On the interpolation of light-scattering responses from irregularly shaped particles

NASA Astrophysics Data System (ADS)

Videen, Gorden; Zubko, Evgenij; Arnold, Jessica A.; MacCall, Benjamin; Weinberger, Alycia J.; Shkuratov, Yuriy; Muñoz, Olga

2018-05-01

Common particle characteristics needed for many applications may include size, eccentricity, porosity and refractive index. Determining such characteristics from scattered light is a primary goal of remote sensing. For other applications, like differentiating a hazardous particle from the natural background, information about higher fidelity particle characteristics may be required, including specific shape or chemical composition. While a complete characterization of a particle system from its scattered light through the inversion process remains unachievable, great strides have been made in providing information in the form of constraints on particle characteristics. Recent advances have been made in quantifying the characteristics of polydispersions of irregularly shaped particles by making comparisons of the light-scattering signals from model simulant particles. We show that when the refractive index is changed, the light-scattering characteristics from polydispersions of such particles behave monotonically over relatively large parameter ranges compared with those of monodisperse distributions of particles having regular shapes, like spheres, spheroids, etc. This allows for their properties to be interpolated, which results in a significant reduction of the computational load when performing inversions.

Field mappers for laser material processing

NASA Astrophysics Data System (ADS)

Blair, Paul; Currie, Matthew; Trela, Natalia; Baker, Howard J.; Murphy, Eoin; Walker, Duncan; McBride, Roy

2016-03-01

The native shape of the single-mode laser beam used for high power material processing applications is circular with a Gaussian intensity profile. Manufacturers are now demanding the ability to transform the intensity profile and shape to be compatible with a new generation of advanced processing applications that require much higher precision and control. We describe the design, fabrication and application of a dual-optic, beam-shaping system for single-mode laser sources, that transforms a Gaussian laser beam by remapping - hence field mapping - the intensity profile to create a wide variety of spot shapes including discs, donuts, XY separable and rotationally symmetric. The pair of optics transform the intensity distribution and subsequently flatten the phase of the beam, with spot sizes and depth of focus close to that of a diffraction limited beam. The field mapping approach to beam-shaping is a refractive solution that does not add speckle to the beam, making it ideal for use with single mode laser sources, moving beyond the limits of conventional field mapping in terms of spot size and achievable shapes. We describe a manufacturing process for refractive optics in fused silica that uses a freeform direct-write process that is especially suited for the fabrication of this type of freeform optic. The beam-shaper described above was manufactured in conventional UV-fused silica using this process. The fabrication process generates a smooth surface (<1nm RMS), leading to laser damage thresholds of greater than 100J/cm2, which is well matched to high power laser sources. Experimental verification of the dual-optic filed mapper is presented.

Optical force on a large sphere illuminated by Bessel beams: comparisons between ray optics method and generalized Lorenz-Mie theory.

PubMed

Song, Shukun; Wang, Neng; Lu, Wanli; Lin, Zhifang

2014-10-01

Optical forces are calculated for a dielectric spherical particle illuminated by a zero-order Bessel beam based on both the generalized Lorenz-Mie theory (GLMT) and the ray optics method (ROM). Particles with positive and negative refractive indices are examined. The peculiar characteristics of the Bessel beam allow for analytical expressions for the beam shape coefficients required in the GLMT as well as a decomposition of optical force into the gradient and the scattering forces irrespective of the particle size, which enable respective comparisons for the gradient and scattering forces between the results obtained from the GLMT and the ROM. Our results demonstrate that the discrepancy between the results obtained from the GLMT and the ROM depends on the particle refractive index n_p, the particle size, and, also, the particle location in the beam field. As the particle size increases, the difference between the results from the GLMT and the ROM shows a general tendency of decreasing, as can be expected, but the change may exhibit oscillatory rather than monotonic behavior. A phase diagram is presented that displays the regime for particle size and refractive index where a specified accuracy can be achieved for optical force by the ROM.

Rapid, Accurate, and Non-Invasive Measurement of Zebrafish Axial Length and Other Eye Dimensions Using SD-OCT Allows Longitudinal Analysis of Myopia and Emmetropization

PubMed Central

Collery, Ross F.; Veth, Kerry N.; Dubis, Adam M.; Carroll, Joseph; Link, Brian A.

2014-01-01

Refractive errors in vision can be caused by aberrant axial length of the eye, irregular corneal shape, or lens abnormalities. Causes of eye length overgrowth include multiple genetic loci, and visual parameters. We evaluate zebrafish as a potential animal model for studies of the genetic, cellular, and signaling basis of emmetropization and myopia. Axial length and other eye dimensions of zebrafish were measured using spectral domain-optical coherence tomography (SD-OCT). We used ocular lens and body metrics to normalize and compare eye size and relative refractive error (difference between observed retinal radial length and controls) in wild-type and lrp2 zebrafish. Zebrafish were dark-reared to assess effects of visual deprivation on eye size. Two relative measurements, ocular axial length to body length and axial length to lens diameter, were found to accurately normalize comparisons of eye sizes between different sized fish (R2 = 0.9548, R2 = 0.9921). Ray-traced focal lengths of wild-type zebrafish lenses were equal to their retinal radii, while lrp2 eyes had longer retinal radii than focal lengths. Both genetic mutation (lrp2) and environmental manipulation (dark-rearing) caused elongated eye axes. lrp2 mutants had relative refractive errors of −0.327 compared to wild-types, and dark-reared wild-type fish had relative refractive errors of −0.132 compared to light-reared siblings. Therefore, zebrafish eye anatomy (axial length, lens radius, retinal radius) can be rapidly and accurately measured by SD-OCT, facilitating longitudinal studies of regulated eye growth and emmetropization. Specifically, genes homologous to human myopia candidates may be modified, inactivated or overexpressed in zebrafish, and myopia-sensitizing conditions used to probe gene-environment interactions. Our studies provide foundation for such investigations into genetic contributions that control eye size and impact refractive errors. PMID:25334040

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.

A Multi-D-Shaped Optical Fiber for Refractive Index Sensing

PubMed Central

Chen, Chien-Hsing; Tsao, Tzu-Chein; Tang, Jaw-Luen; Wu, Wei-Te

2010-01-01

A novel class of multi-D-shaped optical fiber suited for refractive index measurements is presented. The multi-D-shaped optical fiber was constructed by forming several D-sections in a multimode optical fiber at localized regions with femtosecond laser pulses. The total number of D-shaped zones fabricated could range from three to seven. Each D-shaped zone covered a sensor volume of 100 μm depth, 250 μm width, and 1 mm length. The mean roughness of the core surface obtained by the AFM images was 231.7 nm, which is relatively smooth. Results of the tensile test indicated that the fibers have sufficient mechanical strength to resist damage from further processing. The multi-D-shaped optical fiber as a high sensitive refractive-index sensor to detect changes in the surrounding refractive index was studied. The results for different concentrations of sucrose solution show that a resolution of 1.27 × 10−3–3.13 × 10−4 RIU is achieved for refractive indices in the range of 1.333 to 1.403, suggesting that the multi-D-shaped fibers are attractive for chemical, biological, and biochemical sensing with aqueous solutions. PMID:22399908

Eye Shape Using Partial Coherence Interferometry, Autorefraction and SD OCT

PubMed Central

Clark, Christopher A.; Elsner, Ann E.; Konynenbelt, Benjamin J.

2015-01-01

Purpose Peripheral refraction and retinal shape may influence refractive development. Peripheral refraction has been shown to have a high degree of variability and can take considerable time to perform. SD OCT and peripheral axial length measures may be more reliable, assuming that the retinal position is more important than the peripheral optics of the lens/cornea. Methods 79 subjects right eyes were imaged for this study (age range: 22 to 34 yr, refractive error: −10 to +5.00.) Thirty deg SD OCT (Spectralis, Heidleberg) images were collected in a radial pattern along with peripheral refraction with an autorefractor (Shin-Nippon Auto-refractor) and peripheral axial length measurements with partial coherence interferometry (PCI) (IOLmaster, Zeiss). Statistics were performed using repeat measures ANOVA in SPSS (IBM), Bland-Altman analyses, and regression. All measures were converted to diopters to allow direct comparison. Results SD OCT showed a retinal shape with an increased curvature for myopes compared to emmetropes/hyperopes. This retinal shape change became significant around 5 deg. The SD OCT analysis for retinal shape provides a resolution of 0.026 dipopters, which is about ten times more accurate than using autorefraction or clinical refractive techniques. Bland-Altman analyses suggest that retinal shape measured by SD OCT and the PCI method were more consistent with one another than either was with AR. Conclusions With more accurate measures of retinal shape using SD OCT, consistent differences between emmetrope/hyperopes and myopes were found nearer to the fovea than previously reported. Retinal shape may be influenced by central refractive error, and not merely peripheral optics. Partial coherence interferometry and SD OCT appear to be more accurate than autorefraction, which may be influenced other factors such as fixation and accommodation. Autorefraction does measure the optics directly, which may be a strength of that method. PMID:25437906

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.

Optical-analog-to-digital conversion based on successive-like approximations in octagonal-shape photonic crystal ring resonators

NASA Astrophysics Data System (ADS)

Tavousi, A.; Mansouri-Birjandi, M. A.

2018-02-01

Implementing intensity-dependent Kerr-like nonlinearity in octagonal-shape photonic crystal ring resonators (OSPCRRs), a new class of optical analog-to-digital converters (ADCs) with low power consumption is presented. Due to its size dependent refractive index, Silicon (Si) nanocrystal is used as nonlinear medium in the proposed ADC. Coding system of optical ADC is based on successive-like approximations which requires only one quantization level to represent each single bit, despite of conventional ADCs that require at least two distinct levels for each bit. Each is representing bit of optical ADC is formed by vertically alignment of double rings of OSPCRRs (DR-OSPCRR) and cascading m number of DR-OSPCRR, forms an m bit ADC. Investigating different parameters of DR-OSPCRR such as refractive indices of rings, lattice refractive index, and coupling coefficients of waveguide-to-ring and ring-to-ring, the ADC's threshold power is tuned. Increasing the number of bits of ADC, increases the overall power consumption of ADC. One can arrange to have any number of bits for this ADC, as long as the power levels are treated carefully. Finite difference time domain (FDTD) in-house codes were used to evaluate the ADC's effectiveness.

In-line open-cavity Fabry-Pérot interferometer formed by C-shaped fiber fortemperature-insensitive refractive index sensing.

PubMed

Wu, Chuang; Liu, Zhengyong; Zhang, A Ping; Guan, Bai-Ou; Tam, Hwa-Yaw

2014-09-08

We report an open-cavity optical fiber Fabry-Pérot interferometer (FPI) capable of measuring refractive index with very low temperature cross-sensitivity. The FPI was constructed by splicing a thin piece of C-shaped fiber between two standard single-mode fibers. The refractive index (RI) response of the FPI was characterized using water-ethanol mixtures with RI in the range of 1.33 to 1.36. The RI sensitivity was measured to be 1368 nm/RIU at the wavelength of 1600 nm with good linearity. Thanks to its all-glass structure, the FPI exhibits very low temperature cross-sensitivity of 3.04 × 10⁻⁷ RIU/°C. The effects of cavity length on the performance of the sensor were also studied. A shorter cavity gives rise to broader measurement range while offering larger detection limit, and vice versa. What's more, the effect of material dispersion of analyte on the sensitivity of open-cavity FPIs was identified for the first time. The sensor is compact in size and easy to fabricate. It is potentially useful for label-free optical sensing of chemical and biological samples.

Spectral solution of the inverse Mie problem

NASA Astrophysics Data System (ADS)

Romanov, Andrey V.; Konokhova, Anastasiya I.; Yastrebova, Ekaterina S.; Gilev, Konstantin V.; Strokotov, Dmitry I.; Chernyshev, Andrei V.; Maltsev, Valeri P.; Yurkin, Maxim A.

2017-10-01

We developed a fast method to determine size and refractive index of homogeneous spheres from the power Fourier spectrum of their light-scattering patterns (LSPs), measured with the scanning flow cytometer. Specifically, we used two spectral parameters: the location of the non-zero peak and zero-frequency amplitude, and numerically inverted the map from the space of particle characteristics (size and refractive index) to the space of spectral parameters. The latter parameters can be reliably resolved only for particle size parameter greater than 11, and the inversion is unique only in the limited range of refractive index with upper limit between 1.1 and 1.25 (relative to the medium) depending on the size parameter and particular definition of uniqueness. The developed method was tested on two experimental samples, milk fat globules and spherized red blood cells, and resulted in accuracy not worse than the reference method based on the least-square fit of the LSP with the Mie theory. Moreover, for particles with significant deviation from the spherical shape the spectral method was much closer to the Mie-fit result than the estimated uncertainty of the latter. The spectral method also showed adequate results for synthetic LSPs of spheroids with aspect ratios up to 1.4. Overall, we present a general framework, which can be used to construct an inverse algorithm for any other experimental signals.

Eye shape using partial coherence interferometry, autorefraction, and SD-OCT.

PubMed

Clark, Christopher A; Elsner, Ann E; Konynenbelt, Benjamin J

2015-01-01

Peripheral refraction and retinal shape may influence refractive development. Peripheral refraction has been shown to have a high degree of variability and can take considerable time to perform. Spectral domain optical coherence tomography (SD-OCT) and peripheral axial length measures may be more reliable, assuming that the retinal position is more important than the peripheral optics of the lens/cornea. Seventy-nine subjects' right eyes were imaged for this study (age range, 22 to 34 years; refractive error, -10 to +5.00). Thirty-degree SD-OCT (Spectralis, Heidelberg Engineering, Heidelberg, Germany) images were collected in a radial pattern along with peripheral refraction with an autorefractor (Shin-Nippon Autorefractor) and peripheral axial length measurements with partial coherence interferometry (IOLMaster, Zeiss). Statistics were performed using repeated-measures analysis of variance in SPSS (IBM, Armonk, NY), Bland-Altman analyses, and regression. All measures were converted to diopters to allow direct comparison. Spectral domain OCT showed a retinal shape with an increased curvature for myopes compared with emmetropes/hyperopes. This retinal shape change became significant around 5 degrees. The SD-OCT analysis for retinal shape provides a resolution of 0.026 diopters, which is about 10 times more accurate than using autorefraction (AR) or clinical refractive techniques. Bland-Altman analyses suggest that retinal shape measured by SD-OCT and the partial coherence interferometry method were more consistent with one another than either was with AR. With more accurate measures of retinal shape using SD-OCT, consistent differences between emmetropes/hyperopes and myopes were found nearer to the fovea than previously reported. Retinal shape may be influenced by central refractive error, and not merely peripheral optics. Partial coherence interferometry and SD-OCT appear to be more accurate than AR, which may be influenced by other factors such as fixation and accommodation. Autorefraction does measure the optics directly, which may be a strength of that method.

Retrievals of Aerosol and Cloud Particle Microphysics Using Polarization and Depolarization Techniques

NASA Technical Reports Server (NTRS)

Mishchenko, Michael; Hansen, James E. (Technical Monitor)

2001-01-01

The recent availability of theoretical techniques for computing single and multiple scattering of light by realistic polydispersions of spherical and nonspherical particles and the strong dependence of the Stokes scattering matrix on particle size, shape, and refractive index make polarization and depolarization measurements a powerful particle characterization tool. In this presentation I will describe recent applications of photopolarimetric and lidar depolarization measurements to remote sensing characterization of tropospheric aerosols, polar stratospheric clouds (PSCs), and contrails. The talk will include (1) a short theoretical overview of the effects of particle microphysics on particle single-scattering characteristics; (2) the use of multi-angle multi-spectral photopolarimetry to retrieve the optical thickness, size distribution, refractive index, and number concentration of tropospheric aerosols over the ocean surface; and (3) the application of the T-matrix method to constraining the PSC and contrail particle microphysics using multi-spectral measurements of lidar backscatter and depolarization.

Explaining negative refraction without negative refractive indices.

PubMed

Talalai, Gregory A; Garner, Timothy J; Weiss, Steven J

2018-03-01

Negative refraction through a triangular prism may be explained without assigning a negative refractive index to the prism by using array theory. For the case of a beam incident upon the wedge, the array theory accurately predicts the beam transmission angle through the prism and provides an estimate of the frequency interval at which negative refraction occurs. The hypotenuse of the prism has a staircase shape because it is built of cubic unit cells. The large phase delay imparted by each unit cell, combined with the staircase shape of the hypotenuse, creates the necessary conditions for negative refraction. Full-wave simulations using the finite-difference time-domain method show that array theory accurately predicts the beam transmission angle.

Optical analysis of time-averaged multiscale Bessel beams generated by a tunable acoustic gradient index of refraction lens.

PubMed

McLeod, Euan; Arnold, Craig B

2008-07-10

Current methods for generating Bessel beams are limited to fixed beam sizes or, in the case of conventional adaptive optics, relatively long switching times between beam shapes. We analyze the multiscale Bessel beams created using an alternative rapidly switchable device: a tunable acoustic gradient index (TAG) lens. The shape of the beams and their nondiffracting, self-healing characteristics are studied experimentally and explained theoretically using both geometric and Fourier optics. By adjusting the electrical driving signal, we can tune the ring spacings, the size of the central spot, and the working distance of the lens. The results presented here will enable researchers to employ dynamic Bessel beams generated by TAG lenses.

The eye lens: age-related trends and individual variations in refractive index and shape parameters.

PubMed

Pierscionek, Barbara; Bahrami, Mehdi; Hoshino, Masato; Uesugi, Kentaro; Regini, Justyn; Yagi, Naoto

2015-10-13

The eye lens grows throughout life by cell accrual on its surface and can change shape to adjust the focussing power of the eye. Varying concentrations of proteins in successive cell layers create a refractive index gradient. The continued growth of the lens and age-related changes in proteins render it less able to alter shape with loss of capacity by the end of the sixth decade of life. Growth and protein ageing alter the refractive index but as accurate measurement of this parameter is difficult, the nature of such alterations remains uncertain. The most accurate method to date for measuring refractive index in intact lenses has been developed at the SPring-8 synchrotron. The technique, based on Talbot interferometry, has an X-ray source and was used to measure refractive index in sixty-six human lenses, aged from 16 to 91 years. Height and width were measured for forty-five lenses. Refractive index contours show decentration in some older lenses but individual variations mask age-related trends. Refractive index profiles along the optic axis have relatively flat central sections with distinct micro-fluctuations and a steep gradient in the cortex but do not exhibit an age-related trend. The refractive index profiles in the equatorial aspect show statistical significance with age, particularly for lenses below the age of sixty that had capacity to alter shape in vivo. The maximum refractive index in the lens centre decreases slightly with age with considerable scatter in the data and there are age-related variations in sagittal thickness and equatorial height.

The eye lens: age-related trends and individual variations in refractive index and shape parameters

PubMed Central

Pierscionek, Barbara; Bahrami, Mehdi; Hoshino, Masato; Uesugi, Kentaro; Regini, Justyn; Yagi, Naoto

2015-01-01

The eye lens grows throughout life by cell accrual on its surface and can change shape to adjust the focussing power of the eye. Varying concentrations of proteins in successive cell layers create a refractive index gradient. The continued growth of the lens and age-related changes in proteins render it less able to alter shape with loss of capacity by the end of the sixth decade of life. Growth and protein ageing alter the refractive index but as accurate measurement of this parameter is difficult, the nature of such alterations remains uncertain. The most accurate method to date for measuring refractive index in intact lenses has been developed at the SPring-8 synchrotron. The technique, based on Talbot interferometry, has an X-ray source and was used to measure refractive index in sixty-six human lenses, aged from 16 to 91 years. Height and width were measured for forty-five lenses. Refractive index contours show decentration in some older lenses but individual variations mask age-related trends. Refractive index profiles along the optic axis have relatively flat central sections with distinct micro-fluctuations and a steep gradient in the cortex but do not exhibit an age-related trend. The refractive index profiles in the equatorial aspect show statistical significance with age, particularly for lenses below the age of sixty that had capacity to alter shape in vivo. The maximum refractive index in the lens centre decreases slightly with age with considerable scatter in the data and there are age-related variations in sagittal thickness and equatorial height. PMID:26416418

Influence of spherical aberration, stimulus spatial frequency, and pupil apodisation on subjective refractions

PubMed Central

Bradley, Arthur; Xu, Renfeng; Thibos, Larry; Marin, Gildas; Hernandez, Martha

2014-01-01

Purpose To test competing hypotheses (Stiles Crawford pupil apodising or superior imaging of high spatial frequencies by the central pupil) for the pupil size independence of subjective refractions in the presence of primary spherical aberration. Methods Subjective refractions were obtained with a variety of test stimuli (high contrast letters, urban cityscape, high and low spatial frequency gratings) while modulating pupil diameter, levels of primary spherical aberration and pupil apodisation. Subjective refractions were also obtained with low-pass and high-pass stimuli and using “darker” and “sharper” subjective criteria. Results Subjective refractions for stimuli containing high spatial frequencies focus a near paraxial region of the pupil and are affected only slightly by level of Seidel spherical aberration, degree of pupil apodisation and pupil diameter, and generally focused a radius of about 1 to 1.5 mm from the pupil centre. Low spatial frequency refractions focus a marginal region of the pupil, and are significantly affected by level of spherical aberration, amount of pupil apodisation, and pupil size. Clinical refractions that employ the “darker” or “sharper” subjective criteria bias the patient to use lower or higher spatial frequencies respectively. Conclusions In the presence of significant levels of spherical aberration, the pupil size independence of subjective refractions occurs with or without Stiles Crawford apodisation for refractions that optimise high spatial frequency content in the image. If low spatial frequencies are optimised by a subjective refraction, spherical refractive error varies with spherical aberration, pupil size, and level of apodisation. As light levels drop from photopic to scotopic, therefore, we expect a shift from pupil size independent to pupil size dependent subjective refractions. Emphasising a “sharper” criterion during subjective refractions will improve image quality for high spatial frequencies and generate pupil size independent refractions. PMID:24397356

Asymptotic Solutions for Optical Properties of Large Particles with Strong Absorption

NASA Technical Reports Server (NTRS)

Yang, Ping; Gao, Bo-Cai; Baum, Bryan A.; Hu, Yong X.; Wiscombe, Warren J.; Mishchenko, Michael I.; Winker, Dave M.; Nasiri, Shaima L.; Einaudi, Franco (Technical Monitor)

2000-01-01

For scattering calculations involving nonspherical particles such as ice crystals, we show that the transverse wave condition is not applicable to the refracted electromagnetic wave in the context of geometric optics when absorption is involved. Either the TM wave condition (i.e., where the magnetic field of the refracted wave is transverse with respect to the wave direction) or the TE wave condition (i.e., where the electric field is transverse with respect to the propagating direction of the wave) may be assumed for the refracted wave in an absorbing medium to locally satisfy the electromagnetic boundary condition in the ray tracing calculation. The wave mode assumed for the refracted wave affects both the reflection and refraction coefficients. As a result, a nonunique solution for these coefficients is derived from the electromagnetic boundary condition. In this study we have identified the appropriate solution for the Fresnel reflection/refraction coefficients in light scattering calculation based on the ray tracing technique. We present the 3 x 2 refraction or transmission matrix that completely accounts for the inhomogeneity of the refracted wave in an absorbing medium. Using the Fresnel coefficients for an absorbing medium, we derive an asymptotic solution in an analytical format for the scattering properties of a general polyhedral particle. Numerical results are presented for hexagonal plates and columns with both preferred and random orientations. The asymptotic theory can produce reasonable accuracy in the phase function calculations in the infrared window region (wavelengths near 10 micron) if the particle size (in diameter) is on the order of 40 micron or larger. However, since strong absorption is assumed in the computation of the single-scattering albedo in the asymptotic theory, the single scattering albedo does not change with variation of the particle size. As a result, the asymptotic theory can lead to substantial errors in the computation of single-scattering albedo for small and moderate particle sizes. However, from comparison of the asymptotic results with the FDTD solution, it is expected that a convergence between the FDTD results and the asymptotic theory results can be reached when the particle size approaches 200 micron. We show that the phase function at side-scattering and backscattering angles is insensitive to particle shape if the random orientation condition is assumed. However, if preferred orientations are assumed for particles, the phase function has a strong dependence on scattering azimuthal angle. The single-scattering albedo also shows very strong dependence on the inclination angle of incident radiation with respect to the rotating axis for the preferred particle orientations.

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.

Determination of absorption coefficient of nanofluids with unknown refractive index from reflection and transmission spectra

NASA Astrophysics Data System (ADS)

Kim, Joong Bae; Lee, Seungyoon; Lee, Kyungeun; Lee, Ikjin; Lee, Bong Jae

2018-07-01

It has been shown that the absorption coefficient of a nanofluid can be actively tuned by changing material, size, shape, and concentration of the nanoparticle suspension. In applications of engineered nanofluids for the direct absorption of solar radiation, it is important to experimentally characterize the absorption coefficient of nanofluids in the solar spectrum. If the refractive index of the base fluid (i.e., the solution without nanoparticles) is known a priori, the absorption coefficient of nanofluids can be easily determined from the transmission spectrum. However, if the refractive index of the base fluid is not known, it is not straightforward to extract the absorption coefficient solely from the transmission spectrum. The present work aims to develop an analytical method of determining the absorption coefficient of nanofluids with unknown refractive index by measuring both reflection and transmission spectra. The proposed method will be validated with deionized water, and the effect of measurement uncertainty will be carefully examined. Finally, the general applicability of the proposed method will also be demonstrated for Therminol VP-1 as well as the Therminol VP-1 - graphite nanofluid.

Accurate bulk density determination of irregularly shaped translucent and opaque aerogels

NASA Astrophysics Data System (ADS)

Petkov, M. P.; Jones, S. M.

2016-05-01

We present a volumetric method for accurate determination of bulk density of aerogels, calculated from extrapolated weight of the dry pure solid and volume estimates based on the Archimedes' principle of volume displacement, using packed 100 μm-sized monodispersed glass spheres as a "quasi-fluid" media. Hard particle packing theory is invoked to demonstrate the reproducibility of the apparent density of the quasi-fluid. Accuracy rivaling that of the refractive index method is demonstrated for both translucent and opaque aerogels with different absorptive properties, as well as for aerogels with regular and irregular shapes.

Light Scattering Analysis of Irregularly Shaped Dust Particles: A Study Using 3-Dimensional Reconstructions from Focused Ion-Beam (FIB) Tomography and Q-Space Analysis

NASA Astrophysics Data System (ADS)

Ortiz-Montalvo, D. L.; Conny, J. M.

2017-12-01

We study the scattering properties of irregularly shaped ambient dust particles. The way in which they scatter and absorb light has implications for aerosol optical remote sensing and aerosol radiative forcing applications. However, understanding light scattering and absorption by non-spherical particles can be very challenging. We used focused ion-beam scanning electron microscopy and energy-dispersive x-ray spectroscopy (FIB-SEM-EDS) to reconstruct three-dimensional (3-D) configurations of dust particles collected from urban and Asian sources. The 3-D reconstructions were then used in a discrete dipole approximation method (DDA) to determine their scattering properties for a range of shapes, sizes, and refractive indices. Scattering properties where obtained using actual-shapes of the particles, as well as, (theoretical) equivalently-sized geometrical shapes like spheres, ellipsoids, cubes, rectangular prisms, and tetrahedrons. We use Q-space analysis to interpret the angular distribution of the scattered light obtained for each particle. Q-space analysis has been recently used to distinguish scattering by particles of different shapes, and it involves plotting the scattered intensity versus the scattering wave vector (q or qR) on a log-log scale, where q = 2ksin(θ/2), k = 2π/λ, and R = particle effective radius. Results from a limited number of particles show that when Q-space analysis is applied, common patterns appear that agree with previous Q-space studies done on ice crystals and other irregularly shaped particles. More specifically, we found similar Q-space regimes including a forward scattering regime of constant intensity when qR < 1, followed by the Guinier regime when qR ≈ 1, which is then followed by a complex power law regime with a -3 slope regime, a transition regime, and then a -4 slope regime. Currently, Q-space comparisons between actual- and geometric shapes are underway with the objective of determining which geometric shape best represents the angular distribution and magnitude of the scattered light. Current work also focuses on the effects of the imaginary part of the refractive index on the light scattering of our dust particles.

Light scattering properties of spheroidal particles

NASA Technical Reports Server (NTRS)

Asano, S.

1979-01-01

In the present paper, the light scattering characteristics of spheroidal particles are evaluated within the framework of a scattering theory developed for a homogeneous isotropic spheroid. This approach is shown to be well suited for computing the scattering quantities of spheroidal particles of fairly large sizes (up to a size parameter of 30). The effects of particle size, shape, index of refraction, and orientation on the scattering efficiency factors and the scattering intensity functions are studied and interpreted physically. It is shown that, in the case of oblique incidence, the scattering properties of a long slender prolate spheroid resemble those of an infinitely long circular cylinder.

Influence of size and shape of sub-micrometer light scattering centers in ZnO-assisted TiO2 photoanode for dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Pham, Trang T. T.; Mathews, Nripan; Lam, Yeng-Ming; Mhaisalkar, Subodh

2018-03-01

Sub-micrometer cavities have been incorporated in the TiO2 photoanode of dye-sensitized solar cell to enhance its optical property with light scattering effect. These are large pores of several hundred nanometers in size and scatter incident light due to the difference refraction index between the scattering center and the surrounding materials, according to Mie theory. The pores are created using polystyrene (PS) or zinc oxide (ZnO) templates reported previously which resulted in ellipsoidal and spherical shapes, respectively. The effect of size and shape of scattering center was modeled using a numerical analysis finite-difference time-domain (FDTD). The scattering cross-section was not affected significantly with different shapes if the total displacement volume of the scattering center is comparable. Experiments were carried out to evaluate the optical property with varying size of ZnO templates. Photovoltaic effect of dye-sensitized solar cells made from these ZnO-assisted films were investigated with incident-photon-to-current efficiency to understand the effect of scattering center size on the enhancement of absorption. With 380 nm macropores incorporated, the power conversion efficiency has increased by 11% mostly thanks to the improved current density, while 170 nm and 500 nm macropores samples did not have increment in sufficiently wide range of absorbing wavelengths.

Refractive Errors

MedlinePlus

... and lens of your eye helps you focus. Refractive errors are vision problems that happen when the shape ... cornea, or aging of the lens. Four common refractive errors are Myopia, or nearsightedness - clear vision close up ...

A scattering database of marine particles and its application in optical analysis

NASA Astrophysics Data System (ADS)

Xu, G.; Yang, P.; Kattawar, G.; Zhang, X.

2016-12-01

In modeling the scattering properties of marine particles (e.g. phytoplankton), the laboratory studies imply a need to properly account for the influence of particle morphology, in addition to size and composition. In this study, a marine particle scattering database is constructed using a collection of distorted hexahedral shapes. Specifically, the scattering properties of each size bin and refractive index are obtained by the ensemble average associated with distorted hexahedra with randomly tilted facets and selected aspect ratios (from elongated to flattened). The randomness degree in shape-generation process defines the geometric irregularity of the particles in the group. The geometric irregularity and particle aspect ratios constitute a set of "shape factors" to be accounted for (e.g. in best-fit analysis). To cover most of the marine particle size range, we combine the Invariant Imbedding T-matrix (II-TM) method and the Physical-Geometric Optics Hybrid (PGOH) method in the calculations. The simulated optical properties are shown and compared with those obtained from Lorenz-Mie Theory. Using the scattering database, we present a preliminary optical analysis of laboratory-measured optical properties of marine particles.

Controlling soliton refraction in optical lattices.

PubMed

Prilepsky, Jaroslaw E; Derevyanko, Stanislav A; Gredeskul, Sergey A

2011-08-19

We show in the framework of the 1D nonlinear Schrödinger equation that the value of the refraction angle of a fundamental soliton beam passing through an optical lattice can be controlled by adjusting either the shape of an individual waveguide or the relative positions of the waveguides. In the case of the shallow refractive index modulation, we develop a general approach for the calculation of the refraction angle change. The shape of a single waveguide crucially affects the refraction direction due to the appearance of a structural form factor in the expression for the density of emitted waves. For a lattice of scatterers, wave-soliton interference inside the lattice leads to the appearance of an additional geometric form factor. As a result, the soliton refraction is more pronounced for the disordered lattices than for the periodic ones. © 2011 American Physical Society

Mesopic pupil size in a refractive surgery population (13,959 eyes).

PubMed

Linke, Stephan J; Baviera, Julio; Munzer, Gur; Fricke, Otto H; Richard, Gisbert; Katz, Toam

2012-08-01

To evaluate factors that may affect mesopic pupil size in refractive surgery candidates. Medical records of 13,959 eyes of 13,959 refractive surgery candidates were reviewed, and one eye per subject was selected randomly for statistical analysis. Detailed ophthalmological examination data were obtained from medical records. Preoperative measurements included uncorrected distance visual acuity, corrected distance visual acuity, manifest and cycloplegic refraction, topography, slit lamp examination, and funduscopy. Mesopic pupil size measurements were performed with Colvard pupillometer. Relationship between mesopic pupil size and age, gender, refractive state, average keratometry, and pachymetry (thinnest point) were analyzed by means of ANOVA (+ANCOVA) and multivariate regression analyses. Overall mesopic pupil size was 6.45 ± 0.82 mm, and mean age was 36.07 years. Mesopic pupil size was 5.96 ± 0.8 mm in hyperopic astigmatism, 6.36 ± 0.83 mm in high astigmatism, and 6.51 ± 0.8 mm in myopic astigmatism. The difference in mesopic pupil size between all refractive subgroups was statistically significant (p < 0.001). Age revealed the strongest correlation (r = -0.405, p < 0.001) with mesopic pupil size. Spherical equivalent showed a moderate correlation (r = -0.136), whereas keratometry (r = -0.064) and pachymetry (r = -0.057) had a weak correlation with mesopic pupil size. No statistically significant difference in mesopic pupil size was noted regarding gender and ocular side. The sum of all analyzed factors (age, refractive state, keratometry, and pachymetry) can only predict the expected pupil size in <20% (R = 0.179, p < 0.001). Our analysis confirmed that age and refractive state are determinative factors on mesopic pupil size. Average keratometry and minimal pachymetry exhibited a statistically significant, but clinically insignificant, impact on mesopic pupil size.

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.

An optical wavefront sensor based on a double layer microlens array.

PubMed

Lin, Vinna; Wei, Hsiang-Chun; Hsieh, Hsin-Ta; Su, Guo-Dung John

2011-01-01

In order to determine light aberrations, Shack-Hartmann optical wavefront sensors make use of microlens arrays (MLA) to divide the incident light into small parts and focus them onto image planes. In this paper, we present the design and fabrication of long focal length MLA with various shapes and arrangements based on a double layer structure for optical wavefront sensing applications. A longer focal length MLA could provide high sensitivity in determining the average slope across each microlens under a given wavefront, and spatial resolution of a wavefront sensor is increased by numbers of microlenses across a detector. In order to extend focal length, we used polydimethysiloxane (PDMS) above MLA on a glass substrate. Because of small refractive index difference between PDMS and MLA interface (UV-resin), the incident light is less refracted and focused in further distance. Other specific focal lengths could also be realized by modifying the refractive index difference without changing the MLA size. Thus, the wavefront sensor could be improved with better sensitivity and higher spatial resolution.

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.

Two step continuous method to synthesize colloidal spheroid gold nanorods.

PubMed

Chandra, S; Doran, J; McCormack, S J

2015-12-01

This research investigated a two-step continuous process to synthesize colloidal suspension of spheroid gold nanorods. In the first step; gold precursor was reduced to seed-like particles in the presence of polyvinylpyrrolidone and ascorbic acid. In continuous second step; silver nitrate and alkaline sodium hydroxide produced various shape and size Au nanoparticles. The shape was manipulated through weight ratio of ascorbic acid to silver nitrate by varying silver nitrate concentration. The specific weight ratio of 1.35-1.75 grew spheroid gold nanorods of aspect ratio ∼1.85 to ∼2.2. Lower weight ratio of 0.5-1.1 formed spherical nanoparticle. The alkaline medium increased the yield of gold nanorods and reduced reaction time at room temperature. The synthesized gold nanorods retained their shape and size in ethanol. The surface plasmon resonance was red shifted by ∼5 nm due to higher refractive index of ethanol than water. Copyright © 2015 Elsevier Inc. All rights reserved.

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.

Groove micro-structure optical fiber refractive index sensor with nanoscale gold film based on surface plasmon resonance

NASA Astrophysics Data System (ADS)

Zhang, Zhen; Li, Shuguang; Liu, Qiang; Feng, Xinxing; Zhang, Shuhuan; Wang, Yujun; Wu, Junjun

2018-07-01

A groove micro-structure optical fiber refractive index sensor with nanoscale gold film based on surface plasmon resonance (SPR) is proposed and analyzed by the finite element method (FEM). Numerical results show that the average sensitivity is 15,933 nm/refractive index unit (RIU) with the refractive index of analyte ranging from 1.40 to 1.43 and the maximum sensitivity is 28,600 nm/RIU and the resolution of the sensor is 3.50 × 10-8 RIU. The groove micro-structure optical fiber refractive index sensor do some changes on the D-shaped fiber sensor, compared with conventional D-shaped fiber sensor, it has a higher sensitivity and it is easier to produce than the traditional SPR sensor.

Background oriented schlieren measurement of the refractive index field of air induced by a hot, cylindrical measurement object.

PubMed

Beermann, Rüdiger; Quentin, Lorenz; Pösch, Andreas; Reithmeier, Eduard; Kästner, Markus

2017-05-10

To optically capture the topography of a hot measurement object with high precision, the light deflection by the inhomogeneous refractive index field-induced by the heat transfer from the measurement object to the ambient medium-has to be considered. We used the 2D background oriented schlieren method with illuminated wavelet background, an optical flow algorithm, and Ciddor's equation to quantify the refractive index field located directly above a red-glowing, hot measurement object. A heat transfer simulation has been implemented to verify the magnitude and the shape of the measured refractive index field. Provided that no forced external flow is disturbing the shape of the convective flow originating from the hot object, a laminar flow can be observed directly above the object, resulting in a sharply bounded, inhomogeneous refractive index field.

Peripheral Refraction Validity of the Shin-Nippon SRW5000 Autorefractor.

PubMed

Osuagwu, Uchechukwu Levi; Suheimat, Marwan; Wolffsohn, James S; Atchison, David A

2016-10-01

To investigate the operation of the Shin-Nippon/Grand Seiko autorefractor and whether higher-order aberrations affect its peripheral refraction measurements. Information on instrument design, together with parameters and equations used to obtain refraction, was obtained from a patent. A model eye simulating the operating principles was tested with an optical design program. Effects of induced defocus and astigmatism on the retinal image were used to calibrate the model eye to match the patent equations. Coma and trefoil were added to assess their effects on the image. Peripheral refraction of a physical model eye was measured along four visual field meridians with the Shin-Nippon/Grand Seiko autorefractor SRW-5000 and a Hartmann-Shack aberrometer, and simulated autorefractor peripheral refraction was derived using the Zernike coefficients from the aberrometer. In simulation, the autorefractor's square image was changed in size by defocus, into rectangles or parallelograms by astigmatism, and into irregular shapes by coma and trefoil. In the presence of 1.0 D oblique astigmatism, errors in refraction were proportional to the higher-order aberrations, with up to 0.8 D sphere and 1.5 D cylinder for ±0.6 μm of coma or trefoil coefficients with a 5-mm-diameter pupil. For the physical model eye, refraction with the aberrometer was similar in all visual field meridians, but refraction with the autorefractor changed more quickly along one oblique meridian and less quickly along the other oblique meridian than along the horizontal and vertical meridians. Simulations predicted that higher-order aberrations would affect refraction in oblique meridians, and this was supported by the experimental measurements with the physical model eye. The autorefractor's peripheral refraction measurements are valid for horizontal and vertical field meridians, but not for oblique field meridians. Similar instruments must be validated before being adopted outside their design scope.

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.

Global scale variability of the mineral dust long-wave refractive index: a new dataset of in situ measurements for climate modeling and remote sensing

NASA Astrophysics Data System (ADS)

Di Biagio, Claudia; Formenti, Paola; Balkanski, Yves; Caponi, Lorenzo; Cazaunau, Mathieu; Pangui, Edouard; Journet, Emilie; Nowak, Sophie; Caquineau, Sandrine; Andreae, Meinrat O.; Kandler, Konrad; Saeed, Thuraya; Piketh, Stuart; Seibert, David; Williams, Earle; Doussin, Jean-François

2017-02-01

Modeling the interaction of dust with long-wave (LW) radiation is still a challenge because of the scarcity of information on the complex refractive index of dust from different source regions. In particular, little is known about the variability of the refractive index as a function of the dust mineralogical composition, which depends on the specific emission source, and its size distribution, which is modified during transport. As a consequence, to date, climate models and remote sensing retrievals generally use a spatially invariant and time-constant value for the dust LW refractive index. In this paper, the variability of the mineral dust LW refractive index as a function of its mineralogical composition and size distribution is explored by in situ measurements in a large smog chamber. Mineral dust aerosols were generated from 19 natural soils from 8 regions: northern Africa, the Sahel, eastern Africa and the Middle East, eastern Asia, North and South America, southern Africa, and Australia. Soil samples were selected from a total of 137 available samples in order to represent the diversity of sources from arid and semi-arid areas worldwide and to account for the heterogeneity of the soil composition at the global scale. Aerosol samples generated from soils were re-suspended in the chamber, where their LW extinction spectra (3-15 µm), size distribution, and mineralogical composition were measured. The generated aerosol exhibits a realistic size distribution and mineralogy, including both the sub- and super-micron fractions, and represents in typical atmospheric proportions the main LW-active minerals, such as clays, quartz, and calcite. The complex refractive index of the aerosol is obtained by an optical inversion based upon the measured extinction spectrum and size distribution. Results from the present study show that the imaginary LW refractive index (k) of dust varies greatly both in magnitude and spectral shape from sample to sample, reflecting the differences in particle composition. In the 3-15 µm spectral range, k is between ˜ 0.001 and 0.92. 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. The imaginary part (k) is observed to vary both from region to region and for varying sources within the same region. Conversely, for the real part (n), which is in the range 0.84-1.94, values are observed to agree for all dust samples across most of the spectrum within the error bars. This implies that while a constant n can be probably assumed for dust from different sources, a varying k should be used both at the global and the regional scale. A linear relationship between the magnitude of the imaginary refractive index at 7.0, 9.2, and 11.4 µm and the mass concentration of calcite and quartz absorbing at these wavelengths was found. We suggest that this may lead to predictive rules to estimate the LW refractive index of dust in specific bands based on an assumed or predicted mineralogical composition, or conversely, to estimate the dust composition from measurements of the LW extinction at specific wavebands. Based on the results of the present study, we recommend that climate models and remote sensing instruments operating at infrared wavelengths, such as IASI (infrared atmospheric sounder interferometer), use regionally dependent refractive indices rather than generic values. Our observations also suggest that the refractive index of dust in the LW does not change as a result of the loss of coarse particles by gravitational settling, so that constant values of n and k could be assumed close to sources and following transport. The whole dataset of the dust complex refractive indices presented in this paper is made available to the scientific community in the Supplement.

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.

Wavefront coherence area for predicting visual acuity of post-PRK and post-PARK refractive surgery patients

NASA Astrophysics Data System (ADS)

Garcia, Daniel D.; van de Pol, Corina; Barsky, Brian A.; Klein, Stanley A.

1999-06-01

Many current corneal topography instruments (called videokeratographs) provide an `acuity index' based on corneal smoothness to analyze expected visual acuity. However, post-refractive surgery patients often exhibit better acuity than is predicted by such indices. One reason for this is that visual acuity may not necessarily be determined by overall corneal smoothness but rather by having some part of the cornea able to focus light coherently onto the fovea. We present a new method of representing visual acuity by measuring the wavefront aberration, using principles from both ray and wave optics. For each point P on the cornea, we measure the size of the associated coherence area whose optical path length (OPL), from a reference plane to P's focus, is within a certain tolerance of the OPL for P. We measured the topographies and vision of 62 eyes of patients who had undergone the corneal refractive surgery procedures of photorefractive keratectomy (PRK) and photorefractive astigmatic keratectomy (PARK). In addition to high contrast visual acuity, our vision tests included low contrast and low luminance to test the contribution of the PRK transition zone. We found our metric for visual acuity to be better than all other metrics at predicting the acuity of low contrast and low luminance. However, high contrast visual acuity was poorly predicted by all of the indices we studied, including our own. The indices provided by current videokeratographs sometimes fail for corneas whose shape differs from simple ellipsoidal models. This is the case with post-PRK and post-PARK refractive surgery patients. Our alternative representation that displays the coherence area of the wavefront has considerable advantages, and promises to be a better predictor of low contrast and low luminance visual acuity than current shape measures.

D-shaped fiber grating refractive index sensor induced by an ultrashort pulse laser.

PubMed

Liao, Changrui; Wang, Qiao; Xu, Lei; Liu, Shen; He, Jun; Zhao, Jing; Li, Zhengyong; Wang, Yiping

2016-03-01

The fabrication of fiber Bragg gratings was here demonstrated using ultrashort pulse laser point-by-point inscription. This is a very convenient means of creating fiber Bragg gratings with different grating periods and works by changing the translation speed of the fiber. The laser energy was first optimized in order to improve the spectral properties of the fiber gratings. Then, fiber Bragg gratings were formed into D-shaped fibers for use as refractive index sensors. A nonlinear relationship was observed between the Bragg wavelength and liquid refractive index, and a sensitivity of ∼30  nm/RIU was observed at 1.450. This shows that D-shaped fiber Bragg gratings might be used to develop promising biochemical sensors.

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.

Laser beam shaping for biomedical microscopy techniques

NASA Astrophysics Data System (ADS)

Laskin, Alexander; Kaiser, Peter; Laskin, Vadim; Ostrun, Aleksei

2016-04-01

Uniform illumination of a working field is very important in optical systems of confocal microscopy and various implementations of fluorescence microscopy like TIR, SSIM, STORM, PALM to enhance performance of these laser-based research techniques. Widely used TEM00 laser sources are characterized by essentially non-uniform Gaussian intensity profile which leads usually to non-uniform intensity distribution in a microscope working field or in a field of microlenses array of a confocal microscope optical system, this non-uniform illumination results in instability of measuring procedure and reducing precision of quantitative measurements. Therefore transformation of typical Gaussian distribution of a TEM00 laser to flat-top (top hat) profile is an actual technical task, it is solved by applying beam shaping optics. Due to high demands to optical image quality the mentioned techniques have specific requirements to a uniform laser beam: flatness of phase front and extended depth of field, - from this point of view the microscopy techniques are similar to holography and interferometry. 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 required in discussed microscopy techniques. We suggest applying refractive field mapping beam shapers 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. The main function of a beam shaper is transformation of laser intensity profile, further beam transformation to provide optimum for a particular technique spot size and shape has to be realized by an imaging optical system which can include microscope objectives and tube lenses. This paper will describe design basics of refractive beam shapers and optical layouts of their applying in microscopy systems. Examples of real implementations and experimental results will be presented as well.

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.

Refractive Index Sensing with D-Shaped Plastic Optical Fibers for Chemical and Biochemical Applications

PubMed Central

Sequeira, Filipa; Duarte, Daniel; Bilro, Lúcia; Rudnitskaya, Alisa; Pesavento, Maria; Zeni, Luigi; Cennamo, Nunzio

2016-01-01

We report the optimization of the length of a D-shaped plastic optical fiber (POF) sensor for refractive index (RI) sensing from a numerical and experimental point of view. The sensing principle is based on total internal reflection (TIR). POFs with 1 mm in diameter were embedded in grooves, realized in planar supports with different lengths, and polished to remove the cladding and part of the core. All D-shaped POF sensors were tested using aqueous medium with different refractive indices (from 1.332 to 1.471) through intensity-based configuration. Results showed two different responses. Considering the refractive index (RI) range (1.33–1.39), the sensitivity and the resolution of the sensor were strongly dependent on the sensing region length. The highest sensitivity (resolution of 6.48 × 10−3 refractive index units, RIU) was obtained with 6 cm sensing length. In the RI range (1.41–1.47), the length of the sensing region was not a critical aspect to obtain the best resolution. These results enable the application of this optical platform for chemical and biochemical evanescent field sensing. The sensor production procedure is very simple, fast, and low-cost. PMID:27983608

Refractive Index Sensing with D-Shaped Plastic Optical Fibers for Chemical and Biochemical Applications.

PubMed

Sequeira, Filipa; Duarte, Daniel; Bilro, Lúcia; Rudnitskaya, Alisa; Pesavento, Maria; Zeni, Luigi; Cennamo, Nunzio

2016-12-13

We report the optimization of the length of a D-shaped plastic optical fiber (POF) sensor for refractive index (RI) sensing from a numerical and experimental point of view. The sensing principle is based on total internal reflection (TIR). POFs with 1 mm in diameter were embedded in grooves, realized in planar supports with different lengths, and polished to remove the cladding and part of the core. All D-shaped POF sensors were tested using aqueous medium with different refractive indices (from 1.332 to 1.471) through intensity-based configuration. Results showed two different responses. Considering the refractive index (RI) range (1.33-1.39), the sensitivity and the resolution of the sensor were strongly dependent on the sensing region length. The highest sensitivity (resolution of 6.48 × 10 -3 refractive index units, RIU) was obtained with 6 cm sensing length. In the RI range (1.41-1.47), the length of the sensing region was not a critical aspect to obtain the best resolution. These results enable the application of this optical platform for chemical and biochemical evanescent field sensing. The sensor production procedure is very simple, fast, and low-cost.

More irregular eye shape in low myopia than in emmetropia.

PubMed

Tabernero, Juan; Schaeffel, Frank

2009-09-01

To improve the description of the peripheral eye shape in myopia and emmetropia by using a new method for continuous measurement of the peripheral refractive state. A scanning photorefractor was designed to record refractive errors in the vertical pupil meridian across the horizontal visual field (up to +/-45 degrees ). The setup consists of a hot mirror that continuously projects the infrared light from a photoretinoscope under different angles of eccentricity into the eye. The movement of the mirror is controlled by using two stepping motors. Refraction in a group of 17 emmetropic subjects and 11 myopic subjects (mean, -4.3 D; SD, 1.7) was measured without spectacle correction. For the analysis of eye shape, the refractive error versus the eccentricity angles was fitted with different polynomials (from second to tenth order). The new setup presents some important advantages over previous techniques: The subject does not have to change gaze during the measurements, and a continuous profile is obtained rather than discrete points. There was a significant difference in the fitting errors between the subjects with myopia and those with emmetropia. Tenth-order polynomials were required in myopic subjects to achieve a quality of fit similar to that in emmetropic subjects fitted with only sixth-order polynomials. Apparently, the peripheral shape of the myopic eye is more "bumpy." A new setup is presented for obtaining continuous peripheral refraction profiles. It was found that the peripheral retinal shape is more irregular even in only moderately myopic eyes, perhaps because the sclera lost some rigidity even at the early stage of myopia.

An Optical Wavefront Sensor Based on a Double Layer Microlens Array

PubMed Central

Lin, Vinna; Wei, Hsiang-Chun; Hsieh, Hsin-Ta; Su, Guo-Dung John

2011-01-01

In order to determine light aberrations, Shack-Hartmann optical wavefront sensors make use of microlens arrays (MLA) to divide the incident light into small parts and focus them onto image planes. In this paper, we present the design and fabrication of long focal length MLA with various shapes and arrangements based on a double layer structure for optical wavefront sensing applications. A longer focal length MLA could provide high sensitivity in determining the average slope across each microlens under a given wavefront, and spatial resolution of a wavefront sensor is increased by numbers of microlenses across a detector. In order to extend focal length, we used polydimethysiloxane (PDMS) above MLA on a glass substrate. Because of small refractive index difference between PDMS and MLA interface (UV-resin), the incident light is less refracted and focused in further distance. Other specific focal lengths could also be realized by modifying the refractive index difference without changing the MLA size. Thus, the wavefront sensor could be improved with better sensitivity and higher spatial resolution. PMID:22346643

Parabolic single-crystal diamond compound refractive lenses for coherent x-ray imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Terentyev, Sergey; Blank, Vladimir D.; Polyakov, Sergey; Zholudev, Sergey; Snigirev, Anatoly A.; Polikarpov, Maxim; Kolodziej, Tomasz; Qian, Jun; Zhou, Hua; Shvyd'ko, Yuri V.

2016-09-01

We demonstrate parabolic single-crystal diamond compound refractive lenses [1] designed for coherent x-ray imaging resilient to extreme thermal and radiation loading expected from next generation light sources. To ensure the preservation of coherence and resilience, the lenses are manufactured from the highest-quality single-crystalline synthetic diamond material grown by a high-pressure high-temperature technique. Picosecond laser milling is applied to machine lenses to parabolic shapes with a 1-micron precision and surface roughness. A compound refractive lens comprised of six lenses with a radius of curvature R=200 microns at the vertex of the parabola and a geometrical aperture A=900 microns focuses 10 keV x-ray photons from an undulator source at the Advanced Photon Source facility to a focal spot size of 10x40 microns^2 with a gain factor of 100. [1] S. Terentyev, V. Blank, S. Polyakov, S. Zholudev, A. Snigirev, M. Polikarpov, T. Kolodziej, J. Qian, H. Zhou, and Yu. Shvyd'ko Applied Physics Letters 107, 111108 (2015); doi: 10.1063/1.4931357

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.

Structural and optical properties of ZnO thin films prepared by RF sputtering at different thicknesses

NASA Astrophysics Data System (ADS)

Hammad, Ahmed H.; Abdel-wahab, M. Sh.; Vattamkandathil, Sajith; Ansari, Akhalakur Rahman

2018-07-01

Hexagonal nanocrystallites of ZnO in the form of thin films were prepared by radio frequency sputtering technique. X-ray diffraction analysis reveals two prominent diffraction planes (002) and (103) at diffraction angles around 34.3 and 62.8°, respectively. The crystallite size increases through (103) plane from 56.1 to 64.8 Å as film thickness changed from 31 nm up to 280 nm while crystallites growth through (002) increased from 124 to 136 Å as film thickness varies from 31 to 107 nm and dropped to 115.8 Å at thickness 280 nm. The particle shape changes from spherical to longitudinal form. The particle size is 25 nm for films of thickness below 107 nm and increases at higher thicknesses (134 and 280 nm) from 30 to 40 nm, respectively. Optical band gap is deduced to be direct with values varied from 3.22 to 3.28 eV and the refractive index are evaluated based on the optical band values according to Moss, Ravindra-Srivastava, and Dimitrov-Sakka models. All refractive index models gave values around 2.3.

Compensation of X-ray mirror shape-errors using refractive optics

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

Sawhney, Kawal, E-mail: Kawal.sawhney@diamond.ac.uk; Laundy, David; Pape, Ian

2016-08-01

Focusing of X-rays to nanometre scale focal spots requires high precision X-ray optics. For nano-focusing mirrors, height errors in the mirror surface retard or advance the X-ray wavefront and after propagation to the focal plane, this distortion of the wavefront causes blurring of the focus resulting in a limit on the spatial resolution. We describe here the implementation of a method for correcting the wavefront that is applied before a focusing mirror using custom-designed refracting structures which locally cancel out the wavefront distortion from the mirror. We demonstrate in measurements on a synchrotron radiation beamline a reduction in the sizemore » of the focal spot of a characterized test mirror by a factor of greater than 10 times. This technique could be used to correct existing synchrotron beamline focusing and nanofocusing optics providing a highly stable wavefront with low distortion for obtaining smaller focus sizes. This method could also correct multilayer or focusing crystal optics allowing larger numerical apertures to be used in order to reduce the diffraction limited focal spot size.« less

Mean effective size and refractive index of transparent atmospheric particulates

NASA Technical Reports Server (NTRS)

Fymat, A. L.

1975-01-01

It is demonstrated that the scattering ratio-principle originally restricted to exact forward and exact backward scattering, and to values of the size parameter and of the product (refractive index x size parameter) less than 0.8 has a much wider applicability. After relaxing these stringent conditions, it is also shown that this principle can be retained as the basis of an experimental technique for retrieving the mean effective size and refractive index of transparent atmospheric particulates.

Surgical Options for the Refractive Correction of Keratoconus: Myth or Reality

PubMed Central

Zaldivar, R.; Aiello, F.; Madrid-Costa, D.

2017-01-01

Keratoconus provides a decrease of quality of life to the patients who suffer from it. The treatment used as well as the method to correct the refractive error of these patients may influence on the impact of the disease on their quality of life. The purpose of this review is to describe the evidence about the conservative surgical treatment for keratoconus aiming to therapeutic and refractive effect. The visual rehabilitation for keratoconic corneas requires addressing three concerns: halting the ectatic process, improving corneal shape, and minimizing the residual refractive error. Cross-linking can halt the disease progression, intrastromal corneal ring segments can improve the corneal shape and hence the visual quality and reduce the refractive error, PRK can correct mild-moderate refractive error, and intraocular lenses can correct from low to high refractive error associated with keratoconus. Any of these surgical options can be performed alone or combined with the other techniques depending on what the case requires. Although it could be considered that the surgical option for the refracto-therapeutic treatment of the keratoconus is a reality, controlled, randomized studies with larger cohorts and longer follow-up periods are needed to determine which refractive procedure and/or sequence are most suitable for each case. PMID:29403662

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.

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

Fabrication Quality Analysis of a Fiber Optic Refractive Index Sensor Created by CO2 Laser Machining

PubMed Central

Chen, Chien-Hsing; Yeh, Bo-Kuan; Tang, Jaw-Luen; Wu, Wei-Te

2013-01-01

This study investigates the CO2 laser-stripped partial cladding of silica-based optic fibers with a core diameter of 400 μm, which enables them to sense the refractive index of the surrounding environment. However, inappropriate treatments during the machining process can generate a number of defects in the optic fiber sensors. Therefore, the quality of optic fiber sensors fabricated using CO2 laser machining must be analyzed. The results show that analysis of the fiber core size after machining can provide preliminary defect detection, and qualitative analysis of the optical transmission defects can be used to identify imperfections that are difficult to observe through size analysis. To more precisely and quantitatively detect fabrication defects, we included a tensile test and numerical aperture measurements in this study. After a series of quality inspections, we proposed improvements to the existing CO2 laser machining parameters, namely, a vertical scanning pathway, 4 W of power, and a feed rate of 9.45 cm/s. Using these improved parameters, we created optical fiber sensors with a core diameter of approximately 400 μm, no obvious optical transmission defects, a numerical aperture of 0.52 ± 0.019, a 0.886 Weibull modulus, and a 1.186 Weibull-shaped parameter. Finally, we used the optical fiber sensor fabricated using the improved parameters to measure the refractive indices of various solutions. The results show that a refractive-index resolution of 1.8 × 10−4 RIU (linear fitting R2 = 0.954) was achieved for sucrose solutions with refractive indices ranging between 1.333 and 1.383. We also adopted the particle plasmon resonance sensing scheme using the fabricated optical fibers. The results provided additional information, specifically, a superior sensor resolution of 5.73 × 10−5 RIU, and greater linearity at R2 = 0.999. PMID:23535636

Parameterization of Photon Tunneling with Application to Ice Cloud Optical Properties at Terrestrial Wavelengths

NASA Astrophysics Data System (ADS)

Mitchell, D. L.

