loss. The analysis is made to compute refractivity distribution of standard (STD) and ITU (International Telecommunication Union) refractivity profiles for various evaporation ducts. It is found that a standard refractivity profile is better than the ITU refractivity profiles for the region at 2015 MHz. Further, it is inferred from the analysis of results that 10 m evaporation duct height is the dominant among all evaporation duct heights considered in the research.

Prevalence of refractive errors in the European adult population: the Gutenberg Health Study (GHS).

PubMed

Wolfram, Christian; Höhn, René; Kottler, Ulrike; Wild, Philipp; Blettner, Maria; Bühren, Jens; Pfeiffer, Norbert; Mirshahi, Alireza

2014-07-01

To study the distribution of refractive errors among adults of European descent. Population-based eye study in Germany with 15010 participants aged 35-74 years. The study participants underwent a detailed ophthalmic examination according to a standardised protocol. Refractive error was determined by an automatic refraction device (Humphrey HARK 599) without cycloplegia. Definitions for the analysis were myopia <-0.5 dioptres (D), hyperopia >+0.5 D, astigmatism >0.5 cylinder D and anisometropia >1.0 D difference in the spherical equivalent between the eyes. Exclusion criterion was previous cataract or refractive surgery. 13959 subjects were eligible. Refractive errors ranged from -21.5 to +13.88 D. Myopia was present in 35.1% of this study sample, hyperopia in 31.8%, astigmatism in 32.3% and anisometropia in 13.5%. The prevalence of myopia decreased, while the prevalence of hyperopia, astigmatism and anisometropia increased with age. 3.5% of the study sample had no refractive correction for their ametropia. Refractive errors affect the majority of the population. The Gutenberg Health Study sample contains more myopes than other study cohorts in adult populations. Our findings do not support the hypothesis of a generally lower prevalence of myopia among adults in Europe as compared with East Asia.

Trends in refractive surgery at an academic center: 2007-2009.

PubMed

Kuo, Irene C

2011-05-14

The United States officially entered a recession in December 2007, and it officially exited the recession in December 2009, according to the National Bureau of Economic Research. Since the economy may affect not only the volume of excimer laser refractive surgery, but also the clinical characteristics of patients undergoing surgery, our goal was to compare the characteristics of patients completing excimer laser refractive surgery and the types of procedures performed in the summer quarter in 2007 and the same quarter in 2009 at an academic center. A secondary goal was to determine whether the volume of astigmatism- or presbyopia-correcting intraocular lenses (IOLs) has concurrently changed because like laser refractive surgery, these "premium" IOLs involve out-of-pocket costs for patients. Retrospective case series. Medical records were reviewed for all patients completing surgery at the Wilmer Laser Vision Center in the summer quarter of 2007 and the summer quarter of 2009. Outcome measures were the proportions of treated refractive errors, the proportion of photorefractive keratectomy (PRK) vs. laser-assisted in-situ keratomileusis (LASIK), and the mean age of patients in each quarter. Chi-square test was used to compare the proportions of treated refractive errors and the proportions of procedures; two-tailed t-test to compare the mean age of patients; and two-tailed z-test to compare proportions of grouped refractive errors in 2007 vs. 2009; alpha = 0.05 for all tests. Refractive errors were grouped by the spherical equivalent of the manifest refraction and were considered "low myopia" for 6 diopters (D) of myopia or less, "high myopia" for more than 6 D, and "hyperopia" for any hyperopia. Billing data were reviewed to obtain the volume of premium IOLs. Volume of laser refractive procedures decreased by at least 30%. The distribution of proportions of treated refractive errors did not change (p = 0.10). The proportion of high myopes, however, decreased (p = 0.05). The proportions of types of procedure changed, with an increase in the proportion of PRK between 2007 and 2009 (p = 0.02). The mean age of patients did not change [42.4 ± 14.4 (standard deviation) years in 2007 vs. 39.6 ± 14.5 years in 2009; p = 0.4]. Astigmatism-correcting IOL and presbyopia-correcting IOL volumes increased 15-fold and three-fold, respectively, between 2007 and 2009. Volume of excimer laser refractive surgery decreased by at least 30% between 2007 and 2009. No significant change in mean age or in the distribution of refractive error was seen, although the proportion of high myopes decreased between summer quarters of 2007 and 2009. PRK gained as a proportion of total cases. Premium IOL volume increased, but still comprised a very small proportion of total IOL volume.

Trends in refractive surgery at an academic center: 2007-2009

PubMed Central

2011-01-01

Background The United States officially entered a recession in December 2007, and it officially exited the recession in December 2009, according to the National Bureau of Economic Research. Since the economy may affect not only the volume of excimer laser refractive surgery, but also the clinical characteristics of patients undergoing surgery, our goal was to compare the characteristics of patients completing excimer laser refractive surgery and the types of procedures performed in the summer quarter in 2007 and the same quarter in 2009 at an academic center. A secondary goal was to determine whether the volume of astigmatism- or presbyopia-correcting intraocular lenses (IOLs) has concurrently changed because like laser refractive surgery, these "premium" IOLs involve out-of-pocket costs for patients. Methods Retrospective case series. Medical records were reviewed for all patients completing surgery at the Wilmer Laser Vision Center in the summer quarter of 2007 and the summer quarter of 2009. Outcome measures were the proportions of treated refractive errors, the proportion of photorefractive keratectomy (PRK) vs. laser-assisted in-situ keratomileusis (LASIK), and the mean age of patients in each quarter. Chi-square test was used to compare the proportions of treated refractive errors and the proportions of procedures; two-tailed t-test to compare the mean age of patients; and two-tailed z-test to compare proportions of grouped refractive errors in 2007 vs. 2009; alpha = 0.05 for all tests. Refractive errors were grouped by the spherical equivalent of the manifest refraction and were considered "low myopia" for 6 diopters (D) of myopia or less, "high myopia" for more than 6 D, and "hyperopia" for any hyperopia. Billing data were reviewed to obtain the volume of premium IOLs. Results Volume of laser refractive procedures decreased by at least 30%. The distribution of proportions of treated refractive errors did not change (p = 0.10). The proportion of high myopes, however, decreased (p = 0.05). The proportions of types of procedure changed, with an increase in the proportion of PRK between 2007 and 2009 (p = 0.02). The mean age of patients did not change [42.4 ± 14.4 (standard deviation) years in 2007 vs. 39.6 ± 14.5 years in 2009; p = 0.4]. Astigmatism-correcting IOL and presbyopia-correcting IOL volumes increased 15-fold and three-fold, respectively, between 2007 and 2009. Conclusions Volume of excimer laser refractive surgery decreased by at least 30% between 2007 and 2009. No significant change in mean age or in the distribution of refractive error was seen, although the proportion of high myopes decreased between summer quarters of 2007 and 2009. PRK gained as a proportion of total cases. Premium IOL volume increased, but still comprised a very small proportion of total IOL volume. PMID:21569564

Crystalline sulfur dioxide: Crystal field splittings, absolute band intensities and complex refractive indices derived from infrared spectra

NASA Technical Reports Server (NTRS)

Khanna, R. K.; Zhao, Guizhi

1986-01-01

The infrared absorption spectra of thin crystalline films of sulfur dioxide at 90 K are reported in the 2700 to 450/cm region. The observed multiplicity of the spectral features in the regions of fundamentals is attributed to factor group splittings of the modes in a biaxial crystal lattice and the naturally present minor S-34, S-36, and O-18 isotopic species. Complex refractive indices determined by an iterative Kramers-Kronig analysis of the extinction data, and absolute band strengths derived from them, are also reported in this region.

The effect of aerosols on the earth-atmosphere albedo

NASA Technical Reports Server (NTRS)

Herman, B. M.; Browning, S. R.

1975-01-01

The paper presents calculations of the change in reflected flux by the earth-atmosphere system in response to increases in the atmospheric aerosol loading for a range of complex indices of refraction, solar elevation angle and ground albedo. Results show that, for small values of ground albedo, the reflected solar flux may either increase or decrease with increasing aerosol loadings, depending upon the complex part of the index of refraction of the aerosols. For high ground albedos, an increase in aerosol levels always results in a decrease of reflected flux (i.e., a warming of the earth-atmosphere system).

A comparison of electronic heterodyne moire deflectometry and electronic heterodyne holographic interferometry for flow measurements

NASA Technical Reports Server (NTRS)

Decker, A. J.; Stricker, J.

1985-01-01

Electronic heterodyne moire deflectometry and electronic heterodyne holographic interferometry are compared as methods for the accurate measurement of refractive index and density change distributions of phase objects. Experimental results are presented to show that the two methods have comparable accuracy for measuring the first derivative of the interferometric fringe shift. The phase object for the measurements is a large crystal of KD*P, whose refractive index distribution can be changed accurately and repeatably for the comparison. Although the refractive index change causes only about one interferometric fringe shift over the entire crystal, the derivative shows considerable detail for the comparison. As electronic phase measurement methods, both methods are very accurate and are intrinsically compatible with computer controlled readout and data processing. Heterodyne moire is relatively inexpensive and has high variable sensitivity. Heterodyne holographic interferometry is better developed, and can be used with poor quality optical access to the experiment.

Recovery of refractivity profiles and pressure and temperature distributions in the lower atmosphere from satellite-to-satellite radio occultation data

NASA Technical Reports Server (NTRS)

Murray, C. W., Jr.

1977-01-01

The feasibility of recovering parameters from one-way range rate between two earth orbiting spacecraft during occultation of the tracking signal by the earth's lower atmosphere. The tracking data is inverted by an integral transformation (Abel transform) to obtain a vertical refractivity profile above the point of closest approach of the ray connecting the satellites. Pressure and temperature distributions can be obtained from values of dry refractivity using the hydrostatic equation and perfect gas law. Two methods are investigated for recovering pressure and temperature parameters. Results show that recovery is much more sensitive to satellite velocity errors than to satellite position errors. An error analysis is performed. An example is given demonstrating recovery of parameters from radio occultation data obtained during satellite-to-satellite tracking of Nimbus 6 by the ATS 6 satellite.

Optical fiber design and the trapping of Cerenkov radiation.

PubMed

Law, S H; Fleming, S C; Suchowerska, N; McKenzie, D R

2006-12-20

Cerenkov radiation is generated in optical fibers immersed in radiation fields and can interfere with signal transmission. We develop a theory for predicting the intensity of Cerenkov radiation generated within the core of a multimode optical fiber by using a ray optic approach and use it to make predictions of the intensity of radiation transmitted down the fiber in propagating modes. The intensity transmitted down the fiber is found to be dominated by bound rays with a contribution from tunneling rays. It is confirmed that for relativistic particles the intensity of the radiation that is transmitted along the fiber is a function of the angle between the particle beam and the fiber axis. The angle of peak intensity is found to be a function of the fiber refractive index difference as well as the core refractive index, with larger refractive index differences shifting the peak significantly toward lower angles. The angular range of the distribution is also significantly increased in both directions by increasing the fiber refractive index difference. The intensity of the radiation is found to be proportional to the cube of the fiber core radius in addition to its dependence on refractive index difference. As the particle energy is reduced into the nonrelativistic range the entire distribution is shifted toward lower angles. Recommendations on minimizing the quantity of Cerenkov light transmitted in the fiber optic system in a radiation field are given.

Effect of TiCl4 treatment on the refractive index of nanoporous TiO2 films

NASA Astrophysics Data System (ADS)

Lee, Jeeyoung; Lee, Myeongkyu

2015-12-01

We investigate the effect of TiCl4 treatment on the refractive index of a nanoporous TiO2 film. A nanoparticulate TiO2 film prepared on a glass substrate was immersed in a TiCl4 aqueous solution. The subsequent reaction of TiCl4 with H2O produces TiO2 and thus modifies the density and the refractive index of the film. With increasing TiCl4 concentration, the refractive index initially increased and then declined after being maximized (n = 2.02 at 633 nm) at 0.08 M concentration. A refractive index change as large as 0.45 could be obtained with the TiCl4 treatment, making it possible to achieve diffraction efficiency exceeding 80% in a diffraction grating-embedded TiO2 film. For high TiCl4 concentrations of 0.32 M and 0.64 M, the refractive index remained nearly unchanged. This was attributed to the limited permeability of high-viscosity TiCl4 solutions into the nanoporous films. The measured pore size distributions were in good agreement with the results of a diffraction analysis and refractive index measurement.

[Extreme (complicated, ultra-high) refractive errors: terminological misconceptions!?

PubMed

Avetisov, S E

2018-01-01

The article reviews development mechanisms of different refractive errors accompanied by marked defocus of light rays reaching the retina. Terminology used for such ametropias includes terms extreme, ultra-high and complicated. Justification of their usage for primary ametropias, whose symptom complex is based on changes in axial eye length, is an ongoing discussion. To comply with thesaurus definitions of 'diagnosis' and 'pathogenesis', to characterize refractive and anatomical-functional disorders in patients with primary ametropias it is proposed to use the terms 'hyperaxial and hypoaxial syndromes' with elaboration of specific symptoms instead of such expressions as extreme (ultra-high) myopia and hypermetropia.

Optofluidic intracavity spectroscopy for spatially, temperature, and wavelength dependent refractometry

NASA Astrophysics Data System (ADS)

Kindt, Joel D.

A microfluidic refractometer was designed based on previous optofluidic intracavity spectroscopy (OFIS) chips utilized to distinguish healthy and cancerous cells. The optofluidic cavity is realized by adding high reflectivity dielectric mirrors to the top and bottom of a microfluidic channel. This creates a plane-plane Fabry-Perot optical cavity in which the resonant wavelengths are highly dependent on the optical path length inside the cavity. Refractometry is a useful method to determine the nature of fluids, including the concentration of a solute in a solvent as well as the temperature of the fluid. Advantages of microfluidic systems are the easy integration with lab-on-chip devices and the need for only small volumes of fluid. The unique abilities of the microfluidic refractometer in this thesis include its spatial, temperature, and wavelength dependence. Spatial dependence of the transmission spectrum is inherent through a spatial filtering process implemented with an optical fiber and microscope objective. A sequence of experimental observations guided the change from using the OFIS chip as a cell discrimination device to a complimentary refractometer. First, it was noted the electrode structure within the microfluidic channel, designed to trap and manipulate biological cells with dielectrophoretic (DEP) forces, caused the resonant wavelengths to blue-shift when the electrodes were energized. This phenomenon is consistent with the negative dn/dT property of water and water-based solutions. Next, it was necessary to develop a method to separate the optical path length into physical path length and refractive index. Air holes were placed near the microfluidic channel to exclusively measure the cavity length with the known refractive index of air. The cavity length was then interpolated across the microfluidic channel, allowing any mechanical changes to be taken into account. After the separation of physical path length and refractive index, it was of interest to characterize the temperature dependent refractive index relationship, n(T), for phosphate buffered saline. Phosphate buffered saline (PBS) is a water-based solution used with our biological cells because it maintains an ion concentration similar to that found in body fluids. The n(T) characterization was performed using a custom-built isothermal apparatus in which the temperature could be controlled. To check for the accuracy of the PBS refractive index measurements, water was also measured and compared with known values in the literature. The literature source of choice has affiliations to NIST and a formulation of refractive index involving temperature and wavelength dependence, two parameters which are necessary for our specialized infrared wavelength range. From the NIST formula, linear approximations were found to be dn/dT = -1.4x10-4 RIU °C-1 and dn/dlambda = -1.5x10-5 RIU nm-1 for water. A comparison with the formulated refractive indices of water indicated the measured values were off. This was attributed to the fact that light penetration into the HfO2/SiO2 dielectric mirrors had not been considered. Once accounted for, the refractive indices of water were consistent with the literature, and the values for PBS are believed to be accurate. A further discovery was the refractive index values at the discrete resonant wavelengths were monotonically decreasing, such that the dn/dlambda slope for water was considerably close to the NIST formula. Thus, n(T,lambda) was characterized for both water and PBS. A refractive index relationship for PBS with spatial, temperature, and wavelength dependence is particularly useful for non-uniform temperature distributions caused by DEP electrodes. First, a maximum temperature can be inferred, which is the desired measurement for cell viability concerns. In addition, a lateral refractive index distribution can be measured to help quantify the gradient index lenses that are formed by the energized electrodes. The non-uniform temperature distribution was also simulated with a finite element analysis software package. This simulated temperature distribution was converted to a refractive index distribution, and focal lengths were calculated for positive and negative gradient index lenses to a smallest possible length of about 10mm.

Improvement of Galilean refractive beam shaping system for accurately generating near-diffraction-limited flattop beam with arbitrary beam size.

PubMed

Ma, Haotong; Liu, Zejin; Jiang, Pengzhi; Xu, Xiaojun; Du, Shaojun

2011-07-04

We propose and demonstrate the improvement of conventional Galilean refractive beam shaping system for accurately generating near-diffraction-limited flattop beam with arbitrary beam size. Based on the detailed study of the refractive beam shaping system, we found that the conventional Galilean beam shaper can only work well for the magnifying beam shaping. Taking the transformation of input beam with Gaussian irradiance distribution into target beam with high order Fermi-Dirac flattop profile as an example, the shaper can only work well at the condition that the size of input and target beam meets R(0) ≥ 1.3 w(0). For the improvement, the shaper is regarded as the combination of magnifying and demagnifying beam shaping system. The surface and phase distributions of the improved Galilean beam shaping system are derived based on Geometric and Fourier Optics. By using the improved Galilean beam shaper, the accurate transformation of input beam with Gaussian irradiance distribution into target beam with flattop irradiance distribution is realized. The irradiance distribution of the output beam is coincident with that of the target beam and the corresponding phase distribution is maintained. The propagation performance of the output beam is greatly improved. Studies of the influences of beam size and beam order on the improved Galilean beam shaping system show that restriction of beam size has been greatly reduced. This improvement can also be used to redistribute the input beam with complicated irradiance distribution into output beam with complicated irradiance distribution.

Light scattering by lunar-like particle size distributions

NASA Technical Reports Server (NTRS)

Goguen, Jay D.

1991-01-01

A fundamental input to models of light scattering from planetary regoliths is the mean phase function of the regolith particles. Using the known size distribution for typical lunar soils, the mean phase function and mean linear polarization for a regolith volume element of spherical particles of any composition were calculated from Mie theory. The two contour plots given here summarize the changes in the mean phase function and linear polarization with changes in the real part of the complex index of refraction, n - ik, for k equals 0.01, the visible wavelength 0.55 micrometers, and the particle size distribution of the typical mature lunar soil 72141. A second figure is a similar index-phase surface, except with k equals 0.1. The index-phase surfaces from this survey are a first order description of scattering by lunar-like regoliths of spherical particles of arbitrary composition. They form the basis of functions that span a large range of parameter-space.

[Epidemiologic study of refractive errors in schoolchildren in socioeconomically deprived regions in Tunisia].

PubMed

Ayed, T; Sokkah, M; Charfi, O; El Matri, L

2002-09-01

This study's purpose was to estimate the prevalence of common refractive errors in schoolchildren in low socioeconomic regions in Tunisia and to assess their effect on school performance. This was a cross-sectional study done from November 1999 to January 2000 within the context of health care screening campaigns carried out by volunteer ophthalmologists and opticians in low-end socioeconomic regions in Tunisia. The concerned population was schoolchildren living in the cities of Tunis and Tabarka (North), Kerkena (Center), and Tozeur (South). We examined a total of 708 children with a mean age of 11.9 +/-3.21 years (from 6 to 20 years) and a sex ratio of 0.84. A cycloplegic refraction examination was performed on all the children. Statistical analyses with the chi squared test and the Fisher exact test allowed us to calculate the prevalence of the refractive errors totally and separately as well as the distribution according to age, sex, and region. We also searched for a possible relation between refractive errors and academic failure. Among the 708 children, 57.2% [CI(95)=53.4-60] had refractive errors, of which 31.6% [CI(95)=28.2-35.2] were hyperopic, whereas 9.1% [CI(95)=7.1-11.5] were myopic. Astigmatism was found in 16.4% [CI(95)=13.7-19.3]. The prevalence of myopia was significantly higher after the age of fourteen. It increased significantly with age (P=0.0003). The prevalence of hyperopia was significantly higher between the ages of 8 and 11 (P=0.0004). Hyperopic astigmatism was significantly more frequent between 6 and 9 years of age (P=0.001). There was no significant difference regarding sex. However, the distribution of the refractive errors by region showed a significantly high level of myopia in Tunis, Kerkena, and Tozeur. This difference disappeared with increasing age. The study of the effect of these refractive errors on school performance of these children from poor areas showed a significant association between all types of refractive errors and academic failure, with an odds ratio of 2.13 for all types of refractive errors, 2.69 for hyperopia, 2.87 for myopia, and 2.73 for astigmatism. This study showed the prevalence of refractive errors in a poor population of schoolchildren and emphasized the importance of such examinations. The ability of a child to participate in the educational experience is at least partially dependent on good vision.

Ultrafast Radiation Detection by Modulation of an Optical Probe Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vernon, S P; Lowry, M E

2006-02-22

We describe a new class of radiation sensor that utilizes optical interferometry to measure radiation-induced changes in the optical refractive index of a semiconductor sensor medium. Radiation absorption in the sensor material produces a transient, non-equilibrium, electron-hole pair distribution that locally modifies the complex, optical refractive index of the sensor medium. Changes in the real (imaginary) part of the local refractive index produce a differential phase shift (absorption) of an optical probe used to interrogate the sensor material. In contrast to conventional radiation detectors where signal levels are proportional to the incident energy, signal levels in these optical sensors aremore » proportional to the incident radiation energy flux. This allows for reduction of the sensor form factor with no degradation in detection sensitivity. Furthermore, since the radiation induced, non-equilibrium electron-hole pair distribution is effectively measured ''in place'' there is no requirement to spatially separate and collect the generated charges; consequently, the sensor risetime is of the order of the hot-electron thermalization time {le} 10 fs and the duration of the index perturbation is determined by the carrier recombination time which is of order {approx} 600 fs in, direct-bandgap semiconductors, with a high density of recombination defects; consequently, the optical sensors can be engineered with sub-ps temporal response. A series of detectors were designed, and incorporated into Mach Zehnder and Fabry-Perot interferometer-based detection systems: proof of concept, lower detection sensitivity, Mach-Zehnder detectors were characterized at beamline 6.3 at SSRL; three generations of high sensitivity single element and imaging Fabry-Perot detectors were measured at the LLNL Europa facility. Our results indicate that this technology can be used to provide x-ray detectors and x-ray imaging systems with single x-ray sensitivity and S/N {approx} 30 at x-ray energies {approx} 10 keV.« less

AERONET derived (BC) aerosol absorption

NASA Astrophysics Data System (ADS)

Kinne, S.

2015-12-01

AERONET is a ground-based sun-/sky-photometer network with good annual statistics at more than 400 sites worldwide. Inversion methods applied to these data define all relevant column aerosol optical properties and reveal even microphysical detail. The extracted data include estimates for aerosol size-distributions and for aerosol refractive indices at four different solar wavelengths. Hereby, the imaginary parts of the refractive indices define the aerosol column absorption. For regional and global averages and radiative impact assessment with off-line radiative transfer, these local data have been extended with distribution patterns offered by AeroCom modeling experiments. Annual and seasonal absorption distributions for total aerosol and estimates for component contributions (such as BC) are presented and associated direct forcing impacts are quantified.

Analysis of the hologram recording on the novel chloride photo-thermo-refractive glass

NASA Astrophysics Data System (ADS)

Ivanov, S. A.; Nikonorov, N. V.; Dubrovin, V. D.; Krykova, V. A.

2017-05-01

In this research, we present new holographic material based on fluoride photo-thermo-refractive glass(PTR) - chloride PTR glass. One of the benefit of this type of PTR glass is positive refractive index change. During this work, for the first-time volume Bragg gratings were recorded in this kind of material. The first experiments revealed that such gratings are mixed i.e. possess both absorption and phase components. Complex analysis shows that both refractive index and absorption coefficient are modulated inside the grating structure. We found out that at first there is no strict dependence of the refractive index change from dosage, but as we continue the process of thermal treatment - dependence is appear. Exposure influence on the refractive index change for this glass differs from fluoride one and shows some sort of saturation after the exposure of 4-6 J/cm2 . We distinguished refractive index change and absorption coefficient change and observed both behavior with increasing thermal treatment time. We found out that the increase of thermal treatment time results in the significant refractive index change. At the same time the absorption does `not practically change. It was found that maximum modulation of refractive index is comparable with fluoride PTR glass and achieves value of 1600 ppm. The modulation of absorption is equal to induced absorption caused by silver nanoparticles and depends from reading wavelength. Our study shows that almost all absorption is modulated inside the grating.

Flexible particle manipulation techniques with conical refraction-based optical tweezers

NASA Astrophysics Data System (ADS)

McDougall, C.; Henderson, Robert; Carnegie, David J.; Sokolovskii, Grigorii S.; Rafailov, Edik U.; McGloin, David

2012-10-01

We present an optimized optical tweezers system based upon the conical refraction of circularly polarized light in a biaxial crystal. The described optical arrangement avoids distortions to the Lloyd plane rings that become apparent when working with circularly polarized light in conventional optical tweezers. We demonstrate that the intensity distribution of the conically diffracted light permits optical manipulation of high and low refractive index particles simultaneously. Such trapping is in three dimensions and not limited to the Lloyd plane rings. By removal of a quarter waveplate the system also permits the study of linearly polarized conical refraction. We show that particle position in the Raman plane is determined by beam power, and indicates that true optical tweezing is not taking place in this part of the beam.

Broadband measurements of aerosol extinction in the ultraviolet spectral region

NASA Astrophysics Data System (ADS)

Washenfelder, R. A.; Flores, J. M.; Brock, C. A.; Brown, S. S.; Rudich, Y.

2013-04-01

Aerosols influence the Earth's radiative budget by scattering and absorbing incoming solar radiation. The optical properties of aerosols vary as a function of wavelength, but few measurements have reported the wavelength dependence of aerosol extinction cross sections and complex refractive indices. We describe a new laboratory instrument to measure aerosol optical extinction as a function of wavelength, using cavity enhanced spectroscopy with a broadband light source. The instrument consists of two broadband channels which span the 360-390 and 385-420 nm spectral regions using two light emitting diodes (LED) and a grating spectrometer with charge-coupled device (CCD) detector. We determined aerosol extinction cross sections and directly observed Mie scattering resonances for aerosols that are purely scattering (polystyrene latex spheres and ammonium sulfate), slightly absorbing (Suwannee River fulvic acid), and strongly absorbing (nigrosin dye). We describe an approach for retrieving refractive indices as a function of wavelength from the measured extinction cross sections over the 360-420 nm wavelength region. The retrieved refractive indices for PSL and ammonium sulfate agree within uncertainty with the literature values for this spectral region. The refractive index determined for nigrosin is 1.78 (± 0.03) + 0.19 (± 0.08)i at 360 nm and 1.63 (± 0.03) + 0.21 (± 0.05)i at 420 nm. The refractive index determined for Suwannee River fulvic acid is 1.71 (± 0.02) + 0.07 (± 0.06)i at 360 nm and 1.66 (± 0.02) + 0.06 (± 0.04)i at 420 nm. These laboratory results support the potential for a field instrument capable of determining ambient aerosol optical extinction, average aerosol extinction cross section, and complex refractive index as a function of wavelength.

Broadband measurements of aerosol extinction in the ultraviolet spectral region

NASA Astrophysics Data System (ADS)

Washenfelder, R. A.; Flores, J. M.; Brock, C. A.; Brown, S. S.; Rudich, Y.

2013-01-01

Aerosols influence the Earth's radiative budget by scattering and absorbing incoming solar radiation. The optical properties of aerosols vary as a function of wavelength, but few measurements have reported the wavelength dependence of aerosol extinction cross-sections and complex refractive indices. We describe a new laboratory instrument to measure aerosol optical extinction as a function of wavelength, using cavity enhanced spectroscopy with a broadband light source. The instrument consists of two broadband channels which span the 360-390 and 385-420 nm spectral regions using two light emitting diodes (LED) and a grating spectrometer with charge-coupled device (CCD) detector. We determined aerosol extinction cross-sections and directly observed Mie scattering resonances for aerosols that are purely scattering (polystyrene latex spheres and ammonium sulfate), slightly absorbing (Suwannee River fulvic acid), and strongly absorbing (nigrosin dye). We describe an approach for retrieving refractive indices as a function of wavelength from the measured extinction cross-sections over the 360-420 nm wavelength region. The retrieved refractive indices for PSL and ammonium sulfate agree within uncertainty with literature values for this spectral region. The refractive index determined for nigrosin is 1.78 (±0.03) + 0.19 (±0.08) i at 360 nm and 1.53 (±0.03) + 0.21 (±0.05) i at 420 nm. The refractive index determined for Suwannee River fulvic acid is 1.71 (±0.02) + 0.07 (±0.06) i at 360 nm and 1.66 (±0.02) + 0.06 (±0.04) i at 420 nm. These laboratory results support the potential for a field instrument capable of determining ambient aerosol optical extinction, average aerosol extinction cross-section, and complex refractive index as a function of wavelength.

Retrieval of the complex refractive index of aerosol droplets from optical tweezers measurements.

PubMed

Miles, Rachael E H; Walker, Jim S; Burnham, Daniel R; Reid, Jonathan P

2012-03-07

The cavity enhanced Raman scattering spectrum recorded from an aerosol droplet provides a unique fingerprint of droplet radius and refractive index, assuming that the droplet is homogeneous in composition. Aerosol optical tweezers are used in this study to capture a single droplet and a Raman fingerprint is recorded using the trapping laser as the source for the Raman excitation. We report here the retrieval of the real part of the refractive index with an uncertainty of ± 0.0012 (better than ± 0.11%), simultaneously measuring the size of the micrometre sized liquid droplet with a precision of better than 1 nm (< ± 0.05% error). In addition, the equilibrium size of the droplet is shown to depend on the laser irradiance due to optical absorption, which elevates the droplet temperature above that of the ambient gas phase. Modulation of the illuminating laser power leads to a modulation in droplet size as the temperature elevation is altered. By measuring induced size changes of <1 nm, we show that the imaginary part of the refractive index can be retrieved even when less than 10 × 10(-9) with an accuracy of better than ± 0.5 × 10(-9). The combination of these measurements allows the complex refractive index of a droplet to be retrieved with high accuracy, with the possibility of making extremely sensitive optical absorption measurements on aerosol samples and the testing of frequently used mixing rules for treating aerosol optical properties. More generally, this method provides an extremely sensitive approach for measuring refractive indices, particularly under solute supersaturation conditions that cannot be accessed by simple bulk-phase measurements.

The ipRGC-Driven Pupil Response with Light Exposure, Refractive Error, and Sleep.

PubMed

Abbott, Kaleb S; Queener, Hope M; Ostrin, Lisa A

2018-04-01

We investigated links between the intrinsically photosensitive retinal ganglion cells, light exposure, refractive error, and sleep. Results showed that morning melatonin was associated with light exposure, with modest differences in sleep quality between myopes and emmetropes. Findings suggest a complex relationship between light exposure and these physiological processes. Intrinsically photosensitive retinal ganglion cells (ipRGCs) signal environmental light, with pathways to the midbrain to control pupil size and circadian rhythm. Evidence suggests that light exposure plays a role in refractive error development. Our goal was to investigate links between light exposure, ipRGCs, refractive error, and sleep. Fifty subjects, aged 17-40, participated (19 emmetropes and 31 myopes). A subset of subjects (n = 24) wore an Actiwatch Spectrum for 1 week. The Pittsburgh Sleep Quality Index (PSQI) was administered, and saliva samples were collected for melatonin analysis. The post-illumination pupil response (PIPR) to 1 s and 5 s long- and short-wavelength stimuli was measured. Pupil metrics included the 6 s and 30 s PIPR and early and late area under the curve. Subjects spent 104.8 ± 46.6 min outdoors per day over the previous week. Morning melatonin concentration (6.9 ± 3.5 pg/ml) was significantly associated with time outdoors and objectively measured light exposure (P = .01 and .002, respectively). Pupil metrics were not significantly associated with light exposure or refractive error. PSQI scores indicated good sleep quality for emmetropes (score 4.2 ± 2.3) and poor sleep quality for myopes (5.6 ± 2.2, P = .04). We found that light exposure and time outdoors influenced morning melatonin concentration. No differences in melatonin or the ipRGC-driven pupil response were observed between refractive error groups, although myopes exhibited poor sleep quality compared to emmetropes. Findings suggest that a complex relationship between light exposure, ipRGCs, refractive error, and sleep exists.

Measuring of temperatures of phase objects using a point-diffraction interferometer plate made with the thermocavitation process

NASA Astrophysics Data System (ADS)

Aguilar, Juan C.; Berriel-Valdos, L. R.; Aguilar, J. Felix; Mejia-Romero, S.

An optical system formed by four point-diffraction interferometers is used for measuring the refractive index distribution of a phase object. The phase of the object is assumed enough smooth to be computed in terms of the Radon Transform and it is processed with a tomographic iterative algorithm. Then, the associated refractive index distribution is calculated. To recovery the phase from the inteferograms we use the Kreis method, which is useful for interferograms having only few fringes. As an application of our technique, the temperature distribution of a candle flame is retrieved, this was made with the aid of the Gladstone-Dale equation. We also describe the process of manufacturing the point-diffraction interferometer (PDI) plates. These were made by means of the thermocavitation process. The obtained three dimensional distribution of temperature is presented.

Uncorrected refractive error and presbyopia among junior high school teachers in Jakarta, Indonesia.

PubMed

Ehrlich, Joshua R; Laoh, Alex; Kourgialis, Nick; Prasetyanti, Widya; Zakiyah, Rima; Faillace, Silvana; Friedman, David S

2013-12-01

To report on the frequency of observed refractive and accommodative errors among junior high school teachers in Jakarta, Indonesia, who participated in a Helen Keller International screening, refraction and spectacle distribution program. A total of 965 teachers from 19 schools were eligible for screening; those with uncorrected distance visual acuity (VA) ≤ 6/12-3 and teachers ≥ 35 years old with uncorrected end-point print size >Jaeger (J) 6 were referred. Autorefraction and subjective refraction were performed for teachers with confirmed decreased VA. Refractive error was considered present if sphere ≤-0.75 diopters (D), sphere ≥+0.25D or cylinder ≤-0.50 D resulted in ≥ 2 lines of improvement in VA. Presbyopia was considered present if an end-point print size >J6 improved by ≥ 1 optotype with the use of a lens ≥+1.00 D. Overall, 866 teachers were screened (89.7% of those eligible) with complete screening data available for 858 (99.0%), among whom 762 failed screening. Distance refraction data were available for 666 of 762 (87.4%) and near refraction data for 520 of 686 (75.8%) teachers who failed screening. Of those screened, 76.2 ± 9.0% of teachers had refractive and/or accommodative error and 57.1 ± 7.6% had uncorrected refractive and/or accommodative error. Overall and uncorrected distance refractive error affected 44.2 ± 3.7% and 36.0 ± 3.6%, respectively; overall and uncorrected presbyopia affected 66.4 ± 8.1% and 41.0 ± 6.6%, respectively. As defined in this program, refractive and accommodative errors were common among teachers in Jakarta.

Measurement and design of refractive corrections using ultrafast laser-induced intra-tissue refractive index shaping in live cats

NASA Astrophysics Data System (ADS)

Brooks, Daniel R.; Wozniak, Kaitlin T.; Knox, Wayne; Ellis, Jonathan D.; Huxlin, Krystel R.

2018-02-01

Intra-Tissue Refractive Index Shaping (IRIS) uses a 405 nm femtosecond laser focused into the stromal region of the cornea to induce a local refractive index change through multiphoton absorption. This refractive index change can be tailored through scanning of the focal region and variations in laser power to create refractive structures, such as gradient index lenses for visual refractive correction. Previously, IRIS was used to create 2.5 mm wide, square, -1 D cylindrical refractive structures in living cats. In the present work, we first wrote 400 μm wide bars of refractive index change at varying powers in enucleated cat globes using a custom flexure-based scanning system. The cornea and surrounding sclera were then removed and mounted into a wet cell. The induced optical phase change was measured with a Mach- Zehnder Interferometer (MZI), and appeared as fringe displacement, whose magnitude was proportional to the refractive index change. The interferograms produced by the MZI were analyzed with a Fourier Transform based algorithm in order to extract the phase change. This provided a phase change versus laser power calibration, which was then used to design the scanning and laser power distribution required to create -1.5 D cylindrical Fresnel lenses in cat cornea covering an area 6 mm in diameter. This prescription was inscribed into the corneas of one eye each of two living cats, under surgical anesthesia. It was then verified in vivo by contrasting wavefront aberration measurements collected pre- IRIS with those obtained over six months post-IRIS using a Shack-Hartmann wavefront sensor.

Assessment of multifocal contact lens over-refraction using an infrared, open-field autorefractor: A preliminary study.

PubMed

Giner, Anna; Aldaba, Mikel; Arjona, Montserrat; Vilaseca, Meritxell; Pujol, Jaume

2015-10-01

To evaluate the usefulness of an infrared open-field autorefractor as a predictor of the refractive error when fitting multifocal contact lenses (MCL). Objective and subjective measurements of the non-cycloplegic distance refractive error were compared in patients wearing MCL. We used the Grand Seiko WAM-5500 autorefractor for the objective measurements. Three commercially available MCL were tested. Twenty-one eyes of sixteen healthy adults were included in the study. Over-refraction was evaluated in terms of spherical equivalent (SE) and astigmatic vectors (J0 and J45). The mean difference±SD of each parameter was calculated. The Kolmogorov-Smirnov test was used to verify the normal distribution. Pearson's correlation, Bland and Altman plot and paired sample t test were used to compare the results obtained with both methods. The mean difference between objective and subjective results of the SE over-refraction was 0.13±0.42D; for astigmatic vectors J0 and J45 were 0.03±0.32D and -0.00±0.17D, respectively. The Kolmogorov-Smirnov test showed a normal distribution for all parameters. The highest Pearson's correlation coefficients were obtained for the SE with values of 0.98 without MCL and 0.97 with MCL. The lowest were obtained for J45 with values of 0.65 without MCL and 0.75 with MCL. Significant correlations were obtained for each parameter. The paired sample t test failed to show significant differences in analyzed parameters except for J0 without MCL. The Grand Seiko WAM-5500 can be used as a screening method of over-refraction in the clinical fitting of MCL. Copyright © 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

Study on the effect of carbon nanotube coating on the refractive index sensing sensitivity of fiber modal interferometer

NASA Astrophysics Data System (ADS)

Zhang, Ya-nan; Xie, Wen-ge; Wang, Jianzhang; Wang, Pengzhao

2018-01-01

Refractive index sensing of liquid is important in the domain of chemistry and biology. Fiber optical sensors provide an excellent way to measure the refractive index due to their feasible integration to other fiber optics components, high sensitivity, small size, and distributed sensing. However, conventional optical sensors have different shortages. To find a practical way to measure the refractive index of liquid, this paper intended to combine Carbon Nanotube (CNT) with non-core fiber (NCF) to prepare a kind of modal interferometer sensor and to explore the effect of CNT coating on refractive index sensing properties of the modal interferometer. Firstly, a structure of single mode non-core single mode (SNS) fiber with a CNT film coating was proposed and simulated. The simulation results showed that the CNT coating could improve the refractive index sensitivity of the interferometer sensor. Then in the experiment part, the CNT solution was fabricated and deposited onto the NCF, and a refractive index sensing system was built to examine the property of the CNT-coated SNS interferometer sensor. During the experiment, the influence factors of sensitivity were summarized by testing the sensing performance under different conditions, and it was demonstrated that the CNT coating could improve the contrast of the interference spectrum, and also had the possibility to increase the refractive index sensitivity of the interferometer sensor.

Reference data set of volcanic ash physicochemical and optical properties

NASA Astrophysics Data System (ADS)

Vogel, A.; Diplas, S.; Durant, A. J.; Azar, A. S.; Sunding, M. F.; Rose, W. I.; Sytchkova, A.; Bonadonna, C.; Krüger, K.; Stohl, A.

2017-09-01

Uncertainty in the physicochemical and optical properties of volcanic ash particles creates errors in the detection and modeling of volcanic ash clouds and in quantification of their potential impacts. In this study, we provide a data set that describes the physicochemical and optical properties of a representative selection of volcanic ash samples from nine different volcanic eruptions covering a wide range of silica contents (50-80 wt % SiO2). We measured and calculated parameters describing the physical (size distribution, complex shape, and dense-rock equivalent mass density), chemical (bulk and surface composition), and optical (complex refractive index from ultraviolet to near-infrared wavelengths) properties of the volcanic ash and classified the samples according to their SiO2 and total alkali contents into the common igneous rock types basalt to rhyolite. We found that the mass density ranges between ρ = 2.49 and 2.98 g/cm3 for rhyolitic to basaltic ash types and that the particle shape varies with changing particle size (d < 100 μm). The complex refractive indices in the wavelength range between λ = 300 nm and 1500 nm depend systematically on the composition of the samples. The real part values vary from n = 1.38 to 1.66 depending on ash type and wavelength and the imaginary part values from k = 0.00027 to 0.00268. We place our results into the context of existing data and thus provide a comprehensive data set that can be used for future and historic eruptions, when only basic information about the magma type producing the ash is known.