2006-12-01

Sometimes deep physical insights can be gained through the comparison of two theories of light scattering. Comparing van de Hulst's anomalous diffraction approximation (ADA) with Mie theory yielded insights on the behavior of the photon tunneling process that resulted in the modified anomalous diffraction approximation (MADA). (Tunneling is the process by which radiation just beyond a particle's physical cross-section may undergo large angle diffraction or absorption, contributing up to 40% of the absorption when wavelength and particle size are comparable.) Although this provided a means of parameterizing the tunneling process in terms of the real index of refraction and size parameter, it did not predict the efficiency of the tunneling process, where an efficiency of 100% is predicted for spheres by Mie theory. This tunneling efficiency, Tf, depends on particle shape and ranges from 0 to 1.0, with 1.0 corresponding to spheres. Similarly, by comparing absorption efficiencies predicted by the Finite Difference Time Domain Method (FDTD) with efficiencies predicted by MADA, Tf was determined for nine different ice particle shapes, including aggregates. This comparison confirmed that Tf is a strong function of ice crystal shape, including the aspect ratio when applicable. Tf was lowest (< 0.36) for aggregates and plates, and largest (> 0.9) for quasi- spherical shapes. A parameterization of Tf was developed in terms of (1) ice particle shape and (2) mean particle size regarding the large mode (D > 70 mm) of the ice particle size distribution. For the small mode, Tf is only a function of ice particle shape. When this Tf parameterization is used in MADA, absorption and extinction efficiency differences between MADA and FDTD are within 14% over the terrestrial wavelength range 3-100 mm for all size distributions and most crystal shapes likely to be found in cirrus clouds. Using hyperspectral radiances, it is demonstrated that Tf can be retrieved from ice clouds. Since Tf is a function of ice particle shape, this may provide a means of retrieving qualitative information on ice particle shape.

Systematic study and comparison of photonic nanojets produced by dielectric microparticles in 2D- and 3D-spatial configurations

NASA Astrophysics Data System (ADS)

Geints, Yu E.; Zemlyanov, A. A.; Minin, O. V.; Minin, I. V.

2018-06-01

We present the systematic study of key characteristics (field intensity enhancement, spatial extents) of the 2D- and 3D-photonic nanojets (PNJs) produced by geometrically-regular micron-sized dielectric particles illuminated by a plane laser wave. By means of the finite-difference time-domain calculations, we highlight the differences and similarities between PNJs in these two spatial configurations for curved- (sphere, circular cylinder) and rectangle-shaped scatterers (cube, square bar). Our findings can be useful, for example, for the design of particle-based high-resolution imaging because the spatial resolution by such systems might be further controlled by the optimization of refractive index contrast and geometrical shape of the particle-lens.

Advances in spinel optical quality, size/shape capacity, and applications

NASA Astrophysics Data System (ADS)

Roy, Donald W.; Martin, Gay G., Jr.

1992-12-01

Polycrystalline MgAl2O4 Spinel, transparent from two hundred nanometers to six microns, offers a unique combination of optical and physical properties. A superior dome and window material with respect to rain and particle erosion, solar radiation, high temperatures and humidity, it is resistant to attack by strong acids, alkali solutions, sea water and jet fuels. Residual microporosity from the powder process used for fabricating Spinel which previously limited the use of Spinel to thin wall thicknesses and small sizes, has been significantly reduced by advanced hot press and hot isostatic press (HIP) technology. It is now possible to manufacture high quality shallow domes up to seven inches in diameter with a two tenths inch thick wall thickness. Eight inch diameter flat windows have been produced for an advanced missile system. Proof of process near hemispherical 8 inch dome blanks have been fabricated. Recent measurements of refractive index, homogeneity, scatter and surface roughness are available for design purposes. Improvement in the optical quality and in size/shape capability along with several successful prototype tests demonstrate that Spinel is ready for inclusion in appropriate production systems.

High transmission Ni compound refractive lens for high energy X-rays

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

Brancewicz, M., E-mail: brancew@spring8.or.jp; Itou, M.; Sakurai, Y.

We present a new planar Ni compound refractive lens for high energy X-rays (116 keV). The lens is composed of identical plano-concave elements with longitudinal parabolic grooves manufactured by a punch technique. In order to increase the lens transmission, the thickness of the single lens at the parabolic groove vertex was reduced to less than 5 μm and the radius of curvature was reduced to about 20 μm. The small radius of curvature allowed us to reduce the number of single elements needed to get the focal length of 3 m to 54 single lenses. The gain parameter has beenmore » significantly improved compared to the previous lenses due to higher transmission, but the focused beam size and its gain are not as good as expected, mostly due to the aberrations caused by the lens shape imperfections.« less

Parabolic single-crystal diamond lenses for coherent x-ray imaging

DOE PAGES

Terentyev, Sergey; Blank, Vladimir; Polyakov, Sergey; ...

2015-09-18

We demonstrate parabolic single-crystal diamond compound refractive lenses designed for coherent x-ray imaging resilient to extreme thermal and radiation loading expected from next generation light sources. To ensure the preservation of coherence and resilience, the lenses are manufactured from the highest-quality single-crystalline synthetic diamond material grown by a high-pressure high-temperature technique. Picosecond laser milling is applied to machine lenses to parabolic shapes with a ≃1 μm precision and surface roughness. The compound refractive lens comprised of six lenses with a radius of curvature R=200 μm at the vertex of the parabola and a geometrical aperture A=900 μm focuses 10 keVmore » x-ray photons from an undulator source at the Advanced Photon Source facility to a focal spot size of ≃20×90 μm 2 with a gain factor of ≃50-100.« less

Analysis of daylight performance of solar light pipes influenced by size and shape of sunlight captures

NASA Astrophysics Data System (ADS)

Wu, Yanpeng; Jin, Rendong; Zhang, Wenming; Liu, Li; Zou, Dachao

2009-11-01

Experimental investigations on three different sunlight captures with diameter 150mm, 212mm, 300mm were carried out under different conditions such as sunny conditions, cloudy conditions and overcast conditions and the two different size solar light pipes with diameter 360mm and 160mm under sunny conditions. The illuminance in the middle of the sunlight capture have relationship with its size, but not linear. To improve the efficiency of the solar light pipes, the structure and the performance of the sunlight capture must be enhanced. For example, University of Science and Technology Beijing Gymnasium, Beijing 2008 Olympic events of Judo and Taekwondo, 148 solar light pipes were installed with the diameter 530mm for each light pipe. Two sunlight captures with different shape were installed and tested. From the measuring results of the illuminance on the work plane of the gymnasium, the improvement sunlight captures have better effects with the size of augmenting and the machining of the internal surface at the same time, so that the refraction increased and the efficiency of solar light pipes improved. The better effects of supplementary lighting for the gymnasium have been achieved.

Repeatability and Reproducibility of Virtual Subjective Refraction.

PubMed

Perches, Sara; Collados, M Victoria; Ares, Jorge

2016-10-01

To establish the repeatability and reproducibility of a virtual refraction process using simulated retinal images. With simulation software, aberrated images corresponding with each step of the refraction process were calculated following the typical protocol of conventional subjective refraction. Fifty external examiners judged simulated retinal images until the best sphero-cylindrical refraction and the best visual acuity were achieved starting from the aberrometry data of three patients. Data analyses were performed to assess repeatability and reproducibility of the virtual refraction as a function of pupil size and aberrometric profile of different patients. SD values achieved in three components of refraction (M, J0, and J45) are lower than 0.25D in repeatability analysis. Regarding reproducibility, we found SD values lower than 0.25D in the most cases. When the results of virtual refraction with different pupil diameters (4 and 6 mm) were compared, the mean of differences (MoD) obtained were not clinically significant (less than 0.25D). Only one of the aberrometry profiles with high uncorrected astigmatism shows poor results for the M component in reproducibility and pupil size dependence analysis. In all cases, vision achieved was better than 0 logMAR. A comparison between the compensation obtained with virtual and conventional subjective refraction was made as an example of this application, showing good quality retinal images in both processes. The present study shows that virtual refraction has similar levels of precision as conventional subjective refraction. Moreover, virtual refraction has also shown that when high low order astigmatism is present, the refraction result is less precise and highly dependent on pupil size.

NV-centers in nanodiamonds: How good they are

NASA Astrophysics Data System (ADS)

Plakhotnik, Taras; Aman, Haroon

2018-02-01

This paper presents a method for determination of the size distribution for diamond nanocrystals containing luminescent nitrogen-vacancy (NV) centers using the luminescence intensity only. We also revise the basic photo physical properties of NV centers and conclude that the luminescence quantum yield of such centers is significantly smaller than the frequently stated 100\\%. The yield can be as low as 5\\% for centers embedded in nanocrystals and depends on their shape and the refractive index of the surrounding medium. The paper also addresses the value of the absorption cross-section of NV centers.

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.

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.

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.

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.

Monodispersepoly[BMA-co-(COPS-I)] Particles by Soap-Free Emulsion Copolymerization and Its Optical Properties as Photonic Crystals.

PubMed

Lee, Ki Chang; Choo, Hun Seung

2015-10-01

In order to study the surfactant-free emulsion copolymerization of benzyl methacrylate (BMA) with sodium 1-allyloxy-2-hydroxypropane sulfonate (COPS-I) and the resulting optical properties, a series of experiments was carried out at various reaction conditions such as the changes of BMA concentration, COPS-I concentration, BMA concentration under a fixed COPS-I amount, initiator and divinyl benzene (DVB) concentration. All the latices showed highly monodispersed spherical particles in the size range of 144~435 nm and the respective shiny structural colors from their colloidal photonic crystals. It is found that the changes in such polymerization factors greatly affect the number of particles and particle diameter, polymerization rate, molecular weight, zeta-potential, and refractive indices. The increase of number of particles led to the increased rate of polymerization and zeta-potential of the latices, on the other hand, to the decreased molecular weight. Refractive indices and the reflectivity increased with COPS-I concentration, on the other hand, and decreased with DVB concentration. Especially, refractive indices of the resulting poly[BMA-co-(COPS-I)] colloidal photonic crystals showed much higher values of 1.65~2.21 than that of polystyrene, due to the formation of core-shell shaped morphology. Monodisperse and high refractive index of poly[BMA-co-(COPS-I)] particles prepared in this work could be used for the study in photonic crystals and electrophoretic display.

Does the foveal shape influence the image formation in human eyes?

NASA Astrophysics Data System (ADS)

Frey, Katharina; Zimmerling, Beatrice; Scheibe, Patrick; Rauscher, Franziska G.; Reichenbach, Andreas; Francke, Mike; Brunner, Robert

2017-10-01

In human eyes, the maximum visual acuity correlates locally with the fovea, a shallow depression in the retina. Previous examinations have been reduced to simple geometrical fovea models derived from postmortem preparations and considering only a few superficial ray propagation aspects. In the current study, an extended and realistic analysis of ray-optical simulations for a comprehensive anatomical realistic eye model for the anterior part and realistic aspherical human foveal topographical profiles deduced from in vivo optical coherence tomography (OCT) are presented, and the refractive index step at the transition from vitreous to retinal tissue is taken into account. The optical effect of a commonly shaped (averaged) and an extraordinarily shaped foveal pit were both compared to the analysis of an assumed pure spherical boundary layer. The influence of the aperture size, wavelength, and incident angle on the spot size and shape, as well as the axial focal and lateral centroid position is investigated, and a lateral displacement of about 2 μm and an axial shift of the best focal position of less than 4 μm are found. These findings indicate only small optical effects that are laterally in the range of inter-receptor distances and axially less than the photoreceptor outer segment dimension.

Ultrahigh sensitivity refractive index sensor of a D-shaped PCF based on surface plasmon resonance.

PubMed

Wu, JunJun; Li, Shuguang; Wang, Xinyu; Shi, Min; Feng, Xinxing; Liu, Yundong

2018-05-20

We propose a D-shaped photonic crystal fiber (PCF) refractive index sensor with ultrahigh sensitivity and a wide detection range. The gold layer is deposited on the polished surface, avoiding filling or coating inside the air holes of the PCF. The influences of the gold layer thickness and the diameter of the larger air holes are investigated. The sensing characteristics of the proposed sensor are analyzed by the finite element method. The maximum sensitivity can reach 31,000  nm/RIU, and the refractive index detection range is from 1.32 to 1.40. Our proposed PCF has excellent sensing characteristics and is competitive in sensing devices.

Facile Growth of High-Yield Gold Nanobipyramids Induced by Chloroplatinic Acid for High Refractive Index Sensing Properties.

PubMed

Fang, Caihong; Zhao, Guili; Xiao, Yanling; Zhao, Jun; Zhang, Zijun; Geng, Baoyou

2016-11-14

Au nanobipyramids (NBPs) have attracted great attention because of their unique localized surface plasmon resonance properties. However, the current growth methods always have low yield or suffer tedious process. Developing new ways to direct synthesis of high-yield Au NBPs using common agents is therefore desirable. Here, we employed chloroplatinic acid as the key shape-directing agent for the first time to grow Au NBPs using a modified seed-mediated method at room temperature. H 2 PtCl 6 was added both during the seed preparation and in growth solution. Metallic Pt, reduced from chloroplatinic acid, will deposit on the surface of the seed nanoparticles and the Au nanocrystals and thus plays a critical role for the formation of Au NBPs. Additionally, the reductant, precursor, and surfactant are all cheap and commonly used. Furthermore, the Au NBPs offer narrow size distribution, two sharp tips, and a shared basis. Au NBPs therefore show much higher refractive index sensitivities than that of the Au nanorods. The refractive index sensitivities and lager figure of merit values of Au NBPs exhibit an increase of 63% and 321% respectively compared to the corresponding values of Au nanorod sample.

Conical Refraction: new observations and a dual cone model.

PubMed

Sokolovskii, G S; Carnegie, D J; Kalkandjiev, T K; Rafailov, E U

2013-05-06

We propose a paraxial dual-cone model of conical refraction involving the interference of two cones of light behind the exit face of the crystal. The supporting experiment is based on beam selecting elements breaking down the conically refracted beam into two separate hollow cones which are symmetrical with one another. The shape of these cones of light is a product of a 'competition' between the divergence caused by the conical refraction and the convergence due to the focusing by the lens. The developed mathematical description of the conical refraction demonstrates an excellent agreement with experiment.

Effective and Accurate Morphology Models for Asian and Saharan Mineral Dust Scattering Properties

NASA Astrophysics Data System (ADS)

Stegmann, P.; Yang, P.

2017-12-01

It is well known that mineral dust particles from desert sources can have a significant influence on the planetary radiation balance. In order to determine the sign and magnitude of the dust radiative forcing effect, complex models have been and continue to be developed. Key factors which influence the single-scattering properties of mineral dust are dust source regions and thus mineralogical composition, and its mixture with water, sea salt, and products of human activity, such as soot. The ensemble of mineral dust scattering particles may then be modeled either as a simple placeholder shape, often ellipsoidal, through the utilization of an appropriate effective medium refractive index scheme. On the other hand, the scattering particles may be represented in a more rigorous manner, such as Voronoi-tessellated aggregates including fractal soot chains. The consequences and differences of either choice are investigated in the project at hand. It will be shown that the effective medium model indicates a drastic dependence of the mineral dust particle composition on the particle size. Thus the refractive index of a dust particle is in fact a function of its size, amongst other factors. Regional differences between African and Asian mineral dust are also of significance.

Calculation of the radiative properties of photosynthetic microorganisms

NASA Astrophysics Data System (ADS)

Dauchet, Jérémi; Blanco, Stéphane; Cornet, Jean-François; Fournier, Richard

2015-08-01

A generic methodological chain for the predictive calculation of the light-scattering and absorption properties of photosynthetic microorganisms within the visible spectrum is presented here. This methodology has been developed in order to provide the radiative properties needed for the analysis of radiative transfer within photobioreactor processes, with a view to enable their optimization for large-scale sustainable production of chemicals for energy and chemistry. It gathers an electromagnetic model of light-particle interaction along with detailed and validated protocols for the determination of input parameters: morphological and structural characteristics of the studied microorganisms as well as their photosynthetic-pigment content. The microorganisms are described as homogeneous equivalent-particles whose shape and size distribution is characterized by image analysis. The imaginary part of their refractive index is obtained thanks to a new and quite extended database of the in vivo absorption spectra of photosynthetic pigments (that is made available to the reader). The real part of the refractive index is then calculated by using the singly subtractive Kramers-Krönig approximation, for which the anchor point is determined with the Bruggeman mixing rule, based on the volume fraction of the microorganism internal-structures and their refractive indices (extracted from a database). Afterwards, the radiative properties are estimated using the Schiff approximation for spheroidal or cylindrical particles, as a first step toward the description of the complexity and diversity of the shapes encountered within the microbial world. Finally, these predictive results are confronted to experimental normal-hemispherical transmittance spectra for validation. This entire procedure is implemented for Rhodospirillum rubrum, Arthrospira platensis and Chlamydomonas reinhardtii, each representative of the main three kinds of photosynthetic microorganisms, i.e. respectively photosynthetic bacteria, cyanobacteria and eukaryotic microalgae. The obtained results are in very good agreement with the experimental measurements when the shape of the microorganisms is well described (in comparison to the standard volume-equivalent sphere approximation). As a main perspective, the consideration of the helical shape of Arthrospira platensis appears to be a key to an accurate estimation of its radiative properties. On the whole, the presented methodological chain also appears of great interest for other scientific communities such as atmospheric science, oceanography, astrophysics and engineering.

Transient establishment of the wavefronts for negative, zero, and positive refraction.

PubMed

Zhao, Wenjuan; Wu, Qiang; Wang, Ride; Gao, Jianshun; Lu, Yao; Zhang, Qi; Qi, Jiwei; Zhang, Chunling; Pan, Chongpei; Rupp, Romano; Xu, Jingjun

2018-01-22

We quantitatively demonstrate transient establishment of wavefronts for negative, zero, and positive refraction through a wedge-shaped metamaterial consisting of periodically arranged split-ring resonators and metallic wires. The wavefronts for the three types of refractions propagate through the second interface of the wedge along positive refraction angles at first, then reorganize, and finally propagate along the effective refraction angles after a period of establishment time respectively. The establishment time of the wavefronts prevents violating causality or superluminal propagation for negative and zero refraction. The establishment time for negative or zero refraction is longer than that for positive refraction. For all three refraction processes, transient establishment processes precede the establishment of steady propagation. Moreover, some detailed characters are proven in our research, including infinite wavelength, uniform phase inside the zero-index material, and the phase velocity being antiparallel to the group velocity in the negative-index material.

Emmetropisation and the aetiology of refractive errors

PubMed Central

Flitcroft, D I

2014-01-01

The distribution of human refractive errors displays features that are not commonly seen in other biological variables. Compared with the more typical Gaussian distribution, adult refraction within a population typically has a negative skew and increased kurtosis (ie is leptokurtotic). This distribution arises from two apparently conflicting tendencies, first, the existence of a mechanism to control eye growth during infancy so as to bring refraction towards emmetropia/low hyperopia (ie emmetropisation) and second, the tendency of many human populations to develop myopia during later childhood and into adulthood. The distribution of refraction therefore changes significantly with age. Analysis of the processes involved in shaping refractive development allows for the creation of a life course model of refractive development. Monte Carlo simulations based on such a model can recreate the variation of refractive distributions seen from birth to adulthood and the impact of increasing myopia prevalence on refractive error distributions in Asia. PMID:24406411

Measurement of the index of refraction of μm crystals by a confocal laser microscope--potential application for the refractive index mapping of μm scale.

PubMed

Kimura, Keisaku; Sato, Seiichi

2014-05-01

A conventional laser microscope can be used to derive the index of refractivity by the ratio of geometrical height of the transparent platelet to the apparent height of the normal incident light for very small crystals in the wide size range. We demonstrate that the simple method is effective for the samples from 100 μm to 16 μm in size using alkali halide crystals as a model system. The method is also applied for the surface fractured micro-crystals and an inclined crystal with microscopic size regime. Furthermore, we present two-dimensional refractive index mapping as well as two-dimensional height profile for the mixture of three alkali halides, KCl, KI, and NaCl, all are μm in size.

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.

Shape and size dependent nonlinear refraction and absorption in citrate-stabilized, near-IR plasmonic silver nanopyramids.

PubMed

Dadhich, Bhavesh Kumar; Kumar, Indrajit; Choubey, Ravi Kant; Bhushan, Bhavya; Priyam, Amiya

2017-10-11

Using a combination of a mild stabilizer and a mild reductant, sodium citrate and hydrazine hydrate, anisotropic silver nanocrystals (NCs) were synthesized with tunable plasmon peaks at 550 nm, 700 nm, 800 nm, 900 nm and 1010 nm (the samples are named Ag-550, Ag-700, Ag-800, Ag-900 and Ag-1010, respectively). TEM investigations revealed that Ag-550 NCs were pentagonal nanoplates while the other four samples were nanopyramids with a pentagonal base with the edge length varying between 15 and 30 nm. The non-linear optical (NLO) properties of these NCs were studied by the Z-scan technique using the CW He-Ne laser (632.8 nm, 15 mW). The shape change from 2D nanoplates (Ag-550) to 3D nanopyramids (Ag-700) resulted in sign reversal of the non-linear refractive index, n 2 , from a negative (-3.164 × 10 -8 cm 2 W -1 ) to a positive one (1.195 × 10 -8 cm 2 W -1 ). This corresponds to a change from a self-defocussing effect to a self-focussing one. Besides shape, the size effect is also prominently observed. Amongst nanopyramids, as the edge length increases, n 2 increases linearly and reaches a maximum of 3.124 × 10 -8 cm 2 W -1 . Doubling the edge length from 15 nm to 30 nm resulted in 162% increase in n 2 . On moving from Ag-550 to Ag-900 NCs, with the increasing plasmon wavelength, the non-linear absorption (NLA) coefficient increased exponentially to a high value of 8.52 × 10 -4 cm W -1 . However, Ag-1010 showed 29% decrease in NLA which is attributed to twinning present in the crystal structure as seen in the HR-TEM images. Due to the tunable NLO properties, these anisotropic Ag NCs hold great potential for applications in optical limiting, switching and data storage.

Mobile Bay turbidity study

NASA Technical Reports Server (NTRS)

Crozier, G. F.; Schroeder, W. W.

1978-01-01

The termination of studies carried on for almost three years in the Mobile Bay area and adjacent continental shelf are reported. The initial results concentrating on the shelf and lower bay were presented in the interim report. The continued scope of work was designed to attempt a refinement of the mathematical model, assess the effectiveness of optical measurement of suspended particulate material and disseminate the acquired information. The optical characteristics of particulate solutions are affected by density gradients within the medium, density of the suspended particles, particle size, particle shape, particle quality, albedo, and the angle of refracted light. Several of these are discussed in detail.

Materials for x-ray refractive lenses minimizing wavefront distortions

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

Roth, Thomas; Alianelli, Lucia; Lengeler, Daniel

2017-06-09

Refraction through curved surfaces, reflection from curved mirrors in grazing incidence, and diffraction from Fresnel zone plates are key hard x-ray focusing mechanisms. In this article, we present materials used for refractive x-ray lenses. Important properties of such x-ray lenses include focusing strength, shape, and the material’s homogeneity and absorption coefficient. Both the properties of the initial material and the fabrication process result in a lens with imperfections, which can lead to unwanted wavefront distortions. Different fabrication methods for one-dimensional and two-dimensional focusing lenses are presented, together with the respective benefits and inconveniences that are mostly due to shape fidelity.more » Different materials and material grades have been investigated in terms of their homogeneity and the absence of inclusions. Single-crystalline materials show high homogeneity, but suffer from unwanted diffracted radiation, which can be avoided using amorphous materials. Lastly, we show that shape imperfections can be corrected using a correction lens.« less

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.

Correlation between refraction level and retinal breaks in myopic eye.

PubMed

Alimanović-Halilović, Emina

2008-11-01

In this study we analyzed 180 myopic eyes in order to determine the refraction that is "critical" for the occurrence of retinal breaks as a main cause of retinal detachment. Detachment of retina involves separation of the neurosensory retina from the pigmented epithelium with the severe impairment of vision. After the focused ophthalmological assessment, determination of objective refraction, indirect binocular ophthalmoscopy, we compared the diagnosed retinal breaks according to the shape with the refraction. All the examined eyes were divided into six groups according to the axis length. Mean age of our patients was between 48,43 and 51,60 years with SD ranging from 13,88 to 18,45. The age differences among the groups were not statistically significant. This study included 102 (56,7%) male and 78 (43,3%) female patients and no statistically significant differences between genders was found regarding the occurrence of retinal breaks compared to refraction. The most dominant ruptures were the round ones (28,2%), followed by oval (25%), the category of multiple small holes (19,2%), horseshoe shaped (15,3%), and finally holes with operculum. In cases with myopic refraction ranging between 3,50 and 7,49 dsph, the frequency of retinal breaks statistically significantly differs from all other analyzed refractions. Also, there is positive correlation between the above mentioned myopic refraction and the frequency of retinal breaks. In order to prevent retinal detachment in a myopic eye, we suggest further thorough examinations of the eye fundus in patients with the above mentioned myopia. Diagnosing retinal breaks involves the application of adequate therapy: laser photocoagulation, cryotherapy, sclera buckling and pneumatic retinopexy.

Microwave analog experiments on optically soft spheroidal scatterers with weak electromagnetic signature

NASA Astrophysics Data System (ADS)

Saleh, H.; Charon, J.; Dauchet, J.; Tortel, H.; Geffrin, J.-M.

2017-07-01

Light scattering by optically soft particles is being theoretically investigated in many radiative studies. An interest is growing up to develop approximate methods when the resolution of Maxwell's equations is impractical due to time and/or memory size problems with objects of complex geometries. The participation of experimental studies is important to assess novel approximations when no reference solution is available. The microwave analogy represents an efficient solution to perform such electromagnetic measurements in controlled conditions. In this paper, we take advantage of the particular features of our microwave device to present an extensive experimental study on the electromagnetic scattering by spheroidal particles analogs with low refractive indices, as a first step toward the assessment of micro-organisms with low refractive index and heterogeneities. The spheroidal analogs are machined from a low density material and they mimic soft particles of interest to the light scattering community. The measurements are confronted to simulations obtained with Finite Element Method and T-Matrix method. A good agreement is obtained even with refractive index as low as 1.13. Scattered signals of low intensities are correctly measured and the position of the targets is precisely controlled. The forward scattering measurements show high sensitivity to noise and require careful extraction. The configuration of the measurement device reveals different technical requirements between forward and backward scattering directions. The results open interesting perspectives about novel measurement procedures as well as about the use of high prototyping technologies to manufacture analogs of precise refractive indices and shapes.

Long-lived monolithic micro-optics for multispectral GRIN applications.

PubMed

Lepicard, Antoine; Bondu, Flavie; Kang, Myungkoo; Sisken, Laura; Yadav, Anupama; Adamietz, Frederic; Rodriguez, Vincent; Richardson, Kathleen; Dussauze, Marc

2018-05-09

The potential for realizing robust, monolithic, near-surface refractive micro-optic elements with long-lived stability is demonstrated in visible and infrared transmitting glasses capable of use in dual band applications. Employing an enhanced understanding of glass chemistry and geometric control of mobile ion migration made possible with electrode patterning, flat, permanent, thermally-poled micro-optic structures have been produced and characterized. Sub-surface (t~5-10 µm) compositional and structural modification during the poling process results in formation of spatially-varying refractive index profiles, exhibiting induced Δn changes up to 5 × 10 -2 which remain stable for >15 months. The universality of this approach applied to monolithic vis-near infrared [NIR] oxide and NIR-midwave infrared [MIR] chalcogenide glass materials is demonstrated for the first time. Element size, shape and gradient profile variation possible through pattern design and fabrication is shown to enable a variety of design options not possible using other GRIN process methodologies.

Relation between Raman backscattering from droplets and bulk water: Effect of refractive index dispersion

NASA Astrophysics Data System (ADS)

Plakhotnik, Taras; Reichardt, Jens

2018-03-01

A theoretical framework is presented that permits investigations of the relation between inelastic backscattering from microparticles and bulk samples of Raman-active materials. It is based on the Lorentz reciprocity theorem and no fundamental restrictions concerning the microparticle shape apply. The approach provides a simple and intuitive explanation for the enhancement of the differential backscattering cross-section in particles in comparison to bulk. The enhancement factor for scattering of water droplets in the diameter range from 0 to 60 μm (vitally important for the a priori measurement of liquid water content of warm clouds with spectroscopic Raman lidars) is about a factor of 1.2-1.6 larger (depending on the size of the sphere) than an earlier study has shown. The numerical calculations are extended to 1000 μm and demonstrate that dispersion of the refractive index of water becomes an important factor for spheres larger than 100 μm. The physics of the oscillatory phenomena predicted by the simulations is explained.

Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction from a Combination of Aerosol in Situ and Remote Sensing Measurements During TARFOX

NASA Technical Reports Server (NTRS)

Redemann, J.; Turco, R. P.; Liou, K. N.; Russell, P. B.; Bergstrom, R. W.; Schmid, B.; Livingston, J. M.; Hobbs, P. V.; Hartley, W. S.; Ismail, S.

2000-01-01

The largest uncertainty in estimates of the effects of atmospheric aerosols on climate stems from uncertainties in the determination of their microphysical properties, including the aerosol complex index of refraction, which in turn determines their optical properties. A novel technique is used to estimate the aerosol complex index of refraction in distinct vertical layers from a combination of aerosol in situ size distribution and remote sensing measurements during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). In particular, aerosol backscatter measurements using the NASA Langley LASE (Lidar Atmospheric Sensing Experiment) instrument and in situ aerosol size distribution data are utilized to derive vertical profiles of the 'effective' aerosol complex index of refraction at 815 nm (i.e., the refractive index that would provide the same backscatter signal in a forward calculation on the basis of the measured in situ particle size distributions for homogeneous, spherical aerosols). A sensitivity study shows that this method yields small errors in the retrieved aerosol refractive indices, provided the errors in the lidar derived aerosol backscatter are less than 30% and random in nature. Absolute errors in the estimated aerosol refractive indices are generally less than 0.04 for the real part and can be as much as 0.042 for the imaginary part in the case of a 30% error in the lidar-derived aerosol backscatter. The measurements of aerosol optical depth from the NASA Ames Airborne Tracking Sunphotometer (AATS-6) are successfully incorporated into the new technique and help constrain the retrieved aerosol refractive indices. An application of the technique to two TARFOX case studies yields the occurrence of vertical layers of distinct aerosol refractive indices. Values of the estimated complex aerosol refractive index range from 1.33 to 1.45 for the real part and 0.001 to 0.008 for the imaginary part. The methodology devised in this study provides, for the first time a complete set of vertically resolved aerosol size distribution and refractive index data, yielding the vertical distribution of aerosol optical properties required for the determination of aersol-induced radiative flux changes

Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction from a Combination of Aerosol in Situ and Remote Sensing Measurements During TARFOX

NASA Technical Reports Server (NTRS)

Redemann, J.; Turco, R. P.; Liou, K. N.; Russell, P. B.; Bergstrom, R. W.; Schmid, B.; Livingston, J. M.; Hobbs, P. V.; Hartley, W. S.; Ismail, S.;

Combined laser-ray tracing and OCT system for biometry of the crystalline lens (Conference Presentation)

NASA Astrophysics Data System (ADS)

Ruggeri, Marco; Maceo Heilman, Bianca M.; Yao, Yue; Chang, Yu-Cherng; Gonzalez, Alex; Rowaan, Cornelis; Mohamed, Ashik; Williams, Siobhan; Durkee, Heather A.; Silgado, Juan; Bernal, Andres; Arrieta-Quintero, Esdras; Ho, Arthur; Parel, Jean-Marie A.; Manns, Fabrice

2017-02-01

Age-related changes in the crystalline lens shape and refractive index gradient produce changes in dioptric power and high-order aberrations that influence the optics of the whole eye and contribute to a decrease in overall visual quality. Despite their key role, the changes in lens shape and refractive index gradient with age and accommodation and their effects on high-order aberrations are still not well understood. The goal of this project was to develop a combined laser ray tracing (LRT) and optical coherence tomography (OCT) system to measure high-order aberrations, shape and refractive index gradient in non-human primate and human lenses. A miniature motorized lens stretching system was built to enable imaging and aberrometry of the lens during simulated accommodation. A positioning system was also built to enable on- and off-axis OCT imaging and aberrometry for characterization of the peripheral defocus of the lens. We demonstrated the capability of the LRT-OCT system to produce OCT images and aberration measurements of crystalline lens with age and accommodation in vitro. In future work, the information acquired with the LRT-OCT system will be used to develop an accurate age-dependent lens model to predict the role of the lens in the development of refractive error and aberrations of the whole eye.

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.

Peripheral refraction and retinal contour in stable and progressive myopia.

PubMed

Faria-Ribeiro, Miguel; Queirós, António; Lopes-Ferreira, Daniela; Jorge, Jorge; González-Méijome, José Manuel

2013-01-01

To compare the patterns of relative peripheral astigmatic refraction (tangential and sagittal power errors) and eccentric eye length between progressing and stable young-adult myopes. Sixty-two right eyes of 62 white patients participated in the study, of which 30 were nonprogressing myopes (NP group) for the last 2 years and 32 were progressing myopes (P group). Groups were matched for mean spherical refraction, axial length, and age. Peripheral refraction and eye length were measured along the horizontal meridian up to 35 and 30 degrees of eccentricity, respectively. There were statistically significant differences between groups (p < 0.001) in the nasal retina for the astigmatic components of peripheral refraction. The P group presented a hyperopic relative sagittal focus at 35 degrees in the nasal retina of +1.00 ± 0.83 diopters, as per comparison with a myopic relative sagittal focus of -0.10 ± 0.98 diopters observed in the NP group (p < 0.001). Retinal contour in the P group had a steeper shape in the nasal region than that in the NP group (t test, p = 0.001). An inverse correlation was found (r = -0.775; p < 0.001) between retinal contour and peripheral refraction. Thus, steeper retinas presented a more hyperopic trend in the periphery. Stable and progressing myopes of matched age, axial length, and central refraction showed significantly different characteristics in their peripheral retinal shape and astigmatic components of tangential and sagittal power errors. The present findings may help explain the mechanisms that regulate ocular growth in humans.

Computation of scattering matrix elements of large and complex shaped absorbing particles with multilevel fast multipole algorithm

NASA Astrophysics Data System (ADS)

Wu, Yueqian; Yang, Minglin; Sheng, Xinqing; Ren, Kuan Fang

2015-05-01

Light scattering properties of absorbing particles, such as the mineral dusts, attract a wide attention due to its importance in geophysical and environment researches. Due to the absorbing effect, light scattering properties of particles with absorption differ from those without absorption. Simple shaped absorbing particles such as spheres and spheroids have been well studied with different methods but little work on large complex shaped particles has been reported. In this paper, the surface Integral Equation (SIE) with Multilevel Fast Multipole Algorithm (MLFMA) is applied to study scattering properties of large non-spherical absorbing particles. SIEs are carefully discretized with piecewise linear basis functions on triangle patches to model whole surface of the particle, hence computation resource needs increase much more slowly with the particle size parameter than the volume discretized methods. To improve further its capability, MLFMA is well parallelized with Message Passing Interface (MPI) on distributed memory computer platform. Without loss of generality, we choose the computation of scattering matrix elements of absorbing dust particles as an example. The comparison of the scattering matrix elements computed by our method and the discrete dipole approximation method (DDA) for an ellipsoid dust particle shows that the precision of our method is very good. The scattering matrix elements of large ellipsoid dusts with different aspect ratios and size parameters are computed. To show the capability of the presented algorithm for complex shaped particles, scattering by asymmetry Chebyshev particle with size parameter larger than 600 of complex refractive index m = 1.555 + 0.004 i and different orientations are studied.

Spacecraft particulate sizing spectrometer

NASA Technical Reports Server (NTRS)

Miranda, Henry A., Jr.

1992-01-01

An evaluation prototype device is described, together with conclusions and several recommendations for follow-on flight hardware. The device detects individual particles crossing an external sensing zone, and produces a histogram displaying the size distribution of particles sensed, over the nominal range of 5 to 50 microns. The output is totally independent of the particle refractive index, and is also largely unaffected by particle shape. The reported diameters are in terms of the equivalent sphere, as judged by the scattered light intercepted by the receiving channels, which develop signals whenever a particle crosses the beam of illumination in the sensing zone. Supporting evidence for the latter assertion is discussed on the basis of experimental test data for non-spherical particulates. Also included is a technical appendix which presents theoretical arguments that provide a firm foundation for this assertion.

Dependence of the absorption and optical surface plasmon scattering of MoS₂ nanoparticles on aspect ratio, size, and media.

PubMed

Yadgarov, Lena; Choi, Charina L; Sedova, Anastasiya; Cohen, Ayala; Rosentsveig, Rita; Bar-Elli, Omri; Oron, Dan; Dai, Hongjie; Tenne, Reshef

2014-04-22

The optical and electronic properties of suspensions of inorganic fullerene-like nanoparticles of MoS2 are studied through light absorption and zeta-potential measurements and compared to those of the corresponding microscopic platelets. The total extinction measurements show that, in addition to excitonic peaks and the indirect band gap transition, a new peak is observed at 700-800 nm. This spectral peak has not been reported previously for MoS2. Comparison of the total extinction and decoupled absorption spectrum indicates that this peak largely originates from scattering. Furthermore, the dependence of this peak on nanoparticle size, shape, and surface charge, as well as solvent refractive index, suggests that this transition arises from a plasmon resonance.

Quantitative analysis of three-dimensional biological cells using interferometric microscopy

NASA Astrophysics Data System (ADS)

Shaked, Natan T.; Wax, Adam

2011-06-01

Live biological cells are three-dimensional microscopic objects that constantly adjust their sizes, shapes and other biophysical features. Wide-field digital interferometry (WFDI) is a holographic technique that is able to record the complex wavefront of the light which has interacted with in-vitro cells in a single camera exposure, where no exogenous contrast agents are required. However, simple quasi-three-dimensional holographic visualization of the cell phase profiles need not be the end of the process. Quantitative analysis should permit extraction of numerical parameters which are useful for cytology or medical diagnosis. Using a transmission-mode setup, the phase profile represents the multiplication between the integral refractive index and the thickness of the sample. These coupled variables may not be distinct when acquiring the phase profiles of dynamic cells. Many morphological parameters which are useful for cell biologists are based on the cell thickness profile rather than on its phase profile. We first overview methods to decouple the cell thickness and its refractive index using the WFDI-based phase profile. Then, we present a whole-cell-imaging approach which is able to extract useful numerical parameters on the cells even in cases where decoupling of cell thickness and refractive index is not possible or desired.

A New Compact Double-Negative Miniaturized Metamaterial for Wideband Operation.

PubMed

Hasan, Md Mehedi; Faruque, Mohammad Rashed Iqbal; Islam, Sikder Sunbeam; Islam, Mohammad Tariqul

2016-10-13

The aim of this paper is to introduce a compact double-negative (DNG) metamaterial that exhibits a negative refractive index (NRI) bandwidth of more than 3.6 GHz considering the frequency from 2 to 14 GHz. In this framework, two arms of the designed unit cell are split in a way that forms a Modified-Z-shape structure of the FR-4 substrate material. The finite integration technique (FIT)-based Computer Simulation Technology (CST) Microwave Studio is applied for computation, and the experimental setup for measuring the performance is performed inside two waveguide ports. Therefore, the measured data complies well with the simulated data of the unit cell at 0-degree and 90-degree rotation angles. The designed unit cell shows a negative refractive index from 3.482 to 7.096 GHz (bandwidth of 3.61 GHz), 7.876 to 10.047 GHz (bandwidth of 2.171 GHz), and 11.594 to 14 GHz (bandwidth of 2.406 GHz) in the microwave spectra. The design also exhibits almost the same wide negative refractive index bandwidth in the major region of the C-band and X-band if it is rotated 90 degrees. However, the novelty of the proposed structure lies in its effective medium ratio of more than 4, wide bandwidth, and compact size.

A New Compact Double-Negative Miniaturized Metamaterial for Wideband Operation

PubMed Central

Hasan, Md. Mehedi; Faruque, Mohammad Rashed Iqbal; Islam, Sikder Sunbeam; Islam, Mohammad Tariqul

2016-01-01

The aim of this paper is to introduce a compact double-negative (DNG) metamaterial that exhibits a negative refractive index (NRI) bandwidth of more than 3.6 GHz considering the frequency from 2 to 14 GHz. In this framework, two arms of the designed unit cell are split in a way that forms a Modified-Z-shape structure of the FR-4 substrate material. The finite integration technique (FIT)-based Computer Simulation Technology (CST) Microwave Studio is applied for computation, and the experimental setup for measuring the performance is performed inside two waveguide ports. Therefore, the measured data complies well with the simulated data of the unit cell at 0-degree and 90-degree rotation angles. The designed unit cell shows a negative refractive index from 3.482 to 7.096 GHz (bandwidth of 3.61 GHz), 7.876 to 10.047 GHz (bandwidth of 2.171 GHz), and 11.594 to 14 GHz (bandwidth of 2.406 GHz) in the microwave spectra. The design also exhibits almost the same wide negative refractive index bandwidth in the major region of the C-band and X-band if it is rotated 90 degrees. However, the novelty of the proposed structure lies in its effective medium ratio of more than 4, wide bandwidth, and compact size. PMID:28773951

Counter-propagating optical trapping system for size and refractive index measurement of microparticles.

PubMed

Flynn, Richard A; Shao, Bing; Chachisvilis, Mirianas; Ozkan, Mihrimah; Esener, Sadik C

2006-01-15

We propose and demonstrate a novel approach to measure the size and refractive index of microparticles based on two beam optical trapping, where forward scattered light is detected to give information about the particle. The counter-propagating optical trap measurement (COTM) system exploits the capability of optical traps to measure pico-Newton forces for microparticles' refractive index and size characterization. Different from the current best technique for microparticles' refractive index measurement, refractometry, a bulk technique requiring changing the fluid composition of the sample, our optical trap technique works with any transparent fluid and enables single particle analysis without the use of biological markers. A ray-optics model is used to explore the physical operation of the COTM system, predict system performance and aid system design. Experiments demonstrate the accuracy of refractive index measurement of Deltan=0.013 and size measurement of 3% of diameter with 2% standard deviation. Present performance is instrumentation limited, and a potential improvement by more than two orders of magnitude can be expected in the future. With further development in parallelism and miniaturization, the system offers advantages for cell manipulation and bioanalysis compatible with lab-on-a-chip systems.

Effect of Pupil Size on Wavefront Refraction during Orthokeratology.

PubMed

Faria-Ribeiro, Miguel; Navarro, Rafael; González-Méijome, José Manuel

2016-11-01

It has been hypothesized that central and peripheral refraction, in eyes treated with myopic overnight orthokeratology, might vary with changes in pupil diameter. The aim of this work was to evaluate the axial and peripheral refraction and optical quality after orthokeratology, using ray tracing software for different pupil sizes. Zemax-EE was used to generate a series of 29 semi-customized model eyes based on the corneal topography changes from 29 patients who had undergone myopic orthokeratology. Wavefront refraction in the central 80 degrees of the visual field was calculated using three different quality metrics criteria: Paraxial curvature matching, minimum root mean square error (minRMS), and the Through Focus Visual Strehl of the Modulation Transfer Function (VSMTF), for 3- and 6-mm pupil diameters. The three metrics predicted significantly different values for foveal and peripheral refractions. Compared with the Paraxial criteria, the other two metrics predicted more myopic refractions on- and off-axis. Interestingly, the VSMTF predicts only a marginal myopic shift in the axial refraction as the pupil changes from 3 to 6 mm. For peripheral refraction, minRMS and VSMTF metric criteria predicted a higher exposure to peripheral defocus as the pupil increases from 3 to 6 mm. The results suggest that the supposed effect of myopic control produced by ortho-k treatments might be dependent on pupil size. Although the foveal refractive error does not seem to change appreciably with the increase in pupil diameter (VSMTF criteria), the high levels of positive spherical aberration will lead to a degradation of lower spatial frequencies, that is more significant under low illumination levels.

Guinea Pig Ciliary Muscle Development

PubMed Central

Pucker, Andrew D.; Carpenter, Ashley R.; McHugh, Kirk M.; Mutti, Donald O.

2014-01-01

Purpose The purpose of this study was to develop a method for quantifying guinea pig ciliary muscle volume (CMV) and to determine its relationship to age and ocular biometric measurements. Methods Six albino guinea pigs eyes were collected at each of five ages (n=30 eyes). Retinoscopy and photography were used to document refractive error, eye size, and eye shape. Serial sections through the excised eyes were made and then labeled with an α-smooth muscle actin antibody. The CM was then visualized with an Olympus BX51 microscope, reconstructed with Stereo Investigator (MBF Bioscience) and analyzed using Neurolucida Explorer (MBF Bioscience). Full (using all sections) and partial (using a subset of sections) reconstruction methods were used to determine CMV. Results There was no significant difference between the full and partial volume determination methods (P = 0.86). The mean CMV of the 1, 10, 20, 30, and 90-day old eyes was 0.40 ± 0.16 mm3, 0.48 ± 0.13 mm3, 0.67 ± 0.15 mm3, 0.86 ± 0.35 mm3, and 1.09 ± 0.63 mm3, respectively. CMV was significantly correlated with log age (P = 0.001), ocular length (P = 0.003), limbal circumference (P = 0.01), and equatorial diameter (P = 0.003). It was not correlated with refractive error (P = 0.73) or eye shape (P = 0.60). Multivariate regression determined that biometric variables were not significantly associated with CMV after adjustment for age. Conclusions Three-dimensional reconstruction was an effective means of determining CMV. These data provide evidence that CM growth occurs with age in tandem with eye size in normal albino guinea pigs. Additional work is needed to determine the relationship between CMV and abnormal ocular growth. PMID:24901488

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.

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.

Peripheral refraction and image blur in four meridians in emmetropes and myopes.

PubMed

Shen, Jie; Spors, Frank; Egan, Donald; Liu, Chunming

2018-01-01

The peripheral refractive error of the human eye has been hypothesized to be a major stimulus for the development of its central refractive error. The purpose of this study was to investigate the changes in the peripheral refractive error across horizontal, vertical and two diagonal meridians in emmetropic and low, moderate and high myopic adults. Thirty-four adult subjects were recruited and aberration was measured using a modified commercial aberrometer. We then computed the refractive error in power vector notation from second-order Zernike terms. Statistical analysis was performed to evaluate the statistical differences in refractive error profiles between the subject groups and across all measured visual field meridians. Small amounts of relative myopic shift were observed in emmetropic and low myopic subjects. However, moderate and high myopic subjects exhibited a relative hyperopic shift in all four meridians. Astigmatism J 0 and J 45 had quadratic or linear changes dependent on the visual field meridians. Peripheral Sphero-Cylindrical Retinal Image Blur increased in emmetropic eyes in most of the measured visual fields. The findings indicate an overall emmetropic or slightly relative myopic periphery (spherical or oblate retinal shape) formed in emmetropes and low myopes, while moderate and high myopes form relative hyperopic periphery (prolate, or less oblate, retinal shape). In general, human emmetropic eyes demonstrate higher amount of peripheral retinal image blur.

The influence of grating shape formation fluctuation on DFB laser diode threshold condition

NASA Astrophysics Data System (ADS)

Bao, Shiwei; Song, Qinghai; Xie, Chunmei

2018-03-01

Not only the grating material refractive index itself but also the Bragg grating physical shape formation affects the coupling strength greatly. The Bragg grating shape includes three factors, namely grating depth, duty ratio and grating angle. During the lithography and wet etching process, there always will be some fluctuation between the target and real grating shape formation after fabrication process. This grating shape fluctuation will affect the DFB coupling coefficient κ , and then consequently threshold current and corresponding wavelength. This paper studied the grating shape formation fluctuation influence to improve the DFB fabrication yield. A truncated normal random distribution fluctuation is considered in this paper. The simulation results conclude that it is better to choose relative thicker grating depth with lower refractive index to obtain a better fabrication tolerance, while not quite necessary to spend too much effort on improving lithography and wet etching process to get a precisely grating duty ratio and grating angle.

The influence of grating shape formation fluctuation on DFB laser diode threshold condition

NASA Astrophysics Data System (ADS)

Bao, Shiwei; Song, Qinghai; Xie, Chunmei

2018-06-01

Not only the grating material refractive index itself but also the Bragg grating physical shape formation affects the coupling strength greatly. The Bragg grating shape includes three factors, namely grating depth, duty ratio and grating angle. During the lithography and wet etching process, there always will be some fluctuation between the target and real grating shape formation after fabrication process. This grating shape fluctuation will affect the DFB coupling coefficient κ, and then consequently threshold current and corresponding wavelength. This paper studied the grating shape formation fluctuation influence to improve the DFB fabrication yield. A truncated normal random distribution fluctuation is considered in this paper. The simulation results conclude that it is better to choose relative thicker grating depth with lower refractive index to obtain a better fabrication tolerance, while not quite necessary to spend too much effort on improving lithography and wet etching process to get a precisely grating duty ratio and grating angle.

Quantitative evaluation of changes in eyeball shape in emmetropization and myopic changes based on elliptic fourier descriptors.

PubMed

Ishii, Kotaro; Iwata, Hiroyoshi; Oshika, Tetsuro

2011-11-04

To evaluate changes in eyeball shape in emmetropization and myopic changes using magnetic resonance imaging (MRI) and elliptic Fourier descriptors (EFDs). The subjects were 105 patients (age range, 1 month-19 years) who underwent head MRI. The refractive error was determined in 30 patients, and eyeball shape was expressed numerically by principal components analysis of standardized EFDs. In the first principal component (PC1; the oblate-to-prolate change), the proportion of variance/total variance in the development of the eyeball shape was 76%. In all subjects, PC1 showed a significant correlation with age (Pearson r = -0.314; P = 0.001), axial length (AL, r = -0.378; P < 0.001), width (r = -0.200, P = 0.0401), oblateness (r = 0.657, P < 0.001), and spherical equivalent refraction (SER, r = 0.438; P = 0.0146; n = 30). In the group containing patients aged 1 month to 6 years (n = 49), PC1 showed a significant correlation with age (r = -0.366; P = 0.0093). In the group containing patients aged 7 to 19 years (n = 56), PC1 showed a significant correlation with SER (r = 0.640; P = 0.0063). The main deformation pattern in the development of the eyeball shape from oblate to prolate was clarified by quantitative analysis based on EFDs. The results showed clear differences between age groups with regard to changes in the shape of the eyeball, the correlation between these changes, and refractive status changes.

Quasi-D-shaped optical fiber plasmonic refractive index sensor

NASA Astrophysics Data System (ADS)

An, Guowen; Li, Shuguang; Wang, Haiyang; Zhang, Xuenan; Yan, Xin

2018-03-01

A quasi-D-shaped photonic crystal fiber plasmonic sensor with a rectangular lattice is proposed by using Au as a plasmonic layer and graphene to enhance the sensing performance. By moving the core to the edge of the fiber, a shorter polishing depth is achieved, which makes the fiber proposed have a greater mechanical strength than other common D-shaped fibers. Benefiting from the natural advantage of the rectangular lattice, the dual sensing channels make the proposed sensor show a maximum wavelength interrogation sensitivity of 3877 nm/RIU with the dynamic refractive index range from 1.33 to 1.42 and a maximum amplitude sensitivity of 1236 RIU-1 with the analyte RI = 1.41 in the visible region. The corresponding resolutions are 2.58 × 10-5 and 8.1 × 10-6 with the methods of the wavelength interrogation method and amplitude- or phase-based method. These advantages make the proposed sensor a competitive candidate for biosensing in the field of refractive index detection, such as water quality analysis, clinical medicine detection, and pharmaceutical testing.

Exact simulation of polarized light reflectance by particle deposits

NASA Astrophysics Data System (ADS)

Ramezan Pour, B.; Mackowski, D. W.

2015-12-01

The use of polarimetric light reflection measurements as a means of identifying the physical and chemical characteristics of particulate materials obviously relies on an accurate model of predicting the effects of particle size, shape, concentration, and refractive index on polarized reflection. The research examines two methods for prediction of reflection from plane parallel layers of wavelength—sized particles. The first method is based on an exact superposition solution to Maxwell's time harmonic wave equations for a deposit of spherical particles that are exposed to a plane incident wave. We use a FORTRAN-90 implementation of this solution (the Multiple Sphere T Matrix (MSTM) code), coupled with parallel computational platforms, to directly simulate the reflection from particle layers. The second method examined is based upon the vector radiative transport equation (RTE). Mie theory is used in our RTE model to predict the extinction coefficient, albedo, and scattering phase function of the particles, and the solution of the RTE is obtained from adding—doubling method applied to a plane—parallel configuration. Our results show that the MSTM and RTE predictions of the Mueller matrix elements converge when particle volume fraction in the particle layer decreases below around five percent. At higher volume fractions the RTE can yield results that, depending on the particle size and refractive index, significantly depart from the exact predictions. The particle regimes which lead to dependent scattering effects, and the application of methods to correct the vector RTE for particle interaction, will be discussed.

Anomalous change of Airy disk with changing size of spherical particles

NASA Astrophysics Data System (ADS)

Pan, Linchao; Zhang, Fugen; Meng, Rui; Xu, Jie; Zuo, Chenze; Ge, Baozhen

2016-02-01

Use of laser diffraction is considered as a method of reliable principle and mature technique in measurements of particle size distributions. It is generally accepted that for a certain relative refractive index, the size of the scattering pattern (also called Airy disk) of spherical particles monotonically decreases with increasing particle size. This fine structure forms the foundation of the laser diffraction method. Here we show that the Airy disk size of non-absorbing spherical particles becomes larger with increasing particle size in certain size ranges. To learn more about this anomalous change of Airy disk (ACAD), we present images of Airy disk and curves of Airy disk size versus particle size for spherical particles of different relative refractive indices by using Mie theory. These figures reveal that ACAD occurs periodically for non-absorbing particles and will disappear when the absorbing efficiency is higher than certain value. Then by using geometrical optics (GO) approximation, we derive the analytical formulae for the bounds of the size ranges where ACAD occurs. From the formulae, we obtain laws of ACAD as follows: (1) for non-absorbing particles, ACAD occurs periodically, and when the particle size tends to infinity, the period tends to a certain value. As the relative refractive index increases, (2) the particle size ranges where ACAD occurs shift to smaller values, (3) the period of ACAD becomes smaller, and (4) the width of the size ranges where ACAD occurs becomes narrower. In addition, we can predict from the formulae that ACAD also exists for particles whose relative refractive index is smaller than 1.

Dynamic diffraction artefacts in Bragg coherent diffractive imaging

DOE PAGES

Hu, Wen; Huang, Xiaojing; Yan, Hanfei

2018-02-01

This article reports a theoretical study on the reconstruction artefacts in Bragg coherent diffractive imaging caused by dynamical diffraction effects. It is shown that, unlike the absorption and refraction effects that can be corrected after reconstruction, dynamical diffraction effects have profound impacts on both the amplitude and the phase of the reconstructed complex object, causing strong artefacts. At the dynamical diffraction limit, the reconstructed shape is no longer correct, as a result of the strong extinction effect. Simulations for hemispherical particles of different sizes show the type, magnitude and extent of the dynamical diffraction artefacts, as well as the conditionsmore » under which they are negligible.« less

Dynamic diffraction artefacts in Bragg coherent diffractive imaging.

PubMed

Hu, Wen; Huang, Xiaojing; Yan, Hanfei

2018-02-01

This article reports a theoretical study on the reconstruction artefacts in Bragg coherent diffractive imaging caused by dynamical diffraction effects. It is shown that, unlike the absorption and refraction effects that can be corrected after reconstruction, dynamical diffraction effects have profound impacts on both the amplitude and the phase of the reconstructed complex object, causing strong artefacts. At the dynamical diffraction limit, the reconstructed shape is no longer correct, as a result of the strong extinction effect. Simulations for hemispherical particles of different sizes show the type, magnitude and extent of the dynamical diffraction artefacts, as well as the conditions under which they are negligible.

Dynamic diffraction artefacts in Bragg coherent diffractive imaging

PubMed Central

Yan, Hanfei

2018-01-01

This article reports a theoretical study on the reconstruction artefacts in Bragg coherent diffractive imaging caused by dynamical diffraction effects. It is shown that, unlike the absorption and refraction effects that can be corrected after reconstruction, dynamical diffraction effects have profound impacts on both the amplitude and the phase of the reconstructed complex object, causing strong artefacts. At the dynamical diffraction limit, the reconstructed shape is no longer correct, as a result of the strong extinction effect. Simulations for hemispherical particles of different sizes show the type, magnitude and extent of the dynamical diffraction artefacts, as well as the conditions under which they are negligible. PMID:29507549

Integral refractive index imaging of flowing cell nuclei using quantitative phase microscopy combined with fluorescence microscopy.

PubMed

Dardikman, Gili; Nygate, Yoav N; Barnea, Itay; Turko, Nir A; Singh, Gyanendra; Javidi, Barham; Shaked, Natan T

2018-03-01

We suggest a new multimodal imaging technique for quantitatively measuring the integral (thickness-average) refractive index of the nuclei of live biological cells in suspension. For this aim, we combined quantitative phase microscopy with simultaneous 2-D fluorescence microscopy. We used 2-D fluorescence microscopy to localize the nucleus inside the quantitative phase map of the cell, as well as for measuring the nucleus radii. As verified offline by both 3-D confocal fluorescence microscopy and 2-D fluorescence microscopy while rotating the cells during flow, the nucleus of cells in suspension that are not during division can be assumed to be an ellipsoid. The entire shape of a cell in suspension can be assumed to be a sphere. Then, the cell and nucleus 3-D shapes can be evaluated based on their in-plain radii available from the 2-D phase and fluorescent measurements, respectively. Finally, the nucleus integral refractive index profile is calculated. We demonstrate the new technique on cancer cells, obtaining nucleus refractive index values that are lower than those of the cytoplasm, coinciding with recent findings. We believe that the proposed technique has the potential to be used for flow cytometry, where full 3-D refractive index tomography is too slow to be implemented during flow.

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.

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.

Properties of oscillating refractive optical wings with one reflective surface

NASA Astrophysics Data System (ADS)

Artusio-Glimpse, Alexandra B.; Swartzlander, Grover A.

2013-09-01

A new modality for optical micromanipulation is under investigation. Optical wings are shaped refractive objects that experience a force and torque owing to the reflection and transmission of uniform light at the object surface. We present wing designs that provide a restoring torque that returns the wing to a source facing orientation while preserving efficient thrust from radiation pressure. The torsional stiffness and orbital period of a set of optical wing cross-sectional shapes are determined from numerical ray-tracing analyses. These results demonstrate the potential to develop an efficient optomechanical device for applications in microbiology and space flight systems.

Temperature effect on refractive index sensing performance of a U-shape tapered plastic optical fiber

NASA Astrophysics Data System (ADS)

Teng, Chuanxin; Yu, Fangda; Jing, Ning; Zheng, Jie

2016-11-01

The temperature dependence of a refractive index (RI) sensing probe based on a U-shape tapered plastic optical fiber (POF) was investigated experimentally. The changes in light propagation loss in the probe induced by temperature are of the same order of magnitude as those induced by measured RI changes. The temperature dependence loss and temperature dependence RI deviation of the sensing probe were measured (at the wavelength of 635 nm) in temperature of 10-60 °C. By extracting pure temperature dependence of the sensing probe alone, the influence of temperature to the sensor was characterized.

Dynamical effects in Bragg coherent x-ray diffraction imaging of finite crystals

NASA Astrophysics Data System (ADS)

Shabalin, A. G.; Yefanov, O. M.; Nosik, V. L.; Bushuev, V. A.; Vartanyants, I. A.

2017-08-01

We present simulations of Bragg coherent x-ray diffractive imaging (CXDI) data from finite crystals in the frame of the dynamical theory of x-ray diffraction. The developed approach is based on a numerical solution of modified Takagi-Taupin equations and can be applied for modeling of a broad range of x-ray diffraction experiments with finite three-dimensional crystals of arbitrary shape also in the presence of strain. We performed simulations for nanocrystals of a cubic and hemispherical shape of different sizes and provided a detailed analysis of artifacts in the Bragg CXDI reconstructions introduced by the dynamical diffraction. Based on our theoretical analysis we developed an analytical procedure to treat effects of refraction and absorption in the reconstruction. Our results elucidate limitations for the kinematical approach in the Bragg CXDI and suggest a natural criterion to distinguish between kinematical and dynamical cases in coherent x-ray diffraction on a finite crystal.

Chitin Nanofibers Extracted from Crab Shells in Broadband Visible Antireflection Coatings with Controlling Layer-by-Layer Deposition and the Application for Durable Antifog Surfaces.

PubMed

Manabe, Kengo; Tanaka, Chie; Moriyama, Yukari; Tenjimbayashi, Mizuki; Nakamura, Chiaki; Tokura, Yuki; Matsubayashi, Takeshi; Kyung, Kyu-Hong; Shiratori, Seimei

2016-11-23

Reflection from various surfaces of many optical systems, such as photovoltaics and displays, is a critical issue for their performance, and antireflection coatings play a pivotal role in a wide variety of optical technologies, reducing light reflectance loss and hence maximizing light transmission. With the current movement toward optically transparent polymeric media and coatings for antireflection technology, the need for economical and environmentally friendly materials and methods without dependence on shape or size has clearly been apparent. Herein, we demonstrate novel antireflection coatings composed of chitin nanofibers (CHINFs), extracted from crab shell as a biomass material through an aqueous-based layer-by-layer self-assembly process to control the porosity. Increasing the number of air spaces inside the membrane led low refractive index, and precise control of refractive index derived from the stacking of the CHINFs achieved the highest transmittance with investigating the surface structure and the refractive index depending on the solution pH. At a wavelength of 550 nm, the transmittance of the coatings was 96.4%, which was 4.8% higher than that of a glass substrate, and their refractive index was 1.30. Further critical properties of the films were the durability and the antifogging performance derived from the mechanical stability and hydrophilicity of CHINFs, respectively. The present study may contribute to a development of systematically designed nanofibrous films which are suitable for optical applications operating at a broadband visible wavelength with durability and antifog surfaces.

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.

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.

Birefringence and anisotropic optical absorption in porous silicon

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

Efimova, A. I., E-mail: efimova@vega.phys.msu.ru; Krutkova, E. Yu.; Golovan', L. A.

2007-10-15

The refractive indices and the coefficients of optical absorption by free charge carriers and local vibrations in porous silicon (por-Si) films, comprising nanometer-sized silicon residues (nanocrystals) separated by nanometer-sized pores (nanopores) formed in the course of electrochemical etching of the initial single crystal silicon, have been studied by polarization-resolved IR absorption spectroscopy techniques. It is shown that the birefringence observed in por-Si is related to the anisotropic shapes of nanocrystals and nanopores, while the anisotropy (dichroism) of absorption by the local vibrational modes is determined predominantly by the microrelief of the surface of nanocrystals. It is demonstrated that silicon-hydrogen surfacemore » bonds in nanocrystals can be restored by means of selective hydrogen thermodesorption with the formation of a considerable number of H-terminated surface Si-Si dimers.« less

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

Determination of the size, concentration, and refractive index of silica nanoparticles from turbidity spectra.

PubMed

Khlebtsov, Boris N; Khanadeev, Vitaly A; Khlebtsov, Nikolai G

2008-08-19

The size and concentration of silica cores determine the size and concentration of silica/gold nanoshells in final preparations. Until now, the concentration of silica/gold nanoshells with Stober's silica core has been evaluated through the material balance assumption. Here, we describe a method for simultaneous determination of the average size and concentration of silica nanospheres from turbidity spectra measured within the 400-600 nm spectral band. As the refractive index of silica nanoparticles is the key input parameter for optical determination of their concentration, we propose an optical method and provide experimental data on a direct determination of the refractive index of silica particles n = 1.475 +/- 0.005. Finally, we exemplify our method by determining the particle size and concentration for 10 samples and compare the results with transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering data.

Generation of highly confined photonic nanojet using crescent-shape refractive index profile in microsphere

NASA Astrophysics Data System (ADS)

Patel, H. S.; Kushwaha, P. K.; Swami, M. K.

2018-05-01

Photonic nanojets (PNJs) owing to their sub-wavelength near-field features have found many interesting applications like nanoscopy, nano photolithography, high density optical storage, enhancement of Raman signal and single molecule spectroscopy etc. More recently, the focus of research has been on tailoring of PNJs either for better confinement and thus higher peak intensity or for elongation of nanojet for high resolution far field applications. In this paper, we show that crescent-shape refractive index profile (CSRP) of microspheres can be used to generate highly confined PNJ. By optimizing the refractive index of different layers in CSRP microsphere, we show a free space confinement down to ∼ λ / 4 . 5 (FWHM ∼ 110 nm for excitation with 500 nm wavelength). Further, it was observed that the optical properties of substrates also modulate the PNJ characteristics and lead to a further improvement in the transverse confinement to ∼ λ / 6 . 7.

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.

Indication of advanced orthokeratology as an additional treatment after refractive surgeries

NASA Astrophysics Data System (ADS)

Mitsui, Iwane; Yamada, Yoshida

2005-04-01

Ortho-K was indicated for twenty-three eyes of thirteen patients after refractive surgeries such as RK(1) ,PRK(2), and LASIK(3). The average of their Uncorrective Visual Acuity (UCVA) after surgeries was 20/30 or worse, and mean spherical equivalent (SE) was -2.42D. They were followed at least two years wearing of Advanced Ortho-K lenses during night. The following studies were examined on their auto-refraction, auto-keratometry, uncorrected and corrected visual acuity, intra-ocular pressure, corneal endothelium, corneal thickness, corneal curvature, and corneal shape for more than two years. 95% of the patients improved in UCVA up to 20/20 or better, 86% of them improved up to 20/15 or better, and 76% of them improved up to 20/10. The mean SEs improved to -1.20+/-1.02D during six months, - 1.03+/-0.83D during one year, and -0.73+/-0.64D during two years. Astigmatism also slightly decreased. Ophthalmologic examinations showed no abnormalities including flap formation, intra-ocular pressure, and endothelium. Among the refractive surgeries as well as RK and PRK, LASIK has been most popularly spread all over the world. However, patient's quality of vision is not always satisfied during and/or after refractive surgeries, because of several complications such as instability of flap formation, unexpected keratoectasia, diffuse lamellar keratitis, epithelial ingrowth, irregularity of corneal surface which caused myopia regression. In such cases, additional surgical procedures should not be indicated easily. However, Ortho-K is safe and effective enough to correct refractive errors still remained or re-appeared after refractive surgeries. It enables to restore the corneal irregularity to the ideal shape.

A method for the detection of the refractive index of irregular shape solid pigments in light absorbing liquid matrix.

PubMed

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

2010-06-15

The immersion liquid method is powerful for the measurement of the refractive index of solid particles in a liquid matrix. However, this method applies best for cases when the liquid matrix is transparent. A problem is usually how to assess the refractive index of a pigment when it is in a colored host liquid. In this article we introduce a method, and show that by combining so-called multifunction spectrophotometer, immersion liquid method and detection of light transmission and reflection we can assess the refractive index of a pigment in a colored liquid, and also the extinction or absorption coefficient of the host liquid.

Analysis of the Light Transmission Ability of Reinforcing Glass Fibers Used in Polymer Composites.

PubMed

Hegedűs, Gergely; Sarkadi, Tamás; Czigány, Tibor

2017-06-10

This goal of our research was to show that E-glass fiber bundles used for reinforcing composites can be enabled to transmit light in a common resin without any special preparation (without removing the sizing). The power of the transmitted light was measured and the attenuation coefficient, which characterizes the fiber bundle, was determined. Although the attenuation coefficient depends on temperature and the wavelength of the light, it is independent of the power of incident light, the quality of coupling, and the length of the specimen. The refractive index of commercially available transparent resins was measured and it was proved that a resin with a refractive index lower than that of the fiber can be used to make a composite whose fibers are capable of transmitting light. The effects of temperature, compression of the fibers, and the shape of fiber ends on the power of transmitted light were examined. The measurement of emitted light can provide information about the health of the fibers. This can be the basis of a simple health monitoring system in the case of general-purpose composite structures.

Analysis of the Light Transmission Ability of Reinforcing Glass Fibers Used in Polymer Composites

PubMed Central

Hegedűs, Gergely; Sarkadi, Tamás; Czigány, Tibor

2017-01-01

This goal of our research was to show that E-glass fiber bundles used for reinforcing composites can be enabled to transmit light in a common resin without any special preparation (without removing the sizing). The power of the transmitted light was measured and the attenuation coefficient, which characterizes the fiber bundle, was determined. Although the attenuation coefficient depends on temperature and the wavelength of the light, it is independent of the power of incident light, the quality of coupling, and the length of the specimen. The refractive index of commercially available transparent resins was measured and it was proved that a resin with a refractive index lower than that of the fiber can be used to make a composite whose fibers are capable of transmitting light. The effects of temperature, compression of the fibers, and the shape of fiber ends on the power of transmitted light were examined. The measurement of emitted light can provide information about the health of the fibers. This can be the basis of a simple health monitoring system in the case of general-purpose composite structures. PMID:28772996

Raman imaging of pharmaceutical materials: refractive index effects on contrast at buried interfaces.

PubMed

Mecker-Pogue, Laura C; Kauffman, John F

2015-02-01

Resolution targets composed of bilayer polydimethylsiloxane (PDMS) devices with buried polyethylene glycol (PEG) channels have been fabricated using traditional photolithographic and micromolding techniques to develop resolution targets that mimic pharmaceutical materials. Raman chemical images of the resulting PEG-in-PDMS devices composed of varying parallel line widths were investigated by imaging the PEG lines through a thin overlayer of PDMS. Additionally, a scattering agent, Al2O3, was introduced at varying concentrations to each layer of the device to explore the effects of scattering materials on Raman images. Features in the resulting chemical images of the PEG lines suggest that reflection at the PEG/PDMS interface contributes to the Raman signal. A model based on geometric optics was developed to simulate the observed image functions of the targets. The results emphasize the influence of refractive index discontinuities at the PEG/PDMS interface on the apparent size and shape of the PEG features. Such findings have an impact on interpretation of Raman images of nonabsorbing, opaque pharmaceutical samples. Published by Elsevier B.V.

Light scattering from normal and cervical cancer cells.

PubMed

Lin, Xiaogang; Wan, Nan; Weng, Lingdong; Zhou, Yong

2017-04-20

The light scattering characteristic plays a very important role in optic imaging and diagnostic applications. For optical detection of the cell, cell scattering characteristics have an extremely vital role. In this paper, we use the finite-difference time-domain (FDTD) algorithm to simulate the propagation and scattering of light in biological cells. The two-dimensional scattering cell models were set up based on the FDTD algorithm. The cell models of normal cells and cancerous cells were established, and the shapes of organelles, such as mitochondria, were elliptical. Based on these models, three aspects of the scattering characteristics were studied. First, the radar cross section (RCS) distribution curves of the corresponding cell models were calculated, then corresponding relationships between the size and the refractive index of the nucleus and light scattering information were analyzed in the three periods of cell canceration. The values of RCS increase positively with the increase of the nucleo-cytoplasmic ratio in the cancerous process when the scattering angle ranges from 0° to 20°. Second, the effect of organelles in the scattering was analyzed. The peak value of the RCS of cells with mitochondria is higher than the cells without mitochondria when the scattering angle ranges from 20° to 180°. Third, we demonstrated that the influence of cell shape is important, and the impact was revealed by the two typical ideal cells: round cells and oval cells. When the scattering angle ranges from 0° to 80°, the peak values and the frequencies of the appearance of the peaks from the two models are roughly similar. It can be concluded that: (1) the size of the nuclei and the change of the refractive index of cells have a certain impact on light scattering information of the whole cell; (2) mitochondria and other small organelles contribute to the cell light scattering characteristics in the larger scattering angle area; and (3) the change of the cell shape significantly influences the value of scattering peak and the deviation of scattering peak position. The results of the numerical simulation will guide subsequent experiments and early diagnosis of cervical cancer.

Retrieving the complex refractive index of atmospheric aerosols from ratios of solar spectral extinction measurements

NASA Technical Reports Server (NTRS)

Fymat, A. L.; Mease, K. D.

1978-01-01

The technique proposed by Fymat (1976) for retrieving the complex refractive index of atmospheric aerosols using narrowband spectral transmission ratios, taken within an overall narrow spectral interval, is investigated in the case of modelled polydispersions of rural, maritime-continental, maritime-sea spray and meteoric dust aerosols. It is confirmed that for not too broad size distributions most of the information comes from a narrow size range of 'active' aerosols so that, under these circumstances, the refractive index components can indeed be retrieved essentially independently of the size distribution. For 0.1% accurate data in three colors, the technique can provide the real and imaginary components of the index respectively within 0.07% and 0.3% accuracy.

Rotating of low-refractive-index microparticles with a quasi-perfect optical vortex.

PubMed

Liang, Yansheng; Lei, Ming; Yan, Shaohui; Li, Manman; Cai, Yanan; Wang, Zhaojun; Yu, Xianghua; Yao, Baoli

2018-01-01

Low-refractive-index microparticles, such as hollow microspheres, have shown great significance in some applications, such as biomedical sensing and targeted drug delivery. However, optical trapping and manipulation of low-refractive-index microparticles are challenging, owing to the repelling force exerted by typical optical traps. In this paper, we demonstrated optical trapping and rotating of large-sized low-refractive-index microparticles by using quasi-perfect optical vortex (quasi-POV) beams, which were generated by Fourier transform of high-order quasi-Bessel beams. Numerical simulation was carried out to characterize the focusing property of the quasi-POV beams. The dynamics of low-refractive-index microparticles in the quasi-POV with various topological charges was investigated in detail. To improve the trapping and rotating performances of the vortex, a point trap was introduced at the center of the ring. Experimental results showed that the quasi-POV was preferable for manipulation of large-sized low-refractive-index microparticles, with its control of the particles' rotating velocity dependent only on the topological charge due to the unchanged orbital radius.

A novel C-shaped, gold nanoparticle coated, embedded polymer waveguide for localized surface plasmon resonance based detection.

PubMed

Prabhakar, Amit; Mukherji, Soumyo

2010-12-21

In this study, a novel embedded optical waveguide based sensor which utilizes localized surface plasmon resonance of gold nanoparticles coated on a C-shaped polymer waveguide is being reported. The sensor, as designed, can be used as an analysis chip for detection of minor variations in the refractive index of its microenvironment, which makes it suitable for wide scale use as an affinity biosensor. The C-shaped waveguide coupled with microfluidic channel was fabricated by single step patterning of SU8 on an oxidized silicon wafer. The absorbance due to the localized surface plasmon resonance (LSPR) of SU8 waveguide bound gold nano particle (GNP) was found to be linear with refractive index changes between 1.33 and 1.37. A GNP coated C-bent waveguide of 200 μ width with a bend radius of 1 mm gave rise to a sensitivity of ~5 ΔA/RIU at 530 nm as compared to the ~2.5 ΔA/RIU (refractive index units) of the same dimension bare C-bend SU8 waveguide. The resolution of the sensor probe was ~2 × 10(-4) RIU.

Accurate measurement of volume and shape of resting and activated blood platelets from light scattering.

PubMed

Moskalensky, Alexander E; Yurkin, Maxim A; Konokhova, Anastasiya I; Strokotov, Dmitry I; Nekrasov, Vyacheslav M; Chernyshev, Andrei V; Tsvetovskaya, Galina A; Chikova, Elena D; Maltsev, Valeri P

2013-01-01

We introduce a novel approach for determination of volume and shape of individual blood platelets modeled as an oblate spheroid from angle-resolved light scattering with flow-cytometric technique. The light-scattering profiles (LSPs) of individual platelets were measured with the scanning flow cytometer and the platelet characteristics were determined from the solution of the inverse light-scattering problem using the precomputed database of theoretical LSPs. We revealed a phenomenon of parameter compensation, which is partly explained in the framework of anomalous diffraction approximation. To overcome this problem, additional a priori information on the platelet refractive index was used. It allowed us to determine the size of each platelet with subdiffraction precision and independent of the particular value of the platelet aspect ratio. The shape (spheroidal aspect ratio) distributions of platelets showed substantial differences between native and activated by 10 μM adenosine diphosphate samples. We expect that the new approach may find use in hematological analyzers for accurate measurement of platelet volume distribution and for determination of the platelet activation efficiency.

Influence of particle aspect ratio on the midinfrared extinction spectra of wavelength-sized ice crystals.

PubMed

Wagner, Robert; Benz, Stefan; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Leisner, Thomas

2007-12-20

We have used the T-matrix method and the discrete dipole approximation to compute the midinfrared extinction cross-sections (4500-800 cm(-1)) of randomly oriented circular ice cylinders for aspect ratios extending up to 10 for oblate and down to 1/6 for prolate particle shapes. Equal-volume sphere diameters ranged from 0.1 to 10 microm for both particle classes. A high degree of particle asphericity provokes a strong distortion of the spectral habitus compared to the extinction spectrum of compactly shaped ice crystals with an aspect ratio around 1. The magnitude and the sign (increase or diminution) of the shape-related changes in both the absorption and the scattering cross-sections crucially depend on the particle size and the values for the real and imaginary part of the complex refractive index. When increasing the particle asphericity for a given equal-volume sphere diameter, the values for the overall extinction cross-sections may change in opposite directions for different parts of the spectrum. We have applied our calculations to the analysis of recent expansion cooling experiments on the formation of cirrus clouds, performed in the large coolable aerosol and cloud chamber AIDA of Forschungszentrum Karlsruhe at a temperature of 210 K. Depending on the nature of the seed particles and the temperature and relative humidity characteristics during the expansion, ice crystals of various shapes and aspect ratios could be produced. For a particular expansion experiment, using Illite mineral dust particles coated with a layer of secondary organic matter as seed aerosol, we have clearly detected the spectral signatures characteristic of strongly aspherical ice crystal habits in the recorded infrared extinction spectra. We demonstrate that the number size distributions and total number concentrations of the ice particles that were generated in this expansion run can only be accurately derived from the recorded infrared spectra when employing aspect ratios as high as 10 in the retrieval approach. Remarkably, the measured spectra could also be accurately fitted when employing an aspect ratio of 1 in the retrieval. The so-deduced ice particle number concentrations, however, exceeded the true values, determined with an optical particle counter, by more than 1 order of magnitude. Thus, the shape-induced spectral changes between the extinction spectra of platelike ice crystals of aspect ratio 10 and compactly shaped particles of aspect ratio 1 can be efficiently balanced by deforming the true number size distribution of the ice cloud. As a result of this severe size/shape ambiguity in the spectral analysis, we consider it indispensable to cross-check the infrared retrieval results of wavelength-sized ice particles with independent reference measurements of either the number size distribution or the particle morphology.

Improving Estimated Optical Constants With MSTM and DDSCAT Modeling

NASA Astrophysics Data System (ADS)

Pitman, K. M.; Wolff, M. J.

2015-12-01

We present numerical experiments to determine quantitatively the effects of mineral particle clustering on Mars spacecraft spectral signatures and to improve upon the values of refractive indices (optical constants n, k) derived from Mars dust laboratory analog spectra such as those from RELAB and MRO CRISM libraries. Whereas spectral properties for Mars analog minerals and actual Mars soil are dominated by aggregates of particles smaller than the size of martian atmospheric dust, the analytic radiative transfer (RT) solutions used to interpret planetary surfaces assume that individual, well-separated particles dominate the spectral signature. Both in RT models and in the refractive index derivation methods that include analytic RT approximations, spheres are also over-used to represent nonspherical particles. Part of the motivation is that the integrated effect over randomly oriented particles on quantities such as single scattering albedo and phase function are relatively less than for single particles. However, we have seen in previous numerical experiments that when varying the shape and size of individual grains within a cluster, the phase function changes in both magnitude and slope, thus the "relatively less" effect is more significant than one might think. Here we examine the wavelength dependence of the forward scattering parameter with multisphere T-matrix (MSTM) and discrete dipole approximation (DDSCAT) codes that compute light scattering by layers of particles on planetary surfaces to see how albedo is affected and integrate our model results into refractive index calculations to remove uncertainties in approximations and parameters that can lower the accuracy of optical constants. By correcting the single scattering albedo and phase function terms in the refractive index determinations, our data will help to improve the understanding of Mars in identifying, mapping the distributions, and quantifying abundances for these minerals and will address long-standing questions on fundamental physics in the martian surface (e.g., what is the fundamental scattering unit for closely packed dust or regolith grains?). This work was supported by NASA's Mars Fundamental Research Program and performed with the Pleiades cluster courtesy of NASA's Advanced Supercomputing Division.

Using refractive optics to broaden the focus of an X-ray mirror.

PubMed

Laundy, David; Sawhney, Kawal; Dhamgaye, Vishal

2017-07-01

X-ray mirrors are widely used at synchrotron radiation sources for focusing X-rays into focal spots of size less than 1 µm. The ability of the beamline optics to change the size of this spot over a range up to tens of micrometres can be an advantage for many experiments such as X-ray microprobe and X-ray diffraction from micrometre-scale crystals. It is a requirement that the beam size change should be reproducible and it is often essential that the change should be rapid, for example taking less than 1 s, in order to allow high data collection rates at modern X-ray sources. In order to provide a controlled broadening of the focused spot of an X-ray mirror, a series of refractive optical elements have been fabricated and installed immediately before the mirror. By translation, a new refractive element is moved into the X-ray beam allowing a variation in the size of the focal spot in the focusing direction. Measurements using a set of prefabricated refractive structures with a test mirror showed that the focused beam size could be varied from less than 1 µm to over 10 µm for X-rays in the energy range 10-20 keV. As the optics is in-line with the X-ray beam, there is no effect on the centroid position of the focus. Accurate positioning of the refractive optics ensures reproducibility in the focused beam profile and no additional re-alignment of the optics is required.

Using refractive optics to broaden the focus of an X-ray mirror

PubMed Central

Dhamgaye, Vishal

2017-01-01

X-ray mirrors are widely used at synchrotron radiation sources for focusing X-rays into focal spots of size less than 1 µm. The ability of the beamline optics to change the size of this spot over a range up to tens of micrometres can be an advantage for many experiments such as X-ray microprobe and X-ray diffraction from micrometre-scale crystals. It is a requirement that the beam size change should be reproducible and it is often essential that the change should be rapid, for example taking less than 1 s, in order to allow high data collection rates at modern X-ray sources. In order to provide a controlled broadening of the focused spot of an X-ray mirror, a series of refractive optical elements have been fabricated and installed immediately before the mirror. By translation, a new refractive element is moved into the X-ray beam allowing a variation in the size of the focal spot in the focusing direction. Measurements using a set of prefabricated refractive structures with a test mirror showed that the focused beam size could be varied from less than 1 µm to over 10 µm for X-rays in the energy range 10–20 keV. As the optics is in-line with the X-ray beam, there is no effect on the centroid position of the focus. Accurate positioning of the refractive optics ensures reproducibility in the focused beam profile and no additional re-alignment of the optics is required. PMID:28664880

[Ophthalmopathy caused by precision work of sorters of precious stones].

PubMed

Feĭgin, A A; Korniushina, T A; Rozenblium, Iu Z

1992-01-01

A total of 440 female workers aged 17 to 50, whose work records ranged from 1 to 29 years, engaged in grading the diamonds by the color, shape, size, and quality (a total of 24 to 33 positions) were examined. A random sample of 110 subjects was singled out; this sample was divided into 2 equal groups with or without asthenopic complaints. The refraction, absolute accommodation volume, and relative accommodation reserves were under study. Comparison of these two groups of workers has shown that subjects with precision ophthalmopathy show a trend to a higher incidence of myopia, reduction of the absolute accommodation volume by 1.6 diopters and of the relative accommodation reserves by 1.3 diopters.

The effect of procedure room temperature and humidity on LASIK outcomes.

PubMed

Seider, Michael I; McLeod, Stephen D; Porco, Travis C; Schallhorn, Steven C

2013-11-01

To determine whether procedure room temperature or humidity during LASIK affect refractive outcomes in a large patient sample. Retrospective cohort study. A total of 202 394 eyes of 105 712 patients aged 18 to 75 years who underwent LASIK at an Optical Express, Inc., location in their United Kingdom and Ireland centers from January 1, 2008, to June 30, 2011, who met inclusion criteria. Patient age, gender, flap creation technique, pre- and 1-month post-LASIK manifest refraction, and ambient temperature and humidity during LASIK were recorded. Effect size determination and univariate and multivariate analyses were performed to characterize the relationships between LASIK procedure room temperature and humidity and postoperative refractive outcome. One month post-LASIK manifest refraction. No clinically significant effect of procedure room temperature or humidity was found on LASIK refractive outcomes. When considering all eyes in our population, an increase of 1°C during LASIK was associated with a 0.003 diopter (D) more hyperopic refraction 1 month postoperatively, and an increase in 1% humidity was associated with a 0.0004 more myopic refraction. These effect sizes were the same or similar when considering only myopic eyes, only hyperopic eyes, and subgroups of eyes stratified by age and preoperative refractive error. Neither procedure room temperature nor humidity during LASIK were found to have a clinically significant relationship with postoperative manifest refraction in our population. Copyright © 2013 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.

The effect of procedure room temperature and humidity on LASIK outcomes

PubMed Central

Seider, Michael I.; McLeod, Stephen D.; Porco, Travis C.; Schallhorn, Steven C.

2013-01-01

Objective To determine if procedure room temperature and humidity during LASIK affects refractive outcomes in a very large patient sample. Design Retrospective cohort study. Participants 202,394 eyes of 105,712 patients aged 18 to 75 years old who underwent LASIK at an Optical Express, Inc. location in their United Kingdom and Ireland centers from January 1, 2008 to June 30, 2011 who met inclusion criteria. Methods Patient age, gender, pre- and one month post-LASIK manifest refraction and flap creation technique were recorded as well as the ambient temperature and humidity during LASIK. Effect size determination, in addition to univariate and multivariate analysis was performed to characterize the relationships between LASIK procedure room temperature and humidity and post-operative refractive outcome. Main Outcome Measures One month post-LASIK manifest refraction. Results No clinically significant effect of procedure room temperature or humidity was found on LASIK refractive outcomes. When considering all eyes in our population, an increase of one degree Celsius during LASIK was associated with a 0.003 diopter more hyperopic refraction one month post-operatively and an increase in one percent humidity was associated with a 0.0004 more myopic refraction. These effect sizes were the same or similar when considering only myopic eyes, only hyperopic eyes and subgroups of eyes stratified by age and pre-operative refractive error. Conclusions Procedure room temperature or humidity during LASIK was found to have no clinically significant relationship with post-operative manifest refraction in our population. PMID:23769199

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.

Comparable change in stromal refractive index of cat and human corneas following blue-IRIS.

PubMed

Wozniak, Kaitlin T; Gearhart, Sara M; Savage, Daniel E; Ellis, Jonathan D; Knox, Wayne H; Huxlin, Krystel R

2017-05-01

Blue intratissue refractive index shaping (blue-IRIS) is a method with potential to correct ocular refraction noninvasively in humans. To date, blue-IRIS has only ever been applied to cat corneas and hydrogels. To test the comparability of refractive index change achievable in cat and human tissues, we used blue-IRIS to write identical phase gratings in ex vivo feline and human corneas. Femtosecond pulses (400 nm) were focused ? 300 ?? ? m below the epithelial surface of excised cat and human corneas and scanned to write phase gratings with lines ? 1 ?? ? m wide, spaced 5 ?? ? m apart, using a scan speed of 5 ?? mm / s . Additional cat corneas were used to test writing at 3 and 7 ?? mm / s in order to document speed dependence of the refractive index change magnitude. The first-order diffraction efficiency was immediately measured and used to calculate the refractive index change attained. Our data show that blue-IRIS induces comparable refractive index changes in feline and human corneas, an essential requirement for further developing its use as a clinical vision correction technique.

Comparable change in stromal refractive index of cat and human corneas following blue-IRIS

NASA Astrophysics Data System (ADS)

Wozniak, Kaitlin T.; Gearhart, Sara M.; Savage, Daniel E.; Ellis, Jonathan D.; Knox, Wayne H.; Huxlin, Krystel R.

2017-05-01

Blue intratissue refractive index shaping (blue-IRIS) is a method with potential to correct ocular refraction noninvasively in humans. To date, blue-IRIS has only ever been applied to cat corneas and hydrogels. To test the comparability of refractive index change achievable in cat and human tissues, we used blue-IRIS to write identical phase gratings in ex vivo feline and human corneas. Femtosecond pulses (400 nm) were focused ˜300 μm below the epithelial surface of excised cat and human corneas and scanned to write phase gratings with lines ˜1 μm wide, spaced 5 μm apart, using a scan speed of 5 mm/s. Additional cat corneas were used to test writing at 3 and 7 mm/s in order to document speed dependence of the refractive index change magnitude. The first-order diffraction efficiency was immediately measured and used to calculate the refractive index change attained. Our data show that blue-IRIS induces comparable refractive index changes in feline and human corneas, an essential requirement for further developing its use as a clinical vision correction technique.

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

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.

On-the-Fly Cross Flow Laser Guided Separation of Aerosol Particles Based on Size, Refractive Index and Density-Theoretical Analysis

DTIC Science & Technology

2010-12-20

Optical chromatography Size determination by eluting particles ,” Talanta 48(3), 551–557 (1999). 15. A. Ashkin, and J. M. Dziedzic, “Optical levitation ...the use of optical force in the gas phase, for example, levitation of airborne particles [15,16], and more recent studies on aerosol optical guiding...On-the-fly cross flow laser guided separation of aerosol particles based on size, refractive index and density–theoretical analysis A. A. Lall

Coherent control of double deflected anomalous modes in ultrathin trapezoid-shaped slit metasurface.

PubMed

Zhu, Z; Liu, H; Wang, D; Li, Y X; Guan, C Y; Zhang, H; Shi, J H

2016-11-22

Coherent light-matter interaction in ultrathin metamaterials has been demonstrated to dynamically modulate intensity, polarization and propagation direction of light. The gradient metasurface with a transverse phase variation usually exhibits an anomalous refracted beam of light dictated by so-called generalized Snell's law. However, less attention has been paid to coherent control of the metasurface with multiple anomalous refracted beams. Here we propose an ultrathin gradient metasurface with single trapezoid-shaped slot antenna as its building block that allows one normal and two deflected transmitted beams. It is numerically demonstrated that such metasurface with multiple scattering modes can be coherently controlled to modulate output intensities by changing the relative phase difference between two counterpropagating coherent beams. Each mode can be coherently switched on/off and two deflected anomalous beams can be synchronously dictated by the phase difference. The coherent control effect in the trapezoid-shaped slit metasurface will offer a promising opportunity for multichannel signals modulation, multichannel sensing and wave front shaping.

Coherent control of double deflected anomalous modes in ultrathin trapezoid-shaped slit metasurface

PubMed Central

Zhu, Z.; Liu, H.; Wang, D.; Li, Y. X.; Guan, C. Y.; Zhang, H.; Shi, J. H.

2016-01-01

Coherent light-matter interaction in ultrathin metamaterials has been demonstrated to dynamically modulate intensity, polarization and propagation direction of light. The gradient metasurface with a transverse phase variation usually exhibits an anomalous refracted beam of light dictated by so-called generalized Snell’s law. However, less attention has been paid to coherent control of the metasurface with multiple anomalous refracted beams. Here we propose an ultrathin gradient metasurface with single trapezoid-shaped slot antenna as its building block that allows one normal and two deflected transmitted beams. It is numerically demonstrated that such metasurface with multiple scattering modes can be coherently controlled to modulate output intensities by changing the relative phase difference between two counterpropagating coherent beams. Each mode can be coherently switched on/off and two deflected anomalous beams can be synchronously dictated by the phase difference. The coherent control effect in the trapezoid-shaped slit metasurface will offer a promising opportunity for multichannel signals modulation, multichannel sensing and wave front shaping. PMID:27874053

Determining the unique refractive index properties of solid polystyrene aerosol using broadband Mie scattering from optically trapped beads.

PubMed

Jones, Stephanie H; King, Martin D; Ward, Andrew D

2013-12-21

A method is described to measure the refractive index dispersion with wavelength of optically trapped solid particles in air. Knowledge of the refraction properties of solid particles is critical for the study of aerosol; both in the laboratory and in the atmosphere for climate studies. Single micron-sized polystyrene beads were optically trapped in air using a vertically aligned counter-propagating configuration of focussed laser beams. Each bead was illuminated using white light from a broadband light emitting diode (LED) and elastic scattering within the bead was collected onto a spectrograph. The resulting Mie spectra were analysed to accurately determine polystyrene bead radii to ±0.4 nm and values of the refractive index to ±0.0005 over a wavelength range of 480-700 nm. We demonstrate that optical trapping combined with elastic scattering can be used to both accurately size polystyrene beads suspended in air and determine their wavelength dependent refractive index. The refractive index dispersions are in close agreement with reported values for polystyrene beads in aqueous dispersion. Our results also demonstrate a variation in the refractive index of polystyrene, from bead to bead, in a commercial sample. The measured variation highlights that care must be taken when using polystyrene beads as a calibration aerosol.

Aberration-free aspherical lens shape for shortening the focal distance of an already convergent beam

PubMed Central

Sutter, John P.; Alianelli, Lucia

2017-01-01

The shapes of single lens surfaces capable of focusing divergent and collimated beams without aberration have already been calculated. However, nanofocusing compound refractive lenses (CRLs) require many consecutive lens surfaces. Here a theoretical example of an X-ray nanofocusing CRL with 48 consecutive surfaces is studied. The surfaces on the downstream end of this CRL accept X-rays that are already converging toward a focus, and refract them toward a new focal point that is closer to the surface. This case, so far missing from the literature, is treated here. The ideal surface for aberration-free focusing of a convergent incident beam is found by analytical computation and by ray tracing to be one sheet of a Cartesian oval. An ‘X-ray approximation’ of the Cartesian oval is worked out for the case of small change in index of refraction across the lens surface. The paraxial approximation of this surface is described. These results will assist the development of large-aperture CRLs for nanofocusing. PMID:29091055

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.

Peripheral defocus does not necessarily affect central refractive development.

PubMed

Schippert, Ruth; Schaeffel, Frank

2006-10-01

Recent experiments in monkeys suggest that deprivation, imposed only in the periphery of the visual field, can induce foveal myopia. This raises the hypothesis that peripheral refractive errors imposed by the spectacle lens correction could influence foveal refractive development also in humans. We have tested this hypothesis in chicks. Chicks wore either full field spectacle lenses (+6.9 D/-7 D), or lenses with central holes of 4, 6, or 8mm diameter, for 4 days (n=6 for each group). Refractions were measured in the central visual field, and at -45 degrees (temporal) and +45 degrees (nasal), and axial lengths were measured by A-scan ultrasonography. As previously described, full field lenses were largely compensated within 4 days (refraction changes with positive lenses: +4.69+/-1.73 D, negative lenses: -5.98+/-1.78 D, both p<0.001, Dunnett's test, to untreated controls). With holes in the center of the lenses, the central refraction remained emmetropic and there was not even a trend of a shift in refraction (all groups: p>0.5, Dunnetts test). At +/-45 degrees , the lenses were partially compensated despite the 4/6/8mm central holes; positive lenses: +2.63 / +1.44 / +0.43 D, negative lenses: -2.57 / -1.06 / +0.06 D. There is extensive local compensation of imposed refractive errors in chickens. For the tested hole sizes, peripherally imposed defocus did not influence central refractive development. To alter central refractive development, the unobstructed part in the central visual field may have to be quite small (hole sizes smaller than 4mm, with the lenses at a vertex distance of 2-3mm).

High-refractive index particles in counter-propagating optical tweezers - manipulation and forces

NASA Astrophysics Data System (ADS)

van der Horst, Astrid

2006-09-01

With a tightly focused single laser beam, also called optical tweezers, particles of a few nanometers up to several micrometers in size can be trapped and manipulated in 3D. The size, shape and refractive index of such colloidal particles are of influence on the optical forces exerted on them in the trap. A higher refractive-index difference between a particle and the surrounding medium will increase the forces. The destabilizing scattering force, however, pushing the particle in the direction of the beam, increases more than the gradient force, directed towards the focus. As a consequence, particles with a certain refractive index cannot be trapped in a single-beam gradient trap, and a limit is set to the force that can be exerted. We developed an experimental setup with two opposing high-numerical objectives. By splitting the laser beam, we created counter-propagating tweezers in which the scattering forces were canceled in the axial direction and high-refractive index and metallic particles could also be trapped. With the use of a separate laser beam combined with a quadrant photodiode, accurate position detection on a trapped particle in the counter-propagating tweezers is possible. We used this to determine trap stiffnesses, and show, with measurements and calculations, an enhancement in trap stiffness of at least 3 times for high-index 1.1-micrometer-diameter titania particles as compared to 1.4-micrometer-diameter silica particles under the same conditions. The ability to exert higher forces with lower laser power finds application in biophysical experiments, where laser damage and heating play a role. The manipulation of high-index and metallic particles also has applications in materials and colloid science, for example to incorporate high-index defects in colloidal photonic crystals. We demonstrate the patterning of high-index particles onto a glass substrate. The sample cell was mounted on a high-accuracy piezo stage combined with a long-range stage with motorized actuators. Because we used image analysis of the patterned structure to accurately find back the starting position and compensate for drift of the sample, we could move far away from the patterning region. This enabled us to select particles from a separate reservoir of a mixture of particles, and, one-by-one, position them at chosen locations. By time-sharing the laser beam using acousto-optic deflectors, we created multiple counter-propagating tweezers. We trapped an array of high-refractive index particles, and were able to move those particles individually. We used such a dynamic array of counter-propagating tweezers to create line-optical tweezers in which we trapped semi-conducting high-refractive index nanorods in three dimensions. We demonstrate full 3D translational and in-plane rotational control over the rods, which could not be held in single-beam line-tweezers. The configuration of two opposing objectives was also used for simultaneous trapping with one objective and confocal imaging of the fluorescently labeled particles using the other objective. By trapping particles with a refractive index contrast in a dispersion of index-matched particles, crystallization could be induced, which was imaged in three dimensions using confocal microscopy.

BPM analysis of all-optical fiber interferometric sensor based on a U-shape microcavity

NASA Astrophysics Data System (ADS)

Wu, Hongbin; Yuan, Lei; Wang, Sumei; Zhao, Longjiang; Cao, Zhitao

2014-02-01

Reflectivity spectrum of beam propagation method (BPM), for the first time to the best of our knowledge, is realized and utilized to model all-optical fiber interferometric sensor formed by a U-shape microcavity embedded in a single mode optical fiber and illustrate the principle of sensor structures varied by the length and the depth of U-shape microcavity. BPM analysis gives a constructive guideline to get a high interferometric fringe visibility which is most important for sensing application. The simulated results are completely in agreement with the interferometric sensor principle of Fabry-Perot interferometer (FPI) theory. With the conclusion of FPI sensor, refractive index (RI) sensitivity and temperature sensitivity are then simulated and obtained as 1049+/-5.2nm/RIU (refractive index unit) within RI range of solutions and 1.04+/-0.03pm/°C respectively.

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.

Effects of local myopic defocus on refractive development in monkeys.

PubMed

Smith, Earl L; Hung, Li-Fang; Huang, Juan; Arumugam, Baskar

2013-11-01

Visual signals that produce myopia are mediated by local, regionally selective mechanisms. However, little is known about spatial integration for signals that slow eye growth. The purpose of this study was to determine whether the effects of myopic defocus are integrated in a local manner in primates. Beginning at 24 ± 2 days of age, seven rhesus monkeys were reared with monocular spectacles that produced 3 diopters (D) of relative myopic defocus in the nasal visual field of the treated eye but allowed unrestricted vision in the temporal field (NF monkeys). Seven monkeys were reared with monocular +3 D lenses that produced relative myopic defocus across the entire field of view (FF monkeys). Comparison data from previous studies were available for 11 control monkeys, 8 monkeys that experienced 3 D of hyperopic defocus in the nasal field, and 6 monkeys exposed to 3 D of hyperopic defocus across the entire field. Refractive development, corneal power, and axial dimensions were assessed at 2- to 4-week intervals using retinoscopy, keratometry, and ultrasonography, respectively. Eye shape was assessed using magnetic resonance imaging. In response to full-field myopic defocus, the FF monkeys developed compensating hyperopic anisometropia, the degree of which was relatively constant across the horizontal meridian. In contrast, the NF monkeys exhibited compensating hyperopic changes in refractive error that were greatest in the nasal visual field. The changes in the pattern of peripheral refractions in the NF monkeys reflected interocular differences in vitreous chamber shape. As with form deprivation and hyperopic defocus, the effects of myopic defocus are mediated by mechanisms that integrate visual signals in a local, regionally selective manner in primates. These results are in agreement with the hypothesis that peripheral vision can influence eye shape and potentially central refractive error in a manner that is independent of central visual experience.

Aerosol properties computed from aircraft-based observations during the ACE- Asia campaign. 2; A case study of lidar ratio closure and aerosol radiative effects

NASA Technical Reports Server (NTRS)

Kuzmanoski, Maja; Box, M. A.; Schmid, B.; Box, G. P.; Wang, J.; Russell, P. B.; Bates, D.; Jonsson, H. H.; Welton, Ellsworth J.; Flagan, R. C.

2005-01-01

For a vertical profile with three distinct layers (marine boundary, pollution and dust), observed during the ACE-Asia campaign, we carried out a comparison between the modeled lidar ratio vertical profile and that obtained from collocated airborne NASA AATS-14 sunphotometer and shipborne Micro-Pulse Lidar (MPL) measurements. Vertically resolved lidar ratio was calculated from two size distribution vertical profiles - one obtained by inversion of sunphotometer-derived extinction spectra, and one measured in-situ - combined with the same refractive index model based on aerosol chemical composition. The aerosol model implies single scattering albedos of 0.78 - 0.81 and 0.93 - 0.96 at 0.523 microns (the wavelength of the lidar measurements), in the pollution and dust layers, respectively. The lidar ratios calculated from the two size distribution profiles have close values in the dust layer; they are however, significantly lower than the lidar ratios derived from combined lidar and sunphotometer measurements, most probably due to the use of a simple nonspherical model with a single particle shape in our calculations. In the pollution layer, the two size distribution profiles yield generally different lidar ratios. The retrieved size distributions yield a lidar ratio which is in better agreement with that derived from lidar/sunphotometer measurements in this layer, with still large differences at certain altitudes (the largest relative difference was 46%). We explain these differences by non-uniqueness of the result of the size distribution retrieval and lack of information on vertical variability of particle refractive index. Radiative transfer calculations for this profile showed significant atmospheric radiative forcing, which occurred mainly in the pollution layer. We demonstrate that if the extinction profile is known then information on the vertical structure of absorption and asymmetry parameter is not significant for estimating forcing at TOA and the surface, while it is of importance for estimating vertical profiles of radiative forcing and heating rates.

The Complex Refractive Index of Volcanic Ash Aerosol Retrieved From Spectral Mass Extinction

NASA Astrophysics Data System (ADS)

Reed, Benjamin E.; Peters, Daniel M.; McPheat, Robert; Grainger, R. G.

2018-01-01

The complex refractive indices of eight volcanic ash samples, chosen to have a representative range of SiO2 contents, were retrieved from simultaneous measurements of their spectral mass extinction coefficient and size distribution. The mass extinction coefficients, at 0.33-19 μm, were measured using two optical systems: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter; values for the effective radius of ash particles measured in this study varied from 0.574 to 1.16 μm. Verification retrievals on high-purity silica aerosol demonstrated that the Rayleigh continuous distribution of ellipsoids (CDEs) scattering model significantly outperformed Mie theory in retrieving the complex refractive index, when compared to literature values. Assuming the silica particles provided a good analogue of volcanic ash, the CDE scattering model was applied to retrieve the complex refractive index of the eight ash samples. The Lorentz formulation of the complex refractive index was used within the retrievals as a convenient way to ensure consistency with the Kramers-Kronig relation. The short-wavelength limit of the electric susceptibility was constrained by using independently measured reference values of the complex refractive index of the ash samples at a visible wavelength. The retrieved values of the complex refractive indices of the ash samples showed considerable variation, highlighting the importance of using accurate refractive index data in ash cloud radiative transfer models.

Sensitivity Analysis of Different Shapes of a Plastic Optical Fiber-Based Immunosensor for Escherichia coli: Simulation and Experimental Results.

PubMed

Rodrigues, Domingos M C; Lopes, Rafaela N; Franco, Marcos A R; Werneck, Marcelo M; Allil, Regina C S B

2017-12-19

Conventional pathogen detection methods require trained personnel, specialized laboratories and can take days to provide a result. Thus, portable biosensors with rapid detection response are vital for the current needs for in-loco quality assays. In this work the authors analyze the characteristics of an immunosensor based on the evanescent field in plastic optical fibers with macro curvature by comparing experimental with simulated results. The work studies different shapes of evanescent-wave based fiber optic sensors, adopting a computational modeling to evaluate the probes with the best sensitivity. The simulation showed that for a U-Shaped sensor, the best results can be achieved with a sensor of 980 µm diameter by 5.0 mm in curvature for refractive index sensing, whereas the meander-shaped sensor with 250 μm in diameter with radius of curvature of 1.5 mm, showed better sensitivity for either bacteria and refractive index (RI) sensing. Then, an immunosensor was developed, firstly to measure refractive index and after that, functionalized to detect Escherichia coli . Based on the results with the simulation, we conducted studies with a real sensor for RI measurements and for Escherichia coli detection aiming to establish the best diameter and curvature radius in order to obtain an optimized sensor. On comparing the experimental results with predictions made from the modelling, good agreements were obtained. The simulations performed allowed the evaluation of new geometric configurations of biosensors that can be easily constructed and that promise improved sensitivity.

Removing singular refractive indices with sculpted surfaces

PubMed Central

Horsley, S. A. R.; Hooper, I. R.; Mitchell–Thomas, R. C.; Quevedo–Teruel, O.

2014-01-01

The advent of Transformation Optics established the link between geometry and material properties, and has resulted in a degree of control over electromagnetic fields that was previously impossible. For waves confined to a surface it is known that there is a simpler, but related, geometrical equivalence between the surface shape and the refractive index, and here we demonstrate that conventional devices possessing a singularity — that is, the requirement of an infinite refractive index — can be realised for waves confined to an appropriately sculpted surface. In particular, we redesign three singular omnidirectional devices: the Eaton lens, the generalized Maxwell Fish–Eye, and the invisible sphere. Our designs perfectly reproduce the behaviour of these singular devices, and can be achieved with simple isotropic media of low refractive index contrast. PMID:24786649

Optical properties of potential condensates in exoplanetary atmospheres

NASA Astrophysics Data System (ADS)

Kitzmann, Daniel; Heng, Kevin

2018-03-01

The prevalence of clouds in currently observable exoplanetary atmospheres motivates the compilation and calculation of their optical properties. First, we present a new open-source Mie scattering code known as LX-MIE, which is able to consider large-size parameters (˜107) using a single computational treatment. We validate LX-MIE against the classical MIEVO code as well as previous studies. Secondly, we embark on an expanded survey of the published literature for both the real and imaginary components of the refractive indices of 32 condensate species. As much as possible, we rely on experimental measurements of the refractive indices and resort to obtaining the real from the imaginary component (or vice versa), via the Kramers-Kronig relation, only in the absence of data. We use these refractive indices as input for LX-MIE to compute the absorption, scattering and extinction efficiencies of all 32 condensate species. Finally, we use a three-parameter function to provide convenient fits to the shape of the extinction efficiency curve. We show that the errors associated with these simple fits in the Wide Field Camera 3 (WFC3), J, H, and K wavebands are ˜ 10 per cent. These fits allow for the extinction cross-section or opacity of the condensate species to be easily included in retrieval analyses of transmission spectra. We discuss prospects for future experimental work. The compilation of the optical constants and LX-MIE is publicly available as part of the open-source Exoclime Simulation Platform (http://www.exoclime.org).

Corneal refractive power and eccentricity in the 40- to 64-year-old population of Shahroud, Iran.

PubMed

Asgari, Soheila; Hashemi, Hassan; Mehravaran, Shiva; Khabazkhoob, Mehdi; Emamian, Mohammad Hassan; Jafarzadehpur, Ebrahim; Shariati, Mohammad; Fotouhi, Akbar

2013-01-01

To determine the normal corneal curvature, power, and eccentricity in an Iranian population and their determinants. This report is part of a population-based study conducted in 2009. Of the 5190 participants of the study, Pentacam data from 8532 eyes of 4266 people who met the inclusion criteria for this analysis were used. For each eye, we extracted minimum and maximum keratometry readings, the average of the 2 readings (mean-K), the difference between these 2 parameters (keratometric astigmatism), and corneal eccentricity. The average mean-K, keratometric astigmatism, and eccentricity were 43.73 ± 2.47, 0.90 ± 0.93, and 0.27 ± 0.63 diopter, respectively. Mean-K was directly correlated with age; inversely correlated with body mass index, axial length, white-to-white corneal diameter, and anterior chamber depth; increased at higher amounts of myopia; and was higher in women compared with men. Keratometric astigmatism was significantly higher in women, increased at higher amount of refractive error, but showed no association with other variables. Eccentricity was correlated indirectly with age and white-to-white corneal diameter, and directly with axial length. It increased with myopia. Compared with other studies, the mean corneal power and eccentricity values were lower in this Iranian population sample. Our findings may have implications for clinical interventions, especially refractive surgery. Further studies can identify the causes of such differences in the shape and size of the cornea, which may also be attributable to the choice of the measuring device.

Peripheral refractive correction and automated perimetric profiles.

PubMed

Wild, J M; Wood, J M; Crews, S J

1988-06-01

The effect of peripheral refractive error correction on the automated perimetric sensitivity profile was investigated on a sample of 10 clinically normal, experienced observers. Peripheral refractive error was determined at eccentricities of 0 degree, 20 degrees and 40 degrees along the temporal meridian of the right eye using the Canon Autoref R-1, an infra-red automated refractor, under the parametric conditions of the Octopus automated perimeter. Perimetric sensitivity was then undertaken at these eccentricities (stimulus sizes 0 and III) with and without the appropriate peripheral refractive correction using the Octopus 201 automated perimeter. Within the measurement limits of the experimental procedures employed, perimetric sensitivity was not influenced by peripheral refractive correction.

Influence of changes in an eye's optical system on refraction

NASA Astrophysics Data System (ADS)

Bartkowska, Janina

1998-10-01

The optical system of eye is composed of cornea, lens, anterior chamber, and vitreous body. In the standard schematic eye there are 6 refracting surfaces. The changes of the curvature radii, of the distances between them, of the refractive indices influence the ametropia, refractive power of the eye and retinal image size. The influence of these changes can be appreciated by ray tracing or by an analytical method. There are presented simplified formulae for the differentials of ametropia and refractive power of the eye with respect to the surfaces curvatures, refracting power of cornea and lens, refractive indices. The relations are valid too for bigger changes if ametropia is measured in the cornea vertex. The formulae for the differentials with respect to distances, lens translation, eye axis length are valid if ametropia is measured in the object focus of the eye.

Consequences of on-line dialysis on polyelectrolyte molar masses determined by size-exclusion chromatography with light scattering detection.

PubMed

Radke, Wolfgang

2016-02-01

Size-exclusion chromatography with light scattering detection experiments conducted on poly(acrylic acid) neutralized to different degrees or using hydroxides with different counterions suggest that the same counterion and degree of neutralization is observed at the detector, irrespective of salt concentration, degree of neutralization and counterion at the time of injection. This strongly supports that during the chromatographic experiment the counterions of the polyelectrolyte are exchanged with those of the eluent, resulting in an effective dialysis of the polyelectrolyte solution during the size-exclusion chromatography experiment. Consequently, the refractive index increment determined by a refractive index detector equals the refractive index increment obtained after excessive dialysis against the pure eluent. Therefore, the species detected and characterized by light scattering coupled to size-exclusion chromatography are not identical to the species injected into the chromatographic system. Despite this structural change during the chromatographic experiments, the correct molar mass for the injected species is obtained by size-exclusion chromatography with light scattering detection. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Refractive index-based determination of detergent concentration and its application to the study of membrane proteins

PubMed Central

Strop, Pavel; Brunger, Axel T.

2005-01-01

The concentration of detergent in membrane protein preparations can have a critical role on protein stability, function, and the potential for crystallization. Unfortunately, dialysis or protein concentration can lead to an unknown amount of detergent in the final membrane protein preparations. Here we present a method for the determination of detergent concentration based on refractive index of the detergent solution. This method was applied to quantitate the amount of detergent remaining in solution after concentration in various concentrators. We found that the ability of the tested detergents to pass through the molecular weight cutoff membrane correlates well with detergent micelle size. Therefore, the micelle size can be used as a rough guide to estimate the retention of a given detergent in various molecular weight cutoff concentrators. The refractive index method is exceptionally informative when coupled with size exclusion chromatography and light scattering, and can be used to determine the oligomeric state of the membrane protein, the size of a protein-associated micelle, as well as the amount and size of the unbound detergent micelle. PMID:16046633

Refractive index-based determination of detergent concentration and its application to the study of membrane proteins.

PubMed

Strop, Pavel; Brunger, Axel T

2005-08-01

The concentration of detergent in membrane protein preparations can have a critical role on protein stability, function, and the potential for crystallization. Unfortunately, dialysis or protein concentration can lead to an unknown amount of detergent in the final membrane protein preparations. Here we present a method for the determination of detergent concentration based on refractive index of the detergent solution. This method was applied to quantitate the amount of detergent remaining in solution after concentration in various concentrators. We found that the ability of the tested detergents to pass through the molecular weight cutoff membrane correlates well with detergent micelle size. Therefore, the micelle size can be used as a rough guide to estimate the retention of a given detergent in various molecular weight cutoff concentrators. The refractive index method is exceptionally informative when coupled with size exclusion chromatography and light scattering, and can be used to determine the oligomeric state of the membrane protein, the size of a protein-associated micelle, as well as the amount and size of the unbound detergent micelle.

Management of irregular astigmatism.

PubMed

Goggin, M; Alpins, N; Schmid, L M

2000-08-01

Using a liberal definition of corneal irregularity, modern videokeratoscopy may define approximately 40% of normal corneas with a toric refractive error as possessing primary irregular astigmatism. The causes of secondary forms of irregular astigmatism include corneal surgery, trauma, dystrophies, and infections. Internal refractive surface and media irregularity or noncorneal astigmatism (ocular residual astigmatism) contribute to irregular astigmatism of the entire refractive path of which crystaline lenticular astigmatism is usually the principal contributing component. Treatment options have increased in recent years, particularly, though not exclusively, through the advent of tailored corneal excimer laser ablations. However, discussion continues concerning the systematic approach necessary to enable treatment to achieve an optimal optical surface for the eye. Discussion also continues as to what constitutes the optimal corneal shape. Some refractive procedures may increase higher order aberrations in the attempt to neutralize refractive astigmatism. The way to further refinement of the commonly performed refractive techniques will ultimately lie in the integrated inclusion of a trio of technologies: topographic analysis of the corneal surface, wavefront analysis of ocular refractive aberrations, and vector planning to enable the appropriate balance in emphasis between these two diagnostic modalities. For the uncommon, irregularly roughened corneas, the ablatable polymer techniques show some promise.

Reflectivity of a disordered monolayer estimated by graded refractive index and scattering models.

PubMed

Diamant, Ruth; Garcí-Valenzuela, Augusto; Fernández-Guasti, Manuel

2012-09-01

Reflectivity of a random monolayer, consisting of transparent spherical particles, is estimated using a graded refractive index model, an effective medium approach, and two scattering models. Two cases, a self-standing film and one with a substrate, are considered. Neither the surrounding medium nor the substrate are absorbing materials. Results at normal incidence, with different particle sizes, covering ratios and refractive indexes, are compared. The purpose of this work is to find under which circumstances, for reflectivity at normal incidence, a particle monolayer behaves as a graded refractive index film.

Optical designs of reflection and refraction collection optics for a JT-60SA core Thomson scattering system

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

Tojo, H.; Hatae, T.; Hamano, T.

2013-09-15

Collection optics for core measurements in a JT-60SA Thomson scattering system were designed. The collection optics will be installed in a limited space and have a wide field of view and wide wavelength range. Two types of the optics are therefore suggested: refraction and reflection types. The reflection system, with a large primary mirror, avoids large chromatic aberrations. Because the size limit of the primary mirror and vignetting due to the secondary mirror affect the total collection throughput, conditions that provide the high throughput are found through an optimization. A refraction system with four lenses forming an Ernostar system ismore » also employed. The use of high-refractive-index glass materials enhances the freedom of the lens curvatures, resulting in suppression of the spherical and coma aberration. Moreover, sufficient throughput can be achieved, even with smaller lenses than that of a previous design given in [H. Tojo, T. Hatae, T. Sakuma, T. Hamano, K. Itami, Y. Aida, S. Suitoh, and D. Fujie, Rev. Sci. Instrum. 81, 10D539 (2010)]. The optical resolutions of the reflection and refraction systems are both sufficient for understanding the spatial structures in plasma. In particular, the spot sizes at the image of the optics are evaluated as ∼0.3 mm and ∼0.4 mm, respectively. The throughput for the two systems, including the pupil size and transmissivity, are also compared. The results show that good measurement accuracy (<10%) even at high electron temperatures (<30 keV) can be expected in the refraction system.« less

Optical designs of reflection and refraction collection optics for a JT-60SA core Thomson scattering system.

PubMed

Tojo, H; Hatae, T; Hamano, T; Sakuma, T; Itami, K

2013-09-01

Collection optics for core measurements in a JT-60SA Thomson scattering system were designed. The collection optics will be installed in a limited space and have a wide field of view and wide wavelength range. Two types of the optics are therefore suggested: refraction and reflection types. The reflection system, with a large primary mirror, avoids large chromatic aberrations. Because the size limit of the primary mirror and vignetting due to the secondary mirror affect the total collection throughput, conditions that provide the high throughput are found through an optimization. A refraction system with four lenses forming an Ernostar system is also employed. The use of high-refractive-index glass materials enhances the freedom of the lens curvatures, resulting in suppression of the spherical and coma aberration. Moreover, sufficient throughput can be achieved, even with smaller lenses than that of a previous design given in [H. Tojo, T. Hatae, T. Sakuma, T. Hamano, K. Itami, Y. Aida, S. Suitoh, and D. Fujie, Rev. Sci. Instrum. 81, 10D539 (2010)]. The optical resolutions of the reflection and refraction systems are both sufficient for understanding the spatial structures in plasma. In particular, the spot sizes at the image of the optics are evaluated as ~0.3 mm and ~0.4 mm, respectively. The throughput for the two systems, including the pupil size and transmissivity, are also compared. The results show that good measurement accuracy (<10%) even at high electron temperatures (<30 keV) can be expected in the refraction system.