Multi-parameter optimization of monolithic high-index contrast grating reflectors

NASA Astrophysics Data System (ADS)

Marciniak, Magdalena; Gebski, Marcin; Dems, Maciej; Wasiak, Michał; Czyszanowski, Tomasz

2016-03-01

Conventional High-index Contrast Gratings (HCG) consist of periodically distributed high refractive index stripes surrounded by low index media. Practically, such low/high index stack can be fabricated in several ways however low refractive index layers are electrical insulators of poor thermal conductivities. Monolithic High-index Contrast Gratings (MHCGs) overcome those limitations since they can be implemented in any material with a real refractive index larger than 1.75 without the need of the combination of low and high refractive index materials. The freedom of use of various materials allows to provide more efficient current injection and better heat flow through the mirror, in contrary to the conventional HCGs. MHCGs can simplify the construction of VCSELs, reducing their epitaxial design to monolithic wafer with carrier confinement and active region inside and etched stripes on both surfaces in post processing. We present numerical analysis of MHCGs using a three-dimensional, fully vectorial optical model. We investigate possible designs of MHCGs using multidimensional optimization of grating parameters for different refractive indices.

Statistics of the residual refraction errors in laser ranging data

NASA Technical Reports Server (NTRS)

Gardner, C. S.

1977-01-01

A theoretical model for the range error covariance was derived by assuming that the residual refraction errors are due entirely to errors in the meteorological data which are used to calculate the atmospheric correction. The properties of the covariance function are illustrated by evaluating the theoretical model for the special case of a dense network of weather stations uniformly distributed within a circle.

Gene Profiling in Experimental Models of Eye Growth: Clues to Myopia Pathogenesis

PubMed Central

Stone, Richard A.; Khurana, Tejvir S.

2010-01-01

To understand the complex regulatory pathways that underlie the development of refractive errors, expression profiling has evaluated gene expression in ocular tissues of well-characterized experimental models that alter postnatal eye growth and induce refractive errors. Derived from a variety of platforms (e.g. differential display, spotted microarrays or Affymetrix GeneChips), gene expression patterns are now being identified in species that include chicken, mouse and primate. Reconciling available results is hindered by varied experimental designs and analytical/statistical features. Continued application of these methods offers promise to provide the much-needed mechanistic framework to develop therapies to normalize refractive development in children. PMID:20363242

MONOCULAR DIPLOPIA DUE TO SPHEROCYLINDRICAL REFRACTIVE ERRORS (AN AMERICAN OPHTHALMOLOGICAL SOCIETY THESIS)

PubMed Central

Archer, Steven M.

2007-01-01

Purpose Ordinary spherocylindrical refractive errors have been recognized as a cause of monocular diplopia for over a century, yet explanation of this phenomenon using geometrical optics has remained problematic. This study tests the hypothesis that the diffraction theory treatment of refractive errors will provide a more satisfactory explanation of monocular diplopia. Methods Diffraction theory calculations were carried out for modulation transfer functions, point spread functions, and line spread functions under conditions of defocus, astigmatism, and mixed spherocylindrical refractive errors. Defocused photographs of inked and projected black lines were made to demonstrate the predicted consequences of the theoretical calculations. Results For certain amounts of defocus, line spread functions resulting from spherical defocus are predicted to have a bimodal intensity distribution that could provide the basis for diplopia with line targets. Multimodal intensity distributions are predicted in point spread functions and provide a basis for diplopia or polyopia of point targets under conditions of astigmatism. The predicted doubling effect is evident in defocused photographs of black lines, but the effect is not as robust as the subjective experience of monocular diplopia. Conclusions Monocular diplopia due to ordinary refractive errors can be predicted from diffraction theory. Higher-order aberrations—such as spherical aberration—are not necessary but may, under some circumstances, enhance the features of monocular diplopia. The physical basis for monocular diplopia is relatively subtle, and enhancement by neural processing is probably needed to account for the robustness of the percept. PMID:18427616

Adjustable internal structure for reconstructing gradient index profile of crystalline lens.

PubMed

Bahrami, Mehdi; Goncharov, Alexander V; Pierscionek, Barbara K

2014-03-01

Employing advanced technologies in studying the crystalline lens of the eye has improved our understanding of the refractive index gradient of the lens. Reconstructing and studying such a complex structure requires models with adaptable internal geometry that can be altered to simulate geometrical and optical changes of the lens with aging. In this Letter, we introduce an optically well-defined, geometrical structure for modeling the gradient refractive index profile of the crystalline lens with the advantage of an adjustable internal structure that is not available with existing models. The refractive index profile assigned to this rotationally symmetric geometry is calculated numerically, yet it is shown that this does not limit the model. The study provides a basis for developing lens models with sophisticated external and internal structures without the need for analytical solutions to calculate refractive index profiles.

Optical-CT 3D Dosimetry Using Fresnel Lenses with Minimal Refractive-Index Matching Fluid

PubMed Central

Bache, Steven; Malcolm, Javian; Adamovics, John; Oldham, Mark

2016-01-01

Telecentric optical computed tomography (optical-CT) is a state-of-the-art method for visualizing and quantifying 3-dimensional dose distributions in radiochromic dosimeters. In this work a prototype telecentric system (DFOS—Duke Fresnel Optical-CT Scanner) is evaluated which incorporates two substantial design changes: the use of Fresnel lenses (reducing lens costs from $10-30K t0 $1-3K) and the use of a ‘solid tank’ (which reduces noise, and the volume of refractively matched fluid from 1ltr to 10cc). The efficacy of DFOS was evaluated by direct comparison against commissioned scanners in our lab. Measured dose distributions from all systems were compared against the predicted dose distributions from a commissioned treatment planning system (TPS). Three treatment plans were investigated including a simple four-field box treatment, a multiple small field delivery, and a complex IMRT treatment. Dosimeters were imaged within 2h post irradiation, using consistent scanning techniques (360 projections acquired at 1 degree intervals, reconstruction at 2mm). DFOS efficacy was evaluated through inspection of dose line-profiles, and 2D and 3D dose and gamma maps. DFOS/TPS gamma pass rates with 3%/3mm dose difference/distance-to-agreement criteria ranged from 89.3% to 92.2%, compared to from 95.6% to 99.0% obtained with the commissioned system. The 3D gamma pass rate between the commissioned system and DFOS was 98.2%. The typical noise rates in DFOS reconstructions were up to 3%, compared to under 2% for the commissioned system. In conclusion, while the introduction of a solid tank proved advantageous with regards to cost and convenience, further work is required to improve the image quality and dose reconstruction accuracy of the new DFOS optical-CT system. PMID:27019460

Optical-CT 3D Dosimetry Using Fresnel Lenses with Minimal Refractive-Index Matching Fluid.

PubMed

Bache, Steven; Malcolm, Javian; Adamovics, John; Oldham, Mark

2016-01-01

Telecentric optical computed tomography (optical-CT) is a state-of-the-art method for visualizing and quantifying 3-dimensional dose distributions in radiochromic dosimeters. In this work a prototype telecentric system (DFOS-Duke Fresnel Optical-CT Scanner) is evaluated which incorporates two substantial design changes: the use of Fresnel lenses (reducing lens costs from $10-30K t0 $1-3K) and the use of a 'solid tank' (which reduces noise, and the volume of refractively matched fluid from 1 ltr to 10 cc). The efficacy of DFOS was evaluated by direct comparison against commissioned scanners in our lab. Measured dose distributions from all systems were compared against the predicted dose distributions from a commissioned treatment planning system (TPS). Three treatment plans were investigated including a simple four-field box treatment, a multiple small field delivery, and a complex IMRT treatment. Dosimeters were imaged within 2 h post irradiation, using consistent scanning techniques (360 projections acquired at 1 degree intervals, reconstruction at 2mm). DFOS efficacy was evaluated through inspection of dose line-profiles, and 2D and 3D dose and gamma maps. DFOS/TPS gamma pass rates with 3%/3mm dose difference/distance-to-agreement criteria ranged from 89.3% to 92.2%, compared to from 95.6% to 99.0% obtained with the commissioned system. The 3D gamma pass rate between the commissioned system and DFOS was 98.2%. The typical noise rates in DFOS reconstructions were up to 3%, compared to under 2% for the commissioned system. In conclusion, while the introduction of a solid tank proved advantageous with regards to cost and convenience, further work is required to improve the image quality and dose reconstruction accuracy of the new DFOS optical-CT system.

Optical properties of reduced graphene oxide and CuFe2O4 composites in the IR region

NASA Astrophysics Data System (ADS)

Ma, De-yue; Li, Xiao-xia; Guo, Yu-xiang; Zeng, Yu-run

2018-01-01

The complex refractive index of reduced graphene oxide and CuFe2O4 composites prepared by hydrothermal method was calculated using infrared Micro-reflective spectra and K-K relation, and the calculation errors were analyzed according to its IR transmission and spectral reflectivity calculated by Fresnel formula. And then normal emissivity of the composite in IR atmospheric window was calculated by means of Fresnel formula and modified refraction angle formula. The calculation accuracy was verified by comparing measured normal total emissivity with the calculated one. The results show that complex refractive index and normal emissivity calculated by the formulas have a high accuracy. It has been found that the composite has a good absorption and radiation characteristics in IR atmospheric window and a strong scattering ability in middle IR region by analyzing its extinction, absorption and radiation properties in IR region. Therefore, it may be used as IR absorption, extinction and radiation materials in some special fields.

Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blank, Beatrix; Kirchartz, Thomas; Lany, Stephan

The success of recently discovered absorber materials for photovoltaic applications has been generating increasing interest in systematic materials screening over the last years. However, the key for a successful materials screening is a suitable selection metric that goes beyond the Shockley-Queisser theory that determines the thermodynamic efficiency limit of an absorber material solely by its band-gap energy. Here, we develop a selection metric to quantify the potential photovoltaic efficiency of a material. Our approach is compatible with detailed balance and applicable in computational and experimental materials screening. We use the complex refractive index to calculate radiative and nonradiative efficiency limitsmore » and the respective optimal thickness in the high mobility limit. We also compare our model to the widely applied selection metric by Yu and Zunger [Phys. Rev. Lett. 108, 068701 (2012)] with respect to their dependence on thickness, internal luminescence quantum efficiency, and refractive index. Finally, the model is applied to complex refractive indices calculated via electronic structure theory.« less

Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis

DOE PAGES

Blank, Beatrix; Kirchartz, Thomas; Lany, Stephan; ...

2017-08-31

The success of recently discovered absorber materials for photovoltaic applications has been generating increasing interest in systematic materials screening over the last years. However, the key for a successful materials screening is a suitable selection metric that goes beyond the Shockley-Queisser theory that determines the thermodynamic efficiency limit of an absorber material solely by its band-gap energy. Here, we develop a selection metric to quantify the potential photovoltaic efficiency of a material. Our approach is compatible with detailed balance and applicable in computational and experimental materials screening. We use the complex refractive index to calculate radiative and nonradiative efficiency limitsmore » and the respective optimal thickness in the high mobility limit. We also compare our model to the widely applied selection metric by Yu and Zunger [Phys. Rev. Lett. 108, 068701 (2012)] with respect to their dependence on thickness, internal luminescence quantum efficiency, and refractive index. Finally, the model is applied to complex refractive indices calculated via electronic structure theory.« less

Spectral refractive index assessment of turbid samples by combining spatial frequency near-infrared spectroscopy with Kramers-Kronig analysis

NASA Astrophysics Data System (ADS)

Meitav, Omri; Shaul, Oren; Abookasis, David

2018-03-01

A practical algorithm for estimating the wavelength-dependent refractive index (RI) of a turbid sample in the spatial frequency domain with the aid of Kramers-Kronig (KK) relations is presented. In it, phase-shifted sinusoidal patterns (structured illumination) are serially projected at a high spatial frequency onto the sample surface (mouse scalp) at different near-infrared wavelengths while a camera mounted normally to the sample surface captures the reflected diffuse light. In the offline analysis pipeline, recorded images at each wavelength are converted to spatial absorption maps by logarithmic function, and once the absorption coefficient information is obtained, the imaginary part (k) of the complex RI (CRI), based on Maxell's equations, can be calculated. Using the data represented by k, the real part of the CRI (n) is then resolved by KK analysis. The wavelength dependence of n ( λ ) is then fitted separately using four standard dispersion models: Cornu, Cauchy, Conrady, and Sellmeier. In addition, three-dimensional surface-profile distribution of n is provided based on phase profilometry principles and a phase-unwrapping-based phase-derivative-variance algorithm. Experimental results demonstrate the capability of the proposed idea for sample's determination of a biological sample's RI value.

Comparison of Methods for Predicting the Compositional Dependence of the Density and Refractive Index of Organic-Aqueous Aerosols.

PubMed

Cai, Chen; Miles, Rachael E H; Cotterell, Michael I; Marsh, Aleksandra; Rovelli, Grazia; Rickards, Andrew M J; Zhang, Yun-Hong; Reid, Jonathan P

2016-08-25

Representing the physicochemical properties of aerosol particles of complex composition is of crucial importance for understanding and predicting aerosol thermodynamic, kinetic, and optical properties and processes and for interpreting and comparing analysis methods. Here, we consider the representations of the density and refractive index of aqueous-organic aerosol with a particular focus on the dependence of these properties on relative humidity and water content, including an examination of the properties of solution aerosol droplets existing at supersaturated solute concentrations. Using bulk phase measurements of density and refractive index for typical organic aerosol components, we provide robust approaches for the estimation of these properties for aerosol at any intermediate composition between pure water and pure solute. Approximately 70 compounds are considered, including mono-, di- and tricarboxylic acids, alcohols, diols, nitriles, sulfoxides, amides, ethers, sugars, amino acids, aminium sulfates, and polyols. We conclude that the molar refraction mixing rule should be used to predict the refractive index of the solution using a density treatment that assumes ideal mixing or, preferably, a polynomial dependence on the square root of the mass fraction of solute, depending on the solubility limit of the organic component. Although the uncertainties in the density and refractive index predictions depend on the range of subsaturated compositional data available for each compound, typical errors for estimating the solution density and refractive index are less than ±0.1% and ±0.05%, respectively. Owing to the direct connection between molar refraction and the molecular polarizability, along with the availability of group contribution models for predicting molecular polarizability for organic species, our rigorous testing of the molar refraction mixing rule provides a route to predicting refractive indices for aqueous solutions containing organic molecules of arbitrary structure.

Refractive errors in patients with newly diagnosed diabetes mellitus.

PubMed

Yarbağ, Abdülhekim; Yazar, Hayrullah; Akdoğan, Mehmet; Pekgör, Ahmet; Kaleli, Suleyman

2015-01-01

Diabetes mellitus is a complex metabolic disorder that involves the small blood vessels, often causing widespread damage to tissues, including the eyes' optic refractive error. In patients with newly diagnosed diabetes mellitus who have unstable blood glucose levels, refraction may be incorrect. We aimed to investigate refraction in patients who were recently diagnosed with diabetes and treated at our centre. This prospective study was performed from February 2013 to January 2014. Patients were diagnosed with diabetes mellitus using laboratory biochemical tests and clinical examination. Venous fasting plasma glucose (fpg) levels were measured along with refractive errors. Two measurements were taken: initially and after four weeks. The last difference between the initial and end refractive measurements were evaluated. Our patients were 100 males and 30 females who had been newly diagnosed with type II DM. The refractive and fpg levels were measured twice in all patients. The average values of the initial measurements were as follows: fpg level, 415 mg/dl; average refractive value, +2.5 D (Dioptres). The average end of period measurements were fpg, 203 mg/dl; average refractive value, +0.75 D. There is a statistically significant difference between after four weeks measurements with initially measurements of fasting plasma glucose (fpg) levels (p<0.05) and there is a statistically significant relationship between changes in fpg changes with glasses ID (p<0.05) and the disappearance of blurred vision (to be greater than 50% success rate) were statistically significant (p<0.05). Also, were detected upon all these results the absence of any age and sex effects (p>0.05). Refractive error is affected in patients with newly diagnosed diabetes mellitus; therefore, plasma glucose levels should be considered in the selection of glasses.

Dependence of atmospheric refractive index structure parameter (Cn2) on the residence time and vertical distribution of aerosols.

PubMed

Anand, N; Satheesh, S K; Krishna Moorthy, K

2017-07-15

Effects of absorbing atmospheric aerosols in modulating the tropospheric refractive index structure parameter (Cn2) are estimated using high resolution radiosonde and multi-satellite data along with a radiative transfer model. We report the influence of variations in residence time and vertical distribution of aerosols in modulating Cn2 and why the aerosol induced atmospheric heating needs to be considered while estimating a free space optical communication link budget. The results show that performance of the link is seriously affected if large concentrations of absorbing aerosols reside for a long time in the atmospheric path.

Liquid core photonic crystal fiber with low-refractive-index liquids for optofluidic applications.

PubMed

Park, Jiyoung; Kang, Doo-Eui; Paulson, Bjorn; Nazari, Tavakol; Oh, Kyunghwan

2014-07-14

A defectless hexagonal air-silica photonic crystal fiber (PCF) structure with its central hole selectively filled by a low-refractive-index liquid is numerically analyzed. Despite the fact that the refractive index of the liquid is significantly lower than that of silica, we found an optimal range of waveguide parameters to ensure light guidance through the liquid core in the fundamental mode, maximizing the light-liquid interaction over a desired wavelength range. Using the vectorial finite element method (FEM), we report detailed parametric studies in terms of the effective index, chromatic dispersion, optical loss, and modal intensity distribution of the liquid core PCFs.

Design and characteristic analysis of shaping optics for optical trepanning

NASA Astrophysics Data System (ADS)

Zeng, D.; Latham, W. P.; Kar, A.

2005-08-01

Optical trepanning is a new laser drilling method using an annular beam. The annular beams allow numerous irradiance profiles to supply laser energy to the workpiece and thus provide more flexibility in affecting the hole quality than a traditional circular laser beam. The refractive axicon system has been designed to generating a collimated annular beam. In this article, calculations of intensity distributions produced by this refractive system are made by evaluating the Kirchhoff-Fresnel diffraction. It is shown that the refractive system is able to transform a Gaussian beam into a full Gaussian annular beam. The base angle of the axicon lens, input laser beam diameter and intensity profiles are found to be important factors for the axcion refractive system. Their effects on the annular beam profiles are analyzed based on the numerical solutions of the diffraction patterns.

Low-loss curved subwavelength grating waveguide based on index engineering

NASA Astrophysics Data System (ADS)

Wang, Zheng; Xu, Xiaochuan; Fan, D. L.; Wang, Yaoguo; Chen, Ray T.

2016-03-01

Subwavelength grating (SWG) waveguide is an intriguing alternative to conventional optical waveguides due to its freedom to tune a few important waveguide properties such as dispersion and refractive index. Devices based on SWG waveguide have demonstrated impressive performances compared to those of conventional waveguides. However, the large loss of SWG waveguide bends jeopardizes their applications in integrated photonics circuits. In this work, we propose that a predistorted refractive index distribution in SWG waveguide bends can effectively decrease the mode mismatch noise and radiation loss simultaneously, and thus significantly reduce the bend loss. Here, we achieved the pre-distortion refractive index distribution by using trapezoidal silicon pillars. This geometry tuning approach is numerically optimized and experimentally demonstrated. The average insertion loss of a 5 μm SWG waveguide bend can be reduced drastically from 5.58 dB to 1.37 dB per 90° bend for quasi-TE polarization. In the future, the proposed approach can be readily adopted to enhance performance of an array of SWG waveguide-based photonics devices.

Laser beam propagation in atmospheric turbulence

NASA Technical Reports Server (NTRS)

Murty, S. S. R.

1979-01-01

The optical effects of atmospheric turbulence on the propagation of low power laser beams are reviewed in this paper. The optical effects are produced by the temperature fluctuations which result in fluctuations of the refractive index of air. The commonly-used models of index-of-refraction fluctuations are presented. Laser beams experience fluctuations of beam size, beam position, and intensity distribution within the beam due to refractive turbulence. Some of the observed effects are qualitatively explained by treating the turbulent atmosphere as a collection of moving gaseous lenses of various sizes. Analytical results and experimental verifications of the variance, covariance and probability distribution of intensity fluctuations in weak turbulence are presented. For stronger turbulence, a saturation of the optical scintillations is observed. The saturation of scintillations involves a progressive break-up of the beam into multiple patches; the beam loses some of its lateral coherence. Heterodyne systems operating in a turbulent atmosphere experience a loss of heterodyne signal due to the destruction of coherence.

Refractometry of melanocyte cell nuclei using optical scatter images recorded by digital Fourier microscopy.

PubMed

Seet, Katrina Y T; Nieminen, Timo A; Zvyagin, Andrei V

2009-01-01

The cell nucleus is the dominant optical scatterer in the cell. Neoplastic cells are characterized by cell nucleus polymorphism and polychromism-i.e., the nuclei exhibits an increase in the distribution of both size and refractive index. The relative size parameter, and its distribution, is proportional to the product of the nucleus size and its relative refractive index and is a useful discriminant between normal and abnormal (cancerous) cells. We demonstrate a recently introduced holographic technique, digital Fourier microscopy (DFM), to provide a sensitive measure of this relative size parameter. Fourier holograms were recorded and optical scatter of individual scatterers were extracted and modeled with Mie theory to determine the relative size parameter. The relative size parameter of individual melanocyte cell nuclei were found to be 16.5+/-0.2, which gives a cell nucleus refractive index of 1.38+/-0.01 and is in good agreement with previously reported data. The relative size parameters of individual malignant melanocyte cell nuclei are expected to be greater than 16.5.

Very Oblique Whistler Mode Propagation in the Radiation Belts: Effects of Hot Plasma and Landau Damping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Q.; Artemyev, A. V.; Mourenas, D.

We present that satellite observations of a significant population of very oblique chorus waves in the outer radiation belt have fueled considerable interest in the effects of these waves on energetic electron scattering and acceleration. However, corresponding diffusion rates are extremely sensitive to the refractive index N, controlled by hot plasma effects including Landau damping and wave dispersion modifications by suprathermal (15–100 eV) electrons. A combined investigation of wave and electron distribution characteristics obtained from the Van Allen Probes shows that peculiarities of the measured electron distribution significantly reduce Landau damping, allowing wave propagation with high N ~ 100–200. Furthermore » comparing measured refractive indexes with theoretical estimates incorporating hot plasma corrections to the wave dispersion, we provide the first experimental demonstration that suprathermal electrons indeed control the upper limit of the refractive index of highly oblique whistler mode waves. In conclusion, such results further support the importance of incorporating very oblique waves into radiation belt models.« less

Tomographic active optical trapping of arbitrarily shaped objects by exploiting 3D refractive index maps

NASA Astrophysics Data System (ADS)

Kim, Kyoohyun; Park, Yongkeun

2017-05-01

Optical trapping can manipulate the three-dimensional (3D) motion of spherical particles based on the simple prediction of optical forces and the responding motion of samples. However, controlling the 3D behaviour of non-spherical particles with arbitrary orientations is extremely challenging, due to experimental difficulties and extensive computations. Here, we achieve the real-time optical control of arbitrarily shaped particles by combining the wavefront shaping of a trapping beam and measurements of the 3D refractive index distribution of samples. Engineering the 3D light field distribution of a trapping beam based on the measured 3D refractive index map of samples generates a light mould, which can manipulate colloidal and biological samples with arbitrary orientations and/or shapes. The present method provides stable control of the orientation and assembly of arbitrarily shaped particles without knowing a priori information about the sample geometry. The proposed method can be directly applied in biophotonics and soft matter physics.

Very Oblique Whistler Mode Propagation in the Radiation Belts: Effects of Hot Plasma and Landau Damping

DOE PAGES

Ma, Q.; Artemyev, A. V.; Mourenas, D.; ...

2017-11-30

We present that satellite observations of a significant population of very oblique chorus waves in the outer radiation belt have fueled considerable interest in the effects of these waves on energetic electron scattering and acceleration. However, corresponding diffusion rates are extremely sensitive to the refractive index N, controlled by hot plasma effects including Landau damping and wave dispersion modifications by suprathermal (15–100 eV) electrons. A combined investigation of wave and electron distribution characteristics obtained from the Van Allen Probes shows that peculiarities of the measured electron distribution significantly reduce Landau damping, allowing wave propagation with high N ~ 100–200. Furthermore » comparing measured refractive indexes with theoretical estimates incorporating hot plasma corrections to the wave dispersion, we provide the first experimental demonstration that suprathermal electrons indeed control the upper limit of the refractive index of highly oblique whistler mode waves. In conclusion, such results further support the importance of incorporating very oblique waves into radiation belt models.« less

Heritability of lenticular myopia in English Springer spaniels.

PubMed

Kubai, Melissa A; Labelle, Amber L; Hamor, Ralph E; Mutti, Donald O; Famula, Thomas R; Murphy, Christopher J

2013-11-08

We determined whether naturally-occurring lenticular myopia in English Springer spaniels (ESS) has a genetic component. Streak retinoscopy was performed on 226 related ESS 30 minutes after the onset of pharmacologic mydriasis and cycloplegia. A pedigree was constructed to determine relationships between affected offspring and parents. Estimation of heritability was done in a Bayesian analysis (facilitated by the MCMCglmm package of R) of refractive error in a model, including terms for sex and coat color. Myopia was defined as ≤-0.5 diopters (D) spherical equivalent. The median refractive error for ESS was 0.25 D (range, -3.5 to +4.5 D). Median age was 0.2 years (range, 0.1-15 years). The prevalence of myopia in related ESS was 19% (42/226). The ESS had a strong correlation (r = 0.95) for refractive error between the two eyes. Moderate heritability was present for refractive error with a mean value of 0.29 (95% highest probability density, 0.07-0.50). The distribution of refractive error, and subsequently lenticular myopia, has a moderate genetic component in ESS. Further investigation of genes responsible for regulation of the development of refractive ocular components in canines is warranted.

Quantitative reconstruction of refractive index distribution and imaging of glucose concentration by using diffusing light.

PubMed

Liang, Xiaoping; Zhang, Qizhi; Jiang, Huabei

2006-11-10

We show that a two-step reconstruction method can be adapted to improve the quantitative accuracy of the refractive index reconstruction in phase-contrast diffuse optical tomography (PCDOT). We also describe the possibility of imaging tissue glucose concentration with PCDOT. In this two-step method, we first use our existing finite-element reconstruction algorithm to recover the position and shape of a target. We then use the position and size of the target as a priori information to reconstruct a single value of the refractive index within the target and background regions using a region reconstruction method. Due to the extremely low contrast available in the refractive index reconstruction, we incorporate a data normalization scheme into the two-step reconstruction to combat the associated low signal-to-noise ratio. Through a series of phantom experiments we find that this two-step reconstruction method can considerably improve the quantitative accuracy of the refractive index reconstruction. The results show that the relative error of the reconstructed refractive index is reduced from 20% to within 1.5%. We also demonstrate the possibility of PCDOT for recovering glucose concentration using these phantom experiments.

Using Seismic Refraction and Ground Penetrating Radar (GPR) to Characterize the Valley Fill in Beaver Meadows, Rocky Mountain National Park

NASA Astrophysics Data System (ADS)

Kramer, N.; Harry, D. L.; Wohl, E. E.

2010-12-01

This study is one of the first to use near surface geophysical techniques to characterize the subsurface stratigraphy in a high alpine, low gradient valley with a past glacial history and to obtain a preliminary grasp on the impact of Holocene beaver activity. Approximately 1 km of seismic refraction data and 5 km of GPR data were collected in Beaver Meadows, Rocky Mountain National Park. An asymmetric wedge of sediment ranging in depth from 0-20 m transverse to the valley profile was identified using seismic refraction. Complementary analysis of the GPR data suggests that the valley fill can be subdivided into till deposited during the Pleistocene glaciations and alluvium deposited during the Holocene. Two main facies were identified in the GPR profiles through pattern recognition. Facie Fd, which consists of chaotic discontinuous reflectors with an abundance of diffractions, is interpreted to be glacial till. Facie Fc, which is a combination of packages of complex slightly continuous reflectors interfingered with continuous horizontal to subhorizontal reflectors, is interpreted to be post-glacial alluvium and includes overbank, pond and in-channel deposits. Fc consistently overlies Fd throughout the study area and is no more than 7 m thick in the middle of the valley. The thickness of Holocene sedimentation (<7 m) is much less than the total amount of valley fill identified in the seismic refraction survey (0-20 m). A subfacie of Fc, Fch, which has reflectors with long periods was identified within Fc and is interpreted to be ponded sediments. The spatial distribution of facie Fch, along with: slight topographical features resembling buried beaver dams, a high abundance of fine sediment including silts and clays, historical records of beavers, and the name "Beaver Meadows" all suggest that Holocene beaver activity played a large role in sediment accumulation at this site, despite the lack of surficial relict beaver dams containing wood.

Matrix method for two-dimensional waveguide mode solution

NASA Astrophysics Data System (ADS)

Sun, Baoguang; Cai, Congzhong; Venkatesh, Balajee Seshasayee

2018-05-01

In this paper, we show that the transfer matrix theory of multilayer optics can be used to solve the modes of any two-dimensional (2D) waveguide for their effective indices and field distributions. A 2D waveguide, even composed of numerous layers, is essentially a multilayer stack and the transmission through the stack can be analysed using the transfer matrix theory. The result is a transfer matrix with four complex value elements, namely A, B, C and D. The effective index of a guided mode satisfies two conditions: (1) evanescent waves exist simultaneously in the first (cladding) layer and last (substrate) layer, and (2) the complex element D vanishes. For a given mode, the field distribution in the waveguide is the result of a 'folded' plane wave. In each layer, there is only propagation and absorption; at each boundary, only reflection and refraction occur, which can be calculated according to the Fresnel equations. As examples, we show that this method can be used to solve modes supported by the multilayer step-index dielectric waveguide, slot waveguide, gradient-index waveguide and various plasmonic waveguides. The results indicate the transfer matrix method is effective for 2D waveguide mode solution in general.

Deciphering the internal complexity of living cells with quantitative phase microscopy: a multiscale approach

NASA Astrophysics Data System (ADS)

Martinez-Torres, Cristina; Laperrousaz, Bastien; Berguiga, Lotfi; Boyer-Provera, Elise; Elezgaray, Juan; Nicolini, Franck E.; Maguer-Satta, Veronique; Arneodo, Alain; Argoul, Françoise

2015-09-01

The distribution of refractive indices (RIs) of a living cell contributes in a nonintuitive manner to its optical phase image and quite rarely can be inverted to recover its internal structure. The interpretation of the quantitative phase images of living cells remains a difficult task because (1) we still have very little knowledge on the impact of its internal macromolecular complexes on the local RI and (2) phase changes produced by light propagation through the sample are mixed with diffraction effects by the internal cell bodies. We propose to implement a two-dimensional wavelet-based contour chain detection method to distinguish internal boundaries based on their greatest optical path difference gradients. These contour chains correspond to the highest image phase contrast and follow the local RI inhomogeneities linked to the intracellular structural intricacy. Their statistics and spatial distribution are the morphological indicators suited for comparing cells of different origins and/or to follow their transformation in pathologic situations. We use this method to compare nonadherent blood cells from primary and laboratory culture origins and to assess the internal transformation of hematopoietic stem cells by the transduction of the BCR-ABL oncogene responsible for the chronic myelogenous leukemia.

Contribution of the gradient refractive index and shape to the crystalline lens spherical aberration and astigmatism.

PubMed

Birkenfeld, Judith; de Castro, Alberto; Ortiz, Sergio; Pascual, Daniel; Marcos, Susana

2013-06-28

The optical properties of the crystalline lens are determined by its shape and refractive index distribution. However, to date, those properties have not been measured together in the same lens, and therefore their relative contributions to optical aberrations are not fully understood. The shape, the optical path difference, and the focal length of ten porcine lenses (age around 6 months) were measured in vitro using Optical Coherence Tomography and laser ray tracing. The 3D Gradient Refractive Index distribution (GRIN) was reconstructed by means of an optimization method based on genetic algorithms. The optimization method searched for the parameters of a 4-variable GRIN model that best fits the distorted posterior surface of the lens in 18 different meridians. Spherical aberration and astigmatism of the lenses were estimated using computational ray tracing, with the reconstructed GRIN lens and an equivalent homogeneous refractive index. For all lenses the posterior radius of curvature was systematically steeper than the anterior one, and the conic constant of both the anterior and posterior positive surfaces was positive. In average, the measured focal length increased with increasing pupil diameter, consistent with a crystalline lens negative spherical aberration. The refractive index of nucleus and surface was reconstructed to an average value of 1.427 and 1.364, respectively, for 633 nm. The results of the GRIN reconstruction showed a wide distribution of the index in all lens samples. The GRIN shifted spherical aberration towards negative values when compared to a homogeneous index. A negative spherical aberration with GRIN was found in 8 of the 10 lenses. The presence of GRIN also produced a decrease in the total amount of lens astigmatism in most lenses, while the axis of astigmatism was only little influenced by the presence of GRIN. To our knowledge, this study is the first systematic experimental study of the relative contribution of geometry and GRIN to the aberrations in a mammal lens. Copyright © 2013 Elsevier Ltd. All rights reserved.

Beam shaping in high-power laser systems with using refractive beam shapers

NASA Astrophysics Data System (ADS)

Laskin, Alexander; Laskin, Vadim

2012-06-01

Beam Shaping of the spatial (transverse) profile of laser beams is highly desirable by building optical systems of high-power lasers as well in various applications with these lasers. Pumping of the crystals of Ti:Sapphire lasers by the laser radiation with uniform (flattop) intensity profile improves performance of these ultrashort pulse high-power lasers in terms of achievable efficiency, peak-power and stability, output beam profile. Specifications of the solid-state lasers built according to MOPA configuration can be also improved when radiation of the master oscillator is homogenized and then is amplified by the power amplifier. Features of building these high power lasers require that a beam shaping solution should be capable to work with single mode and multimode beams, provide flattop and super-Gauss intensity distributions, the consistency and divergence of a beam after the intensity re-distribution should be conserved and low absorption provided. These specific conditions are perfectly fulfilled by the refractive field mapping beam shapers due to their unique features: almost lossless intensity profile transformation, low output divergence, high transmittance and flatness of output beam profile, extended depth of field, adaptability to real intensity profiles of TEM00 and multimode laser sources. Combining of the refractive field mapping beam shapers with other optical components, like beam-expanders, relay imaging lenses, anamorphic optics makes it possible to generate the laser spots of necessary shape, size and intensity distribution. There are plenty of applications of high-power lasers where beam shaping bring benefits: irradiating photocathode of Free Electron Lasers (FEL), material ablation, micromachining, annealing in display making techniques, cladding, heat treating and others. This paper will describe some design basics of refractive beam shapers of the field mapping type, with emphasis on the features important for building and applications of high-power laser sources. There will be presented results of applying the refractive beam shapers in real installations.

Inversion for Refractivity Parameters Using a Dynamic Adaptive Cuckoo Search with Crossover Operator Algorithm

PubMed Central

Zhang, Zhihua; Sheng, Zheng; Shi, Hanqing; Fan, Zhiqiang

2016-01-01

Using the RFC technique to estimate refractivity parameters is a complex nonlinear optimization problem. In this paper, an improved cuckoo search (CS) algorithm is proposed to deal with this problem. To enhance the performance of the CS algorithm, a parameter dynamic adaptive operation and crossover operation were integrated into the standard CS (DACS-CO). Rechenberg's 1/5 criteria combined with learning factor were used to control the parameter dynamic adaptive adjusting process. The crossover operation of genetic algorithm was utilized to guarantee the population diversity. The new hybrid algorithm has better local search ability and contributes to superior performance. To verify the ability of the DACS-CO algorithm to estimate atmospheric refractivity parameters, the simulation data and real radar clutter data are both implemented. The numerical experiments demonstrate that the DACS-CO algorithm can provide an effective method for near-real-time estimation of the atmospheric refractivity profile from radar clutter. PMID:27212938

Peres experiment using photons: No test for hypercomplex (quaternionic) quantum theories

NASA Astrophysics Data System (ADS)

Adler, Stephen L.

2017-06-01

Assuming the standard axioms for quaternionic quantum theory and a spatially localized scattering interaction, the S matrix in quaternionic quantum theory is complex valued, not quaternionic. Using the standard connections between the S matrix, the forward scattering amplitude for electromagnetic wave scattering, and the index of refraction, we show that the index of refraction is necessarily complex, not quaternionic. This implies that the recent optical experiment of Procopio et al. [Nat. Commun. 8, 15044 (2017), 10.1038/ncomms15044] based on the Peres proposal does not test for hypercomplex or quaternionic quantum effects arising within the standard Hilbert space framework. Such a test requires looking at near zone fields, not radiation zone fields.

Measurement of infrared refractive indices of organic and organophosphorous compounds for optical modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tonkyn, Russell G.; Danby, Tyler O.; Birnbaum, Jerome C.

The complex optical refractive index contains the optical constants, n(more » $$\\tilde{u}$$)and k($$\\tilde{u}$$), which correspond to the dispersion and absorption of light within a medium, respectively. By obtaining the optical constants one can in principle model most optical phenomena in media and at interfaces including reflection, refraction and dispersion. We have developed improved protocols based on the use of multiple path lengths to determine the optical constants for dozens of liquids, including organic and organophosphorous compounds. Detailed description of the protocols to determine the infrared indices will be presented, along with preliminary results using the constants with their applications to optical modeling.« less

Thermophysical properties of N, N-dimethylacetamide mixtures with n-butanol

NASA Astrophysics Data System (ADS)

Maharolkar, Aruna P.; Murugkar, A. G.; Khirade, P. W.; Mehrotra, S. C.

2017-09-01

The refraction, dielectric, viscosity, density, data of the binary mixtures of N, N-dimethylacetamide (DMA) with n-butanol at 308.15 and 313.15 K. The measured parameters used to obtain derived properties like Bruggeman factor, molar refraction and excess static dielectric constant, excess inverse relaxation time, excess molar volume and excess viscosity, excess molar refraction. The variation in magnitude with composition and temperature of these quantities has been used to discuss the type, strength and nature of binary interactions. Results confirm that there are strong hydrogen-bond interactions between unlike molecules of DMA+ n-butanol mixtures and that 1: 1 complexes are formed and strength of intermolecular interaction increases with temperature.

Correlation of field seismic refraction data with 3-D laboratory ultrasonic sounding data during exploration of a dimension stone deposit

NASA Astrophysics Data System (ADS)

Přikryl, Richard; Vilhelm, Jan; Lokajíček, Tomáš; Pros, Zdeněk; Klíma, Karel

2004-05-01

Multidirectional field seismic refraction data have been combined with 3-D laboratory ultrasonic sounding data in a preliminary exploration of a new dimension stone deposit in the Czech Republic. Rock fabric was interpreted from a detailed laboratory analysis of a 3-D P-wave velocity pattern and can be classified as pronounced orthorhombic due to a complex tectonometamorphic history of the rock. The P-wave velocity pattern recorded from laboratory measurements can be satisfactorily correlated with the anisotropy of P-wave velocity data acquired from field seismic refraction data. Rock fabric anisotropy also contributes to the observed anisotropy of strength and static deformational properties.

A seismic refraction technique used for subsurface investigations at Meteor Crater, Arizona

NASA Technical Reports Server (NTRS)

Ackermann, H. D.; Godson, R. H.; Watkins, J. S.

1975-01-01

A seismic refraction technique for interpreting the subsurface shape and velocity distribution of an anomalous surface feature such as an impact crater is described. The method requires the existence of a relatively deep refracting horizon and combines data obtained from both standard shallow refraction spreads and distant offset shots by using the deep refractor as a source of initial arrivals. Results obtained from applying the technique to Meteor crater generally agree with the known structure of the crater deduced by other investigators and provide new data on an extensive fractured zone surrounding the crater. The breccia lens is computed to extend roughly 190 m below the crater floor, about 30 m less than the value deduced from early drilling data. Rocks around the crater are fractured as distant as 900 m from the rim crest and to a depth of at least 800 m beneath the crater floor.

Recovery of atmospheric refractivity profiles from simulated satellite-to-satellite tracking data

NASA Technical Reports Server (NTRS)

Murray, C. W., Jr.; Rangaswamy, S.

1975-01-01

Techniques for recovering atmospheric refractivity profiles from simulated satellite-to-satellite tracking data are documented. Examples are given using the geometric configuration of the ATS-6/NIMBUS-6 Tracking Experiment. The underlying refractivity model for the lower atmosphere has the spherically symmetric form N = exp P(s) where P(s) is a polynomial in the normalized height s. For the simulation used, the Herglotz-Wiechert technique recovered values which were 0.4% and 40% different from the input values at the surface and at a height of 33 kilometers, respectively. Using the same input data, the model fitting technique recovered refractivity values 0.05% and 1% different from the input values at the surface and at a height of 50 kilometers, respectively. It is also shown that if ionospheric and water vapor effects can be properly modelled or effectively removed from the data, pressure and temperature distributions can be obtained.