Asymmetrical flow field-flow fractionation with multi-angle light scattering and quasi-elastic light scattering for characterization of polymersomes: comparison with classical techniques.

PubMed

Till, Ugo; Gaucher-Delmas, Mireille; Saint-Aguet, Pascale; Hamon, Glenn; Marty, Jean-Daniel; Chassenieux, Christophe; Payré, Bruno; Goudounèche, Dominique; Mingotaud, Anne-Françoise; Violleau, Frédéric

2014-12-01

Polymersomes formed from amphiphilic block copolymers, such as poly(ethyleneoxide-b-ε-caprolactone) (PEO-b-PCL) or poly(ethyleneoxide-b-methylmethacrylate), were characterized by asymmetrical flow field-flow fractionation coupled with quasi-elastic light scattering (QELS), multi-angle light scattering (MALS), and refractive index detection, leading to the determination of their size, shape, and molecular weight. The method was cross-examined with more classical ones, like batch dynamic and static light scattering, electron microscopy, and atomic force microscopy. The results show good complementarities between all the techniques; asymmetrical flow field-flow fractionation being the most pertinent one when the sample exhibits several different types of population.

Lenticular accommodation in relation to ametropia: the chick model.

PubMed

Choh, Vivian; Sivak, Jacob G

2005-03-04

Our goal was to determine whether experimentally induced ametropias have an effect on lenticular accommodation and spherical aberration. Form-deprivation myopia and hyperopia were induced in one eye of hatchling chicks by application of a translucent goggle and +15 D lens, respectively. After 7 days, eyes were enucleated and lenses were optically scanned prior to accommodation, during accommodation, and after accommodation. Accommodation was induced by electrical stimulation of the ciliary nerve. Lenticular focal lengths for form-deprived eyes were significantly shorter than for their controls and accommodation-associated changes in focal length were significantly smaller in myopic eyes compared to their controls. For eyes imposed with +15 D blur, focal lengths were longer than those for their controls and accommodative changes were greater. Spherical aberration of the lens increased with accommodation in both form-deprived and lens-treated birds, but induction of ametropia had no effect on lenticular spherical aberration in general. Nonmonotonicity from lenticular spherical aberration increased during accommodation but effects of refractive error were equivocal. The crystalline lens contributes to refractive error changes of the eye both in the case of myopia and hyperopia. These changes are likely attributable to global changes in the size and shape of the eye.

Simulation and Implementation of a Morphology-Tuned Gold Nano-Islands Integrated Plasmonic Sensor

PubMed Central

Ozhikandathil, Jayan; Packirisamy, Muthukumaran

2014-01-01

This work presents simulation, analysis and implementation of morphology tuning of gold nano-island structures deposited by a novel convective assembly technique. The gold nano-islands were simulated using 3D Finite-Difference Time-Domain (FDTD) techniques to investigate the effect of morphological changes and adsorption of protein layers on the localized surface plasmon resonance (LSPR) properties. Gold nano-island structures were deposited on glass substrates by a novel and low-cost convective assembly process. The structure formed by an uncontrolled deposition method resulted in a nano-cluster morphology, which was annealed at various temperatures to tune the optical absorbance properties by transforming the nano-clusters to a nano-island morphology by modifying the structural shape and interparticle separation distances. The dependence of the size and the interparticle separation distance of the nano-islands on the LSPR properties were analyzed in the simulation. The effect of adsorption of protein layer on the nano-island structures was simulated and a relation between the thickness and the refractive index of the protein layer on the LSPR peak was presented. Further, the sensitivity of the gold nano-island integrated sensor against refractive index was computed and compared with the experimental results. PMID:24932868

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.

Refractive index of liquid mixtures: theory and experiment.

PubMed

Reis, João Carlos R; Lampreia, Isabel M S; Santos, Angela F S; Moita, Maria Luísa C J; Douhéret, Gérard

2010-12-03

An innovative approach is presented to interpret the refractive index of binary liquid mixtures. The concept of refractive index "before mixing" is introduced and shown to be given by the volume-fraction mixing rule of the pure-component refractive indices (Arago-Biot formula). The refractive index of thermodynamically ideal liquid mixtures is demonstrated to be given by the volume-fraction mixing rule of the pure-component squared refractive indices (Newton formula). This theoretical formulation entails a positive change of refractive index upon ideal mixing, which is interpreted in terms of dissimilar London dispersion forces centred in the dissimilar molecules making up the mixture. For real liquid mixtures, the refractive index of mixing and the excess refractive index are introduced in a thermodynamic manner. Examples of mixtures are cited for which excess refractive indices and excess molar volumes show all of the four possible sign combinations, a fact that jeopardises the finding of a general equation linking these two excess properties. Refractive indices of 69 mixtures of water with the amphiphile (R,S)-1-propoxypropan-2-ol are reported at five temperatures in the range 283-303 K. The ideal and real refractive properties of this binary system are discussed. Pear-shaped plots of excess refractive indices against excess molar volumes show that extreme positive values of excess refractive index occur at a substantially lower mole fraction of the amphiphile than extreme negative values of excess molar volume. Analysis of these plots provides insights into the mixing schemes that occur in different composition segments. A nearly linear variation is found when Balankina's ratios between excess and ideal values of refractive indices are plotted against ratios between excess and ideal values of molar volumes. It is concluded that, when coupled with volumetric properties, the new thermodynamic functions defined for the analysis of refractive indices of liquid mixtures give important complementary information on the mixing process over the whole composition range.

Radio jet refraction in galactic atmospheres with static pressure gradients

NASA Technical Reports Server (NTRS)

Henriksen, R. N.; Vallee, J. P.; Bridle, A. H.

1981-01-01

A theory based on the refraction of radio jets in the extended atmosphere of an elliptical galaxy, is proposed for double radio sources with a Z or S morphology. The model describes a collimated jet of supersonic material that bends self-consistently under the influence of external static pressure gradients, and may alternatively be seen as a continuous-jet version of the buoyancy model proposed by Gull (1973). Emphasis is placed on (1) S-shaped radio sources identified with isolated galaxies, such as 3C 293, whose radio structures should be free of distortions resulting from motion relative to a cluster medium, and (2) small-scale, galaxy-dominated rather than environment-dominated S-shaped sources such as the inner jet structure of Fornax A.

Photorefractive keratectomy at 193 nm using an erodible mask

NASA Astrophysics Data System (ADS)

Gordon, Michael; Brint, Stephen F.; Durrie, Daniel S.; Seiler, Theo; Friedman, Marc D.; Johnsson, N. M. F.; King, Michael C.; Muller, David F.

1992-08-01

Clinical experience with more than ten thousand sighted eyes has demonstrated great promise for correcting myopia with photorefractive keratectomy (PRK). Previously reported techniques have incorporated computer-controlled irises, diaphragms, and apertures to regulate the desired distribution of 193 nm radiation onto the eye. This paper reports on an entirely new approach for performing PRK which utilizes an erodible mask to control the shape transfer process. Compared to the more traditional techniques, the erodible mask offers promise of correcting a broad range of refractive errors. In this paper the erodible mask and associated hardware are described in detail. We describe the shape transfer experiments used to predict the functional relationship between the desired refractive correction and the mask shape. We report on early clinical results from five patients with myopic astigmatism. We conclude that the early shape transfer experiments overestimated the spherical component of the correction by 1.25 diopters and underestimated the cylindrical component by approximately 0.85 diopters. The data suggest there may be biological effects which evoke different healing responses when myopic PRK corrections are performed with and without astigmatism. Clinical trials are proceeding with the mask shapes adjusted for these observations.

Measurements of refractive index and size of a spherical drop from Gaussian beam scattering in the primary rainbow region

NASA Astrophysics Data System (ADS)

Yu, Haitao; Sun, Hui; Shen, Jianqi; Tropea, Cameron

2018-03-01

The primary rainbow observed when light is scattered by a spherical drop has been exploited in the past to measure drop size and relative refractive index. However, if higher spatial resolution is required in denser drop ensembles/sprays, and to avoid then multiple drops simultaneously appearing in the measurement volume, a highly focused beam is desirable, inevitably with a Gaussian intensity profile. The present study examines the primary rainbow pattern resulting when a Gaussian beam is scattered by a spherical drop and estimates the attainable accuracy when extracting size and refractive index. The scattering is computed using generalized Lorenz-Mie theory (GLMT) and Debye series decomposition of the Gaussian beam scattering. The results of these simulations show that the measurement accuracy is dependent on both the beam waist radius and the position of the drop in the beam waist.

Optical biosensors for cell adhesion.

PubMed

Ramsden, Jeremy J; Horvath, Robert

2009-01-01

Planar optical waveguides offer an ideal substratum for cells on which to reside. The materials from which the waveguides are made--high refractive index transparent dielectrics--correspond to the coatings of medical implants (e.g., the oxides of niobium, tantalum, and titanium) or the high molecular weight polymers used for culture flasks (e.g., polystyrene). The waveguides can furthermore be modified both chemically and morphologically while retaining their full capability for generating an evanescent optical field that has its greatest strength at the interface between the solid substratum and the liquid phase with which it is invariably in contact (i.e., the culture medium bathing the cells), decaying exponentially perpendicular to the interface at a rate controllable by varying the material parameters of the waveguide. Analysis of the perturbation of the evanescent field by the presence of living cells within it enables their size, number density, shape, refractive index (linked to their constitution) and so forth to be determined, the number of parameters depending on the number of waveguide lightmodes analyzed. No labeling of any kind is necessary, and convenient measurement setups are fully compatible with maintaining the cells in their usual environment. If the temporal evolution of the perturbation is analyzed, even more information can be obtained, such as the amount of material (microexudate) secreted by the cell while residing on the surface. Separation of parallel effects simultaneously contributing to the perturbation of the evanescent field can be accomplished by analysis of coupling peak shape when a grating coupler is used to measure the propagation constants of the waveguide lightmodes.

Investigation of 2D photonic crystal structure based channel drop filter using quad shaped photonic crystal ring resonator for CWDM system

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

Chhipa, Mayur Kumar, E-mail: mayurchhipa1@gmail.com; Dusad, Lalit Kumar; Rajasthan Technical University, Kota, Rajasthan

In this paper, the design & performance of two dimensional (2-D) photonic crystal structure based channel drop filter is investigated using quad shaped photonic crystal ring resonator. In this paper, Photonic Crystal (PhC) based on square lattice periodic arrays of Gallium Indium Phosphide (GaInP) rods in air structure have been investigated using Finite Difference Time Domain (FDTD) method and photonic band gap is being calculated using Plane Wave Expansion (PWE) method. The PhC designs have been optimized for telecommunication wavelength λ= 1571 nm by varying the rods lattice constant. The number of rods in Z and X directions is 21 andmore » 20, with lattice constant 0.540 nm it illustrates that the arrangement of Gallium Indium Phosphide (GaInP) rods in the structure which gives the overall size of the device around 11.4 µm × 10.8 µm. The designed filter gives good dropping efficiency using 3.298, refractive index. The designed structure is useful for CWDM systems. This device may serve as a key component in photonic integrated circuits. The device is ultra compact with the overall size around 123 µm{sup 2}.« less

Glucose Sensor Using U-Shaped Optical Fiber Probe with Gold Nanoparticles and Glucose Oxidase

PubMed Central

Chen, Kuan-Chieh; Li, Yu-Le; Wu, Chao-Wei

2018-01-01

In this study, we proposed a U-shaped optical fiber probe fabricated using a flame heating method. The probe was packaged in glass tube to reduce human factors during experimental testing of the probe as a glucose sensor. The U-shaped fiber probe was found to have high sensitivity in detecting the very small molecule. When the sensor was dipped in solutions with different refractive indexes, its wavelength or transmission loss changed. We used electrostatic self-assembly to bond gold nanoparticles and glucose oxidase (GOD) onto the sensor’s surface. The results over five cycles of the experiment showed that, as the glucose concentration increased, the refractive index of the sensor decreased and its spectrum wavelength shifted. The best wavelength sensitivity was 2.899 nm/%, and the linearity was 0.9771. The best transmission loss sensitivity was 5.101 dB/%, and the linearity was 0.9734. Therefore, the proposed U-shaped optical fiber probe with gold nanoparticles and GOD has good potential for use as a blood sugar sensor in the future. PMID:29659536

Glucose Sensor Using U-Shaped Optical Fiber Probe with Gold Nanoparticles and Glucose Oxidase.

PubMed

Chen, Kuan-Chieh; Li, Yu-Le; Wu, Chao-Wei; Chiang, Chia-Chin

2018-04-16

In this study, we proposed a U-shaped optical fiber probe fabricated using a flame heating method. The probe was packaged in glass tube to reduce human factors during experimental testing of the probe as a glucose sensor. The U-shaped fiber probe was found to have high sensitivity in detecting the very small molecule. When the sensor was dipped in solutions with different refractive indexes, its wavelength or transmission loss changed. We used electrostatic self-assembly to bond gold nanoparticles and glucose oxidase (GOD) onto the sensor’s surface. The results over five cycles of the experiment showed that, as the glucose concentration increased, the refractive index of the sensor decreased and its spectrum wavelength shifted. The best wavelength sensitivity was 2.899 nm/%, and the linearity was 0.9771. The best transmission loss sensitivity was 5.101 dB/%, and the linearity was 0.9734. Therefore, the proposed U-shaped optical fiber probe with gold nanoparticles and GOD has good potential for use as a blood sugar sensor in the future.

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.

Extracting concentrated guided light.

PubMed

Ries, H; Segal, A; Karni, J

1997-05-01

The maximum concentration of radiation is proportional to the square of the refractive index of the medium in which it propagates. A medium with a high refractive index can also serve as a lightguide for concentrated radiation. However, if concentrated radiation is extracted from one medium, with a high refractive index, to another, whose index is lower (e.g., from fused silica into air), part of the radiation may be lost because of the total internal reflection at the interface. We present polygonal shapes suitable for efficient extraction of the concentrated radiation in a controllable way, without increasing the cross-section area (or diameter) of the lightguide. It is shown analytically and experimentally that the use of a secondary concentrator, followed by such a light extractor, both having a high refractive index, can provide considerably more power to a solar receiver with a specific aperture.

Low cost fiber optic sensing of sugar solution

NASA Astrophysics Data System (ADS)

Muthuraju, M. E.; Patlolla, Anurag Reddy; Vadakkapattu Canthadai, Badrinath; Pachava, Vengalrao

2015-03-01

The demand for highly sensitive and reliable sensors to assess the refractive index of liquid get many applications in chemical and biomedical areas. Indeed, the physical parameters such as concentration, pressure and density, etc., can be found using the refractive index of liquid. In contrast to the conventional refractometer for measurement, optical fiber sensor has several advantages like remote sensing, small in size, low cost, immune to EMI etc., In this paper we have discussed determination of refractive index of sugar solution using optical fiber. An intensity modulated low cost plastic fiber optic refractive index sensor has been designed for the study. The sensor is based on principle of change in angle of reflected light caused by refractive index change of the medium surrounding the fiber. The experimental results obtained for the sugar solution of different refractive indices prove that the fiber optic sensor is cable of measuring the refractive indices as well as the concentrations.

Metamaterials with gradient negative index of refraction.

PubMed

Pinchuk, Anatoliy O; Schatz, George C

2007-10-01

We propose a new metamaterial with a gradient negative index of refraction, which can focus a collimated beam of light coming from a distant object. A slab of the negative refractive index metamaterial has a focal length that can be tuned by changing the gradient of the negative refractive index. A thin metal film pierced with holes of appropriate size or spacing between them can be used as a metamaterial with the gradient negative index of refraction. We use finite-difference time-domain calculations to show the focusing of a plane electromagnetic wave passing through a system of equidistantly spaced holes in a metal slab with decreasing diameters toward the edges of the slab.

Scattering properties of ultrafast laser-induced refractive index shaping lenticular structures in hydrogels

NASA Astrophysics Data System (ADS)

Wozniak, Kaitlin T.; Germer, Thomas A.; Butler, Sam C.; Brooks, Daniel R.; Huxlin, Krystel R.; Ellis, Jonathan D.

2018-02-01

We present measurements of light scatter induced by a new ultrafast laser technique being developed for laser refractive correction in transparent ophthalmic materials such as cornea, contact lenses, and/or intraocular lenses. In this new technique, called intra-tissue refractive index shaping (IRIS), a 405 nm femtosecond laser is focused and scanned below the corneal surface, inducing a spatially-varying refractive index change that corrects vision errors. In contrast with traditional laser correction techniques, such as laser in-situ keratomileusis (LASIK) or photorefractive keratectomy (PRK), IRIS does not operate via photoablation, but rather changes the refractive index of transparent materials such as cornea and hydrogels. A concern with any laser eye correction technique is additional scatter induced by the process, which can adversely affect vision, especially at night. The goal of this investigation is to identify sources of scatter induced by IRIS and to mitigate possible effects on visual performance in ophthalmic applications. Preliminary light scattering measurements on patterns written into hydrogel showed four sources of scatter, differentiated by distinct behaviors: (1) scattering from scanned lines; (2) scattering from stitching errors, resulting from adjacent scanning fields not being aligned to one another; (3) diffraction from Fresnel zone discontinuities; and (4) long-period variations in the scans that created distinct diffraction peaks, likely due to inconsistent line spacing in the writing instrument. By knowing the nature of these different scattering errors, it will now be possible to modify and optimize the design of IRIS structures to mitigate potential deficits in visual performance in human clinical trials.

[Effectiveness of eyeglasses for protection against ultraviolet rays].

PubMed

Sakamoto, Y; Kojima, M; Sasaki, K

1999-05-01

The relationship between eyeglass size and protection of the eye surface from the effects of solar ultraviolet (UV) rays was investigated. Solar UV rays irradiating the eye surface were measured on a mannequin which modeled the standard facial bone structure of a Japanese female. UV sensor chips (photo-sensitivity: 260-400 nm) were attached to the ocular surface of the lid fissure. UV measurement was done from 12:00 to 15:00 on a sunny day in March. UV intensity was measured under the following conditions: 1) with or without eyeglasses, 2) wearing sunglasses with side protectors, and 3) wearing a cap with a 7 cm brim. Eyeglasses of four frame sizes (width: 48-57 mm) were put on the mannequin. All lenses were made of plastic and coated so as to be impervious to rays shorter than 400 nm. The refractive power was 0 diopters. At the same time, UV irradiation intensity from all directions (excluding from the earth direction) was measured using a polyhedron type UV sensor with 25 sensor chips. Except for eyeglasses with the smallest frame size, eyeglasses effectively reduced UV exposure to sunlight from the upper front direction. However, protection against rays from the upper temporal direction was extremely poor. Sunlight from the upper back was reflected by the posterior surface of the eyeglasses and reached the eye surface. The efficacy of eyeglasses against UV depends on their size. The shape of the eyeglasses and reflection from the posterior lens surface are also of great importance. Small eyeglasses do not offer ideal UV protection for the Japanese face shape.

Change in peripheral refraction and curvature of field of the human eye with accommodation

NASA Astrophysics Data System (ADS)

Ho, Arthur; Zimmermann, Frederik; Whatham, Andrew; Martinez, Aldo; Delgado, Stephanie; Lazon de la Jara, Percy; Sankaridurg, Padmaja

2009-02-01

Recent research showed that the peripheral refractive state is a sufficient stimulus for myopia progression. This finding led to the suggestion that devices that control peripheral refraction may be efficacious in controlling myopia progression. This study aims to understand whether the optical effect of such devices may be affected by near focus. In particular, we seek to understand the influence of accommodation on peripheral refraction and curvature of field of the eye. Refraction was measured in twenty young subjects using an autorefractor at 0° (i.e. along visual axis), and 20°, 30° and 40° field angles both nasal and temporal to the visual axis. All measurements were conducted at 2.5 m, 40 cm and 30 cm viewing distances. Refractive errors were corrected using a soft contact lens during all measurements. As field angle increased, refraction became less hyperopic. Peripheral refraction also became less hyperopic at nearer viewing distances (i.e. with increasing accommodation). Astigmatism (J180) increased with field angle as well as with accommodation. Adopting a third-order aberration theory approach, the position of the Petzval surface relative to the retinal surface was estimated by considering the relative peripheral refractive error (RPRE) and J180 terms of peripheral refraction. Results for the estimated dioptric position of the Petzval surface relative to the retina showed substantial asymmetry. While temporal field tended to agree with theoretical predictions, nasal response departed dramatically from the model eye predictions. With increasing accommodation, peripheral refraction becomes less hyperopic while the Petzval surface showed asymmetry in its change in position. The change in the optical components (i.e. cornea and/or lens as opposed to retinal shape or position) is implicated as at least one of the contributors of this shift in peripheral refraction during accommodation.

Refractive power and biometric properties of the nonhuman primate isolated crystalline lens.

PubMed

Borja, David; Manns, Fabrice; Ho, Arthur; Ziebarth, Noel M; Acosta, Ana Carolina; Arrieta-Quintera, Esdras; Augusteyn, Robert C; Parel, Jean-Marie

2010-04-01

Purpose. To characterize the age dependence of shape, refractive power, and refractive index of isolated lenses from nonhuman primates. Methods. Measurements were performed on ex vivo lenses from cynomolgus monkeys (cyno: n = 120; age, 2.7-14.3 years), rhesus monkeys (n = 61; age, 0.7-13.3 years), and hamadryas baboons (baboon: n = 16; age, 1.7-27.3 years). Lens thickness, diameter, and surface curvatures were measured with an optical comparator. Lens refractive power was measured with a custom optical system based on the Scheiner principle. The refractive contributions of the gradient, the surfaces, and the equivalent refractive index were calculated with optical ray-tracing software. The age dependence of the optical and biometric parameters was assessed. Results. Over the measured age range isolated lens thickness decreased (baboon: -0.04, cyno: -0.05, and rhesus: -0.06 mm/y) and equatorial diameter increased (logarithmically for the baboon and rhesus, and linearly for cyno: 0.07 mm/y). The isolated lens surfaces flattened and the corresponding refractive power from the surfaces decreased with age (-0.33, -0.48, and -0.68 D/y). The isolated lens equivalent refractive index decreased (only significant for the baboon, -0.001 D/y), and as a result the total isolated lens refractive power decreased with age (baboon: -1.26, cyno: -0.97, and rhesus: -1.76 D/y). Conclusions. The age-dependent trends in the optical and biometric properties, growth, and aging, of nonhuman primate lenses are similar to those of the pre-presbyopic human lens. As the lens ages, the decrease in refractive contributions from the gradient refractive index causes a rapid age-dependent decrease in maximally accommodated lens refractive power.

Impact of Radiatively Interactive Dust Aerosols in the NASA GEOS-5 Climate Model: Sensitivity to Dust Particle Shape and Refractive Index

NASA Technical Reports Server (NTRS)

Colarco, Peter R.; Nowottnick, Edward Paul; Randles, Cynthia A.; Yi, Bingqi; Yang, Ping; Kim, Kyu-Myong; Smith, Jamison A.; Bardeen, Charles D.

2013-01-01

We investigate the radiative effects of dust aerosols in the NASA GEOS-5 atmospheric general circulation model. GEOS-5 is improved with the inclusion of a sectional aerosol and cloud microphysics module, the Community Aerosol and Radiation Model for Atmospheres (CARMA). Into CARMA we introduce treatment of the dust and sea salt aerosol lifecycle, including sources, transport evolution, and sinks. The aerosols are radiatively coupled to GEOS-5, and we perform a series of multi-decade AMIP-style simulations in which dust optical properties (spectral refractive index and particle shape distribution) are varied. Optical properties assuming spherical dust particles are from Mie theory, while those for non-spherical shape distributions are drawn from a recently available database for tri-axial ellipsoids. The climatologies of the various simulations generally compare well to data from the MODIS, MISR, and CALIOP space-based sensors, the ground-based AERONET, and surface measurements of dust deposition and concentration. Focusing on the summertime Saharan dust cycle we show significant variability in our simulations resulting from different choices of dust optical properties. Atmospheric heating due to dust enhances surface winds over important Saharan dust sources, and we find a positive feedback where increased dust absorption leads to increased dust emissions. We further find that increased dust absorption leads to a strengthening of the summertime Hadley cell circulation, increasing dust lofting to higher altitudes and strengthening the African Easterly Jet. This leads to a longer atmospheric residence time, higher altitude, and generally more northward transport of dust in simulations with the most absorbing dust optical properties. We find that particle shape, although important for radiance simulations, is a minor effect compared to choices of refractive index, although total atmospheric forcing is enhanced by greater than 10 percent for simulations incorporating a spheroidal shape distribution versus ellipsoidal or spherical shapes.

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.

Refractive index sensor based on total scattering of plasmonic nanotube

NASA Astrophysics Data System (ADS)

Yao, Kaiqiang; Zeng, Qingbing; Hu, Zengrong; Zhan, Yaohui

2018-03-01

Plasmonic nanostructures can couple free space light into anultrafine space; therefore,they are employed extensively in the refractive index sensors to minimize the device size or further improve the detection sensitivity. In this work, the optical response of the plasmonic nanotube are investigated comprehensively by using full wave finite element method. With a subwavelength scale, the silver nanotube have prominent scattering peaks in the visible range, which is very suitable for observing through the dark field microscope. The geometric dependence of the scattering spectra and the sensing performance are evaluated carefully. Results show that the scattering peaks are in linear relationship to the circumstance refractive index and a sensitivity of 337 nm/RIUcan be achieved easily by such a plasmonicnanotube with an optimized size.

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.

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.

New Objective Refraction Metric Based on Sphere Fitting to the Wavefront

PubMed Central

Martínez-Finkelshtein, Andreí

2017-01-01

Purpose To develop an objective refraction formula based on the ocular wavefront error (WFE) expressed in terms of Zernike coefficients and pupil radius, which would be an accurate predictor of subjective spherical equivalent (SE) for different pupil sizes. Methods A sphere is fitted to the ocular wavefront at the center and at a variable distance, t. The optimal fitting distance, topt, is obtained empirically from a dataset of 308 eyes as a function of objective refraction pupil radius, r0, and used to define the formula of a new wavefront refraction metric (MTR). The metric is tested in another, independent dataset of 200 eyes. Results For pupil radii r0 ≤ 2 mm, the new metric predicts the equivalent sphere with similar accuracy (<0.1D), however, for r0 > 2 mm, the mean error of traditional metrics can increase beyond 0.25D, and the MTR remains accurate. The proposed metric allows clinicians to obtain an accurate clinical spherical equivalent value without rescaling/refitting of the wavefront coefficients. It has the potential to be developed into a metric which will be able to predict full spherocylindrical refraction for the desired illumination conditions and corresponding pupil size. PMID:29104804

New Objective Refraction Metric Based on Sphere Fitting to the Wavefront.

PubMed

Jaskulski, Mateusz; Martínez-Finkelshtein, Andreí; López-Gil, Norberto

2017-01-01

To develop an objective refraction formula based on the ocular wavefront error (WFE) expressed in terms of Zernike coefficients and pupil radius, which would be an accurate predictor of subjective spherical equivalent (SE) for different pupil sizes. A sphere is fitted to the ocular wavefront at the center and at a variable distance, t . The optimal fitting distance, t opt , is obtained empirically from a dataset of 308 eyes as a function of objective refraction pupil radius, r 0 , and used to define the formula of a new wavefront refraction metric (MTR). The metric is tested in another, independent dataset of 200 eyes. For pupil radii r 0 ≤ 2 mm, the new metric predicts the equivalent sphere with similar accuracy (<0.1D), however, for r 0 > 2 mm, the mean error of traditional metrics can increase beyond 0.25D, and the MTR remains accurate. The proposed metric allows clinicians to obtain an accurate clinical spherical equivalent value without rescaling/refitting of the wavefront coefficients. It has the potential to be developed into a metric which will be able to predict full spherocylindrical refraction for the desired illumination conditions and corresponding pupil size.

Fast calculation of the light differential scattering cross section of optically soft and convex bodies

NASA Astrophysics Data System (ADS)

Gruy, Frédéric

2014-02-01

Depending on the range of size and the refractive index value, an optically soft particle follows Rayleigh-Debye-Gans or RDG approximation or Van de Hulst approximation. Practically the first one is valid for small particles whereas the second one works for large particles. Klett and Sutherland (Klett JD, Sutherland RA. App. Opt. 1992;31:373) proved that the Wentzel-Kramers-Brillouin or WKB approximation leads to accurate values of the differential scattering cross section of sphere and cylinder over a wide range of size. In this paper we extend the work of Klett and Sutherland by proposing a method allowing a fast calculation of the differential scattering cross section for any shape of particle with a given orientation and illuminated by unpolarized light. Our method is based on a geometrical approximation of the particle by replacing each geometrical cross section by an ellipse and then by exactly evaluating the differential scattering cross section of the newly generated body. The latter one contains only two single integrals.

Complex Refractive Index of Ammonium Nitrate in the 2-20 micron Spectral Range

NASA Technical Reports Server (NTRS)

Jarzembski, Maurice A.; Norman, Mark L.; Fuller, Kirk A.; Srivastava, Vandana; Cutten, Dean R.

2002-01-01

Using high resolution Fourier Transform Infrared Spectroscopy (FTIR) absorbance/transmittance spectral data for ammonium sulfate (AMS), calcium carbonate (CAC) and ammonium nitrate (AMN), comparisons were made with previously published complex refractive indices data for AMS and CAC to infer experimental parameters to determine the imaginary refractive index for AMN in the infrared wavelength range from 2 to 20 microns. Kramers-Kronig mathematical relations were applied to calculate the real refractive index for the three compositions. Excellent agreement for AMS and CAC with the published values was found, validating the complex refractive indices obtained for AMN. Backscatter calculations using a lognormal size distribution for AMS, AMN, and CAC aerosols were performed to show differences in their backscattered spectra.

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.

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.

Low-loss negative index metamaterials for X, Ku, and K microwave bands

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

Lee, David A.; Vedral, L. James; Smith, David A.

2015-04-15

Low-loss, negative-index of refraction metamaterials were designed and tested for X, Ku, and K microwave frequency bands. An S-shaped, split-ring resonator was used as a unit cell to design homogeneous slabs of negative-index metamaterials. Then, the slabs of metamaterials were cut unto prisms to measure experimentally the negative index of refraction of a plane electromagnetic wave. Theoretical simulations using High-Frequency Structural Simulator, a finite element equation solver, were in good agreement with experimental measurements. The negative index of refraction was retrieved from the angle- and frequency-dependence of the transmitted intensity of the microwave beam through the metamaterial prism and comparedmore » well to simulations; in addition, near-field electromagnetic intensity mapping was conducted with an infrared camera, and there was also a good match with the simulations for expected frequency ranges for the negative index of refraction.« less

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

Refractive index dependence of Papilio Ulysses butterfly wings reflectance spectra

NASA Astrophysics Data System (ADS)

Isnaeni, Muslimin, Ahmad Novi; Birowosuto, Muhammad Danang

2016-02-01

We have observed and utilized butterfly wings of Papilio Ulysses for refractive index sensor. We noticed this butterfly wings have photonic crystal structure, which causes blue color appearance on the wings. The photonic crystal structure, which consists of cuticle and air void, is approximated as one dimensional photonic crystal structure. This photonic crystal structure opens potential to several optical devices application, such as refractive index sensor. We have utilized small piece of Papilio Ulysses butterfly wings to characterize refractive index of several liquid base on reflectance spectrum of butterfly wings in the presence of sample liquid. For comparison, we simulated reflectance spectrum of one dimensional photonic crystal structure having material parameter based on real structure of butterfly wings. We found that reflectance spectrum peaks shifted as refractive index of sample changes. Although there is a slight difference in reflectance spectrum peaks between measured spectrum and calculated spectrum, the trend of reflectance spectrum peaks as function of sample's refractive index is the similar. We assume that during the measurement, the air void that filled by sample liquid is expanded due to liquid pressure. This change of void shape causes non-similarity between measured spectrum and calculated spectrum.

Determining Nanoparticle Inhalation Exposure in the Prosthetics Laboratory at Walter Reed National Military Medical Center

DTIC Science & Technology

2013-04-29

monotonic for particles sized between 500 and 1500 nm. There is also a response error for different refractive indexes of particles (59). In addition, all...accuracy when a range of refractive indexes is present. Detector response error ranges from 50-100%, depending on the refractive index present (17...Respiratory Diseases. Journal of American Medical Association 295 1127-33 13. Eftim E, Samet J, anes H, McDermott A, Dominici F. 2008. Fine

Effect of temperature on the shape of spatial quasi-periodic oscillations of the refractive index of alkali atoms in an optically dense medium with a closed excitation contour of Δ type

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

Barantsev, K A; Litvinov, A N

2014-10-31

A theory of a closed excitation contour (Δ system) of a three-level atom in an optically dense medium is constructed with allowance for temperature. The spatial quasi-periodic oscillations of the refractive index in the system under study are shown to damp with increasing temperature. The range of temperatures at which these oscillations are most pronounced is found. (quantum optics)

Simulation of polarization-dependent film with subwavelength nano-hole array

NASA Astrophysics Data System (ADS)

Yu, Yue; Wei, Dong; Long, Huabao; Xin, Zhaowei; Zhang, Xinyu; Wang, Haiwei; Xie, Changsheng

2018-02-01

When lightwave passes through a metal thin film with a periodic subwavelength hole arrays structure, its transmittance is significantly improved in the partial band compared to other wavelength. Changing the size of the hole, the period or metal material, will make the transmission curve different. Here, we add a layer of dielectric material on the surface of the metal film, such as liquid crystal(LC), by controlling voltage on LC to change the refractive index of this layer, then we can change the transmission curve, and achieve using voltage to move the transmission curve. When there is need for polarization, the holes can be made of a rectangle whose length and width are different or other shapes, for different polarization state of the light, and the film will display different transmission characteristics.

Refraction-compensated motion tracking of unrestrained small animals in positron emission tomography.

PubMed

Kyme, Andre; Meikle, Steven; Baldock, Clive; Fulton, Roger

2012-08-01

Motion-compensated radiotracer imaging of fully conscious rodents represents an important paradigm shift for preclinical investigations. In such studies, if motion tracking is performed through a transparent enclosure containing the awake animal, light refraction at the interface will introduce errors in stereo pose estimation. We have performed a thorough investigation of how this impacts the accuracy of pose estimates and the resulting motion correction, and developed an efficient method to predict and correct for refraction-based error. The refraction model underlying this study was validated using a state-of-the-art motion tracking system. Refraction-based error was shown to be dependent on tracking marker size, working distance, and interface thickness and tilt. Correcting for refraction error improved the spatial resolution and quantitative accuracy of motion-corrected positron emission tomography images. Since the methods are general, they may also be useful in other contexts where data are corrupted by refraction effects. Crown Copyright © 2012. Published by Elsevier B.V. All rights reserved.

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.

Optical and Biometric Characteristics of Anisomyopia in Human Adults

PubMed Central

Tian, Yibin; Tarrant, Janice; Wildsoet, Christine F.

2011-01-01

Purpose To investigate the role of higher order optical aberrations and thus retinal image degradation in the development of myopia, through the characterization of anisomyopia in human adults in terms of their optical and biometric characteristics. Methods The following data were collected from both eyes of fifteen young adult anisometropic myopes and sixteen isometropic myopes: subjective and objective refractive errors, corneal power and shape, monochromatic optical aberrations, anterior chamber depth, lens thickness, vitreous chamber depth, and best corrected visual acuity. Monochromatic aberrations were analyzed in terms of their higher order components, and further analyzed in terms of 31 optical quality metrics. Interocular differences for the two groups (anisomyopes vs. isomyopes) were compared and the relationship between measured ocular parameters and refractive errors also analyzed across all eyes. Results As expected, anisomyopes and isomyopes differed significantly in terms of interocular differences in vitreous chamber depth, axial length and refractive error. However, interocular differences in other optical properties showed no significant intergroup differences. Overall, higher myopia was associated with deeper anterior and vitreous chambers, higher astigmatism, more prolate corneas, and more positive spherical aberration. Other measured optical and biometric parameters were not significantly correlated with spherical refractive error, although some optical quality metrics and corneal astigmatism were significantly correlated with refractive astigmatism. Conclusions An optical cause for anisomyopia related to increased higher order aberrations is not supported by our data. Corneal shape changes and increased astigmatism in more myopic eyes may be a by-product of the increased anterior chamber growth in these eyes; likewise, the increased positive spherical aberration in more myopic eyes may be a product of myopic eye growth. PMID:21797915

Synthesis of multimetallic nanoparticles by seeded methods

NASA Astrophysics Data System (ADS)

Weiner, Rebecca Gayle

This dissertation focuses on the synthesis of metal nanocrystals (NCs) by seeded methods, in which preformed seeds serve as platforms for growth. Metal NCs are of interest due to their tunable optical and catalytic properties, which arise from their composition and crystallite size and shape. Moreover, multimetallic NCs are potentially multifunctional due to the integration of the properties of each metal within one structure. However, such structures are difficult to synthesize with structural definition due to differences in precursor reduction rates and the size-dependent solubility of bimetallic phases. Seed-mediated co-reduction (SMCR) is a method developed in the Skrabalak Laboratory that couples the advantages of a seeded method with co-reduction methods to achieve multimetallic nanomaterials with defined shape and architecture. This approach was originally demonstrated in a model Au-Pd system in which Au and Pd precursors were simultaneously reduced to deposit metal onto shape-controlled Au or Pd NC seeds. Using SMCR, uniformly branched core shell Au Au-Pd and Pd Au-Pd NCs were synthesized, with the shape of the seeds directing the symmetry of the final structures. By varying the seed shape and the temperature at which metal deposition occurs, the roles of adatom diffusion and seed shape on final NC morphology were decoupled. Moreover, by selecting seeds of a composition (Ag) different than the depositing metals (Au and Pd), trimetallic nanostructures are possible, including shape-controlled Ag Au-Pd NCs and hollow Au-Pd-Ag nanoparticles (NPs). The latter architecture arises through galvanic replacement. Shape-controlled core shell NCs with trimetallic shells are also possible by co-reducing three metal precursors (Ag, Au, and Pd) with shape-controlled Au seeds; for example, convex octopods, concave cubes, and truncated octahedra were achieved in this initial demonstration and was enabled by varying the ratio of Ag to Au/Pd in the overgrowth step as well as reaction pH. Ultimately, the final multimetallic nanostructure depends on the kinetics of metal deposition as well as seed composition, shape, reactivity, and crystallinity. In elucidating the roles of these parameters in nanomaterial synthesis, the rational design of new functional NCs becomes possible, which capitalize on the unique optical and catalytic properties of structurally defined multimetallic structures. In fact, branched Au-Pd NCs with high symmetry were found to be effective refractive index-based hydrogen sensors.

Propagation of Ince-Gaussian beams in uniaxial crystals orthogonal to the optical axis

NASA Astrophysics Data System (ADS)

Xu, Y. Q.; Zhou, G. Q.

2012-03-01

An analytical propagation expression of an Ince-Gaussian beam in uniaxial crystals orthogonal to the optical axis is derived. The uniaxial crystal considered here has the property of the extraordinary refractive index being larger than the ordinary refractive index. The Ince-Gaussian beam in the transversal direction along the optical axis spreads more rapidly than that in the other transversal direction. With increasing the ratio of the extraordinary refractive index to the ordinary refractive index, the spreading of the Ince-Gaussian beam in the transversal direction along the optical axis increases and the spreading of the Ince-Gaussian beam in the other transversal direction decreases. The effective beam size in the transversal direction along the optical axis is always larger than that in the other transversal direction. When the even and odd modes of Ince-Gaussian beams exist simultaneously, the effective beam size in the direction along the optical axis of the odd Ince-Gaussian beam is smaller than that of the even Ince-Gaussian beam in the corresponding direction, and the effective beam size in the transversal direction orthogonal to the optical axis of the odd Ince-Gaussian beam is larger than that of the even Ince-Gaussian beam in the corresponding direction.

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.

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.

Fundamentals of negative refractive index optical trapping: forces and radiation pressures exerted by focused Gaussian beams using the generalized Lorenz-Mie theory

PubMed Central

Ambrosio, Leonardo A.; Hernández-Figueroa, Hugo E.

2010-01-01

Based on the generalized Lorenz-Mie theory (GLMT), this paper reveals, for the first time in the literature, the principal characteristics of the optical forces and radiation pressure cross-sections exerted on homogeneous, linear, isotropic and spherical hypothetical negative refractive index (NRI) particles under the influence of focused Gaussian beams in the Mie regime. Starting with ray optics considerations, the analysis is then extended through calculating the Mie coefficients and the beam-shape coefficients for incident focused Gaussian beams. Results reveal new and interesting trapping properties which are not observed for commonly positive refractive index particles and, in this way, new potential applications in biomedical optics can be devised. PMID:21258549

Fundamentals of negative refractive index optical trapping: forces and radiation pressures exerted by focused Gaussian beams using the generalized Lorenz-Mie theory.

PubMed

Ambrosio, Leonardo A; Hernández-Figueroa, Hugo E

2010-11-04

Based on the generalized Lorenz-Mie theory (GLMT), this paper reveals, for the first time in the literature, the principal characteristics of the optical forces and radiation pressure cross-sections exerted on homogeneous, linear, isotropic and spherical hypothetical negative refractive index (NRI) particles under the influence of focused Gaussian beams in the Mie regime. Starting with ray optics considerations, the analysis is then extended through calculating the Mie coefficients and the beam-shape coefficients for incident focused Gaussian beams. Results reveal new and interesting trapping properties which are not observed for commonly positive refractive index particles and, in this way, new potential applications in biomedical optics can be devised.

Ultrasensitive Mach-Zehnder Interferometric Temperature Sensor Based on Liquid-Filled D-Shaped Fiber Cavity.

PubMed

Zhang, Hui; Gao, Shecheng; Luo, Yunhan; Chen, Zhenshi; Xiong, Songsong; Wan, Lei; Huang, Xincheng; Huang, Bingsen; Feng, Yuanhua; He, Miao; Liu, Weiping; Chen, Zhe; Li, Zhaohui

2018-04-17

A liquid-filled D-shaped fiber (DF) cavity serving as an in-fiber Mach–Zehnder interferometer (MZI) has been proposed and experimentally demonstrated for temperature sensing with ultrahigh sensitivity. The miniature MZI is constructed by splicing a segment of DF between two single-mode fibers (SMFs) to form a microcavity (MC) for filling and replacement of various refractive index (RI) liquids. By adjusting the effective RI difference between the DF and MC (the two interference arms), experimental and calculated results indicate that the interference spectra show different degrees of temperature dependence. As the effective RI of the liquid-filled MC approaches that of the DF, temperature sensitivity up to −84.72 nm/°C with a linear correlation coefficient of 0.9953 has been experimentally achieved for a device with the MC length of 456 μm, filled with liquid RI of 1.482. Apart from ultrahigh sensitivity, the proposed MCMZI device possesses additional advantages of its miniature size and simple configuration; these features make it promising and competitive in various temperature sensing applications, such as consumer electronics, biological treatments, and medical diagnosis.

Müller glia-derived PRSS56 is required to sustain ocular axial growth and prevent refractive error.

PubMed

Paylakhi, Seyyedhassan; Labelle-Dumais, Cassandre; Tolman, Nicholas G; Sellarole, Michael A; Seymens, Yusef; Saunders, Joseph; Lakosha, Hesham; deVries, Wilhelmine N; Orr, Andrew C; Topilko, Piotr; John, Simon Wm; Nair, K Saidas

2018-03-01

A mismatch between optical power and ocular axial length results in refractive errors. Uncorrected refractive errors constitute the most common cause of vision loss and second leading cause of blindness worldwide. Although the retina is known to play a critical role in regulating ocular growth and refractive development, the precise factors and mechanisms involved are poorly defined. We have previously identified a role for the secreted serine protease PRSS56 in ocular size determination and PRSS56 variants have been implicated in the etiology of both hyperopia and myopia, highlighting its importance in refractive development. Here, we use a combination of genetic mouse models to demonstrate that Prss56 mutations leading to reduced ocular size and hyperopia act via a loss of function mechanism. Using a conditional gene targeting strategy, we show that PRSS56 derived from Müller glia contributes to ocular growth, implicating a new retinal cell type in ocular size determination. Importantly, we demonstrate that persistent activity of PRSS56 is required during distinct developmental stages spanning the pre- and post-eye opening periods to ensure optimal ocular growth. Thus, our mouse data provide evidence for the existence of a molecule contributing to both the prenatal and postnatal stages of human ocular growth. Finally, we demonstrate that genetic inactivation of Prss56 rescues axial elongation in a mouse model of myopia caused by a null mutation in Egr1. Overall, our findings identify PRSS56 as a potential therapeutic target for modulating ocular growth aimed at preventing or slowing down myopia, which is reaching epidemic proportions.

Müller glia-derived PRSS56 is required to sustain ocular axial growth and prevent refractive error

PubMed Central

Tolman, Nicholas G; Sellarole, Michael A.; Saunders, Joseph; Lakosha, Hesham; Topilko, Piotr; John, Simon WM.

2018-01-01

A mismatch between optical power and ocular axial length results in refractive errors. Uncorrected refractive errors constitute the most common cause of vision loss and second leading cause of blindness worldwide. Although the retina is known to play a critical role in regulating ocular growth and refractive development, the precise factors and mechanisms involved are poorly defined. We have previously identified a role for the secreted serine protease PRSS56 in ocular size determination and PRSS56 variants have been implicated in the etiology of both hyperopia and myopia, highlighting its importance in refractive development. Here, we use a combination of genetic mouse models to demonstrate that Prss56 mutations leading to reduced ocular size and hyperopia act via a loss of function mechanism. Using a conditional gene targeting strategy, we show that PRSS56 derived from Müller glia contributes to ocular growth, implicating a new retinal cell type in ocular size determination. Importantly, we demonstrate that persistent activity of PRSS56 is required during distinct developmental stages spanning the pre- and post-eye opening periods to ensure optimal ocular growth. Thus, our mouse data provide evidence for the existence of a molecule contributing to both the prenatal and postnatal stages of human ocular growth. Finally, we demonstrate that genetic inactivation of Prss56 rescues axial elongation in a mouse model of myopia caused by a null mutation in Egr1. Overall, our findings identify PRSS56 as a potential therapeutic target for modulating ocular growth aimed at preventing or slowing down myopia, which is reaching epidemic proportions. PMID:29529029

Rashba and Dresselhaus spin-orbit couplings effects on electromagnetically induced transparency of a lens-shaped quantum dot: External electric and magnetic fields

NASA Astrophysics Data System (ADS)

Zamani, A.; Setareh, F.; Azargoshasb, T.; Niknam, E.; Mohammadhosseini, E.

2017-06-01

In this article the spin of electron as well as simultaneous effects of Rashba and Dresselhaus spin-orbit interactions are considered for a lens-shaped GaAs quantum dot and the influences of applied electric field and Zeeman effect on the electromagnetically induced transparency (EIT) of this system are investigated. To do so, the absorption, refractive index as well as the group velocity of the probe light pulse are presented and discussed. Study of the absorption and refractive index reveals that, at a particular frequency of probe field, absorption diminishes, refractive index becomes unity and so the EIT occurs. Furthermore, the investigation of group velocity show that, around such frequency the probe propagation is sub-luminal, which shifts to super-luminal for higher and lower frequencies. Our results illustrate that the EIT frequency, transparency window and sub(super)-luminal frequency intervals are strongly sensitive to applied fields in the presence of spin-orbit couplings. It is found that, in comparison with the investigations with negligence of spin, the EIT behavior under the effects of applied fields are quite different.

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.

[The relations of corneal, lenticular and total astigmatism].

PubMed

Liang, D; Guan, Z; Lin, J

1995-06-01

To determine the relations of corneal, lenticular and total astigmatism and the changes of the astigmatism with age. Out-patients with refractive errors were refracted with retinoscope after using cycloplegic drops and measured the radii of anterior corneal curvature. One hundred and ninety-four cases (382 eyes) with refractive errors were studied. Of the eyes 67.9% had regular corneal astigmatism, 68.1% irregular lenticular astigmatism and 60.7% regular total astigmatism, 88.5% of the corneal astigmatism has the same quality as the total astigmatism. The total astigmatism in 46% of the eyes included the summation of corneal and lenticular astigmatism, but in 41.3% of the eyes irregular lenticular astigmatism corrected the regular corneal astigmatism. The astigmatism of cornea, lens and total astigmatism changed from regular to irregular with the increase of age. The linear correlation analysis showed a positive correlation between the power of horizontal corneal refraction and age, and a negative corrlation between the power of vertical corneal refraction and age. The shape of cornea was the major cause of total astigmatism. The influence of lens on the total astigmatism was different. The reasons for the change of the total astigmatism from regular to irregular with the increase of age were the changes of the power of corneal refraction, particularly the increase of the power of horizontal corneal refraction and lenticular irregular astigmatism.

The Bubble Box: Towards an Automated Visual Sensor for 3D Analysis and Characterization of Marine Gas Release Sites.

PubMed

Jordt, Anne; Zelenka, Claudius; von Deimling, Jens Schneider; Koch, Reinhard; Köser, Kevin

2015-12-05

Several acoustic and optical techniques have been used for characterizing natural and anthropogenic gas leaks (carbon dioxide, methane) from the ocean floor. Here, single-camera based methods for bubble stream observation have become an important tool, as they help estimating flux and bubble sizes under certain assumptions. However, they record only a projection of a bubble into the camera and therefore cannot capture the full 3D shape, which is particularly important for larger, non-spherical bubbles. The unknown distance of the bubble to the camera (making it appear larger or smaller than expected) as well as refraction at the camera interface introduce extra uncertainties. In this article, we introduce our wide baseline stereo-camera deep-sea sensor bubble box that overcomes these limitations, as it observes bubbles from two orthogonal directions using calibrated cameras. Besides the setup and the hardware of the system, we discuss appropriate calibration and the different automated processing steps deblurring, detection, tracking, and 3D fitting that are crucial to arrive at a 3D ellipsoidal shape and rise speed of each bubble. The obtained values for single bubbles can be aggregated into statistical bubble size distributions or fluxes for extrapolation based on diffusion and dissolution models and large scale acoustic surveys. We demonstrate and evaluate the wide baseline stereo measurement model using a controlled test setup with ground truth information.

The Bubble Box: Towards an Automated Visual Sensor for 3D Analysis and Characterization of Marine Gas Release Sites

PubMed Central

Jordt, Anne; Zelenka, Claudius; Schneider von Deimling, Jens; Koch, Reinhard; Köser, Kevin

2015-01-01

Several acoustic and optical techniques have been used for characterizing natural and anthropogenic gas leaks (carbon dioxide, methane) from the ocean floor. Here, single-camera based methods for bubble stream observation have become an important tool, as they help estimating flux and bubble sizes under certain assumptions. However, they record only a projection of a bubble into the camera and therefore cannot capture the full 3D shape, which is particularly important for larger, non-spherical bubbles. The unknown distance of the bubble to the camera (making it appear larger or smaller than expected) as well as refraction at the camera interface introduce extra uncertainties. In this article, we introduce our wide baseline stereo-camera deep-sea sensor bubble box that overcomes these limitations, as it observes bubbles from two orthogonal directions using calibrated cameras. Besides the setup and the hardware of the system, we discuss appropriate calibration and the different automated processing steps deblurring, detection, tracking, and 3D fitting that are crucial to arrive at a 3D ellipsoidal shape and rise speed of each bubble. The obtained values for single bubbles can be aggregated into statistical bubble size distributions or fluxes for extrapolation based on diffusion and dissolution models and large scale acoustic surveys. We demonstrate and evaluate the wide baseline stereo measurement model using a controlled test setup with ground truth information. PMID:26690168

Organic component vapor pressures and hygroscopicities of aqueous aerosol measured by optical tweezers.

PubMed

Cai, Chen; Stewart, David J; Reid, Jonathan P; Zhang, Yun-hong; Ohm, Peter; Dutcher, Cari S; Clegg, Simon L

2015-01-29

Measurements of the hygroscopic response of aerosol and the particle-to-gas partitioning of semivolatile organic compounds are crucial for providing more accurate descriptions of the compositional and size distributions of atmospheric aerosol. Concurrent measurements of particle size and composition (inferred from refractive index) are reported here using optical tweezers to isolate and probe individual aerosol droplets over extended timeframes. The measurements are shown to allow accurate retrievals of component vapor pressures and hygroscopic response through examining correlated variations in size and composition for binary droplets containing water and a single organic component. Measurements are reported for a homologous series of dicarboxylic acids, maleic acid, citric acid, glycerol, or 1,2,6-hexanetriol. An assessment of the inherent uncertainties in such measurements when measuring only particle size is provided to confirm the value of such a correlational approach. We also show that the method of molar refraction provides an accurate characterization of the compositional dependence of the refractive index of the solutions. In this method, the density of the pure liquid solute is the largest uncertainty and must be either known or inferred from subsaturated measurements with an error of <±2.5% to discriminate between different thermodynamic treatments.

Effects of Hyperfine Particles on Reflectance Spectra from 0.3 to 25 μm

NASA Astrophysics Data System (ADS)

Mustard, John F.; Hays, John E.

1997-01-01

Fine grained particles <50 μm in size dominate particle size distributions of many planetary surfaces. Despite the predominance of fine particles in planetary regoliths, there have been few investigations of the systematic effects of the finest particles on reflectance spectra, and on the ability of quantitative models to extract compositional and/or textural information from remote observations. The effects of fine particles that are approximately the same size as the wavelength of light on reflectance spectra were investigated using narrow particle size separates of the minerals olivine and quartz across the wavelength range 0.3 to 25 μm. The minerals were ground with a mortar and pestle and sieved into five particle size separates of 5-μm intervals from <5 μm to 20-25 μm. The exact particle size distributions were determined with a particle size analyzer and are shown to be Gaussian about a mean within the range of each sieve separate. The reflectance spectra, obtained using a combination of a bidirectional reflectance spectrometer and an FTIR, exhibited a number of systematic changes as the particle size decreased to become approximately the same size and smaller than the wavelength. In the region of volume scattering, the spectra exhibited a sharp drop in reflectance with the finest particle size separates. Christiansen features became saturated when the imaginary part of the index of refraction was non-negligible, while the restrahlen bands showed continuous decrease in spectral contrast and some change in the shape of the bands with decreasing particle size, though the principal features diagnostic of composition were relatively unaffected. The transparency features showed several important changes with decreasing particle size: the spectral contrast increased then decreased, the position of the maximum reflectance of the transparency features shifted systematically to shorter wavelengths, and the symmetry of the features changed. Mie theory predicts that the extinction and scattering efficiencies should decline rapidly when particle size and wavelength are approximately equal. Using these relationships, a critical diameter where this change is predicted to occur was calculated as a function of wavelength and shown to be effective for explaining qualitatively the observed changes. Each of the mineral particle size series were then modeled quantitatively using Mie calculations to determine single-scattering albedo and a Hapke model to calculate reflectance. The models include the complex indices of refraction for olivine and quartz and the exact particle size distributions. The olivine particle size series was well modeled by these calculations, and correctly reproduced the systematic changes in the volume scattering region, the Christiansen feature, restrahlen bands, and transparency features. The quartz particle size series were less well modeled, with the greatest discrepancies in the restrahlen bands and the overall spectral contrast.

A Bio-Inspired Polymeric Gradient Refractive Index (GRIN) Human Eye Lens

DTIC Science & Technology

2012-11-19

confirmation of the desired aspheric surface shape. Furthermore, the wavefronts of aspheric posterior GRIN and PMMA lenses were measured and...compared a homogenous PMMA lens of an identical geometry. Finally, the anterior and posterior GRIN lenses were assembled into a bio-inspired GRIN...topography and exhibited confirmation of the desired aspheric surface shape. Furthermore, the wavefronts of aspheric posterior GRIN and PMMA lenses were

Plasmon assisted enhanced nonlinear refraction of monodispersed silver nanoparticles and their tunability.

PubMed

Lama, Pemba; Suslov, Anatoliy; Walser, Ardie D; Dorsinville, Roger

2014-06-02

Nonlinear optical characterizations were performed on monodispersed silver (Ag) nanoparticles (NPs) of various sizes using a picosecond Z-scan technique with excitation wavelengths of 532 nm and 1064 nm. The Ag NPs were fabricated using a heterogeneous condensation technique in a gas medium. The nonlinear refraction values were higher for the monodispersed Ag NPs whose surface plasmon resonance (SPR) peak is closer to the excitation wavelength. The higher nonlinear optical response is explained in terms of an electric field enhancement near the SPR. Moreover, the fabrication method allows the tailoring of the nonlinear refraction index of the Ag NPs by tuning the SPR peak of the sample. A comparison of the nonlinear refraction index of the monodispersed and polydispersed Ag NPs showed that the nonlinear refractive index of the monodispersed Ag NPs is higher.

Miniature interferometer for refractive index measurement in microfluidic chip

NASA Astrophysics Data System (ADS)

Chen, Minghui; Geiser, Martial; Truffer, Frederic; Song, Chengli

2012-12-01

The design and development of the miniaturized interferometer for measurement of the refractive index or concentration of sub-microliter volume aqueous solution in microfludic chip is presented. It is manifested by a successful measurement of the refractive index of sugar-water solution, by utilizing a laser diode for light source and the small robust instrumentation for practical implementation. Theoretically, the measurement principle and the feasibility of the system are analyzed. Experimental device is constructed with a diode laser, lens, two optical plate and a complementary metal oxide semiconductor (CMOS). Through measuring the positional changes of the interference fringes, the refractive index change are retrieved. A refractive index change of 10-4 is inferred from the measured image data. The entire system is approximately the size of half and a deck of cards and can operate on battery power for long time.

Remote sensing of environmental particulate pollutants - Optical methods for determinations of size distribution and complex refractive index

NASA Technical Reports Server (NTRS)

Fymat, A. L.

1978-01-01

A unifying approach, based on a generalization of Pearson's differential equation of statistical theory, is proposed for both the representation of particulate size distribution and the interpretation of radiometric measurements in terms of this parameter. A single-parameter gamma-type distribution is introduced, and it is shown that inversion can only provide the dimensionless parameter, r/ab (where r = particle radius, a = effective radius, b = effective variance), at least when the distribution vanishes at both ends. The basic inversion problem in reconstructing the particle size distribution is analyzed, and the existing methods are reviewed (with emphasis on their capabilities) and classified. A two-step strategy is proposed for simultaneously determining the complex refractive index and reconstructing the size distribution of atmospheric particulates.

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.

Bilateral reading performance of 4 multifocal intraocular lens models and a monofocal intraocular lens under bright lighting conditions.

PubMed

Rasp, Max; Bachernegg, Alexander; Seyeddain, Orang; Ruckhofer, Josef; Emesz, Martin; Stoiber, Josef; Grabner, Günther; Dexl, Alois K

2012-11-01

To compare changes in reading performance parameters after implantation of 4 multifocal intraocular lens (IOL) models and a monofocal IOL. Department of Ophthalmology, Paracelsus Medical University, Salzburg, Austria. Prospective randomized controlled clinical trial. Patients with bilateral cataract without additional ocular pathology were scheduled for bilateral implantation of Acri.Smart 48S monofocal, Acrysof Restor SN6AD3 apodized multifocal, AT LISA 366D diffractive multifocal, Tecnis ZMA00 diffractive multifocal, or Rezoom refractive multifocal IOLs. Bilateral corrected and uncorrected reading acuity, reading distance, mean and maximum reading speeds, and smallest log-scaled print size of a Radner reading chart were evaluated under bright lighting conditions (500 lux) using the Salzburg Reading Desk. Pupil size was not measured throughout the trial. The minimum follow-up was 12 months. The diffractive multifocal groups had significantly better uncorrected reading acuity and uncorrected smallest print size than the monofocal and refractive multifocal groups 1, 6, and 12 months postoperatively. The diffractive IOL groups had comparable uncorrected reading distance of approximately 32 cm, which was larger in the monofocal group (38.9 ± 8.4 cm) and refractive multifocal group (37.1 ± 7.3 cm) at the last visit. Patients with diffractive IOLs could read print sizes of approximately 0.74 to 0.87 mm, which was much better than in the monofocal and refractive multifocal groups. The diffractive AT LISA IOL provided the best reading speed values (mean and maximum, corrected and uncorrected). Multifocal IOLs with a diffractive component provided good reading performance that was significantly better than that obtained with a refractive multifocal or monofocal IOL. Drs. Grabner and Dexl were patent owners of the Salzburg Reading Desk technology (now owned by SRD-Vision, LLC). No other author has a financial or proprietary interest in any material or method mentioned. Copyright © 2012 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Frequency of under-corrected refractive errors in elderly Chinese in Beijing.

PubMed

Xu, Liang; Li, Jianjun; Cui, Tongtong; Tong, Zhongbiao; Fan, Guizhi; Yang, Hua; Sun, Baochen; Zheng, Yuanyuan; Jonas, Jost B

2006-07-01

The aim of the study was to evaluate the prevalence of under-corrected refractive error among elderly Chinese in the Beijing area. The population-based, cross-sectional, cohort study comprised 4,439 subjects out of 5,324 subjects asked to participate (response rate 83.4%) with an age of 40+ years. It was divided into a rural part [1,973 (44.4%) subjects] and an urban part [2,466 (55.6%) subjects]. Habitual and best-corrected visual acuity was measured. Under-corrected refractive error was defined as an improvement in visual acuity of the better eye of at least two lines with best possible refractive correction. The rate of under-corrected refractive error was 19.4% (95% confidence interval, 18.2, 20.6). In a multiple regression analysis, prevalence and size of under-corrected refractive error in the better eye was significantly associated with lower level of education (P<0.001), female gender (P<0.001), and age (P=0.001). Under-correction of refractive error is relatively common among elderly Chinese in the Beijing area when compared with data from other populations.

Thermally tunable broadband terahertz metamaterials with negative refractive index

NASA Astrophysics Data System (ADS)

Li, Weili; Meng, Qinglong; Huang, Renshuai; Zhong, Zheqiang; Zhang, Bin

2018-04-01

A thermally tunable broadband metamaterials with negative refractive index (NRI) is investigated in terahertz (THz) region theoretically. The metamaterials is designed by fabricating two stand-up opposite L shape metallic structures on fused quartz substrate, and the indium antimonide (InSb) is filled in the bottom gap of the two L shape structures. The tunability is attributed to the InSb because the InSb can changes the capacitance of the gap area by adjusting the temperature. The transmission characteristics and the retrieved electromagnetic parameters of the metamaterials are analyzed. Results indicate that the resonant frequency and amplitude modulation of the metamaterials can be tuned continuously in broadband range (about 0.62 THz), and the phase modulation from - 2 to 3 rad is also achieved within broadband range (about 0.8 THz). In addition, the metamaterials shows dual-band NRI behaviors at 0 . 4- 0 . 9 THz and 1 . 06- 1 . 15 THz when the temperature increases to 400 K. The wedge-shaped prism simulations are implemented to verify the NRI characteristics and indicate that the NRI of the metamaterials can be achieved.

Features of optical surfaces of multifocal diffractive-refractive eye lenses

NASA Astrophysics Data System (ADS)

Lenkova, G. A.

2017-09-01

This paper considers shape features of the surface structures of multifocal intraocular lenses (IOLs), which, unlike bifocal IOLs, generate additional foci or extends the depth of focus, which not only corrects near and far vision but also provides good vision at intermediate distances. Expansion of the field of clear vision is achieved due to the effects of diffraction, interference, and refraction (change in the radius of curvature of the lens surface). The optical characteristics of the most famous multifocal IOLs (trifocal and quadrafocal lenses and lenses with extended focal area) are given.

Reading ability with pseudophakic monovision and with refractive multifocal intraocular lenses: comparative study.

PubMed

Ito, Misae; Shimizu, Kimiya

2009-09-01

To the compare the reading ability after bilateral cataract surgery in patients who had pseudophakic monovision achieved by monofocal intraocular lens (IOL) implantation and patients who had refractive multifocal IOL implantation. Department of Ophthalmology, Kitasato University Hospital, Kanagawa, Japan. This study evaluated patients who had bilateral cataract surgery using the monovision method with monofocal IOL implantation to correct presbyopia (monovision group) or who had bilateral cataract surgery with refractive multifocal IOL implantation (multifocal group). In the monovision group, the dominant eye was corrected for distance vision and the nondominant eye for near vision. The maximum reading speed, critical character size, and reading acuity were measured binocularly without refractive correction using MNREAD-J acuity charts. The monovision group comprised 38 patients and the multifocal group, 22 patients. The mean maximum reading speed was 350.5 characters per minute (cpm) +/- 62.3 (SD) in the monovision group and 355.0 +/- 53.3 cpm in the multifocal group; the difference was not statistically significant. The mean critical character size was 0.24 +/- 0.12 logMAR and 0.40 +/- 0.16 logMAR, respectively (P<.05). The mean reading acuity was 0.05 +/- 0.12 logMAR and 0.19 +/- 0.11 logMAR, respectively (P<.01). The monovision group had better critical character size and reading acuity results. The monovision method group had better reading ability; however, careful patient selection is essential.

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.

Physical properties of ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various anions and the bis(trifluoromethylsulfonyl)imide anion with various cations.

PubMed

Jin, Hui; O'Hare, Bernie; Dong, Jing; Arzhantsev, Sergei; Baker, Gary A; Wishart, James F; Benesi, Alan J; Maroncelli, Mark

2008-01-10

Physical properties of 4 room-temperature ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various perfluorinated anions and the bis(trifluoromethylsulfonyl)imide (Tf2N-) anion with 12 pyrrolidinium-, ammonium-, and hydroxyl-containing cations are reported. Electronic structure methods are used to calculate properties related to the size, shape, and dipole moment of individual ions. Experimental measurements of phase-transition temperatures, densities, refractive indices, surface tensions, solvatochromic polarities based on absorption of Nile Red, 19F chemical shifts of the Tf2N- anion, temperature-dependent viscosities, conductivities, and cation diffusion coefficients are reported. Correlations among the measured quantities as well as the use of surface tension and molar volume for estimating Hildebrand solubility parameters of ionic liquids are also discussed.

Self-compensation of thermal lens in high-power diode pumped solid-state lasers

NASA Astrophysics Data System (ADS)

Wang, Xiao-Jun

2010-02-01

We present a comprehensive model to describe the optic-thermal coupling in the diode pumped solid-state lasers (DPSSL). The thermal transition of particles at the upper laser level leads the heat-generation of laser crystals to depend on shape of the laser beam, while the laser field is also influenced by the temperature because of the thermal excitation of doped particles among various Stark levels. These effects, together with the usual thermal-optic effect that induces a fluctuation of the refraction index by an inhomogeneous temperature distribution, cause a complicated coupling between the laser field and the temperature field. We show that the optic-thermal coupling plays an important role in high-power DPSSL with larger size beam. That effect may yield a self-compensation for the thermal lens and improve the beam quality.

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;

Dispersion and shape engineered plasmonic nanosensors

NASA Astrophysics Data System (ADS)

Jeong, Hyeon-Ho; Mark, Andrew G.; Alarcón-Correa, Mariana; Kim, Insook; Oswald, Peter; Lee, Tung-Chun; Fischer, Peer

2016-04-01

Biosensors based on the localized surface plasmon resonance (LSPR) of individual metallic nanoparticles promise to deliver modular, low-cost sensing with high-detection thresholds. However, they continue to suffer from relatively low sensitivity and figures of merit (FOMs). Herein we introduce the idea of sensitivity enhancement of LSPR sensors through engineering of the material dispersion function. Employing dispersion and shape engineering of chiral nanoparticles leads to remarkable refractive index sensitivities (1,091 nm RIU-1 at λ=921 nm) and FOMs (>2,800 RIU-1). A key feature is that the polarization-dependent extinction of the nanoparticles is now characterized by rich spectral features, including bipolar peaks and nulls, suitable for tracking refractive index changes. This sensing modality offers strong optical contrast even in the presence of highly absorbing media, an important consideration for use in complex biological media with limited transmission. The technique is sensitive to surface-specific binding events which we demonstrate through biotin-avidin surface coupling.

Refractive index and strain sensor based on twin-core fiber with a novel T-shaped taper

NASA Astrophysics Data System (ADS)

Zhang, Chuanbiao; Ning, Tigang; Li, Jing; Zheng, JingJing; Gao, Xuekai; Pei, Li

2018-06-01

A compact in-fiber Mach-Zehnder interferometer (MZI) based on twin-core fiber (TCF) with a novel T-shaped taper is proposed and demonstrated. The taper was firstly fabricated by a short section of TCF, and then spliced with a section of cleaved single mode fiber (SMF). When the light transmit into the TCF, multiple modes will be excited and will propagate within the TCF. In experiment, the proposed device had a maximum interferometric extinction ratio about 17 dB. And the refractive index (RI), strain, and temperature response properties of the sensor have been investigated, which show a relatively high RI, strain sensitivity and low temperature cross sensitivity. Hence, the sensor can be a suitable candidate in the biochemical and physical sensing applications. And due to its easy and controllable fabrication, the novel drawing technology can be applied to more multicore optical fibers.

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.

Study of structural and optical properties of ZnS zigzag nanostructured thin films

NASA Astrophysics Data System (ADS)

Rahchamani, Seyyed Zabihollah; Rezagholipour Dizaji, Hamid; Ehsani, Mohammad Hossein

2015-11-01

Zinc sulfide (ZnS) nanostructured thin films of different thicknesses with zigzag shapes have been deposited on glass substrates by glancing angle deposition (GLAD) technique. Employing a homemade accessory attached to the substrate holder enabled the authors to control the substrate temperature and substrate angle. The prepared samples were subjected to X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV-VIS. spectroscopy techniques. The structural studies revealed that the film deposited at room temperature crystallized in cubic structure. The FESEM images of the samples confirmed the formation of zigzag nano-columnar shape with mean diameter about 60-80 nm. By using the data obtained from optical studies, the real part of the refractive index (n), the absorption coefficient (α) and the band gap (Eg) of the samples were calculated. The results show that the refractive indices of the prepared films are very sensitive to deposition conditions.

A Sensitivity Study on the Effects of Particle Chemistry, Asphericity and Size on the Mass Extinction Efficiency of Mineral Dust in the Earth's Atmosphere: From the Near to Thermal IR

NASA Technical Reports Server (NTRS)

Hansell, R. A., Jr.; Reid, J. S.; Tsay, S. C.; Roush, T. L.; Kalashnikova, O. V.

2011-01-01

To determine a plausible range of mass extinction efficiencies (MEE) of terrestrial atmospheric dust from the near to thermal IR, sensitivity analyses are performed over an extended range of dust microphysical and chemistry perturbations. The IR values are subsequently compared to those in the near-IR, to evaluate spectral relationships in their optical properties. Synthesized size distributions consistent with measurements, model particle size, while composition is defined by the refractive indices of minerals routinely observed in dust, including the widely used OPAC/Hess parameterization. Single-scattering properties of representative dust particle shapes are calculated using the T-matrix, Discrete Dipole Approximation and Lorenz-Mie light-scattering codes. For the parameterizations examined, MEE ranges from nearly zero to 1.2 square meters per gram, with the higher values associated with non-spheres composed of quartz and gypsum. At near-IR wavelengths, MEE for non-spheres generally exceeds those for spheres, while in the thermal IR, shape-induced changes in MEE strongly depend on volume median diameter (VMD) and wavelength, particularly for MEE evaluated at the mineral resonant frequencies. MEE spectral distributions appear to follow particle geometry and are evidence for shape dependency in the optical properties. It is also shown that non-spheres best reproduce the positions of prominent absorption peaks found in silicates. Generally, angular particles exhibit wider and more symmetric MEE spectral distribution patterns from 8-10 micrometers than those with smooth surfaces, likely due to their edge-effects. Lastly, MEE ratios allow for inferring dust optical properties across the visible-IR spectrum. We conclude the MEE of dust aerosol are significant for the parameter space investigated, and are a key component for remote sensing applications and the study of direct aerosol radiative effects.

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.

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

Hemiretinal form deprivation: evidence for local control of eye growth and refractive development in infant monkeys.

PubMed

Smith, Earl L; Huang, Juan; Hung, Li-Fang; Blasdel, Terry L; Humbird, Tammy L; Bockhorst, Kurt H

2009-11-01

To determine whether refractive development in primates is mediated by local retinal mechanisms, the authors examined the effects of hemiretinal form deprivation on ocular growth and the pattern of peripheral refractions in rhesus monkeys. Beginning at approximately 3 weeks of age, nine infant monkeys were reared wearing monocular diffuser lenses that eliminated form vision in the nasal field (nasal field diffuser [NFD]). Control data were obtained from the nontreated fellow eyes, 24 normal monkeys, and 19 monkeys treated with full-field diffusers. Refractive development was assessed by retinoscopy performed along the pupillary axis and at eccentricities of 15 degrees, 30 degrees, and 45 degrees. Central axial dimensions and eye shape were assessed by A-scan ultrasonography and magnetic resonance imaging, respectively. Hemiretinal form deprivation altered refractive development in a regionally selective manner, typically producing myopia in the treated hemifields. In particular, six of the NFD monkeys exhibited substantial amounts (-1.81 to -9.00 D) of relative myopia in the nasal field that were most obvious at the 15 degrees and 30 degrees nasal field eccentricities. The other three NFD monkeys exhibited small amounts of relative hyperopia in the treated field. The alterations in peripheral refraction were associated with local, region-specific alterations in vitreous chamber depth in the treated hemiretina. The effects of form deprivation on refractive development and eye growth in primates are mediated by mechanisms, presumably retinal, that integrate visual signals in a spatially restricted manner and exert their influence locally.

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.

Refractive index measurements of single, spherical cells using digital holographic microscopy.

PubMed

Schürmann, Mirjam; Scholze, Jana; Müller, Paul; Chan, Chii J; Ekpenyong, Andrew E; Chalut, Kevin J; Guck, Jochen

2015-01-01

In this chapter, we introduce digital holographic microscopy (DHM) as a marker-free method to determine the refractive index of single, spherical cells in suspension. The refractive index is a conclusive measure in a biological context. Cell conditions, such as differentiation or infection, are known to yield significant changes in the refractive index. Furthermore, the refractive index of biological tissue determines the way it interacts with light. Besides the biological relevance of this interaction in the retina, a lot of methods used in biology, including microscopy, rely on light-tissue or light-cell interactions. Hence, determining the refractive index of cells using DHM is valuable in many biological applications. This chapter covers the main topics that are important for the implementation of DHM: setup, sample preparation, and analysis. First, the optical setup is described in detail including notes and suggestions for the implementation. Following that, a protocol for the sample and measurement preparation is explained. In the analysis section, an algorithm for the determination of quantitative phase maps is described. Subsequently, all intermediate steps for the calculation of the refractive index of suspended cells are presented, exploiting their spherical shape. In the last section, a discussion of possible extensions to the setup, further measurement configurations, and additional analysis methods are given. Throughout this chapter, we describe a simple, robust, and thus easily reproducible implementation of DHM. The different possibilities for extensions show the diverse fields of application for this technique. Copyright © 2015 Elsevier Inc. All rights reserved.

On the effective refractive index of blood

NASA Astrophysics Data System (ADS)

Nahmad-Rohen, Alexander; Contreras-Tello, Humberto; Morales-Luna, Gesuri; García-Valenzuela, Augusto

2016-01-01

We calculated the real and imaginary parts of the effective refractive index {n}{eff} of blood as functions of wavelength from 400 to 800 nm; we employed van de Hulst’s theory, together with the anomalous diffraction approximation, for the calculation. We modelled blood as a mixture of plasma and erythrocytes. Our results indicate that erythrocyte orientation has a strong effect on {n}{eff}, making blood an optically anisotropic medium except when the erythrocytes are randomly oriented. In the case in which their symmetry axis is perpendicular to the wave vector, {n}{eff} equals the refractive index of plasma at certain wavelengths. Furthermore, the erythrocytes’ shape affects their contribution to {n}{eff} in an important way, implying that studies on the effective refractive index of blood should avoid approximating them as spheres or spheroids. Finally, the effective refractive index of blood predicted by van de Hulst’s theory is different from what would be obtained by averaging the refractive indices of its constituents weighted by volume; such a volume-weighted average is appropriate only for haemolysed blood. We then measured the real part of the refractive index of various blood solutions using two different experimental setups. One of the most important results of our expriment is that {n}{eff} is measurable to a good degree of precision even for undiluted blood, although not all measuring apparatuses are appropriate. The experimental data is self-consistent and in reasonable agreement with our theoretical calculations.

Ring-shaped dysphotopsia associated with posterior chamber phakic implantable collamer lenses with a central hole.

PubMed

Eom, Youngsub; Kim, Dae Wook; Ryu, Dongok; Kim, Jun-Heon; Yang, Seul Ki; Song, Jong Suk; Kim, Sug-Whan; Kim, Hyo Myung

2017-05-01

To evaluate the incidence of central hole-induced ring-shaped dysphotopsia after posterior chamber phakic implantable collamer lens (ICL) with central hole (hole ICL) implantation and to investigate the causes of central hole-induced dysphotopsia. The clinical study enrolled 29 eyes of 15 consecutive myopic patients implanted with hole ICL. The incidence of ring-shaped dysphotopsia after hole ICL implantation was evaluated. In the experimental simulation study, non-sequential ray tracing was used to construct myopic human eye models with hole ICL and ICL without a central hole (conventional ICL). Simulated retinal images measured in log-scale irradiance were compared between the two ICLs for an extended Lambertian light-emitting disc object 20 cm in diameter placed 2 m from the corneal vertex. To investigate the causes of hole-induced dysphotopsia, a series of retinal images were simulated using point sources at infinity with well-defined field angles (0 to -20°) and multiple ICL models. Of 29 eyes, 15 experienced ring-shaped dysphotopsia after hole ICL implantation. The simulation study using an extended Lambertian source showed that hole ICL-evoked ring-shaped dysphotopsia was formed at a retinal field angle of ±40°. Component-level analysis using a well-defined off-axis point source from infinity revealed that ring-shaped dysphotopsia was generated by stray light refraction from the inner wall of the hole and the posterior ICL surface. Hole ICL-evoked ring-shaped dysphotopsia was related to light refraction at the central hole structure. Surgeons are advised to explain to patients the possibility of ring-shaped dysphotopsia after hole ICL implantation. © 2016 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

T-matrix Study of Scattering and Absorption of Light by Biomass Burning Aerosols

NASA Astrophysics Data System (ADS)

Poudel, Samin

The uncertainty in the measurements of aerosol optical properties has made it difficult to quantify the global impact of aerosols on Earth's climate and limits our ability to predict future climate changes. Morphology, size, volume, shape, fuel type, burning conditions, aging, and changes in chemical composition due to atmospheric processing of soot play a significant part in determining the optical properties of aerosols. The T-matrix method has been successfully used to reproduce experimental results of optical properties of spherical and non-spherical particles. In this work we applied the T-matrix method to extract the refractive index of biomass burning soot (burning pine tree) by reproducing experimentally determined single scattering albedo (SSA), scattering and extinction cross section values obtained by burning pine and collecting aerosols in two different ways: (1) from an outdoor burn drum to burn pine and collect soot in distilled water using an impinger and re-aerosolized the soot after several days to measure extinction and scattering cross sections using cavity ring down spectroscopy and nephelometry and (2) from a tube furnace in the lab to burn pine and the soot was introduced into an indoor smog chamber and soot particles sampled directly into the cavity ring down system and the nephelometer to measure extinction and scattering cross sections. Filter samples were also collected from both types of burning and electron microscopy images were used to obtain morphology and size information to conduct T-Matrix calculations. The experimentally measured optical properties from the impinger samples were reproduced using a refractive index of 1.345 + i0.096 for 300 and 400nm particles, while the results from the tube furnace samples were reproduced using 1.88 + i0.024 for 200 nm particles and 1.47 + i0.047 for 300 nm particles. This suggests that the impinger samples do not represent fresh soot since they are more absorbing and have lower SSA values compared to ours and other similar laboratory and field measurements for fresh soot. Morphology information from images of filter samples was used in the T-matrix calculation using refractive index of 1.88 + i0.024 to reproduce the SSA values for the fresh soot. It is shown that refractive indices used for fresh diesel soot or soot produced from propane 1.76 + i0.57 cannot be applied to biomass burning soot, as it provides a significantly lower SSA values in both cases.

A Near Zero Refractive Index Metamaterial for Electromagnetic Invisibility Cloaking Operation

PubMed Central

Islam, Sikder Sunbeam; Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

2015-01-01

The paper reveals the design of a unit cell of a metamaterial that shows more than 2 GHz wideband near zero refractive index (NZRI) property in the C-band region of microwave spectra. The two arms of the unit cell were splitted in such a way that forms a near-pi-shape structure on epoxy resin fiber (FR-4) substrate material. The reflection and transmission characteristics of the unit cell were achieved by utilizing finite integration technique based simulation software. Measured results were presented, which complied well with simulated results. The unit cell was then applied to build a single layer rectangular-shaped cloak that operates in the C-band region where a metal cylinder was perfectly hidden electromagnetically by reducing the scattering width below zero. Moreover, the unit cell shows NZRI property there. The experimental result for the cloak operation was presented in terms of S-parameters as well. In addition, the same metamaterial shell was also adopted for designing an eye-shaped and triangular-shaped cloak structure to cloak the same object, and cloaking operation is achieved in the C-band, as well with slightly better cloaking performance. The novel design, NZRI property, and single layer C-band cloaking operation has made the design a promising one in the electromagnetic paradigm. PMID:28793472

A Near Zero Refractive Index Metamaterial for Electromagnetic Invisibility Cloaking Operation.

PubMed

Islam, Sikder Sunbeam; Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

2015-07-29

The paper reveals the design of a unit cell of a metamaterial that shows more than 2 GHz wideband near zero refractive index (NZRI) property in the C-band region of microwave spectra. The two arms of the unit cell were splitted in such a way that forms a near-pi-shape structure on epoxy resin fiber (FR-4) substrate material. The reflection and transmission characteristics of the unit cell were achieved by utilizing finite integration technique based simulation software. Measured results were presented, which complied well with simulated results. The unit cell was then applied to build a single layer rectangular-shaped cloak that operates in the C-band region where a metal cylinder was perfectly hidden electromagnetically by reducing the scattering width below zero. Moreover, the unit cell shows NZRI property there. The experimental result for the cloak operation was presented in terms of S-parameters as well. In addition, the same metamaterial shell was also adopted for designing an eye-shaped and triangular-shaped cloak structure to cloak the same object, and cloaking operation is achieved in the C-band, as well with slightly better cloaking performance. The novel design, NZRI property, and single layer C-band cloaking operation has made the design a promising one in the electromagnetic paradigm.

Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial.

PubMed

Zhu, R; Liu, X N; Hu, G K; Sun, C T; Huang, G L

2014-11-24

Negative refraction of elastic waves has been studied and experimentally demonstrated in three- and two-dimensional phononic crystals, but Bragg scattering is impractical for low-frequency wave control because of the need to scale the structures to manageable sizes. Here we present an elastic metamaterial with chiral microstructure made of a single-phase solid material that aims to achieve subwavelength negative refraction of elastic waves. Both negative effective mass density and modulus are observed owing to simultaneous translational and rotational resonances. We experimentally demonstrate negative refraction of the longitudinal elastic wave at the deep-subwavelength scale in the metamaterial fabricated in a stainless steel plate. The experimental measurements are in good agreement with numerical simulations. Moreover, wave mode conversion related with negative refraction is revealed and discussed. The proposed elastic metamaterial may thus be used as a flat lens for elastic wave focusing.

Contrasting cellular damage after Blue-IRIS and Femto-LASIK in cat cornea.

PubMed

Wozniak, Kaitlin T; Elkins, Noah; Brooks, Daniel R; Savage, Daniel E; MacRae, Scott; Ellis, Jonathan D; Knox, Wayne H; Huxlin, Krystel R

2017-12-01

Blue-intra-tissue refractive index shaping (Blue-IRIS) is a new approach to laser refractive correction of optical aberrations in the eye, which alters the refractive index of the cornea rather than changing its shape. Before it can be implemented in humans, it is critical to establish whether and to what extent, Blue-IRIS damages the cornea. Here, we contrasted the impact of -1.5 D cylinder refractive corrections inscribed using either Blue-IRIS or femtosecond laser in-situ keratomileusis (femto-LASIK) on corneal cell viability. Blue-IRIS was used to write a -1.5 D cylinder gradient index (GRIN) lens over a 2.5 mm by 2.5 mm area into the mid-stromal region of the cornea in six freshly-enucleated feline eyes. The same correction (-1.5 D cylinder) was inscribed into another four cat eyes using femto-LASIK. Six hours later, all corneas were processed for histology and stained for terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) and p-γ-H2AX to label damaged cells. In Blue-IRIS-treated corneas, no tissue was removed and TUNEL-stained cells were confined to the laser focal zone in the stroma. In femto-LASIK, photoablation removed 14 μm of anterior stroma, but in addition, TUNEL-positive cells clustered across the femto-flap, the epithelium at the flap edges and the stroma below the ablation zone. Keratocytes positive for p-γ-H2AX were seen adjacent to all Blue-IRIS focal zones, but were completely absent from femto-LASIK-treated corneas. Unlike femto-LASIK, Blue-IRIS attains refractive correction in the cornea without tissue removal and only causes minimal, localized keratocyte death within the laser focal zones. In addition, Blue-IRIS induced DNA modifications associated with phosphorylation of γ-H2AX in keratocytes adjacent to the laser focal zones. We posit that this p-γ-H2AX response is related to alterations in chromatin structure caused by localized changes in osmolarity, a possible mechanism for the induced refractive index changes. Copyright © 2017 Elsevier Ltd. All rights reserved.

Simulation and experiment for depth sizing of cracks in anchor bolts by ultrasonic phased array technology

NASA Astrophysics Data System (ADS)

Lin, Shan

2018-04-01

There have been lots of reports about the occurrence of cracks in bolts in aging nuclear and thermal power plants. Sizing of such cracks is crucial for assessing the integrity of bolts. Currently, hammering and visual tests are used to detect cracks in bolts. However, they are not applicable for sizing cracks. Although the tip diffraction method is well known as a crack sizing technique, reflection echoes from threads make it difficult to apply this technique to bolts. This paper addresses a method for depth sizing of cracks in bolts by means of ultrasonic phased array technology. Numerical results of wave propagation in bolts by the finite element method (FEM) shows that a peak associated within the vicinity of a crack tip can be observed in the curve of echo intensity versus refraction angle for deep cracks. The refraction angle with respect to this peak decreases as crack depth increases. Such numerical results are verified by experiments on bolt specimens that have electrical discharge machining notches or fatigue cracks with different depths. In the experiment, a 10-MHz linear array probe is used. Depth of cracks in bolts using the refraction angle associated with the peak is determined and compared to actual depths. The comparison shows that accurately determining a crack depth from the inspection results is possible.

The effect of mydriasis from phenylephrine on corneal shape.

PubMed

Huang, Ronnie Y C; Lam, Andrew K C

2007-01-01

A previous study reported that pharmacologically-dilated pupils changed the corneal shape. Researchers used mydriatic agents with significant cycloplegic effect. The current study investigates the effect of mydriasis on corneal shape using phenylephrine alone, where phenylephrine has minimal effect on the accommodative system and whether corneal topography can be done after pupil dilation. Forty-four young healthy subjects with one eye randomly selected for mydriasis were used in this study. Twenty-two received one drop of 2.5% phenylephrine (group 1); the other 22 subjects had one drop of 0.4% benoxinate instilled prior to the application of 2.5% phenylephrine (group 2). They were matched for age and refractive error. Anterior chamber depth, pupil size and corneal parameters were compared before and after mydriasis. The corneal parameters included best-fit sphere (BFS), surface asymmetry index (SAI), surface regularity index (SRI) and the axial and tangential powers in the form of flattest and steepest powers, and in the form of M, J(0), and J(45) vector presentation. Group 1 and group 2 subjects had similar pre-mydriatic baseline ocular parameters. The mean (+/- SD) pupil dilation was 1.24 +/- 0.59 mm for group 1 and 1.80 +/- 0.95 mm for group 2. The dilation was significantly larger in group 2 (unpaired t-tests: t = 2.36, p = 0.02). There were no significant changes in corneal parameters from mydriasis in either group. Previous investigations used mydriatic agents, which affected not only the pupil size but also accommodation. The current study found that mydriasis from phenylephrine, with minimal effect on accommodation, did not result in significant corneal alteration, and corneal topography can be measured after pupil dilation with phenylephrine.

A compact and lightweight off-axis lightguide prism in near to eye display

NASA Astrophysics Data System (ADS)

Zhuang, Zhenfeng; Cheng, Qijia; Surman, Phil; Zheng, Yuanjin; Sun, Xiao Wei

2017-06-01

We propose a method to improve the design of an off-axis lightguide configuration for near to eye displays (NED) using freeform optics technology. The advantage of this modified optical system, which includes an organic light-emitting diode (OLED), a doublet lens, an imaging lightguide prism and a compensation prism, is that it increases optical length path, offers a smaller size, as well as avoids the obstructed views, and matches the user's head shape. In this system, the light emitted from the OLED passes through the doublet lens and is refracted/reflected by the imaging lightguide prism, which is used to magnify the image from the microdisplay, while the compensation prism is utilized to correct the light ray shift so that a low-distortion image can be observed in a real-world setting. A NED with a 4 mm diameter exit pupil, 21.5° diagonal full field of view (FoV), 23 mm eye relief, and a size of 33 mm by 9.3 mm by 16 mm is designed. The developed system is compact, lightweight and suitable for entertainment and education application.

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.

Multi-Wavelength Measurement of Soot Optical Properties: Influence of Non-Absorbing Coatings

NASA Astrophysics Data System (ADS)

Freedman, Andrew; Renbaum-Wollf, Lindsay; Forestieri, Sara; Lambe, Andrew; Cappa, Christopher; Davidovits, Paul; Onasch, Timothy

2015-04-01

Soot, a product of incomplete combustion, plays an important role in the earth's climate system through the absorption and scattering of solar radiation. Important in quantifying the direct radiative impacts of soot in climate models, and specifically of black carbon (BC), is the assumed BC refractive index and shape-dependent interaction of light with BC particles. The latter assumption carries significant uncertainty because BC particles are fractal-like, being agglomerates of smaller (20-40 nm) spherules, yet many optical models such as Mie theory in particular, typically assume a spherical particle morphology. It remains unclear under what conditions this is an acceptable assumption. To investigate the ability of various optical models to reproduce observed BC optical properties, we obtained measurements of light absorption, scattering and extinction coefficients and thus single scattering albedo (SSA) of size-resolved soot particles. Measurements were made on denuded soot particles produced using both methane and ethylene as fuels. In addition, these soot particles were coated with dioctyl sebacate or sulfuric acid and the enhancement in the apparent mass absorption coefficient determined. Extinction and absorption were measured using a dual cavity ringdown photoacoustic spectrometer (CRD-PAS) at 405 nm and 532 nm. Scattering and extinction were measured using a CAPS PMssa single scattering albedo monitor (Aerodyne) at 630 nm. Soot particle mass was quantified using a centrifugal particle mass analyzer (CPMA, Cambustion), mobility size with a scanning mobility particle sizer (SMPS, TSI) and soot concentration with a CPC (Brechtel). The results will be interpreted in light of both Mie theory which assumes spherical and uniform particles and Rayleigh-Debye-Gans (RDG) theory, which assumes that the absorption properties of soot are dictated by the individual spherules. For denuded soot, effective refractive indices will be determined.

On the sighted ancestry of blindness - exceptionally preserved eyes of Mesozoic polychelidan lobsters.

PubMed

Audo, Denis; Haug, Joachim T; Haug, Carolin; Charbonnier, Sylvain; Schweigert, Günter; Müller, Carsten H G; Harzsch, Steffen

2016-01-01

Modern representatives of Polychelida (Polychelidae) are considered to be entirely blind and have largely reduced eyes, possibly as an adaptation to deep-sea environments. Fossil species of Polychelida, however, appear to have well-developed compound eyes preserved as anterior bulges with distinct sculpturation. We documented the shapes and sizes of eyes and ommatidia based upon exceptionally preserved fossil polychelidans from Binton (Hettangian, United-Kingdom), Osteno (Sinemurian, Italy), Posidonia Shale (Toarcian, Germany), La Voulte-sur-Rhône (Callovian, France), and Solnhofen-type plattenkalks (Kimmeridgian-Tithonian, Germany). For purposes of comparison, sizes of the eyes of several other polychelidans without preserved ommatidia were documented. Sizes of ommatidia and eyes were statistically compared against carapace length, taxonomic group, and outcrop. Nine species possess eyes with square facets; Rosenfeldia oppeli (Woodward, 1866), however, displays hexagonal facets. The sizes of eyes and ommatidia are a function of carapace length. No significant differences were discerned between polychelidans from different outcrops; Eryonidae, however, have significantly smaller eyes than other groups. Fossil eyes bearing square facets are similar to the reflective superposition eyes found in many extant decapods. As such, they are the earliest example of superposition eyes. As reflective superposition is considered plesiomorphic for Reptantia, this optic type was probably retained in Polychelida. The two smallest specimens, a Palaeopentacheles roettenbacheri (Münster, 1839) and a Hellerocaris falloti (Van Straelen, 1923), are interpreted as juveniles. Both possess square-shaped facets, a typical post-larval feature. The eye morphology of these small specimens, which are far smaller than many extant eryoneicus larvae, suggests that Jurassic polychelidans did not develop via giant eryoneicus larvae. In contrast, another species we examined, Rosenfeldia oppeli (Woodward, 1866), did not possess square-shaped facets, but rather hexagonal ones, which suggests that this species did not possess reflective superposition eyes. The hexagonal facets may indicate either another type of superposition eye (refractive or parabolic superposition), or an apposition eye. As decapod larvae possess apposition eyes with hexagonal facets, it is most parsimonious to consider eyes of R. oppeli as apposition eyes evolved through paedomorphic heterochrony. Polychelidan probably originally had reflective superposition. R. oppeli, however, probably gained apposition eyes through paedomorphosis.

Underwater refraction-polarization patterns of skylight perceived by aquatic animals through Snell's window of the flat water surface.

PubMed

Horváth, G; Varjú, D

1995-06-01

The grass shrimp (Palaemonetes vulgaris) orients itself by means of the polarization pattern of the sky visible through Snell's window of the water surface. The celestial polarization pattern viewed from water is distorted and modified because of refraction and repolarization of skylight at the air-water interface. This work provides a quantitative account of the repolarization of skylight transmitted through a flat water surface. The degree and direction of linear polarization, the transmissivity and the shape of the refraction-polarization oval are calculated at the air-water interface as functions of the polarization characteristics and the incident angle of partially linearly polarized incoming light. Two-dimensional patterns of linear polarization ellipses and of the degree and direction of polarization of skylight are presented for different zenith distances of the sun. The corresponding underwater refraction-polarization patterns are computed. Transmissivity patterns of a flat water surface are calculated for unpolarized light of an overcast sky and for partially polarized light of clear skies as a function of the zenith distance of the sun. The role of these refraction-polarization patterns in orientation and polarization vision of the grass shrimp (P. vulgaris) and rainbow trout (Oncorhyncus mykiss) is reviewed. The effects of cloud cover, surface waves and water turbidity on the refraction-polarization patterns are briefly discussed.

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.

Effect of reflection and refraction on NEXAFS spectra measured in TEY mode

PubMed Central

2018-01-01

The evolution of near-edge X-ray absorption fine structure in the vicinity of the K-absorption edge of oxygen for HfO2 over a wide range of incidence angles is analyzed by simultaneous implementation of the total-electron-yield (TEY) method and X-ray reflection spectroscopy. It is established that the effect of refraction on the TEY spectrum is greater than that of reflection and extends into the angular region up to angles 2θc. Within angles that are less than the critical angle, both the reflection and refraction strongly distort the shape of the TEY spectrum. Limitations of the technique for the calculation of optical constants from the reflection spectra using the Kramers–Kronig relation in the limited energy region in the vicinity of thresholds are discussed in detail. PMID:29271772

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.

On the Immersion Liquid Evaporation Method Based on the Dynamic Sweep of Magnitude of the Refractive Index of a Binary Liquid Mixture: A Case Study on Determining Mineral Particle Light Dispersion.

PubMed

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

2017-07-01

This is a feasibility study of a modified immersion liquid technique for determining the refractive index of micro-sized particles. The practical challenge of the traditional liquid immersion method is to find or produce a suitable host liquid whose refractive index equals that of a solid particle. Usually, the immersion liquid method uses a set of immersion liquids with different refractive indices or continuously mixes two liquids with different refractive indices, e.g., using a pumping system. Here, the phenomenon of liquid evaporation has been utilized in defining the time-dependent refractive index variation of the host liquid. From the spectral transmittance data measured during the evaporation process, the refractive index of a solid particle in the host liquid can be determined as a function of the wavelength. The method was tested using calcium fluoride (CaF 2 ) particles with an immersion liquid mixed from diethyl ether and diffusion pump fluid. The dispersion data obtained were consistent with the literature values thus indicating the proper functioning of the proposed procedure.

Effects of lenses with different power profiles on eye shape in chickens.

PubMed

Tepelus, Tudor Cosmin; Vazquez, Daniel; Seidemann, Anne; Uttenweiler, Dietmar; Schaeffel, Frank

2012-02-01

Defocus imposed to the periphery of the visual field can affect the development of foveal/central refractive errors. To make use of this observation, lenses can be designed to reduce myopia progression, but it is important to know which power profiles of the lenses are most effective. We have studied this question in chickens. Sixty male white leghorn chickens were used. From day 7 after hatching, they were treated for 5 days either with full field -7D or +7D lenses, with -7D lenses with a 4mm central hole, with hemi-field lenses of the same power, or with two different types of radial refractive gradient (RRG) lenses with increasing positive power from the center to the periphery, which were designed by Rodenstock GmbH, Munich, Germany. A macro file was written for "ImageJ" to trace and average the outlines of several excised eyes after treatment. Shapes of fellow control eyes and lens-treated eyes were compared in the horizontal and vertical meridians. Refractions were determined at -45°, 0°, and 45° over the horizontal visual field, at the beginning and at the end of experiments, using automated infrared photoretinoscopy. (1) Eye length, as determined by the new automated eye shape tracing technique, was well correlated with A-scan ultrasound data. (2) The effects of previously tested lens designs were reproduced with the new tracing technique. Full field lenses were by far the most effective (-7D: external axial length +0.24mm with an increase in eye volume of about 6%, +7D: -0.08 mm, with a decrease in eye volume of about 2%). Hemi-field lenses and negative lenses with a 4mm central hole induced conspicuous local changes in eye shape. (3) The first type of RRG lenses with a plano zone of about 4mm (equivalent to about ± 12.52° in the visual field for a vertex distance of 5mm) had no apparent effect on central refractions but induced small hyperopic shifts in the periphery, more significant in the temporal retina (+1.70 ± 1.70 D, p<0.001, paired t-test to untreated fellow eyes). The second type of RRG lenses with a small plano zone of 2mm (equivalent to ± 6.34°) induced peripheral hyperopia but also changed the central refraction (temporal retina +1.50 ± 1.17D, p<0.001, central retina +0.77 ± 1.15 D, p<0.01, nasal retina +1.47±1.35D, p<0.001, paired t-test to untreated control eyes). In the afoveate chick, RRG lenses have an effect on central refraction and eye growth only if the central plano zone is small (<4mm). For the second type of RRG lens with a central plano zone of about 2mm, inhibitory effects on eye growth were detected in both the center and periphery even though the optical power of the lenses in the periphery was low. Copyright © 2011 Elsevier Ltd. All rights reserved.

Single scan femtosecond laser transverse writing of depressed cladding waveguides enabled by three-dimensional focal field engineering.

PubMed

Zhang, Qian; Yang, Dong; Qi, Jia; Cheng, Ya; Gong, Qihuang; Li, Yan

2017-06-12

We report single scan transverse writing of depressed cladding waveguides inside ZBLAN glass with the longitudinally oriented annular ring-shaped focal intensity distribution of the femtosecond laser. The entire region of depressed cladding at the cross section, where a negative change of refraction index is induced, can be modified simultaneously with the ring-shaped focal intensity profile. The fabricated waveguides exhibit good single guided mode.

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

A computational method for the Helmholtz equation in unbounded domains based on the minimization of an integral functional

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

Ciraolo, Giulio, E-mail: g.ciraolo@math.unipa.it; Gargano, Francesco, E-mail: gargano@math.unipa.it; Sciacca, Vincenzo, E-mail: sciacca@math.unipa.it

2013-08-01

We study a new approach to the problem of transparent boundary conditions for the Helmholtz equation in unbounded domains. Our approach is based on the minimization of an integral functional arising from a volume integral formulation of the radiation condition. The index of refraction does not need to be constant at infinity and may have some angular dependency as well as perturbations. We prove analytical results on the convergence of the approximate solution. Numerical examples for different shapes of the artificial boundary and for non-constant indexes of refraction will be presented.

Role of intraocular lens parameters in visual rehabilitation of patients after extracapsular cataract extraction

NASA Astrophysics Data System (ADS)

Bakutkin, Valery V.; Galanzha, Vladimir A.

2001-01-01

The main method of cataract treatment is micro surgical removing of the opaque lens from the eye with implantation of an intra ocular lens. We performed the comparative study of using various IOL models differing in its materials, index of refraction, spectral properties, configuration, shape, size and other features. Before and after the IOL implantation we performed the following test: visual acuity measuring, refractometry, keratometry, laser interferometric retinometry, color perception assessment, digital photo- and videorecording of the eye with image processing and some others. We found a number of correlations between the IOL properties and some characteristics of the patient's vision. The decentration of the IOL optical part more than 1,5 mm conduced to the non-corneal astigmatism and the prismatic effect. A small diameter of the IOL optical part and high index of refraction promotes to the appearance of the optical aberrations. Leucosapphire IOLs revealed the high degree of light reflection and the minimal adhesive ability of the IOL surface. Leucosapphire IOL revealed the high degree of light reflection and the minimal adhesive ability of the IOL surface. PMMA IOL revealed the low reflective power and the high adhesive ability. The best color vision was revealed in patients with PMMA IOL with an additional compound absorbing not only UV light but also short-wave blue light.

Modeling TiO2's refractive index function from bulk to nanoparticles

NASA Astrophysics Data System (ADS)

Jalava, Juho-Pertti; Taavitsainen, Veli-Matti; Lamminmäki, Ralf-Johan; Lindholm, Minna; Auvinen, Sami; Alatalo, Matti; Vartiainen, Erik; Haario, Heikki

2015-12-01

In recent decades, the use of nanomaterials has become very common. Different nanomaterials are being used in over 1600 consumer products. Nanomaterials have been defined as having at least one dimension in the range of 1-100 nm. Such materials often have unique properties. Despite some warnings of applying bulk optical constants for nano size materials, stated already in 1980s, bulk constants are still commonly used in the light scattering measurements of nano size particles. Titanium dioxide is one of the materials that is manufactured and used as an engineered nanomaterial in increasing quantities. Due to the aforementioned facts, it is quite crucial for successful research and production of nanoparticles to find out the dependence of the refractive index function (RIF) of the material on its crystal size. We have earlier performed several ab initio computations for obtaining the dependence of the RIF of TiO2 on the crystal or on the cluster size, for particles of size up to ca. 2 nm. Extending the calculations to greater sizes has turned out to be infeasible due to the unbearable increase in computational time. However, in this study we show how the crystal-size-dependent-RIF (CS-RIF), for both rutile and anatase can be modeled from measured extinction or turbidity spectra of samples with varying crystal and particle sizes. For computing the turbidity spectrum, we constructed a model including primary crystals whose distributions were parameterized by mean and standard deviation, and also including aggregates consisting of mean sized primary particles, parameterized just by mean aggregate size. Mainly because of the long computing times Mie calculation was used in the computation of extinction spectra. However, in practical process applications, the obtained RIF will be used together with the T-matrix method. We constructed the RIFs used in the model using generalized oscillator model (GOM) as expanded to crystal size dependence. The unknown parameters of the model were solved using nonlinear least squares estimation. When the crystal size becomes smaller than the bulk size the shape of the estimated CS-RIFs reveal two distinct regions for both rutile and anatase. In the first region, starting apparently already from ca. 200 nm, the height of both the real part and the imaginary part of CS-RIF decreases on crystal diameter. However, the band gap remains constant. In the second region, starting when the crystal diameter is decreased to ca. 3 nm, a blue shift starts to increase the band gap. The band gap dependence on crystal size is quite consistent with the existing experimental values. Consequently, it is of great importance to use CS-RIF in light scattering measurements for nanoparticle size determination. Neglecting this, the smaller particles in the size distribution will have too small values, already for sub-micrometer particles, naturally distorting also the mean value. To our knowledge, this is the first time ever that a CS-RIF from bulk to 1 nm size is determined for any material.

Ultrasensitive Mach-Zehnder Interferometric Temperature Sensor Based on Liquid-Filled D-Shaped Fiber Cavity

PubMed Central

Zhang, Hui; Gao, Shecheng; Luo, Yunhan; Xiong, Songsong; Wan, Lei; Huang, Xincheng; Huang, Bingsen; Feng, Yuanhua; He, Miao; Liu, Weiping; Chen, Zhe; Li, Zhaohui

2018-01-01

A liquid-filled D-shaped fiber (DF) cavity serving as an in-fiber Mach–Zehnder interferometer (MZI) has been proposed and experimentally demonstrated for temperature sensing with ultrahigh sensitivity. The miniature MZI is constructed by splicing a segment of DF between two single-mode fibers (SMFs) to form a microcavity (MC) for filling and replacement of various refractive index (RI) liquids. By adjusting the effective RI difference between the DF and MC (the two interference arms), experimental and calculated results indicate that the interference spectra show different degrees of temperature dependence. As the effective RI of the liquid-filled MC approaches that of the DF, temperature sensitivity up to −84.72 nm/°C with a linear correlation coefficient of 0.9953 has been experimentally achieved for a device with the MC length of 456 μm, filled with liquid RI of 1.482. Apart from ultrahigh sensitivity, the proposed MCMZI device possesses additional advantages of its miniature size and simple configuration; these features make it promising and competitive in various temperature sensing applications, such as consumer electronics, biological treatments, and medical diagnosis. PMID:29673220

An optomechanical model eye for ophthalmological refractive studies.

PubMed

Arianpour, Ashkan; Tremblay, Eric J; Stamenov, Igor; Ford, Joseph E; Schanzlin, David J; Lo, Yuhwa

2013-02-01

To create an accurate, low-cost optomechanical model eye for investigation of refractive errors in clinical and basic research studies. An optomechanical fluid-filled eye model with dimensions consistent with the human eye was designed and fabricated. Optical simulations were performed on the optomechanical eye model, and the quantified resolution and refractive errors were compared with the widely used Navarro eye model using the ray-tracing software ZEMAX (Radiant Zemax, Redmond, WA). The resolution of the physical optomechanical eye model was then quantified with a complementary metal-oxide semiconductor imager using the image resolution software SFR Plus (Imatest, Boulder, CO). Refractive, manufacturing, and assembling errors were also assessed. A refractive intraocular lens (IOL) and a diffractive IOL were added to the optomechanical eye model for tests and analyses of a 1951 U.S. Air Force target chart. Resolution and aberrations of the optomechanical eye model and the Navarro eye model were qualitatively similar in ZEMAX simulations. Experimental testing found that the optomechanical eye model reproduced properties pertinent to human eyes, including resolution better than 20/20 visual acuity and a decrease in resolution as the field of view increased in size. The IOLs were also integrated into the optomechanical eye model to image objects at distances of 15, 10, and 3 feet, and they indicated a resolution of 22.8 cycles per degree at 15 feet. A life-sized optomechanical eye model with the flexibility to be patient-specific was designed and constructed. The model had the resolution of a healthy human eye and recreated normal refractive errors. This model may be useful in the evaluation of IOLs for cataract surgery. Copyright 2013, SLACK Incorporated.

Stability and instability for low refractive-index-contrast particle trapping in a dual-beam optical trap.

PubMed

Huff, Alison; Melton, Charles N; Hirst, Linda S; Sharping, Jay E

2015-10-01

A dual-beam optical trap is used to trap and manipulate dielectric particles. When the refractive index of these particles is comparable to that of the surrounding medium, equilibrium trapping locations within the system shift from stable to unstable depending on fiber separation and particle size. This is due to to the relationship between gradient and scattering forces. We experimentally and computationally study the transitions between stable and unstable trapping of poly(methyl methacrylate) beads for a range of parameters relevant to experimental setups involving giant unilamellar vesicles. We present stability maps for various fiber separations and particle sizes, and find that careful attention to particle size and configuration is necessary to obtain reproducible quantitative results for soft matter stretching experiments.

Stability and instability for low refractive-index-contrast particle trapping in a dual-beam optical trap

PubMed Central

Huff, Alison; Melton, Charles N.; Hirst, Linda S.; Sharping, Jay E.

2015-01-01

A dual-beam optical trap is used to trap and manipulate dielectric particles. When the refractive index of these particles is comparable to that of the surrounding medium, equilibrium trapping locations within the system shift from stable to unstable depending on fiber separation and particle size. This is due to to the relationship between gradient and scattering forces. We experimentally and computationally study the transitions between stable and unstable trapping of poly(methyl methacrylate) beads for a range of parameters relevant to experimental setups involving giant unilamellar vesicles. We present stability maps for various fiber separations and particle sizes, and find that careful attention to particle size and configuration is necessary to obtain reproducible quantitative results for soft matter stretching experiments. PMID:26504632

Visual Acuity and Over-refraction in Myopic Children Fitted with Soft Multifocal Contact Lenses.

PubMed

Schulle, Krystal L; Berntsen, David A; Sinnott, Loraine T; Bickle, Katherine M; Gostovic, Anita T; Pierce, Gilbert E; Jones-Jordan, Lisa A; Mutti, Donald O; Walline, Jeffrey J

2018-04-01

Practitioners fitting contact lenses for myopia control frequently question whether a myopic child can achieve good vision with a high-add multifocal. We demonstrate that visual acuity is not different than spectacles with a commercially available, center-distance soft multifocal contact lens (MFCL) (Biofinity Multifocal "D"; +2.50 D add). To determine the spherical over-refraction (SOR) necessary to obtain best-corrected visual acuity (BCVA) when fitting myopic children with a center-distance soft MFCL. Children (n = 294) aged 7 to 11 years with myopia (spherical component) of -0.75 to -5.00 diopters (D) (inclusive) and 1.00 D cylinder or less (corneal plane) were fitted bilaterally with +2.50 D add Biofinity "D" MFCLs. The initial MFCL power was the spherical equivalent of a standardized subjective refraction, rounded to the nearest 0.25 D step (corneal plane). An SOR was performed monocularly (each eye) to achieve BCVA. Binocular, high-contrast logMAR acuity was measured with manifest spectacle correction and MFCLs with over-refraction. Photopic pupil size was measured with a pupilometer. The mean (±SD) age was 10.3 ± 1.2 years, and the mean (±SD) SOR needed to achieve BCVA was OD: -0.61 ± 0.24 D/OS: -0.58 ± 0.27 D. There was no difference in binocular high-contrast visual acuity (logMAR) between spectacles (-0.01 ± 0.06) and best-corrected MFCLs (-0.01 ± 0.07) (P = .59). The mean (±SD) photopic pupil size (5.4 ± 0.7 mm) was not correlated with best MFCL correction or the over-refraction magnitude (both P ≥ .09). Children achieved BCVA with +2.50 D add MFCLs that was not different than with spectacles. Children typically required an over-refraction of -0.50 to -0.75 D to achieve BCVA. With a careful over-refraction, these +2.50 D add MFCLs provide good distance acuity, making them viable candidates for myopia control.

Refraction Correction in 3D Transcranial Ultrasound Imaging

PubMed Central

Lindsey, Brooks D.; Smith, Stephen W.

2014-01-01

We present the first correction of refraction in three-dimensional (3D) ultrasound imaging using an iterative approach that traces propagation paths through a two-layer planar tissue model, applying Snell’s law in 3D. This approach is applied to real-time 3D transcranial ultrasound imaging by precomputing delays offline for several skull thicknesses, allowing the user to switch between three sets of delays for phased array imaging at the push of a button. Simulations indicate that refraction correction may be expected to increase sensitivity, reduce beam steering errors, and partially restore lost spatial resolution, with the greatest improvements occurring at the largest steering angles. Distorted images of cylindrical lesions were created by imaging through an acrylic plate in a tissue-mimicking phantom. As a result of correcting for refraction, lesions were restored to 93.6% of their original diameter in the lateral direction and 98.1% of their original shape along the long axis of the cylinders. In imaging two healthy volunteers, the mean brightness increased by 8.3% and showed no spatial dependency. PMID:24275538

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.

Biophotonics sensor acclimatization to stem cells environment

NASA Astrophysics Data System (ADS)

Mohamad Shahimin, Mukhzeer

2017-11-01

The ability to discriminate, characterise and purify biological cells from heterogeneous population of cells is fundamental to numerous prognosis and diagnosis applications; often forming the basis for current and emerging clinical protocols in stem cell therapy. Current sorting approaches exploit differences in cell density, specific immunologic targets, or receptor-ligand interactions to isolate particular cells. Identification of novel properties by which different cell types may be discerned and of new ways for their selective manipulation are clearly fundamental components for improving sorting methodologies. Biophotonics sensor developed by our team are potentially capable of discriminating cells according to their refractive index (which is highly dependable on the organelles inside the cell), size (indicator to cell stage) and shape (in certain cases as an indicator to cell type). The sensor, which already discriminate particles efficiently, is modified to acclimatize into biological environment, especially for stem cell applications.

Linearized T-Matrix and Mie Scattering Computations

NASA Technical Reports Server (NTRS)

Spurr, R.; Wang, J.; Zeng, J.; Mishchenko, M. I.

2011-01-01

We present a new linearization of T-Matrix and Mie computations for light scattering by non-spherical and spherical particles, respectively. In addition to the usual extinction and scattering cross-sections and the scattering matrix outputs, the linearized models will generate analytical derivatives of these optical properties with respect to the real and imaginary parts of the particle refractive index, and (for non-spherical scatterers) with respect to the ''shape'' parameter (the spheroid aspect ratio, cylinder diameter/height ratio, Chebyshev particle deformation factor). These derivatives are based on the essential linearity of Maxwell's theory. Analytical derivatives are also available for polydisperse particle size distribution parameters such as the mode radius. The T-matrix formulation is based on the NASA Goddard Institute for Space Studies FORTRAN 77 code developed in the 1990s. The linearized scattering codes presented here are in FORTRAN 90 and will be made publicly available.

Optimizing phase to enhance optical trap stiffness.

PubMed

Taylor, Michael A

2017-04-03

Phase optimization offers promising capabilities in optical tweezers, allowing huge increases in the applied forces, trap stiff-ness, or measurement sensitivity. One key obstacle to potential applications is the lack of an efficient algorithm to compute an optimized phase profile, with enhanced trapping experiments relying on slow programs that would take up to a week to converge. Here we introduce an algorithm that reduces the wait from days to minutes. We characterize the achievable in-crease in trap stiffness and its dependence on particle size, refractive index, and optical polarization. We further show that phase-only control can achieve almost all of the enhancement possible with full wavefront shaping; for instance phase control allows 62 times higher trap stiffness for 10 μm silica spheres in water, while amplitude control and non-trivial polarization further increase this by 1.26 and 1.01 respectively. This algorithm will facilitate future applications in optical trapping, and more generally in wavefront optimization.

Numerical study of influence of different dispersed components of crystal cloud on transmission of radiant energy

NASA Astrophysics Data System (ADS)

Shefer, Olga

2017-11-01

The calculated results of the transmission of visible and infrared radiation by an atmosphere layer involving ensembles of large preferentially oriented crystals and spherical particles are presented. To calculate extinction characteristics, the physical optics method and the Mie theory are applied. Among all atmospheric particles, both the small particles that are commensurable with the wavelength of the incident radiation and the large plates and the columns are distinguished by the most pronounced dependence of the transmission on spectra of radiant energy. The work illustrates features of influence of parameters of the particle size distribution, particle aspect ratios, orientation and particle refractive index, also polarization state of the incident radiation on the transmission. The predominant effect of the plates on the wavelength dependence of the transmission is shown. A separated and cooperative contributes of the large plates and the small volume shape particles to the common transmission by medium are considered.

Temperature and strain characterization of long period gratings in air guiding fiber

NASA Astrophysics Data System (ADS)

Iadicicco, Agostino; Cutolo, Antonello; Cusano, Andrea; Campopiano, Stefania

2013-05-01

This paper reports on the fabrication of Long Period Gratings (LPGs) in hollow-core air-silica photonic bandgap fibers by using pressure assisted Electrode Arc Discharge (EAD) technique. In particular, the fabrication procedure relies on the combined use of EAD step, to locally heat the HC fiber, and of a static pressure (slightly higher than the external one) inside the fiber holes, to modify the holes. This procedure permits to preserve the holey structure of the host fiber avoiding any hole collapsing and it enables a local effective refractive index change due to the size and shape modifications of core and cladding holes. Periodically repeated EAD treatments permit the fabrication of LPGs based devices in hollow core optical fibers enabling new functionalities hitherto not possible. Here, the experimental fabrication of LPG prototypes with different periods and lengths are discussed. And, the HC-LPGs sensitivity to environmental parameters such as strain and temperature are investigated.

Design of refractive laser beam shapers to generate complex irradiance profiles

NASA Astrophysics Data System (ADS)

Li, Meijie; Meuret, Youri; Duerr, Fabian; Vervaeke, Michael; Thienpont, Hugo

2014-05-01

A Gaussian laser beam is reshaped to have specific irradiance distributions in many applications in order to ensure optimal system performance. Refractive optics are commonly used for laser beam shaping. A refractive laser beam shaper is typically formed by either two plano-aspheric lenses or by one thick lens with two aspherical surfaces. Ray mapping is a general optical design technique to design refractive beam shapers based on geometric optics. This design technique in principle allows to generate any rotational-symmetric irradiance profile, yet in literature ray mapping is mainly developed to transform a Gaussian irradiance profile to a uniform profile. For more complex profiles especially with low intensity in the inner region, like a Dark Hollow Gaussian (DHG) irradiance profile, ray mapping technique is not directly applicable in practice. In order to these complex profiles, the numerical effort of calculating the aspherical surface points and fitting a surface with sufficient accuracy increases considerably. In this work we evaluate different sampling approaches and surface fitting methods. This allows us to propose and demonstrate a comprehensive numerical approach to efficiently design refractive laser beam shapers to generate rotational-symmetric collimated beams with a complex irradiance profile. Ray tracing analysis for several complex irradiance profiles demonstrates excellent performance of the designed lenses and the versatility of our design procedure.