Simulation of imperfections in plastic lenses - transferring local refractive index changes into surface shape modifications

NASA Astrophysics Data System (ADS)

Arasa, Josep; Pizarro, Carles; Blanco, Patricia

2016-06-01

Injection molded plastic lenses have continuously improved their performance regarding optical quality and nowadays are as usual as glass lenses in image forming devices. However, during the manufacturing process unavoidable fluctuations in material density occur, resulting in local changes in the distribution of refractive index, which degrade the imaging properties of the polymer lens. Such material density fluctuations correlate to phase delays, which opens a path for their mapping. However, it is difficult to transfer the measured variations in refractive index into conventional optical simulation tool. Thus, we propose a method to convert the local variations in refractive index into local changes of one surface of the lens, which can then be described as a free-form surface, easy to introduce in conventional simulation tools. The proposed method was tested on a commercial gradient index (GRIN) lens for a set of six different object positions, using the MTF sagittal and tangential cuts to compare the differences between the real lens and a lens with homogenous refractive index, and the last surface converted into a free-form shape containing the internal refractive index changes. The same procedure was used to reproduce the local refractive index changes of an injected plastic lens with local index changes measured using an in-house built polariscopic arrangement, showing the capability of the method to provide successful results.

Refractive Index Effects on Radiation in an Absorbing, Emitting, and Scattering Laminated Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting temperature radiative energy flow in a two-region semitransparent laminated layer in the limit of zero heat conduction. The composite is heated on its two sides by unequal amounts of incident radiation. The two layers of the composite have different refractive indices, and each material absorbs, emits, and isotropically scatters radiation. The interfaces are diffuse, and all interface reflections are included. To illustrate the thermal behavior that is readily calculated from the equations, typical results an given for various optical thicknesses and refractive indices of the layers. Internal reflections have a substantial effect on the temperature distribution and radiative heat flow.

Process equipped with a sloped UV lamp for the fabrication of gradient-refractive-index lenses.

PubMed

Liu, Jui-Hsiang; Chiu, Yi-Hong

2009-05-01

In this investigation, a method for the preparation of gradient-refractive-index (GRIN) lenses by UV-energy-controlled polymerization has been developed. A glass reaction tube equipped with a sloped UV lamp was designed. Methyl methacrylate and diphenyl sulfide were used as the reactive monomer and nonreactive dopant, respectively. Ciba IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone) was used as the initiator. The effects of initiator concentration, the addition of acrylic polymers, and the preparation conditions on the optical characteristics of the GRIN lenses produced by this method were also investigated. Refractive index distributions and image transmission properties were estimated for all GRIN lenses prepared.

Dynamical measurement of refractive index distribution using digital holographic interferometry based on total internal reflection.

PubMed

Zhang, Jiwei; Di, Jianglei; Li, Ying; Xi, Teli; Zhao, Jianlin

2015-10-19

We present a method for dynamically measuring the refractive index distribution in a large range based on the combination of digital holographic interferometry and total internal reflection. A series of holograms, carrying the index information of mixed liquids adhered on a total reflection prism surface, are recorded with CCD during the diffusion process. Phase shift differences of the reflected light are reconstructed exploiting the principle of double-exposure holographic interferometry. According to the relationship between the reflection phase shift difference and the liquid index, two dimensional index distributions can be directly figured out, assuming that the index of air near the prism surface is constant. The proposed method can also be applied to measure the index of solid media and monitor the index variation during some chemical reaction processes.

MIE Theory Sensitivity Studies. The Effects of Aerosol Complex Refractive Index and Size Distribution Variations on Extinction and Absorption Coefficients. Part 1. Tabulated Computational Results

DTIC Science & Technology

1977-11-01

0- - - 5 43- 65 -08-0- o3630S-01 .20,428-03 .69q .200 -. 010 .36506-01 .36129-01 .37754-03 󈨉q .200 -. 025 .36608-01 .35687-01 o81707-03 6494 .200...3177Tý𔃺 t- - .-- 5 -0 1.060 1.600 -6.000 .46412-rl .41401-01 .50114=02 -- •T.73i -. 01 1• 65 !9--- .3 l-Ot-- 7 377-02 1-060 1.700 -. 003 .46537-C1 .44156-01...IAD Reports Control Symbol S OSD- 1366 1. RESEARCH AND DEVELOPMENT TECHNICAL REPORT S•ECOM-DR-77- 5 MIE THEORY SENSITIVITY STUDIES - Si THE EFFECTS OF

[Trends of refractive correction in the Japanese Ground Self-Defense Forces: examination after the Great East Japan earthquake].

PubMed

Harimoto, Kouzo; Kato, Naoko; Shoji, Takuhei; Goto, Hiroya; Tokuno, Shinichi; Fujii, Manabu; Takeuchi, Masaru

2014-02-01

To investigate the trends in refractive correction in Japanese Ground Self-Defense Forces' (JGSDF) soldiers. A questionnaire was distributed to 519 soldiers of the Camp Funaoka in the northeastern region. Five hundred and sixteen subjects (99.4%) responded. In total, 246 soldiers (47.7%) wore spectacles or contact lenses. Among the contact lens wearers, 52 had experienced problems previously and 35 reported problems that occurred during military exercises. With regard to military exercises, 66.9% and 63.5% of the spectacle or disposable soft contact lens-users reported inconvenience. Among contact lens users, 33.1% reported that they changed to new sterilized contact lenses only occasionally and 61.9% did not change their contact lenses at all during exercises. During disaster-relief work, subjects worried 'very' (21.5%) or 'somewhat' (46.9%) about problems associated with their spectacles or contact lenses. Twenty-four had undergone refractive surgery (4.9%). About one-half of the JGSDF soldiers surveyed required refractive correction. Attention to convenient and safe refractive correction in the military is warranted.

Refractive index profilometry using the total internally reflected light field.

PubMed

Das, Tania; Bhattacharya, K

2017-11-20

A full-field polarization-based technique is presented for quantitative evaluation of the spatial distribution of the refractive index in macro and micro samples. The sample is mounted on a glass-air interface of a prism, illuminated by a linearly polarized collimated light beam, and two intensity frames are digitally recorded with specific orientations of an analyzer. The pair of intensity data frames captured with this simple setup is combined through an algorithm specially developed for the purpose, to yield the phase difference between the transverse electric and transverse magnetic components of the total internally reflected light field. The phase difference is then related to the refractive index of the sample. Experimental results for refractive index variations in a laser-etched glass plate and red blood corpuscles are presented. One of the salient features of the proposed technique is that the depth of measurement is dependent on the penetration depth of the sample's evanescent field, which is typically of the order of a few hundred nanometers, thereby facilitating refractive index measurements along a thin section of the sample.

Observation of cooperative Mie scattering from an ultracold atomic cloud

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bender, H.; Stehle, C.; Slama, S.

Scattering of light at a distribution of scatterers is an intrinsically cooperative process, which means that the scattering rate and the angular distribution of the scattered light are essentially governed by bulk properties of the distribution, such as its size, shape, and density, although local disorder and density fluctuations may have an important impact on the cooperativity. Via measurements of the radiation pressure force exerted by a far-detuned laser beam on a very small and dense cloud of ultracold atoms, we are able to identify the respective roles of superradiant acceleration of the scattering rate and of Mie scattering inmore » the cooperative process. They lead, respectively, to a suppression or an enhancement of the radiation pressure force. We observe a maximum in the radiation pressure force as a function of the phase shift induced in the incident laser beam by the cloud's refractive index. The maximum marks the borderline of the validity of the Rayleigh-Debye-Gans approximation from a regime, where Mie scattering is more complex. Our observations thus help to clarify the intricate relationship between Rayleigh scattering of light at a coarse-grained ensemble of individual scatterers and Mie scattering at the bulk density distribution.« less

The inverse problem of refraction travel times, part II: Quantifying refraction nonuniqueness using a three-layer model

USGS Publications Warehouse

Ivanov, J.; Miller, R.D.; Xia, J.; Steeples, D.

2005-01-01

This paper is the second of a set of two papers in which we study the inverse refraction problem. The first paper, "Types of Geophysical Nonuniqueness through Minimization," studies and classifies the types of nonuniqueness that exist when solving inverse problems depending on the participation of a priori information required to obtain reliable solutions of inverse geophysical problems. In view of the classification developed, in this paper we study the type of nonuniqueness associated with the inverse refraction problem. An approach for obtaining a realistic solution to the inverse refraction problem is offered in a third paper that is in preparation. The nonuniqueness of the inverse refraction problem is examined by using a simple three-layer model. Like many other inverse geophysical problems, the inverse refraction problem does not have a unique solution. Conventionally, nonuniqueness is considered to be a result of insufficient data and/or error in the data, for any fixed number of model parameters. This study illustrates that even for overdetermined and error free data, nonlinear inverse refraction problems exhibit exact-data nonuniqueness, which further complicates the problem of nonuniqueness. By evaluating the nonuniqueness of the inverse refraction problem, this paper targets the improvement of refraction inversion algorithms, and as a result, the achievement of more realistic solutions. The nonuniqueness of the inverse refraction problem is examined initially by using a simple three-layer model. The observations and conclusions of the three-layer model nonuniqueness study are used to evaluate the nonuniqueness of more complicated n-layer models and multi-parameter cell models such as in refraction tomography. For any fixed number of model parameters, the inverse refraction problem exhibits continuous ranges of exact-data nonuniqueness. Such an unfavorable type of nonuniqueness can be uniquely solved only by providing abundant a priori information. Insufficient a priori information during the inversion is the reason why refraction methods often may not produce desired results or even fail. This work also demonstrates that the application of the smoothing constraints, typical when solving ill-posed inverse problems, has a dual and contradictory role when applied to the ill-posed inverse problem of refraction travel times. This observation indicates that smoothing constraints may play such a two-fold role when applied to other inverse problems. Other factors that contribute to inverse-refraction-problem nonuniqueness are also considered, including indeterminacy, statistical data-error distribution, numerical error and instability, finite data, and model parameters. ?? Birkha??user Verlag, Basel, 2005.

High Prevalence of Refractive Errors in 7 Year Old Children in Iran.

PubMed

Hashemi, Hassan; Yekta, Abbasali; Jafarzadehpur, Ebrahim; Ostadimoghaddam, Hadi; Etemad, Koorosh; Asharlous, Amir; Nabovati, Payam; Khabazkhoob, Mehdi

2016-02-01

The latest WHO report indicates that refractive errors are the leading cause of visual impairment throughout the world. The aim of this study was to determine the prevalence of myopia, hyperopia, and astigmatism in 7 yr old children in Iran. In a cross-sectional study in 2013 with multistage cluster sampling, first graders were randomly selected from 8 cities in Iran. All children were tested by an optometrist for uncorrected and corrected vision, and non-cycloplegic and cycloplegic refraction. Refractive errors in this study were determined based on spherical equivalent (SE) cyloplegic refraction. From 4614 selected children, 89.0% participated in the study, and 4072 were eligible. The prevalence rates of myopia, hyperopia and astigmatism were 3.04% (95% CI: 2.30-3.78), 6.20% (95% CI: 5.27-7.14), and 17.43% (95% CI: 15.39-19.46), respectively. Prevalence of myopia (P=0.925) and astigmatism (P=0.056) were not statistically significantly different between the two genders, but the odds of hyperopia were 1.11 (95% CI: 1.01-2.05) times higher in girls (P=0.011). The prevalence of with-the-rule astigmatism was 12.59%, against-the-rule was 2.07%, and oblique 2.65%. Overall, 22.8% (95% CI: 19.7-24.9) of the schoolchildren in this study had at least one type of refractive error. One out of every 5 schoolchildren had some refractive error. Conducting multicenter studies throughout the Middle East can be very helpful in understanding the current distribution patterns and etiology of refractive errors compared to the previous decade.

Use of analyte-modulated modal power distribution in multimode optical fibers for simultaneous single-wavelength evanescent-wave refractometry and spectrometry.

PubMed

Potyrailo, R A; Ruddy, V P; Hieftje, G M

1999-11-01

A new method is described for the simultaneous determination of absorbance and refractive index of a sample medium. The method is based on measurement of the analyte-modulated modal power distribution (MPD) in a multimode waveguide. In turn, the MPD is quantified by the far-field spatial pattern and intensity of light, i.e., the Fraunhofer diffraction pattern (registered on a CCD camera), that emerges from a multimode optical fiber. Operationally, light that is sent down the fiber interacts with the surrounding analyte-containing medium by means of the evanescent wave at the fiber boundary. The light flux in the propagating beam and the internal reflection angles within the fiber are both affected by optical absorption connected with the analyte and by the refractive index of the analyte-containing medium. In turn, these angles are reflected in the angular divergence of the beam as it leaves the fiber. As a result, the Fraunhofer diffraction pattern of that beam yields two parameters that can, together, be used to deduce refractive index and absorbance. This MPD based detection offers important advantages over traditional evanescent-wave detection strategies which rely on recording only the total transmitted optical power or its lost fraction. First, simultaneous determination of sample refractive index and absorbance is possible at a single probe wavelength. Second, the sensitivity of refractometric and absorption measurements can be controlled simply, either by adjusting the distance between the end face of the fiber and the CCD detector or by monitoring selected modal groups at the fiber output. As a demonstration of these capabilities, several weakly absorbing solutions were examined, with refractive indices in the range from 1.3330 to 1.4553 and with absorption coefficients in the range 0-16 cm-1. The new detection strategy is likely to be important in applications in which sample coloration varies and when it is necessary to compensate for variations in the refractive index of a sample.

Refractive Error in a Sample of Black High School Children in South Africa.

PubMed

Wajuihian, Samuel Otabor; Hansraj, Rekha

2017-12-01

This study focused on a cohort that has not been studied and who currently have limited access to eye care services. The findings, while improving the understanding of the distribution of refractive errors, also enabled identification of children requiring intervention and provided a guide for future resource allocation. The aim of conducting the study was to determine the prevalence and distribution of refractive error and its association with gender, age, and school grade level. Using a multistage random cluster sampling, 1586 children, 632 males (40%) and 954 females (60%), were selected. Their ages ranged between 13 and 18 years with a mean of 15.81 ± 1.56 years. The visual functions evaluated included visual acuity using the logarithm of minimum angle of resolution chart and refractive error measured using the autorefractor and then refined subjectively. Axis astigmatism was presented in the vector method where positive values of J0 indicated with-the-rule astigmatism, negative values indicated against-the-rule astigmatism, whereas J45 represented oblique astigmatism. Overall, patients were myopic with a mean spherical power for right eye of -0.02 ± 0.47; mean astigmatic cylinder power was -0.09 ± 0.27 with mainly with-the-rule astigmatism (J0 = 0.01 ± 0.11). The prevalence estimates were as follows: myopia (at least -0.50) 7% (95% confidence interval [CI], 6 to 9%), hyperopia (at least 0.5) 5% (95% CI, 4 to 6%), astigmatism (at least -0.75 cylinder) 3% (95% CI, 2 to 4%), and anisometropia 3% (95% CI, 2 to 4%). There was no significant association between refractive error and any of the categories (gender, age, and grade levels). The prevalence of refractive error in the sample of high school children was relatively low. Myopia was the most prevalent, and findings on its association with age suggest that the prevalence of myopia may be stabilizing at late teenage years.

Two-component scattering model and the electron density spectrum

NASA Astrophysics Data System (ADS)

Zhou, A. Z.; Tan, J. Y.; Esamdin, A.; Wu, X. J.

2010-02-01

In this paper, we discuss a rigorous treatment of the refractive scintillation caused by a two-component interstellar scattering medium and a Kolmogorov form of density spectrum. It is assumed that the interstellar scattering medium is composed of a thin-screen interstellar medium (ISM) and an extended interstellar medium. We consider the case that the scattering of the thin screen concentrates in a thin layer represented by a δ function distribution and that the scattering density of the extended irregular medium satisfies the Gaussian distribution. We investigate and develop equations for the flux density structure function corresponding to this two-component ISM geometry in the scattering density distribution and compare our result with the observations. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation than does the single extended medium model. The level of refractive scintillation is strongly sensitive to the distribution of scattering material along the line of sight (LOS). The theoretical modulation indices are comparatively less sensitive to the scattering strength of the thin-screen medium, but they critically depend on the distance from the observer to the thin screen. The logarithmic slope of the structure function is sensitive to the scattering strength of the thin-screen medium, but is relatively insensitive to the thin-screen location. Therefore, the proposed model can be applied to interpret the structure functions of flux density observed in pulsar PSR B2111 + 46 and PSR B0136 + 57. The result suggests that the medium consists of a discontinuous distribution of plasma turbulence embedded in the interstellar medium. Thus our work provides some insight into the distribution of the scattering along the LOS to the pulsar PSR B2111 + 46 and PSR B0136 + 57.

Predicting of the refractive index of haemoglobin using the Hybrid GA-SVR approach.

PubMed

Oyehan, Tajudeen A; Alade, Ibrahim O; Bagudu, Aliyu; Sulaiman, Kazeem O; Olatunji, Sunday O; Saleh, Tawfik A

2018-04-30

The optical properties of blood play crucial roles in medical diagnostics and treatment, and in the design of new medical devices. Haemoglobin is a vital constituent of the blood whose optical properties affect all of the optical properties of human blood. The refractive index of haemoglobin has been reported to strongly depend on its concentration which is a function of the physiology of biological cells. This makes the refractive index of haemoglobin an essential non-invasive bio-marker of diseases. Unfortunately, the complexity of blood tissue makes it challenging to experimentally measure the refractive index of haemoglobin. While a few studies have reported on the refractive index of haemoglobin, there is no solid consensus with the data obtained due to different measuring instruments and the conditions of the experiments. Moreover, obtaining the refractive index via an experimental approach is quite laborious. In this work, an accurate, fast and relatively convenient strategy to estimate the refractive index of haemoglobin is reported. Thus, the GA-SVR model is presented for the prediction of the refractive index of haemoglobin using wavelength, temperature, and the concentration of haemoglobin as descriptors. The model developed is characterised by an excellent accuracy and very low error estimates. The correlation coefficients obtained in these studies are 99.94% and 99.91% for the training and testing results, respectively. In addition, the result shows an almost perfect match with the experimental data and also demonstrates significant improvement over a recent mathematical model available in the literature. The GA-SVR model predictions also give insights into the influence of concentration, wavelength, and temperature on the RI measurement values. The model outcome can be used not only to accurately estimate the refractive index of haemoglobin but also could provide a reliable common ground to benchmark the experimental refractive index results. Copyright © 2018 Elsevier Ltd. All rights reserved.

Rainbow schlieren and its applications

NASA Technical Reports Server (NTRS)

Howes, W. L.

1984-01-01

In this modification of the schlieren apparatus the knife-edge is replaced by a radial-rainbow filter with a transparent center and opaque surround. Consequently, refractive-index inhomogeneities in the test section appear varicolored, whereas uniformities appear white. The rainbow schlieren is simple, is easy to use, and accentuates detail regarding inhomogeneities more than the ordinary schlieren. The rainbow schlieren permits quantitative evaluation of certain refractive-index distributions, including turbulence, by simple calculations from observations of hue rather than irradiance.

[Refraction after Implantation of Multifocal and Presbyopia-Correcting Intraocular Lenses].

PubMed

Kretz, F T A; Linz, K; Mueller, M; Gerl, M; Koss, M J; Gerl, R H; Auffarth, G U

2015-08-01

Nowadays, further developments in the field of intraocular lenses offer a higher level of spectacle independence for our patients. As light gets scattered on different focal points a wider range of defocus is created. This greater defocus area makes it more difficult for us to determine the objective or subjective refraction. This contribution is concerned with the difficulties of measuring visual acuity in different intraocular lens designs and different measurement distances. Measuring refraction after implantation of a multifocal intraocular lens is a complex procedure and the experience of the examiner plays a crucial role. Retinoscopy, keratometry and the defocus curve are reliable methods for testing, while the auto refractometer, bichromatic testing and the cross-cylinder have limitations. Georg Thieme Verlag KG Stuttgart · New York.

Fundamental optical properties of linear and cyclic alkanes: VUV absorbance and index of refraction.

PubMed

Costner, Elizabeth A; Long, Brian K; Navar, Carlos; Jockusch, Steffen; Lei, Xuegong; Zimmerman, Paul; Campion, Alan; Turro, Nicholas J; Willson, C Grant

2009-08-20

VUV absorbance and index of refraction data for a series of linear and cyclic alkanes have been collected in order to understand the relationship between the electronic excitation wavelength (or absorbance edge), index of refraction, and molecular structure. The absorbance edge and index for a homologous series of both linear and cyclic alkanes increase with increasing carbon number. The optical properties of complex cycloalkanes do not vary predictably with increasing carbon number but instead depend on variations in the hydrocarbon structure in addition to hydrocarbon size. An understanding of the fundamental optical properties of this class of compounds is directly applicable to the identification of a high index and low-absorbance fluid for 193 nm immersion lithography.

High-refractive index of acrylate embedding resin clarifies mouse brain tissue

NASA Astrophysics Data System (ADS)

Zhou, Hongfu; Xiong, Yumiao; Wang, Yu; Wang, Xiaojun; Li, Pei; Gang, Yadong; Liu, Xiuli; Zeng, Shaoqun

2017-11-01

Biological tissue transparency combined with light-sheet fluorescence microscopy is a useful method for studying the neural structure of biological tissues. The development of light-sheet fluorescence microscopy also promotes progress in biological tissue clearing methods. The current clarifying methods mostly use liquid reagent to denature protein or remove lipids first, to eliminate or reduce the scattering index or refractive index of the biological tissue. However, denaturing protein and removing lipids require complex procedures or an extended time period. Therefore, here we have developed acrylate resin with a high refractive index, which causes clearing of biological tissue directly after polymerization. This method can improve endogenous fluorescence retention by adjusting the pH value of the resin monomer.

Analytic Scattering and Refraction Models for Exoplanet Transit Spectra

NASA Astrophysics Data System (ADS)

Robinson, Tyler D.; Fortney, Jonathan J.; Hubbard, William B.

2017-12-01

Observations of exoplanet transit spectra are essential to understanding the physics and chemistry of distant worlds. The effects of opacity sources and many physical processes combine to set the shape of a transit spectrum. Two such key processes—refraction and cloud and/or haze forward-scattering—have seen substantial recent study. However, models of these processes are typically complex, which prevents their incorporation into observational analyses and standard transit spectrum tools. In this work, we develop analytic expressions that allow for the efficient parameterization of forward-scattering and refraction effects in transit spectra. We derive an effective slant optical depth that includes a correction for forward-scattered light, and present an analytic form of this correction. We validate our correction against a full-physics transit spectrum model that includes scattering, and we explore the extent to which the omission of forward-scattering effects may bias models. Also, we verify a common analytic expression for the location of a refractive boundary, which we express in terms of the maximum pressure probed in a transit spectrum. This expression is designed to be easily incorporated into existing tools, and we discuss how the detection of a refractive boundary could help indicate the background atmospheric composition by constraining the bulk refractivity of the atmosphere. Finally, we show that opacity from Rayleigh scattering and collision-induced absorption will outweigh the effects of refraction for Jupiter-like atmospheres whose equilibrium temperatures are above 400-500 K.

Corneal Power Distribution and Functional Optical Zone Following Small Incision Lenticule Extraction for Myopia.

PubMed

Qian, Yishan; Huang, Jia; Zhou, Xingtao; Hanna, Rewais Benjamin

2015-08-01

To evaluate corneal power distribution using the ray tracing method (corneal power) in eyes undergoing small incision lenticule extraction (SMILE) surgery and compare the functional optical zone with two lenticular sizes. This retrospective study evaluated 128 patients who underwent SMILE for the correction of myopia and astigmatism with a lenticular diameter of 6.5 mm (the 6.5-mm group) and 6.2 mm (the 6.2-mm group). The data include refraction, correction, and corneal power obtained via a Scheimpflug camera from the pupil center to 8 mm. The surgically induced changes in corneal power (Δcorneal power) were compared to correction and Δrefraction. The functional optical zone was defined as the largest ring diameter when the difference between the ring power and the pupil center power was 1.50 diopters or less. The functional optical zone was compared between two lenticular diameter groups. Corneal power distribution was measured by the ray tracing method. In the 6.5-mm group (n=100), Δcorneal power at 5 mm showed the smallest difference from Δrefraction and Δcorneal power at 0 mm exhibited the smallest difference from correction. In the 6.2-mm group (n=28), Δcorneal power at 2 mm displayed the lowest dissimilarity from Δrefraction and Δcorneal power at 4 mm demonstrated the lowest dissimilarity from correction. There was no significant difference between the mean postoperative functional optical zones in either group when their spherical equivalents were matched. Total corneal refactive power can be used in the evaluation of surgically induced changes following SMILE. A lenticular diameter of 6.2 mm should be recommended for patients with high myopia because there is no functional difference in the optical zone. Copyright 2015, SLACK Incorporated.

The Relationship between Crystalline Lens Power and Refractive Error in Older Chinese Adults: The Shanghai Eye Study.

PubMed

He, Jiangnan; Lu, Lina; He, Xiangui; Xu, Xian; Du, Xuan; Zhang, Bo; Zhao, Huijuan; Sha, Jida; Zhu, Jianfeng; Zou, Haidong; Xu, Xun

2017-01-01

To report calculated crystalline lens power and describe the distribution of ocular biometry and its association with refractive error in older Chinese adults. Random clustering sampling was used to identify adults aged 50 years and above in Xuhui and Baoshan districts of Shanghai. Refraction was determined by subjective refraction that achieved the best corrected vision based on monocular measurement. Ocular biometry was measured by IOL Master. The crystalline lens power of right eyes was calculated using modified Bennett-Rabbetts formula. We analyzed 6099 normal phakic right eyes. The mean crystalline lens power was 20.34 ± 2.24D (range: 13.40-36.08). Lens power, spherical equivalent, and anterior chamber depth changed linearly with age; however, axial length, corneal power and AL/CR ratio did not vary with age. The overall prevalence of hyperopia, myopia, and high myopia was 48.48% (95% CI: 47.23%-49.74%), 22.82% (95% CI: 21.77%-23.88%), and 4.57% (95% CI: 4.05-5.10), respectively. The prevalence of hyperopia increased linearly with age while lens power decreased with age. In multivariate models, refractive error was strongly correlated with axial length, lens power, corneal power, and anterior chamber depth; refractive error was slightly correlated with best corrected visual acuity, age and sex. Lens power, hyperopia, and spherical equivalent changed linearly with age; Moreover, the continuous loss of lens power produced hyperopic shifts in refraction in subjects aged more than 50 years.

Linear self-focusing of continuous UV laser beam in photo-thermo-refractive glasses.

PubMed

Sidorov, Alexander I; Gorbyak, Veronika V; Nikonorov, Nikolay V

2018-03-19

The experimental and theoretical study of continuous UV laser beam propagation through thick silver-containing photo-thermo-refractive glass is presented. It is shown for the first time that self-action of UV Gaussian beam in glass results in its self-focusing. The observed linear effect is non-reversible and is caused by the transformation of subnanosized charged silver molecular clusters to neutral state under UV laser radiation. Such transformation is accompanied by the increase of molecular clusters polarizability and the refractive index increase in irradiated area. As a result, an extended positive lens is formed in glass bulk. In a theoretical study of linear self-focusing effect, the "aberration-free" approximation was used, taking into account spatial distribution of induced absorption.

Effect of parallel refraction on magnetospheric upper hybrid waves

NASA Technical Reports Server (NTRS)

Engel, J.; Kennel, C. F.

1984-01-01

Large amplitude (not less than 10 mV/m) electrostatic plasma waves near the upper hybrid (UH) frequency have been observed from 0 to 50 deg magnetic latitude (MLAT) during satellite plasma-pause crossings. A three-dimensional numerical ray-tracing calculation, based on an electron distribution measured during a GEOS 1 dayside intense upper-hybrid wave event, suggests how UH waves might achieve such large amplitudes away from the geomagnetic equator. Refractive effects largely control the wave amplification and, in particular, the unavoidable refraction due to parallel geomagnetic field gradients restricts growth to levels below those observed. However, a cold electron density gradient parallel to the field can lead to upper hybrid wave growth that can account for the observed emission levels.

Influence of local inhomogeneities induced in corneal ablation on the evolution of contrast sensitivity

NASA Astrophysics Data System (ADS)

Ortiz, Dolores; Saiz, Jose M.; González, Francisco

2004-04-01

The presence of local inhomogeneities in corneal tissue after refractive surgery has an influence on visual performance. Here we focus on the corneal ablation associated with Lasik surgery and its effect on the modulation transfer function (MTF) that we obtained by modifying a personalized Kooijman model. Inhomogeneities induced by the ablation occur in the form of Gaussian-distributed refractive-index variations of a given correlation length. We show how variation of refractive-index deviation and correlation length (size) of the inhomogeneities allows us to obtain pairs of values that are able to achieve a MTF evolution similar to that observed for contrast sensitivity in the same patients. An estimate of the characteristics of the local effects is obtained.

Post-LASIK dry eye

PubMed Central

Shtein, Roni M

2011-01-01

Laser-assisted in situ keratomileusis (LASIK) is a frequently performed corneal refractive surgery with excellent refractive outcomes. The most common complication of LASIK is dry eyes, with virtually all patients developing some degree of dryness in the immediate postoperative period. Identifying preoperative dry eyes, and conscientious attention and treatment in the perioperative time period, can lead to enhanced patient satisfaction and more accurate visual outcomes. Improved understanding of the development of dry eyes after LASIK will advance our understanding of the complex pathophysiology of dry eye disease. PMID:22174730

A numerical procedure for solving the inverse scattering problem for stratified dielectric media

NASA Astrophysics Data System (ADS)

Vogelzang, E.; Yevick, D.; Ferwerda, H. A.

1983-05-01

In this paper the refractive index profile of a dielectric stratified medium, terminated by a perfect conductor, is calculated from the complex reflection coefficient for monochromatic plane waves, incident from different directions. The advantage of this approach is that the dispersion of the refractive index does not enter the calculations. The calculation is based on the Marchenko and Gelfand-Levitan equations taking into account the bound modes of the layer. Some illustrative numerical examples are presented.

Angular distribution of Cherenkov radiation from relativistic heavy ions taking into account deceleration in the radiator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bogdanov, O. V., E-mail: bov@tpu.ru; Fiks, E. I.; Pivovarov, Yu. L.

2012-09-15

Numerical methods are used to study the dependence of the structure and the width of the angular distribution of Vavilov-Cherenkov radiation with a fixed wavelength in the vicinity of the Cherenkov cone on the radiator parameters (thickness and refractive index), as well as on the parameters of the relativistic heavy ion beam (charge and initial energy). The deceleration of relativistic heavy ions in the radiator, which decreases the velocity of ions, modifies the condition of structural interference of the waves emitted from various segments of the trajectory; as a result, a complex distribution of Vavilov-Cherenkov radiation appears. The main quantitymore » is the stopping power of a thin layer of the radiator (average loss of the ion energy), which is calculated by the Bethe-Bloch formula and using the SRIM code package. A simple formula is obtained to estimate the angular distribution width of Cherenkov radiation (with a fixed wavelength) from relativistic heavy ions taking into account the deceleration in the radiator. The measurement of this width can provide direct information on the charge of the ion that passes through the radiator, which extends the potentialities of Cherenkov detectors. The isotopic effect (dependence of the angular distribution of Vavilov-Cherenkov radiation on the ion mass) is also considered.« less

Using laser induced breakdown spectroscopy and acoustic radiation force elasticity microscope to measure the spatial distribution of corneal elasticity

NASA Astrophysics Data System (ADS)

Sun, Hui; Li, Xin; Fan, Zhongwei; Kurtz, Ron; Juhasz, Tibor

2017-02-01

Corneal biomechanics plays an important role in determining the eye's structural integrity, optical power and the overall quality of vision. It also plays an increasingly recognized role in corneal transplant and refractive surgery, affecting the predictability, quality and stability of final visual outcome [1]. A critical limitation to increasing our understanding of how corneal biomechanics controls corneal stability and refraction is the lack of non-invasive technologies that microscopically measure local biomechanical properties, such as corneal elasticity within the 3D space. Bubble based acoustic radiation force elastic microscopy (ARFEM) introduce the opportunity to measure the inhomogeneous elastic properties of the cornea by the movement of a micron size cavitation bubble generated by a low energy femtosecond laser pulse [2, 3]. Laser induced breakdown spectroscopy (LIBS) also known as laser induced plasma spectroscopy (LIPS) or laser spark spectrometry (LSS) is an atomic emission spectroscopy [4]. The LIBS principle of operation is quite simple, although the physical processes involved in the laser matter interaction are complex and still not completely understood. In one sentence for description, the laser pulses are focused down to a target so as to generate plasma that vaporizes a small amount of material which the emitted spectrum is measured to analysis the elements of the target.

Installation restoration research program: Assessment of geophysical methods for subsurface geologic mapping, cluster 13, Edgewood Area, Aberdeen Proving Ground, Maryland. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butler, D.K.; Sharp, M.K.; Sjostrom, K.J.

1996-10-01

Seismic refraction, electrical resistivity, and transient electromagnetic surveys were conducted at a portion of Cluster 13, Edgewood Area of Aberdeen Proving Ground, Maryland. Seismic refraction cross sections map the topsoil layer and the water table (saturated zone). The water table elevations from the seismic surveys correlate closely with water table elevations in nearby monitoring wells. Electrical resistivity cross sections reveal a very complicated distribution of sandy and clayey facies in the upper 10 - 15 m of the subsurface. A continuous surficial (topsoil) layer correlates with the surficial layer of the seismic section and nearby boring logs. The complexity andmore » details of the electrical resistivity cross section correlate well with boring and geophysical logs from nearby wells. The transient electromagnetic surveys map the Pleistocene-Cretaceous boundary, the saprolite, and the top of the Precambrian crystalline rocks. Conducting the transient electromagnetic surveys on a grid pattern allows the construction of a three-dimensional representation of subsurface geology (as represented by variations of electrical resistivity). Thickness and depth of the saprolitic layer and depth to top of the Precambrian rocks are consistent with generalized geologic cross sections for the Edgewood Area and depths projected from reported depths at the Aberdeen Proving Ground NW boundary using regional dips.« less

Arrange and average algorithm for the retrieval of aerosol parameters from multiwavelength high-spectral-resolution lidar/Raman lidar data.

PubMed

Chemyakin, Eduard; Müller, Detlef; Burton, Sharon; Kolgotin, Alexei; Hostetler, Chris; Ferrare, Richard

2014-11-01

We present the results of a feasibility study in which a simple, automated, and unsupervised algorithm, which we call the arrange and average algorithm, is used to infer microphysical parameters (complex refractive index, effective radius, total number, surface area, and volume concentrations) of atmospheric aerosol particles. The algorithm uses backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm as input information. Testing of the algorithm is based on synthetic optical data that are computed from prescribed monomodal particle size distributions and complex refractive indices that describe spherical, primarily fine mode pollution particles. We tested the performance of the algorithm for the "3 backscatter (β)+2 extinction (α)" configuration of a multiwavelength aerosol high-spectral-resolution lidar (HSRL) or Raman lidar. We investigated the degree to which the microphysical results retrieved by this algorithm depends on the number of input backscatter and extinction coefficients. For example, we tested "3β+1α," "2β+1α," and "3β" lidar configurations. This arrange and average algorithm can be used in two ways. First, it can be applied for quick data processing of experimental data acquired with lidar. Fast automated retrievals of microphysical particle properties are needed in view of the enormous amount of data that can be acquired by the NASA Langley Research Center's airborne "3β+2α" High-Spectral-Resolution Lidar (HSRL-2). It would prove useful for the growing number of ground-based multiwavelength lidar networks, and it would provide an option for analyzing the vast amount of optical data acquired with a future spaceborne multiwavelength lidar. The second potential application is to improve the microphysical particle characterization with our existing inversion algorithm that uses Tikhonov's inversion with regularization. This advanced algorithm has recently undergone development to allow automated and unsupervised processing; the arrange and average algorithm can be used as a preclassifier to further improve its speed and precision. First tests of the performance of arrange and average algorithm are encouraging. We used a set of 48 different monomodal particle size distributions, 4 real parts and 15 imaginary parts of the complex refractive index. All in all we tested 2880 different optical data sets for 0%, 10%, and 20% Gaussian measurement noise (one-standard deviation). In the case of the "3β+2α" configuration with 10% measurement noise, we retrieve the particle effective radius to within 27% for 1964 (68.2%) of the test optical data sets. The number concentration is obtained to 76%, the surface area concentration to 16%, and the volume concentration to 30% precision. The "3β" configuration performs significantly poorer. The performance of the "3β+1α" and "2β+1α" configurations is intermediate between the "3β+2α" and the "3β."

Evanescent field characteristics of eccentric core optical fiber for distributed sensing.

PubMed

Liu, Jianxia; Yuan, Libo

2014-03-01

Fundamental core-mode cutoff and evanescent field are considered for an eccentric core optical fiber (ECOF). A method has been proposed to calculate the core-mode cutoff by solving the eigenvalue equations of an ECOF. Using conformal mapping, the asymmetric geometrical structure can be transformed into a simple, easily solved axisymmetric optical fiber with three layers. The variation of the fundamental core-mode cut-off frequency (V(c)) is also calculated with different eccentric distances, wavelengths, core radii, and coating refractive indices. The fractional power of evanescent fields for ECOF is also calculated with the eccentric distances and coating refractive indices. These calculations are necessary to design the structural parameters of an ECOF for long-distance, single-mode distributed evanescent field absorption sensors.

Complex index of refraction estimation from degree of polarization with diffuse scattering consideration.

PubMed

Zhan, Hanyu; Voelz, David G; Cho, Sang-Yeon; Xiao, Xifeng

2015-11-20

The estimation of the refractive index from optical scattering off a target's surface is an important task for remote sensing applications. Optical polarimetry is an approach that shows promise for refractive index estimation. However, this estimation often relies on polarimetric models that are limited to specular targets involving single surface scattering. Here, an analytic model is developed for the degree of polarization (DOP) associated with reflection from a rough surface that includes the effect of diffuse scattering. A multiplicative factor is derived to account for the diffuse component and evaluation of the model indicates that diffuse scattering can significantly affect the DOP values. The scattering model is used in a new approach for refractive index estimation from a series of DOP values that involves jointly estimating n, k, and ρ(d)with a nonlinear equation solver. The approach is shown to work well with simulation data and additive noise. When applied to laboratory-measured DOP values, the approach produces significantly improved index estimation results relative to reference values.

Spectroscopic refractometer for transparent and absorbing liquids by reflection of white light near the critical angle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanchez-Perez, C.; Garcia-Valenzuela, A.

2012-11-15

We propose and evaluate a spectroscopic refractometer device to measure the refractive index dispersion of transparent and absorbing solutions. The angle-dependent reflectivity of a white beam of light in an internal reflection configuration around the critical angle is spectrally analyzed. The refractive index in a wavelength range from 400 nm to 900 nm is obtained from the angle-reflectivity curve around the critical angle at each wavelength. The device does not use angle scanning mechanisms, decreasing considerably the complexity of the instrument in comparison to previous proposals. As a result, the measurements are obtained relatively fast. Nevertheless, a good experimental resolutionmore » in refractive index of about {Delta}n Almost-Equal-To 10{sup -4} at all the wavelengths is achieved in the case of transparent solutions. The calibration procedure of the device is discussed in detail. We also present measurements of the refractive index dispersion of rhodamine 6G-methanol solutions, which has a strong absorption band in the visible spectra.« less

Reversed rainbow with a nonlocal metamaterial

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgado, Tiago A., E-mail: tiago.morgado@co.it.pt; Marcos, João S.; Silveirinha, Mário G., E-mail: mario.silveirinha@co.it.pt

2014-12-29

One of the intriguing potentials of metamaterials is the possibility to realize a nonlocal electromagnetic reaction, such that the effective medium response at a given point is fundamentally entangled with the macroscopic field distribution at long distances. Here, it is experimentally and numerically verified that a microwave nonlocal metamaterial formed by crossed metallic wires enables a low-loss broadband anomalous material response such that the refractive index decreases with frequency. Notably, it is shown that an electromagnetic beam refracted by our metamaterial prism creates a reversed microwave rainbow.

Comparison of techniques for approximating ocean bottom topography in a wave-refraction computer model

NASA Technical Reports Server (NTRS)

Poole, L. R.

1975-01-01

A study of the effects of using different methods for approximating bottom topography in a wave-refraction computer model was conducted. Approximation techniques involving quadratic least squares, cubic least squares, and constrained bicubic polynomial interpolation were compared for computed wave patterns and parameters in the region of Saco Bay, Maine. Although substantial local differences can be attributed to use of the different approximation techniques, results indicated that overall computed wave patterns and parameter distributions were quite similar.

Rainbow Schlieren

NASA Technical Reports Server (NTRS)

Howes, W. L.