Refraction corrected calibration for aquatic locomotion research: application of Snell's law improves spatial accuracy.

PubMed

Henrion, Sebastian; Spoor, Cees W; Pieters, Remco P M; Müller, Ulrike K; van Leeuwen, Johan L

2015-07-07

Images of underwater objects are distorted by refraction at the water-glass-air interfaces and these distortions can lead to substantial errors when reconstructing the objects' position and shape. So far, aquatic locomotion studies have minimized refraction in their experimental setups and used the direct linear transform algorithm (DLT) to reconstruct position information, which does not model refraction explicitly. Here we present a refraction corrected ray-tracing algorithm (RCRT) that reconstructs position information using Snell's law. We validated this reconstruction by calculating 3D reconstruction error-the difference between actual and reconstructed position of a marker. We found that reconstruction error is small (typically less than 1%). Compared with the DLT algorithm, the RCRT has overall lower reconstruction errors, especially outside the calibration volume, and errors are essentially insensitive to camera position and orientation and the number and position of the calibration points. To demonstrate the effectiveness of the RCRT, we tracked an anatomical marker on a seahorse recorded with four cameras to reconstruct the swimming trajectory for six different camera configurations. The RCRT algorithm is accurate and robust and it allows cameras to be oriented at large angles of incidence and facilitates the development of accurate tracking algorithms to quantify aquatic manoeuvers.

Automatic diagnostic system for measuring ocular refractive errors

NASA Astrophysics Data System (ADS)

Ventura, Liliane; Chiaradia, Caio; de Sousa, Sidney J. F.; de Castro, Jarbas C.

1996-05-01

Ocular refractive errors (myopia, hyperopia and astigmatism) are automatic and objectively determined by projecting a light target onto the retina using an infra-red (850 nm) diode laser. The light vergence which emerges from the eye (light scattered from the retina) is evaluated in order to determine the corresponding ametropia. The system basically consists of projecting a target (ring) onto the retina and analyzing the scattered light with a CCD camera. The light scattered by the eye is divided into six portions (3 meridians) by using a mask and a set of six prisms. The distance between the two images provided by each of the meridians, leads to the refractive error of the referred meridian. Hence, it is possible to determine the refractive error at three different meridians, which gives the exact solution for the eye's refractive error (spherical and cylindrical components and the axis of the astigmatism). The computational basis used for the image analysis is a heuristic search, which provides satisfactory calculation times for our purposes. The peculiar shape of the target, a ring, provides a wider range of measurement and also saves parts of the retina from unnecessary laser irradiation. Measurements were done in artificial and in vivo eyes (using cicloplegics) and the results were in good agreement with the retinoscopic measurements.

Influence of the corneal optical zone on the point-spread function of the human eye

NASA Astrophysics Data System (ADS)

Rol, Pascal O.; Parel, Jean-Marie A.

1992-08-01

In refractive surgery, a number of surgical techniques have been developed to correct ametropia (refractive defaults) of the eye by changing the exterior shape of the cornea. Because the air-cornea interface makes up for about two thirds of the refractive power of the eye, a refractive correction can be obtained by a suitable reshaping of the cornea. Postoperatively, it is usually observed that the corneal region consists of two or more zones which are characterized by different optical parameters exhibiting in particular different focal distances. Under normal circumstances, only the central area of the cornea is involved in the formation of the retinal image. However, if part of the light entering the eye through peripheral portions of the cornea with refractive properties different from the central area can pass the pupil, an out-of-focus `ghost' image may be overlaid on the retina causing a blur. 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 diameter of the central zone, i.e., the optical zone which is of importance for vision.

Fabrication of rigid and flexible refractive-index-matched flow phantoms for flow visualisation and optical flow measurements

NASA Astrophysics Data System (ADS)

Geoghegan, P. H.; Buchmann, N. A.; Spence, C. J. T.; Moore, S.; Jermy, M.

2012-05-01

A method for the construction of both rigid and compliant (flexible) transparent flow phantoms of biological flow structures, suitable for PIV and other optical flow methods with refractive-index-matched working fluid is described in detail. Methods for matching the in vivo compliance and elastic wave propagation wavelength are presented. The manipulation of MRI and CT scan data through an investment casting mould is described. A method for the casting of bubble-free phantoms in silicone elastomer is given. The method is applied to fabricate flexible phantoms of the carotid artery (with and without stenosis), the carotid artery bifurcation (idealised and patient-specific) and the human upper airway (nasal cavity). The fidelity of the phantoms to the original scan data is measured, and it is shown that the cross-sectional error is less than 5% for phantoms of simple shape but up to 16% for complex cross-sectional shapes such as the nasal cavity. This error is mainly due to the application of a PVA coating to the inner mould and can be reduced by shrinking the digital model. Sixteen per cent variation in area is less than the natural patient to patient variation of the physiological geometries. The compliance of the phantom walls is controlled within physiologically realistic ranges, by choice of the wall thickness, transmural pressure and Young's modulus of the elastomer. Data for the dependence of Young's modulus on curing temperature are given for Sylgard 184. Data for the temperature dependence of density, viscosity and refractive index of the refractive-index-matched working liquid (i.e. water-glycerol mixtures) are also presented.

In-line microfluidic refractometer based on C-shaped fiber assisted photonic crystal fiber Sagnac interferometer.

PubMed

Wu, Chuang; Tse, Ming-Leung Vincent; Liu, Zhengyong; Guan, Bai-Ou; Lu, Chao; Tam, Hwa-Yaw

2013-09-01

We propose and demonstrate a highly sensitive in-line photonic crystal fiber (PCF) microfluidic refractometer. Ultrathin C-shaped fibers are spliced in-between the PCF and standard single-mode fibers. The C-shaped fibers provide openings for liquid to flow in and out of the PCF. Based on a Sagnac interferometer, the refractive index (RI) response of the device is investigated theoretically and experimentally. A high sensitivity of 6621 nm/RIU for liquid RI from 1.330 to 1.333 is achieved in the experiment, which agrees well with the theoretical analysis.

Inversion of multiwavelength Raman lidar data for retrieval of bimodal aerosol size distribution

NASA Astrophysics Data System (ADS)

Veselovskii, Igor; Kolgotin, Alexei; Griaznov, Vadim; Müller, Detlef; Franke, Kathleen; Whiteman, David N.

2004-02-01

We report on the feasibility of deriving microphysical parameters of bimodal particle size distributions from Mie-Raman lidar based on a triple Nd:YAG laser. Such an instrument provides backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm. The inversion method employed is Tikhonov's inversion with regularization. Special attention has been paid to extend the particle size range for which this inversion scheme works to ~10 μm, which makes this algorithm applicable to large particles, e.g., investigations concerning the hygroscopic growth of aerosols. Simulations showed that surface area, volume concentration, and effective radius are derived to an accuracy of ~50% for a variety of bimodal particle size distributions. For particle size distributions with an effective radius of <1 μm the real part of the complex refractive index was retrieved to an accuracy of +/-0.05, the imaginary part was retrieved to 50% uncertainty. Simulations dealing with a mode-dependent complex refractive index showed that an average complex refractive index is derived that lies between the values for the two individual modes. Thus it becomes possible to investigate external mixtures of particle size distributions, which, for example, might be present along continental rims along which anthropogenic pollution mixes with marine aerosols. Measurement cases obtained from the Institute for Tropospheric Research six-wavelength aerosol lidar observations during the Indian Ocean Experiment were used to test the capabilities of the algorithm for experimental data sets. A benchmark test was attempted for the case representing anthropogenic aerosols between a broken cloud deck. A strong contribution of particle volume in the coarse mode of the particle size distribution was found.

Inversion of multiwavelength Raman lidar data for retrieval of bimodal aerosol size distribution.

PubMed

Veselovskii, Igor; Kolgotin, Alexei; Griaznov, Vadim; Müller, Detlef; Franke, Kathleen; Whiteman, David N

2004-02-10

We report on the feasibility of deriving microphysical parameters of bimodal particle size distributions from Mie-Raman lidar based on a triple Nd:YAG laser. Such an instrument provides backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm. The inversion method employed is Tikhonov's inversion with regularization. Special attention has been paid to extend the particle size range for which this inversion scheme works to approximately 10 microm, which makes this algorithm applicable to large particles, e.g., investigations concerning the hygroscopic growth of aerosols. Simulations showed that surface area, volume concentration, and effective radius are derived to an accuracy of approximately 50% for a variety of bimodal particle size distributions. For particle size distributions with an effective radius of < 1 microm the real part of the complex refractive index was retrieved to an accuracy of +/- 0.05, the imaginary part was retrieved to 50% uncertainty. Simulations dealing with a mode-dependent complex refractive index showed that an average complex refractive index is derived that lies between the values for the two individual modes. Thus it becomes possible to investigate external mixtures of particle size distributions, which, for example, might be present along continental rims along which anthropogenic pollution mixes with marine aerosols. Measurement cases obtained from the Institute for Tropospheric Research six-wavelength aerosol lidar observations during the Indian Ocean Experiment were used to test the capabilities of the algorithm for experimental data sets. A benchmark test was attempted for the case representing anthropogenic aerosols between a broken cloud deck. A strong contribution of particle volume in the coarse mode of the particle size distribution was found.

Comparisons of refractive errors between twins and singletons in Chinese school-age samples.

PubMed

Hur, Yoon-Mi; Zheng, Yingfeng; Huang, Wenyong; Ding, Xiaohu; He, Mingguang

2009-02-01

Studies have reported that refractive errors are associated with premature births. As twins have higher prevalence of prematurity than singletons, it is important to assess similarity of the prevalence of refractive errors in twins and singletons for proper interpretations and generalizations of the findings from twin studies. We compared refractive errors and diopter hours between 561 pairs of twins and 3757 singletons who are representative of school-age children (7-15 years) residing in an urban area of southern China. We found that the means and variances of the continuous measurement of spherical equivalent refractive error and diopter hours were not significantly different between twins and singletons. Although the prevalence of myopia was comparable between twins and singletons, that of hyperopia and astigmatism was slightly but significantly higher in twins than in singletons. These results are inconsistent with those of adult studies that showed no differences in refractive errors between twins and singletons. Given that the sample size of twins is relatively small and that this study is the first to demonstrate minor differences in refractive errors between twins and singletons, future replications are necessary to determine whether the slightly higher prevalence of refractive errors in twins than in singletons found in this study was due to a sampling error or to the developmental delay often observed in twins in childhood.

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.

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.

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.

Impact of Primary Spherical Aberration, Spatial Frequency and Stiles Crawford Apodization on Wavefront determined Refractive Error: A Computational Study

PubMed Central

Xu, Renfeng; Bradley, Arthur; Thibos, Larry N.

2013-01-01

Purpose We tested the hypothesis that pupil apodization is the basis for central pupil bias of spherical refractions in eyes with spherical aberration. Methods We employed Fourier computational optics in which we vary spherical aberration levels, pupil size, and pupil apodization (Stiles Crawford Effect) within the pupil function, from which point spread functions and optical transfer functions were computed. Through-focus analysis determined the refractive correction that optimized retinal image quality. Results For a large pupil (7 mm), as spherical aberration levels increase, refractions that optimize the visual Strehl ratio mirror refractions that maximize high spatial frequency modulation in the image and both focus a near paraxial region of the pupil. These refractions are not affected by Stiles Crawford Effect apodization. Refractions that optimize low spatial frequency modulation come close to minimizing wavefront RMS, and vary with level of spherical aberration and Stiles Crawford Effect. In the presence of significant levels of spherical aberration (e.g. C40 = 0.4 µm, 7mm pupil), low spatial frequency refractions can induce −0.7D myopic shift compared to high SF refraction, and refractions that maximize image contrast of a 3 cycle per degree square-wave grating can cause −0.75D myopic drift relative to refractions that maximize image sharpness. Discussion Because of small depth of focus associated with high spatial frequency stimuli, the large change in dioptric power across the pupil caused by spherical aberration limits the effective aperture contributing to the image of high spatial frequencies. Thus, when imaging high spatial frequencies, spherical aberration effectively induces an annular aperture defining that portion of the pupil contributing to a well-focused image. As spherical focus is manipulated during the refraction procedure, the dimensions of the annular aperture change. Image quality is maximized when the inner radius of the induced annulus falls to zero, thus defining a circular near paraxial region of the pupil that determines refraction outcome. PMID:23683093

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.

Linear and Nonlinear Optical Properties of Spherical Quantum Dots: Effects of Hydrogenic Impurity and Conduction Band Non-Parabolicity

NASA Astrophysics Data System (ADS)

Rezaei, G.; Vaseghi, B.; Doostimotlagh, N. A.

2012-03-01

Simultaneous effects of an on-center hydrogenic impurity and band edge non-parabolicity on intersubband optical absorption coefficients and refractive index changes of a typical GaAs/AlxGa1-x As spherical quantum dot are theoretically investigated, using the Luttinger—Kohn effective mass equation. So, electronic structure and optical properties of the system are studied by means of the matrix diagonalization technique and compact density matrix approach, respectively. Finally, effects of an impurity, band edge non-parabolicity, incident light intensity and the dot size on the linear, the third-order nonlinear and the total optical absorption coefficients and refractive index changes are investigated. Our results indicate that, the magnitudes of these optical quantities increase and their peaks shift to higher energies as the influences of the impurity and the band edge non-parabolicity are considered. Moreover, incident light intensity and the dot size have considerable effects on the optical absorption coefficients and refractive index changes.

Refractive-index-matched hydrogel materials for measuring flow-structure interactions

NASA Astrophysics Data System (ADS)

Byron, Margaret L.; Variano, Evan A.

2013-02-01

In imaging-based studies of flow around solid objects, it is useful to have materials that are refractive-index-matched to the surrounding fluid. However, materials currently in use are usually rigid and matched to liquids that are either expensive or highly viscous. This does not allow for measurements at high Reynolds number, nor accurate modeling of flexible structures. This work explores the use of two hydrogels (agarose and polyacrylamide) as refractive-index-matched models in water. These hydrogels are inexpensive, can be cast into desired shapes, and have flexibility that can be tuned to match biological materials. The use of water as the fluid phase allows this method to be implemented immediately in many experimental facilities and permits investigation of high-Reynolds-number phenomena. We explain fabrication methods and present a summary of the physical and optical properties of both gels, and then show measurements demonstrating the use of hydrogel models in quantitative imaging.

Extraordinary-mode refractive-index change produced by the linear electro-optic effect in LiNbO3 and reverse-poled LiNbO3

NASA Astrophysics Data System (ADS)

Boyd, Joseph T.; Servizzi, Anthony J.; Sriram, S.; Kingsley, Stuart A.

1995-07-01

To examine aspects of an integrated photonic electric-field sensor, we calculate electro-optically induced refractive-index change in regular and reverse-poled LiNbO3. Specifically, for y-propagating extraordinary modes, we determine how index change depends on electric-field magnitude and direction. To accomplish this, changes in index-ellipsoid shape and orientation are found by the use of a numerical eigenvalue procedure to diagonalize the impermeability tensor; then, refractive index is calculated by the use of a vector reference-frame transformation and a small perturbation approximation. A general formula is inferred from calculations for specific field directions. Electro-optic coefficients for reverse-poled LiNbO3 are obtained by application of a tensor reference-frame transformation to those of LiNbO3. The index-calculation procedure has utility beyond the problem that is considered.

Refractive Index Sensor Based on a Metal-Insulator-Metal Waveguide Coupled with a Symmetric Structure.

PubMed

Yan, Shubin; Zhang, Meng; Zhao, Xuefeng; Zhang, Yanjun; Wang, Jicheng; Jin, Wen

2017-12-11

In this study, a new refractive index sensor based on a metal-insulator-metal waveguide coupled with a notched ring resonator and stub is designed. The finite element method is used to study the propagation characteristics of the sensor. According to the calculation results, the transmission spectrum exhibits a typical Fano resonance shape. The phenomenon of Fano resonance is caused by the coupling between the broadband spectrum and narrowband spectrum. In the design, the broadband spectrum signal is generated by the stub, while the narrowband spectrum signal is generated by the notched ring resonator. In addition, the structural parameters of the resonators and the structure filled with media of different refractive indices are varied to study the sensing properties. The maximum achieved sensitivity of the sensor reached 1071.4 nm/RIU. The results reveal potential applications of the coupled system in the field of sensors.

Thick lens chromatic effective focal length variation versus bending

NASA Astrophysics Data System (ADS)

Sparrold, Scott

2017-11-01

Longitudinal chromatic aberration (LCA) can limit the optical performance in refractive optical systems. Understanding a singlet's chromatic change of effective focal leads to insights and methods to control LCA. Long established, first order theory, shows the chromatic change in focal length for a zero thickness lens is proportional to it's focal length divided by the lens V number or inverse dispersion. This work presents the derivation of an equation for a thick singlet's chromatic change in effective focal length as a function of center thickness, t, dispersion, V, index of refraction, n, and the Coddington shape factor, K. A plot of bending versus chromatic focal length variation is presented. Lens thickness does not influence chromatic variation of effective focal length for a convex plano or plano convex lens. A lens's center thickness'influence on chromatic focal length variation is more pronounced for lower indices of refraction.

Wavelength-dependent scattering in human eye with cataracts.

PubMed

Kelly-Pérez, Ismael; Méndez-Aguilar, Emilia M; Treviño-Palacios, Carlos G; Bruce, Neil C; Berriel-Valdos, Luis R; Al-Hohamedi, Haroun; Bende, Thomas

2018-03-02

The gradual process in which the crystalline lens is cloudy due to the appearance of elements giving rise to variations in the refractive index is known as cataract. Clinical assessment is usually complicated because it considers patient's perception, and individuals with similar development have different visual deficits. This work presents a model which considers the fluctuations in the refractive index as spherical particles produce measurable scatter radial profiles patterns on the retina. Measurements for 2 different wavelengths simultaneously provide information on particle size and a quantitative assessment by measurement of the fluctuations of the refractive index. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

How To Prepare Materials With a Desired Refraction Coefficient?

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

Ramm, A. G.

2010-05-21

In this talk a method is described for preparing materials with a desired refraction coefficient. The method consists of embedding into a material with known refraction coefficient many small particles of size a. The number of particles per unit volume around any point is prescribed, the distance between neighboring particles is O(a{sup (2-kappa/3)}) as a->0, 00. The refraction coefficient is themore » coefficient n{sup 2}(x) in the wave equation [nabla{sup 2}+kappa{sup 2}n{sup 2}(x)]u = 0.« less

Spot diameters for scanning photorefractive keratectomy: a comparative study

NASA Astrophysics Data System (ADS)

Manns, Fabrice; Parel, Jean-Marie A.

1998-06-01

Purpose: The purpose of this study was to compare with computer simulations the duration, smoothness and accuracy of scanning photo-refractive keratectomy with spot diameters ranging from 0.2 to 1 mm. Methods: We calculated the number of pulses per diopter of flattening for spot sizes varying from 0.2 to 1 mm. We also computed the corneal shape after the correction of 4 diopters of myopia and 4 diopters of astigmatism with a 6 mm ablation zone and a spot size of 0.4 mm with 600 mJ/cm2 peak radiant exposure and 0.8 mm with 300 mJ/cm2 peak radiant exposure. The accuracy and smoothness of the ablations were compared. Results: The repetition rate required to produce corrections of myopia with a 6 mm ablation zone in a duration of 5 s per diopter is on the order of 1 kHz for spot sizes smaller than 0.5 mm, and of 100 Hz for spot sizes larger than 0.5 mm. The accuracy and smoothness after the correction of myopia and astigmatism with small and large spot sizes were not significantly different. Conclusions: This study seems to indicate that there is no theoretical advantage for using either smaller spots with higher radiant exposures or larger spots with lower radiant exposures. However, at fixed radiant exposure, treatments with smaller spots require a larger duration of surgery but provide a better accuracy for the correction of astigmatism.

Reflected GPS Power for the Detection of Surface Roughness Patterns in Coastal Water

NASA Technical Reports Server (NTRS)

Oertel, George, F.; Allen, Thomas R.

2000-01-01

Coastal bays formed by the barrier islands of Delaware, Maryland and Virginia are parts of a coastal region known as a "Coastal Compartment". The coastal compartment between the Chesapeake and Delaware Bays is actually the mosaic of landscapes on the headland of the interfluve that separates these large drainage basins. The coastal compartments form a variety of different-shaped waterways landward of the coastline. Shape differences along the boundaries produce differences in exposure to wind and waves. Different shoreface topographies seaward of the coastline also influence surface roughness by changing wave-refraction patterns. Surface-water roughness (caused by waves) is controlled by a number of parameters, including fetch, shielding, exposure corridors, water-mass boundary conditions, wetland vegetation and water depth in coastal bays. In the coastal ocean, surface roughness patterns are controlled by shoreface shoaling and inlet refraction patterns in the coastal ocean. Knowledge of wave phenomena in the nearshore and backbarrier areas is needed to understand how wave climate influences important ecosystems in estuaries and bays.

Thomas Young's contribution to visual optics: the Bakerian Lecture "on the mechanism of the eye".

PubMed

Atchison, David A; Charman, W Neil

2010-10-15

Thomas Young (1773-1829) carried out major pioneering work in many different subjects. In 1800 he gave the Bakerian Lecture of the Royal Society on the topic of the "mechanism of the eye": this was published in the following year (T. Young, 1801). Young used his own design of optometer to measure refraction and accommodation, and discovered his own astigmatism. He considered the different possible origins of accommodation and confirmed that it was due to change in shape of the lens rather than to change in shape of the cornea or an increase in axial length. However, the paper also dealt with many other aspects of visual and ophthalmic optics, such as biometric parameters, peripheral refraction, longitudinal chromatic aberration, depth-of-focus and instrument myopia. These aspects of the paper have previously received little attention. We now give detailed consideration to these and other less-familiar features of Young's work and conclude that his studies remain relevant to many of the topics which currently engage visual scientists.

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

[Research on the measurement range of particle size with total light scattering method in vis-IR region].

PubMed

Sun, Xiao-gang; Tang, Hong; Dai, Jing-min

2008-12-01

The problem of determining the particle size range in the visible-infrared region was studied using the independent model algorithm in the total scattering technique. By the analysis and comparison of the accuracy of the inversion results for different R-R distributions, the measurement range of particle size was determined. Meanwhile, the corrected extinction coefficient was used instead of the original extinction coefficient, which could determine the measurement range of particle size with higher accuracy. Simulation experiments illustrate that the particle size distribution can be retrieved very well in the range from 0. 05 to 18 microm at relative refractive index m=1.235 in the visible-infrared spectral region, and the measurement range of particle size will vary with the varied wavelength range and relative refractive index. It is feasible to use the constrained least squares inversion method in the independent model to overcome the influence of the measurement error, and the inverse results are all still satisfactory when 1% stochastic noise is added to the value of the light extinction.

Trapping two types of particles using a double-ring-shaped radially polarized beam

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

Zhang Yaoju; Ding Biaofeng; Suyama, Taikei

An optical-trap method based on the illumination of a double-ring-shaped radially polarized beam (R-TEM{sub 11}*) is proposed. The numerical results based on the vector diffraction theory show that a highly focused R-TEM{sub 11}* beam not only can produce a bright spot but also can form an optical cage in the focal region by changing the truncation parameter {beta}, defined as the ratio of the radius of the aperture to the waist of the beam. The radiation forces acting on Rayleigh particles are calculated by using the Rayleigh scattering theory. The bright spot generated by the R-TEM{sub 11}* beam with amore » {beta} value close to 2 can three-dimensionally trap a particle with a refractive index larger than that of the ambient. An optical cage or three-dimensional dark spot generated by the R-TEM{sub 11}* beam with a {beta} value close to 1.3 can three-dimensionally trap a particle with refractive index smaller than that of the ambient. Because the adjustment of the truncation parameter can be actualized by simply changing the radius of a circular aperture inserted in the front of the lens, only one optical-trap system in the present method can be used to three-dimensionally trap two types of particles with different refractive indices.« less

Stress-induced microcrack density evolution in β-eucryptite ceramics: Experimental observations and possible route to strain hardening

DOE PAGES

Müller, B. R.; Cooper, R. C.; Lange, A.; ...

2017-11-01

In order to investigate their microcracking behaviour, the microstructures of several β-eucryptite ceramics, obtained from glass precursor and cerammed to yield different grain sizes and microcrack densities, were characterized by laboratory and synchrotron x-ray refraction and tomography. Here, results were compared with those obtained from scanning electron microscopy (SEM). In SEM images, the characterized materials appeared fully dense but computed tomography showed the presence of pore clusters. Uniaxial tensile testing was performed on specimens while strain maps were recorded and analyzed by Digital Image Correlation (DIC). X-ray refraction techniques were applied on specimens before and after tensile testing to measuremore » the amount of the internal specific surface (i.e., area per unit volume). X-ray refraction revealed that (a) the small grain size (SGS) material contained a large specific surface, originating from the grain boundaries and the interfaces of TiO 2 precipitates; (b) the medium (MGS) and large grain size (LGS) materials possessed higher amounts of specific surface compared to SGS material due to microcracks, which decreased after tensile loading; (c) the precursor glass had negligible internal surface. The unexpected decrease in the internal surface of MGS and LGS after tensile testing is explained by the presence of compressive regions in the DIC strain maps and further by theoretical arguments. It is suggested that while some microcracks merge via propagation, more close mechanically, thereby explaining the observed X-ray refraction results. Lastly, the mechanisms proposed would allow the development of a strain hardening route in ceramics.« less

Stress-induced microcrack density evolution in β-eucryptite ceramics: Experimental observations and possible route to strain hardening

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

Müller, B. R.; Cooper, R. C.; Lange, A.

In order to investigate their microcracking behaviour, the microstructures of several β-eucryptite ceramics, obtained from glass precursor and cerammed to yield different grain sizes and microcrack densities, were characterized by laboratory and synchrotron x-ray refraction and tomography. Here, results were compared with those obtained from scanning electron microscopy (SEM). In SEM images, the characterized materials appeared fully dense but computed tomography showed the presence of pore clusters. Uniaxial tensile testing was performed on specimens while strain maps were recorded and analyzed by Digital Image Correlation (DIC). X-ray refraction techniques were applied on specimens before and after tensile testing to measuremore » the amount of the internal specific surface (i.e., area per unit volume). X-ray refraction revealed that (a) the small grain size (SGS) material contained a large specific surface, originating from the grain boundaries and the interfaces of TiO 2 precipitates; (b) the medium (MGS) and large grain size (LGS) materials possessed higher amounts of specific surface compared to SGS material due to microcracks, which decreased after tensile loading; (c) the precursor glass had negligible internal surface. The unexpected decrease in the internal surface of MGS and LGS after tensile testing is explained by the presence of compressive regions in the DIC strain maps and further by theoretical arguments. It is suggested that while some microcracks merge via propagation, more close mechanically, thereby explaining the observed X-ray refraction results. Lastly, the mechanisms proposed would allow the development of a strain hardening route in ceramics.« less

Feasibility study: Monodisperse polymer particles containing laser-excitable dyes

NASA Technical Reports Server (NTRS)

Venkateswarlu, Putcha; He, K. X.; Sharma, A.

1993-01-01

The optical properties associated with small particles, which include aerosols, hydrosols and solid microspheres have an impact on several areas of science and engineering. Since the advent of high-speed computers and lasers, the interaction of light with matter in the form of small particles with a discontinuous optical boundary relative to the surroundings has been much better understood. Various nonlinear optical effects have been observed involving interaction of a laser beam with both solid microspheres and liquid microdroplets. These include observation of second and third harmonic generation, four wave mixing, optical visibility, two photon absorption, observation of stimulated emission and lasing, and Stimulated Raman Scattering. Many of these effects are observed with laser intensities which are orders of magnitude less than that required by threshold condition for interactions in macroscopic bulk medium. The primary reason for this is twofold. The front surface of the microsphere acts as a thick lens to enhance the internal intensity of the input laser radiation, and the spherical shape of the droplet acts as an optical cavity to provide feedback at specific wavelengths corresponding to the whispering gallery modes or the morphology dependent resonances (MDR's). The most interesting and significant recent finding in this field is undoubtedly the existence of resonance peaks in linear and nonlinear optical spectra. Such resonance peaks are only dependent on the particle morphology, which means the size, shape and refractive index of the particle. Because of the simultaneous presence of these resonances, they have been referred to by many names, including structural resonances, whispering modes or whispering gallery modes, creeping waves, circumferential waves, surfaces modes, and virtual modes. All of these names refer to the same phenomena, i.e. morphology dependent resonances (MDR's) which has already been described and predicted precisely by electromagnetic theory and Loentz-Mie theory since 1908. MDR's can become important when the particle size (radius a) approaches and exceeds the wavelength of the electromagnetic wave (lambda) and the refractive index of the particle is greater than that of the surrounding medium. Such resonances are easiest to observe from a single particle with high symmetry, such as a sphere, spheroid, or cylinder. MDR's correspond to solutions of the characteristic equations of the electromagnetic fields in the presence of a sphere.

Optical properties of soot particles: measurement - model comparison

NASA Astrophysics Data System (ADS)

Forestieri, S.; Lambe, A. T.; Lack, D.; Massoli, P.; Cross, E. S.; Dubey, M.; Mazzoleni, C.; Olfert, J.; Freedman, A.; Davidovits, P.; Onasch, T. B.; Cappa, C. D.

2013-12-01

Soot, a product of incomplete combustion, plays an important role in the earth's climate system through the absorption and scattering of solar radiation. In order to accurately model the direct radiative impact of black carbon (BC), the refractive index and shape dependent scattering and absorption characteristics must be known. At present, the assumed shape remains highly uncertain because BC particles are fractal-like, being agglomerates of smaller (20-40 nm) spherules, yet traditional optical models such as Mie theory typically assume a spherical particle morphology. To investigate the ability of various optical models to reproduce observed BC optical properties, we measured light absorption and extinction coefficients of methane and ethylene flame soot particles. Optical properties were measured by multiple instruments: absorption by a dual cavity ringdown photoacoustic spectrometer (CRD-PAS), absorption and scattering by a 3-wavelength photoacoustic/nephelometer spectrometer (PASS-3) and extinction and scattering by a cavity attenuated phase shift spectrometer (CAPS). Soot particle mass was quantified using a centrifugal particle mass analyzer (CPMA) and mobility size was measured with a scanning mobility particle sizer (SMPS). Measurements were made for nascent soot particles and for collapsed soot particles following coating with dioctyl sebacate or sulfuric acid and thermal denuding to remove the coating. Wavelength-dependent refractive indices for the sampled particles were derived by fitting the observed absorption and extinction cross-sections to spherical particle Mie theory and Rayleigh-Debye-Gans theory. The Rayleigh-Debye-Gans approximation assumes that the absorption properties of soot are dictated by the individual spherules and neglects interaction between them. In general, Mie theory reproduces the observed absorption and extinction cross-sections for particles with volume equivalent diameters (VED) < ~160 nm, but systematically predicts lower absorption cross-sections relative to observations for larger particles with VED > ~160 nm. The discrepancy is most pronounced for measurements made at shorter wavelengths. In contrast, Rayleigh-Debye-Gans theory, which does not assume spherical particle morphology, exhibited good agreement with the observations for all particle diameters and wavelengths. These results indicate that the use of Mie theory to describe the absorption behavior of particles >160 nm VED will underestimate the absorption by these particles. Concurrent measurements of the absorption Angstrom exponent and the single scattering albedo, and their dependence on particle size, will also be discussed.

Refractive index gradient measurement across the thickness of a dielectric film by the prism coupling method

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

Sokolov, Viktor I; Panchenko, Vladislav Ya; Seminogov, V N

2012-08-31

A method is proposed for measuring the refractive index gradient n(z) in nonuniformly thick dielectric films. The method is based on the excitation of waveguide modes in a film using the prism coupling technique and on the calculation of n(z) and film thickness H{sub f} with the help of the angular positions of the TE or TM modes. The method can be used for an arbitrary shape of the index modulation over the film thickness in the limit of a small gradient [{Delta} n(z)/n(z) || 1]. (laser applications and other topics in quantum electronics)

Photothermoplastic recording media and its application in the holographic method of determination of the refractive index of liquid objects.

PubMed

Davidenko, N A; Davidenko, I I; Pavlov, V A; Chuprina, N G; Kravchenko, V V; Kuranda, N N; Mokrinskaya, E V; Studzinsky, S L

2018-03-10

The photothermoplastic medium based on the films of photosensitive polymeric composites with semiconductor properties is developed for application in optical information recording and storage, in holographic interferometry, as well as for medical purposes. This medium was used in the modified holographic device for determination of changes of the refractive index of homogeneous and inhomogeneous liquid objects. The technique and holographic equipment were modified by employing the specially developed and produced transparent cuvette of special shape and the phase shifting interferometry method. Experimentally demonstrated precision of the measurements is not less than 10 -5 .

Real refractive indices of infrared-characterized nitric-acid/ice films: Implications for optical measurements of polar stratospheric clouds

NASA Technical Reports Server (NTRS)

Middlebrook, Ann M.; Berland, Brian S.; George, Steven M.; Tolbert, Margaret A.; Toon, Owen B.

1994-01-01

The infrared spectra of nitric-acid/ice films representative of polar stratospheric clouds (PSCs) were collected with simultaneous optical interference measurements to determine the real refractive indices at lambda = 632 nm. Ice and amphorous nitric-acid/ice films were prepared by condensation of water and nitric acid vapors onto a wedged Al2O3 substrate. The real refractive indices of these films were determined from the optical interference of a reflected helium-neon laser during film growth. The indices of the amphorous films varied smoothly from n = 1.30 for ice to n = 1.49 for nitric acid, similar to observations in previous work. We were unable to obtain the refractive index of crystlline films during adsorption because of optical scattering caused by surface roughness. Therefore crystlline nitric acid hydrate films were prepared by annealing amphorous nitric-acid/ice films. Further heating caused desorption of the crystalline hydrate films. During desorption, the refractive indices for ice, NAM (nitric acid monohydrate), alpha- and beta-NAT (nitric acid trihydrate) films were measured using the optical interference technique. In agreement with earlier data, the real refractive indices for ice and NAM determined in desorption were n = 1.30 +/- 0.01 and n = 1.53 +/- 0.03, respectively. The real refractive indices for alpha- and beta-NAT were found to be n = 1.51 +/- 0.01 and n greater than or equal to 1.46, respectively. Our measurements also suggest that the shape of crystalline nitric acid particles may depend on whether they nucleate from the liquid or by vapor deposition. If confirmed by future studies, this observation may provide a means of distinguishing the nucleation mechanism of crystalline PSCs.

chroma: Chromatic effects for LSST weak lensing

NASA Astrophysics Data System (ADS)

Meyers, Joshua E.; Burchat, Patricia R.

2018-04-01

Chroma investigates biases originating from two chromatic effects in the atmosphere: differential chromatic refraction (DCR), and wavelength dependence of seeing. These biases arise when using the point spread function (PSF) measured with stars to estimate the shapes of galaxies with different spectral energy distributions (SEDs) than the stars.

Even Illumination from Fiber-Optic-Coupled Laser Diodes

NASA Technical Reports Server (NTRS)

Howard, Richard T.

2006-01-01

A method of equipping fiber-optic-coupled laser diodes to evenly illuminate specified fields of view has been proposed. The essence of the method is to shape the tips of the optical fibers into suitably designed diffractive optical elements. One of the main benefits afforded by the method would be more nearly complete utilization of the available light. Diffractive optics is a relatively new field of optics in which laser beams are shaped by use of diffraction instead of refraction.

Transverse writing of three-dimensional tubular optical waveguides in glass with a slit-shaped femtosecond laser beam

PubMed Central

Liao, Yang; Qi, Jia; Wang, Peng; Chu, Wei; Wang, Zhaohui; Qiao, Lingling; Cheng, Ya

2016-01-01

We report on fabrication of tubular optical waveguides buried in ZBLAN glass based on transverse femtosecond laser direct writing. Irradiation in ZBLAN with focused femtosecond laser pulses leads to decrease of refractive index in the modified region. Tubular optical waveguides of variable mode areas are fabricated by forming the four sides of the cladding with slit-shaped femtosecond laser pulses, ensuring single mode waveguiding with a mode field dimension as small as ~4 μm. PMID:27346285

Generation of an ultra-flexible focused top-hat beam profile with aspheres

NASA Astrophysics Data System (ADS)

Möhl, A.; Wickenhagen, S.; Fuchs, U.

2017-02-01

The demand for a uniform intensity distribution in the focal region of the working beam is growing steadily, especially in the field of laser material processing. To generate such a top-hat beam profile, it was shown in the past, that the use of refractive beam shaping solutions provides very good results. In this work, existing beam shaping knowledge is combined with an intelligent modular approach to create a new beam shaping solution, that simplifies both, handling and integration into existing set-ups. Furthermore, the present system enables not just a flattop intensity distribution, but even donut shaped beam profile without adding any further components to the system. Additionally, this beam shaping system is built and successfully tested. Some results of the characterization are presented.

Multi-Instrument Manager Tool for Data Acquisition and Merging of Optical and Electrical Mobility Size Distributions

NASA Astrophysics Data System (ADS)

Tritscher, Torsten; Koched, Amine; Han, Hee-Siew; Filimundi, Eric; Johnson, Tim; Elzey, Sherrie; Avenido, Aaron; Kykal, Carsten; Bischof, Oliver F.

2015-05-01

Electrical mobility classification (EC) followed by Condensation Particle Counter (CPC) detection is the technique combined in Scanning Mobility Particle Sizers(SMPS) to retrieve nanoparticle size distributions in the range from 2.5 nm to 1 μm. The detectable size range of SMPS systems can be extended by the addition of an Optical Particle Sizer(OPS) that covers larger sizes from 300 nm to 10 μm. This optical sizing method reports an optical equivalent diameter, which is often different from the electrical mobility diameter measured by the standard SMPS technique. Multi-Instrument Manager (MIMTM) software developed by TSI incorporates algorithms that facilitate merging SMPS data sets with data based on optical equivalent diameter to compile single, wide-range size distributions. Here we present MIM 2.0, the next-generation of the data merging tool that offers many advanced features for data merging and post-processing. MIM 2.0 allows direct data acquisition with OPS and NanoScan SMPS instruments to retrieve real-time particle size distributions from 10 nm to 10 μm, which we show in a case study at a fireplace. The merged data can be adjusted using one of the merging options, which automatically determines an overall aerosol effective refractive index. As a result an indirect and average characterization of aerosol optical and shape properties is possible. The merging tool allows several pre-settings, data averaging and adjustments, as well as the export of data sets and fitted graphs. MIM 2.0 also features several post-processing options for SMPS data and differences can be visualized in a multi-peak sample over a narrow size range.

Raman spectra and optical trapping of highly refractive and nontransparent particles

NASA Astrophysics Data System (ADS)

Xie, Changan; Li, Yong-qing

2002-08-01

We measured the Raman spectra of single optically trapped highly refractive and nontransparent microscopic particles suspended in a liquid using an inverted confocal laser-tweezers-Raman-spectroscopy system. A low-power diode-laser beam of TEM00 mode was used both for optical trapping and Raman excitation of refractive, absorptive, and reflective metal particles. To form a stable trap for a nontransparent particle, the beam focus was located near the top of the particle and the particle was pushed against a glass plate by the axial repulsive force. Raman spectra from single micron-sized crystals with high index of refraction including silicon, germanium, and KNbO3, and from absorptive particles of black and color paints were recorded. Surface-enhanced Raman scattering of R6G and phenylalanine molecules absorbed on the surface of a trapped cluster of silver particles was also demonstrated.

Single-shot Z(eff) dense plasma diagnostic through simultaneous refraction and attenuation measurements with a Talbot-Lau x-ray moiré deflectometer.

PubMed

Valdivia, M P; Stutman, D; Finkenthal, M

2015-04-01

The Talbot-Lau x-ray moiré deflectometer is a powerful plasma diagnostic capable of delivering simultaneous refraction and attenuation information through the accurate detection of x-ray phase shift and intensity. The diagnostic can provide the index of refraction n=1-δ+iβ of an object (dense plasma, for example) placed in the x-ray beam by independently measuring both δ and β, which are directly related to the electron density n(e) and the attenuation coefficient μ, respectively. Since δ and β depend on the effective atomic number Z(eff), a map can be obtained from the ratio between phase and absorption images acquired in a single shot. The Talbot-Lau x-ray moiré deflectometer and its corresponding data acquisition and processing are briefly described to illustrate how the above is achieved; Z(eff) values of test objects within the 4-12 range were obtained experimentally through simultaneous refraction and attenuation measurements. We show that Z(eff) mapping of objects does not require previous knowledge of sample length or shape. The determination of Z(eff) from refraction and attenuation measurements with moiré deflectometry could be of high interest to various domains of high energy density research, such as shocked materials and inertial confinement fusion experiments, as well as material science and nondestructive testing.

Simplified mathematics for customized refractive surgery.

PubMed

Preussner, Paul Rolf; Wahl, Jochen

2003-03-01

To describe a simple mathematical approach to customized corneal refractive surgery or customized intraocular lens (IOL) design that allows "hypervision" and to investigate the accuracy limits. University eye hospital, Mainz, Germany. Corneal shape and at least 1 IOL surface are approximated by the well-known Cartesian conic section curves (ellipsoid, paraboloid, or hyperboloid). They are characterized by only 2 parameters, the vertex radius and the numerical eccentricity. Residual refraction errors for this approximation are calculated by numerical ray tracing. These errors can be displayed as a 2-dimensional refraction map across the pupil or by blurring the image of a Landolt ring superimposed on the retinal receptor grid, giving an overall impression of the visual outcome. If the eye is made emmetropic for paraxial rays and if the numerical eccentricities of the cornea and lens are appropriately fitted to each other, the residual refractive errors are small enough to allow hypervision. Visual acuity of at least 2.0 (20/10) appears to be possible, particularly for mesopic pupil diameters. However, customized optics may have limited application due to their sensitivity to misalignment errors such as decentrations or rotations. The mathematical approach described by Descartes 350 years ago is adequate to calculate hypervision optics for the human eye. The availability of suitable mathematical tools should, however, not be viewed with too much optimism as long as the accuracy of the implementation in surgical procedures is limited.

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.

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.

Using InterWave Aberrometry to Measure and Improve the Quality of Vision in LASIK Surgery

PubMed Central

Thompson, Keith P.; Staver, P. Randall; Garcia, Jose R.; Burns, Stephen A.; Webb, Robert H.; Stulting, R. Doyle

2005-01-01

Objective To compare visual outcomes in eyes undergoing aberrometry-guided (InterWave) LASIK with those in eyes undergoing standard LASIK treatment based upon refractive measures. Design Single-center, comparative, interventional, consecutive case series. Participants Four hundred two consecutive eyes undergoing LASIK were analyzed retrospectively. One group, 106 eyes undergoing primary LASIK and 224 eyes undergoing LASIK enhancement, was treated with standard LASIK treatment using a 5.5-mm optical zone, 1.5-mm transition zone laser with the settings determined by manifest refraction. The second group, 44 untreated (primary) eyes and 28 previously treated (enhancement) eyes, received a multipass, multistage treatment in which the laser settings for each stage were determined by aberrometry measurements. Eyes with desired monovision (undercorrected) outcome and preoperative hyperopia were excluded from the study. Intervention An aberrometry-guided laser treatment (InterWave LASIK) was compared with the standard LASIK treatment based upon the manifest refraction. Main Outcome Measures Uncorrected visual acuity (VA), manifest refraction, best spectacle-corrected VA (BSCVA), severity of halos, and root mean square (RMS) retinal blur area measured at 3 months postoperatively. Results Three months postoperatively there was no difference in uncorrected VA, BSCVA, refraction, or RMS retinal blur areas for pupil sizes of 3.5 mm between eyes treated by InterWave and those treated by standard LASIK. However, InterWave LASIK reduced the retinal blur area by 48% (P<0.0103) and 58% (P<0.0004) in primary cases and 43% (P<0.0430) and 74% (P<0.0271) in enhancement cases, respectively, for pupil sizes of 4.5 and 6.5 mm relative to standard LASIK treatments. Patients undergoing InterWave-guided treatment reported less severity of halo (0.37 vs. 0.98 [P<0.016] for primary cases and 0.35 vs. 0.73 [P<0.04] for enhancement cases). Conclusion InterWave LASIK achieved acuity and refractive results equivalent to those of standard LASIK treatment based upon refraction, but resulted in superior quality mesopic vision. PMID:15234139

Prevalence and pattern of refractive errors among primary school children in Al Hassa , Saudi Arabia.

PubMed

Al Wadaani, Fahd Abdullah; Amin, Tarek Tawfik; Ali, Ayub; Khan, Atuar Rahman

2012-11-11

Some 12.8 million in the age group 5-15 years are visually impaired from uncorrected or inadequately corrected refractive errors. In Saudi Arabia, the size of this public health problem is not well defined especially among primary schoolchildren. The purpose of this cross-sectional study was to assess the prevalence and pattern of refractive errors among primary school children in Al Hassa, Saudi Arabia.  A total of 2246 Saudi primary school children aged 6 to 14 years of both genders were selected using multistage sampling method form 30 primary schools located in the three different areas of Al Hassa. School children were interviewed to collect demographics and vision data using a special data collection form followed by screening for refractive errors by trained optometrists within the school premises using a standardized protocol. Assessment of visual acuity and ocular motility evaluation were carried out and cover-uncover test was performed. Children detected with defective vision were referred for further examination employing subjective refraction with auto refractometer and objective refraction using streak retinoscopy after 1% cyclopentolate. Of the screened school children (N=2002), the overall prevalence of refractive errors was 13.7% (n=274), higher among females (Odds ratio, OR=1.39, P=0.012) and significantly more among students of rural residence (OR=2.40, P=0.001). The prevalence of refractive errors was disproportionately more among those aged 12-14 years (OR=9.02, P=0.001). Only 9.4% of students with poor vision were wore spectacles for correction. Myopia was the most commonly encountered refractive error among both genders (65.7% of the total errors encountered). Uncorrected refractive errors affected a sizable portion of primary school children in Al Hassa, Saudi Arabia. Primary schoolchildren especially females, rural and older children represents high risk group for refractive errors for which the included children were unaware.

Prevalence and Pattern of Refractive Errors among Primary School Children in Al Hassa, Saudi Arabia

PubMed Central

Wadaani, Fahd Abdullah Al; Amin, Tarek Tawfik; Ali, Ayub; Khan, Ataur Rahman

2013-01-01

Some 12.8 million in the age group 5–15 years are visually impaired from uncorrected or inadequately corrected refractive errors. In Saudi Arabia, the size of this public health problem is not well defined especially among primary schoolchildren. The purpose of this cross-sectional study was to assess the prevalence and pattern of refractive errors among primary school children in Al Hassa, Saudi Arabia. A total of 2246 Saudi primary school children aged 6 to 14 years of both genders were selected using multistage sampling method form 30 primary schools located in the three different areas of Al Hassa. School children were interviewed to collect demographics and vision data using a special data collection form followed by screening for refractive errors by trained optometrists within the school premises using a standardized protocol. Assessment of visual acuity and ocular motility evaluation were carried out and cover-uncover test was performed. Children detected with defective vision were referred for further examination employing subjective refraction with auto refractometer and objective refraction using streak retinoscopy after 1% cyclopentolate. Of the screened school children (N=2002), the overall prevalence of refractive errors was 13.7% (n=274), higher among females (Odds ratio, OR=1.39, P=0.012) and significantly more among students of rural residence (OR=2.40, P=0.001). The prevalence of refractive errors was disproportionately more among those aged 12-14 years (OR=9.02, P=0.001). Only 9.4% of students with poor vision were wore spectacles for correction. Myopia was the most commonly encountered refractive error among both genders (65.7% of the total errors encountered). Uncorrected refractive errors affected a sizable portion of primary school children in Al Hassa, Saudi Arabia. Primary schoolchildren especially females, rural and older children represents high risk group for refractive errors for which the included children were unaware. PMID:23283044

Calibration correction of an active scattering spectrometer probe to account for refractive index of stratospheric aerosols

NASA Technical Reports Server (NTRS)

Pueschel, R. F.; Overbeck, V. R.; Snetsinger, K. G.; Russell, P. B.; Ferry, G. V.

1990-01-01

The use of the active scattering spectrometer probe (ASAS-X) to measure sulfuric acid aerosols on U-2 and ER-2 research aircraft has yielded results that are at times ambiguous due to the dependence of particles' optical signatures on refractive index as well as physical dimensions. The calibration correction of the ASAS-X optical spectrometer probe for stratospheric aerosol studies is validated through an independent and simultaneous sampling of the particles with impactors; sizing and counting of particles on SEM images yields total particle areas and volumes. Upon correction of calibration in light of these data, spectrometer results averaged over four size distributions are found to agree with similarly averaged impactor results to within a few percent: indicating that the optical properties or chemical composition of the sample aerosol must be known in order to achieve accurate optical aerosol spectrometer size analysis.

Nanocrystal doped matrixes

DOEpatents

Parce, J. Wallace; Bernatis, Paul; Dubrow, Robert; Freeman, William P.; Gamoras, Joel; Kan, Shihai; Meisel, Andreas; Qian, Baixin; Whiteford, Jeffery A.; Ziebarth, Jonathan

2010-01-12

Matrixes doped with semiconductor nanocrystals are provided. In certain embodiments, the semiconductor nanocrystals have a size and composition such that they absorb or emit light at particular wavelengths. The nanocrystals can comprise ligands that allow for mixing with various matrix materials, including polymers, such that a minimal portion of light is scattered by the matrixes. The matrixes of the present invention can also be utilized in refractive index matching applications. In other embodiments, semiconductor nanocrystals are embedded within matrixes to form a nanocrystal density gradient, thereby creating an effective refractive index gradient. The matrixes of the present invention can also be used as filters and antireflective coatings on optical devices and as down-converting layers. Processes for producing matrixes comprising semiconductor nanocrystals are also provided. Nanostructures having high quantum efficiency, small size, and/or a narrow size distribution are also described, as are methods of producing indium phosphide nanostructures and core-shell nanostructures with Group II-VI shells.

Detection range enhancement using circularly polarized light in scattering environments for infrared wavelengths

DOE PAGES

van der Laan, J. D.; Sandia National Lab.; Scrymgeour, D. A.; ...

2015-03-13

We find for infrared wavelengths there are broad ranges of particle sizes and refractive indices that represent fog and rain where the use of circular polarization can persist to longer ranges than linear polarization. Using polarization tracking Monte Carlo simulations for varying particle size, wavelength, and refractive index, we show that for specific scene parameters circular polarization outperforms linear polarization in maintaining the intended polarization state for large optical depths. This enhancement with circular polarization can be exploited to improve range and target detection in obscurant environments that are important in many critical sensing applications. Specifically, circular polarization persists bettermore » than linear for radiation fog in the short-wave infrared, for advection fog in the short-wave infrared and the long-wave infrared, and large particle sizes of Sahara dust around the 4 micron wavelength.« less

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.

Beam shaping to provide round and square-shaped beams in optical systems of high-power lasers

NASA Astrophysics Data System (ADS)

Laskin, Alexander; Laskin, Vadim

2016-05-01

Optical systems of modern high-power lasers require control of irradiance distribution: round or square-shaped flat-top or super-Gaussian irradiance profiles are optimum for amplification in MOPA lasers and for thermal load management while pumping of crystals of solid-state ultra-short pulse lasers to control heat and minimize its impact on the laser power and beam quality while maximizing overall laser efficiency, variable profiles are also important in irradiating of photocathode of Free Electron lasers (FEL). It is suggested to solve the task of irradiance re-distribution using field mapping refractive beam shapers like piShaper. The operational principle of these devices presumes transformation of laser beam intensity from Gaussian to flat-top one with high flatness of output wavefront, saving of beam consistency, providing collimated output beam of low divergence, high transmittance, extended depth of field, negligible residual wave aberration, and achromatic design provides capability to work with ultra-short pulse lasers having broad spectrum. Using the same piShaper device it is possible to realize beams with flat-top, inverse Gauss or super Gauss irradiance distribution by simple variation of input beam diameter, and the beam shape can be round or square with soft edges. This paper will describe some design basics of refractive beam shapers of the field mapping type and optical layouts of their applying in optical systems of high-power lasers. Examples of real implementations and experimental results will be presented as well.

In vivo flow cytometry for blood cell analysis using differential epi-detection of forward scattered light

NASA Astrophysics Data System (ADS)

Paudel, Hari P.; Jung, Yookyung; Raphael, Anthony; Alt, Clemens; Wu, Juwell; Runnels, Judith; Lin, Charles P.

2018-02-01

The present standard of blood cell analysis is an invasive procedure requiring the extraction of patient's blood, followed by ex-vivo analysis using a flow cytometer or a hemocytometer. We are developing a noninvasive optical technique that alleviates the need for blood extraction. For in-vivo blood analysis we need a high speed, high resolution and high contrast label-free imaging technique. In this proceeding report, we reported a label-free method based on differential epi-detection of forward scattered light, a method inspired by Jerome Mertz's oblique back-illumination microscopy (OBM) (Ford et al, Nat. Meth. 9(12) 2012). The differential epi-detection of forward light gives phase contrast image at diffraction-limited resolution. Unlike reflection confocal microscopy (RCM), which detects only sharp refractive index variation and suffers from speckle noise, this technique is suitable for detection of subtle variation of refractive index in biological tissue and it provides the shape and the size of cells. A custom built high speed electronic detection circuit board produces a real-time differential signal which yields image contrast based on phase gradient in the sample. We recorded blood flow in-vivo at 17.2k lines per second in line scan mode, or 30 frames per second (full frame), or 120 frame per second (quarter frame) in frame scan mode. The image contrast and speed of line scan data recording show the potential of the system for noninvasive blood cell analysis.

Childhood exposure to constricted living space: a possible environmental threat for myopia development.

PubMed

Choi, Kai Yip; Yu, Wing Yan; Lam, Christie Hang I; Li, Zhe Chuang; Chin, Man Pan; Lakshmanan, Yamunadevi; Wong, Francisca Siu Yin; Do, Chi Wai; Lee, Paul Hong; Chan, Henry Ho Lung

2017-09-01

People in Hong Kong generally live in a densely populated area and their homes are smaller compared with most other cities worldwide. Interestingly, East Asian cities with high population densities seem to have higher myopia prevalence, but the association between them has not been established. This study investigated whether the crowded habitat in Hong Kong is associated with refractive error among children. In total, 1075 subjects [Mean age (S.D.): 9.95 years (0.97), 586 boys] were recruited. Information such as demographics, living environment, parental education and ocular status were collected using parental questionnaires. The ocular axial length and refractive status of all subjects were measured by qualified personnel. Ocular axial length was found to be significantly longer among those living in districts with a higher population density (F 2,1072  = 6.15, p = 0.002) and those living in a smaller home (F 2,1072  = 3.16, p = 0.04). Axial lengths were the same among different types of housing (F 3,1071  = 1.24, p = 0.29). Non-cycloplegic autorefraction suggested a more negative refractive error in those living in districts with a higher population density (F 2,1072  = 7.88, p < 0.001) and those living in a smaller home (F 2,1072  = 4.25, p = 0.02). After adjustment for other confounding covariates, the population density and home size also significantly predicted axial length and non-cycloplegic refractive error in the multiple linear regression model, while axial length and refractive error had no relationship with types of housing. Axial length in children and childhood refractive error were associated with high population density and small home size. A constricted living space may be an environmental threat for myopia development in children. © 2017 The Authors Ophthalmic & Physiological Optics © 2017 The College of Optometrists.

Reflecting anastigmatic optical systems: a retrospective

NASA Astrophysics Data System (ADS)

Rakich, Andrew

2017-11-01

Reflecting anastigmatic optical systems hold several inherent advantages over refracting equivalents; such as compactness, absence of color, high "refractive efficiency", wide bandwidth, and size-scalability to enormous apertures. Such advantages have led to these systems becoming, increasingly since their first deliberate development in 1905, the "go-to" solution for various classes of optical design problem. This paper describes in broad terms the history of the development of this class of optical system, with an emphasis on the early history.

A Soft 3D Acoustic Metafluid with Dual-Band Negative Refractive Index.

PubMed

Raffy, Simon; Mascaro, Benoit; Brunet, Thomas; Mondain-Monval, Olivier; Leng, Jacques

2016-03-02

Spherical silica xerogels are efficient acoustic Mie resonators. When these sub-wavelength inclusions are dispersed in a matrix, the final metafluid may display a negative acoustic refractive index upon a set of precise constraints concerning material properties, concentration, size, and dispersity of the inclusions. Because xerogels may sustain both pressure and shear waves, several bands with negative index can be tailored. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Refractive waveguide non-mechanical beam steering (NMBS) in the MWIR

NASA Astrophysics Data System (ADS)

Myers, Jason D.; Frantz, Jesse A.; Spillmann, Christopher M.; Bekele, Robel Y.; Kolacz, Jakub; Gotjen, Henry; Naciri, Jawad; Shaw, Brandon; Sanghera, Jas S.

2018-02-01

Beam steering is a crucial technology for a number of applications, including chemical sensing/mapping and light detection and ranging (LIDAR). Traditional beam steering approaches rely on mechanical movement, such as the realignment of mirrors in gimbal mounts. The mechanical approach to steering has several drawbacks, including large size, weight and power usage (SWAP), and frequent mechanical failures. Recently, alternative non-mechanical approaches have been proposed and developed, but these technologies do not meet the demanding requirements for many beam steering applications. Here, we highlight the development efforts into a particular non-mechanical beam steering (NMBS) approach, refractive waveguides, for application in the MWIR. These waveguides are based on an Ulrich-coupled slab waveguide with a liquid crystal (LC) top cladding; by selectively applying an electric field across the liquid crystal through a prismatic electrode, steering is achieved by creating refraction at prismatic interfaces as light propagates through the device. For applications in the MWIR, we describe a versatile waveguide architecture based on chalcogenide glasses that have a wide range of refractive indices, transmission windows, and dispersion properties. We have further developed robust shadow-masking methods to taper the subcladding layers in the coupling region. We have demonstrated devices with >10° of steering in the MWIR and a number of advantageous properties for beam steering applications, including low-power operation, compact size, and fast point-to-point steering.

Clinical features of subepithelial layer irregularities of cornea.

PubMed

Lee, Yong Woo; Gye, Hyo Jung; Choi, Chul Young

2015-07-01

To illustrate surgical outcomes of subepithelial irregularities that were identified incidentally during laser refractive surgery. The study group consisted of 406 patients who underwent 787 surface ablation refractive surgeries. Ophthalmologic evaluations were performed before each procedure and at 1, 3 and 6 months post-operatively. Subepithelial irregularities were evaluated by analyzing still photographs captured from video recordings. Sizes and locations were determined by a calibrated scale located at the major axis of the tracking system's reticle. Subepithelial irregularities were identified in 27 eyes during 787 surface ablation refractive surgeries. Most of the subepithelial irregularities did not show any abnormalities in the wavefront aberrometer. However, one case with diameter greater than 1.00 mm and one case of clustered multiple subepithelial irregularities with moderate size were corresponded significant coma (Z31) and increased higher order aberration (HOA) in the HOA gradient map. Corneal subepithelial irregularities may be related to problems that include significantly increased localized HOA and remaining permanent subepithelial opacity. Subepithelial irregularity should be considered even if the surface of the cornea is intact and there are no specific findings measured by corneal topography.

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.

Terahertz multistatic reflection imaging.

PubMed

Dorney, Timothy D; Symes, William W; Baraniuk, Richard G; Mittleman, Daniel M

2002-07-01

We describe a new imaging method using single-cycle pulses of terahertz (THz) radiation. This technique emulates the data collection and image processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a migration procedure to solve the inverse problem; this permits us to reconstruct the location, the shape, and the refractive index of targets. We show examples for both metallic and dielectric model targets, and we perform velocity analysis on dielectric targets to estimate the refractive indices of imaged components. These results broaden the capabilities of THz imaging systems and also demonstrate the viability of the THz system as a test bed for the exploration of new seismic processing methods.

Refraction seismic studies in the Miami River, Whitewater River, and Mill Creek valleys, Hamilton and Butler Counties, Ohio

USGS Publications Warehouse

Watkins, Joel S.

1963-01-01

Between September 17 and November 9, 1962, the U.S. Geological Survey, in cooperation with Ohio Division of Water, Miami Conservancy District, and c,ty of Cincinnati, Ohio, co.,:ducted a refraction seismic study in Hamilton and Butler Counties, southwest Ohio. The area lies between Hamilton, Ohio, and the Ohio River and includes a preglacial valley now occupied by portions of the Miami River, Whitewater River, and Mill Creek. The valley is partially filled with glacial debris which yields large quantities of good-quality water. The object of the study was to determine the thickness of these glacial deposits and the shape of the preglacial valley.

Optical characterization of extremely small volumes of liquid in sub-micro-holes by simultaneous reflectivity, ellipsometry and spectrometry.

PubMed

Holgado, M; Casquel, R; Sánchez, B; Molpeceres, C; Morales, M; Ocaña, J L

2007-10-01

We have fabricated and characterized a lattice of submicron cone-shaped holes on a SiO(2)/Si wafer. Reflectivity profiles as a function of angle of incidence and polarization, phase shift and spectrometry are obtained for several fluids with different refractive indexes filling the holes. The optical setup allows measuring in the center of a single hole and collecting all data simultaneously, which can be applied for measuring extremely low volumes of fluid (in the order of 0.1 femtolitres) and label-free immunoassays, as it works as a refractive index sensor. A three layer film stack model is defined to perform theoretical calculations.

Analytical transmission cross-coefficients for pink beam X-ray microscopy based on compound refractive lenses.

PubMed

Falch, Ken Vidar; Detlefs, Carsten; Snigirev, Anatoly; Mathiesen, Ragnvald H

2018-01-01

Analytical expressions for the transmission cross-coefficients for x-ray microscopes based on compound refractive lenses are derived based on Gaussian approximations of the source shape and energy spectrum. The effects of partial coherence, defocus, beam convergence, as well as lateral and longitudinal chromatic aberrations are accounted for and discussed. Taking the incoherent limit of the transmission cross-coefficients, a compact analytical expression for the modulation transfer function of the system is obtained, and the resulting point, line and edge spread functions are presented. Finally, analytical expressions for optimal numerical aperture, coherence ratio, and bandwidth are given. Copyright © 2017 Elsevier B.V. All rights reserved.

Building achromatic refractive beam shapers

NASA Astrophysics Data System (ADS)

Laskin, Alexander; Shealy, David

2014-10-01

Achromatic beam shapers can provide beam shaping in a certain spectral band and are very important for various laser techniques, such as, applications based on ultra-short pulse lasers with pulse width <100 fs, confocal microscopy, multicolour holography, life sciences fluorescence techniques, where several lasers in spectrum 405-650 nm are used simultaneously, for example 405-650 nm. Conditions of energy re-distribution and zero wave aberration are strictly fulfilled in ordinary plano-aspheric lens pair beam shapers for a definite wavelength only. Hence, these beam shapers work efficiently in relatively narrow, few nm spectrum. To provide acceptable beam quality for refractive beam shaping over a wide spectrum, an achromatizing design condition should be added. Consequently, the typical beam shaper design contains more than two-lenses, to avoid any damaging and other undesirable effects the lenses of beam shaper should be air-spaced. We suggest a two-step method of designing the beam shaper: 1) achromatizing of each plano-aspheric lens using a buried achromatizing surface ("chromatic radius"), then each beam shaper component presents a cemented doublet lens, 2) "splitting" the cemented lenses and realizing air-spaced lens design using optical systems design software. This method allows for using an achromatic design principle during the first step of the design, and then, refining the design by using optimization software. We shall present examples of this design procedure for an achromatic Keplerian beam shaper and for the design of an achromatic Galilean type of beam shaper. Experimental results of operation of refractive beam shapers will be presented as well.

Optical characterization of a low solubility organic compound.

PubMed

Huber, H E

1981-10-01

The X, Y, and Z principal vibration directions along with the principal refractive indexes, optic angle, optical sign, birefringence, optical orientation, and crystal system for the low solubility compound 5-(tetradecyloxy)-2-furancarboxylic acid were determined with a polarizing microscope and spindle stage. The X and Z principal vibration directions are not coincident with the a and c crystallographic axes; however, the Y direction is considered to be coincident with the b axis. Therefore, the crystal is assigned to the monoclinic crystal system. The bladed/lath-shaped crystals rest on one of the two large orthopinacoid (100) faces and present the microscopist with a single plane of optical symmetry. A beta refractive index of 1.555 is observed with the crystal axis of elongation parallel to the polarizer, and a gamma of 1.600-1.660 is observed in the contiguous extinction position. Determination of the optic angle principal vibration directions, and principal refractive indexes was facilitated by mounting the crystals on a spindle stage for rotation about the b crystallographic axis (optic normal).

Diffractive-refractive optics: X-ray splitter.

PubMed

Hrdý, Jaromír

2010-01-01

The possibility of splitting a thin (e.g. undulator) X-ray beam based on diffraction-refraction effects is discussed. The beam is diffracted from a crystal whose diffracting surface has the shape of a roof with the ridge lying in the plane of diffraction. The crystal is cut asymmetrically. One half of the beam impinges on the left-hand part of the roof and the other half impinges on the right-hand side of the roof. Owing to refraction the left part of the beam is deviated to the left whereas the right part is deviated to the right. The device proposed consists of two channel-cut crystals with roof-like diffraction surfaces; the crystals are set in a dispersive position. The separation of the beams after splitting is calculated at a distance of 10 m from the crystals for various asymmetry and inclination angles. It is shown that such a splitting may be utilized for long beamlines. Advantages and disadvantages of this method are discussed.

Saw-tooth refractive x-ray optics with sub-micron resolution

NASA Astrophysics Data System (ADS)

Cederstrom, Bjorn; Ribbing, Carolina; Lundqvist, Mats

2002-11-01

Saw-tooth refractive x-ray lenses have been used to focus a synchrotron beam to sub-μm line width. These lenses are free from spherical aberration and work in analogy with 1-D focusing parabolic compound refractive lenses. However, the focal length can be varied by a simple mechanical procedure. Silicon lenses were fabricated by wet anisotropic etching, and epoxy replicas were molded from the silicon masters. Theses lenses provided 1-D intensity gains up to a factor of 40 and the smallest focal line width was 0.74 μm, very close to the theoretical expectation. Two crossed lenses were put in series to obtain 2-D focusing and the 80 μm by 275 μm source was imaged to 1.0 μm by 5.4 μm. Beryllium lenses were fabricated using conventional computer-controlled milling. The focal line width was 1.7 μm, nearly 3 times larger than predicted by theory. This can be attributed to large surface roughness and a bent lens shape.

Thin metal bilayer for surface plasmon resonance sensors in a multimode plastic optical fiber: the case of palladium and gold metal films

NASA Astrophysics Data System (ADS)

Cennamo, Nunzio; Zuppella, Paola; Bacco, Davide; Corso, Alain J.; Pelizzo, Maria G.; Pesavento, Maria; Zeni, Luigi

2016-05-01

A novel sensing platform based on thin metal bilayer for surface plasmon resonance (SPR) in a D-shaped plastic optical fiber (POF) has been designed, implemented and tested. The experimental results are congruent with the numerical studies. This platform has been properly optimized to work in the 1.38 -1.42 refractive index range and it exhibits excellent sensitivity. This refractive index range is very interesting for bio-chemical applications, where the polymer layer are used as receptors (e.g. molecularly imprinted polymer) or to immobilize the bio-receptor on the metal surface. The proposed metallic bilayer is based on palladium and gold films and replaces the traditional gold by exhibiting higher performances. Furthermore, the deposition of the thin bilayer is a single process and no further manufacturing step is required. In fact, in this case the photoresist buffer layer between the POF core and the metal layer, usually required to increase the refractive index range, is no longer necessary.

Rigorous description of holograms of particles illuminated by an astigmatic elliptical Gaussian beam

NASA Astrophysics Data System (ADS)

Yuan, Y. J.; Ren, K. F.; Coëtmellec, S.; Lebrun, D.

2009-02-01

The digital holography is a non-intrusive optical metrology and well adapted for the measurement of the size and velocity field of particles in the spray of a fluid. The simplified model of an opaque disk is often used in the treatment of the diagrams and therefore the refraction and the third dimension diffraction of the particle are not taken into account. We present in this paper a rigorous description of the holographic diagrams and evaluate the effects of the refraction and the third dimension diffraction by comparison to the opaque disk model. It is found that the effects are important when the real part of the refractive index is near unity or the imaginary part is non zero but small.

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.

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.

A field study of large-scale oscillation ripples in a very coarse-grained, high-energy marine environment

USGS Publications Warehouse

Hirschaut, D.W.; Dingler, J.R.

1982-01-01

Monastery Beach, Carmel, California is a pocket beach that sits within 200 m of the head of Carmel Submarine Canyon. Coarse to very coarse sand covers both the beach and adjacent shelf; in the latter area incoming waves have shaped the sand into large oscillation ripples. The accessibility of this area and a variable wave climate produce a unique opportunity to study large-scale coarse-grained ripples in a high-energy environment. These ripples, which only occur in very coarse sand, form under the intense, wave-generated currents that exist during storm conditions. Once formed, these ripples do not significantly change under lower energy waves. On three separate occasions scuba divers measured ripples and collected sand samples from ripple crests near fixed reference stakes along three transects. Ripple wavelength and grain size decreased with an increase in water depth. Sediment sorting was best closest to the surf zone and poorest at the rim of Carmel Canyon. Cobbles and gravel observed in ripple troughs represent lag deposits. Carmel Canyon refracts waves approaching Monastery Beach such that wave energy is focused towards the northern and southern portions of the beach, leaving the central part of the beach lower in energy. This energy distribution causes spatial variations in the ripples and grain sizes with the shortest wavelengths and smallest grain sizes being in the central part of the shelf.

Lamping process and application of ultra small U-shaped, whispery gallery mode (WGM) based optic fiber sensors

NASA Astrophysics Data System (ADS)

Chang, Yuan Cheng; Chiang, Chia Chin

2015-07-01

This study success to smaller and control the diameter of single mode optical fiber whispery gallery mode (WGM) to diameter 0.8 mm nonetching and nontaping treated. The sensitivity of this type ultra-small U-shape WGM strengthens neither etching nor taping fibre. The sensitivity we apply to thermo test depends on wavelength shift from 40 ~ 96°C (R2 = 0.99 ). The specially characteristics of the optical fiber could be tested for temperature, refraction, vibration, concussion, and CO2 detection.

The influence of thermal and free carrier dispersion effects on all-optical wavelength conversion in a silicon racetrack-shaped microring resonator

NASA Astrophysics Data System (ADS)

Wang, Zhaolu; Liu, Hongjun; Sun, Qibing; Huang, Nan; Li, Shaopeng; Han, Jing

2016-07-01

We experimentally demonstrate ultra-low pump power wavelength conversion based on four-wave mixing in a silicon racetrack-shaped microring resonator. When the pump and signal are located at the resonance wavelengths, wavelength conversion with a pump power of only 1 mW can be realized in this microring resonator because of the resonant enhancement of the device. However, saturation of the conversion efficiency occurs because of the shift of the resonance peak, which is caused by the change of the effective refractive index induced by a combination of thermal and free carrier dispersion effects, and it is demonstrated that the thermal effect is the leading-order factor for the change of the refractive index. The maximum conversion efficiency of  -21 dB is obtained when the pump power is less than 12 mW. This ultra-low-power on-chip wavelength convertor based on a silicon microring resonator can find important potential applications in highly integrated optical circuits for all-optical signal processing.

Ultraviolet Satellite Measurements of Volcanic Ash. Chapter 12

NASA Technical Reports Server (NTRS)

Carn, S. A.; Krotkov, N. A.

2016-01-01

Ultraviolet (UV) remote sensing of volcanic ash and other absorbing aerosols from space began with the launch of the first Total Ozone Mapping Spectrometer (TOMS) instrument in 1978. Subsequent UV satellite missions (TOMS, GOME, SCIAMACHY, OMI, GOME-2, OMPS) have extended UV ash measurements to the present, generating a unique multidecadal record. A UV Aerosol Index (UVAI) based on two near-UV wavelengths, equally applicable to multispectral (TOMS, DSCOVR) or hyperspectral (GOME, SCIAMACHY, OMI, GOME-2, OMPS) instruments, has been used to derive a unique absorbing aerosol climatology across multiple UV satellite missions. Advantages of UV ash measurements relative to infrared (IR) techniques include the ability to detect ash at any altitude (assuming no clouds), above clouds, and over bright surfaces, where visible and IR techniques may fail. Disadvantages include the daytime-only restriction and nonspecificity to silicate ash, since UV measurements are sensitive to any UV-absorbing aerosol, including smoke, desert dust, and pollution. However, simultaneous retrieval of sulfur dioxide (SO2) abundance and UVAI provides robust discrimination of volcanic clouds. Although the UVAI is only semiquantitative, it has proved successful at detecting and tracking volcanic ash clouds from many volcanic eruptions since 1978. NASA A-Train measurements since 2006 (eg, CALIOP) have provided much improved constraints on volcanic ash altitude, and also permit identification of aerosol type through sensor synergy. Quantitative UV retrievals of ash optical depth, effective particle size, and ash column mass are possible and require assumptions of ash refractive index, particle size distribution, and ash layer altitude. The lack of extensive ash refractive index data in the UV-visible and the effects of ash particle shape on retrievals introduce significant uncertainty in the retrieved parameters, although limited validation against IR ash retrievals has been successful. In this contribution, we review UV ash detection and retrieval techniques and provide examples of volcanic eruptions detected in the approx. 37 year data record.

Application of Scanning-Imaging X-Ray Microscopy to Fluid Inclusion Candidates in Carbonates of Carbonaceous Chondrites

NASA Technical Reports Server (NTRS)

Tsuchiyama, Akira; Nakano, Tsukasa; Miyake, Akira; Akihisa, Takeuchi; Uesugi, Kentaro; Suzuki, Yoshio; Kitayama, Akira; Matsuno, Junya; Zolensky, Michael E.

2016-01-01

In order to search for such fluid inclusions in carbonaceous chondrites, a nondestructive technique using x-ray micro-absorption tomography combined with FIB sampling was developed and applied to a carbonaceous chondrite. They found fluid inclusion candidates in calcite grains, which were formed by aqueous alteration. However, they could not determine whether they are really aqueous fluids or merely voids. Phase and absorption contrast images can be simultaneously obtained in 3D by using scanning-imaging x-ray microscopy (SIXM). In refractive index, n=1-sigma+i(beta), in the real part, 1-sigma is the refractive index with decrement, sigma, which is nearly proportional to the density, and the imaginary part, beta, is the extinction coefficient, which is related to the liner attenuation coefficient, mu. Many phases, including water and organic materials as well as minerals, can be identified by SIXM, and this technique has potential availability for Hayabusa-2 sample analysis too. In this study, we examined quantitative performance of d and m values and the spatial resolution in SIXM by using standard materials, and applied this technique to carbonaceous chondrite samples. We used POM ([CH2O]n), silicon, quartz, forsterite, corundum, magnetite and nickel as standard materials for examining the sigma and mu values. A fluid inclusion in terrestrial quartz and bi-valve shell (Atrina vexillum), which are composed of calcite and organic layers with different thickness, were also used for examining the spatial resolution. The Ivuna (CI) and Sutter's Mill (CM) meteorites were used as carbonaceous chondrite samples. Rod- or cube-shaped samples 20-30 micron in size were extracted by using FIB from cross-sectional surfaces of the standard materials or polished thin sections of the chondrites, which was previously observed with SEM. Then, the sample was attached to a thin W-needle and imaged by SIXM system at beamline BL47XU, SPring-8, Japan. The slice thickness was 109.3 nm and the pixel size was mostly 100 nm.

[Analysis of visible extinction spectrum of particle system and selection of optimal wavelength].

PubMed

Sun, Xiao-gang; Tang, Hong; Yuan, Gui-bin

2008-09-01

In the total light scattering particle sizing technique, the extinction spectrum of particle system contains some information about the particle size and refractive index. The visible extinction spectra of the common monomodal and biomodal R-R particle size distribution were computed, and the variation in the visible extinction spectrum with the particle size and refractive index was analyzed. The corresponding wavelengths were selected as the measurement wavelengths at which the second order differential extinction spectrum was discontinuous. Furthermore, the minimum and the maximum wavelengths in the visible region were also selected as the measurement wavelengths. The genetic algorithm was used as the inversion method under the dependent model The computer simulation and experiments illustrate that it is feasible to make an analysis of the extinction spectrum and use this selection method of the optimal wavelength in the total light scattering particle sizing. The rough contour of the particle size distribution can be determined after the analysis of visible extinction spectrum, so the search range of the particle size parameter is reduced in the optimal algorithm, and then a more accurate inversion result can be obtained using the selection method. The inversion results of monomodal and biomodal distribution are all still satisfactory when 1% stochastic noise is put in the transmission extinction measurement values.

Pre- and Postcycloplegic Refractions in Children and Adolescents

PubMed Central

Zhu, Dan; Wang, Yan; Yang, Xianrong; Yang, Dayong; Guo, Kai; Guo, Yuanyuan; Jing, Xinxia; Pan, Chen-Wei

2016-01-01

Purpose To determine the difference between cycloplegic and non-cycloplegic refractive error and its associated factors in Chinese children and adolescents with a high prevalence of myopia. Methods A school-based study including 1565 students aged 6 to 21 years was conducted in 2013 in Ejina, Inner Mongolia, China. Comprehensive eye examinations were performed. Pre-and postcycloplegic refractive error were measured using an auto-refractor. For cycloplegic refraction, one drop of topical 1.0% cyclopentolate was administered to each eye twice with a 5-minute interval and a third drop was administered 15 minutes after the second drop if the pupil size was less than 6 mm or if the pupillary light reflex was still present. Results Two drops of cyclopentolate were found to be sufficient in 59% of the study participants while the other 41% need an additional drop. The prevalence of myopia was 89.5% in participants aged over 12 years and 68.6% in those aged 12 years or younger (P<0.001). When myopia was defined as spherical equivalent (SE) of less than -0.5 diopter (D), the prevalence estimates were 76.7% (95% confidence interval [CI] 74.6–78.8) and 54.1% (95%CI 51.6–56.6) before and after cycloplegic refraction, respectively. When hyperopia was defined as SE of more than 0.5D, the prevalence was only 2.8% (95%CI 1.9–3.6) before cycloplegic refraction while it was 15.5% (95%CI 13.7–17.3) after cycloplegic refraction. Increased difference between cycloplegic and non-cycloplegic refractive error was associated with decreased intraocular pressures (P = 0.01). Conclusions Lack of cycloplegia in refractive error measurement was associated with significant misclassifications in both myopia and hyperopia among Chinese children and adolescents. Decreased intraocular pressure was related to a greater difference between cycloplegic and non-cycloplegic refractive error. PMID:27907165

Pre- and Postcycloplegic Refractions in Children and Adolescents.

PubMed

Zhu, Dan; Wang, Yan; Yang, Xianrong; Yang, Dayong; Guo, Kai; Guo, Yuanyuan; Jing, Xinxia; Pan, Chen-Wei

2016-01-01

To determine the difference between cycloplegic and non-cycloplegic refractive error and its associated factors in Chinese children and adolescents with a high prevalence of myopia. A school-based study including 1565 students aged 6 to 21 years was conducted in 2013 in Ejina, Inner Mongolia, China. Comprehensive eye examinations were performed. Pre-and postcycloplegic refractive error were measured using an auto-refractor. For cycloplegic refraction, one drop of topical 1.0% cyclopentolate was administered to each eye twice with a 5-minute interval and a third drop was administered 15 minutes after the second drop if the pupil size was less than 6 mm or if the pupillary light reflex was still present. Two drops of cyclopentolate were found to be sufficient in 59% of the study participants while the other 41% need an additional drop. The prevalence of myopia was 89.5% in participants aged over 12 years and 68.6% in those aged 12 years or younger (P<0.001). When myopia was defined as spherical equivalent (SE) of less than -0.5 diopter (D), the prevalence estimates were 76.7% (95% confidence interval [CI] 74.6-78.8) and 54.1% (95%CI 51.6-56.6) before and after cycloplegic refraction, respectively. When hyperopia was defined as SE of more than 0.5D, the prevalence was only 2.8% (95%CI 1.9-3.6) before cycloplegic refraction while it was 15.5% (95%CI 13.7-17.3) after cycloplegic refraction. Increased difference between cycloplegic and non-cycloplegic refractive error was associated with decreased intraocular pressures (P = 0.01). Lack of cycloplegia in refractive error measurement was associated with significant misclassifications in both myopia and hyperopia among Chinese children and adolescents. Decreased intraocular pressure was related to a greater difference between cycloplegic and non-cycloplegic refractive error.

Single-shot Z eff dense plasma diagnostic through simultaneous refraction and attenuation measurements with a Talbot–Lau x-ray moiré deflectometer

DOE PAGES

Valdivia, M. P.; Stutman, D.; Finkenthal, M.

2015-03-23

The Talbot–Lau x-ray moiré deflectometer is a powerful plasma diagnostic capable of delivering simultaneous refraction and attenuation information through the accurate detection of x-ray phase shift and intensity. The diagnostic can provide the index of refraction n=1₋δ + iβ of an object (dense plasma, for example) placed in the x-ray beam by independently measuring both δ and β, which are directly related to the electron density n e and the attenuation coefficient μ respectively. Since δ and β depend on the effective atomic number Z eff, a map can be obtained from the ratio between phase and absorption images acquiredmore » in a single shot. The Talbot–Lau x-ray moiré deflectometer and its corresponding data acquisition and processing are briefly described to illustrate how the above is achieved; Z eff values of test objects within the 4₋12 range were obtained experimentally through simultaneous refraction and attenuation measurements. We show that Z eff mapping of objects does not require previous knowledge of sample length or shape. In conclusion, the determination of Z eff from refraction and attenuation measurements with moiré deflectometry could be of high interest to various domains of high energy density research, such as shocked materials and inertial confinement fusion experiments, as well as material science and nondestructive testing.« less

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.

Enhanced middle-infrared light transmission through Au/SiO(x)N(y)/Au aperture arrays.

PubMed

Xiao, Gongli; Yao, Xiang; Ji, Xinming; Zhou, Jia; Bao, Zongming; Huang, Yiping

2011-12-01

The enhanced middle-infrared light transmission through Au/SiO(x)N(y)/Au aperture arrays by changing the refractive index and the thickness of a dielectric layer was studied experimentally. The results indicated that the transmission spectra was highly dependent on the refractive index and the thickness of SiO(x)N(y). We found that the transmission peaks redshifted regularly along with the refractive index from 1.6 to 1.8, owing to the role of surface plasmon polaritons (SPP) coupling in the Au/SiO(x)N(y)/Au cascaded metallic structure. Simultaneously, a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO2.1N0.3/Au cascaded metallic structure with small refractive index (1.6) than in Au/SiO0.6N1/Au cascaded metallic structure with large refractive index (1.8). When the thickness of SiO(x)N(y) changes from 0.2 to 0.4 microm, the shape of transmission spectra exhibits a large change. It was found that a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO(x)N(y)/Au cascaded metallic structure with a thin dielectric film (0.2 microm), with the increase of SiO(x)N(y) film's thickness, the transmission peak gradually widened and disappeared finally. This effect is useful in applications of biochemical sensing and tunable integrated plasmonic devices in the middle-infrared region.

Single-shot Z eff dense plasma diagnostic through simultaneous refraction and attenuation measurements with a Talbot–Lau x-ray moiré deflectometer

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

Valdivia, M. P.; Stutman, D.; Finkenthal, M.

The Talbot–Lau x-ray moiré deflectometer is a powerful plasma diagnostic capable of delivering simultaneous refraction and attenuation information through the accurate detection of x-ray phase shift and intensity. The diagnostic can provide the index of refraction n=1₋δ + iβ of an object (dense plasma, for example) placed in the x-ray beam by independently measuring both δ and β, which are directly related to the electron density n e and the attenuation coefficient μ respectively. Since δ and β depend on the effective atomic number Z eff, a map can be obtained from the ratio between phase and absorption images acquiredmore » in a single shot. The Talbot–Lau x-ray moiré deflectometer and its corresponding data acquisition and processing are briefly described to illustrate how the above is achieved; Z eff values of test objects within the 4₋12 range were obtained experimentally through simultaneous refraction and attenuation measurements. We show that Z eff mapping of objects does not require previous knowledge of sample length or shape. In conclusion, the determination of Z eff from refraction and attenuation measurements with moiré deflectometry could be of high interest to various domains of high energy density research, such as shocked materials and inertial confinement fusion experiments, as well as material science and nondestructive testing.« less

Evaluation of refractive correction for standard automated perimetry in eyes wearing multifocal contact lenses

PubMed Central

Hirasawa, Kazunori; Ito, Hikaru; Ohori, Yukari; Takano, Yui; Shoji, Nobuyuki

2017-01-01

AIM To evaluate the refractive correction for standard automated perimetry (SAP) in eyes with refractive multifocal contact lenses (CL) in healthy young participants. METHODS Twenty-nine eyes of 29 participants were included. Accommodation was paralyzed in all participants with 1% cyclopentolate hydrochloride. SAP was performed using the Humphrey SITA-standard 24-2 and 10-2 protocol under three refractive conditions: monofocal CL corrected for near distance (baseline); multifocal CL corrected for distance (mCL-D); and mCL-D corrected for near vision using a spectacle lens (mCL-N). Primary outcome measures were the foveal threshold, mean deviation (MD), and pattern standard deviation (PSD). RESULTS The foveal threshold of mCL-N with both the 24-2 and 10-2 protocols significantly decreased by 2.2-2.5 dB (P<0.001), while that of mCL-D with the 24-2 protocol significantly decreased by 1.5 dB (P=0.0427), as compared with that of baseline. Although there was no significant difference between the MD of baseline and mCL-D with the 24-2 and 10-2 protocols, the MD of mCL-N was significantly decreased by 1.0-1.3 dB (P<0.001) as compared with that of both baseline and mCL-D, with both 24-2 and 10-2 protocols. There was no significant difference in the PSD among the three refractive conditions with both the 24-2 and 10-2 protocols. CONCLUSION Despite the induced mydriasis and the optical design of the multifocal lens used in this study, our results indicated that, when the dome-shaped visual field test is performed with eyes with large pupils and wearing refractive multifocal CLs, distance correction without additional near correction is to be recommended. PMID:29062776

Evaluation of refractive correction for standard automated perimetry in eyes wearing multifocal contact lenses.

PubMed

Hirasawa, Kazunori; Ito, Hikaru; Ohori, Yukari; Takano, Yui; Shoji, Nobuyuki

2017-01-01

To evaluate the refractive correction for standard automated perimetry (SAP) in eyes with refractive multifocal contact lenses (CL) in healthy young participants. Twenty-nine eyes of 29 participants were included. Accommodation was paralyzed in all participants with 1% cyclopentolate hydrochloride. SAP was performed using the Humphrey SITA-standard 24-2 and 10-2 protocol under three refractive conditions: monofocal CL corrected for near distance (baseline); multifocal CL corrected for distance (mCL-D); and mCL-D corrected for near vision using a spectacle lens (mCL-N). Primary outcome measures were the foveal threshold, mean deviation (MD), and pattern standard deviation (PSD). The foveal threshold of mCL-N with both the 24-2 and 10-2 protocols significantly decreased by 2.2-2.5 dB ( P <0.001), while that of mCL-D with the 24-2 protocol significantly decreased by 1.5 dB ( P =0.0427), as compared with that of baseline. Although there was no significant difference between the MD of baseline and mCL-D with the 24-2 and 10-2 protocols, the MD of mCL-N was significantly decreased by 1.0-1.3 dB ( P <0.001) as compared with that of both baseline and mCL-D, with both 24-2 and 10-2 protocols. There was no significant difference in the PSD among the three refractive conditions with both the 24-2 and 10-2 protocols. Despite the induced mydriasis and the optical design of the multifocal lens used in this study, our results indicated that, when the dome-shaped visual field test is performed with eyes with large pupils and wearing refractive multifocal CLs, distance correction without additional near correction is to be recommended.

Effects of Foveal Ablation on the Pattern of Peripheral Refractive Errors in Normal and Form-deprived Infant Rhesus Monkeys (Macaca mulatta)

PubMed Central

Huang, Juan; Hung, Li-Fang

2011-01-01

Purpose. The purpose of this study was to determine whether visual signals from the fovea contribute to the changes in the pattern of peripheral refractions associated with form deprivation myopia in monkeys. Methods. Monocular form-deprivation was produced in 18 rhesus monkeys by securing diffusers in front of their treated eyes between 22 ± 2 and 155 ± 17 days of age. In eight of these form-deprived monkeys, the fovea and most of the perifovea of the treated eye were ablated by laser photocoagulation at the start of the diffuser-rearing period. Each eye's refractive status was measured by retinoscopy along the pupillary axis and at 15° intervals along the horizontal meridian to eccentricities of 45°. Control data were obtained from 12 normal monkeys and five monkeys that had monocular foveal ablations and were subsequently reared with unrestricted vision. Results. Foveal ablation, by itself, did not produce systematic alterations in either the central or peripheral refractive errors of the treated eyes. In addition, foveal ablation did not alter the patterns of peripheral refractions in monkeys with form-deprivation myopia. The patterns of peripheral refractive errors in the two groups of form-deprived monkeys, either with or without foveal ablation, were qualitatively similar (treated eyes: F = 0.31, P = 0.74; anisometropia: F = 0.61, P = 0.59), but significantly different from those found in the normal monkeys (F = 8.46 and 9.38 respectively, P < 0.05). Conclusions. Central retinal signals do not contribute in an essential way to the alterations in eye shape that occur during the development of vision-induced axial myopia. PMID:21693598

Prevalence and risk factors for refractive errors in the Singapore Malay Eye Survey.

PubMed

Saw, Seang-Mei; Chan, Yiong-Huak; Wong, Wan-Ling; Shankar, Anoop; Sandar, Mya; Aung, Tin; Tan, Donald T H; Mitchell, Paul; Wong, Tien Yin

2008-10-01

To describe the prevalence and risk factors for myopia and other refractive errors in an urban Malay population in Singapore. Population-based, cross-sectional study. Persons of Malay ethnicity, between 40 and 80 years of age, living in Singapore. Refractive error was determined by subjective refraction and if unavailable by autorefraction. Data were analyzed for 2974 adults without previous cataract surgery and who had right eye refraction data. Risk factor data, such as education levels and near work activity, were obtained from a face-to-face interview. Myopia, defined as spherical equivalent (SE) refraction less than -0.5 diopters (D), astigmatism as cylinder less than -0.5 D, hyperopia as SE greater than 0.5 D, and anisometropia as the difference in SE greater than 1.0 D. The prevalence of myopia in the right eye was 30.7% (9.4% unilateral myopia and 21.3% bilateral myopia), the prevalence of astigmatism in the right eye was 33.3% (95% confidence interval [CI, 33.0-33.5), the prevalence of hyperopia in the right eye was 27.4% (95% CI, 24.7-27.6), and the prevalence of anisometropia was 9.9% (95% CI, 9.7-10.0). There was a U-shaped relationship between increasing age and the prevalence of myopia, which was partially explained by the age-related increase in the prevalence of cataract. In a multiple logistic regression model, female sex, age, higher educational level, and cataract were associated with myopia. Adults with myopia were more likely to have astigmatism (P<0.001) in multivariate analyses. A quarter of older adult Malay people in Singapore had myopia. Compared with previous reports of similarly aged Singapore Chinese adults, the prevalence of myopia, astigmatism, and anisometropia was lower, whereas the prevalence of hyperopia was similar.

First Demonstration of Ocular Refractive Change Using Blue-IRIS in Live Cats

PubMed Central

Savage, Daniel E.; Brooks, Daniel R.; DeMagistris, Margaret; Xu, Lisen; MacRae, Scott; Ellis, Jonathan D.; Knox, Wayne H.; Huxlin, Krystel R.

2014-01-01

Purpose. To determine the efficacy of intratissue refractive index shaping (IRIS) using 400-nm femtosecond laser pulses (blue light) for writing refractive structures directly into live cat corneas in vivo, and to assess the longevity of these structures in the eyes of living cats. Methods. Four eyes from two adult cats underwent Blue-IRIS. Light at 400 nm with 100-femtosecond (fs) pulses were tightly focused into the corneal stroma of each eye at an 80-MHz repetition rate. These pulses locally increased the refractive index of the corneal stroma via an endogenous, two-photon absorption process and were used to inscribe three-layered, gradient index patterns into the cat corneas. The optical effects of the patterns were then tracked using optical coherence tomography (OCT) and Shack-Hartmann wavefront sensing. Results. Blue-IRIS patterns locally changed ocular cylinder by −1.4 ± 0.3 diopters (D), defocus by −2.0 ± 0.5 D, and higher-order root mean square (HORMS) by 0.31 ± 0.04 μm at 1 month post-IRIS, without significant changes in corneal thickness or curvature. Refractive changes were maintained for the duration they were tracked, 12 months post-IRIS in one eye, and just more than 3 months in the remaining three eyes. Conclusions. Blue-IRIS can be used to inscribe refractive structures into live cat cornea in vivo that are stable for at least 12 months, and are not associated with significant alterations in corneal thicknesses or radii of curvature. This result is a critical step toward establishing Blue-IRIS as a promising technique for noninvasive vision correction. PMID:24985471

First demonstration of ocular refractive change using blue-IRIS in live cats.

PubMed

Savage, Daniel E; Brooks, Daniel R; DeMagistris, Margaret; Xu, Lisen; MacRae, Scott; Ellis, Jonathan D; Knox, Wayne H; Huxlin, Krystel R

2014-07-01

To determine the efficacy of intratissue refractive index shaping (IRIS) using 400-nm femtosecond laser pulses (blue light) for writing refractive structures directly into live cat corneas in vivo, and to assess the longevity of these structures in the eyes of living cats. Four eyes from two adult cats underwent Blue-IRIS. Light at 400 nm with 100-femtosecond (fs) pulses were tightly focused into the corneal stroma of each eye at an 80-MHz repetition rate. These pulses locally increased the refractive index of the corneal stroma via an endogenous, two-photon absorption process and were used to inscribe three-layered, gradient index patterns into the cat corneas. The optical effects of the patterns were then tracked using optical coherence tomography (OCT) and Shack-Hartmann wavefront sensing. Blue-IRIS patterns locally changed ocular cylinder by -1.4 ± 0.3 diopters (D), defocus by -2.0 ± 0.5 D, and higher-order root mean square (HORMS) by 0.31 ± 0.04 μm at 1 month post-IRIS, without significant changes in corneal thickness or curvature. Refractive changes were maintained for the duration they were tracked, 12 months post-IRIS in one eye, and just more than 3 months in the remaining three eyes. Blue-IRIS can be used to inscribe refractive structures into live cat cornea in vivo that are stable for at least 12 months, and are not associated with significant alterations in corneal thicknesses or radii of curvature. This result is a critical step toward establishing Blue-IRIS as a promising technique for noninvasive vision correction. Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc.

Negative refraction imaging of acoustic metamaterial lens in the supersonic range

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

Han, Jianning; Wen, Tingdun; Key Laboratory of Electronic Testing Technology, North University of China, Taiyuan 030051

2014-05-15

Acoustic metamaterials with negative refraction index is the most promising method to overcome the diffraction limit of acoustic imaging to achieve ultrahigh resolution. In this paper, we use localized resonant phononic crystal as the unit cell to construct the acoustic negative refraction lens. Based on the vibration model of the phononic crystal, negative quality parameters of the lens are obtained while excited near the system resonance frequency. Simulation results show that negative refraction of the acoustic lens can be achieved when a sound wave transmiting through the phononic crystal plate. The patterns of the imaging field agree well with thatmore » of the incident wave, while the dispersion is very weak. The unit cell size in the simulation is 0.0005 m and the wavelength of the sound source is 0.02 m, from which we show that acoustic signal can be manipulated through structures with dimensions much smaller than the wavelength of incident wave.« less

Direct Demonstration of the Concept of Unrestricted Effective-Medium Approximation

NASA Technical Reports Server (NTRS)

Mishchenko, Michael I.; Dlugach, Zhanna M.; Zakharova, Nadezhda T.

2014-01-01

The modified unrestricted effective-medium refractive index is defined as one that yields accurate values of a representative set of far-field scattering characteristics (including the scattering matrix) for an object made of randomly heterogeneous materials. We validate the concept of the modified unrestricted effective-medium refractive index by comparing numerically exact superposition T-matrix results for a spherical host randomly filled with a large number of identical small inclusions and Lorenz-Mie results for a homogeneous spherical counterpart. A remarkable quantitative agreement between the superposition T-matrix and Lorenz-Mie scattering matrices over the entire range of scattering angles demonstrates unequivocally that the modified unrestricted effective-medium refractive index is a sound (albeit still phenomenological) concept provided that the size parameter of the inclusions is sufficiently small and their number is sufficiently large. Furthermore, it appears that in cases when the concept of the modified unrestricted effective-medium refractive index works, its actual value is close to that predicted by the Maxwell-Garnett mixing rule.

Design of a sector bowtie nano-rectenna for optical power and infrared detection

NASA Astrophysics Data System (ADS)

Wang, Kai; Hu, Haifeng; Lu, Shan; Guo, Lingju; He, Tao

2015-10-01

We designed a sector bowtie nanoantenna integrated with a rectifier (Au-TiO x -Ti diode) for collecting infrared energy. The optical performance of the metallic bowtie nanoantenna was numerically investigated at infrared frequencies (5-30 μm) using three-dimensional frequency-domain electromagnetic field calculation software based on the finite element method. The simulation results indicate that the resonance wavelength and local field enhancement are greatly affected by the shape and size of the bowtie nanoantenna, as well as the relative permittivity and conductivity of the dielectric layer. The output current of the rectified nano-rectenna is substantially at nanoampere magnitude with an electric field intensity of 1 V/m. Moreover, the power conversion efficiency for devices with three different substrates illustrates that a substrate with a larger refractive index yields a higher efficiency and longer infrared response wavelength. Consequently, the optimized structure can provide theoretical support for the design of novel optical rectennas and fabrication of optoelectronic devices.

On-chip plasmon-induced transparency based on plasmonic coupled nanocavities

PubMed Central

Zhu, Yu; Hu, Xiaoyong; Yang, Hong; Gong, Qihuang

2014-01-01

On-chip plasmon-induced transparency offers the possibility of realization of ultrahigh-speed information processing chips. Unfortunately, little experimental progress has been made to date because it is difficult to obtain on-chip plasmon-induced transparency using only a single meta-molecule in plasmonic circuits. Here, we report a simple and efficient strategy to realize on-chip plasmon-induced transparency in a nanoscale U-shaped plasmonic waveguide side-coupled nanocavity pair. High tunability in the transparency window is achieved by covering the pair with different organic polymer layers. It is possible to realize ultrafast all-optical tunability based on pump light-induced refractive index change of a graphene cover layer. Compared with previous reports, the overall feature size of the plasmonic nanostructure is reduced by more than three orders of magnitude, while ultrahigh tunability of the transparency window is maintained. This work also provides a superior platform for the study of the various physical effects and phenomena of nonlinear optics and quantum optics. PMID:24435059

On-chip plasmon-induced transparency based on plasmonic coupled nanocavities.

PubMed

Zhu, Yu; Hu, Xiaoyong; Yang, Hong; Gong, Qihuang

2014-01-17

On-chip plasmon-induced transparency offers the possibility of realization of ultrahigh-speed information processing chips. Unfortunately, little experimental progress has been made to date because it is difficult to obtain on-chip plasmon-induced transparency using only a single meta-molecule in plasmonic circuits. Here, we report a simple and efficient strategy to realize on-chip plasmon-induced transparency in a nanoscale U-shaped plasmonic waveguide side-coupled nanocavity pair. High tunability in the transparency window is achieved by covering the pair with different organic polymer layers. It is possible to realize ultrafast all-optical tunability based on pump light-induced refractive index change of a graphene cover layer. Compared with previous reports, the overall feature size of the plasmonic nanostructure is reduced by more than three orders of magnitude, while ultrahigh tunability of the transparency window is maintained. This work also provides a superior platform for the study of the various physical effects and phenomena of nonlinear optics and quantum optics.

Cerium doped glasses: search for a new scintillator

NASA Astrophysics Data System (ADS)

Kielty, Matthew William

Single crystals have been the standard material when it comes to scintillators, but with the ability to easily be produced at a considerably lower cost and fabricated into tailored sizes and shapes there is increasing interest in the development of glass scintillators as an alternative. Ce-doped borosilicate and phosphate glasses were investigated focusing on the effect of different modifiers on their optical properties and luminescence. The borosilicate glasses were prepared aiming at the detection of thermal neutrons, utilizing B-10, while the phosphate glasses were targeting the detection of gamma-rays taking advantage of high Z elements such as, Ba, Bi, Ta, Pb and W. Structural characteristics determined by Raman spectroscopy were coupled with results from photoluminescence and UV-visible transmission measurements, while the index of refraction was estimated using the Gladstone-Dale relation using experimentally obtained density values. This work revealed barium, with its superior optical transmission and luminescent properties, to be the best high Z element for inclusion in the phosphate glasses studied.

Novel Passivating/Antireflective Coatings for Space Solar Cells

NASA Technical Reports Server (NTRS)

Faur, Mircea; Faur, Maria; Bailey, S. G.; Flood, D. J.; Faur, H. M.; Mateescu, C. G.; Alterovitz, S. A.; Scheiman, D.; Jenkins, P. P.; Brinker, D. J.

2005-01-01

We are developing a novel process to grow passivating/antireflective (AR) coatings for terrestrial and space solar cells. Our approach involves a Room Temperature Wet Chemical Growth (RTWCG) process, which was pioneered, and is under development at SPECMAT, Inc., under a Reimbursable Space Act Agreement with NASA Glenn Research Center. The RTWCG passivating/AR coatings with graded index of refraction are applied in one easy step on finished (bare) cells. The RTWCG coatings grown on planar, textured and porous Si, as well as on poly-Si, CuInSe2, and III-V substrates, show excellent uniformity irrespective of surface topography, crystal orientation, size and shape. In this paper we present some preliminary results of the RTWCG coatings on Si and III-V substrates that show very good potential for use as a passivation/AR coating for space solar cell applications. Compared to coatings grown using conventional techniques, the RTWCG coatings have the potential to reduce reflection losses and improve current collection near the illuminated surface of space solar cells, while reducing the fabrication costs.

Biodiesel sensing using silicon-on-insulator technologies

NASA Astrophysics Data System (ADS)

Casas Bedoya, Alvaro; Ling, Meng Y.; Brouckaert, Joost; Yebo, Nebiyu A.; Van Thourhout, Dries; Baets, Roel G.

2009-05-01

By measuring the transmission of Biodiesel/Diesel mixtures in the near- and far-infrared wavelength ranges, it is possible to predict the blend level with a high accuracy. Conventional photospectrometers are typically large and expensive and have a performance that often exceeds the requirements for most applications. For automotive applications for example, what counts is size, robustness and most important cost. As a result the miniaturization of the spectrometer can be seen as an attractive implementation of a Biodiesel sensor. Using Silicon-on-Insulator (SOI) this spectrometer miniaturization can be achieved. Due to the large refractive index contrast of the SOI material system, photonic devices can be made very compact. Moreover, they can be manufactured on high-quality SOI substrates using waferscale CMOS fabrication tools, making them cheap for the market. In this paper, we show that it is possible to determine Biodiesel blend levels using an SOI spectrometer-on-a-chip. We demonstrate absorption measurements using spiral shaped waveguides and we also present the spectrometer design for on-chip Biodiesel blend level measurements.

Nine Loci for Ocular Axial Length Identified through Genome-wide Association Studies, Including Shared Loci with Refractive Error

PubMed Central

Cheng, Ching-Yu; Schache, Maria; Ikram, M. Kamran; Young, Terri L.; Guggenheim, Jeremy A.; Vitart, Veronique; MacGregor, Stuart; Verhoeven, Virginie J.M.; Barathi, Veluchamy A.; Liao, Jiemin; Hysi, Pirro G.; Bailey-Wilson, Joan E.; St. Pourcain, Beate; Kemp, John P.; McMahon, George; Timpson, Nicholas J.; Evans, David M.; Montgomery, Grant W.; Mishra, Aniket; Wang, Ya Xing; Wang, Jie Jin; Rochtchina, Elena; Polasek, Ozren; Wright, Alan F.; Amin, Najaf; van Leeuwen, Elisabeth M.; Wilson, James F.; Pennell, Craig E.; van Duijn, Cornelia M.; de Jong, Paulus T.V.M.; Vingerling, Johannes R.; Zhou, Xin; Chen, Peng; Li, Ruoying; Tay, Wan-Ting; Zheng, Yingfeng; Chew, Merwyn; Rahi, Jugnoo S.; Hysi, Pirro G.; Yoshimura, Nagahisa; Yamashiro, Kenji; Miyake, Masahiro; Delcourt, Cécile; Maubaret, Cecilia; Williams, Cathy; Guggenheim, Jeremy A.; Northstone, Kate; Ring, Susan M.; Davey-Smith, George; Craig, Jamie E.; Burdon, Kathryn P.; Fogarty, Rhys D.; Iyengar, Sudha K.; Igo, Robert P.; Chew, Emily; Janmahasathian, Sarayut; Iyengar, Sudha K.; Igo, Robert P.; Chew, Emily; Janmahasathian, Sarayut; Stambolian, Dwight; Wilson, Joan E. Bailey; MacGregor, Stuart; Lu, Yi; Jonas, Jost B.; Xu, Liang; Saw, Seang-Mei; Baird, Paul N.; Rochtchina, Elena; Mitchell, Paul; Wang, Jie Jin; Jonas, Jost B.; Nangia, Vinay; Hayward, Caroline; Wright, Alan F.; Vitart, Veronique; Polasek, Ozren; Campbell, Harry; Vitart, Veronique; Rudan, Igor; Vatavuk, Zoran; Vitart, Veronique; Paterson, Andrew D.; Hosseini, S. Mohsen; Iyengar, Sudha K.; Igo, Robert P.; Fondran, Jeremy R.; Young, Terri L.; Feng, Sheng; Verhoeven, Virginie J.M.; Klaver, Caroline C.; van Duijn, Cornelia M.; Metspalu, Andres; Haller, Toomas; Mihailov, Evelin; Pärssinen, Olavi; Wedenoja, Juho; Wilson, Joan E. Bailey; Wojciechowski, Robert; Baird, Paul N.; Schache, Maria; Pfeiffer, Norbert; Höhn, René; Pang, Chi Pui; Chen, Peng; Meitinger, Thomas; Oexle, Konrad; Wegner, Aharon; Yoshimura, Nagahisa; Yamashiro, Kenji; Miyake, Masahiro; Pärssinen, Olavi; Yip, Shea Ping; Ho, Daniel W.H.; Pirastu, Mario; Murgia, Federico; Portas, Laura; Biino, Genevra; Wilson, James F.; Fleck, Brian; Vitart, Veronique; Stambolian, Dwight; Wilson, Joan E. Bailey; Hewitt, Alex W.; Ang, Wei; Verhoeven, Virginie J.M.; Klaver, Caroline C.; van Duijn, Cornelia M.; Saw, Seang-Mei; Wong, Tien-Yin; Teo, Yik-Ying; Fan, Qiao; Cheng, Ching-Yu; Zhou, Xin; Ikram, M. Kamran; Saw, Seang-Mei; Teo, Yik-Ying; Fan, Qiao; Cheng, Ching-Yu; Zhou, Xin; Ikram, M. Kamran; Saw, Seang-Mei; Wong, Tien-Yin; Teo, Yik-Ying; Fan, Qiao; Cheng, Ching-Yu; Zhou, Xin; Ikram, M. Kamran; Saw, Seang-Mei; Wong, Tien-Yin; Teo, Yik-Ying; Fan, Qiao; Cheng, Ching-Yu; Zhou, Xin; Ikram, M. Kamran; Saw, Seang-Mei; Tai, E-Shyong; Teo, Yik-Ying; Fan, Qiao; Cheng, Ching-Yu; Zhou, Xin; Ikram, M. Kamran; Saw, Seang-Mei; Teo, Yik-Ying; Fan, Qiao; Cheng, Ching-Yu; Zhou, Xin; Ikram, M. Kamran; Mackey, David A.; MacGregor, Stuart; Hammond, Christopher J.; Hysi, Pirro G.; Deangelis, Margaret M.; Morrison, Margaux; Zhou, Xiangtian; Chen, Wei; Paterson, Andrew D.; Hosseini, S. Mohsen; Mizuki, Nobuhisa; Meguro, Akira; Lehtimäki, Terho; Mäkelä, Kari-Matti; Raitakari, Olli; Kähönen, Mika; Burdon, Kathryn P.; Craig, Jamie E.; Iyengar, Sudha K.; Igo, Robert P.; Lass, Jonathan H.; Reinhart, William; Belin, Michael W.; Schultze, Robert L.; Morason, Todd; Sugar, Alan; Mian, Shahzad; Soong, Hunson Kaz; Colby, Kathryn; Jurkunas, Ula; Yee, Richard; Vital, Mark; Alfonso, Eduardo; Karp, Carol; Lee, Yunhee; Yoo, Sonia; Hammersmith, Kristin; Cohen, Elisabeth; Laibson, Peter; Rapuano, Christopher; Ayres, Brandon; Croasdale, Christopher; Caudill, James; Patel, Sanjay; Baratz, Keith; Bourne, William; Maguire, Leo; Sugar, Joel; Tu, Elmer; Djalilian, Ali; Mootha, Vinod; McCulley, James; Bowman, Wayne; Cavanaugh, H. Dwight; Verity, Steven; Verdier, David; Renucci, Ann; Oliva, Matt; Rotkis, Walter; Hardten, David R.; Fahmy, Ahmad; Brown, Marlene; Reeves, Sherman; Davis, Elizabeth A.; Lindstrom, Richard; Hauswirth, Scott; Hamilton, Stephen; Lee, W. Barry; Price, Francis; Price, Marianne; Kelly, Kathleen; Peters, Faye; Shaughnessy, Michael; Steinemann, Thomas; Dupps, B.J.; Meisler, David M.; Mifflin, Mark; Olson, Randal; Aldave, Anthony; Holland, Gary; Mondino, Bartly J.; Rosenwasser, George; Gorovoy, Mark; Dunn, Steven P.; Heidemann, David G.; Terry, Mark; Shamie, Neda; Rosenfeld, Steven I.; Suedekum, Brandon; Hwang, David; Stone, Donald; Chodosh, James; Galentine, Paul G.; Bardenstein, David; Goddard, Katrina; Chin, Hemin; Mannis, Mark; Varma, Rohit; Borecki, Ingrid; Chew, Emily Y.; Haller, Toomas; Mihailov, Evelin; Metspalu, Andres; Wedenoja, Juho; Simpson, Claire L.; Wojciechowski, Robert; Höhn, René; Mirshahi, Alireza; Zeller, Tanja; Pfeiffer, Norbert; Lackner, Karl J.; Donnelly, Peter; Barroso, Ines; Blackwell, Jenefer M.; Bramon, Elvira; Brown, Matthew A.; Casas, Juan P.; Corvin, Aiden; Deloukas, Panos; Duncanson, Audrey; Jankowski, Janusz; Markus, Hugh S.; Mathew, Christopher G.; Palmer, Colin N.A.; Plomin, Robert; Rautanen, Anna; Sawcer, Stephen J.; Trembath, Richard C.; Viswanathan, Ananth C.; Wood, Nicholas W.; Spencer, Chris C.A.; Band, Gavin; Bellenguez, Céline; Freeman, Colin; Hellenthal, Garrett; Giannoulatou, Eleni; Pirinen, Matti; Pearson, Richard; Strange, Amy; Su, Zhan; Vukcevic, Damjan; Donnelly, Peter; Langford, Cordelia; Hunt, Sarah E.; Edkins, Sarah; Gwilliam, Rhian; Blackburn, Hannah; Bumpstead, Suzannah J.; Dronov, Serge; Gillman, Matthew; Gray, Emma; Hammond, Naomi; Jayakumar, Alagurevathi; McCann, Owen T.; Liddle, Jennifer; Potter, Simon C.; Ravindrarajah, Radhi; Ricketts, Michelle; Waller, Matthew; Weston, Paul; Widaa, Sara; Whittaker, Pamela; Barroso, Ines; Deloukas, Panos; Mathew, Christopher G.; Blackwell, Jenefer M.; Brown, Matthew A.; Corvin, Aiden; Spencer, Chris C.A.; Bettecken, Thomas; Meitinger, Thomas; Oexle, Konrad; Pirastu, Mario; Portas, Laura; Nag, Abhishek; Williams, Katie M.; Yonova-Doing, Ekaterina; Klein, Ronald; Klein, Barbara E.; Hosseini, S. Mohsen; Paterson, Andrew D.; Genuth, S.; Nathan, D.M.; Zinman, B.; Crofford, O.; Crandall, J.; Reid, M.; Brown-Friday, J.; Engel, S.; Sheindlin, J.; Martinez, H.; Shamoon, H.; Engel, H.; Phillips, M.; Gubitosi-Klug, R.; Mayer, L.; Pendegast, S.; Zegarra, H.; Miller, D.; Singerman, L.; Smith-Brewer, S.; Novak, M.; Quin, J.; Dahms, W.; Genuth, Saul; Palmert, M.; Brillon, D.; Lackaye, M.E.; Kiss, S.; Chan, R.; Reppucci, V.; Lee, T.; Heinemann, M.; Whitehouse, F.; Kruger, D.; Jones, J.K.; McLellan, M.; Carey, J.D.; Angus, E.; Thomas, A.; Galprin, A.; Bergenstal, R.; Johnson, M.; Spencer, M.; Morgan, K.; Etzwiler, D.; Kendall, D.; Aiello, Lloyd Paul; Golden, E.; Jacobson, A.; Beaser, R.; Ganda, O.; Hamdy, O.; Wolpert, H.; Sharuk, G.; Arrigg, P.; Schlossman, D.; Rosenzwieg, J.; Rand, L.; Nathan, D.M.; Larkin, M.; Ong, M.; Godine, J.; Cagliero, E.; Lou, P.; Folino, K.; Fritz, S.; Crowell, S.; Hansen, K.; Gauthier-Kelly, C.; Service, J.; Ziegler, G.; Luttrell, L.; Caulder, S.; Lopes-Virella, M.; Colwell, J.; Soule, J.; Fernandes, J.; Hermayer, K.; Kwon, S.; Brabham, M.; Blevins, A.; Parker, J.; Lee, D.; Patel, N.; Pittman, C.; Lindsey, P.; Bracey, M.; Lee, K.; Nutaitis, M.; Farr, A.; Elsing, S.; Thompson, T.; Selby, J.; Lyons, T.; Yacoub-Wasef, S.; Szpiech, M.; Wood, D.; Mayfield, R.; Molitch, M.; Schaefer, B.; Jampol, L.; Lyon, A.; Gill, M.; Strugula, Z.; Kaminski, L.; Mirza, R.; Simjanoski, E.; Ryan, D.; Kolterman, O.; Lorenzi, G.; Goldbaum, M.; Sivitz, W.; Bayless, M.; Counts, D.; Johnsonbaugh, S.; Hebdon, M.; Salemi, P.; Liss, R.; Donner, T.; Gordon, J.; Hemady, R.; Kowarski, A.; Ostrowski, D.; Steidl, S.; Jones, B.; Herman, W.H.; Martin, C.L.; Pop-Busui, R.; Sarma, A.; Albers, J.; Feldman, E.; Kim, K.; Elner, S.; Comer, G.; Gardner, T.; Hackel, R.; Prusak, R.; Goings, L.; Smith, A.; Gothrup, J.; Titus, P.; Lee, J.; Brandle, M.; Prosser, L.; Greene, D.A.; Stevens, M.J.; Vine, A.K.; Bantle, J.; Wimmergren, N.; Cochrane, A.; Olsen, T.; Steuer, E.; Rath, P.; Rogness, B.; Hainsworth, D.; Goldstein, D.; Hitt, S.; Giangiacomo, J.; Schade, D.S.; Canady, J.L.; Chapin, J.E.; Ketai, L.H.; Braunstein, C.S.; Bourne, P.A.; Schwartz, S.; Brucker, A.; Maschak-Carey, B.J.; Baker, L.; Orchard, T.; Silvers, N.; Ryan, C.; Songer, T.; Doft, B.; Olson, S.; Bergren, R.L.; Lobes, L.; Rath, P. Paczan; Becker, D.; Rubinstein, D.; Conrad, P.W.; Yalamanchi, S.; Drash, A.; Morrison, A.; Bernal, M.L.; Vaccaro-Kish, J.; Malone, J.; Pavan, P.R.; Grove, N.; Iyer, M.N.; Burrows, A.F.; Tanaka, E.A.; Gstalder, R.; Dagogo-Jack, S.; Wigley, C.; Ricks, H.; Kitabchi, A.; Murphy, M.B.; Moser, S.; Meyer, D.; Iannacone, A.; Chaum, E.; Yoser, S.; Bryer-Ash, M.; Schussler, S.; Lambeth, H.; Raskin, P.; Strowig, S.; Zinman, B.; Barnie, A.; Devenyi, R.; Mandelcorn, M.; Brent, M.; Rogers, S.; Gordon, A.; Palmer, J.; Catton, S.; Brunzell, J.; Wessells, H.; de Boer, I.H.; Hokanson, J.; Purnell, J.; Ginsberg, J.; Kinyoun, J.; Deeb, S.; Weiss, M.; Meekins, G.; Distad, J.; Van Ottingham, L.; Dupre, J.; Harth, J.; Nicolle, D.; Driscoll, M.; Mahon, J.; Canny, C.; May, M.; Lipps, J.; Agarwal, A.; Adkins, T.; Survant, L.; Pate, R.L.; Munn, G.E.; Lorenz, R.; Feman, S.; White, N.; Levandoski, L.; Boniuk, I.; Grand, G.; Thomas, M.; Joseph, D.D.; Blinder, K.; Shah, G.; Boniuk; Burgess; Santiago, J.; Tamborlane, W.; Gatcomb, P.; Stoessel, K.; Taylor, K.; Goldstein, J.; Novella, S.; Mojibian, H.; Cornfeld, D.; Lima, J.; Bluemke, D.; Turkbey, E.; van der Geest, R.J.; Liu, C.; Malayeri, A.; Jain, A.; Miao, C.; Chahal, H.; Jarboe, R.; Maynard, J.; Gubitosi-Klug, R.; Quin, J.; Gaston, P.; Palmert, M.; Trail, R.; Dahms, W.; Lachin, J.; Cleary, P.; Backlund, J.; Sun, W.; Braffett, B.; Klumpp, K.; Chan, K.; Diminick, L.; Rosenberg, D.; Petty, B.; Determan, A.; Kenny, D.; Rutledge, B.; Younes, Naji; Dews, L.; Hawkins, M.; Cowie, C.; Fradkin, J.; Siebert, C.; Eastman, R.; Danis, R.; Gangaputra, S.; Neill, S.; Davis, M.; Hubbard, L.; Wabers, H.; Burger, M.; Dingledine, J.; Gama, V.; Sussman, R.; Steffes, M.; Bucksa, J.; Nowicki, M.; Chavers, B.; O’Leary, D.; Polak, J.; Harrington, A.; Funk, L.; Crow, R.; Gloeb, B.; Thomas, S.; O’Donnell, C.; Soliman, E.; Zhang, Z.M.; Prineas, R.; Campbell, C.; Ryan, C.; Sandstrom, D.; Williams, T.; Geckle, M.; Cupelli, E.; Thoma, F.; Burzuk, B.; Woodfill, T.; Low, P.; Sommer, C.; Nickander, K.; Budoff, M.; Detrano, R.; Wong, N.; Fox, M.; Kim, L.; Oudiz, R.; Weir, G.; Espeland, M.; Manolio, T.; Rand, L.; Singer, D.; Stern, M.; Boulton, A.E.; Clark, C.; D’Agostino, R.; Lopes-Virella, M.; Garvey, W.T.; Lyons, T.J.; Jenkins, A.; Virella, G.; Jaffa, A.; Carter, Rickey; Lackland, D.; Brabham, M.; McGee, D.; Zheng, D.; Mayfield, R.K.; Boright, A.; Bull, S.; Sun, L.; Scherer, S.; Zinman, B.; Natarajan, R.; Miao, F.; Zhang, L.; Chen;, Z.; Nathan, D.M.; Makela, Kari-Matti; Lehtimaki, Terho; Kahonen, Mika; Raitakari, Olli; Yoshimura, Nagahisa; Matsuda, Fumihiko; Chen, Li Jia; Pang, Chi Pui; Yip, Shea Ping; Yap, Maurice K.H.; Meguro, Akira; Mizuki, Nobuhisa; Inoko, Hidetoshi; Foster, Paul J.; Zhao, Jing Hua; Vithana, Eranga; Tai, E-Shyong; Fan, Qiao; Xu, Liang; Campbell, Harry; Fleck, Brian; Rudan, Igor; Aung, Tin; Hofman, Albert; Uitterlinden, André G.; Bencic, Goran; Khor, Chiea-Chuen; Forward, Hannah; Pärssinen, Olavi; Mitchell, Paul; Rivadeneira, Fernando; Hewitt, Alex W.; Williams, Cathy; Oostra, Ben A.; Teo, Yik-Ying; Hammond, Christopher J.; Stambolian, Dwight; Mackey, David A.; Klaver, Caroline C.W.; Wong, Tien-Yin; Saw, Seang-Mei; Baird, Paul N.