1983-01-01

The rainbow schlieren is an apparatus in which the usual schlieren knife edge cutoff is replaced by a radial rainbow filter with a transparent center and an opaque surround. With this apparatus most refractive index nonuniformities in the test section appear varicolored whereas uniformities appear white. The rainbow schlieren is simple, easy to use, and relatively inexpensive and gives much greater detail regarding nonuniformities than does the ordinary schlieren. Moreover, the rainbow schlieren permits quantitative evaluation of certain refractive index distributions, including those involving turbulence, by simple calculations.

Demonstration of Simplified Field Test Methods for the Measurement of Diesel Particulate Matter (PM) from Military Diesel Engines

DTIC Science & Technology

2008-07-01

EPA emission standards, the EPA has also specified the measurement methods . According to EPA, the most accurate and precise method of determining ...function of particle size and refractive index . If particle size distributions and refractive indices in diesel exhaust strongly depend on the...to correct the bias of the raw SFTM data and align the data with the values determined by the federal reference method . Thus, to use these methods a

Status of holographic interferometry at University of Michigan

NASA Technical Reports Server (NTRS)

Vest, Charles

1987-01-01

Reflection holograms were taken of a jet of air injected traverse to a subsonic stream. The technique of reflection holograms allowed maximum viewing angle and minimum distance to the jet. Holographic interferometry is being used to measure the temperature distribution in a growing crystal. Computations of the temperatures are being made. A phase shift interferometer was used to study flows with very weak changes in refractive index, of the order of 1 shift. Tomographic techniques are being developed for strong refractive cases.

Develop Roll-to-Roll Manufacturing Process of ZrO 2 Nanocrystals/Acrylic Nanocomposites for High Refractive Index Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joshi, Pooran C.; Compton, Brett G.; Li, Jianlin

2015-04-01

The purpose of this Cooperative Research and Development Agreement (CRADA) was to develop and evaluate ZrO 2/acrylic nanocomposite coatings for integrated optoelectronic applications. The formulations engineered to be compatible with roll-to-roll process were evaluated in terms of optical and dielectric properties. The uniform distribution of the ZrO 2 nanocrystals in the polymer matrix resulted in highly tunable refractive index and dielectric response suitable for advanced photonic and electronic device applications.

Effect of atmospheric refraction on radiative transfer in visible and near-infrared band: Model development, validation, and applications

NASA Astrophysics Data System (ADS)

Hu, Shuai; Gao, Tai-chang; Li, Hao; Liu, Lei; Liu, Xi-chuan; Zhang, Ting; Cheng, Tian-ji; Li, Wan-tong; Dai, Zhong-hua; Su, Xiaojian

2016-03-01

Refraction is an important factor influencing radiative transfer since it can modify the propagation trajectory and polarization states of lights; therefore, it is necessary to quantitively evaluate the effect of atmospheric refraction on radiative transfer process. To this end, a new atmospheric radiative transfer model including refraction process is proposed. The model accuracy is validated against benchmark results, literature results, and well-tested radiative transfer models such as discrete coordinate method and RT3/PolRadtran. The impact of atmospheric refraction on both polarized radiance and fluxes is discussed for pure Rayleigh scattering atmosphere, atmosphere with aerosol, and cloud. The results show that atmospheric refraction has a significant influence on both the radiance and polarization states of diffuse light, where the relative change of the radiance of reflected light and transmitted light due to refraction can achieve 6.3% and 7.4% for Rayleigh scattering atmosphere, 7.2% and 7.8% for atmosphere with aerosol, and 6.2% and 6.8% for cloudy atmosphere, respectively. The relative change of the degree of polarization ranges from near zero in the horizon to 9.5% near neutral points. The angular distribution pattern of the relative change of the radiance for atmosphere with aerosol and cloud is very similar to that for pure Rayleigh scattering case, where its magnitude decreases gradually with the increasing of zenith angle for reflected light; but for transmitted light, the variation characteristics is opposite. The impact of refraction is gradually enhanced with the increasing of solar zenith angles and the optical depth of aerosol and cloud. As the wavelength of incident light increases, the impact declines rapidly for Rayleigh scattering medium. The relative change of the fluxes due to refraction is most notable for Middle Latitude Winter profile (about 8.2043% and 7.3225% for the transmitted and reflected light, respectively, at 0.35 µm). With increasing the optical depth of aerosol, the influence of refraction on the fluxes is gradually enhanced. For cloudy atmosphere, the relative changes of the fluxes due to refraction are not very sensitive to the variation of cloud optical depth and effective radius of cloud drops.

High Prevalence of Refractive Errors in 7 Year Old Children in Iran

PubMed Central

HASHEMI, Hassan; YEKTA, Abbasali; JAFARZADEHPUR, Ebrahim; OSTADIMOGHADDAM, Hadi; ETEMAD, Koorosh; ASHARLOUS, Amir; NABOVATI, Payam; KHABAZKHOOB, Mehdi

2016-01-01

Background: The latest WHO report indicates that refractive errors are the leading cause of visual impairment throughout the world. The aim of this study was to determine the prevalence of myopia, hyperopia, and astigmatism in 7 yr old children in Iran. Methods: In a cross-sectional study in 2013 with multistage cluster sampling, first graders were randomly selected from 8 cities in Iran. All children were tested by an optometrist for uncorrected and corrected vision, and non-cycloplegic and cycloplegic refraction. Refractive errors in this study were determined based on spherical equivalent (SE) cyloplegic refraction. Results: From 4614 selected children, 89.0% participated in the study, and 4072 were eligible. The prevalence rates of myopia, hyperopia and astigmatism were 3.04% (95% CI: 2.30–3.78), 6.20% (95% CI: 5.27–7.14), and 17.43% (95% CI: 15.39–19.46), respectively. Prevalence of myopia (P=0.925) and astigmatism (P=0.056) were not statistically significantly different between the two genders, but the odds of hyperopia were 1.11 (95% CI: 1.01–2.05) times higher in girls (P=0.011). The prevalence of with-the-rule astigmatism was 12.59%, against-the-rule was 2.07%, and oblique 2.65%. Overall, 22.8% (95% CI: 19.7–24.9) of the schoolchildren in this study had at least one type of refractive error. Conclusion: One out of every 5 schoolchildren had some refractive error. Conducting multicenter studies throughout the Middle East can be very helpful in understanding the current distribution patterns and etiology of refractive errors compared to the previous decade. PMID:27114984

Impact of substrate etching on plasmonic elements and metamaterials: preventing red shift and improving refractive index sensitivity.

PubMed

Moritake, Yuto; Tanaka, Takuo

2018-02-05

We propose and demonstrate the elimination of substrate influence on plasmon resonance by using selective and isotropic etching of substrates. Preventing the red shift of the resonance due to substrates and improving refractive index sensitivity were experimentally demonstrated by using plasmonic nanostructures fabricated on silicon substrates. Applying substrate etching decreases the effective refractive index around the metal nanostructures, resulting in elimination of the red shift. Improvement of sensitivity to the refractive index environment was demonstrated by using plasmonic metamaterials with Fano resonance based on far field interference. Change in quality factors (Q-factors) of the Fano resonance by substrate etching was also investigated in detail. The presence of a closely positioned substrate distorts the electric field distribution and degrades the Q-factors. Substrate etching dramatically increased the refractive index sensitivity reaching to 1532 nm/RIU since the electric fields under the nanostructures became accessible through substrate etching. The FOM was improved compared to the case without the substrate etching. The method presented in this paper is applicable to a variety of plasmonic structures to eliminate the influence of substrates for realizing high performance plasmonic devices.

INTEGRATED AND FIBER OPTICS: Investigation of the refractive index profile of inhomogeneous iron garnet films containing bismuth

NASA Astrophysics Data System (ADS)

Arzamastseva, G. V.; Kravchenko, V. B.; Filimonova, L. M.

1989-02-01

The refractive index n of quasihomogeneous iron garnet films with the composition (YGdYb)3 - xBixFe5 - yAlyO12 increased considerably as a result of reduction in the growth temperature Tg. This was attributed mainly by an increase in x and a reduction in y. The dependences n(Tg) were used to select the conditions for growth of inhomogeneous (across the thickness) films and to predict the refractive index profile n(z), where z was measured from the free surface along the normal to the film. The spectra of optical modes were analyzed in the WKB approximation and this yielded the n(z) profiles for films with a refractive index n decreasing monotonically from the free surface and for films with the symmetric profile n(z) (buried waveguides). The n(z) profiles were compared with the distributions of the compensation temperature Tc(z), and of x(z) and y(z) across the thickness.

Enhanced vibrational spectroscopy, intracellular refractive indexing for label-free biosensing and bioimaging by multiband plasmonic-antenna array.

PubMed

Chen, Cheng-Kuang; Chang, Ming-Hsuan; Wu, Hsieh-Ting; Lee, Yao-Chang; Yen, Ta-Jen

2014-10-15

In this study, we report a multiband plasmonic-antenna array that bridges optical biosensing and intracellular bioimaging without requiring a labeling process or coupler. First, a compact plasmonic-antenna array is designed exhibiting a bandwidth of several octaves for use in both multi-band plasmonic resonance-enhanced vibrational spectroscopy and refractive index probing. Second, a single-element plasmonic antenna can be used as a multifunctional sensing pixel that enables mapping the distribution of targets in thin films and biological specimens by enhancing the signals of vibrational signatures and sensing the refractive index contrast. Finally, using the fabricated plasmonic-antenna array yielded reliable intracellular observation was demonstrated from the vibrational signatures and intracellular refractive index contrast requiring neither labeling nor a coupler. These unique features enable the plasmonic-antenna array to function in a label-free manner, facilitating bio-sensing and imaging development. Copyright © 2014 Elsevier B.V. All rights reserved.

Self-Reference Refractive Index Sensor Based on Independently Controlled Double Resonances in Side-Coupled U-Shaped Resonators.

PubMed

Ren, Xiaobin; Ren, Kun; Ming, Chengguo

2018-04-28

A plasmonic, refractive, index nanosensor is investigated theoretically and numerically in two U-shaped cavities side-coupled to a metal⁻dielectric⁻metal (MDM) waveguide. A transparency window between two transmission dips is observed. The physical origin of the transmission phenomenon is revealed by mapping the magnetic field distribution. Independent double resonances are realized through the proposed design. Double resonances showed diverse responses to the variations of the structural dimensions. In particular, they presented different dependences on a refraction index of the medium in an individual resonator. One resonance exhibited a remarkable shift with the increase of the refraction index; however, the other resonance remained unchanged. On the basis of this unique characteristic of differing sensitivities, self-reference sensing is discussed. The nanosensor yielded a high sensitivity of 917 nm/RIU and a figure of merit of 180 RIU −1 . This work is helpful in terms of the design of on-chip optical sensors with high sensitivity and improved detection accuracy in complicated environments.

Subsurface Characterization using Geophysical Seismic Refraction Survey for Slope Stabilization Design with Soil Nailing

NASA Astrophysics Data System (ADS)

Ashraf Mohamad Ismail, Mohd; Ng, Soon Min; Hazreek Zainal Abidin, Mohd; Madun, Aziman

2018-04-01

The application of geophysical seismic refraction for slope stabilization design using soil nailing method was demonstrated in this study. The potential weak layer of the study area is first identify prior to determining the appropriate length and location of the soil nail. A total of 7 seismic refraction survey lines were conducted at the study area with standard procedures. The refraction data were then analyzed by using the Pickwin and Plotrefa computer software package to obtain the seismic velocity profiles distribution. These results were correlated with the complementary borehole data to interpret the subsurface profile of the study area. It has been identified that layer 1 to 3 is the potential weak zone susceptible to slope failure. Hence, soil nails should be installed to transfer the tensile load from the less stable layer 3 to the more stable layer 4. The soil-nail interaction will provide a reinforcing action to the soil mass thereby increasing the stability of the slope.

Two-Flux Method for Transient Radiative Transfer in a Semitransparent Layer

NASA Technical Reports Server (NTRS)

Siegel, Robert

1996-01-01

The two-flux method was used to obtain transient solutions for a plane layer including internal reflections and scattering. The layer was initially at uniform temperature, and was heated or cooled by external radiation and convection. The two-flux equations were examined as a means for evaluating the radiative flux gradient in the transient energy equation. Comparisons of transient temperature distributions using the two-flux method were made with results where the radiative flux gradient was evaluated from the exact radiative transfer equations. Good agreement was obtained for optical thicknesses from 0.5 to 5 and for refractive indices of 1 and 2. Illustrative results obtained with the two-flux method demonstrate the effect of isotropic scattering coupled with changing the refractive index. For small absorption with large scattering the maximum layer temperature is increased when the refractive index is increased. For larger absorption the effect is opposite, and the maximum temperature decreases with increased refractive index .

Hybrid Ni/SiO2/Au dimer arrays for high-resolution refractive index sensing

NASA Astrophysics Data System (ADS)

Pourjamal, Sara; Kataja, Mikko; Maccaferri, Nicolò; Vavassori, Paolo; van Dijken, Sebastiaan

2018-05-01

We introduce a novel magnetoplasmonic sensor concept for sensitive detection of refractive index changes. The sensor consists of a periodic array of Ni/SiO2/Au dimer nanodisks. Combined effects of near-field interactions between the Ni and Au disks within the individual dimers and far-field diffractive coupling between the dimers of the array produce narrow linewidth features in the magneto-optical Faraday spectrum. We associate these features with the excitation of surface lattice resonances and show that they exhibit a spectral shift when the refractive index of the surrounding environment is varied. Because the resonances are sharp, refractive index changes are accurately detected by tracking the wavelength where the Faraday signal crosses 0. Compared to random distributions of pure Ni nanodisks or Ni/SiO2/Au dimers or periodic arrays of Ni nanodisks, the sensing figure of merit of the hybrid magnetoplasmonic array is more than one order of magnitude larger.

Interlobate esker architecture and related hydrogeological features derived from a combination of high-resolution reflection seismics and refraction tomography, Virttaankangas, southwest Finland

NASA Astrophysics Data System (ADS)

Maries, Georgiana; Ahokangas, Elina; Mäkinen, Joni; Pasanen, Antti; Malehmir, Alireza

2017-05-01

A novel high-resolution (2-4 m source and receiver spacing) reflection and refraction seismic survey was carried out for aquifer characterization and to confirm the existing depositional model of the interlobate esker of Virttaankangas, which is part of the Säkylänharju-Virttaankangas glaciofluvial esker-chain complex in southwest Finland. The interlobate esker complex hosting the managed aquifer recharge (MAR) plant is the source of the entire water supply for the city of Turku and its surrounding municipalities. An accurate delineation of the aquifer is therefore critical for long-term MAR planning and sustainable use of the esker resources. Moreover, an additional target was to resolve the poorly known stratigraphy of the 70-100-m-thick glacial deposits overlying a zone of fractured bedrock. Bedrock surface as well as fracture zones were confirmed through combined reflection seismic and refraction tomography results and further validated against existing borehole information. The high-resolution seismic data proved successful in accurately delineating the esker cores and revealing complex stratigraphy from fan lobes to kettle holes, providing valuable information for potential new pumping wells. This study illustrates the potential of geophysical methods for fast and cost-effective esker studies, in particular the digital-based landstreamer and its combination with geophone-based wireless recorders, where the cover sediments are reasonably thick.

Giant Pockels effect in ZnO-F films deposited on bare glasses

NASA Astrophysics Data System (ADS)

Kityk, I. V.; Ebothe, J.; El Hichou, A.; Addou, M.; Bougrine, A.; Sahraoui, B.

2002-06-01

A giant linear electro-optics (Pockels) effect (up to 17 pm V-1) (for wavelength about 435 nm) in ZnO crystalline films doped with fluorine and deposited on bare glass has been found. For description of the observed phenomenon, a complex approach including self-consistent band structure calculations together with an appropriate molecular dynamics simulation of the interface structure was applied. Experimental ellipsometric and refractive index measurements confirm an efficiency of the mentioned approach for description of the observed interface (between the film and glass) processes. The origin of the observed effect is caused by substantial non-centrosymmetric charge density distribution between the ZnO wurtzite-like crystalline films and the bare glass substrate, as well as by additional charge density polarization caused by fluorine atoms.

Fully 3D refraction correction dosimetry system.

PubMed

Manjappa, Rakesh; Makki, S Sharath; Kumar, Rajesh; Vasu, Ram Mohan; Kanhirodan, Rajan

2016-02-21

The irradiation of selective regions in a polymer gel dosimeter results in an increase in optical density and refractive index (RI) at those regions. An optical tomography-based dosimeter depends on rayline path through the dosimeter to estimate and reconstruct the dose distribution. The refraction of light passing through a dose region results in artefacts in the reconstructed images. These refraction errors are dependant on the scanning geometry and collection optics. We developed a fully 3D image reconstruction algorithm, algebraic reconstruction technique-refraction correction (ART-rc) that corrects for the refractive index mismatches present in a gel dosimeter scanner not only at the boundary, but also for any rayline refraction due to multiple dose regions inside the dosimeter. In this study, simulation and experimental studies have been carried out to reconstruct a 3D dose volume using 2D CCD measurements taken for various views. The study also focuses on the effectiveness of using different refractive-index matching media surrounding the gel dosimeter. Since the optical density is assumed to be low for a dosimeter, the filtered backprojection is routinely used for reconstruction. We carry out the reconstructions using conventional algebraic reconstruction (ART) and refractive index corrected ART (ART-rc) algorithms. The reconstructions based on FDK algorithm for cone-beam tomography has also been carried out for comparison. Line scanners and point detectors, are used to obtain reconstructions plane by plane. The rays passing through dose region with a RI mismatch does not reach the detector in the same plane depending on the angle of incidence and RI. In the fully 3D scanning setup using 2D array detectors, light rays that undergo refraction are still collected and hence can still be accounted for in the reconstruction algorithm. It is found that, for the central region of the dosimeter, the usable radius using ART-rc algorithm with water as RI matched medium is 71.8%, an increase of 6.4% compared to that achieved using conventional ART algorithm. Smaller diameter dosimeters are scanned with dry air scanning by using a wide-angle lens that collects refracted light. The images reconstructed using cone beam geometry is seen to deteriorate in some planes as those regions are not scanned. Refraction correction is important and needs to be taken in to consideration to achieve quantitatively accurate dose reconstructions. Refraction modeling is crucial in array based scanners as it is not possible to identify refracted rays in the sinogram space.

Experimental and numerical study of underwater beam propagation in a Rayleigh-Bénard turbulence tank.

PubMed

Nootz, Gero; Matt, Silvia; Kanaev, Andrey; Judd, Kyle P; Hou, Weilin

2017-08-01

The propagation of a laser beam through Rayleigh-Bénard (RB) turbulence is investigated experimentally and by way of numerical simulation. For the experimental part, a focused laser beam transversed a 5  m×0.5  m×0.5  m water filled tank lengthwise. The tank is heated from the bottom and cooled from the top to produce convective RB turbulence. The effect of the turbulence on the beam is recorded on the exit of the beam from the tank. From the centroid motion of the beam, the index of refraction structure constant Cn2 is determined. For the numerical efforts RB turbulence is simulated for a tank of the same geometry. The simulated temperature fields are converted to the index of refraction distributions, and Cn2 is extracted from the index of refraction structure functions, as well as from the simulated beam wander. To model the effect on beam propagation, the simulated index of refraction fields are converted to discrete index of refraction phase screens. These phase screens are then used in a split-step beam propagation method to investigate the effect of the turbulence on a laser beam. The beam wander as well as the index of refraction structure parameter Cn2 determined from the experiment and simulation are compared and found to be in good agreement.

Determination of polar stratospheric cloud particle refractive indices by use of in situ optical measurements and T-matrix calculations.

PubMed

Scarchilli, Claudio; Adriani, Alberto; Cairo, Francesco; Di Donfrancesco, Guido; Buontempo, Carlo; Snels, Marcel; Moriconi, Maria Luisa; Deshler, Terry; Larsen, Niels; Luo, Beiping; Mauersberger, Konrad; Ovarlez, Joelle; Rosen, Jim; Schreiner, Jochen

2005-06-01

A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.

Nonlinear optical studies of curcumin metal derivatives with cw laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henari, F. Z., E-mail: fzhenari@rcsi-mub.com; Cassidy, S.

2015-03-30

We report on measurements of the nonlinear refractive index and nonlinear absorption coefficients for curcumin and curcumin metal complexes of boron, copper, and iron at different wavelengths using the Z-scan technique. These materials are found to be novel nonlinear media. It was found that the addition of metals slightly influences its nonlinearity. These materials show a large negative nonlinear refractive index of the order of 10{sup −7} cm{sup 2}/W and negative nonlinear absorption of the order of 10{sup −6} cm/W. The origin of the nonlinearity was investigated by comparison of the formalism that is known as the Gaussian decomposition modelmore » with the thermal lens model. The optical limiting behavior based on the nonlinear refractive index was also investigated.« less

Engineering the Complex-Valued Constitutive Parameters of Metamaterials for Perfect Absorption

NASA Astrophysics Data System (ADS)

Wang, Pengwei; Chen, Naibo; Tang, Chaojun; Chen, Jing; Liu, Fanxin; Sheng, Saiqian; Yan, Bo; Sui, Chenghua

2017-04-01

We theoretically studied how to directly engineer the constitutive parameters of metamaterials for perfect absorbers of electromagnetic waves. As an example, we numerically investigated the necessary refractive index n and extinction coefficient k and the relative permittivity ɛ and permeability μ of a metamaterial anti-reflection layer, which could cancel the reflection from a hydrogenated amorphous silicon (α-Si:H) thin film on a metal substrate, within the visible wavelength range from 300 to 800 nm. We found that the metamaterial anti-reflection layer should have a negative refractive index ( n < 0) for short-wavelength visible light but have a positive refractive index ( n > 0) for long-wavelength visible light. The relative permittivity ɛ and permeability μ could be fitted by the Lorentz model, which exhibited electric and magnetic resonances, respectively.

Early Intervention and Nonpharmacological Therapy of Myopia in Young Adults

PubMed Central

Gładysiak, Aleksandra; Ślęzak, Daniel

2018-01-01

Myopia is a condition of the eye where parallel rays focus in front of, instead of on, the retina, which results in excessive refractive power of the cornea or the lens or eyeball elongation. Studies carried out in recent years show that the etiology of myopia is complex with genetic and environmental factors playing a role. Refraction defects decrease the quality of vision, while progressing myopia can lead to partial loss of vision, which can be particularly dramatic in young adults. Therefore, it is so crucial to take appropriate actions aimed at preventing myopia progression. This is a review of nonpharmacological therapeutic possibilities of refraction defect prevention in young adults, with special regard to myofascial therapy, osteopathy, and massage of acupuncture points surrounding the eye. PMID:29576878

High-refractive index of acrylate embedding resin clarifies mouse brain tissue.

PubMed

Zhou, Hongfu; Xiong, Yumiao; Wang, Yu; Wang, Xiaojun; Li, Pei; Gang, Yadong; Liu, Xiuli; Zeng, Shaoqun

2017-11-01

Biological tissue transparency combined with light-sheet fluorescence microscopy is a useful method for studying the neural structure of biological tissues. The development of light-sheet fluorescence microscopy also promotes progress in biological tissue clearing methods. The current clarifying methods mostly use liquid reagent to denature protein or remove lipids first, to eliminate or reduce the scattering index or refractive index of the biological tissue. However, denaturing protein and removing lipids require complex procedures or an extended time period. Therefore, here we have developed acrylate resin with a high refractive index, which causes clearing of biological tissue directly after polymerization. This method can improve endogenous fluorescence retention by adjusting the pH value of the resin monomer. (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

Broadband All-angle Negative Refraction by Optimized Phononic Crystals.

PubMed

Li, Yang Fan; Meng, Fei; Zhou, Shiwei; Lu, Ming-Hui; Huang, Xiaodong

2017-08-07

All-angle negative refraction (AANR) of phononic crystals and its frequency range are dependent on mechanical properties of constituent materials and their spatial distribution. So far, it is impossible to achieve the maximum operation frequency range of AANR theoretically. In this paper, we will present a numerical approach for designing a two-dimensional phononic crystal with broadband AANR without negative index. Through analyzing the mechanism of AANR, a topology optimization problem aiming at broadband AANR is established and solved by bi-directional evolutionary structural optimization method. The optimal steel/air phononic crystal exhibits a record AANR range over 20% and its refractive properties and focusing effects are further investigated. The results demonstrate the multifunctionality of a flat phononic slab including superlensing effect near upper AANR frequencies and self-collimation at lower AANR frequencies.

Linearity in the response of photopolymers as optical recording media.

PubMed

Gallego, Sergi; Marquez, Andrés; Guardiola, Francisco J; Riquelme, Marina; Fernández, Roberto; Pascual, Inmaculada; Beléndez, Augusto

2013-05-06

Photopolymer are appealing materials for diffractive elements recording. Two of their properties when they are illuminated are useful for this goal: the relief surface changes and the refractive index modifications. To this goal the linearity in the material response is crucial to design the optimum irradiance for each element. In this paper we measured directly some parameters to know how linear is the material response, in terms of the refractive index modulation versus exposure, then we can predict the refractive index distributions during recording. We have analyzed at different recording intensities the evolution of monomer diffusion during recording for photopolymers based on PVA/Acrylamide. This model has been successfully applied to PVA/Acrylamide photopolymers to predict the transmitted diffracted orders and the agreement with experimental values has been increased.

The Relationship between Crystalline Lens Power and Refractive Error in Older Chinese Adults: The Shanghai Eye Study

PubMed Central

He, Jiangnan; Lu, Lina; He, Xiangui; Xu, Xian; Du, Xuan; Zhang, Bo; Zhao, Huijuan; Sha, Jida; Zhu, Jianfeng; Zou, Haidong; Xu, Xun

2017-01-01

Purpose To report calculated crystalline lens power and describe the distribution of ocular biometry and its association with refractive error in older Chinese adults. Methods Random clustering sampling was used to identify adults aged 50 years and above in Xuhui and Baoshan districts of Shanghai. Refraction was determined by subjective refraction that achieved the best corrected vision based on monocular measurement. Ocular biometry was measured by IOL Master. The crystalline lens power of right eyes was calculated using modified Bennett-Rabbetts formula. Results We analyzed 6099 normal phakic right eyes. The mean crystalline lens power was 20.34 ± 2.24D (range: 13.40–36.08). Lens power, spherical equivalent, and anterior chamber depth changed linearly with age; however, axial length, corneal power and AL/CR ratio did not vary with age. The overall prevalence of hyperopia, myopia, and high myopia was 48.48% (95% CI: 47.23%–49.74%), 22.82% (95% CI: 21.77%–23.88%), and 4.57% (95% CI: 4.05–5.10), respectively. The prevalence of hyperopia increased linearly with age while lens power decreased with age. In multivariate models, refractive error was strongly correlated with axial length, lens power, corneal power, and anterior chamber depth; refractive error was slightly correlated with best corrected visual acuity, age and sex. Conclusion Lens power, hyperopia, and spherical equivalent changed linearly with age; Moreover, the continuous loss of lens power produced hyperopic shifts in refraction in subjects aged more than 50 years. PMID:28114313

Prevalence of refractive errors in children in Equatorial Guinea.

PubMed

Soler, Margarita; Anera, Rosario G; Castro, José J; Jiménez, Raimundo; Jiménez, José R

2015-01-01

The aim of this work is to evaluate the epidemiological aspects of the refractive errors in school-aged children in Malabo (Island of Bioko), Equatorial Guinea (western-central Africa). A total of 425 schoolchildren (209 male subjects and 216 female subjects, aged between 6 and 16 years) were examined to evaluate their refraction errors in Malabo, Equatorial Guinea (western-central Africa). The examination included autorefraction with cycloplegia, measurement of visual acuity (VA) for far vision, and the curvature radii of the main meridians of the anterior surface of the cornea. A low prevalence of myopia was found (≤-0.50 diopters [D] spherical equivalent), with unilateral and bilateral myopia being 10.4 and 5.2%, respectively. The prevalence of unilateral and bilateral hypermetropia (≥2.0 D spherical equivalent) was 3.1 and 1.6%, respectively. Astigmatism (≤-0.75 D) was found in unilateral form in 32.5% of these children, whereas bilateral astigmatism was found in 11.8%. After excluding children having any ocular pathology, the low prevalence of high refractive errors signified good VA in these children. Significant differences were found in the distribution of the refractive errors by age and type of schooling (public or private) but not by sex. In general, the radii of the anterior of the cornea did not vary significantly with age. The mean refractive errors found were low and therefore VA was high in these children. There was a low prevalence of myopia, with significantly higher values in those who attended private schools (educationally and socioeconomically more demanding). Astigmatism was the most frequent refractive error.

Imaginary refractive index and other microphysical properties of volcanic ash, Sarahan dust, and other mineral aerosols

NASA Astrophysics Data System (ADS)

Rocha Lima, A.; Martins, J.; Krotkov, N. A.; Artaxo, P.; Todd, M.; Ben Ami, Y.; Dolgos, G.; Espinosa, R.

2013-12-01

Aerosol properties are essential to support remote sensing measurements, atmospheric circulation and climate models. This research aims to improve the understanding of the optical and microphysical properties of different types of aerosols particles. Samples of volcanic ash, Saharan dust and other mineral aerosols particles were analyzed by different techniques. Ground samples were sieved down to 45um, de-agglomerated and resuspended in the laboratory using a Fluidized Bed Aerosol Generator (FBAG). Particles were collected on Nuclepore filters into PM10, PM2.5, or PM1.0. and analyzed by different techniques, such as Scanning Electron Microscopy (SEM) for determination of size distribution and shape, spectral reflectance for determination of the optical absorption properties as a function of the wavelength, material density, and X-Ray fluorescence for the elemental composition. The spectral imaginary part of refractive index from the UV to the short wave infrared (SWIR) wavelength was derived empirically from the measurements of the spectral mass absorption coefficient, size distribution and density of the material. Some selected samples were also analyzed with the Polarized Imaging Nephelometer (PI-Neph) instrument for the characterization of the aerosol polarized phase function. This work compares results of the spectral refractive index of different materials obtained by our methodology with those available in the literature. In some cases there are significant differences both in magnitude and spectral dependence of the imaginary refractive index. These differences are evaluated and discussed in this work.

Copper(II) complex with 6-methylpyridine-2-carboxyclic acid: Experimental and computational study on the XRD, FT-IR and UV-Vis spectra, refractive index, band gap and NLO parameters

NASA Astrophysics Data System (ADS)

Altürk, Sümeyye; Avcı, Davut; Başoğlu, Adil; Tamer, Ömer; Atalay, Yusuf; Dege, Necmi

2018-02-01

Crystal structure of the synthesized copper(II) complex with 6-methylpyridine-2-carboxylic acid, [Cu(6-Mepic)2·H2O]·H2O, was determined by XRD, FT-IR and UV-Vis spectroscopic techniques. Furthermore, the geometry optimization, harmonic vibration frequencies for the Cu(II) complex were carried out by using Density Functional Theory calculations with HSEh1PBE/6-311G(d,p)/LanL2DZ level. Electronic absorption wavelengths were obtained by using TD-DFT/HSEh1PBE/6-311G(d,p)/LanL2DZ level with CPCM model and major contributions were determined via Swizard/Chemissian program. Additionally, the refractive index, linear optical (LO) and non-nonlinear optical (NLO) parameters of the Cu(II) complex were calculated at HSEh1PBE/6-311G(d,p) level. The experimental and computed small energy gap shows the charge transfer in the Cu(II) complex. Finally, the hyperconjugative interactions and intramolecular charge transfer (ICT) were studied by performing of natural bond orbital (NBO) analysis.

Copper(II) complex with 6-methylpyridine-2-carboxyclic acid: Experimental and computational study on the XRD, FT-IR and UV-Vis spectra, refractive index, band gap and NLO parameters.

PubMed

Altürk, Sümeyye; Avcı, Davut; Başoğlu, Adil; Tamer, Ömer; Atalay, Yusuf; Dege, Necmi

2018-02-05

Crystal structure of the synthesized copper(II) complex with 6-methylpyridine-2-carboxylic acid, [Cu(6-Mepic) 2 ·H 2 O]·H 2 O, was determined by XRD, FT-IR and UV-Vis spectroscopic techniques. Furthermore, the geometry optimization, harmonic vibration frequencies for the Cu(II) complex were carried out by using Density Functional Theory calculations with HSEh1PBE/6-311G(d,p)/LanL2DZ level. Electronic absorption wavelengths were obtained by using TD-DFT/HSEh1PBE/6-311G(d,p)/LanL2DZ level with CPCM model and major contributions were determined via Swizard/Chemissian program. Additionally, the refractive index, linear optical (LO) and non-nonlinear optical (NLO) parameters of the Cu(II) complex were calculated at HSEh1PBE/6-311G(d,p) level. The experimental and computed small energy gap shows the charge transfer in the Cu(II) complex. Finally, the hyperconjugative interactions and intramolecular charge transfer (ICT) were studied by performing of natural bond orbital (NBO) analysis. Copyright © 2017 Elsevier B.V. All rights reserved.

Optical design of a LED searchlight system

NASA Astrophysics Data System (ADS)

Gong, Chen; Xu, Haiping; Liang, Jinhua; Liu, Yunfei; Yuan, Zengquan

2018-01-01

A 1200m visible searchlight system is designed based on photometry and application of geometric optics. To generate intensity distribution of this relatively powerful light beam we propose to use a high power LED and several refractive optical elements, which are composed of two plane-convex lenses and a conventional Fresnel lens. Two plane-convex lenses enable refraction of the side rays from the LED to the front direction which incident on the Fresnel lens. Fresnel lens, in its turn, concentrate the light flux and provide a nearly collimated beam to meet the requirement of forming a well-illuminated area across the road in the far field. Simulation data shows that this searchlight allow generating an appropriate illumination distribution for the long range requirements. A proof-of-concept prototype producing acceptable illuminance is developed.

Brain tumor imaging of rat fresh tissue using terahertz spectroscopy

NASA Astrophysics Data System (ADS)

Yamaguchi, Sayuri; Fukushi, Yasuko; Kubota, Oichi; Itsuji, Takeaki; Ouchi, Toshihiko; Yamamoto, Seiji

2016-07-01

Tumor imaging by terahertz spectroscopy of fresh tissue without dye is demonstrated using samples from a rat glioma model. The complex refractive index spectrum obtained by a reflection terahertz time-domain spectroscopy system can discriminate between normal and tumor tissues. Both the refractive index and absorption coefficient of tumor tissues are higher than those of normal tissues and can be attributed to the higher cell density and water content of the tumor region. The results of this study indicate that terahertz technology is useful for detecting brain tumor tissue.

An original method to determine complex refractive index of liquids by spectroscopic ellipsometry and illustrated applications

NASA Astrophysics Data System (ADS)

Stchakovsky, M.; Battie, Y.; Naciri, A. En

2017-11-01

We present a method to characterize optical properties of liquids by spectroscopic ellipsometry. The experiments use a specific liquid cell that avoids disturbance of waves at air-liquid interface and allows the determination of the real and the imaginary part of the refractive index, with a sensitivity of the latter below 10-4. The method is illustrated by results obtained with a spectroscopic phase modulation ellipsometer on several liquids such as deionised water, microscope oil and protein solution. Comparisons of the method with standard techniques are given.

Anatomy of a metamorphic core complex: seismic refraction/wide-angle reflection profiling in southeastern California and western Arizona

USGS Publications Warehouse

McCarthy, J.; Larkin, S.P.; Fuis, G.S.; Simpson, R.W.; Howard, K.A.

1991-01-01

The metamorphic core complex belt in southeastern California and western Arizona is a NW-SE trending zone of unusually large Tertiary extension and uplift. Midcrustal rocks exposed in this belt raise questions about the crustal thickness, crustal structure, and the tectonic evolution of the region. Three seismic refraction/wide-angle reflection profiles were collected to address these issues. The results presented here, which focus on the Whipple and Buckskin-Rawhide mountains, yield a consistent three-dimensiional image of this part of the metamorphic core complex belt. The final model consists of a thin veneer (<2 km) of upper plate and fractured lower plate rocks (1.5-5.5 km s-1) overlying a fairly homogeneous basement (~6.0 km s-1) and a localized high-velocity (6.4 km s -1) body situated beneath the western Whipple Mountains. A prominent midcrustal reflection is identified beneath the Whipple and Buckskin Rawhide mountains between 10 and 20km depth. -from Authors

EphA2 and Src regulate equatorial cell morphogenesis during lens development

PubMed Central

Cheng, Catherine; Ansari, Moham M.; Cooper, Jonathan A.; Gong, Xiaohua

2013-01-01

High refractive index and transparency of the eye lens require uniformly shaped and precisely aligned lens fiber cells. During lens development, equatorial epithelial cells undergo cell-to-cell alignment to form meridional rows of hexagonal cells. The mechanism that controls this morphogenesis from randomly packed cuboidal epithelial cells to highly organized hexagonal fiber cells remains unknown. In Epha2-/- mouse lenses, equatorial epithelial cells fail to form precisely aligned meridional rows; moreover, the lens fulcrum, where the apical tips of elongating epithelial cells constrict to form an anchor point before fiber cell differentiation and elongation at the equator, is disrupted. Phosphorylated Src-Y424 and cortactin-Y466, actin and EphA2 cluster at the vertices of wild-type hexagonal epithelial cells in organized meridional rows. However, phosphorylated Src and phosphorylated cortactin are not detected in disorganized Epha2-/- cells with altered F-actin distribution. E-cadherin junctions, which are normally located at the basal-lateral ends of equatorial epithelial cells and are diminished in newly differentiating fiber cells, become widely distributed in the apical, lateral and basal sides of epithelial cells and persist in differentiating fiber cells in Epha2-/- lenses. Src-/- equatorial epithelial cells also fail to form precisely aligned meridional rows and lens fulcrum. These results indicate that EphA2/Src signaling is essential for the formation of the lens fulcrum. EphA2 also regulates Src/cortactin/F-actin complexes at the vertices of hexagonal equatorial cells for cell-to-cell alignment. This mechanistic information explains how EphA2 mutations lead to disorganized lens cells that subsequently contribute to altered refractive index and cataracts in humans and mice. PMID:24026120

Twist phase-induced characteristics changes of a radially polarized Gaussian Schell-Model beam in a uniaxial crystal orthogonal to the optical axis

NASA Astrophysics Data System (ADS)

Cao, Pengfei; Fu, Wenyu

2017-10-01

Based on the extended Huygens-Fresnel integral formula and unified theory of coherence and polarization, we obtained the cross-spectral density matrix elements for a radially polarized partially coherent twist (RPPCT) beam in a uniaxial crystal. Moreover, compared with free space, we explore numerically the evolution properties of a RPPCT beam in a uniaxial crystal. The calculation results show that the evolution properties of a RPPCT beam in crystals are substantially different from its properties in free space. These properties in crystals are mainly determined by the twist factor and the ratio of extraordinary index to ordinary refractive index. In a uniaxial crystal, the distribution of the intensity of a RPPCT beam all exhibits non-circular symmetry, and these distributions change with twist factor and the ratio of extraordinary index to ordinary refractive index. The twist factor affects their rotation orientation angles, and the ratio of extraordinary index to ordinary refractive index impacts their twisted levels. This novel characteristics can be used for free-space optical communications, particle manipulation and nonlinear optics, where partially coherent beam with controlled profile and twist factor are required.

Contribution of in situ geophysical methods for the definition of the São Sebastião crater model (Azores)

NASA Astrophysics Data System (ADS)

Lopes, Isabel; Deidda, Gian Piero; Mendes, Manuela; Strobbia, Claudio; Santos, Jaime

2013-11-01

The area located inside the São Sebastião volcanic crater, at the southeast end of Terceira Island (Azores), is characterized by an important amplification of ground motion with respect to the surrounding area, as clearly demonstrated by the spatial distribution of the damage that occurred during the Terceira earthquake (the strongest earthquake felt in the Island during the recent decades - 01/01/1980 - M = 7.2). Geological and geophysical studies have been conducted, to characterize the volcanic crater and understand the different site effects that occurred in the village of São Sebastião. The complexity of the subsurface geology, with intercalations of compact basalt and soft pyroclastic deposits, is associated to extreme vertical and lateral velocity contrasts, and poses a serious challenge to different geophysical characterization methods. The available qualitative model did not allow a complete understanding of the site effects. A new seismic campaign has been designed and acquired, and a single, geologically consistent geophysical model has been generated integrating the existing and new data. The new campaign included two cross-line P-wave seismic refraction profiles, four short SH-wave seismic reflection profiles, and seven multichannel surface wave acquisitions. The integration and joint interpretation of geophysical and geological data allowed mutual validation and confirmation of data processing steps. In particular, the use of refraction, reflection and surface wave techniques allowed facing the complexity of a geology that can pose different challenges to all the methods when used individually: velocity inversions, limited reflectivity, and lateral variations. It is shown how the integration of seismic data from different methods, in the framework of a geological model, allowed the geometrical and dynamic characterization of the site. Correlation with further borehole information, then allowed the definition of a subsoil model for the crater, providing information that allowed a better understanding of the earthquake site effects in the São Sebastião village. The new near-surface geological model includes a lava layer within the soft infill materials of the crater. This new model matches closely with the damage distribution map, and explains the spatial variation of building stock performance in the 1980 earthquake.

Boundary Layer Aerosol Composition over Sierra Nevada Mountains using 9.11- and 10.59-micron CW Lidars and Modeled Backscatter from Size Distribution Data

NASA Technical Reports Server (NTRS)

Cutten, D. R.; Jarzembski, M. A.; Srivastava, V.; Pueschel, R. F.; Howard, S. D.; McCaul, E. W., Jr.

2003-01-01

An inversion technique has been developed to determine volume fractions of an atmospheric aerosol composed primarily of ammonium sulfate and ammonium nitrate and water combined with fixed concentration of elemental and organic carbon. It is based on measured aerosol backscatter obtained with 9.11 - and 10.59-micron wavelength continuous wave CO2 lidars and modeled backscatter from aerosol size distribution data. The technique is demonstrated during a flight of the NASA DC-8 aircraft over the Sierra Nevada Mountain Range, California on 19 September, 1995. Volume fraction of each component and effective complex refractive index of the composite particle were determined assuming an internally mixed composite aerosol model. The volume fractions were also used to re-compute aerosol backscatter, providing good agreement with the lidar-measured data. The robustness of the technique for determining volume fractions was extended with a comparison of calculated 2.1,-micron backscatter from size distribution data with the measured lidar data converted to 2.1,-micron backscatter using an earlier derived algorithm, verifying the algorithm as well as the backscatter calculations.

Ultrahigh refractive index chalcogenide based copolymers for infrared optics (Conference Presentation)

NASA Astrophysics Data System (ADS)

Anderson, Laura E.; Namnabat, Soha; Char, Kookheon; Glass, Richard; Norwood, Robert A.; Pyun, Jeffrey

2016-09-01

Current trends in technology development demand increased miniaturization and higher level integration of electronic and photonic components. Such needs arise in emerging imaging systems, optoelectronic devices, optical interconnects and photonic integrated circuits. Compact, integrated photonics requires high refractive index materials, which primarily comprise crystalline and amorphous semiconductors, as well as chalcogenide glasses, which can possess refractive indices higher than 4 and good infrared transparency. There is currently no high refractive index (n 2 or above) that has the low cost production and ease of processing available in optical polymers. Such polymers would potentially cover applications that are not convenient or possible with crystalline and vitreous semiconductors. Examples of such applications include micro lens arrays for image sensors, optical adhesives for bonding and antireflection coatings, and high contrast optical waveguides. While much of the focus has been in the telecommunications transparency regions, significant new opportunities exist for a polymer which is capable of transmitting efficiently in the MWIR region. While there are polymers that have been synthesized with refractive indices as high as 1.75, these polymers are generally conjugated and incorporate heteroatoms such as sulfur or metals, and generally have complex and expensive syntheses. Here we report on new chalcogenide based copolymers with very high refractive index (n 2) that also have good optical transmission properties in the near-, short- and mid-wave infrared up to 5µm. These polymers are rich in sulfur, have low hydrogen content and were made using inverse vulcanization.

Nonlinear optical coupler using a doped optical waveguide

DOEpatents

Pantell, Richard H.; Sadowski, Robert W.; Digonnet, Michel J. F.; Shaw, Herbert J.

1994-01-01

An optical mode coupling apparatus includes an Erbium-doped optical waveguide in which an optical signal at a signal wavelength propagates in a first spatial propagation mode and a second spatial propagation mode of the waveguide. The optical signal propagating in the waveguide has a beat length. The coupling apparatus includes a pump source of perturbational light signal at a perturbational wavelength that propagates in the waveguide in the first spatial propagation mode. The perturbational signal has a sufficient intensity distribution in the waveguide that it causes a perturbation of the effective refractive index of the first spatial propagation mode of the waveguide in accordance with the optical Kerr effect. The perturbation of the effective refractive index of the first spatial propagation mode of the optical waveguide causes a change in the differential phase delay in the optical signal propagating in the first and second spatial propagation modes. The change in the differential phase delay is detected as a change in the intensity distribution between two lobes of the optical intensity distribution pattern of an output signal. The perturbational light signal can be selectively enabled and disabled to selectively change the intensity distribution in the two lobes of the optical intensity distribution pattern.

Assumption-free estimation of the genetic contribution to refractive error across childhood.

PubMed

Guggenheim, Jeremy A; St Pourcain, Beate; McMahon, George; Timpson, Nicholas J; Evans, David M; Williams, Cathy

2015-01-01

Studies in relatives have generally yielded high heritability estimates for refractive error: twins 75-90%, families 15-70%. However, because related individuals often share a common environment, these estimates are inflated (via misallocation of unique/common environment variance). We calculated a lower-bound heritability estimate for refractive error free from such bias. Between the ages 7 and 15 years, participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) underwent non-cycloplegic autorefraction at regular research clinics. At each age, an estimate of the variance in refractive error explained by single nucleotide polymorphism (SNP) genetic variants was calculated using genome-wide complex trait analysis (GCTA) using high-density genome-wide SNP genotype information (minimum N at each age=3,404). The variance in refractive error explained by the SNPs ("SNP heritability") was stable over childhood: Across age 7-15 years, SNP heritability averaged 0.28 (SE=0.08, p<0.001). The genetic correlation for refractive error between visits varied from 0.77 to 1.00 (all p<0.001) demonstrating that a common set of SNPs was responsible for the genetic contribution to refractive error across this period of childhood. Simulations suggested lack of cycloplegia during autorefraction led to a small underestimation of SNP heritability (adjusted SNP heritability=0.35; SE=0.09). To put these results in context, the variance in refractive error explained (or predicted) by the time participants spent outdoors was <0.005 and by the time spent reading was <0.01, based on a parental questionnaire completed when the child was aged 8-9 years old. Genetic variation captured by common SNPs explained approximately 35% of the variation in refractive error between unrelated subjects. This value sets an upper limit for predicting refractive error using existing SNP genotyping arrays, although higher-density genotyping in larger samples and inclusion of interaction effects is expected to raise this figure toward twin- and family-based heritability estimates. The same SNPs influenced refractive error across much of childhood. Notwithstanding the strong evidence of association between time outdoors and myopia, and time reading and myopia, less than 1% of the variance in myopia at age 15 was explained by crude measures of these two risk factors, indicating that their effects may be limited, at least when averaged over the whole population.

Optical side-effects of fs-laser treatment in refractive surgery investigated by means of a model eye

PubMed Central

Ackermann, Roland; Kammel, Robert; Merker, Marina; Kamm, Andreas; Tünnermann, Andreas; Nolte, Stefan

2013-01-01

Optical side-effects of fs-laser treatment in refractive surgery are investigated by means of a model eye. We show that rainbow glare is the predominant perturbation, which can be avoided by randomly distributing laser spots within the lens. For corneal applications such as fs-LASIK, even a regular grid with spot-to-spot distances of ~3 µm is sufficient to minimize rainbow glare perception. Contrast sensitivity is affected, when the lens is treated with large 3D-patterns. PMID:23413236

Properties of material in the submillimeter wave region (instrumentation and measurement of index of refraction)

NASA Technical Reports Server (NTRS)

Lally, J.; Meister, R.

1983-01-01

The Properties of Materials in the Submillimeter Wave Region study was initiated to instrument a system and to make measurements of the complex index of refraction in the wavelength region between 0.1 to 1.0 millimeters. While refractive index data is available for a number of solids and liquids there still exists a need for an additional systematic study of dielectric properties to add to the existing data, to consider the accuracy of the existing data, and to extend measurements in this wavelength region for other selected mateials. The materials chosen for consideration would be those with useful thermal, mechanical, and electrical characteristics. The data is necessary for development of optical components which, for example, include beamsplitters, attenuators, lenses, grids, all useful for development of instrumentation in this relatively unexploited portion of the spectrum.

Polarization-based index of refraction and reflection angle estimation for remote sensing applications.

PubMed

Thilak, Vimal; Voelz, David G; Creusere, Charles D

2007-10-20

A passive-polarization-based imaging system records the polarization state of light reflected by objects that are illuminated with an unpolarized and generally uncontrolled source. Such systems can be useful in many remote sensing applications including target detection, object segmentation, and material classification. We present a method to jointly estimate the complex index of refraction and the reflection angle (reflected zenith angle) of a target from multiple measurements collected by a passive polarimeter. An expression for the degree of polarization is derived from the microfacet polarimetric bidirectional reflectance model for the case of scattering in the plane of incidence. Using this expression, we develop a nonlinear least-squares estimation algorithm for extracting an apparent index of refraction and the reflection angle from a set of polarization measurements collected from multiple source positions. Computer simulation results show that the estimation accuracy generally improves with an increasing number of source position measurements. Laboratory results indicate that the proposed method is effective for recovering the reflection angle and that the estimated index of refraction provides a feature vector that is robust to the reflection angle.

Polarization-based index of refraction and reflection angle estimation for remote sensing applications

NASA Astrophysics Data System (ADS)

Thilak, Vimal; Voelz, David G.; Creusere, Charles D.

2007-10-01

A passive-polarization-based imaging system records the polarization state of light reflected by objects that are illuminated with an unpolarized and generally uncontrolled source. Such systems can be useful in many remote sensing applications including target detection, object segmentation, and material classification. We present a method to jointly estimate the complex index of refraction and the reflection angle (reflected zenith angle) of a target from multiple measurements collected by a passive polarimeter. An expression for the degree of polarization is derived from the microfacet polarimetric bidirectional reflectance model for the case of scattering in the plane of incidence. Using this expression, we develop a nonlinear least-squares estimation algorithm for extracting an apparent index of refraction and the reflection angle from a set of polarization measurements collected from multiple source positions. Computer simulation results show that the estimation accuracy generally improves with an increasing number of source position measurements. Laboratory results indicate that the proposed method is effective for recovering the reflection angle and that the estimated index of refraction provides a feature vector that is robust to the reflection angle.

Determination of migration of ion-implanted Ar and Zn in silica by backscattering spectrometry

NASA Astrophysics Data System (ADS)

Szilágyi, E.; Bányász, I.; Kótai, E.; Németh, A.; Major, C.; Fried, M.; Battistig, G.

2015-03-01

It is well known that the refractive indices of lots of materials can be modified by ion implantation, which is important for waveguide fabrication. In this work the effect of Ar and Zn ion implantation on silica layers was investigated by Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE). Silica layers produced by chemical vapour deposition technique on single crystal silicon wafers were implanted by Ar and Zn ions with a fluence of 1-2 ×1016 Ar/cm2 and 2.5 ×1016 Zn/cm2, respectively. The refractive indices of the implanted silica layers before and after annealing at 300°C and 600°C were determined by SE. The migration of the implanted element was studied by real-time RBS up to 500°C. It was found that the implanted Ar escapes from the sample at 300°C. Although the refractive indices of the Ar-implanted silica layers were increased compared to the as-grown samples, after the annealing this increase in the refractive indices vanished. In case of the Zn-implanted silica layer both the distribution of the Zn and the change in the refractive indices were found to be stable. Zn implantation seems to be an ideal choice for producing waveguides.

Ozone: Unresolved discrepancies for dipole oscillator strength distributions, dipole sums, and van der Waals coefficients

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Thakkar, Ajit J.

2011-08-01

Dipole oscillator strength distributions (DOSDs) for ozone are constructed from experimental photoabsorption cross-sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule, the high-energy behavior of the dipole-oscillator-strength density, and molar refractivity data. A lack of photoabsorption data in the intermediate energy region from 24 to 524 eV necessitates the use of a mixture rule in that region. For this purpose, a DOSD for O2 is constructed first. The dipole properties for O2 are essentially the same as those obtained in earlier work even though most of the input data is from more recent experiments. A discrepancy is found between the refractivity data and photoabsorption data in the 10-20.6 eV range for ozone. A reliable ozone DOSD of the sort obtained for many other species remains out of reach. However, it is suggested that the true dipole properties of ozone lie between those predicted by two distributions that we present.

Infrared complex refractive index of astrophysical ices exposed to cosmic rays simulated in the laboratory

NASA Astrophysics Data System (ADS)

Rocha, W. R. M.; Pilling, S.; de Barros, A. L. F.; Andrade, D. P. P.; Rothard, H.; Boduch, P.

2017-01-01

In the dense and cold regions of the interstellar medium, molecules can be adsorbed on to dust grains to form ice mantles. Once formed, these can be processed by ionizing radiation coming from the stellar or interstellar medium, leading to the formation of several new molecules in the ice. Among the different types of ionizing radiation, cosmic rays play an important role in solid-phase chemistry because of the large amount of energy deposited in the ices. The physicochemical changes induced by the energetic processing of astrophysical ices are recorded in a intrinsic parameter of the matter called the complex refractive index. In this paper, for the first time, we present a catalogue containing 39 complex refractive indices (n, k) in the infrared from 5000 to 600 cm-1 (2.0-16.6 μm) for 13 different water-containing ices processed in the laboratory by cosmic ray analogues. The calculation was performed using the NKABS - an acronym of the determination of N and K from absorbance data - code,which employs the Lambert-Beer and Kramers-Kronig equations to calculate the values of n and k. The results are also available at the following web site: http://www1.univap.br/gaa/nkabs-database/data.htm. As a test case, H2O:NH3:CO2:CH4 ice was employed in a radiative transfer simulation of a protoplanetary disc to show that these data are indispensable to reproduce the spectrum of ices containing young stellar objects.

Sourcebook of locations of geophysical surveys in tunnels and horizontal holes, including results of seismic refraction surveys, Rainier Mesa, Aqueduct Mesa, and Area 16, Nevada Test Site

USGS Publications Warehouse

Carroll, R.D.; Kibler, J.E.

1983-01-01

Seismic refraction surveys have been obtained sporadically in tunnels in zeolitized tuff at the Nevada Test Site since the late 1950's. Commencing in 1967 and continuing to date (1982), .extensive measurements of shear- and compressional-wave velocities have been made in five tunnel complexes in Rainier and Aqueduct Mesas and in one tunnel complex in Shoshone Mountain. The results of these surveys to 1980 are compiled in this report. In addition, extensive horizontal drilling was initiated in 1967 in connection with geologic exploration in these tunnel complexes for sites for nuclear weapons tests. Seismic and electrical surveys were conducted in the majority of these holes. The type and location of these tunnel and borehole surveys are indexed in this report. Synthesis of the seismic refraction data indicates a mean compressional-wave velocity near the nuclear device point (WP) of 23 tunnel events of 2,430 m/s (7,970 f/s) with a range of 1,846-2,753 m/s (6,060-9,030 f/s). The mean shear-wave velocity of 17 tunnel events is 1,276 m/s (4,190 f/s) with a range of 1,140-1,392 m/s (3,740-4,570 f/s). Experience indicates that these velocity variations are due chiefly to the extent of fracturing and (or) the presence of partially saturated rock in the region of the survey.

Modeling liquid organic thin films on substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernacki, Bruce E.; Johnson, Timothy J.; Myers, Tanya L.

We present the rationale, methods, and results of modeling of thin film organic liquids on various substrates. These liquids may coat surfaces (substrates) either as a result of their production, dispersal via aerosols or spills. Identification of unknown coated surfaces using either reflectance or emittance spectroscopy cannot be accomplished simply through reference to reflectance signature libraries since neither the thickness of the liquid layer nor the substrate type is known beforehand and both contribute to the signature. Liquid spectral libraries offer the complex index of refraction (n,k) as a function of wavelength which by itself is useful only for thickmore » (bulk) liquid layers via computation of reflectance and transmittance coefficients using the Fresnel equations. Thin liquid layers both reflect and refract incident light in combination with reflectance from the substrate. We show modeling of various organic liquids on substrates using commercial thin film design and modeling software, as well as Monte Carlo ray tracing software to demonstrate the variety of potential signatures encountered that depend on the thickness of the liquid layer as well as the characteristics of the substrate (metal or dielectric). These substrates give rise to transflectance behavior, while many dielectric substrates have rich absorption features that provide complex signatures that combine attributes of both the liquid and the substrate. Knowledge of the complex index of refraction of both target liquids and substrates is essential in order to synthesize spectra necessary in the application of target identification algorithms.« less

Manipulation of acoustic wavefront by gradient metasurface based on Helmholtz Resonators.

PubMed

Lan, Jun; Li, Yifeng; Xu, Yue; Liu, Xiaozhou

2017-09-06

We designed a gradient acoustic metasurface to manipulate acoustic wavefront freely. The broad bandwidth and high efficiency transmission are achieved by the acoustic metasurface which is constructed with a series of unit cells to provide desired discrete acoustic velocity distribution. Each unit cell is composed of a decorated metal plate with four periodically arrayed Helmholtz resonators (HRs) and a single slit. The design employs a gradient velocity to redirect refracted wave and the impedance matching between the metasurface and the background medium can be realized by adjusting the slit width of unit cell. The theoretical and numerical results show that some excellent wavefront manipulations are demonstrated by anomalous refraction, non-diffracting Bessel beam, sub-wavelength flat focusing, and effective tunable acoustic negative refraction. Our designed structure may offer potential applications for the imaging system, beam steering and acoustic lens.

Study on the transverse chromatic aberration of the individual eye model after LASIK refractive surgery

NASA Astrophysics Data System (ADS)

Zhang, Mei; Wang, Zhao-Qi; Wang, Yan; Zuo, Tong

2010-10-01

The aim of this research is to study the properties of the transverse chromatic aberration (TCA) after the LASIK refractive surgery based on the individual eye model involving the angle between visual axis and optical axis. According to the measurements of the corneal surfaces, the optical axis lengths and the wavefront aberrations, the individual eye models before and after LASIK refractive surgery are constructed for 15 eyes by using ZEMAX optic design software, while the angle between the visual axis and optical axis is calculated from the data of the anterior corneal surface. The constructed eye models are then used to investigate the variation of the TCA after the surgery. The statistical distributions of the magnitude of the foveal TCA for 15 eyes over the visible spectrum are provided. Finally, we investigate the influence of the TCA on the visual quality and compare the results with previous research. The TCA is an indispensable criterion to evaluate the performance of the refractive surgery. This research is very meaningful for the studies of not only foveal vision but also the peripheral vision.

Optimization of refractive liquid crystal lenses using an efficient multigrid simulation.

PubMed

Milton, Harry; Brimicombe, Paul; Morgan, Philip; Gleeson, Helen; Clamp, John

2012-05-07

A multigrid computational model has been developed to assess the performance of refractive liquid crystal lenses, which is up to 40 times faster than previous techniques. Using this model, the optimum geometries producing an ideal parabolic voltage distribution were deduced for refractive liquid crystal lenses with diameters from 1 to 9 mm. The ratio of insulation thickness to lens diameter was determined to be 1:2 for small diameter lenses, tending to 1:3 for larger lenses. The model is used to propose a new method of lens operation with lower operating voltages needed to induce specific optical powers. The operating voltages are calculated for the induction of optical powers between + 1.00 D and + 3.00 D in a 3 mm diameter lens, with the speed of the simulation facilitating the optimization of the refractive index profile. We demonstrate that the relationship between additional applied voltage and optical power is approximately linear for optical powers under + 3.00 D. The versatility of the computational simulation has also been demonstrated by modeling of in-plane electrode liquid crystal devices.

Refractive ocular conditions and reasons for spectacles renewal in a resource-limited economy

PubMed Central

2010-01-01

Background Although a leading cause of visual impairment and a treatable cause of blindness globally, the pattern of refractive errors in many populations is unknown. This study determined the pattern of refractive ocular conditions, reasons for spectacles renewal and the effect of correction on refractive errors in a resource-limited community. Methods A retrospective review of case records of 1,413 consecutive patients seen in a private optometry practice, Nigeria between January 2006 and July 2007. Results A total number of 1,216 (86.1%) patients comprising of (486, 40%) males and (730, 60%) females with a mean age of 41.02 years SD 14.19 were analyzed. The age distribution peaked at peri-adolescent and the middle age years. The main ocular complaints were spectacles loss and discomfort (412, 33.9%), blurred near vision (399, 32.8%) and asthenopia (255, 20.9%). The mean duration of ocular symptoms before consultation was 2.05 years SD 1.92. The most common refractive errors include presbyopia (431, 35.3%), hyperopic astigmatism (240, 19.7%) and presbyopia with hyperopia (276, 22.7%). Only (59, 4.9%) had myopia. Following correction, there were reductions in magnitudes of the blind (VA<3/60) and visually impaired (VA<6/18-3/60) patients by (18, 58.1%) and (89, 81.7%) respectively. The main reasons for renewal of spectacles were broken lenses/frame/scratched lenses/lenses' falling off (47, 63.4%). Conclusions Adequate correction of refractive errors reduces visual impairment and avoidable blindness and to achieve optimal control of refractive errors in the community, services should be targeted at individuals in the peri-adolescent and the middle age years. PMID:20459676

Refractive ocular conditions and reasons for spectacles renewal in a resource-limited economy.

PubMed

Ayanniyi, Abdulkabir A; Folorunso, Francisca N; Adepoju, Feyisayo G

2010-05-07

Although a leading cause of visual impairment and a treatable cause of blindness globally, the pattern of refractive errors in many populations is unknown. This study determined the pattern of refractive ocular conditions, reasons for spectacles renewal and the effect of correction on refractive errors in a resource-limited community. A retrospective review of case records of 1,413 consecutive patients seen in a private optometry practice, Nigeria between January 2006 and July 2007. A total number of 1,216 (86.1%) patients comprising of (486, 40%) males and (730, 60%) females with a mean age of 41.02 years SD 14.19 were analyzed. The age distribution peaked at peri-adolescent and the middle age years. The main ocular complaints were spectacles loss and discomfort (412, 33.9%), blurred near vision (399, 32.8%) and asthenopia (255, 20.9%). The mean duration of ocular symptoms before consultation was 2.05 years SD 1.92. The most common refractive errors include presbyopia (431, 35.3%), hyperopic astigmatism (240, 19.7%) and presbyopia with hyperopia (276, 22.7%). Only (59, 4.9%) had myopia. Following correction, there were reductions in magnitudes of the blind (VA<3/60) and visually impaired (VA<6/18-3/60) patients by (18, 58.1%) and (89, 81.7%) respectively. The main reasons for renewal of spectacles were broken lenses/frame/scratched lenses/lenses' falling off (47, 63.4%). Adequate correction of refractive errors reduces visual impairment and avoidable blindness and to achieve optimal control of refractive errors in the community, services should be targeted at individuals in the peri-adolescent and the middle age years.

Low dose reconstruction algorithm for differential phase contrast imaging.

PubMed

Wang, Zhentian; Huang, Zhifeng; Zhang, Li; Chen, Zhiqiang; Kang, Kejun; Yin, Hongxia; Wang, Zhenchang; Marco, Stampanoni

2011-01-01

Differential phase contrast imaging computed tomography (DPCI-CT) is a novel x-ray inspection method to reconstruct the distribution of refraction index rather than the attenuation coefficient in weakly absorbing samples. In this paper, we propose an iterative reconstruction algorithm for DPCI-CT which benefits from the new compressed sensing theory. We first realize a differential algebraic reconstruction technique (DART) by discretizing the projection process of the differential phase contrast imaging into a linear partial derivative matrix. In this way the compressed sensing reconstruction problem of DPCI reconstruction can be transformed to a resolved problem in the transmission imaging CT. Our algorithm has the potential to reconstruct the refraction index distribution of the sample from highly undersampled projection data. Thus it can significantly reduce the dose and inspection time. The proposed algorithm has been validated by numerical simulations and actual experiments.

Optical generation of millimeter-wave pulses using a fiber Bragg grating in a fiber-optics system.

PubMed

Ye, Qing; Qu, Ronghui; Fang, Zujie

2007-04-10

A scheme is proposed to transform an optical pulse into a millimeter-wave frequency modulation pulse by using a weak fiber Bragg grating (FBG) in a fiber-optics system. The Fourier transformation method is used to obtain the required spectrum response function of the FBG for the Gaussian pulse, soliton pulse, and Lorenz shape pulse. On the condition of the first-order Born approximation of the weak fiber grating, the relation of the refractive index distribution and the spectrum response function of the FBG satisfies the Fourier transformation, and the corresponding refractive index distribution forms are obtained for single-frequency modulation and linear-frequency modulation millimeter-wave pulse generation. The performances of the designed fiber gratings are also studied by a numerical simulation method for a supershort pulse transmission.

Beam shaping optics to enhance performance of interferometry techniques in grating manufacture

NASA Astrophysics Data System (ADS)

Laskin, Alexander; Laskin, Vadim; Ostrun, Aleksei

2018-02-01

Improving of industrial holographic and interferometry techniques is of great importance in interference lithography, computer-generated holography, holographic data storage, interferometry recording of Bragg gratings as well as gratings of various types in semiconductor industry. Performance of mentioned techniques is essentially enhanced by providing a light beam with flat phase front and flat-top irradiance distribution. Therefore, transformation of Gaussian distribution of a TEM00 laser to flat-top (top hat, uniform) distribution is an important optical task. There are different refractive and diffractive beam shaping approaches used in laser industrial and scientific applications, but only few of them are capable to fulfil the optimum conditions for beam quality demanding holography and interferometry. As a solution it is suggested to apply refractive field mapping beam shaping optics πShaper, which operational principle presumes almost lossless transformation of Gaussian to flat-top beam with flatness of output wavefront, conserving of beam consistency, providing collimated low divergent output beam, high transmittance, extended depth of field, negligible wave aberration, and achromatic design provides capability to work with several lasers with different wavelengths simultaneously. High optical quality of resulting flat-top beam allows applying additional optical components to build various imaging optical systems for variation of beam size and shape to fulfil requirements of a particular application. This paper will describe design basics of refractive beam shapers and optical layouts of their applying in holography and laser interference lithography. Examples of real implementations and experimental results will be presented as well.

Simultaneous Retrieval of Effective Refractive Index and Density from Size Distribution and Light Scattering Data: Weakly-Absorbing Aerosol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kassianov, Evgueni I.; Barnard, James C.; Pekour, Mikhail S.

2014-10-01

We propose here a novel approach for retrieving in parallel the effective density and real refractive index of weakly absorbing aerosol from optical and size distribution measurements. Here we define “weakly absorbing” as aerosol single-scattering albedos that exceed 0.95 at 0.5 um.The required optical measurements are the scattering coefficient and the hemispheric backscatter fraction, obtained in this work from an integrating nephelometer. The required size spectra come from a Scanning Mobility Particle Sizer and an Aerodynamic Particle Sizer. The performance of this approach is first evaluated using a sensitivity study with synthetically generated but measurement-related inputs. The sensitivity study revealsmore » that the proposed approach is robust to random noise; additionally the uncertainties of the retrieval are almost linearly proportional to the measurement errors, and these uncertainties are smaller for the real refractive index than for the effective density. Next, actual measurements are used to evaluate our approach. These measurements include the optical, microphysical, and chemical properties of weakly absorbing aerosol which are representative of a variety of coastal summertime conditions observed during the Two-Column Aerosol Project (TCAP; http://campaign.arm.gov/tcap/). The evaluation includes calculating the root mean square error (RMSE) between the aerosol characteristics retrieved by our approach, and the same quantities calculated using the conventional volume mixing rule for chemical constituents. For dry conditions (defined in this work as relative humidity less than 55%) and sub-micron particles, a very good (RMSE~3%) and reasonable (RMSE~28%) agreement is obtained for the retrieved real refractive index (1.49±0.02) and effective density (1.68±0.21), respectively. Our approach permits discrimination between the retrieved aerosol characteristics of sub-micron and sub-10micron particles. The evaluation results also reveal that the retrieved density and refractive index tend to decrease with an increase of the relative humidity.« less

New vistas in refractive laser beam shaping with an analytic design approach

NASA Astrophysics Data System (ADS)

Duerr, Fabian; Thienpont, Hugo

2014-05-01

Many commercial, medical and scientific applications of the laser have been developed since its invention. Some of these applications require a specific beam irradiance distribution to ensure optimal performance. Often, it is possible to apply geometrical methods to design laser beam shapers. This common design approach is based on the ray mapping between the input plane and the output beam. Geometric ray mapping designs with two plano-aspheric lenses have been thoroughly studied in the past. Even though analytic expressions for various ray mapping functions do exist, the surface profiles of the lenses are still calculated numerically. In this work, we present an alternative novel design approach that allows direct calculation of the rotational symmetric lens profiles described by analytic functions. Starting from the example of a basic beam expander, a set of functional differential equations is derived from Fermat's principle. This formalism allows calculating the exact lens profiles described by Taylor series coefficients up to very high orders. To demonstrate the versatility of this new approach, two further cases are solved: a Gaussian to at-top irradiance beam shaping system, and a beam shaping system that generates a more complex dark-hollow Gaussian (donut-like) irradiance profile with zero intensity in the on-axis region. The presented ray tracing results confirm the high accuracy of all calculated solutions and indicate the potential of this design approach for refractive beam shaping applications.

Full Modeling of High-Intensity Focused Ultrasound and Thermal Heating in the Kidney Using Realistic Patient Models.

PubMed

Suomi, Visa; Jaros, Jiri; Treeby, Bradley; Cleveland, Robin O

2018-05-01

High-intensity focused ultrasound (HIFU) therapy can be used for noninvasive treatment of kidney (renal) cancer, but the clinical outcomes have been variable. In this study, the efficacy of renal HIFU therapy was studied using nonlinear acoustic and thermal simulations in three patients. The acoustic simulations were conducted with and without refraction in order to investigate its effect on the shape, size, and pressure distribution at the focus. The values for the attenuation, sound speed, perfusion, and thermal conductivity of the kidney were varied over the reported ranges to determine the effect of variability on heating. Furthermore, the phase aberration was studied in order to quantify the underlying phase shifts using a second-order polynomial function. The ultrasound field intensity was found to drop on average 11.1 dB with refraction and 6.4 dB without refraction. Reflection at tissue interfaces was found to result in a loss less than 0.1 dB. Focal point splitting due to refraction significantly reduced the heating efficacy. Of all the tissue parameters, perfusion was found to affect the heating the most. Small changes in temperature were seen with varying attenuation and thermal conductivity, but no visible changes were present with sound speed variations. The aberration study revealed an underlying trend in the spatial distribution of the phase shifts. The results show that the efficacy of HIFU therapy in the kidney could be improved with aberration correction. A method is proposed by which patient specific pretreatment calculations could be used to overcome the aberration and therefore make ultrasound treatment possible.

Isosbestics in Infrared Aerosol Spectra: Proposed Applications for Remote Sensing.

DTIC Science & Technology

1989-04-01

droplet solutions and chemical reactions if the complex indices of refraction are known. The technique seems most applicable in the Rayleigh regime. Remote ... sensing , Isosbestics, Infrared, Infrared spectra, Atmosphere, Water, Aerosols, Rayleigh regime.

Modification of Kirchhoff migration with variable sound speed and attenuation for acoustic imaging of media and application to tomographic imaging of the breast

PubMed Central

Schmidt, Steven; Duric, Nebojsa; Li, Cuiping; Roy, Olivier; Huang, Zhi-Feng

2011-01-01

Purpose: To explore the feasibility of improving cross-sectional reflection imaging of the breast using refractive and attenuation corrections derived from ultrasound tomography data. Methods: The authors have adapted the planar Kirchhoff migration method, commonly used in geophysics to reconstruct reflection images, for use in ultrasound tomography imaging of the breast. Furthermore, the authors extended this method to allow for refractive and attenuative corrections. Using clinical data obtained with a breast imaging prototype, the authors applied this method to generate cross-sectional reflection images of the breast that were corrected using known distributions of sound speed and attenuation obtained from the same data. Results: A comparison of images reconstructed with and without the corrections showed varying degrees of improvement. The sound speed correction resulted in sharpening of detail, while the attenuation correction reduced the central darkening caused by path length dependent losses. The improvements appeared to be greatest when dense tissue was involved and the least for fatty tissue. These results are consistent with the expectation that denser tissues lead to both greater refractive effects and greater attenuation. Conclusions: Although conventional ultrasound techniques use time-gain control to correct for attenuation gradients, these corrections lead to artifacts because the true attenuation distribution is not known. The use of constant sound speed leads to additional artifacts that arise from not knowing the sound speed distribution. The authors show that in the context of ultrasound tomography, it is possible to construct reflection images of the breast that correct for inhomogeneous distributions of both sound speed and attenuation. PMID:21452737

The association between refractive cutoffs for spectacle provision and visual improvement among school-aged children in South Africa.

PubMed

Congdon, Nathan G; Patel, Nita; Esteso, Paul; Chikwembani, Florence; Webber, Fiona; Msithini, Robert Bongi; Ratcliffe, Amy

2008-01-01

To evaluate different refractive cutoffs for spectacle provision with regards to their impact on visual improvement and spectacle compliance. Prospective study of visual improvement and spectacle compliance. South African school children aged 6-19 years receiving free spectacles in a programme supported by Helen Keller International. Refractive error, age, gender, urban versus rural residence, presenting and best-corrected vision were recorded for participants. Spectacle wear was observed directly at an unannounced follow-up examination 4-11 months after initial provision of spectacles. The association between five proposed refractive cutoff protocols and visual improvement and spectacle compliance were examined in separate multivariate models. Refractive cutoffs for spectacle distribution which would effectively identify children with improved vision, and those more likely to comply with spectacle wear. Among 8520 children screened, 810 (9.5%) received spectacles, of whom 636 (79%) were aged 10-14 years, 530 (65%) were girls, 324 (40%) had vision improvement > or = 3 lines, and 483 (60%) were examined 6.4+/-1.5 (range 4.6 to 10.9) months after spectacle dispensing. Among examined children, 149 (31%) were wearing or carrying their glasses. Children meeting cutoffs < or = -0.75 D of myopia, > or = +1.00 D of hyperopia and > or = +0.75 D of astigmatism had significantly greater improvement in vision than children failing to meet these criteria, when adjusting for age, gender and urban versus rural residence. None of the proposed refractive protocols discriminated between children wearing and not wearing spectacles. Presenting vision and improvement in vision were unassociated with subsequent spectacle wear, but girls (p < or = 0.0006 for all models) were more likely to be wearing glasses than were boys. To the best of our knowledge, this is the first suggested refractive cutoff for glasses dispensing validated with respect to key programme outcomes. The lack of association between spectacle retention and either refractive error or vision may have been due to the relatively modest degree of refractive error in this African population.

Polarization manipulation in single refractive prism based holography lithography

NASA Astrophysics Data System (ADS)

Xiong, Wenjie; Xu, Yi; Xiao, Yujian; Lv, Xiaoxu; Wu, Lijun

2015-01-01

We propose theoretically and demonstrate experimentally a simple but effective strategy for polarization manipulation in single refractive prism based holographic lithography. By tuning the polarization of a single laser beam, we can obtain the pill shape interference pattern with a high-contrast where a complex optical setup and multiple polarizers are needed in the conventional holography lithography. Fabrication of pill shape two-dimensional polymer photonic crystals using one beam and one shoot holography lithography is shown as an example to support our theoretical results. This integrated polarization manipulation technique can release the crucial stability restrictions imposed on the multiple beams holography lithography.

Refractive index and solubility control of para-cymene solutions for index-matched fluid-structure interaction studies

NASA Astrophysics Data System (ADS)

Fort, Charles; Fu, Christopher D.; Weichselbaum, Noah A.; Bardet, Philippe M.

2015-12-01

To deploy optical diagnostics such as particle image velocimetry or planar laser-induced fluorescence (PLIF) in complex geometries, it is beneficial to use index-matched facilities. A binary mixture of para-cymene and cinnamaldehyde provides a viable option for matching the refractive index of acrylic, a common material for scaled models and test sections. This fluid is particularly appropriate for large-scale facilities and when a low-density and low-viscosity fluid is sought, such as in fluid-structure interaction studies. This binary solution has relatively low kinematic viscosity and density; its use enables the experimentalist to select operating temperature and to increase fluorescence signal in PLIF experiments. Measurements of spectral and temperature dependence of refractive index, density, and kinematic viscosity are reported. The effect of the binary mixture on solubility control of Rhodamine 6G is also characterized.

On the volume-dependence of the index of refraction from the viewpoint of the complex dielectric function and the Kramers-Kronig relation.

PubMed

Rocquefelte, Xavier; Jobic, Stéphane; Whangbo, Myung-Hwan

2006-02-16

How indices of refraction n(omega) of insulating solids are affected by the volume dilution of an optical entity and the mixing of different, noninteracting simple solid components was examined on the basis of the dielectric function epsilon(1)(omega) + iepsilon(2)(omega). For closely related insulating solids with an identical composition and the formula unit volume V, the relation [epsilon(1)(omega) - 1]V = constant was found by combining the relation epsilon(2)(omega)V = constant with the Kramers-Kronig relation. This relation becomes [n(2)(omega) - 1]V = constant for the index of refraction n(omega) determined for the incident light with energy less than the band gap (i.e., h omega < E(g)). For a narrow range of change in the formula unit volume, the latter relation is well approximated by a linear relation between n and 1/V.

Cladding-like waveguide fabricated by cooperation of ultrafast laser writing and ion irradiation: characterization and laser generation.

PubMed

Lv, Jinman; Shang, Zhen; Tan, Yang; Vázquez de Aldana, Javier Rodríguez; Chen, Feng

2017-08-07

We report the surface cladding-like waveguide fabricated by the cooperation of the ultrafast laser writing and the ion irradiation. The ultrafast laser writes tracks near the surface of the Nd:YAG crystal, constructing a semi-circle columnar structure with a decreased refractive index of - 0.00208. Then, the Nd:YAG crystal is irradiated by the Carbon ion beam, forming an enhanced-well in the semi-circle columnar with an increased refractive index of + 0.0024. Tracks and the enhanced-well consisted a surface cladding-like waveguide. Utilizing this cladding-like waveguide as the gain medium for the waveguide lasing, optimized characterizations were observed compared with the monolayer waveguide. This work demonstrates the refractive index of the Nd:YAG crystal can be well tailored by the cooperation of the ultrafast laser writing and the ion irradiation, which provides an convenient way to fabricate the complex and multilayered photonics devices.

Swept-frequency feedback interferometry using terahertz frequency QCLs: a method for imaging and materials analysis.

PubMed

Rakić, Aleksandar D; Taimre, Thomas; Bertling, Karl; Lim, Yah Leng; Dean, Paul; Indjin, Dragan; Ikonić, Zoran; Harrison, Paul; Valavanis, Alexander; Khanna, Suraj P; Lachab, Mohammad; Wilson, Stephen J; Linfield, Edmund H; Davies, A Giles

2013-09-23

The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser.

Low cost ellipsometer using a standard commercial polarimeter

NASA Astrophysics Data System (ADS)

Velosa, F.; Abreu, M.

2017-08-01

Ellipsometry is an optical technique to characterize materials or phenomena that occurs at an interface or thin film between two different media. In this paper, we present an experimental low-cost version of a photometric ellipsometer, assembled with commonly found material at every Optics laboratory. The polarization parameters measurement was performed using a Thorlabs PAX5710 polarimeter. The uncertainty computed using the Guide to the Expression of Uncertainty in Measurement (GUM) procedures. With the assembled ellipsometer we were able to measure the thickness of a 10 nm thick SiO2 thin film deposited upon Si, and the complex refractive index of Gold and Tantalum samples. The SiO2 thickness we achieved had an experimental deviation of 4.5% with 2.00 nm uncertainty. The value complex refractive index of Gold and Tantalum measured agrees with the different values found in several references. The uncertainty values were found to be mostly limited by the polarimeter's uncertainty.

Real refractive indices and formation yields of secondary organic aerosol generated from photooxidation of limonene and α-pinene: the effect of the HC/NO(x) ratio.

PubMed

Kim, Hwajin; Barkey, Brian; Paulson, Suzanne E

2012-06-21

The refractive index is an important property affecting aerosol optical properties, which in turn help determine the aerosol direct effect and satellite retrieval results. Here, we investigate the real refractive indices (m(r)) of secondary organic aerosols (SOA) generated from the photooxidation of limonene and α-pinene with different HC/NO(x) ratios. Refractive indices were obtained from polar nephelometer data using parallel and perpendicular polarized 532 nm light combined with measured size distributions, and retrievals were performed using a genetic algorithm and Mie-Lorenz scattering theory. The absolute error associated with the m(r) retrieval is ±0.03, and reliable retrievals are possible for mass concentrations above 5-20 μg/m(3) depending on particle size. The limonene SOA data suggest the most important factor controlling the refractive index is the HC/NO(x) ratio; the refractive index is much less sensitive to the aerosol age or mass concentration. The refractive index ranges from about 1.34 to 1.56 for limonene and from 1.36 to 1.52 for α-pinene, and generally decreases as the HC/NO(x) ratio increases. Especially for limonene, the particle diameter is also inversely related to the HC/NO(x) ratio; the final size mode increases from 220 to 330 nm as the HC/NO(x) ratio decreases from 33 to 6. In an effort to explore the ability of models from the literature to explain the observed refractive indices, a recent limonene oxidation mechanism was combined with SOA partitioning and a structure-property relationship for estimating refractive indices of condensing species. The resulting refractive indices fell in a much narrower range (1.475 ± 0.02) of m(r) than observed experimentally. We hypothesize the experimentally observed high m(r) values are due to oligomerization and the low values to water uptake, small soluble molecules such as glyoxal and other factors, each of which is not included in the oxidation mechanism. Aerosol formation yields were measured over the mass concentration range from 6 to ∼150 μg/m(3), over which they increased steadily, and were higher for high HC/NO(x) ratio experiments.

Wet refractivity tomography with an improved Kalman-Filter method

NASA Astrophysics Data System (ADS)

Cao, Yunchang; Chen, Yongqi; Li, Pingwha

2006-10-01

An improved retrieval method, which uses the solution with a Gaussian constraint as the initial state variables for the Kalman Filtering (KF) method, was developed to retrieve the wet refractivity profiles from slant wet delays (SWD) extracted by the double-differenced (DD) GPS method. The accuracy of the GPS-derived SWDs is also tested in this study against the measurements of a water vapor radiometer (WVR) and a weather model. It is concluded that the GPS-derived SWDs have similar accuracy to those measured with WVR and are much higher in quality than those derived from the weather model used. The developed method is used to retrieve the 3D wet refractivity distribution in the Hong Kong region. The retrieved profiles agree well with the radiosonde observations, with a difference of about 4 mm km-1 in the low levels. The accurate profiles obtained with this method are applicable in a number of meteorological applications.

Theoretical model for a thin cylindrical film optical fiber fluorosensor

NASA Technical Reports Server (NTRS)

Egalon, Claudio O.; Rogowski, Robert S.

1992-01-01

The analytical treatment of power efficiency (P(eff) is undertaken for the case of a positively guiding optical fiber with a thin-film source distributed in the core-cladding interface. The approach adopts the exact solution of the cylindrical optical fiber with an infinite cladding to account for differences between the indices of refraction of the core and the cladding. The excitation of low-loss leaky modes by the cladding is ignored, and only the injection by the evanescent field is considered. The formulas permit the analysis of the power-injection efficiency of fibers with arbitrary differences in indices of refraction. P(eff) does not always increase with V number, but rather varies slightly with wavelength and fiber-core radius and varies significantly with the difference in the indices of refraction. The theoretical results of the work are of interest for designing an atomic-O chemical sensor based on evanescent-wave coupling.

Sci—Fri PM: Dosimetry—01: Radiation-induced refraction artefacts in the optical CT readout of polymer gel dosimeters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, Warren G; Jirasek, Andrew; Wells, Derek M

2014-08-15

Polymer gel dosimeters (PGDs) are a desirable tool for the verification of advanced radiotherapy treatments. Fully 3D, deformable, and tissue-equivalent, the PGD polymerizes wherever it absorbs dose. To measure the dose absorbed by a PGD, optical computed tomography (CT) can be used to evaluate, in full 3D, the opacity distribution that coincides with polymerization. In addition to an increase in opacity with dose, an increase in refractive index (RI) is also known to occur in irradiated polymer gels. The increase in RI is slight and was previously assumed insignificant. This work reveals the effects that radiation-induced RI changes can havemore » on the optical CT readout of PGDs. A fan-beam optical CT scanner was used to image a cylindrical PGD irradiated by a pair of 3×3 cm{sup 2}, 6 MV photon beams in an orthogonal arrangement. Investigative scans were performed to evaluate refraction errors occurring: i) within the plane, and ii) out of the plane of the fan-beam. In-plane refraction was shown to cause distinct streaking artefacts along dose gradients (i.e. RI gradients) due to higher intensity rays being refracted into more opaque regions. Out-of-plane refraction was shown to produce severe, widespread artefacts due to rays missing the detector array. An iterative Savitzky-Golay filtering technique was developed to reduce both types of artefacts by specifically targeting structured errors in sinogram space. Results introduce a new category of imaging artefacts to be aware of when using optical CT for PGD readout.« less

Improvements to GPS Airborne Radio Occultation in the Lower Troposphere Through Implementation of the Phase Matching Method

NASA Astrophysics Data System (ADS)

Wang, K.-N.; Garrison, J. L.; Haase, J. S.; Murphy, B. J.

2017-10-01

Airborne radio occultation (ARO) is a remote sensing technique for atmospheric sounding using Global Positioning System signals received by an airborne instrument. The atmospheric refractivity profile, which depends on pressure, temperature, and water vapor, can be retrieved by measuring the signal delay due to the refractive medium through which the signal traverses. The ARO system was developed to make repeated observations within an individual meteorological event such as a tropical storm, regardless of the presence of clouds and precipitation, and complements existing observation techniques such as dropsondes and satellite remote sensing. RO systems can suffer multipath ray propagation in the lower troposphere if there are strong refractivity gradients, for example, due to a highly variable moisture distribution or a sharp boundary layer, interfering with continuous carrier phase tracking as well as complicating retrievals. The phase matching method has now been adapted for ARO and is shown to reduce negative biases in the refractivity retrieval by providing robust retrievals of bending angle in the presence of multipath. The retrieval results are presented for a flight campaign in September 2010 for Hurricane Karl in the Caribbean Sea. The accuracy is assessed through comparison with the European Centre for Medium Range Weather Forecasts Interim Reanalysis. The fractional difference in refractivity can be maintained at a standard deviation of 2% from flight level down to a height of 2 km. The phase matching method decreases the negative refractivity bias by as much as 4% over the classical geometrical optics retrieval method.

Influence of shape and gradient refractive index in the accommodative changes of spherical aberration in nonhuman primate crystalline lenses.

PubMed

de Castro, Alberto; Birkenfeld, Judith; Maceo, Bianca; Manns, Fabrice; Arrieta, Esdras; Parel, Jean-Marie; Marcos, Susana

2013-09-11

To estimate changes in surface shape and gradient refractive index (GRIN) profile in primate lenses as a function of accommodation. To quantify the contribution of surface shape and GRIN to spherical aberration changes with accommodation. Crystalline lenses from 15 cynomolgus monkeys were studied in vitro under different levels of accommodation produced by a stretching system. Lens shape was obtained from optical coherence tomography (OCT) cross-sectional images. The GRIN was reconstructed with a search algorithm using the optical path measured from OCT images and the measured back focal length. The spherical aberration of the lens was estimated as a function of accommodation using the reconstructed GRIN and a homogeneous refractive index. The lens anterior and posterior radii of curvature decreased with increasing lens power. Both surfaces exhibited negative asphericities in the unaccommodated state. The anterior surface conic constant shifted toward less negative values with accommodation, while the value of the posterior remained constant. GRIN parameters remained constant with accommodation. The lens spherical aberration with GRIN distribution was negative and higher in magnitude than that with a homogeneous equivalent refractive index (by 29% and 53% in the unaccommodated and fully accommodated states, respectively). Spherical aberration with the equivalent refractive index shifted with accommodation toward negative values (-0.070 μm/diopter [D]), but the reconstructed GRIN shifted it farther (-0.124 μm/D). When compared with the lens with the homogeneous equivalent refractive index, the reconstructed GRIN lens has more negative spherical aberration and a larger shift toward more negative values with accommodation.

Quasi-linear diffusion coefficients for highly oblique whistler mode waves

NASA Astrophysics Data System (ADS)

Albert, J. M.

2017-05-01

Quasi-linear diffusion coefficients are considered for highly oblique whistler mode waves, which exhibit a singular "resonance cone" in cold plasma theory. The refractive index becomes both very large and rapidly varying as a function of wave parameters, making the diffusion coefficients difficult to calculate and to characterize. Since such waves have been repeatedly observed both outside and inside the plasmasphere, this problem has received renewed attention. Here the diffusion equations are analytically treated in the limit of large refractive index μ. It is shown that a common approximation to the refractive index allows the associated "normalization integral" to be evaluated in closed form and that this can be exploited in the numerical evaluation of the exact expression. The overall diffusion coefficient formulas for large μ are then reduced to a very simple form, and the remaining integral and sum over resonances are approximated analytically. These formulas are typically written for a modeled distribution of wave magnetic field intensity, but this may not be appropriate for highly oblique whistlers, which become quasi-electrostatic. Thus, the analysis is also presented in terms of wave electric field intensity. The final results depend strongly on the maximum μ (or μ∥) used to model the wave distribution, so realistic determination of these limiting values becomes paramount.

Three-dimensional inverse problem of geometrical optics: a mathematical comparison between Fermat's principle and the eikonal equation.

PubMed

Borghero, Francesco; Demontis, Francesco

2016-09-01

In the framework of geometrical optics, we consider the following inverse problem: given a two-parameter family of curves (congruence) (i.e., f(x,y,z)=c₁,g(x,y,z)=c₂), construct the refractive-index distribution function n=n(x,y,z) of a 3D continuous transparent inhomogeneous isotropic medium, allowing for the creation of the given congruence as a family of monochromatic light rays. We solve this problem by following two different procedures: 1. By applying Fermat's principle, we establish a system of two first-order linear nonhomogeneous PDEs in the unique unknown function n=n(x,y,z) relating the assigned congruence of rays with all possible refractive-index profiles compatible with this family. Moreover, we furnish analytical proof that the family of rays must be a normal congruence. 2. By applying the eikonal equation, we establish a second system of two first-order linear homogeneous PDEs whose solutions give the equation S(x,y,z)=const. of the geometric wavefronts and, consequently, all pertinent refractive-index distribution functions n=n(x,y,z). Finally, we make a comparison between the two procedures described above, discussing appropriate examples having exact solutions.

Fresnel's original interpretation of complex numbers in 19th century optics

NASA Astrophysics Data System (ADS)

Karam, Ricardo

2018-04-01

In 1823, Fresnel published an original (physical) interpretation of complex numbers in his investigations of refraction and reflection of polarized light. This is arguably the first time that complex numbers were given a physical interpretation, which led to a better understanding of elliptical and circular polarizations. This rather unknown episode of the history of physics is described in this work, and some of the pedagogical lessons that can be extracted from it are discussed.

Characterizing Protein Complexes with UV absorption, Light Scattering, and Refractive Index Detection.

NASA Astrophysics Data System (ADS)

Trainoff, Steven

2009-03-01

Many modern pharmaceuticals and naturally occurring biomolecules consist of complexes of proteins and polyethylene glycol or carbohydrates. In the case of vaccine development, these complexes are often used to induce or amplify immune responses. For protein therapeutics they are used to modify solubility and function, or to control the rate of degradation and elimination of a drug from the body. Characterizing the stoichiometry of these complexes is an important industrial problem that presents a formidable challenge to analytical instrument designers. Traditional analytical methods, such as using florescent tagging, chemical assays, and mass spectrometry perturb the system so dramatically that the complexes are often destroyed or uncontrollably modified by the measurement. A solution to this problem consists of fractionating the samples and then measuring the fractions using sequential non-invasive detectors that are sensitive to different components of the complex. We present results using UV absorption, which is primarily sensitive to the protein fraction, Light Scattering, which measures the total weight average molar mass, and Refractive Index detection, which measures the net concentration. We also present a solution of the problem inter-detector band-broadening problem that has heretofore made this approach impractical. Presented will be instrumentation and an analysis method that overcome these obstacles and make this technique a reliable and robust way of non-invasively characterizing these industrially important compounds.

Self-Consistent Model of Magnetospheric Ring Current and Propagating Electromagnetic Ion Cyclotron Waves: Waves in Multi-Ion Magnetosphere

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Gamayunov, K. V.; Gallagher, D. L.; Kozyra, J. U.

2006-01-01

The further development of a self-consistent theoretical model of interacting ring current ions and electromagnetic ion cyclotron waves (Khazanov et al., 2003) is presented In order to adequately take into account wave propagation and refraction in a multi-ion magnetosphere, we explicitly include the ray tracing equations in our previous self-consistent model and use the general form of the wave kinetic equation. This is a major new feature of the present model and, to the best of our knowledge, the ray tracing equations for the first time are explicitly employed on a global magnetospheric scale in order to self-consistently simulate the spatial, temporal, and spectral evolution of the ring current and of electromagnetic ion cyclotron waves To demonstrate the effects of EMIC wave propagation and refraction on the wave energy distribution and evolution, we simulate the May 1998 storm. The main findings of our simulation can be summarized as follows. First, owing to the density gradient at the plasmapause, the net wave refraction is suppressed, and He+-mode grows preferably at the plasmapause. This result is in total agreement with previous ray tracing studies and is very clearly found in presented B field spectrograms. Second, comparison of global wave distributions with the results from another ring current model (Kozyra et al., 1997) reveals that this new model provides more intense and more highly plasmapause-organized wave distributions during the May 1998 storm period Finally, it is found that He(+)-mode energy distributions are not Gaussian distributions and most important that wave energy can occupy not only the region of generation, i.e., the region of small wave normal angles, but all wave normal angles, including those to near 90 . The latter is extremely crucial for energy transfer to thermal plasmaspheric electrons by resonant Landau damping and subsequent downward heat transport and excitation of stable auroral red arcs.

Self-Consistent Model of Magnetospheric Ring Current and Propagating Electromagnetic Ion Cyclotron Waves. 1; Waves in Multi Ion Magnetosphere

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Gumayunov, K. V.; Gallagher, D. L.; Kozyra, J. U.

2006-01-01

The further development of a self-consistent theoretical model of interacting ring current ions and electromagnetic ion cyclotron waves [Khazanov et al., 2003] is presented. In order to adequately take into account the wave propagation and refraction in a multi-ion plasmasphere, we explicitly include the ray tracing equations in our previous self-consistent model and use the general form of the wave kinetic equation. This is a major new feature of the present model and, to the best of our knowledge, the ray tracing equations for the first time are explicitly employed on a global magnetospheric scale in order to self-consistently simulate spatial, temporal, and spectral evolutions of the ring current and electromagnetic ion cyclotron waves. To demonstrate the effects of EMIC wave propagation and refraction on the EMIC wave energy distributions and evolution we simulate the May 1998 storm. The main findings of our simulation can be summarized as follows. First, due to the density gradient at the plasmapause, the net wave refraction is suppressed, and He(+)-mode grows preferably at plasmapause. This result is in a total agreement with the previous ray tracing studies, and very clear observed in presented B-field spectrograms. Second, comparison the global wave distributions with the results from other ring current model [Kozyra et al., 1997] reveals that our model provides more intense and higher plasmapause organized distributions during the May, 1998 storm period. Finally, the found He(+)-mode energy distributions are not Gaussian distributions, and most important that wave energy can occupy not only the region of generation, i. e. the region of small wave normal angles, but the entire wave normal angle region and even only the region near 90 degrees. The latter is extremely crucial for energy transfer to thermal plasmaspheric electrons by resonant Landau damping, and subsequent downward heat transport and excitation of stable auroral red arcs.

Measuring the complex optical conductivity of graphene by Fabry-Pérot reflectance spectroscopy [Determination of the optical index for few-layer graphene by reflectivity spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghamsari, Behnood G.; Tosado, Jacob; Yamamoto, Mahito

Here, we have experimentally studied the optical refractive index of few-layer graphene through reflection spectroscopy at visible wavelengths. A laser scanning microscope (LSM) with a coherent supercontinuum laser source measured the reflectivity of an exfoliated graphene flake on a Si/SiO 2 substrate, containing monolayer, bilayer and trilayer areas, as the wavelength of the laser was varied from 545nm to 710nm. The complex refractive index of few-layer graphene, n-ik, was extracted from the reflectivity contrast to the bare substrate and the Fresnel reflection theory. Since the SiO 2 thickness enters to the modeling as a parameter, it was precisely measured atmore » the location of the sample. It was found that a common constant optical index cannot explain the wavelength-dependent reflectivity data for single-, double- and three-layer graphene simultaneously, but rather each individual few-layer graphene possesses a unique optical index whose complex values were precisely and accurately determined from the experimental data.« less

Measuring the complex optical conductivity of graphene by Fabry-Pérot reflectance spectroscopy [Determination of the optical index for few-layer graphene by reflectivity spectroscopy

DOE PAGES

Ghamsari, Behnood G.; Tosado, Jacob; Yamamoto, Mahito; ...

2016-09-29

Here, we have experimentally studied the optical refractive index of few-layer graphene through reflection spectroscopy at visible wavelengths. A laser scanning microscope (LSM) with a coherent supercontinuum laser source measured the reflectivity of an exfoliated graphene flake on a Si/SiO 2 substrate, containing monolayer, bilayer and trilayer areas, as the wavelength of the laser was varied from 545nm to 710nm. The complex refractive index of few-layer graphene, n-ik, was extracted from the reflectivity contrast to the bare substrate and the Fresnel reflection theory. Since the SiO 2 thickness enters to the modeling as a parameter, it was precisely measured atmore » the location of the sample. It was found that a common constant optical index cannot explain the wavelength-dependent reflectivity data for single-, double- and three-layer graphene simultaneously, but rather each individual few-layer graphene possesses a unique optical index whose complex values were precisely and accurately determined from the experimental data.« less

Systematic Relationships Between Lidar Observables and Sizes And Mineral Composition Of Dust Aerosols

NASA Technical Reports Server (NTRS)

Van Diedenhoven, Bastiaan; Stangl, Alexander; Perlwitz, Jan; Fridlind, Ann M.; Chowdhary, Jacek; Cairns, Brian

2015-01-01

The physical and chemical properties of soil dust aerosol particles fundamentally affect their interaction with climate, including shortwave absorption and radiative forcing, nucleation of cloud droplets and ice crystals, heterogeneous formation of sulfates and nitrates on the surface of dust particles, and atmospheric processing of iron into bioavailable forms that increase the productivity of marine phytoplankton. Lidar measurements, such as extinction-to-backscatter, color and depolarization ratios, are frequently used to distinguish between aerosol types with different physical and chemical properties. The chemical composition of aerosol particles determines their complex refractive index, hence affecting their backscattering properties. Here we present a study on how dust aerosol backscattering and depolarization properties at wavelengths of 355, 532 and 1064 nm are related to size and complex refractive index, which varies with the mineral composition of the dust. Dust aerosols are represented by collections of spheroids with a range of prolate and oblate aspect ratios and their optical properties are obtained using T-matrix calculations. We find simple, systematic relationships between lidar observables and the dust size and complex refractive index that may aid the use of space-based or airborne lidars for direct retrieval of dust properties or for the evaluation of chemical transport models using forward simulated lidar variables. In addition, we present first results on the spatial variation of forward-simulated lidar variables based on a dust model that accounts for the atmospheric cycle of eight different mineral types plus internal mixtures of seven mineral types with iron oxides, which was recently implemented in the NASA GISS Earth System ModelE2.

Holographic intravital microscopy for 2-D and 3-D imaging intact circulating blood cells in microcapillaries of live mice

NASA Astrophysics Data System (ADS)

Kim, Kyoohyun; Choe, Kibaek; Park, Inwon; Kim, Pilhan; Park, Yongkeun

2016-09-01

Intravital microscopy is an essential tool that reveals behaviours of live cells under conditions close to natural physiological states. So far, although various approaches for imaging cells in vivo have been proposed, most require the use of labelling and also provide only qualitative imaging information. Holographic imaging approach based on measuring the refractive index distributions of cells, however, circumvent these problems and offer quantitative and label-free imaging capability. Here, we demonstrate in vivo two- and three-dimensional holographic imaging of circulating blood cells in intact microcapillaries of live mice. The measured refractive index distributions of blood cells provide morphological and biochemical properties including three-dimensional cell shape, haemoglobin concentration, and haemoglobin contents at the individual cell level. With the present method, alterations in blood flow dynamics in live healthy and sepsis-model mice were also investigated.

Transient Heat Transfer in a Semitransparent Radiating Layer with Boundary Convection and Surface Reflections

NASA Technical Reports Server (NTRS)

Siegel, Robert

1996-01-01

Surface convection and refractive index are examined during transient radiative heating or cooling of a grey semitransparent layer with internal absorption, emission and conduction. Each side of the layer is exposed to hot or cold radiative surroundings, while each boundary is heated or cooled by convection. Emission within the layer and internal reflections depend on the layer refractive index. The reflected energy and heat conduction distribute energy across the layer and partially equalize the transient temperature distributions. Solutions are given to demonstrate the effect of radiative heating for layers with various optical thicknesses, the behavior of the layer heated by radiation on one side and convectively cooled on the other, and a layer heated by convection while being cooled by radiation. The numerical method is an implicit finite difference procedure with non-uniform space and time increments. The basic method developed in earlier work is expanded to include external convection and incident radiation.

Experimental and simulated study of a composite structure metamaterial absorber

NASA Astrophysics Data System (ADS)

Li, Shengyong; Ai, Xiaochuan; Wu, Ronghua; Chen, Jiajun

2017-11-01

In this paper, a high performance metamaterial absorber is designed and experimental studied. Measured results indicate that a perfect absorption band and a short-wavelength absorption peak are achieved in the near-infrared spectrum. Current strength distributions reveal that the absorption band is excited by the cavity resonance. And electric field distributions show that the short-wavelength absorption peak is excited by the horizontal coupled of localized surface plasmon (LSP) modes near hole edges. On the one hand, the absorption property of the measured metamaterial absorber can be enhanced through optimizing the structural parameters (a, w, and H). On the other hand, the absorption property is sensitive to the change of refractive index of environmental medias. A sensing scheme is proposed for refractive index detecting based on the figure of merit (FOM) value. Measured results indicate that the proposed sensing scheme can achieve high FOM value with different environmental medias (water, glucose solution).

Single-molecule spectromicroscopy: a route towards sub-wavelength refractometry.

PubMed

Anikushina, T A; Gladush, M G; Gorshelev, A A; Naumov, A V

2015-01-01

We suggest a novel approach for spatially resolved probing of local fluctuations of the refractive index n in solids by means of single-molecule (SM) spectroscopy. It is based on the dependence T1(n) of the effective radiative lifetime T1 of dye centres in solids on n due to the local-field effects. Detection of SM zero-phonon lines at low temperatures gives the values of the SM natural spectral linewidth (which is inversely proportional to T1) and makes it possible to reveal the distribution of the local n values in solids. Here we demonstrate this possibility on the example of amorphous polyethylene and polycrystalline naphthalene doped with terrylene. In particular, we show that the obtained distributions of lifetime limited spectral linewidths of terrylene molecules embedded into these matrices are due to the spatial fluctuations of the refractive index local values.

Potential to Detect Hydrogen Concentration Gradients with Palladium Infused Mesoporous-Titania on D-Shaped Optical Fiber.

PubMed

Poole, Zsolt L; Ohodnicki, Paul R; Yan, Aidong; Lin, Yuankun; Chen, Kevin P

2017-01-27

A distributed sensing capable high temperature D-shaped optical fiber modified with a palladium nanoparticle sensitized mesoporous (∼5 nm) TiO 2 film, is demonstrated. The refractive index of the TiO 2 film was reduced using block copolymer templating in order to realize a mesoporous matrix, accommodating integration with optical fiber. The constructed sensor was analyzed by performing direct transmission loss measurements, and by analyzing the behavior of an integrated fiber Bragg grating. The inscribed grating should reveal whether the refractive index of the composite film experiences changes upon exposure to hydrogen. In addition, with frequency domain reflectometry the distributed sensing potential of the developed sensor for hydrogen concentrations of up to 10% is examined. The results show the possibility of detecting chemical gradients with sub-cm resolution at temperatures greater than 500 °C.

Automatic enhancement of skin fluorescence localization due to refractive index matching

NASA Astrophysics Data System (ADS)

Churmakov, Dmitry Y.; Meglinski, Igor V.; Piletsky, Sergey A.; Greenhalgh, Douglas A.

2004-07-01

Fluorescence diagnostic techniques are notable amongst many other optical methods, as they offer high sensitivity and non-invasive measurements of tissue properties. However, a combination of multiple scattering and physical heterogeneity of biological tissues hampers the interpretation of the fluorescence measurements. The analyses of the spatial distribution of endogenous and exogenous fluorophores excitations within tissues and their contribution to the detected signal localization are essential for many applications. We have developed a novel Monte Carlo technique that gives a graphical perception of how the excitation and fluorescence detected signal are localized in tissues. Our model takes into account spatial distribution of fluorophores and their quantum yields. We demonstrate that matching of the refractive indices of ambient medium and topical skin layer improves spatial localization of the detected fluorescence signal within the tissue. This result is consistent with the recent conclusion that administering biocompatible agents results in higher image contrast.

Nonlinear Programming shallow tomography improves deep structure imaging

NASA Astrophysics Data System (ADS)

Li, J.; Morozov, I.

2004-05-01

In areas with strong variations in topography or near-surface lithology, conventional seismic data processing methods do not produce clear images, neither shallow nor deep. The conventional reflection data processing methods do not resolve stacking velocities at very shallow depth; however, refraction tomography can be used to obtain the near-surface velocities. We use Nonlinear Programming (NP) via known velocity and depth in points from shallow boreholes and outcrop as well as derivation of slowness as constraint conditions to gain accurate shallow velocities. We apply this method to a 2D reflection survey shot across the Flame Mountain, a typical mountain with high gas reserve volume in Western China, by PetroChina and BGP in 1990s. The area has a highly rugged topography with strong variations of lithology near the surface. Over its hillside, the quality of reflection data is very good, but on the mountain ridge, reflection quality is poorer. Because of strong noise, only the first breaks are clear in the records, with velocities varying by more than 3 times in the near offsets. Because this region contains a steep cliff and an overthrust fold, it is very difficult to find a standard refraction horizon, therefore, GLI refractive statics conventional field and residual statics do not result in a good image. Our processing approach includes: 1) The Herglotz-Wiechert method to derive a starting velocity model which is better than horizontal velocity model; 2) using shallow boreholes and geological data, construct smoothness constraints on the velocity field as well as; 3) perform tomographic velocity inversion by NP algorithm; 4) by using the resulting accurate shallow velocities, derive the statics to correct the seismic data for the complex near-surface velocity variations. The result indicates that shallow refraction tomography can greatly improve deep seismic images in complex surface conditions.

Identification of a Candidate Gene for Astigmatism

PubMed Central

Lopes, Margarida C.; Hysi, Pirro G.; Verhoeven, Virginie J. M.; Macgregor, Stuart; Hewitt, Alex W.; Montgomery, Grant W.; Cumberland, Phillippa; Vingerling, Johannes R.; Young, Terri L.; van Duijn, Cornelia M.; Oostra, Ben; Uitterlinden, Andre G.; Rahi, Jugnoo S.; Mackey, David A.; Klaver, Caroline C. W.; Andrew, Toby; Hammond, Christopher J.

2013-01-01

Purpose. Astigmatism is a common refractive error that reduces vision, where the curvature and refractive power of the cornea in one meridian are less than those of the perpendicular axis. It is a complex trait likely to be influenced by both genetic and environmental factors. Twin studies of astigmatism have found approximately 60% of phenotypic variance is explained by genetic factors. This study aimed to identify susceptibility loci for astigmatism. Methods. We performed a meta-analysis of seven genome-wide association studies that included 22,100 individuals of European descent, where astigmatism was defined as the number of diopters of cylinder prescription, using fixed effect inverse variance-weighted methods. Results. A susceptibility locus was identified with lead single nucleotide polymorphism rs3771395 on chromosome 2p13.3 (meta-analysis, P = 1.97 × 10−7) in the VAX2 gene. VAX2 plays an important role in the development of the dorsoventral axis of the eye. Animal studies have shown a gradient in astigmatism along the vertical plane, with corresponding changes in refraction, particularly in the ventral field. Conclusions. This finding advances the understanding of refractive error, and provides new potential pathways to be evaluated with regard to the development of astigmatism. PMID:23322567

Shallow subsurface imaging of northern Cascadia margin using downward continued short-streamer data

NASA Astrophysics Data System (ADS)

Yelisetti, S.; Ghosal, D.; Spence, G.

2017-12-01

Since Eocene, the Juan de Fuca plate has been subducting beneath the North American plate, scrapping off sediments from the down going plate, accreting to the margin forming frontal accretionary wedge, Crescent terrane and the Pacific Rim terrane, which are separated by landward dipping Crescent thrust and Tofino faults. In 1989, the Geological Survey of Canada has acquired several multichannel seismic lines along the northern Cascadia margin to study the subduction zone processes and the formation and distribution of methane hydrates in the accreted sediment section. Seismic reflections and refractions are recorded on a 3.6 km streamer up to 14 s using 4 ms sample rate with 183 m near-offset. In this study, we present the migrated image of line 89-06 which indicate the top of the down-going plate and several landward dipping frontal thrusts. Additionally, a bottom simulating reflector (BSR) is identified over a 20 km distance at a depth of 250 m beneath the seafloor within the accretionary wedge sediments where the water depth is around 1500-2000 m. Preliminary velocity analyses corresponding to the BSR reflection using semblance method indicate high-velocity sediment with P-wave velocities of 2.0 km/s. To better constrain the velocity distribution of such shallow subsurface features, we have analyzed the refracted arrivals from the seaward part of the Tofino basin sediment section. Specifically, we have downward continued the shot and receiver gathers to the seafloor bringing the far offset refracted phases to near offset as first arrivals. Since the refractions are not well captured over the trench deposits due to large water depth ( 2500 m) and limited streamer length, the downward continued results do not show refracted arrivals very clearly at the near offset. In contrast, moving landward along the frontal slope with gradual decrease in water depth to 1300 m and less, the effect of downward continuation seems to be more prominent bringing the refracted phases to near offset more clearly as first arrivals. More detailed first arrival tomographic velocity analysis is currently underway using these downward continued datasets. The tomographic velocity model will then be used as a starting model for future full waveform inversion to obtain the high-resolution velocity and attenuation models of the accreted sediments.

Aerosol properties in the upper clouds of Venus from glory observations by the Venus Monitoring Camera (Venus Express mission)

NASA Astrophysics Data System (ADS)

Markiewicz, Wojciech J.; Petrova, Elena V.; Shalygina, Oksana S.

2018-01-01

From the angular positions of the glory features observed on the upper cloud deck of Venus in three VMC channels (at 0.365, 0.513, and 0.965 μm), the dominating sizes of cloud particles and their refractive indices have been retrieved, and their spatial and temporal variations have been analyzed. For this, the phase profiles of brightness were compared to the single-scattering phase functions of particles of different sizes, since diffuse multiple scattering in the clouds does not move the angular positions of the glory, which is produced by the single scattering by cloud particles, but only makes them less pronounced. We presented the measured phase profiles in two ways: they were built for individual images and for individual small regions observed in series of successive images. The analysis of the data of both types has yielded consistent results. The presently retrieved radii of cloud particle average approximately 1.0-1.2 μm (though some values reach 1.4 μm) and demonstrate a variable pattern versus latitude and local solar time (LST). The decrease of particle sizes at high latitudes (down to 0.6 μm at 60°S) earlier found from the 0.965-μm and partly 0.365-μm data has been definitely confirmed in the analysis of the data of all three channels considered. To obtain the consistent estimates of particle sizes from the UV glory maximum and minimum positions, we have to vary the effective variance of the particle sizes, while it was fixed constant in our previous studies. The twofold increase of this parameter (from 0.07 to 0.14) diminishes the estimates of particle sizes by 10-15%, while the effect on the retrieved refractive index is negligible. The obtained estimates of the refractive index are more or less uniformly distributed over the covered latitude and LST ranges, and most of them are higher than those of concentrated sulfuric acid solution. This confirms our previous result obtained only at 0.965 μm, and now we may state that the cases of a relatively high real part of the refractive index are often observed for the 1-μm mode of cloud particles on Venus. Consequently, an additional component with a high value of the refractive index is required to be present in the cloud droplets. We suggest that this component is in small submicron particles; during the condensation process, they become incorporated into sulfuric acid droplets, which results in forming the complex UV absorbing particles with an increased refractive index. We suppose that this material can be ferric chloride that is one of the candidates for the so-called unknown UV absorber in the upper clouds of Venus.

Aircraft Natural/Artificial Icing

DTIC Science & Technology

2009-02-12

LWC are 0.1 to 0.8 g/m3 for stratiform clouds and 0.2 to 2.5 g/m3 for cumuliform clouds. The drop size distribution in the cloud is usually...cloud hydrometeor size distributions from 0.5 to 50 um, particle shape (discrimination between water and ice), particle optical properties (refractive...index), precipitation size distributions from 25 um to 1550 um, liquid water content from 0.01 to 3 gm-3 and aircraft velocity and atmospheric

Seismic and potential field studies over the East Midlands

NASA Astrophysics Data System (ADS)

Kirk, Wayne John

A seismic refraction profile was undertaken to investigate the source of an aeromagnetic anomaly located above the Widmerpool Gulf, East Midlands. Ten shots were fired into 51 stations at c. 1.5km spacing in a 70km profile during 41 days recording. The refraction data were processed using standard techniques to improve the data quality. A new filtering technique, known as Correlated Adaptive Noise Cancellation was tested on synthetic data and successfully applied to controlled source and quarry blast data. Study of strong motion data reveals that the previous method of site calibration is invalid. A new calibration technique, known as the Scaled Amplitude method is presented to provide safer charge size estimation. Raytrace modelling of the refraction data and two dimensional gravity interpretation confirms the presence of the Widmerpool Gulf but no support is found for the postulated intrusion. Two dimensional magnetic interpretation revealed that the aeromagnetic anomaly could be modelled with a Carboniferous igneous source. A Lower Palaeozoic refractor with a velocity of 6.0 km/s is identified at a maximum depth of c. 2.85km beneath the Widmerpool Gulf. Carboniferous and post-Carboniferous sediments within the gulf have velocities between 2.6-5.5 km/s with a strong vertical gradient. At the gulf margins, a refractor with a constant velocity of 5.2 km/s is identified as Dinantian limestone. A low velocity layer of proposed unaltered Lower Palaeozoics is identified beneath the limestone at the eastern edge of the Derbyshire Dome. The existence and areal extent of this layer are also determined from seismic reflection data. Image analysis of potential field data, presents a model identifying 3 structural provinces, the Midlands Microcraton, the Welsh and English Caledonides and a central region of complex linears. This model is used to explain the distribution of basement rocks determined from seismic and gravity profiles.

Does Your Optical Particle Counter Measure What You Think it Does? Calibration and Refractive Index Correction Methods.

NASA Astrophysics Data System (ADS)

Rosenberg, Phil; Dean, Angela; Williams, Paul; Dorsey, James; Minikin, Andreas; Pickering, Martyn; Petzold, Andreas

2013-04-01

Optical Particle Counters (OPCs) are the de-facto standard for in-situ measurements of airborne aerosol size distributions and small cloud particles over a wide size range. This is particularly the case on airborne platforms where fast response is important. OPCs measure scattered light from individual particles and generally bin particles according to the measured peak amount of light scattered (the OPC's response). Most manufacturers provide a table along with their instrument which indicates the particle diameters which represent the edges of each bin. It is important to correct the particle size reported by OPCs for the refractive index of the particles being measured, which is often not the same as for those used during calibration. However, the OPC's response is not a monotonic function of particle diameter and obvious problems occur when refractive index corrections are attempted, but multiple diameters correspond to the same OPC response. Here we recommend that OPCs are calibrated in terms of particle scattering cross section as this is a monotonic (usually linear) function of an OPC's response. We present a method for converting a bin's boundaries in terms of scattering cross section into a bin centre and bin width in terms of diameter for any aerosol species for which the scattering properties are known. The relationship between diameter and scattering cross section can be arbitrarily complex and does not need to be monotonic; it can be based on Mie-Lorenz theory or any other scattering theory. Software has been provided on the Sourceforge open source repository for scientific users to implement such methods in their own measurement and calibration routines. As a case study data is presented showing data from Passive Cavity Aerosol Spectrometer Probe (PCASP) and a Cloud Droplet Probe (CDP) calibrated using polystyrene latex spheres and glass beads before being deployed as part of the Fennec project to measure airborne dust in the inaccessible regions of the Sahara.

Angle-resolved spectral Fabry-Pérot interferometer for single-shot measurement of refractive index dispersion over a broadband spectrum

NASA Astrophysics Data System (ADS)

Dong, J. T.; Ji, F.; Xia, H. J.; Liu, Z. J.; Zhang, T. D.; Yang, L.

2018-01-01

An angle-resolved spectral Fabry-Pérot interferometer is reported for fast and accurate measurement of the refractive index dispersion of optical materials with parallel plate shape. The light sheet from the wavelength tunable laser is incident on the parallel plate with converging angles. The transmitted interference light for each angle is dispersed and captured by a 2D sensor, in which the rows and the columns are used to simultaneously record the intensities as a function of wavelength and incident angle, respectively. The interferogram, named angle-resolved spectral intensity distribution, is analyzed by fitting the phase information instead of finding the fringe peak locations that present periodic ambiguity. The refractive index dispersion and the physical thickness can be then retrieved from a single-shot interferogram within 18 s. Experimental results of an optical substrate standard indicate that the accuracy of the refractive index dispersion is less than 2.5  ×  10-5 and the relative uncertainty of the thickness is 6  ×  10-5 mm (3σ) due to the high stability and the single-shot measurement of the proposed system.

Monolithic subwavelength high refractive-index-contrast grating VCSELs

NASA Astrophysics Data System (ADS)

Gebski, Marcin; Dems, Maciej; Lott, James A.; Czyszanowski, Tomasz

2016-03-01

In this paper we present optical design and simulation results of vertical-cavity surface-emitting lasers (VCSELs) that incorporate monolithic subwavelength high refractive-index-contrast grating (MHCG) mirrors - a new variety of HCG mirror that is composed of high index material surrounded only on one side by low index material. We show the impact of an MHCG mirror on the performance of 980 nm VCSELs designed for high bit rate and energy-efficient optical data communications. In our design, all or part of the all-semiconductor top coupling distributed Bragg reflector mirror is replaced by an undoped gallium-arsenide MHCG. We show how the optical field intensity distribution of the VCSEL's fundamental mode is controlled by the combination of the number of residual distributed Bragg reflector (DBR) mirror periods and the physical design of the topmost gallium-arsenide MHCG. Additionally, we numerically investigate the confinement factors of our VCSELs and show that this parameter for the MHCG DBR VCSELs may only be properly determined in two or three dimensions due to the periodic nature of the grating mirror.

Measurement of Heat Transfer in Unbonded Silica Fibrous Insulation and Comparison with Theory

NASA Technical Reports Server (NTRS)

Daryabeigi, Kamran; Knutson, Jeffrey R.; Cunnington, George R.

2007-01-01

Effective thermal conductivity of a high porosity unbonded silica fibrous insulation specimen was measured over a pressure range of 0.001 to 750 torr (0.1 to 101.3 x 10(exp 3) Pa), and with large temperature gradients maintained across the sample thickness: hot side temperature range of 360 to 1360 K, with the cold side at room temperature. The measurements were compared with the theoretical solution of combined radiation/conduction heat transfer. The previously developed radiation heat transfer model used in this study is based on a modified diffusion approximation, and uses deterministic parameters that define the composition and morphology of the medium: distributions of fiber size and orientation, fiber volume fractions, and the spectral complex refractive index of the fibers. The close agreement between experimental and theoretical data further verifies the theoretical model over a wide range of temperatures and pressures.

Inverse atmospheric radiative transfer problems - A nonlinear minimization search method of solution. [aerosol pollution monitoring

NASA Technical Reports Server (NTRS)

Fymat, A. L.

1976-01-01

The paper studies the inversion of the radiative transfer equation describing the interaction of electromagnetic radiation with atmospheric aerosols. The interaction can be considered as the propagation in the aerosol medium of two light beams: the direct beam in the line-of-sight attenuated by absorption and scattering, and the diffuse beam arising from scattering into the viewing direction, which propagates more or less in random fashion. The latter beam has single scattering and multiple scattering contributions. In the former case and for single scattering, the problem is reducible to first-kind Fredholm equations, while for multiple scattering it is necessary to invert partial integrodifferential equations. A nonlinear minimization search method, applicable to the solution of both types of problems has been developed, and is applied here to the problem of monitoring aerosol pollution, namely the complex refractive index and size distribution of aerosol particles.

Seismic refraction studies of volcanic crust in Costa Rica and of critical zones in the southern Sierra Nevada, California and Laramie Range, Wyoming

NASA Astrophysics Data System (ADS)

Hayes, Jorden L.

This work demonstrates the utility of seismic refraction surveys to understanding geologic processes at a range of scales. Each chapter presents subsurface maps of seismic p-wave velocities, which vary due to contrasts in elastic material properties. In the following chapters we examine seismic p-wave velocity variations that result from volcanic and tectonic processes within Earth's crust and chemical and physical weathering processes within Earth's near-surface environment. Chapter one presents results from an across-arc wide-angle seismic refraction survey of the Costa Rican volcanic front. These results support the hypothesis that juvenile continental crust may form along volcanic island arcs if built upon relatively thick substrates (i.e., large igneous provinces). Comparisons of velocity-depth functions show that velocities within the active arc of Costa Rica are lower than other modern island arcs (i.e., volcanic arcs built upon oceanic crust) and within the high-velocity extreme of bulk continental crust. Chapter two shows that physical processes can dominate over chemical processes in generating porosity in the deep critical zone and outlines a new framework for interpreting subsurface chemical and physical weathering at the landscape scale. Direct measurements of saprolite from boreholes at the Southern Sierra Nevada Critical Zone Observatory show that, contrary to convention, saprolite may experience high levels of volumetric strain (>35%) and uniform mass loss in the upper 11 m. By combining observations from boreholes and seismic refraction surveys we create a map of volumetric strain across the landscape. Variations in inferred volumetric strain are consistent with opening-mode fracture patterns predicted by topographic and tectonic stress models. Chapter three is a characterization of fracture distribution in the deep critical zone from geophysical and borehole observations in the Laramie Mountains, Wyoming. Data from core and down-hole acoustic televiewer images show that fracture density not only decreases with depth but also varies with topography. Comparisons of seismic p-wave velocities and fracture density show that increases in seismic velocity at our site (i.e., from 1-4 km/s) correspond to decreasing fracture density. Observations of a seismological boundary layer coupled with weathering interpreted in borehole images suggest a significant change in chemical weathering with depth. These results emphasize the complex interplay of chemical and physical processes in the deep critical zone.

Broadband impedance-matched electromagnetic structured ferrite composite in the megahertz range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parke, L.; Hibbins, A. P.; Sambles, J. R.

2014-06-02

A high refractive-index structured ferrite composite is designed to experimentally demonstrate broadband impedance matching to free-space. It consists of an array of ferrite cubes that are anisotropically spaced, thereby allowing for independent control of the effective complex permeability and permittivity. Despite having a refractive index of 9.5, the array gives less than 1% reflection and over 90% transmission of normally incident radiation up to 70 MHz for one of the orthogonal linear polarisations lying in a symmetry plane of the array. This result presents a route to the design of MHz-frequency ferrite composites with bespoke electromagnetic parameters for antenna miniaturisation.

Broadband optical extinction measurements and complex refractive indices in the ultraviolet spectral region for biogenic secondary organic aerosol exposed to ammonia

NASA Astrophysics Data System (ADS)

Flores, J.; Washenfelder, R. A.; Lee, H.; Segev, L.; Nizkorodov, S.; Brown, S. S.; Rudich, Y.

2013-12-01

The interaction between aerosols and sunlight plays an important role in the radiative balance of Earth's atmosphere. Aerosols can both scatter and absorb solar radiation causing surface cooling and heating of the atmosphere. These interactions depend on the optical properties of the aerosols (i.e., complex refractive index). Secondary organic aerosol (SOA) account for a significant fraction of the tropospheric aerosol. However, their chemical, physical, and optical properties, especially as they are processed in the atmosphere (aging), are still poorly understood. In this study, SOA formed by the ozonolysis of various biogenic volatile organic compound (BVOC) precursors (α-pinene, limonene, and α-humulene) were exposed to humid air containing various concentrations of gaseous ammonia which has been shown to cause the biogenic SOA to ';brown' on filters. The extent of absorption of the SOA in the aerosol phase cause by the exposure to gaseous ammonia was measured by a newly developed instrument to measure aerosol extinction as a function of wavelength using Broadband Cavity Enhanced Spectroscopy (BBCES) with a broadband light source. Size-selected measurements of the humid SOA exposed to NH3 for about 1.5 hours were used to derive complex refractive indices (RI) as a function of wavelength in the UV spectral region (from 360 - 420nm). The imaginary part of the refractive index did not exceed 0.05 in the 360 - 420 nm range for SOA formed from the three BVOCs even at high concentrations of NH3 (>1ppm), allowing to place an upper limit of k = 0.05. Furthermore, the small k values are consistent with bulk UV-VIS measurements. However, for the α-pinene SOA, the real part of the RI slightly increased from n = 1.49 to n = 1.55 with negligible spectral dependence. For limonene and α-humulene the real part remind constant within error calculations. Based on these observations, reactive uptake of gaseous ammonia is not expected to significantly affect absorption and scattering properties of SOA particles.

Visual symptoms associated with refractive errors among Thangka artists of Kathmandu valley.

PubMed

Dhungel, Deepa; Shrestha, Gauri Shankar

2017-12-21

Prolong near work, especially among people with uncorrected refractive error is considered a potential source of visual symptoms. The present study aims to determine the visual symptoms and the association of those with refractive errors among Thangka artists. In a descriptive cross-sectional study, 242 (46.1%) participants of 525 thangka artists examined, with age ranged between 16 years to 39 years which comprised of 112 participants with significant refractive errors and 130 absolutely emmetropic participants, were enrolled from six Thangka painting schools. The visual symptoms were assessed using a structured questionnaire consisting of nine items and scoring from 0 to 6 consecutive scales. The eye examination included detailed anterior and posterior segment examination, objective and subjective refraction, and assessment of heterophoria, vergence and accommodation. Symptoms were presented in percentage and median. Variation in distribution of participants and symptoms was analysed using the Kruskal Wallis test for mean, and the correlation with the Pearson correlation coefficient. A significance level of 0.05 was applied for 95% confidence interval. The majority of participants (65.1%) among refractive error group (REG) were above the age of 30 years, with a male predominance (61.6%), compared to the participants in the normal cohort group (NCG), where majority of them (72.3%) were below 30 years of age (72.3%) and female (51.5%). Overall, the visual symptoms are high among Thangka artists. However, blurred vision (p = 0.003) and dry eye (p = 0.004) are higher among the REG than the NCG. Females have slightly higher symptoms than males. Most of the symptoms, such as sore/aching eye (p = 0.003), feeling dry (p = 0.005) and blurred vision (p = 0.02) are significantly associated with astigmatism. Thangka artists present with significant proportion of refractive error and visual symptoms, especially among females. The most commonly reported symptoms are blurred vision, dry eye and watering of the eye. The visual symptoms are more correlated with astigmatism.

Comparison of Whole Eye vs. First-Surface Astigmatism in Down Syndrome

PubMed Central

Knowlton, Rachel; Marsack, Jason D.; Leach, Norman E.; Herring, Ralph J.; Anderson, Heather A.

2016-01-01

Purpose Individuals with Down syndrome (DS) have structural differences in the cornea and lens, as compared to the general population. This study investigates objectively measured refractive and corneal astigmatism, as well as calculated internal astigmatism in subjects with and without DS. Methods Refractive (Grand Seiko autorefraction) and anterior corneal astigmatism (difference between steep and flat keratometry obtained with Zeiss Atlas corneal topography) were measured in 128 subjects with DS (mean age = 24.8±8.7 yrs) and 137 controls without DS (mean age = 24.9±9.9 yrs), with 1 eye randomly selected for analysis per subject. Refractive astigmatism and corneal astigmatism were converted to vector notation (J0, J45) to calculate internal astigmatism (Refractive – Corneal) and then converted back to minus cylinder form. Results Mean refractive astigmatism was significantly greater in subjects with DS than controls (−1.94±1.30DC vs −0.66±0.60DC, t=−10.16, p<0.001), as was mean corneal astigmatism (1.70±1.04DC vs 1.02±0.63DC, t=6.38, p<0.001) and mean internal astigmatism (−1.07±0.68DC vs −0.77±0.41DC, t=−4.21, p<0.001). A positive linear correlation between corneal and refractive astigmatism was observed for both study populations for both the J0 and J45 vectors (p<0.001 for all comparisons, R2 range = 0.31 to 0.74). The distributions of astigmatism orientation differed significantly between the two study populations when compared across all three types of astigmatism (Chi-Square, p<0.001). Conclusions This study demonstrates that corneal astigmatism is predictive of overall refractive astigmatism in individuals with DS, as it is in the general population. The greater magnitudes of astigmatism and wider variation of astigmatism orientation in individuals with DS for refractive, corneal, and calculated internal astigmatism is likely attributable to previously reported differences in the structure of the cornea and internal optical components of the eye from that of the general population. PMID:26002006

Influence of Shape and Gradient Refractive Index in the Accommodative Changes of Spherical Aberration in Nonhuman Primate Crystalline Lenses

PubMed Central

de Castro, Alberto; Birkenfeld, Judith; Maceo, Bianca; Manns, Fabrice; Arrieta, Esdras; Parel, Jean-Marie; Marcos, Susana

2013-01-01

Purpose. To estimate changes in surface shape and gradient refractive index (GRIN) profile in primate lenses as a function of accommodation. To quantify the contribution of surface shape and GRIN to spherical aberration changes with accommodation. Methods. Crystalline lenses from 15 cynomolgus monkeys were studied in vitro under different levels of accommodation produced by a stretching system. Lens shape was obtained from optical coherence tomography (OCT) cross-sectional images. The GRIN was reconstructed with a search algorithm using the optical path measured from OCT images and the measured back focal length. The spherical aberration of the lens was estimated as a function of accommodation using the reconstructed GRIN and a homogeneous refractive index. Results. The lens anterior and posterior radii of curvature decreased with increasing lens power. Both surfaces exhibited negative asphericities in the unaccommodated state. The anterior surface conic constant shifted toward less negative values with accommodation, while the value of the posterior remained constant. GRIN parameters remained constant with accommodation. The lens spherical aberration with GRIN distribution was negative and higher in magnitude than that with a homogeneous equivalent refractive index (by 29% and 53% in the unaccommodated and fully accommodated states, respectively). Spherical aberration with the equivalent refractive index shifted with accommodation toward negative values (−0.070 μm/diopter [D]), but the reconstructed GRIN shifted it farther (−0.124 μm/D). Conclusions. When compared with the lens with the homogeneous equivalent refractive index, the reconstructed GRIN lens has more negative spherical aberration and a larger shift toward more negative values with accommodation. PMID:23927893

Ametropias in school-age children in Fada N'Gourma (Burkina Faso, Africa).

PubMed

Jiménez, Raimundo; Soler, Margarita; Anera, Rosario G; Castro, José J; Pérez, M Angustias; Salas, Carlos

2012-01-01

To assess epidemiological aspects of refractive errors in school-age children in Burkina Faso (west-central Africa). A total of 315 school children (ranging from 6 to 16 years of age and belonging to different ethnic groups) taken at random from two urban schools in eastern Burkina Faso were examined to assess their refractive error, which was determined by non-cycloplegic retinoscopy with optical fogging. The standard Refractive Error Study in Children (RESC) definitions of refractive errors were used: myopia ≤-0.5 D spherical equivalent (SE) in at least one eye, hyperopia ≥2 D SE in at least one eye, astigmatism ≤-0.75 D cylinder in at least one eye, and anisometropia ≥1 D SE difference between the two eyes. Unilateral myopia and bilateral myopia were found in 2.5 and 1%, respectively; unilateral hyperopia in 17.1%, bilateral hyperopia in 8.6%; astigmatism in at least one eye in 11.7%. The highest prevalence value (18.4%) of astigmatism (≤-0.75 D) in at least one eye was found in the Gourmantché ethnic group. The low prevalence of large refractive errors makes visual acuity in these children very good (visual acuity logarithm of the minimum angle of resolution -0.073 ± 0.123 SD). There was a low prevalence of myopia in these African school children. Clinically significant high hyperopia (≥+2 D SE) was also uncommon. There were no significant differences between the distributions of refractive errors according to gender or ethnicity. With respect to age groups, the prevalences of hyperopia and astigmatism were significantly higher in the younger age groups.

Tapered optical fiber tip probes based on focused ion beam-milled Fabry-Perot microcavities

NASA Astrophysics Data System (ADS)

André, Ricardo M.; Warren-Smith, Stephen C.; Becker, Martin; Dellith, Jan; Rothhardt, Manfred; Zibaii, M. I.; Latifi, H.; Marques, Manuel B.; Bartelt, Hartmut; Frazão, Orlando

2016-09-01

Focused ion beam technology is combined with dynamic chemical etching to create microcavities in tapered optical fiber tips, resulting in fiber probes for temperature and refractive index sensing. Dynamic chemical etching uses hydrofluoric acid and a syringe pump to etch standard optical fibers into cone structures called tapered fiber tips where the length, shape, and cone angle can be precisely controlled. On these tips, focused ion beam is used to mill several different types of Fabry-Perot microcavities. Two main cavity types are initially compared and then combined to form a third, complex cavity structure. In the first case, a gap is milled on the tapered fiber tip which allows the external medium to penetrate the light guiding region and thus presents sensitivity to external refractive index changes. In the second, two slots that function as mirrors are milled on the tip creating a silica cavity that is only sensitive to temperature changes. Finally, both cavities are combined on a single tapered fiber tip, resulting in a multi-cavity structure capable of discriminating between temperature and refractive index variations. This dual characterization is performed with the aid of a fast Fourier transform method to separate the contributions of each cavity and thus of temperature and refractive index. Ultimately, a tapered optical fiber tip probe with sub-standard dimensions containing a multi-cavity structure is projected, fabricated, characterized and applied as a sensing element for simultaneous temperature and refractive index discrimination.

Optical-mechanical properties of diseased cells measured by interferometry

NASA Astrophysics Data System (ADS)

Shaked, Natan T.; Bishitz, Y.; Gabai, H.; Girshovitz, P.

2013-04-01

Interferometric phase microscopy (IPM) enables to obtain quantitative optical thickness profiles of transparent samples, including live cells in-vitro, and track them in time with sub-nanometer accuracy without any external labeling, contact or force application on the sample. The optical thickness measured by IPM is a multiplication between the cell integral refractive index differences and its physical thickness. Based on the time-dependent optical thickness profile, one can generate the optical thickness fluctuation map. For biological cells that are adhered to the surface, the variance of the physical thickness fluctuations in time is inversely proportional to the spring factor indicating on cell stiffness, where softer cells are expected fluctuating more than more rigid cells. For homogenous refractive index cells, such as red blood cells, we can calculate a map indicating on the cell stiffness per each spatial point on the cell. Therefore, it is possible to obtain novel diagnosis and monitoring tools for diseases changing the morphology and the mechanical properties of these cells such as malaria, certain types of anaemia and thalassemia. For cells with a complex refractive-index structure, such as cancer cells, decoupling refractive index and physical thickness is not possible in single-exposure mode. In these cases, we measure a closely related parameter, under the assumption that the refractive index does not change much within less than a second of measurement. Using these techniques, we lately found that cancer cells fluctuate significantly more than healthy cells, and that metastatic cancer cells fluctuate significantly more than primary cancer cells.

Comparative analysis of ferroelectric domain statistics via nonlinear diffraction in random nonlinear materials.

PubMed

Wang, B; Switowski, K; Cojocaru, C; Roppo, V; Sheng, Y; Scalora, M; Kisielewski, J; Pawlak, D; Vilaseca, R; Akhouayri, H; Krolikowski, W; Trull, J

2018-01-22

We present an indirect, non-destructive optical method for domain statistic characterization in disordered nonlinear crystals having homogeneous refractive index and spatially random distribution of ferroelectric domains. This method relies on the analysis of the wave-dependent spatial distribution of the second harmonic, in the plane perpendicular to the optical axis in combination with numerical simulations. We apply this technique to the characterization of two different media, Calcium Barium Niobate and Strontium Barium Niobate, with drastically different statistical distributions of ferroelectric domains.

The temperature dependence of inelastic light scattering from small particles for use in combustion diagnostic instrumentation

NASA Technical Reports Server (NTRS)

Cloud, Stanley D.

1987-01-01

A computer calculation of the expected angular distribution of coherent anti-Stokes Raman scattering (CARS) from micrometer size polystyrene spheres based on a Mie-type model, and a pilot experiment to test the feasibility of measuring CARS angular distributions from micrometer size polystyrene spheres by simply suspending them in water are discussed. The computer calculations predict a very interesting structure in the angular distributions that depends strongly on the size and relative refractive index of the spheres.

Simulation of the influence of aerosol particles on Stokes parameters of polarized skylight

NASA Astrophysics Data System (ADS)

Li, L.; Li, Z. Q.; Wendisch, M.

2014-03-01

Microphysical properties and chemical compositions of aerosol particles determine polarized radiance distribution in the atmosphere. In this paper, the influences of different aerosol properties (particle size, shape, real and imaginary parts of refractive index) on Stokes parameters of polarized skylight in the solar principal and almucantar planes are studied by using vector radiative transfer simulations. The results show high sensitivity of the normalized Stokes parameters due to fine particle size, shape and real part of refractive index of aerosols. It is possible to utilize the strength variations at the peak positions of the normalized Stokes parameters in the principal and almucantar planes to identify aerosol types.

Refractive collimation beam shaper design and sensitivity analysis using a free-form profile construction method.

PubMed

Tsai, Chung-Yu

2017-07-01

A refractive laser beam shaper comprising two free-form profiles is presented. The profiles are designed using a free-form profile construction method such that each incident ray is directed in a certain user-specified direction or to a particular point on the target surface so as to achieve the required illumination distribution of the output beam. The validity of the proposed design method is demonstrated by means of ZEMAX simulations. The method is mathematically straightforward and easily implemented in computer code. It thus provides a convenient tool for the design and sensitivity analysis of laser beam shapers and similar optical components.

Physically based reflectance model utilizing polarization measurement.

PubMed

Nakano, Takayuki; Tamagawa, Yasuhisa

2005-05-20

A surface bidirectional reflectance distribution function (BRDF) depends on both the optical properties of the material and the microstructure of the surface and appears as combination of these factors. We propose a method for modeling the BRDF based on a separate optical-property (refractive-index) estimation by polarization measurement. Because the BRDF and the refractive index for precisely the same place can be determined, errors cased by individual difference or spatial dependence can be eliminated. Our BRDF model treats the surface as an aggregation of microfacets, and the diffractive effect is negligible because of randomness. An example model of a painted aluminum plate is presented.

Robust optimization of the laser induced damage threshold of dielectric mirrors for high power lasers.

PubMed

Chorel, Marine; Lanternier, Thomas; Lavastre, Éric; Bonod, Nicolas; Bousquet, Bruno; Néauport, Jérôme

2018-04-30

We report on a numerical optimization of the laser induced damage threshold of multi-dielectric high reflection mirrors in the sub-picosecond regime. We highlight the interplay between the electric field distribution, refractive index and intrinsic laser induced damage threshold of the materials on the overall laser induced damage threshold (LIDT) of the multilayer. We describe an optimization method of the multilayer that minimizes the field enhancement in high refractive index materials while preserving a near perfect reflectivity. This method yields a significant improvement of the damage resistance since a maximum increase of 40% can be achieved on the overall LIDT of the multilayer.

Ray tracing matrix approach for refractive index mismatch aberrations in confocal microscopy.

PubMed

Nastyshyn, S Yu; Bolesta, I M; Lychkovskyy, E; Vankevych, P I; Yakovlev, M Yu; Pansu, B; Nastishin, Yu A

2017-03-20

The 2×2 ray tracing matrix (RTM) method is employed for the description of optical aberrations caused by the refractive index mismatch (RIM) in fluorescent confocal polarization microscopy. We predict and experimentally confirm that due to the RIM a liquid crystal layer with highly non-uniform director distribution appears to be imaged as a layer with non-uniform thickness, which shows up in the roughness of the rear surface. For the off-axial focusing of the probing beam in a droplet dispersed in an immiscible liquid, we have developed an extended method still keeping the 2×2 dimensionality of the RTM.

The gradient index lens of the eye: an opto-biological synchrony.

PubMed

Pierscionek, Barbara K; Regini, Justyn W

2012-07-01

The refractive power of a lens is determined largely by its surface curvatures and the refractive index of its medium. These properties can also be used to control the sharpness of focus and hence the image quality. One of the most effective ways of doing this is with a gradient index. Eye lenses of all species, thus far, measured, are gradient index (GRIN) structures. The index gradation is one that increases from the periphery of the lens to its centre but the steepness of the gradient and the magnitudes of the refractive index vary so that the optics of the lens accords with visual demands. The structural proteins, the crystallins, which create the index gradient, also vary from species to species, in type and relative distribution across the tissue. The crystallin classes do not contribute equally to the refractive index, and this may be related to their structure and amino acid content. This article compares GRIN forms in eye lenses of varying species, the relevance of these forms to visual requirements, and the relationship between refractive index and the structural proteins. Consideration is given to the dynamics of a living lens, potential variations in the GRIN form with physiological changes and the possible link between discontinuities in the gradient and growth. Finally, the property of birefringence and the characteristic polarisation patterns seen in highly ordered crystals that have also been observed in specially prepared eye lenses are described and discussed. Copyright © 2012 Elsevier Ltd. All rights reserved.

Complex interferometry potential in case of sufficiently stable diagnostic system

NASA Astrophysics Data System (ADS)

Kalal, M.

2016-06-01

Classical interferometry is one of the key methods among active optical diagnostics. Its more advanced version, which allows recording and subsequent reconstruction of up to three sets of data using just one data object —a complex interferogram—was developed in the past and became known as complex interferometry. Employing this diagnostics, not only the usual phase shift, but also the amplitude of the probing beam as well as the fringe contrast (leading directly to the phase shift time derivative) can be reconstructed simultaneously from such a complex interferogram. In this paper it will be demonstrated that even in the case of a not particularly good diagnostic beam quality these three quantities can be reconstructed with a high degree of accuracy provided both the diagnostic beam as well as the corresponding optical line feature a reasonable stability. Such stability requirement is important as in an ideal case four shots need to be gradually recorded (one by one): the signal complex interferogram, the reference interferogram as well as the intensity structures of the signal and reference part of the diagnostic beam. Two examples of complex interferograms obtained in experiments will be analyzed: the laser produced plasma (spark in the air) and the high pressure gas jet. A general ray-tracing based iterative algorithm will be outlined in order to increase a precision of the index of refraction spatial profile taking into account refraction effects (omitted in the Abel inversion) and employing the original reconstructed phase shift and amplitude.

Underwater binocular imaging of aerial objects versus the position of eyes relative to the flat water surface.

PubMed

Barta, András; Horváth, Gábor

2003-12-01

The apparent position, size, and shape of aerial objects viewed binocularly from water change as a result of the refraction of light at the water surface. Earlier studies of the refraction-distorted structure of the aerial binocular visual field of underwater observers were restricted to either vertically or horizontally oriented eyes. Here we calculate the position of the binocular image point of an aerial object point viewed by two arbitrarily positioned underwater eyes when the water surface is flat. Assuming that binocular image fusion is performed by appropriate vergent eye movements to bring the object's image onto the foveae, the structure of the aerial binocular visual field is computed and visualized as a function of the relative positions of the eyes. We also analyze two erroneous representations of the underwater imaging of aerial objects that have occurred in the literature. It is demonstrated that the structure of the aerial binocular visual field of underwater observers distorted by refraction is more complex than has been thought previously.

THz conductivities of indium-tin-oxide nanowhiskers as a graded-refractive-index structure.

PubMed

Yang, Chan-Shan; Chang, Chia-Hua; Lin, Mao-Hsiang; Yu, Peichen; Wada, Osamu; Pan, Ci-Ling

2012-07-02

Indium-tin-oxide (ITO) nanowhiskers with attractive electrical and anti-reflection properties were prepared by the glancing-angle electron-beam evaporation technique. Structural and crystalline properties of such nanostructures were examined by scanning transmission electron microscopy and X-ray diffraction. Their frequency-dependent complex conductivities, refractive indices and absorption coefficients have been characterized with terahertz time-domain spectroscopy (THz-TDS), in which the nanowhiskers were considered as a graded-refractive-index (GRIN) structure instead of the usual thin film model. The electrical properties of ITO GRIN structures are analyzed and fitted well with Drude-Smith model in the 0.2~2.0 THz band. Our results indicate that the ITO nanowhiskers and its bottom layer atop the substrate exhibit longer carrier scattering times than ITO thin films. This signifies that ITO nanowhiskers have an excellent crystallinity with large grain size, consistent with X-ray data. Besides, we show a strong backscattering effect and fully carrier localization in the ITO nanowhiskers.

Delayed visual attention caused by high myopic refractive error.

PubMed

Winges, Kimberly M; Zarpellon, Ursula; Hou, Chuan; Good, William V

2005-06-01

Delayed visual maturation (DVM) is usually a retrospective diagnosis given to infants who are born with no or poor visually-directed behavior, despite normal acuity on objective testing, but who recover months later. This condition can be organized into several types based on associated neurodevelopmental or ocular findings, but the etiology of DVM is probably complex and involves multiple possible origins. Here we report two infants who presented with delayed visual maturation (attention). They were visually unresponsive at birth but were later found to have high myopic errors. Patient 1 had -4 D right eye, -5 D left eye. Patient 2 had -9 D o.u. Upon spectacle correction at 5 and 4 months, respectively, both infants immediately displayed visually-directed behavior, suggesting that a high refractive error was the cause of inattention in these patients. These findings could add to knowledge surrounding DVM and the diagnosis of apparently blind infants. Findings presented here also indicate the importance of prompt refractive error measurement in such cases.

Mode-independent attenuation in evanescent-field sensors

NASA Astrophysics Data System (ADS)

Gnewuch, Harald; Renner, Hagen

1995-03-01

Generally, the total power attenuation in multimode evanescent-field sensor waveguides is nonproportional to the bulk absorbance because the modal attenuation constants differ. Hence a direct measurement is difficult and is additionally aggravated because the waveguide absorbance is highly sensitive to the specific launching conditions at the waveguide input. A general asymptotic formula for the modal power attenuation in strongly asymmetric inhomogeneous planar waveguides with arbitrarily distributed weak absorption in the low-index superstrate is derived. Explicit expressions for typical refractive-index profiles are given. Except when very close to the cutoff, the predicted asymptotic attenuation behavior agrees well with exact calculations. The ratio of TM versus TE absorption has been derived to be (2 - n0 2/nf2 ) for arbitrary profiles. Waveguides with a linear refractive-index profile show mode-independent attenuation coefficients within each polarization. Further, the asymptotic sensitivity is independent of the wavelength, so that it should be possible to directly measure the spectral variation of the bulk absorption. The mode independence of the attenuation has been verified experimentally for a second-order polynomial profile, which is close to a linear refractive-index distribution. In contrast, the attenuation in the step-profile waveguide has been found to depend strongly on the mode number, as predicted by theory. A strong spread of the modal attenuation coefficients is also predicted for the parabolic-profile waveguide sensor.

Effective group index of refraction in non-thermal plasma photonic crystals

NASA Astrophysics Data System (ADS)

Mousavi, A.; Sadegzadeh, S.

2015-11-01

Plasma photonic crystals (PPCs) are periodic arrays that consist of alternate layers of micro-plasma and dielectric. These structures are used to control the propagation of electromagnetic waves. This paper presents a survey of research on the effect of non-thermal plasma with bi-Maxwellian distribution function on one dimensional PPC. A plasma with temperature anisotropy is not in thermodynamic equilibrium and can be described by the bi-Maxwellian distribution function. By using Kronig-Penny's model, the dispersion relation of electromagnetic modes in one dimensional non-thermal PPC (NPPC) is derived. The band structure, group velocity vg, and effective group index of refraction neff(g) of such NPPC structure with TeO2 as the material of dielectric layers have been studied. The concept of negative group velocity and negative neff(g), which indicates an anomalous behaviour of the PPCs, are also observed in the NPPC structures. Our numerical results provide confirmatory evidence that unlike PPCs there are finite group velocity and non-zero effective group indexes of refraction in photonic band gaps (PBGs) that lie in certain ranges of normalized frequency. In other words, inside the PBGs of NPPCs, neff(g) becomes non-zero and photons travel with a finite group velocity. In this special case, this velocity varies alternately between 20c and negative values of the order 103c (c is the speed of light in vacuum).

Retrieval of aerosol optical and micro-physical properties with 2D-MAX-DOAS

NASA Astrophysics Data System (ADS)

Ortega, Ivan; Coburn, Sean; Hostetler, Chris; Ferrare, Rich; Hair, Johnathan; Kassianov, Evgueni; Barnard, James; Berg, Larry; Schmid, Beat; Tomlinson, Jason; Hodges, Gary; Lantz, Kathy; Wagner, Thomas; Volkamer, Rainer

2015-04-01

Recent retrievals of 2 dimensional (2D) Multi-AXis Differential Optical Absorption Spectroscopy (2D-MAX-DOAS) have highlighted its importance in order to infer diurnal horizontal in-homogeneities around the measurement site. In this work, we expand the capabilities of 2D measurements in order to estimate simultaneously aerosol optical and micro-physical properties. Specifically, we present a retrieval method to obtain: (1) aerosol optical thickness (AOT) in the boundary layer (BL) and free troposphere (FT) and (2) the effective complex refractive index and the effective radius of the aerosol column size distribution. The retrieval method to obtain AOT is based on an iterative comparison of measured normalized radiances, oxygen collision pair (O4), and absolute Raman Scattering Probability (RSP) with the forward model calculations derived with the radiative transfer model McArtim based on defined aerosol extinction profiles. Once the aerosol load is determined we use multiple scattering phase functions and single scattering albedo (SSA) obtained with Mie calculations which then constrain the RTM to forward model solar almucantar normalized radiances. The simulated almucantar normalized radiances are then compared to the measured normalized radiances. The best-fit, determined by minimizing the root mean square, retrieves the complex refractive index, and effective radius. We apply the retrieval approach described above to measurements carried out during the 2012 intensive operation period of the Two Column Aerosol Project (TCAP) held on Cape Cod, MA, USA. Results are presented for two ideal case studies with both large and small aerosol loading and similar air mass outflow from the northeast coast of the US over the West Atlantic Ocean. The aerosol optical properties are compared with several independent instruments, including the NASA Langley airborne High Spectral Resolution Lidar (HSRL-2) for highly resolved extinction profiles during the overpasses, and with the co-located Multi Filter Rotating Shadow band Radiometer (MFRSR), and the Cimel Sun photometer for aerosol load at several wavelengths. To test aerosol horizontal homogeneity we use quantitatively analysis of asymmetry of solar azimuth normalized radiances and RSP. The aerosol column microphysical properties will be compared with merged size distribution of several in-situ instruments from airborne measurements during overpasses of the DoE-G1 aircraft around the ground measurement site.

Measurement of the refractive index of air in a low-pressure regime and the applicability of traditional empirical formulae

NASA Astrophysics Data System (ADS)

Schödel, René; Walkov, Alexander; Voigt, Michael; Bartl, Guido

2018-06-01

The refractive index of air is a major limiting factor in length measurements by interferometry, which are mostly performed under atmospheric conditions. Therefore, especially in the last century, measurement and description of the air refractive index was a key point in order to achieve accuracy in the realisation of the length by interferometry. Nevertheless, interferometric length measurements performed in vacuum are much more accurate since the wavelength of the light is not affected by the air refractive index. However, compared with thermal conditions in air, in high vacuum heat conduction is missing. In such a situation, dependent on the radiative thermal equilibrium, a temperature distribution can be very inhomogeneous. Using a so-called contact gas instead of high vacuum is a very effective way to enable heat conduction on nearly the same level as under atmospheric pressure conditions whereby keeping the effect of the air refractive index on a small level. As physics predicts, and as we have demonstrated previously, helium seems like the optimal contact gas because of its large heat conduction and its refractive index that can be calculated from precisely known parameters. On the other hand, helium gas situated in a vacuum chamber could easily be contaminated, e.g. by air leakage from outside. Above the boiling point of oxygen (‑183 °C) it is therefore beneficial to use dry air as a contact gas. In such an approach, the air refractive index could be calculated based on measured quantities for pressure and temperature. However, existing formulas for the air refractive index are not valid in the low-pressure regime. Although it seems reasonable that the refractivity (n  ‑  1) of dry air simply downscales with the pressure, to our knowledge there is no experimental evidence for the applicability of any empirical formula. This evidence is given in the present paper which reports on highly accurate measurements of the air refractive index for the wavelengths 532 nm, 633 nm and 780 nm in the low-pressure regime from 0 Pa to 1300 Pa. In our approach, using a vacuum cell, n  ‑  1 is obtained from the comparison of optical path lengths in vacuum and air along the same path by imaging interferometry. These measured values are compared with the ones obtained from Bönsch’s formula. An agreement of  ±10‑9 is found in the low-pressure regime. Accordingly, this formula could be applied for the accurate determination of the refractive index of dry air even at low pressures, provided that the pressure is measured with high accuracy.

Comparison of LOPES measurements with CoREAS and REAS 3.11 simulations

NASA Astrophysics Data System (ADS)

Ludwig, M.; Apel, W. D.; Arteaga-Velázquez, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Chiavassa, A.; Daumiller, K.; de Souza, V.; Di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Fuchs, B.; Fuhrmann, D.; Gemmeke, H.; Grupen, C.; Haug, M.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Mathes, H. J.; Melissas, M.; Morello, C.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Zabierowski, J.; Zensus, J. A.

2013-05-01

In the previous years, LOPES emerged as a very successful experiment measuring the radio emission from air showers in the MHz frequency range. In parallel, the theoretical description of radio emission was developed further and REAS became a widely used simulation Monte Carlo code. REAS 3 as well as CoREAS are based on the endpoint formalism, i.e. they calculate the emission of the air-shower without assuming specific emission mechanisms. While REAS 3 is based on histograms derived from CORSIKA simulations, CoREAS is directly implemented into CORSIKA without loss of information due to histogramming of the particle distributions. In contrast to the earlier versions of REAS, the newest version REAS 3.11 and CoREAS take into account a realistic atmospheric refractive index. To improve the understanding of the emission processes and judge the quality of the simulations, we compare their predictions with high-quality events measured by LOPES. We present results concerning the lateral distribution measured with 30 east-west aligned LOPES antennas. Only the simulation codes including the refractive index (REAS 3.11 and CoREAS) are able to reproduce the slope of measured lateral distributions, but REAS 3.0 predicts too steep lateral distributions, and does not predict rising lateral distributions as seen in a few LOPES events. Moreover, REAS 3.11 predicts an absolute amplitude compatible with the LOPES measurements.

Propagation in Striated Media

DTIC Science & Technology

1976-05-01

random walk photon scattering, geometric optics refraction at a thin phase screen, plane wave scattering from a thin screen in the Fraunhofer limit and...significant cases. In the geometric optics regime the distribution of density of allowable multipath rays is gsslanly distributed and the power...3.1 Random Walk Approach to Scattering 10 3.2 Phase Screen Approximation to Strong Scattering 13 3.3 Ray Optics and Stationary Phase Analysis 21 3,3,1

Size-exclusion chromatography for the determination of the boiling point distribution of high-boiling petroleum fractions.

PubMed

Boczkaj, Grzegorz; Przyjazny, Andrzej; Kamiński, Marian

2015-03-01

The paper describes a new procedure for the determination of boiling point distribution of high-boiling petroleum fractions using size-exclusion chromatography with refractive index detection. Thus far, the determination of boiling range distribution by chromatography has been accomplished using simulated distillation with gas chromatography with flame ionization detection. This study revealed that in spite of substantial differences in the separation mechanism and the detection mode, the size-exclusion chromatography technique yields similar results for the determination of boiling point distribution compared with simulated distillation and novel empty column gas chromatography. The developed procedure using size-exclusion chromatography has a substantial applicability, especially for the determination of exact final boiling point values for high-boiling mixtures, for which a standard high-temperature simulated distillation would have to be used. In this case, the precision of final boiling point determination is low due to the high final temperatures of the gas chromatograph oven and an insufficient thermal stability of both the gas chromatography stationary phase and the sample. Additionally, the use of high-performance liquid chromatography detectors more sensitive than refractive index detection allows a lower detection limit for high-molar-mass aromatic compounds, and thus increases the sensitivity of final boiling point determination. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Speckle measurements of density and temperature profiles in a model gas circuit breaker

NASA Astrophysics Data System (ADS)

Stoller, P. C.; Panousis, E.; Carstensen, J.; Doiron, C. B.; Färber, R.

2015-01-01

Speckle imaging was used to measure the density and temperature distribution in the arc zone of a model high voltage circuit breaker during the high current phase and under conditions simulating those present during current-zero crossings (current-zero-like arc); the arc was stabilized by a transonic, axial flow of synthetic air. A single probe beam was used; thus, accurate reconstruction was only possible for axially symmetric gas flows and arc channels. The displacement of speckles with respect to a reference image was converted to a line-of-sight integrated deflection angle, which was in turn converted into an axially symmetric refractive index distribution using a multistep process that made use of the inverse Radon transform. The Gladstone-Dale relation, which gives the index of refraction as a function of density, was extended to high temperatures by taking into account dissociation and ionization processes. The temperature and density were determined uniquely by assuming that the pressure distribution in the case of cold gas flow (in the absence of an arc) is not modified significantly by the arc. The electric conductivity distribution was calculated from the temperature profile and compared to measurements of the arc voltage and to previous results published in the literature for similar experimental conditions.

Fuel film thickness measurements using refractive index matching in a stratified-charge SI engine operated on E30 and alkylate fuels

NASA Astrophysics Data System (ADS)

Ding, Carl-Philipp; Sjöberg, Magnus; Vuilleumier, David; Reuss, David L.; He, Xu; Böhm, Benjamin

2018-03-01

This study shows fuel film measurements in a spark-ignited direct injection engine using refractive index matching (RIM). The RIM technique is applied to measure the fuel impingement of a high research octane number gasoline fuel with 30 vol% ethanol content at two intake pressures and coolant temperatures. Measurements are conducted for an alkylate fuel at one operating case, as well. It is shown that the fuel volume on the piston surface increases for lower intake pressure and lower coolant temperature and that the alkylate fuel shows very little spray impingement. The fuel films can be linked to increased soot emissions. A detailed description of the calibration technique is provided and measurement uncertainties are discussed. The dependency of the RIM signal on refractive index changes is measured. The RIM technique provides quantitative film thickness measurements up to 0.9 µm in this engine. For thicker films, semi-quantitative results of film thickness can be utilized to study the distribution of impinged fuel.

Wavelength-multiplexing surface plasmon holographic microscopy.

PubMed

Zhang, Jiwei; Dai, Siqing; Zhong, Jinzhan; Xi, Teli; Ma, Chaojie; Li, Ying; Di, Jianglei; Zhao, Jianlin

2018-05-14

Surface plasmon holographic microscopy (SPHM), which combines surface plasmon microscopy with digital holographic microscopy, can be applied for amplitude- and phase-contrast surface plasmon resonance (SPR) imaging. In this paper, we propose an improved SPHM with the wavelength multiplexing technique based on two laser sources and a common-path hologram recording configuration. Through recording and reconstructing the SPR images at two wavelengths simultaneously employing the improved SPHM, tiny variation of dielectric refractive index in near field is quantitatively monitored with an extended measurement range while maintaining the high sensitivity. Moreover, imaging onion tissues is performed to demonstrate that the detection sensitivities of two wavelengths can compensate for each other in SPR imaging. The proposed wavelength-multiplexing SPHM presents simple structure, high temporal stability and inherent capability of phase curvature compensation, as well as shows great potentials for further applications in monitoring diverse dynamic processes related with refractive index variations and imaging biological tissues with low-contrast refractive index distributions in the near field.

Corneal polarimetry after LASIK refractive surgery

NASA Astrophysics Data System (ADS)

Bueno, Juan M.; Berrio, Esther; Artal, Pablo

2006-01-01

Imaging polarimetry provides spatially resolved information on the polarization properties of a system. In the case of the living human eye, polarization could be related to the corneal biomechanical properties, which vary from the normal state as a result of surgery or pathologies. We have used an aberro-polariscope, which we recently developed, to determine and to compare the spatially resolved maps of polarization parameters across the pupil between normal healthy and post-LASIK eyes. The depolarization distribution is not uniform across the pupil, with post-surgery eyes presenting larger levels of depolarization. While retardation increases along the radius in normal eyes, this pattern becomes irregular after LASIK refractive surgery. The maps of slow axis also differ in normal and post-surgery eyes, with a larger disorder in post-LASIK eyes. Since these changes in polarization indicate subtle structural modifications of the cornea, this approach can be useful in a clinical environment to follow the biomechanical and optical changes of the cornea after refractive surgery or for the early diagnosis of different corneal pathologies.

Scattering of sound by atmospheric turbulence predictions in a refractive shadow zone

NASA Technical Reports Server (NTRS)

Mcbride, Walton E.; Bass, Henry E.; Raspet, Richard; Gilbert, Kenneth E.

1990-01-01

According to ray theory, regions exist in an upward refracting atmosphere where no sound should be present. Experiments show, however, that appreciable sound levels penetrate these so-called shadow zones. Two mechanisms contribute to sound in the shadow zone: diffraction and turbulent scattering of sound. Diffractive effects can be pronounced at lower frequencies but are small at high frequencies. In the short wavelength limit, then, scattering due to turbulence should be the predominant mechanism involved in producing the sound levels measured in shadow zones. No existing analytical method includes turbulence effects in the prediction of sound pressure levels in upward refractive shadow zones. In order to obtain quantitative average sound pressure level predictions, a numerical simulation of the effect of atmospheric turbulence on sound propagation is performed. The simulation is based on scattering from randomly distributed scattering centers ('turbules'). Sound pressure levels are computed for many realizations of a turbulent atmosphere. Predictions from the numerical simulation are compared with existing theories and experimental data.

Angular distributions of reflected and refracted relativistic electron beams crossing a thin planar target at a small angle to its surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serov, A. V., E-mail: serov@x4u.lebedev.ru; Mamonov, I. A.; Kol’tsov, A. V., E-mail: koltsov@x4u.lebedev.ru

2015-10-15

The scattering of electrons by aluminum, copper, and lead foils, as well as by bimetallic aluminum-lead and aluminum-copper foils, has been studied experimentally. A microtron with an energy of particles of 7.4 MeV has been used as a source of electrons. The beam of particles incident on a target at small angles is split into particles reflected from the foil, which constitute a reflected beam, and particles crossing the foil, which constitute a refracted beam. The effect of the material and thickness of the foil, as well as the angle between the initial trajectory of the beam and the planemore » of the target, on the direction of motion and the angular divergence of the beam crossing the foil and the beam reflected from the foil has been analyzed. Furthermore, the effect of the sequence of metal layers in bimetallic films on the angles of refraction and reflection of the beam has been examined.« less

Low-loss planar metamaterials electromagnetically induced transparency for sensitive refractive index sensing

NASA Astrophysics Data System (ADS)

Tian, Ying; Hu, Sen; Huang, Xiaojun; Yu, Zetai; Lin, Hai; Yang, Helin

2017-10-01

A low-loss and high transmission electromagnetically induced transparency like (EIT- like) structure is experimentally and numerically demonstrated in this paper. The proposed planar structure based on EIT-like metamaterial consists of two separate split-ring resonators, and its resulting transmission level can maximally reach 0.89 with significant suppression of radiation loss. According to the effective medium theory, the imaginary parts of the effective permittivity and permeability of the metamaterial are used as the evidence of low-loss. In the analysis, the simulated surface current, magnetic field distribution and coupled oscillator model reveal the principle of high transmittance EIT-effect. Furthermore, the peak of transparency frequency is highly sensitive to the variation of refractive index in the background medium. The sensor based on the proposed EIT structure can achieve a sensitivity of 1.69 GHz/RIU (refractive index unit) and a figure of merit of 11.66. Such metamaterials have potential perspectives in sensing and chiral slow light devices.

Nondestructive measurement of an optical fiber refractive-index profile by a transmitted-light differential interference contact microscope.

PubMed

Liu, Zhongyao; Dong, Xiaoman; Chen, Qianghua; Yin, Chunyong; Xu, Yuxian; Zheng, Yingjun

2004-03-01

A novel transmitted-light differential interference contrast (DIC) system is used for nondestructive measurement of the refractive-index profile (RIP) of an optical fiber. By means of this system the phase of a measured light beam can be modulated with an analyzer, and the phase distribution of a fiber is obtained by calculation of the various interference patterns. The measurement theory and structure and some typical applications of this system are demonstrated. The results of measuring RIPs in graded-index fiber are presented. Both the experimental results and theoretical analysis show that the system takes the advantage of high index resolution and of sufficient measurement accuracy for measuring the refractive index of the optical fiber. The system has strong ability to overcome environmental disturbance because of its common-path design. Moreover, one can use the system to measure the RIP along the fiber axis and acquire an image of the three-dimensional RIP of the fiber.

Measuring the molecular second hyperpolarizability in absorptive solutions by the third harmonic generation ratio technique.

PubMed

Tokarz, Danielle; Cisek, Richard; Prent, Nicole; Fekl, Ulrich; Barzda, Virginijus

2012-11-28

Measurement of the second hyperpolarizability (γ) values of compounds can provide insight into the molecular structural requirements for enhancement of third harmonic generation (THG) signal. A convenient method for measuring the γ of compounds in solutions was developed by implementing the THG ratio method which is based on measuring the THG intensity from two interfaces using a nonlinear optical microscope while accounting for the refractive index of solutions at the fundamental and third harmonic wavelengths. We demonstrated that the difference in refractive index at both wavelengths strongly influenced the calculation of γ values when compounds have absorption near the third harmonic or fundamental wavelength. To this end, a refractometer with the wavelength tuning range from UV to near IR was constructed, and the measured refractive indices were used to extract the γ values. The γ values of carotenoids and chlorophylls found in photosynthetic pigment-protein complexes were explored. Large differences in the refractive index at third harmonic and fundamental wavelengths for chlorophylls result in γ values that are more than two orders of magnitude larger than γ values for carotenoids as well as the sign of chlorophylls'γ values is negative while carotenoids have positive γ values. Copyright © 2012 Elsevier B.V. All rights reserved.

Low-loss 3D-laser-written mid-infrared LiNbO₃ depressed-index cladding waveguides for both TE and TM polarizations.

PubMed

Nguyen, Huu-Dat; Ródenas, Airán; Vázquez de Aldana, Javier R; Martín, Guillermo; Martínez, Javier; Aguiló, Magdalena; Pujol, Maria Cinta; Díaz, Francesc

2017-02-20

We report mid-infrared LiNbO₃ depressed-index microstructured cladding waveguides fabricated by three-dimensional laser writing showing low propagation losses (~1.5 dB/cm) at 3.68 µm wavelength for both the transverse electric and magnetic polarized modes, a feature previously unachieved due to the strong anisotropic properties of this type of laser microstructured waveguides and which is of fundamental importance for many photonic applications. Using a heuristic modeling-testing iteration design approach which takes into account cladding induced stress-optic index changes, the fabricated cladding microstructure provides low-loss single mode operation for the mid-IR for both orthogonal polarizations. The dependence of the localized refractive index changes within the cladding microstructure with post-fabrication thermal annealing processes was also investigated, revealing its complex dependence of the laser induced refractive index changes on laser fabrication conditions and thermal post-processing steps. The waveguide modes properties and their dependence on thermal post-processing were numerically modeled and fitted to the experimental values by systematically varying three fundamental parameters of this type of waveguides: depressed refractive index values at sub-micron laser-written tracks, track size changes, and piezo-optic induced refractive index changes.

Heuristic modelling of laser written mid-infrared LiNbO₃ stressed-cladding waveguides.

PubMed

Nguyen, Huu-Dat; Ródenas, Airán; Vázquez de Aldana, Javier R; Martínez, Javier; Chen, Feng; Aguiló, Magdalena; Pujol, Maria Cinta; Díaz, Francesc

2016-04-04

Mid-infrared lithium niobate cladding waveguides have great potential in low-loss on-chip non-linear optical instruments such as mid-infrared spectrometers and frequency converters, but their three-dimensional femtosecond-laser fabrication is currently not well understood due to the complex interplay between achievable depressed index values and the stress-optic refractive index changes arising as a function of both laser fabrication parameters, and cladding arrangement. Moreover, both the stress-field anisotropy and the asymmetric shape of low-index tracks yield highly birefringent waveguides not useful for most applications where controlling and manipulating the polarization state of a light beam is crucial. To achieve true high performance devices a fundamental understanding on how these waveguides behave and how they can be ultimately optimized is required. In this work we employ a heuristic modelling approach based on the use of standard optical characterization data along with standard computational numerical methods to obtain a satisfactory approximate solution to the problem of designing realistic laser-written circuit building-blocks, such as straight waveguides, bends and evanescent splitters. We infer basic waveguide design parameters such as the complex index of refraction of laser-written tracks at 3.68 µm mid-infrared wavelengths, as well as the cross-sectional stress-optic index maps, obtaining an overall waveguide simulation that closely matches the measured mid-infrared waveguide properties in terms of anisotropy, mode field distributions and propagation losses. We then explore experimentally feasible waveguide designs in the search of a single-mode low-loss behaviour for both ordinary and extraordinary polarizations. We evaluate the overall losses of s-bend components unveiling the expected radiation bend losses of this type of waveguides, and finally showcase a prototype design of a low-loss evanescent splitter. Developing a realistic waveguide model with which robust waveguide designs can be developed will be key for exploiting the potential of the technology.

Laser characterization of the depth profile of complex refractive index of PMMA implanted with 50 keV silicon ions

NASA Astrophysics Data System (ADS)

Stefanov, Ivan L.; Stoyanov, Hristiyan Y.; Petrova, Elitza; Russev, Stoyan C.; Tsutsumanova, Gichka G.; Hadjichristov, Georgi B.

2013-03-01

The depth profile of the complex refractive index of silicon ion (Si+) implanted polymethylmethacrylate (PMMA) is studied, in particular PMMA implanted with Si+ ions accelerated to a relatively low energy of 50 keV and at a fluence of 3.2 × 1015 cm-2. The ion-modified material with nano-clustered structure formed in the near(sub)surface layer of a thickness of about 100 nm is optically characterized by simulation based on reflection ellipsometry measurements at a wavelength of 632.8 nm (He-Ne laser). Being of importance for applications of ion-implanted PMMA in integrated optics, optoelectronics and optical communications, the effect of the index depth profile of Si+-implanted PMMA on the profile of the reflected laser beam due to laser-induced thermo-lensing in reflection is also analyzed upon illumination with a low power cw laser (wavelength 532 nm, optical power 10 - 50 mW).

Peripapillary retinal nerve fiber layer thickness in a population of 6-year-old children: findings by optical coherence tomography.

PubMed

Huynh, Son C; Wang, Xiu Ying; Rochtchina, Elena; Mitchell, Paul

2006-09-01

To study the distribution of retinal nerve fiber layer (RNFL) thickness by ocular and demographic variables in a population-based study of young children. Population-based cross-sectional study. One thousand seven hundred sixty-five of 2238 (78.9%) eligible 6-year-old children participated in the Sydney Childhood Eye Study between 2003 and 2004. Mean age was 6.7 years (50.9% boys). Detailed examination included cycloplegic autorefraction and measurement of axial length. Retinal nerve fiber layer scans using an optical coherence tomographer were performed with a circular scan pattern of 3.4-mm diameter. Multivariate analyses were performed to examine the distribution of RNFL parameters with gender, ethnicity, axial length, and refraction. Peripapillary RNFL thickness and RNFL(estimated integral) (RNFL(EI)), which measures the total cross-sectional area of ganglion cell axons converging onto the optic nerve head. Peripapillary RNFL thickness and RNFL(EI) were normally distributed. The mean+/-standard deviation RNFL average thickness was 103.7+/-11.4 microm and RNFL(EI) was 1.05+/-0.12 mm2. Retinal nerve fiber layer thickness was least for the temporal quadrant (75.7+/-14.7 microm), followed by the nasal (81.7+/-19.6 microm), inferior (127.8+/-20.5 microm), and superior (129.5+/-20.6 microm) quadrants. Multivariate adjusted RNFL average thickness was marginally greater in boys than in girls (104.7 microm vs. 103.2 microm; P = 0.007) and in East Asian than in white children (107.7 microm vs. 102.7 microm; P<0.0001). The RNFL was thinner with greater axial length (P(trend)<0.0001) and less positive spherical equivalent refractions (P(trend) = 0.004). Retinal nerve fiber layer average thickness and RNFL(EI) followed a normal distribution. Retinal nerve fiber layer thickness varied marginally with gender, but differences were more marked between white and East Asian children. Retinal nerve fiber layer thinning was associated with increasing axial length and less positive refractions.

Retrieval of aerosol optical and physical properties from ground-based measurements for Zanjan, a city in Northwest Iran

NASA Astrophysics Data System (ADS)

Masoumi, A.; Khalesifard, H. R.; Bayat, A.; Moradhaseli, R.

2013-02-01

A ground-based sun and sky scanning radiometer, CIMEL CE 318-2 sunphotometer, has been used to study the atmosphere of Zanjan, a city in Northwest Iran (36.70°N, 48.51°E, and 1800 m above the mean sea level) in the periods of October 2006-October 2008, and January-September 2010. Direct sun and solar principal plane sky radiance measurements by the sunphotometer have been used to retrieve the optical and physical properties of atmospheric aerosols, such as aerosol optical depth (AOD), Ångström exponent (α), single scattering albedo (SSA), refractive index, and volume size distributions. About 50 dusty days (daily averaged AOD (870) > 0.35, α < 0.5) have been recorded during the mentioned periods. Considering the different values obtained for SSA, real part of refractive index, and volume size distributions, it has been found that just dust and anthropogenic aerosols are making the atmospheric aerosols in this region. In these recordings it has been observed that AODs (Ångström exponents) were increasing (decreasing) during spring and early summer. This was accompanied by increase of SSA, real part of refractive index, and coarse mode part of volume size distributions of aerosols. This behavior could be due to transport of dust, mostly from Tigris-Euphrates basin or sometimes with lower probability from the region between Caspian and Aral seas and rarely from sources inside the Iran plateau like the Qom dry lake, especially in dry seasons. In this work NCEP/NCAR reanalysis, HYSPLIT model back trajectories, and MODIS Deep Blue AODs have been used to track the air masses and dust plumes during the recorded dust events.

Using the combination refraction-reflection solid to design omni-directional light source used in underwater wireless optical communication

NASA Astrophysics Data System (ADS)

Rao, Jionghui; Yao, Wenming; Wen, Linqiang

2015-10-01

Underwater wireless optical communication is a communication technology which uses laser as an information carrier and transmits data through water. Underwater wireless optical communication has some good features such as broader bandwidth, high transmission rate, better security, anti—interference performance. Therefore, it is promising to be widely used in the civil and military communication domains. It is also suitable for high-speed, short-range communication between underwater mobile vehicles. This paper presents a design approach of omni-directional light source used in underwater wireless optical communication, using TRACEPRO simulation tool to help design a combination solid composed of the lens, conical reflector and parabolic reflector, and using the modulated DPSS green laser in the transmitter module to output the laser beam in small divergence angles, after expanded by the combination refraction-reflection solid, the angle turns into a space divergence angle of 2π, achieving the omni-directional light source of hemisphere space, and test in the air and underwater, the result shows that the effect is fine. This paper analyzes the experimental test in the air and water, in order to make further improvement of the uniformity of light distribution, we optimize the reflector surface parameters of combination refraction-reflection solid and test in the air and water. The result shows that omni-directional light source used in underwater wireless optical communication optimized could achieve the uniformity of light distribution of underwater space divergence angle of 2π. Omni-directional light source used in underwater wireless optical communication designed in this paper has the characteristics of small size and uniformity of light distribution, it is suitable for application between UUVs, AUVs, Swimmer Delivery Vehicles (SDVs) and other underwater vehicle fleet, it realizes point-to-multipoint communications.

Refractive-index measurements in freezing sea-ice and sodium chloride brines.

PubMed

Maykut, G A; Light, B

1995-02-20

Sea ice contains numerous pockets of brine and precipitated salts whose size and number distributions change dramatically with temperature. Theoretical treatment of scattering produced by these inclusions requires information on refractive-index differences among the brine, salts, and surrounding ice. Lacking specific data on refractive-index variations in the brine, we carried out laboratory measurements in freezing-equilibrium solutions between -2 and -32 °C. Index values at 589 nm increased from 1.341 to 1.397 over this temperature range, corresponding to salinities of 35 and 240 parts per thousand (ppt). Spectral data were also taken at 50-nm intervals between 400 and 700 nm in nonequilibrium solutions with salinities ranging up to 300 ppt. Spectral gradients increased slightly with salinity but showed no measurable dependence on temperature between +12 and -16 °C. The Lorentz-Lorenz equation, combined with data on density, molar refractivities, and brine composition, yielded temperature-dependent index predictions in excellent agreement with the experimental data. Similar index and density measurements in freezing sodium chloride brines yielded values nearly identical to those in the sea-ice brines. The absence of mirabilite crystals in sodium chloride ice, however, will cause it to have higher transmissivity and lower reflectivity than sea ice above -22 °C.

Path profiles of Cn2 derived from radiometer temperature measurements and geometrical ray tracing

NASA Astrophysics Data System (ADS)

Vyhnalek, Brian E.

2017-02-01

Atmospheric turbulence has significant impairments on the operation of Free-Space Optical (FSO) communication systems, in particular temporal and spatial intensity fluctuations at the receiving aperture resulting in power surges and fades, changes in angle of arrival, spatial coherence degradation, etc. The refractive index structure parameter C 2 n is a statistical measure of the strength of turbulence in the atmosphere and is highly dependent upon vertical height. Therefore to understand atmospheric turbulence effects on vertical FSO communication links such as space-to-ground links, it is necessary to specify C 2 n profiles along the atmospheric propagation path. To avoid the limitations on the applicability of classical approaches, propagation simulation through geometrical ray tracing is applied. This is achieved by considering the atmosphere along the optical propagation path as a spatial distribution of spherical bubbles with varying relative refractive index deviations representing turbulent eddies. The relative deviations of the refractive index are statistically determined from altitude-dependent and time varying temperature fluctuations, as measured by a microwave profiling radiometer. For each representative atmosphere ray paths are analyzed using geometrical optics, which is particularly advantageous in situations of strong turbulence where there is severe wavefront distortion and discontinuity. The refractive index structure parameter is then determined as a function of height and time.

Path Profiles of Cn2 Derived from Radiometer Temperature Measurements and Geometrical Ray Tracing

NASA Technical Reports Server (NTRS)

Vyhnalek, Brian E.

2017-01-01

Atmospheric turbulence has significant impairments on the operation of Free-Space Optical (FSO) communication systems, in particular temporal and spatial intensity fluctuations at the receiving aperture resulting in power surges and fades, changes in angle of arrival, spatial coherence degradation, etc. The refractive index structure parameter Cn2 is a statistical measure of the strength of turbulence in the atmosphere and is highly dependent upon vertical height. Therefore to understand atmospheric turbulence effects on vertical FSO communication links such as space-to-ground links, it is necessary to specify Cn2 profiles along the atmospheric propagation path. To avoid the limitations on the applicability of classical approaches, propagation simulation through geometrical ray tracing is applied. This is achieved by considering the atmosphere along the optical propagation path as a spatial distribution of spherical bubbles with varying relative refractive index deviations representing turbulent eddies. The relative deviations of the refractive index are statistically determined from altitude-dependent and time-varying temperature fluctuations, as measured by a microwave profiling radiometer. For each representative atmosphere ray paths are analyzed using geometrical optics, which is particularly advantageous in situations of strong turbulence where there is severe wavefront distortion and discontinuity. The refractive index structure parameter is then determined as a function of height and time.

Imaging the source region of the 2003 San Simeon earthquake within the weak Franciscan subduction complex, central California

USGS Publications Warehouse

Hauksson, E.; Oppenheimer, D.; Brocher, T.M.

2004-01-01

Data collected from the 2003 Mw6.5 San Simeon earthquake sequence in central California and a 1986 seismic refraction experiment demonstrate that the weak Franciscan subduction complex suffered brittle failure in a region without significant velocity contrast across a slip plane. Relocated hypocenters suggest a spatial relationship between the seismicity and the Oceanic fault, although blind faulting on a nearby, unknown fault is an equally plausible alternative. The aftershock volume is sandwiched between the Nacimiento and Oceanic faults and is characterized by rocks of low compressional velocity (Vp) abutted to the east and west by rocks of higher Vp. This volume of inferred Franciscan rocks is embedded within the larger Santa Lucia anticline. Pore fluids, whose presence is implied by elevated Vp/Vs values, may locally decrease normal stress and limit the aftershock depth distribution between 3 to 10 km within the hanging wall. The paucity of aftershocks along the mainshock rupture surface may reflect either the absence of a damage zone or an almost complete stress drop within the low Vp or weak rock matrix surrounding the mainshock rupture. Copyright 2004 by the American Geophysical Union.

Temperature dependence of nu3 and nu4 bandwidths and complex refractive indices for crystalline methane

NASA Technical Reports Server (NTRS)

Ngoh, M. A.; Khanna, R. K.; Fox, K.

1993-01-01

Infrared spectra of thin films of pure CH4 have been measured for a range of temperatures from 22 to 68 K. The bandwidth for the fundamental nu3 near 3000/cm varies from 12.7 to 33.2/cm, while that for nu4 near 1300/cm varies from 6.2 to 16.0/cm. The real and imaginary parts of the index of refraction also exhibit significant dependence on temperature. These broadband measurements at low temperatures are useful for an understanding of clouds and hazes in the atmosphere of Uranus, clouds and ices in the atmosphere of Titan, and ices on the surfaces of Pluto and Triton.

Constrained dipole oscillator strength distributions, sum rules, and dispersion coefficients for Br2 and BrCN

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Thakkar, Ajit J.

2017-03-01

Dipole oscillator strength distributions for Br2 and BrCN are constructed from photoabsorption cross-sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule, the high-energy behavior of the dipole-oscillator-strength density and molar refractivity data when available. The distributions are used to predict dipole sum rules S (k) , mean excitation energies I (k) , and van der Waals C6 coefficients. Coupled-cluster calculations of the static dipole polarizabilities of Br2 and BrCN are reported for comparison with the values of S (- 2) extracted from the distributions.

Simultaneous identification of optical constants and PSD of spherical particles by multi-wavelength scattering-transmittance measurement

NASA Astrophysics Data System (ADS)

Zhang, Jun-You; Qi, Hong; Ren, Ya-Tao; Ruan, Li-Ming

2018-04-01

An accurate and stable identification technique is developed to retrieve the optical constants and particle size distributions (PSDs) of particle system simultaneously from the multi-wavelength scattering-transmittance signals by using the improved quantum particle swarm optimization algorithm. The Mie theory are selected to calculate the directional laser intensity scattered by particles and the spectral collimated transmittance. The sensitivity and objective function distribution analysis were conducted to evaluate the mathematical properties (i.e. ill-posedness and multimodality) of the inverse problems under three different optical signals combinations (i.e. the single-wavelength multi-angle light scattering signal, the single-wavelength multi-angle light scattering and spectral transmittance signal, and the multi-angle light scattering and spectral transmittance signal). It was found the best global convergence performance can be obtained by using the multi-wavelength scattering-transmittance signals. Meanwhile, the present technique have been tested under different Gaussian measurement noise to prove its feasibility in a large solution space. All the results show that the inverse technique by using multi-wavelength scattering-transmittance signals is effective and suitable for retrieving the optical complex refractive indices and PSD of particle system simultaneously.

Measurement of 3D refractive index distribution by optical diffraction tomography

NASA Astrophysics Data System (ADS)

Chi, Weining; Wang, Dayong; Wang, Yunxin; Zhao, Jie; Rong, Lu; Yuan, Yuanyuan

2018-01-01

Optical Diffraction Tomography (ODT), as a novel 3D imaging technique, can obtain a 3D refractive index (RI) distribution to reveal the important optical properties of transparent samples. According to the theory of ODT, an optical diffraction tomography setup is built based on the Mach-Zehnder interferometer. The propagation direction of object beam is controlled by a 2D translation stage, and 121 holograms based on different illumination angles are recorded by a Charge-coupled Device (CCD). In order to prove the validity and accuracy of the ODT, the 3D RI profile of microsphere with a known RI is firstly measured. An iterative constraint algorithm is employed to improve the imaging accuracy effectively. The 3D morphology and average RI of the microsphere are consistent with that of the actual situation, and the RI error is less than 0.0033. Then, an optical element fabricated by laser with a non-uniform RI is taken as the sample. Its 3D RI profile is obtained by the optical diffraction tomography system.

Dependence of the forward light scattering on the refractive index of particles

NASA Astrophysics Data System (ADS)

Guo, Lufang; Shen, Jianqi

2018-05-01

In particle sizing technique based on forward light scattering, the scattered light signal (SLS) is closely related to the relative refractive index (RRI) of the particles to the surrounding, especially when the particles are transparent (or weakly absorbent) and the particles are small in size. The interference between the diffraction (Diff) and the multiple internal reflections (MIR) of scattered light can lead to the oscillation of the SLS on RRI and the abnormal intervals, especially for narrowly-distributed small particle systems. This makes the inverse problem more difficult. In order to improve the inverse results, Tikhonov regularization algorithm with B-spline functions is proposed, in which the matrix element is calculated for a range of particle sizes instead using the mean particle diameter of size fractions. In this way, the influence of abnormal intervals on the inverse results can be eliminated. In addition, for measurements on narrowly distributed small particles, it is suggested to detect the SLS in a wider scattering angle to include more information.

Accurate radiative transfer calculations for layered media.

PubMed

Selden, Adrian C

2016-07-01

Simple yet accurate results for radiative transfer in layered media with discontinuous refractive index are obtained by the method of K-integrals. These are certain weighted integrals applied to the angular intensity distribution at the refracting boundaries. The radiative intensity is expressed as the sum of the asymptotic angular intensity distribution valid in the depth of the scattering medium and a transient term valid near the boundary. Integrated boundary equations are obtained, yielding simple linear equations for the intensity coefficients, enabling the angular emission intensity and the diffuse reflectance (albedo) and transmittance of the scattering layer to be calculated without solving the radiative transfer equation directly. Examples are given of half-space, slab, interface, and double-layer calculations, and extensions to multilayer systems are indicated. The K-integral method is orders of magnitude more accurate than diffusion theory and can be applied to layered scattering media with a wide range of scattering albedos, with potential applications to biomedical and ocean optics.

Genetic Engineering of Optical Properties of Biomaterials

NASA Astrophysics Data System (ADS)

Gourley, Paul; Naviaux, Robert; Yaffe, Michael

2008-03-01

Baker's yeast cells are easily cultured and can be manipulated genetically to produce large numbers of bioparticles (cells and mitochondria) with controllable size and optical properties. We have recently employed nanolaser spectroscopy to study the refractive index of individual cells and isolated mitochondria from two mutant strains. Results show that biomolecular changes induced by mutation can produce bioparticles with radical changes in refractive index. Wild-type mitochondria exhibit a distribution with a well-defined mean and small variance. In striking contrast, mitochondria from one mutant strain produced a histogram that is highly collapsed with a ten-fold decrease in the mean and standard deviation. In a second mutant strain we observed an opposite effect with the mean nearly unchanged but the variance increased nearly a thousand-fold. Both histograms could be self-consistently modeled with a single, log-normal distribution. The strains were further examined by 2-dimensional gel electrophoresis to measure changes in protein composition. All of these data show that genetic manipulation of cells represents a new approach to engineering optical properties of bioparticles.

Numerical analyses for thinned fiber Bragg grating under uneven surrounding refractive index environment

NASA Astrophysics Data System (ADS)

Luo, Bin-bin; Zhao, Ming-fu; Zhou, Xiao-jun; Huang, De-yi; Wang, Shao-fei; Cao, Xue-mei

2011-12-01

Based on the fiber waveguide models, a modified transfer matrix method was utilized to calculate the reflection spectrum of the thinned fiber Bragg grating (ThFBG) under the uneven surrounding refractive index (SRI) environment. Tow SRI ranges, including the high SRI region (from 1.42 to the fiber cladding index) and the low ones (from 1.33 to about 1.36), were considered. Numerical results showed that the responsive characteristics of the reflectance spectrum of the ThFBG were closely related to the properties of the SRI distribution, first, the original reflection spectrum of the ThFBG would split into many tinny resonant peaks and the reflectance spectrums are asymmetric since the uneven SRI distributions, second, the number of the resonant peaks, the decline of the amplitude, and the degree of the asymmetric of the reflectance spectrums would increase as the increase in the SRI gradient and the D-value of the SRI between the tow ends of the ThFBG. The same numerical approach could be used to analyze the responsive characteristics of the ThFBG under the uneven medium environment where the SRI distribution was any other functions.

Size-exclusion chromatography of perfluorosulfonated ionomers.

PubMed

Mourey, T H; Slater, L A; Galipo, R C; Koestner, R J

2011-08-26

A size-exclusion chromatography (SEC) method in N,N-dimethylformamide containing 0.1 M LiNO(3) is shown to be suitable for the determination of molar mass distributions of three classes of perfluorosulfonated ionomers, including Nafion(®). Autoclaving sample preparation is optimized to prepare molecular solutions free of aggregates, and a solvent exchange method concentrates the autoclaved samples to enable the use of molar-mass-sensitive detection. Calibration curves obtained from light scattering and viscometry detection suggest minor variation in the specific refractive index increment across the molecular size distributions, which introduces inaccuracies in the calculation of local absolute molar masses and intrinsic viscosities. Conformation plots that combine apparent molar masses from light scattering detection with apparent intrinsic viscosities from viscometry detection partially compensate for the variations in refractive index increment. The conformation plots are consistent with compact polymer conformations, and they provide Mark-Houwink-Sakurada constants that can be used to calculate molar mass distributions without molar-mass-sensitive detection. Unperturbed dimensions and characteristic ratios calculated from viscosity-molar mass relationships indicate unusually free rotation of the perfluoroalkane backbones and may suggest limitations to applying two-parameter excluded volume theories for these ionomers. Copyright © 2011 Elsevier B.V. All rights reserved.

High sensitivity phase retrieval method in grating-based x-ray phase contrast imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Zhao; Gao, Kun; Chen, Jian

2015-02-15

Purpose: Grating-based x-ray phase contrast imaging is considered as one of the most promising techniques for future medical imaging. Many different methods have been developed to retrieve phase signal, among which the phase stepping (PS) method is widely used. However, further practical implementations are hindered, due to its complex scanning mode and high radiation dose. In contrast, the reverse projection (RP) method is a novel fast and low dose extraction approach. In this contribution, the authors present a quantitative analysis of the noise properties of the refraction signals retrieved by the two methods and compare their sensitivities. Methods: Using themore » error propagation formula, the authors analyze theoretically the signal-to-noise ratios (SNRs) of the refraction images retrieved by the two methods. Then, the sensitivities of the two extraction methods are compared under an identical exposure dose. Numerical experiments are performed to validate the theoretical results and provide some quantitative insight. Results: The SNRs of the two methods are both dependent on the system parameters, but in different ways. Comparison between their sensitivities reveals that for the refraction signal, the RP method possesses a higher sensitivity, especially in the case of high visibility and/or at the edge of the object. Conclusions: Compared with the PS method, the RP method has a superior sensitivity and provides refraction images with a higher SNR. Therefore, one can obtain highly sensitive refraction images in grating-based phase contrast imaging. This is very important for future preclinical and clinical implementations.« less

A microlens array based on polymer network liquid crystal

NASA Astrophysics Data System (ADS)

Xu, Miao; Zhou, Zuowei; Ren, Hongwen; Hee Lee, Seung; Wang, Qionghua

2013-02-01

Using UV light to expose a homogeneous cell containing liquid crystal (LC)/monomer mixture through a patterned photomask, we prepared a polymer network liquid crystal (PNLC) microlens array. In each microlens, the formed polymer network presents a central-symmetrical inhomogeneous morphology and LC exhibits a gradient refractive index distribution. By applying an external voltage to the cell, the gradient of the LC refractive index is changed. As a result, the focal length of the microlens can be tuned. Our PNLC microlens array has the advantages of low operating voltage, easy fabrication, and good stability. This kind of microlens array has potential applications in image processing, optical communications, and switchable 2D/3D displays.

Local reconstruction in computed tomography of diffraction enhanced imaging

NASA Astrophysics Data System (ADS)

Huang, Zhi-Feng; Zhang, Li; Kang, Ke-Jun; Chen, Zhi-Qiang; Zhu, Pei-Ping; Yuan, Qing-Xi; Huang, Wan-Xia

2007-07-01

Computed tomography of diffraction enhanced imaging (DEI-CT) based on synchrotron radiation source has extremely high sensitivity of weakly absorbing low-Z samples in medical and biological fields. The authors propose a modified backprojection filtration(BPF)-type algorithm based on PI-line segments to reconstruct region of interest from truncated refraction-angle projection data in DEI-CT. The distribution of refractive index decrement in the sample can be directly estimated from its reconstruction images, which has been proved by experiments at the Beijing Synchrotron Radiation Facility. The algorithm paves the way for local reconstruction of large-size samples by the use of DEI-CT with small field of view based on synchrotron radiation source.

Evaluation of thermal load during laser corneal refractive surgery using infrared thermography

NASA Astrophysics Data System (ADS)

Brunsmann, U.; Sauer, U.; Arba-Mosquera, S.; Magnago, T.; Triefenbach, N.

2010-09-01

Infrared thermography is used for evaluation of the mean temperature as a measure of thermal load during corneal refractive surgery. An experimental method to determine emissivity and to calibrate the thermografic system is presented. In a case study on the porcine eye two dimensional temperature distributions with lateral resolution of 170 μm and line scans with temporal resolution of 13 μs are discussed with respect to the meaning of mean temperature. Using the newest generation of surgery equipment it is shown, that the mean temperature rise can be kept below 5 °C during myopic laser in situ keratomileusis (LASIK) treatments corresponding to an aberration-free correction of -2.75 diopter.

Fine tuning of the dichroic behavior of Bragg reflectors based on anisotropically nanostructured silicon

NASA Astrophysics Data System (ADS)

Diener, J.; Künzner, N.; Kovalev, D.; Gross, E.; Koch, F.; Fujii, M.

2003-05-01

Electro-chemical etching of heavily doped, (110) oriented, p+ (boron) doped silicon wafers results in porous silicon (PSi) layers which exhibit a strong in-plane anisotropy of the refractive index (birefringence). Single- and multiple layers of anisotropically nanostructured silicon (Si) have been fabricated and studied by polarization-resolved reflection and transmission measurements. Dielectric stacks of birefringent PSi acting as distributed Bragg reflectors have two distinct reflection bands depending on the polarization of the incident linearly polarized light. This effect is caused by a three-dimensional (in plane and in-depth) variation of the refraction index. The possibility of fine tuning the two orthogonally polarized reflection bands and their spectral splitting is demonstrated.

Determination of optical parameters of atmospheric particulates from ground-based polarimeter measurements

NASA Technical Reports Server (NTRS)

Kuriyan, J. G.; Phillips, D. H.; Willson, R. C.

1974-01-01

This paper describes the theoretical analysis that is required to infer, from polarimeter measurements of skylight, the size distribution, refractive index and abundance of particulates in the atmosphere. To illustrate the viability of the method, some data obtained at UCLA is analyzed and the atmospheric parameters are derived. The explicit demonstration of the redundancy in the description of aerosol distributions suggests that radiation field measurements will not uniquely determine the modal radius of the size distribution. In spite of this nonuniqueness information useful to heat budget calculations can be derived.

Refraction and visual acuity in a national Danish cohort of 4-year-old children of extremely preterm delivery.

PubMed

Fledelius, Hans C; Bangsgaard, Regitze; Slidsborg, Carina; laCour, Morten

2015-06-01

A recent threefold increase in laser treatment for advanced retinopathy of prematurity (ROP) triggered a nationwide preschool ophthalmic and developmental status among extremely preterm survivors. Here, we discuss refraction and visual acuity. Survivors (n = 178) from a national birth cohort (February 2004 to March 2006) of gestational age <28 weeks (PT) and 56 full-term (FT) controls attended for evaluation at age 4 years. Cycloplegic refraction and keratometry were achieved by Retinomax autokeratorefractor and visual acuities by symbol recognition (HOTV, logMAR). The refractive distribution presented a myopic tail (4.5%) and a hyperopic tail (11.9% ≥+2.5 D) as special preterm features, and corneas were more curved. Astigmatism and anisometropia were only marginally increased, and visual acuities were generally good. Best-corrected binocular median logMAR visual acuity was 0.1 in FT and 0.2 in PT, in Snellen equivalents 0.8 and 0.63. Snellen acuity ≤0.5 occurred across the ROP subgroups, but mainly in those with at least ROP stage 3. Two children had low vision. The overall fair outcome for refraction and function is in accordance with other recent northern Europe experience. The results differ in particular from the poorer ophthalmic outcomes reported in the pioneer US treatment studies (cryotherapy for ROP and ETROP). The diode laser ablations (n = 32) appeared effective in our series; except one child, all treated subjects had good or fair social vision at the age of 4 years. © 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

Computed estimation of visual acuity after laser refractive keratectomy

NASA Astrophysics Data System (ADS)

Rol, Pascal O.; Parel, Jean-Marie A.; Hanna, Khalil

1991-06-01

A number of surgical techniques has been developed to correct ametropia (refractive defaults) of the eye by changing the anterior corneal radius. Because the air-cornea interface makes up for about two-third of the refractive power of the eye, a refractive correction is obtained by a suitable photoablation of the cornea. For this purpose, e.g., an ArF excimer laser which emits a wavelength of 193 nm is being used. After a mechanical removal of the epithelium, the Bowman's layer and the corneal stroma are photoablated on typically 50% of the central surface of the cornea with various precomputed shapes. Methods using a variable diaphragm1 or a scanning slit2 are being utilized. After regrowth of the epithelium, a smooth interface with air develops itself, which can be attributed to a mechanical equilibration. Yet, SEM studies have shown that with such kind of treatments, irregularities can remain in the new stromal surface (Fig. 1). A possible explanation for this effect is associated with an inhomogeneous energy distribution of the laser beam profile3. To some extent, the stromal surface is equalized by the epithelial layer during healing& However, as the corneal epithelium and stroma have different refractive indices, a scatter of the incident light may result causing a haze in the cornea and a blur of the image at the retina. In such a case the resolution and the contrast performance of the eye which is expected from a successful operation, may be reduced. This study is an attempt to quantify the vision blur as a function of the deformation observed at the epithelium-stroma interface.

Refractive errors and strabismus in Down's syndrome in Korea.

PubMed

Han, Dae Heon; Kim, Kyun Hyung; Paik, Hae Jung

2012-12-01

The aims of this study were to examine the distribution of refractive errors and clinical characteristics of strabismus in Korean patients with Down's syndrome. A total of 41 Korean patients with Down's syndrome were screened for strabismus and refractive errors in 2009. A total of 41 patients with an average age of 11.9 years (range, 2 to 36 years) were screened. Eighteen patients (43.9%) had strabismus. Ten (23.4%) of 18 patients exhibited esotropia and the others had intermittent exotropia. The most frequently detected type of esotropia was acquired non-accommodative esotropia, and that of exotropia was the basic type. Fifteen patients (36.6%) had hypermetropia and 20 (48.8%) had myopia. The patients with esotropia had refractive errors of +4.89 diopters (D, ±3.73) and the patients with exotropia had refractive errors of -0.31 D (±1.78). Six of ten patients with esotropia had an accommodation weakness. Twenty one patients (63.4%) had astigmatism. Eleven (28.6%) of 21 patients had anisometropia and six (14.6%) of those had clinically significant anisometropia. In Korean patients with Down's syndrome, esotropia was more common than exotropia and hypermetropia more common than myopia. Especially, Down's syndrome patients with esotropia generally exhibit clinically significant hyperopic errors (>+3.00 D) and evidence of under-accommodation. Thus, hypermetropia and accommodation weakness could be possible factors in esotropia when it occurs in Down's syndrome patients. Based on the results of this study, eye examinations of Down's syndrome patients should routinely include a measure of accommodation at near distances, and bifocals should be considered for those with evidence of under-accommodation.

Determining the infrared radiative effects of Saharan dust: a radiative transfer modelling study based on vertically resolved measurements at Lampedusa

NASA Astrophysics Data System (ADS)

Meloni, Daniela; di Sarra, Alcide; Brogniez, Gérard; Denjean, Cyrielle; De Silvestri, Lorenzo; Di Iorio, Tatiana; Formenti, Paola; Gómez-Amo, José L.; Gröbner, Julian; Kouremeti, Natalia; Liuzzi, Giuliano; Mallet, Marc; Pace, Giandomenico; Sferlazzo, Damiano M.

2018-03-01

Detailed measurements of radiation, atmospheric and aerosol properties were carried out in summer 2013 during the Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region (ADRIMED) campaign in the framework of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) experiment. This study focusses on the characterization of infrared (IR) optical properties and direct radiative effects of mineral dust, based on three vertical profiles of atmospheric and aerosol properties and IR broadband and narrowband radiation from airborne measurements, made in conjunction with radiosonde and ground-based observations at Lampedusa, in the central Mediterranean. Satellite IR spectra from the Infrared Atmospheric Sounder Interferometer (IASI) are also included in the analysis. The atmospheric and aerosol properties are used as input to a radiative transfer model, and various IR radiation parameters (upward and downward irradiance, nadir and zenith brightness temperature at different altitudes) are calculated and compared with observations. The model calculations are made for different sets of dust particle size distribution (PSD) and refractive index (RI), derived from observations and from the literature. The main results of the analysis are that the IR dust radiative forcing is non-negligible and strongly depends on PSD and RI. When calculations are made using the in situ measured size distribution, it is possible to identify the refractive index that produces the best match with observed IR irradiances and brightness temperatures (BTs). The most appropriate refractive indices correspond to those determined from independent measurements of mineral dust aerosols from the source regions (Tunisia, Algeria, Morocco) of dust transported over Lampedusa, suggesting that differences in the source properties should be taken into account. With the in situ size distribution and the most appropriate refractive index the estimated dust IR radiative forcing efficiency is +23.7 W m-2 at the surface, -7.9 W m-2 within the atmosphere, and +15.8 W m-2 at the top of the atmosphere. The use of column-integrated dust PSD from AERONET may also produce a good agreement with measured irradiances and BTs, but with significantly different values of the RI. This implies large differences, up to a factor of 2.5 at surface, in the estimated dust radiative forcing, and in the IR heating rate. This study shows that spectrally resolved measurements of BTs are important to better constrain the dust IR optical properties, and to obtain a reliable estimate of its radiative effects. Efforts should be directed at obtaining an improved description of the dust size distribution and its vertical distribution, as well as at including regionally resolved optical properties.