2013-01-01

Refractive errors are common eye disorders of public health importance worldwide. Ocular axial length (AL) is the major determinant of refraction and thus of myopia and hyperopia. We conducted a meta-analysis of genome-wide association studies for AL, combining 12,531 Europeans and 8,216 Asians. We identified eight genome-wide significant loci for AL (RSPO1, C3orf26, LAMA2, GJD2, ZNRF3, CD55, MIP, and ALPPL2) and confirmed one previously reported AL locus (ZC3H11B). Of the nine loci, five (LAMA2, GJD2, CD55, ALPPL2, and ZC3H11B) were associated with refraction in 18 independent cohorts (n = 23,591). Differential gene expression was observed for these loci in minus-lens-induced myopia mouse experiments and human ocular tissues. Two of the AL genes, RSPO1 and ZNRF3, are involved in Wnt signaling, a pathway playing a major role in the regulation of eyeball size. This study provides evidence of shared genes between AL and refraction, but importantly also suggests that these traits may have unique pathways. PMID:24144296

Simultaneous measurement of refractive index and temperature based on all-dielectric metasurface.

PubMed

Hu, Jie; Lang, Tingting; Shi, Guo-Hua

2017-06-26

In this paper, a novel kind of sensors for simultaneous measurement of refractive index and temperature based on all-dielectric metasurfaces is proposed. The metasurfaces are constructed by an array of silicon nanoblocks on top of the bulk fused silica substrate. We used three-dimensional full wave electromagnetic field simulation by finite integral method to accurately calculate the transmission spectrum of the metasurfaces. Two transmission dips corresponding to the electric and magnetic resonances are observed. Both dips shift as the ambient refractive index or the temperature changes. Simulation results show that the sensing sensitivities of two dips to the refractive index are 243.44 nm/RIU and 159.43 nm/RIU, respectively, while the sensitivities to the temperature are 50.47 pm/°C and 75.20 pm/°C, respectively. After introducing four holes into each silicon nanoblock, the electromagnetic field overlap in the surrounding medium can be further promoted, and the sensitivities to the refractive index increase to 306.71 nm/RIU and 204.27 nm/RIU, respectively. Our proposed sensors have advantages of polarization insensitive, small size, and low loss, which offer them high potential applications in physical, biological and chemical sensing fields.

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.

All-angle negative refraction and active flat lensing of ultraviolet light.

PubMed

Xu, Ting; Agrawal, Amit; Abashin, Maxim; Chau, Kenneth J; Lezec, Henri J

2013-05-23

Decades ago, Veselago predicted that a material with simultaneously negative electric and magnetic polarization responses would yield a 'left-handed' medium in which light propagates with opposite phase and energy velocities--a condition described by a negative refractive index. He proposed that a flat slab of left-handed material possessing an isotropic refractive index of -1 could act like an imaging lens in free space. Left-handed materials do not occur naturally, and it has only recently become possible to achieve a left-handed response using metamaterials, that is, electromagnetic structures engineered on subwavelength scales to elicit tailored polarization responses. So far, left-handed responses have typically been implemented using resonant metamaterials composed of periodic arrays of unit cells containing inductive-capacitive resonators and conductive wires. Negative refractive indices that are isotropic in two or three dimensions at microwave frequencies have been achieved in resonant metamaterials with centimetre-scale features. Scaling the left-handed response to higher frequencies, such as infrared or visible, has been done by shrinking critical dimensions to submicrometre scales by means of top-down nanofabrication. This miniaturization has, however, so far been achieved at the cost of reduced unit-cell symmetry, yielding a refractive index that is negative along only one axis. Moreover, lithographic scaling limits have so far precluded the fabrication of resonant metamaterials with left-handed responses at frequencies beyond the visible. Here we report the experimental implementation of a bulk metamaterial with a left-handed response to ultraviolet light. The structure, based on stacked plasmonic waveguides, yields an omnidirectional left-handed response for transverse magnetic polarization characterized by a negative refractive index. By engineering the structure to have a refractive index close to -1 over a broad angular range, we achieve Veselago flat lensing, in free space, of arbitrarily shaped, two-dimensional objects beyond the near field. We further demonstrate active, all-optical modulation of the image transferred by the flat lens.

Effects of refractive errors on visual evoked magnetic fields.

PubMed

Suzuki, Masaya; Nagae, Mizuki; Nagata, Yuko; Kumagai, Naoya; Inui, Koji; Kakigi, Ryusuke

2015-11-09

The latency and amplitude of visual evoked cortical responses are known to be affected by refractive states, suggesting that they may be used as an objective index of refractive errors. In order to establish an easy and reliable method for this purpose, we herein examined the effects of refractive errors on visual evoked magnetic fields (VEFs). Binocular VEFs following the presentation of a simple grating of 0.16 cd/m(2) in the lower visual field were recorded in 12 healthy volunteers and compared among four refractive states: 0D, +1D, +2D, and +4D, by using plus lenses. The low-luminance visual stimulus evoked a main MEG response at approximately 120 ms (M100) that reversed its polarity between the upper and lower visual field stimulations and originated from the occipital midline area. When refractive errors were induced by plus lenses, the latency of M100 increased, while its amplitude decreased with an increase in power of the lens. Differences from the control condition (+0D) were significant for all three lenses examined. The results of dipole analyses showed that evoked fields for the control (+0D) condition were explainable by one dipole in the primary visual cortex (V1), while other sources, presumably in V3 or V6, slightly contributed to shape M100 for the +2D or +4D condition. The present results showed that the latency and amplitude of M100 are both useful indicators for assessing refractive states. The contribution of neural sources other than V1 to M100 was modest under the 0D and +1D conditions. By considering the nature of the activity of M100 including its high sensitivity to a spatial frequency and lower visual field dominance, a simple low-luminance grating stimulus at an optimal spatial frequency in the lower visual field appears appropriate for obtaining data on high S/N ratios and reducing the load on subjects.

Sub-wavelength Laser Nanopatterning using Droplet Lenses

NASA Astrophysics Data System (ADS)

Duocastella, Martí; Florian, Camilo; Serra, Pere; Diaspro, Alberto

2015-11-01

When a drop of liquid falls onto a screen, e.g. a cell phone, the pixels lying underneath appear magnified. This lensing effect is a combination of the curvature and refractive index of the liquid droplet. Here, the spontaneous formation of such lenses is exploited to overcome the diffraction limit of a conventional laser direct-writing system. In particular, micro-droplets are first laser-printed at user-defined locations on a surface and they are later used as lenses to focus the same laser beam. Under conditions described herein, nanopatterns can be obtained with a reduction in spot size primarily limited by the refractive index of the liquid. This all-optics approach is demonstrated by writing arbitrary patterns with a feature size around 280 nm, about one fourth of the processing wavelength.

Weak-guidance-theory review of dispersion and birefringence management by laser inscription

NASA Astrophysics Data System (ADS)

Zheltikov, A. M.; Reid, D. T.

2008-01-01

A brief review of laser inscription of micro- and nanophotonic structures in transparent materials is provided in terms of a compact and convenient formalism based on the theory of weak optical waveguides. We derive physically instructive approximate expressions allowing propagation constants of laser-inscribed micro- and nanowaveguides to be calculated as functions of the transverse waveguide size, refractive index step, and dielectric properties of the host material. Based on this analysis, we demonstrate that dispersion engineering capabilities of laser micromachining techniques are limited by the smallness of the refractive index step typical of laser-inscribed structures. However, a laser inscription of waveguides in pre-formed micro- and nanostructures suggests a variety of interesting options for a fine dispersion and birefringence tuning of small-size waveguides and photonic wires.

Real Time Measurement of the Size Distribution of Particulate Matter by a Light Scattering Method

ERIC Educational Resources Information Center

Gravatt, C. C., Jr.

1973-01-01

Discusses a light scattering instrument designed to measure the size of particles in an air flow in approximately 25 microseconds and at a concentration as high as 10,000 particles/cc. Indicates that the measurement can be made for all particles, independent of their index of refraction. (CC)

Elastic and Inelastic Light Scattering by Microdroplets

NASA Astrophysics Data System (ADS)

Huckaby, James Longinus

A technique for simultaneously determining microdroplet radius, refractive index and its dispersion is developed and demonstrated for three droplet compounds. Based on the accurate determination of the spectral positions of a set of scattered field optical resonances, the technique is shown to provide size and refractive index values to within a relative error of 5 times 10^{-5}, while also providing the refractive index as a function of wavenumber. A method for unambiguously distinguishing droplet growth by the formation of a layer from homogeneous growth is presented and demonstrated. This method employs the precise determination of the spectral positions of optical resonances associated with the transverse magnetic (TM) and transverse electric (TE) scattered fields from a sphere. The method relies upon the observation that the formation of a coating having a different refractive index than the core droplet results in substantially different spectral shifts of the scattered TE and TM resonances. This method was applied to examine absorption and coating events. Droplet size changes of as small as 3.0 nm due to the absorption of vapor were induced and measured. Coatings of perfluorinated polyether on polyphenol ether droplets were generated and shown to produce peak shifts consistent with theory. The observation of a large number of internal field resonances of the droplet with the incident wavenumber in the Raman spectra of microdroplets is reported. An argument based on the observed density of these internal resonances is made for the observation of all internal field resonances through the techniques described.

Height, weight, body mass index and ocular biometry in patients with sickle cell disease.

PubMed

Osuobeni, Ebi Peter; Okpala, Iheanyi; Williamson, Tom H; Thomas, Peter

2009-03-01

To investigate the effects of physical size on refractive error and the dimensions of optical components in sickle cell disease (SCD). The design was cross sectional. Height and weight of adult patients suffering from SCD were measured, and body mass index (BMI) was calculated. Anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD) and axial length (AL) were measured using A-scan ultrasonography. Corneal radius of curvature (CR) was measured using a keratometer. Non-cycloplegic refractive error was determined subjectively. Subjects with SC genotype were significantly taller than those with SS genotype. In the unadjusted data, height was correlated with VCD [p = 0.02, 0.44 mm deeper per 10 cm increase in height, 95% CI (0.65, 8.25)] and AL [p = 0.03, 0.42 mm longer for every 10 cm increase in height, 95%CI (0.49, 7.99)]. The relationship between height, VCD and AL was absent after adjustment for age, gender, genotype and weight. BMI (kg m(-2)) was correlated with AL/CR ratio in both unadjusted (p = 0.04, -0.10 decrease per 1 kg m(-2), 95% CI (-0.018, -0.001) and adjusted data (p = 0.05, -0.10 decrease per 10 kg m(-2), 95% CI (-0.0189, 0.0001). Refractive error was not related to height, weight or BMI. Physical size does not affect refractive error or optical components in adult patients with SCD.

Methods and apparatus for controlling dispersions of nanoparticles

DOEpatents

Lavrentovich, Oleg D; Golovin, Andrii B

2014-10-21

Electrically reconfigurable metamaterial with spatially varied refractive index is proposed for applications such as optical devices and lenses. The apparatus and method comprises a metamaterial in which the refractive indices are modified in space and time by applying one or more electric fields. The metamaterials are electrically controllable and reconfigurable, and consist of metal (gold, silver, etc.) particles of different shapes, such as rods, with dimension much smaller than the wavelength of light, dispersed in a dielectric medium. The metamaterial is controlled by applying a non-uniform electric field that causes two effects: (1) It aligns the metallic anisometric particles with respect to the direction of the applied electric field and (2) It redistributes particles in space, making their local concentration position dependent.

Refraction and Ocular Biometry of Preschool Children in Shanghai, China

PubMed Central

He, Xiangui; You, Xiaofang; Wang, Bingjie; Tan, Hui; Zhu, Jianfeng

2018-01-01

Purpose To investigate the refraction and ocular biometry characteristics and to examine the prevalence of refractive errors in preschool children aged 3 to 6 years in Shanghai, China. Methods A school-based cross-sectional study was conducted in Jiading and Xuhui District, Shanghai, in 2013. We randomly selected 7 kindergartens in Jiading District and 10 kindergartens in Xuhui District, with a probability proportionate to size. The children underwent comprehensive eye examinations, including cycloplegic refraction and biometric measurements. Myopia, hyperopia, astigmatism were defined as spherical equivalent (SE) ≤ −0.50 D, SE ≥ +2.00 D, and cylindrical diopters ≤ −1.00 D. Results The mean SE for 3- to 6-year-old children was +1.20 D (standard deviation [SD] 1.05), and the mean axial length (AL) was 22.29 mm (SD 0.73). The overall prevalence of myopia and astigmatism was 3.7% and 18.3%, respectively. No difference in prevalence of astigmatism was found across age groups. There was a statistically significant association between lower cylindrical diopters and higher spherical diopters (Spearman's correlation: −0.21, P < 0.001). Conclusion Chinese children aged 3 to 6 years in the Shanghai area were mostly mildly hyperopic, with a low prevalence of myopia. Refractive astigmatism for children may be relatively stable throughout the preschool stage. Astigmatism was significantly associated with refractive error. PMID:29692930

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.

Validation of two-dimensional and three-dimensional measurements of subpleural alveolar size parameters by optical coherence tomography

PubMed Central

Warger, William C.; Hostens, Jeroen; Namati, Eman; Birngruber, Reginald; Bouma, Brett E.; Tearney, Guillermo J.

2012-01-01

Abstract. Optical coherence tomography (OCT) has been increasingly used for imaging pulmonary alveoli. Only a few studies, however, have quantified individual alveolar areas, and the validity of alveolar volumes represented within OCT images has not been shown. To validate quantitative measurements of alveoli from OCT images, we compared the cross-sectional area, perimeter, volume, and surface area of matched subpleural alveoli from microcomputed tomography (micro-CT) and OCT images of fixed air-filled swine samples. The relative change in size between different alveoli was extremely well correlated (r>0.9, P<0.0001), but OCT images underestimated absolute sizes compared to micro-CT by 27% (area), 7% (perimeter), 46% (volume), and 25% (surface area) on average. We hypothesized that the differences resulted from refraction at the tissue–air interfaces and developed a ray-tracing model that approximates the reconstructed alveolar size within OCT images. Using this model and OCT measurements of the refractive index for lung tissue (1.41 for fresh, 1.53 for fixed), we derived equations to obtain absolute size measurements of superellipse and circular alveoli with the use of predictive correction factors. These methods and results should enable the quantification of alveolar sizes from OCT images in vivo. PMID:23235834

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.

Validation of two-dimensional and three-dimensional measurements of subpleural alveolar size parameters by optical coherence tomography

NASA Astrophysics Data System (ADS)

Unglert, Carolin I.; Warger, William C.; Hostens, Jeroen; Namati, Eman; Birngruber, Reginald; Bouma, Brett E.; Tearney, Guillermo J.

2012-12-01

Optical coherence tomography (OCT) has been increasingly used for imaging pulmonary alveoli. Only a few studies, however, have quantified individual alveolar areas, and the validity of alveolar volumes represented within OCT images has not been shown. To validate quantitative measurements of alveoli from OCT images, we compared the cross-sectional area, perimeter, volume, and surface area of matched subpleural alveoli from microcomputed tomography (micro-CT) and OCT images of fixed air-filled swine samples. The relative change in size between different alveoli was extremely well correlated (r>0.9, P<0.0001), but OCT images underestimated absolute sizes compared to micro-CT by 27% (area), 7% (perimeter), 46% (volume), and 25% (surface area) on average. We hypothesized that the differences resulted from refraction at the tissue-air interfaces and developed a ray-tracing model that approximates the reconstructed alveolar size within OCT images. Using this model and OCT measurements of the refractive index for lung tissue (1.41 for fresh, 1.53 for fixed), we derived equations to obtain absolute size measurements of superellipse and circular alveoli with the use of predictive correction factors. These methods and results should enable the quantification of alveolar sizes from OCT images in vivo.

Light-scattering flow cytometry for identification and characterization of blood microparticles

NASA Astrophysics Data System (ADS)

Konokhova, Anastasiya I.; Yurkin, Maxim A.; Moskalensky, Alexander E.; Chernyshev, Andrei V.; Tsvetovskaya, Galina A.; Chikova, Elena D.; Maltsev, Valeri P.

2012-05-01

We describe a novel approach to study blood microparticles using the scanning flow cytometer, which measures light scattering patterns (LSPs) of individual particles. Starting from platelet-rich plasma, we separated spherical microparticles from non-spherical plasma constituents, such as platelets and cell debris, based on similarity of their LSP to that of sphere. This provides a label-free method for identification (detection) of microparticles, including those larger than 1 μm. Next, we rigorously characterized each measured particle, determining its size and refractive index including errors of these estimates. Finally, we employed a deconvolution algorithm to determine size and refractive index distributions of the whole population of microparticles, accounting for largely different reliability of individual measurements. Developed methods were tested on a blood sample of a healthy donor, resulting in good agreement with literature data. The only limitation of this approach is size detection limit, which is currently about 0.5 μm due to used laser wavelength of 0.66 μm.

A model predicting the evolution of ice particle size spectra and radiative properties of cirrus clouds. Part 2: Dependence of absorption and extinction on ice crystal morphology

NASA Technical Reports Server (NTRS)

Mitchell, David L.; Arnott, W. Patrick

1994-01-01

This study builds upon the microphysical modeling described in Part 1 by deriving formulations for the extinction and absorption coefficients in terms of the size distribution parameters predicted from the micro-physical model. The optical depth and single scatter albedo of a cirrus cloud can then be determined, which, along with the asymmetry parameter, are the input parameters needed by cloud radiation models. Through the use of anomalous diffraction theory, analytical expressions were developed describing the absorption and extinction coefficients and the single scatter albedo as functions of size distribution parameters, ice crystal shapes (or habits), wavelength, and refractive index. The extinction coefficient was formulated in terms of the projected area of the size distribution, while the absorption coefficient was formulated in terms of both the projected area and mass of the size distribution. These properties were formulated as explicit functions of ice crystal geometry and were not based on an 'effective radius.' Based on simulations of the second cirrus case study described in Part 1, absorption coefficients predicted in the near infrared for hexagonal columns and rosettes were up to 47% and 71% lower, respectively, than absorption coefficients predicted by using equivalent area spheres. This resulted in single scatter albedos in the near-infrared that were considerably greater than those predicted by the equivalent area sphere method. Reflectances in this region should therefore be underestimated using the equivalent area sphere approach. Cloud optical depth was found to depend on ice crystal habit. When the simulated cirrus cloud contained only bullet rosettes, the optical depth was 142% greater than when the cloud contained only hexagonal columns. This increase produced a doubling in cloud albedo. In the near-infrared (IR), the single scatter albedo also exhibited a significant dependence on ice crystal habit. More research is needed on the geometrical properties of ice crystals before the influence of ice crystal shape on cirrus radiative properties can be adequately understood. This study provides a way of coupling the radiative properties of absorption, extinction, and single scatter albedo to the microphysical properties of cirrus clouds. The dependence of extinction and absorption on ice crystal shape was not just due to geometrical differences between crystal types, but was also due to the effect these differences had on the evolution of ice particle size spectra. The ice particle growth model in Part 1 and the radiative properties treated here are based on analytical formulations, and thus represent a computationally efficient means of modeling the microphysical and radiative properties of cirrus clouds.

Immersion Refractometry of Isolated Bacterial Cell Walls

PubMed Central

Marquis, Robert E.

1973-01-01

Immersion-refractometric and light-scattering measurements were adapted to determinations of average refractive indices and physical compactness of isolated bacterial cell walls. The structures were immersed in solutions containing various concentrations of polymer molecules that cannot penetrate into wall pores, and then an estimate was made of the polymer concentration or the refractive index of the polymer solution in which light scattering was reduced to zero. Because each wall preparation was heterogeneous, the refractive index of the medium for zero light scattering had to be estimated by extrapolation. Refractive indices for walls suspended in bovine serum albumin solutions ranged from 1.348 for walls of the rod form of Arthrobacter crystallopoietes to 1.382 for walls of the teichoic acid deficient, 52A5 strain of Staphylococcus aureus. These indices were used to calculate approximate values for solids content per milliliter, and the calculated values agreed closely with those estimated from a knowledge of dextran-impermeable volumes per gram, dry weight, of the walls. When large molecules such as dextrans or serum albumin were used for immersion refractometry, the refractive indices obtained were for entire walls, including both wall polymers and wall water. When smaller molecules that can penetrate wall pores to various extents were used with Micrococcus lysodeikticus walls, the average, apparent refractive index of the structures increased as the molecular size of probing molecules was decreased. It was possible to obtain an estimate of 1.45 to 1.46 for the refractive index of wall polymers, predominantly peptidoglycans in this case, by extrapolating the curve for refractive index versus molecular radius to a value of 0.2 nm, the approximate radius of a water molecule. This relatively low value for polymer refractive index was interpreted as evidence in favor of the amorphous, elastic model of peptidoglycan structure and against the crystalline, rigid model. PMID:4201772

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

Mehta, Sheetal, E-mail: smehta-29@yahoo.com; Das, Kallol; Keller, Jag Mohan, E-mail: smehta-29@yahoo.com

Poly (methyl methacrylate) (PMMA) and Iodine hybrid matrixes have been prepared and characterized. The optical properties of the prepared I-PMMA hybrid composites were characterized by linear absorption studies and these composites have been found to contain embedded Iodine nanoparticles. The size of the nanoparticles was found to be a function of the Iodine content of PMMA. Refractive index measurements were undertaken for different wavelengths. The results showed that the refractive index of the composite is dependent on thermal annealing and also varies nonlinearly with the doping concentration at low Iodine concentration or in the region of nanoparticles formation.

Robust and Bright Photoluminescence from Colloidal Nanocrystal/Al2O3 Composite Films Fabricated by Atomic Layer Deposition.

PubMed

Palei, Milan; Caligiuri, Vincenzo; Kudera, Stefan; Krahne, Roman

2018-06-22

Colloidal nanocrystals are a promising fluorescent class of materials whose spontaneous emission features can be tuned over a broad spectral range via their composition, geometry, and size. However, toward embedding nanocrystal films in elaborated device geometries, one significant drawback is the sensitivity of their emission properties on further fabrication processes like lithography, metal or oxide deposition, etc. In this work, we demonstrate how bright-emitting and robust thin films can be obtained by combining nanocrystal deposition from solutions via spin coating with subsequent atomic layer deposition of alumina. For the resulting composite films, the layer thickness can be controlled on the nanoscale and their refractive index can be finely tuned by the amount of deposited alumina. Ellipsometry is used to measure the real and imaginary part of the dielectric permittivity, which gives direct access to the wavelength dependent refractive index and absorbance of the film. Detailed analysis of the photophysics of thin films of core-shell nanocrystals with different shapes and different shell thicknesses allows to correlate the behavior of the photoluminescence and of the decay lifetime to the changes in the nonradiative rate that are induced by the alumina deposition. We show that the photoemission properties of such composite films are stable in wavelength and intensity over several months and that the photoluminescence completely recovers from heating processes up to 240 °C. The latter is particularly interesting since it demonstrates robustness to the typical heat treatment that is needed in several process steps like resist-based lithography and deposition by thermal or electron beam evaporation of metals or oxides.

Intraocular lens fabrication

DOEpatents

Salazar, M.A.; Foreman, L.R.

1997-07-08

This invention describes a method for fabricating an intraocular lens made from clear Teflon{trademark}, Mylar{trademark}, or other thermoplastic material having a thickness of about 0.025 millimeters. These plastic materials are thermoformable and biocompatable with the human eye. The two shaped lenses are bonded together with a variety of procedures which may include thermosetting and solvent based adhesives, laser and impulse welding, and ultrasonic bonding. The fill tube, which is used to inject a refractive filling material is formed with the lens so as not to damage the lens shape. A hypodermic tube may be included inside the fill tube. 13 figs.

Intraocular lens fabrication

DOEpatents

Salazar, Mike A.; Foreman, Larry R.

1997-01-01

This invention describes a method for fabricating an intraocular lens made rom clear Teflon.TM., Mylar.TM., or other thermoplastic material having a thickness of about 0.025 millimeters. These plastic materials are thermoformable and biocompatable with the human eye. The two shaped lenses are bonded together with a variety of procedures which may include thermosetting and solvent based adhesives, laser and impulse welding, and ultrasonic bonding. The fill tube, which is used to inject a refractive filling material is formed with the lens so as not to damage the lens shape. A hypodermic tube may be included inside the fill tube.

Nonimaging achromatic shaped Fresnel lenses for ultrahigh solar concentration.

PubMed

Languy, Fabian; Habraken, Serge

2013-05-15

The maximum concentration ratio achievable with a solar concentrator made of a single refractive primary optics is much more limited by the chromatic aberration than by any other aberration. Therefore achromatic doublets made with poly(methyl methacrylate) and polycarbonate are of great interest to enhance the concentration ratio and to achieve a spectrally uniform flux on the receiver. In this Letter, shaped achromatic Fresnel lenses are investigated. One lossless design is of high interest since it provides spectrally and spatially uniform flux without being affected by soiling problems. With this design an optical concentration ratio of about 8500× can be achieved.

A huge diversity of metopids (Ciliophora, Armophorea) in soil from the Murray River floodplain, Australia. I. Description of five new species and redescription of Metopus setosus Kahl, 1927.

PubMed

Vďačný, Peter; Foissner, Wilhelm

2017-04-01

Six metopid ciliates from soil of the Murray River floodplain in Australia were studied using live observation, various silver impregnation methods, scanning electron microscopy, and multivariate statistics. One of the species is affiliated with M. setosus while the others represent new taxa. Metopus filum nov. spec. is distinguished from most congeners by the slender body, the absence of cortical granules, and the low number of ciliary rows and adoral polykinetids. Metopus palaeformides nov. spec. most resembles Heterometopus palaeformis (Kahl, 1927) Foissner, 2016b but they can be distinguished by body size, the number of adoral polykinetids, and the oral area pattern. Metopus murrayensis nov. spec. is outstanding in having a globular macronucleus surrounded by innumerable refractive granules and a conspicuously thick preoral dome. Metopus rex nov. spec. and M. magnus nov. spec. are easily distinguished from most congeners by their large body size and the shape of the macronucleus. Moreover, M. rex displays up to 30μm long endosymbiotic bacteria while the micronucleus of M. magnus is uniquely situated in a small macronuclear concavity. Multivariate statistics corroborates the distinctness of these six metopid populations. Copyright © 2016 Elsevier GmbH. All rights reserved.

Extraction of citral oil from lemongrass (Cymbopogon Citratus) by steam-water distillation technique

NASA Astrophysics Data System (ADS)

Alam, P. N.; Husin, H.; Asnawi, T. M.; Adisalamun

2018-04-01

In Indonesia, production of citral oil from lemon grass (Cymbopogon Cytratus) is done by a traditional technique whereby a low yield results. To improve the yield, an appropriate extraction technology is required. In this research, a steam-water distillation technique was applied to extract the essential oil from the lemongrass. The effects of sample particle size and bed volume on yield and quality of citral oil produced were investigated. The drying and refining time of 2 hours were used as fixed variables. This research results that minimum citral oil yield of 0.53% was obtained on sample particle size of 3 cm and bed volume of 80%, whereas the maximum yield of 1.95% on sample particle size of 15 cm and bed volume of 40%. The lowest specific gravity of 0.80 and the highest specific gravity of 0.905 were obtained on sample particle size of 8 cm with bed volume of 80% and particle size of 12 cm with bed volume of 70%, respectively. The lowest refractive index of 1.480 and the highest refractive index of 1.495 were obtained on sample particle size of 8 cm with bed volume of 70% and sample particle size of 15 cm with bed volume of 40%, respectively. The solubility of the produced citral oil in alcohol was 70% in ratio of 1:1, and the citral oil concentration obtained was around 79%.

Aerosol Abundances and Optical Characteristics in the Pacific Basin Free Troposphere

NASA Technical Reports Server (NTRS)

Pueschel, R. F.; Livingston, J. M.; Ferry, G. V.; deFelice, T. E.

1994-01-01

During NASA's Global Backscatter Experiment (GLOBE) mission flights in November 1989 and May 1990, a DC-8 research aircraft probed the Pacific Basin free troposphere for about 90 flight hours in each month between +72 and -62 degrees latitude, +130 and -120 degrees longitude, and up to 39,000 feet pressure altitudes. Aerosols were sampled continuously in situ by optical particle counters to measure concentration and particle size, and during 48 10-min intervals during each mission by wire impactors for concentration, size, composition, phase and shape analyses. The optical particle counters cover a particle diameter range between 0.3 and 20 microns; wire impactors extend the range down to 0.03 microns. Results of particle number, size, shape, together with the assumption of a refractive index corresponding to (NH4)2SO4 to account for the prevalence of aerosol sulfur, were utilized in a Mie algorithm to calculate aerosol extinction and backscatter for a range of wavelengths (0.385 less than lambda less than 10.64 microns). Computations for 22 randomly selected size distributions yield coefficients of extinction E(0.525) = (2.03 +/- 1.20) x 10(exp -4) km(exp -1) and backscatter beta(0.525) = (6.45 +/- 3.49) x 10(exp -6) km(exp -1) sr(exp -1) in the visible, and E(10.64) = (8.13 +/- 6.47) x 10(exp -6) km(exp -1) and beta(10.64) = (9.98 +/- 10.69) x 10(exp -8) km(exp -1) sr(exp -1) in the infrared, respectively. Large particles (D greater than 0.3 microns) contribute two-thirds to the total extinction in the visible (lambda = 0.525 microns), and almost 100% in the infrared (lambda = 10.64 microns). These results have been used to define an IR optical aerosol climatology of the Pacific Basin free troposphere, from which it follows that the infrared backscatter coefficient at lambda = 9.25 microns wavelength fluctuates between 5.0 x 10(exp -10) and 2.0 x 10(exp -7) km(exp -1) sr(exp -1) with a modal value 2.0 x 10(exp -8) km(exp -1) sr(exp -1).

Curvature of the localized surface plasmon resonance peak.

PubMed

Chen, Peng; Liedberg, Bo

2014-08-05

Localized surface plasmon resonance (LSPR) occurring in noble metal nanoparticles (e.g., Au) is a widely used phenomenon to report molecular interactions. Traditional LSPR sensors typically monitor shifts in the peak position or extinction in response to local refractive index changes in the close vicinity of the nanoparticle surface. The ability to resolve minute shifts/extinction changes is to a large extent limited by instrumental noise. A new strategy to evaluate LSPR responses utilizing changes in the shape of the extinction spectrum (the curvature) is proposed. The response of curvature to refractive index changes is investigated theoretically using Mie theory and an analytical expression relating the curvature to the refractive index is presented. The experimentally derived curvatures for 13 nm spherical gold nanoparticles (AuNPs) exposed to solvents with different bulk refractive indices confirm the theoretical predictions. Moreover, both the calculated and experimental findings suggest that the curvature is approximately a linear function of refractive index in regimes relevant to bio and chemical sensing. We demonstrate that curvature is superior over peak shift and extinction both in terms of signal-to-noise (S/N) ratio and reliability of LSPR sensors. With a curvature, one could readily monitor submonolayer adsorption of a low molecular weight thiol molecule (M(w) = 458.6) onto 13 nm AuNPs. It is also worthwhile mentioning that curvature is virtually insensitive to instrumental instabilities and artifacts occurring during measurement. Instabilities such as baseline tilt and shift, shift in peak position as well as sharp spikes/steps in the extinction spectra do not induce artifacts in the sensorgrams of curvature.

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.

Characterization of cells and bacteria by photophoretic velocimetry

NASA Astrophysics Data System (ADS)

Helmbrecht, Clemens; Niessner, Reinhard; Haisch, Christoph

2008-02-01

The migration induced by intensive light is termed photophoresis. We could show that the evaluation of light-induced velocities of microparticles, bacteria and cells suspended in water is valuable for the prediction of their intrinsic properties. Two different laser setups were evaluated for photophoretic migration, a He-Ne laser (P = 45 mW, λ = 633 nm) and a diode-pumped cw-Nd:YAG (P = 1.1 W, λ = 532 nm). When analyzing the migration behavior of particles, we find significant differences depending on both, geometrical size and refractive index. We describe migration of PS particles of different size as well as with different refractive index but same diameter, SiO II and melamine resin. The potential for the separation of biological matter is shown as velocity distributions of heat killed bacteria of Escherichia coli, Salmonella enteritidis, and baker's yeast is reported.

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.

Near-infrared left-handed metamaterials made of arrays of upright split-ring pairs

NASA Astrophysics Data System (ADS)

Chan, Hsun-Chi; Sun, Shulin; Guo, Guang-Yu

2018-07-01

Electromagnetic metamaterials are man-made structures that have novel properties such as a negative refraction index, not attainable in naturally occurring materials. Although negative index materials (NIMs) in microwave frequencies were demonstrated in 2001, it is still challenging to design NIMs for optical frequencies especially those with both negative permittivity and negative permeability (known as left-handed metamaterials (LHMs)). Here, by going beyond the traditional concept of the combination of artificial electronic and magnetic meta-atoms to design NIMs, we propose a novel LHM composed of an array of upright split-ring pairs working in the near-infrared region. Our electromagnetic simulations reveal the underlying mechanism that the coupling of the two rings can stimulate simultaneously both the electric and magnetic resonances. The proposed structure has a highest refractive index of  ‑2, a highest figure of merit of 21, good air-matched impedance and 180 nm double negative bandwidth, which excel the performances of many previous proposals. We also numerically demonstrate the negative refraction of this metamaterial in both the single-layer form and wedge-shaped lens.

Size and shape in Melipona quadrifasciata anthidioides Lepeletier, 1836 (Hymenoptera; Meliponini).

PubMed

Nunes, L A; Passos, G B; Carvalho, C A L; Araújo, E D

2013-11-01

This study aimed to identify differences in wing shape among populations of Melipona quadrifasciata anthidioides obtained in 23 locations in the semi-arid region of Bahia state (Brazil). Analysis of the Procrustes distances among mean wing shapes indicated that population structure did not determine shape variation. Instead, populations were structured geographically according to wing size. The Partial Mantel Test between morphometric (shape and size) distance matrices and altitude, taking geographic distances into account, was used for a more detailed understanding of size and shape determinants. A partial Mantel test between morphometris (shape and size) variation and altitude, taking geographic distances into account, revealed that size (but not shape) is largely influenced by altitude (r = 0.54 p < 0.01). These results indicate greater evolutionary constraints for the shape variation, which must be directly associated with aerodynamic issues in this structure. The size, however, indicates that the bees tend to have larger wings in populations located at higher altitudes.

Refraction in the lower troposphere: Higher order image distortion effects due to refractive profile curvature

NASA Astrophysics Data System (ADS)

Short, Daniel J.

There are many applications that rely on the propagation of light through the atmosphere - all of which are subject to atmospheric conditions. While there are obvious processes such as scattering due to particulates like clouds and dust that affect the received intensity of the radiation, the clear atmosphere can also cause significant effects. Refraction is a clear air effect that can cause a variety of phenomena such as apparent relocation, stretching and compression of objects when viewed through the atmosphere. Recently, there has been significant interest in studying the refractive effects for low angle paths within the troposphere, and in particular, near-horizontal paths in the Earth's boundary layer, which is adjacent to the ground. Refractive effects in this case become problematic for many terrestrial optical applications. For example, the pointing of a free space optical communication or a remote sensing system can suffer wandering effects, high-resolution imagery can present distorted and/or dislocated targets, optical tracking of targets can be inaccurate, and optical geodetic surveying accuracy is also very sensitive to the effects of refraction. The work in this dissertation was inspired by data from a time-lapse camera system that collects images of distant targets over a near-horizontal path along the ground. This system was used previously to study apparent diurnal image displacement and this dissertation extends that work by exploring the higher order effects that result from curvature in the vertical refractive index profile of the atmosphere. There are surprisingly few experiments involving atmospheric refractive effects that carefully correlate field data to analytical expressions and other factors such as meteorological data. In working with the time-lapse data, which is comprised of sequences of hundreds or thousands of images collected over durations of weeks or months, it is important to develop straightforward analysis techniques that can be applied to characterize the refractive effects. To help with the time-lapse image refraction analysis process, a second order ray trace scheme has been developed. The ray trace is based on existing lens system tracing procedures, but is adapted for use with the atmospheric refractivity profile. The standard practice of ray tracing uses linear approximations through each element to obtain a ray path, however, the method described in this dissertation uses a quadratic correction term in order to more accurately and efficiently simulate the curvature of rays as they propagate through a gradient refractive index medium such as the atmosphere. Although a variety of finite element solutions have been implemented to describe ray trajectories in nonlinear refractive mediums, the new ray tracer described here is much easier to implement and provides quick, intuitive results. The method is tested against exact analytical ray height solutions for known profiles and was found to give nearly identical results. The ray trace was then applied to real atmospheric data and was found to give plausible results. The tay trace gives a visual aid in understanding the physical path the light takes in traversing the potential field. This will be beneficial in linking optical data to weather model data in an effort to develop a forecasting model for refraction. By selecting the correct boundary and initial conditions, we are able to model rays through the profile. Understanding the system will ultimately help in later analysis. A primary objective of this dissertation is to expand on the work mentioned above on image dislocation and consider the effects of towering (stretching) and stooping (compression) in the imagery. These effects can be explained as a type of lensing by the atmosphere due to nonlinear gradients. To achieve towering and stooping, a curved vertical index profile is required. Where a positive lensing action by the medium causes some ray focusing, back projection from at the arrival angles shows the target viewed by an observer will appear stretched, or magnified (towering). Conversely, with a negative lensing action the target viewed will appear shortened or compressed (stooping). The lensing can be modeled with a parabolic refractive index profile and the curvature of the profile is characterized by the curvature parameter alpha (units: m-1). The objective of chapter 4 is to estimate the curvature parameter from an analysis of the images collected by the camera system. In effect, the camera acts as a device that measures ray angle of arrival so image changes that appear as a stretch can be related to changes in the curvature of the index profile. Time-lapse images of the F & A Dairy products building in Las Cruces, NM (15.3 km range from the camera at the NMSU campus) were analyzed using a manual cursor-marking MATLAB script developed for this project. For several different dates, we found the largest stretches occur in the morning. For example, a comparison of two morning images separated by an hour shows the apparent height of the building in a second image gained about 34 pixels compared to the first image. The refractive index curvature change for this case is calculated and found to be alpha = 6.0 x 10-5 m-1 . As the day progressed the image slowly compressed back to the early morning size. Optical measurements of the local index of refraction profile of the atmosphere have been made in the past but usually only for isolated events or time periods. There is little data to describe occurrence probabilities, spatial or temporal properties, or relative strength of effects for different seasons, or even durations of weeks. In this dissertation, time-lapse image data from two separate weeks were analyzed for daily stretching/compressing events and presented graphically. The results show a systematic trend of dramatic size changes in the morning and a slow progression to normal building size as the day continues. Using the optical data presented in chapter 5 and the method for determining a in chapter 4, a method using analytical expressions is presented for determining the refractivity. After a solution is found, two checks are done to test the validity of the results. The first check is simulated in a ray trace model to verify the results are physically relevant and produce rays that can plausibly lead to the correct apparent building size. The second check is a comparison of the estimated gradient index profile from the inversion with the values of the numerical weather model. Using the data from week of November 2014, a day from October 2014, and a day from the March 2015, the optical data was inverted to solve for the refractivity constants dh and z in order to recreate an approximate refractivity profile responsible for the observed stretching. Example values found for the constants are dh=21.49m and z=30m for November 26, 2014. The profile that is created by these constants was found to be fairly consistent with available weather model data.

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.

Photonic jet reconstruction for particle refractive index measurement by digital in-line holography.

PubMed

Sentis, Matthias P L; Onofri, Fabrice R A; Lamadie, Fabrice

2017-01-23

A new and computationally efficient approach is proposed for determining the refractive index of spherical and transparent particles, in addition to their size and 3D position, using digital in-line holography. The method is based on the localization of the maximum intensity position of the photonic jet with respect to the particle center retrieved from the back propagation of recorded holograms. Rigorous electromagnetic calculations and experimental results demonstrate that for liquid-liquid systems and droplets with a radius > 30µm, a refractive index measurement with a resolution inferior to 4 × 10^-3 is achievable, revealing a significant potential for the use of this method to investigate multiphase flows. The resolution for solid or liquid particles in gas is expected to be lower but sufficient for the recognition of particle material.

Differentiating gold nanorod samples using particle size and shape distributions from transmission electron microscope images

NASA Astrophysics Data System (ADS)

Grulke, Eric A.; Wu, Xiaochun; Ji, Yinglu; Buhr, Egbert; Yamamoto, Kazuhiro; Song, Nam Woong; Stefaniak, Aleksandr B.; Schwegler-Berry, Diane; Burchett, Woodrow W.; Lambert, Joshua; Stromberg, Arnold J.

2018-04-01

Size and shape distributions of gold nanorod samples are critical to their physico-chemical properties, especially their longitudinal surface plasmon resonance. This interlaboratory comparison study developed methods for measuring and evaluating size and shape distributions for gold nanorod samples using transmission electron microscopy (TEM) images. The objective was to determine whether two different samples, which had different performance attributes in their application, were different with respect to their size and/or shape descriptor distributions. Touching particles in the captured images were identified using a ruggedness shape descriptor. Nanorods could be distinguished from nanocubes using an elongational shape descriptor. A non-parametric statistical test showed that cumulative distributions of an elongational shape descriptor, that is, the aspect ratio, were statistically different between the two samples for all laboratories. While the scale parameters of size and shape distributions were similar for both samples, the width parameters of size and shape distributions were statistically different. This protocol fulfills an important need for a standardized approach to measure gold nanorod size and shape distributions for applications in which quantitative measurements and comparisons are important. Furthermore, the validated protocol workflow can be automated, thus providing consistent and rapid measurements of nanorod size and shape distributions for researchers, regulatory agencies, and industry.

Nine loci for ocular axial length identified through genome-wide association studies, including shared loci with refractive error.

PubMed

Cheng, Ching-Yu; Schache, Maria; Ikram, M Kamran; Young, Terri L; Guggenheim, Jeremy A; Vitart, Veronique; MacGregor, Stuart; Verhoeven, Virginie J M; Barathi, Veluchamy A; Liao, Jiemin; Hysi, Pirro G; Bailey-Wilson, Joan E; St Pourcain, Beate; Kemp, John P; McMahon, George; Timpson, Nicholas J; Evans, David M; Montgomery, Grant W; Mishra, Aniket; Wang, Ya Xing; Wang, Jie Jin; Rochtchina, Elena; Polasek, Ozren; Wright, Alan F; Amin, Najaf; van Leeuwen, Elisabeth M; Wilson, James F; Pennell, Craig E; van Duijn, Cornelia M; de Jong, Paulus T V M; Vingerling, Johannes R; Zhou, Xin; Chen, Peng; Li, Ruoying; Tay, Wan-Ting; Zheng, Yingfeng; Chew, Merwyn; Burdon, Kathryn P; Craig, Jamie E; Iyengar, Sudha K; Igo, Robert P; Lass, Jonathan H; Chew, Emily Y; Haller, Toomas; Mihailov, Evelin; Metspalu, Andres; Wedenoja, Juho; Simpson, Claire L; Wojciechowski, Robert; Höhn, René; Mirshahi, Alireza; Zeller, Tanja; Pfeiffer, Norbert; Lackner, Karl J; Bettecken, Thomas; Meitinger, Thomas; Oexle, Konrad; Pirastu, Mario; Portas, Laura; Nag, Abhishek; Williams, Katie M; Yonova-Doing, Ekaterina; Klein, Ronald; Klein, Barbara E; Hosseini, S Mohsen; Paterson, Andrew D; Makela, Kari-Matti; Lehtimaki, Terho; Kahonen, Mika; Raitakari, Olli; Yoshimura, Nagahisa; Matsuda, Fumihiko; Chen, Li Jia; Pang, Chi Pui; Yip, Shea Ping; Yap, Maurice K H; Meguro, Akira; Mizuki, Nobuhisa; Inoko, Hidetoshi; Foster, Paul J; Zhao, Jing Hua; Vithana, Eranga; Tai, E-Shyong; Fan, Qiao; Xu, Liang; Campbell, Harry; Fleck, Brian; Rudan, Igor; Aung, Tin; Hofman, Albert; Uitterlinden, André G; Bencic, Goran; Khor, Chiea-Chuen; Forward, Hannah; Pärssinen, Olavi; Mitchell, Paul; Rivadeneira, Fernando; Hewitt, Alex W; Williams, Cathy; Oostra, Ben A; Teo, Yik-Ying; Hammond, Christopher J; Stambolian, Dwight; Mackey, David A; Klaver, Caroline C W; Wong, Tien-Yin; Saw, Seang-Mei; Baird, Paul N

2013-08-08

Refractive errors are common eye disorders of public health importance worldwide. Ocular axial length (AL) is the major determinant of refraction and thus of myopia and hyperopia. We conducted a meta-analysis of genome-wide association studies for AL, combining 12,531 Europeans and 8,216 Asians. We identified eight genome-wide significant loci for AL (RSPO1, C3orf26, LAMA2, GJD2, ZNRF3, CD55, MIP, and ALPPL2) and confirmed one previously reported AL locus (ZC3H11B). Of the nine loci, five (LAMA2, GJD2, CD55, ALPPL2, and ZC3H11B) were associated with refraction in 18 independent cohorts (n = 23,591). Differential gene expression was observed for these loci in minus-lens-induced myopia mouse experiments and human ocular tissues. Two of the AL genes, RSPO1 and ZNRF3, are involved in Wnt signaling, a pathway playing a major role in the regulation of eyeball size. This study provides evidence of shared genes between AL and refraction, but importantly also suggests that these traits may have unique pathways. Copyright © 2013 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.

Impact of atmospheric refraction: how deeply can we probe exo-earth's atmospheres during primary eclipse observations?

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

Bétrémieux, Yan; Kaltenegger, Lisa, E-mail: betremieux@mpia.de

2014-08-10

Most models used to predict or fit exoplanet transmission spectra do not include all the effects of atmospheric refraction. Namely, the angular size of the star with respect to the planet can limit the lowest altitude, or highest density and pressure, probed during primary eclipses as no rays passing below this critical altitude can reach the observer. We discuss this geometrical effect of refraction for all exoplanets and tabulate the critical altitude, density, and pressure for an exoplanet identical to Earth with a 1 bar N{sub 2}/O{sub 2} atmosphere as a function of both the incident stellar flux (Venus, Earth,more » and Mars-like) at the top of the atmosphere and the spectral type (O5-M9) of the host star. We show that such a habitable exo-Earth can be probed to a surface pressure of 1 bar only around the coolest stars. We present 0.4-5.0 μm model transmission spectra of Earth's atmosphere viewed as a transiting exoplanet, and show how atmospheric refraction modifies the transmission spectrum depending on the spectral type of the host star. We demonstrate that refraction is another phenomenon that can potentially explain flat transmission spectra over some spectral regions.« less

Development of a refractive error quality of life scale for Thai adults (the REQ-Thai).

PubMed

Sukhawarn, Roongthip; Wiratchai, Nonglak; Tatsanavivat, Pyatat; Pitiyanuwat, Somwung; Kanato, Manop; Srivannaboon, Sabong; Guyatt, Gordon H

2011-08-01

To develop a scale for measuring refractive error quality of life (QOL) for Thai adults. The full survey comprised 424 respondents from 5 medical centers in Bangkok and from 3 medical centers in Chiangmai, Songkla and KhonKaen provinces. Participants were emmetropes and persons with refractive correction with visual acuity of 20/30 or better An item reduction process was employed by combining 3 methods-expert opinion, impact method and item-total correlation methods. The classical reliability testing and the validity testing including convergent, discriminative and construct validity was performed. The developed questionnaire comprised 87 items in 6 dimensions: 1) quality of vision, 2) visual function, 3) social function, 4) psychological function, 5) symptoms and 6) refractive correction problems. It is the 5-level Likert scale type. The Cronbach's Alpha coefficients of its dimensions ranged from 0.756 to 0. 979. All validity testing were shown to be valid. The construct validity was validated by the confirmatory factor analysis. A short version questionnaire comprised 48 items with good reliability and validity was also developed. This is the first validated instrument for measuring refractive error quality of life for Thai adults that was developed with strong research methodology and large sample size.

Plasmonic refractive index sensing using strongly coupled metal nanoantennas: nonlocal limitations.

PubMed

Wang, Hancong

2018-06-25

Localized surface plasmon resonance based on coupled metallic nanoparticles has been extensively studied in the refractive index sensing and the detection of molecules. The amount of resonance peak-shift depends on the refractive index of surrounding medium and the geometry/symmetry of plasmonic oligomers. It has recently been found that as the feature size or the gap distance of plasmonic nanostructures approaches several nanometers, quantum effects can change the plasmon coupling in nanoparticles. However, most of the research on plasmonic sensing has been done based on classical local calculations even for the interparticle gap below ~3 nm, in which the nonlocal screening plays an important role. Here, we theoretically investigate the nonlocal effect on the evolution of various plasmon resonance modes in strongly coupled nanoparticle dimer and trimer antennas with the gap down to 1 nm. Then, the refractive index sensing in these nonlocal systems is evaluated and compared with the results in classical calculations. We find that in the nonlocal regime, both refractive index sensibility factor and figure of merit are actually smaller than their classical counterparts mainly due to the saturation of plasmon shifts. These results would be beneficial for the understanding of interaction between light and nonlocal plasmonic nanostructures and the development of plasmonic devices such as nanosensors and nanoantennas.

Rapid assessment of nonlinear optical propagation effects in dielectrics

PubMed Central

Hoyo, J. del; de la Cruz, A. Ruiz; Grace, E.; Ferrer, A.; Siegel, J.; Pasquazi, A.; Assanto, G.; Solis, J.

2015-01-01

Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation of the laser beam in order to predict the optimal range of processing parameters in a wide variety of cases. We develop here a method based on the simple monitoring of the nonlinear beam shaping against numerical prediction. The numerical code solves the nonlinear Schrödinger equation with nonlinear absorption under simplified conditions by employing a state-of-the art computationally efficient approach. By comparing with experimental results we can rapidly estimate the nonlinear refractive index and nonlinear absorption coefficients of the material. The validity of this approach has been tested in a variety of experiments where nonlinearities play a key role, like spatial soliton shaping or fs-laser waveguide writing. The approach provides excellent results for propagated power densities for which free carrier generation effects can be neglected. Above such a threshold, the peculiarities of the nonlinear propagation of elliptical beams enable acquiring an instantaneous picture of the deposition of energy inside the material realistic enough to estimate the effective nonlinear refractive index and nonlinear absorption coefficients that can be used for predicting the spatial distribution of energy deposition inside the material and controlling the beam in the writing process. PMID:25564243

Porous Silicon Gradient Refractive Index Micro-Optics.

PubMed

Krueger, Neil A; Holsteen, Aaron L; Kang, Seung-Kyun; Ocier, Christian R; Zhou, Weijun; Mensing, Glennys; Rogers, John A; Brongersma, Mark L; Braun, Paul V

2016-12-14

The emergence and growth of transformation optics over the past decade has revitalized interest in how a gradient refractive index (GRIN) can be used to control light propagation. Two-dimensional demonstrations with lithographically defined silicon (Si) have displayed the power of GRIN optics and also represent a promising opportunity for integrating compact optical elements within Si photonic integrated circuits. Here, we demonstrate the fabrication of three-dimensional Si-based GRIN micro-optics through the shape-defined formation of porous Si (PSi). Conventional microfabrication creates Si square microcolumns (SMCs) that can be electrochemically etched into PSi elements with nanoscale porosity along the shape-defined etching pathway, which imparts the geometry with structural birefringence. Free-space characterization of the transmitted intensity distribution through a homogeneously etched PSi SMC exhibits polarization splitting behavior resembling that of dielectric metasurfaces that require considerably more laborious fabrication. Coupled birefringence/GRIN effects are studied by way of PSi SMCs etched with a linear (increasing from edge to center) GRIN profile. The transmitted intensity distribution shows polarization-selective focusing behavior with one polarization focused to a diffraction-limited spot and the orthogonal polarization focused into two laterally displaced foci. Optical thickness-based analysis readily predicts the experimentally observed phenomena, which strongly match finite-element electromagnetic simulations.

Corneal Biomechanics in Ectatic Diseases: Refractive Surgery Implications

PubMed Central

Ambrósio, Jr, Renato; Correia, Fernando Faria; Lopes, Bernardo; Salomão, Marcella Q.; Luz, Allan; Dawson, Daniel G.; Elsheikh, Ahmed; Vinciguerra, Riccardo; Vinciguerra, Paolo; Roberts, Cynthia J.

2017-01-01

Background: Ectasia development occurs due to a chronic corneal biomechanical decompensation or weakness, resulting in stromal thinning and corneal protrusion. This leads to corneal steepening, increase in astigmatism, and irregularity. In corneal refractive surgery, the detection of mild forms of ectasia pre-operatively is essential to avoid post-operative progressive ectasia, which also depends on the impact of the procedure on the cornea. Method: The advent of 3D tomography is proven as a significant advancement to further characterize corneal shape beyond front surface topography, which is still relevant. While screening tests for ectasia had been limited to corneal shape (geometry) assessment, clinical biomechanical assessment has been possible since the introduction of the Ocular Response Analyzer (Reichert Ophthalmic Instruments, Buffalo, USA) in 2005 and the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) in 2010. Direct clinical biomechanical evaluation is recognized as paramount, especially in detection of mild ectatic cases and characterization of the susceptibility for ectasia progression for any cornea. Conclusions: The purpose of this review is to describe the current state of clinical evaluation of corneal biomechanics, focusing on the most recent advances of commercially available instruments and also on future developments, such as Brillouin microscopy. PMID:28932334

Cross-phase-modulation-induced temporal reflection and waveguiding of optical pulses

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

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. In this paper we investigate the practicalmore » conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of pump pulses as well as the nature of medium dispersion at the pump and probe wavelength (normal versus anomalous) play important roles. A super-Gaussian shape of pump pulses is particularly helpful because of its relatively sharp edges. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton,whose unique properties can be exploited to advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating timing jitter.« less

Cross-phase-modulation-induced temporal reflection and waveguiding of optical pulses

DOE PAGES

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

2018-01-31

Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. In this paper we investigate the practicalmore » conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of pump pulses as well as the nature of medium dispersion at the pump and probe wavelength (normal versus anomalous) play important roles. A super-Gaussian shape of pump pulses is particularly helpful because of its relatively sharp edges. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton,whose unique properties can be exploited to advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating timing jitter.« less

Rapid assessment of nonlinear optical propagation effects in dielectrics.

PubMed

del Hoyo, J; de la Cruz, A Ruiz; Grace, E; Ferrer, A; Siegel, J; Pasquazi, A; Assanto, G; Solis, J

2015-01-07

Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation of the laser beam in order to predict the optimal range of processing parameters in a wide variety of cases. We develop here a method based on the simple monitoring of the nonlinear beam shaping against numerical prediction. The numerical code solves the nonlinear Schrödinger equation with nonlinear absorption under simplified conditions by employing a state-of-the art computationally efficient approach. By comparing with experimental results we can rapidly estimate the nonlinear refractive index and nonlinear absorption coefficients of the material. The validity of this approach has been tested in a variety of experiments where nonlinearities play a key role, like spatial soliton shaping or fs-laser waveguide writing. The approach provides excellent results for propagated power densities for which free carrier generation effects can be neglected. Above such a threshold, the peculiarities of the nonlinear propagation of elliptical beams enable acquiring an instantaneous picture of the deposition of energy inside the material realistic enough to estimate the effective nonlinear refractive index and nonlinear absorption coefficients that can be used for predicting the spatial distribution of energy deposition inside the material and controlling the beam in the writing process.

Rapid assessment of nonlinear optical propagation effects in dielectrics

NASA Astrophysics Data System (ADS)

Hoyo, J. Del; de La Cruz, A. Ruiz; Grace, E.; Ferrer, A.; Siegel, J.; Pasquazi, A.; Assanto, G.; Solis, J.

2015-01-01

Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation of the laser beam in order to predict the optimal range of processing parameters in a wide variety of cases. We develop here a method based on the simple monitoring of the nonlinear beam shaping against numerical prediction. The numerical code solves the nonlinear Schrödinger equation with nonlinear absorption under simplified conditions by employing a state-of-the art computationally efficient approach. By comparing with experimental results we can rapidly estimate the nonlinear refractive index and nonlinear absorption coefficients of the material. The validity of this approach has been tested in a variety of experiments where nonlinearities play a key role, like spatial soliton shaping or fs-laser waveguide writing. The approach provides excellent results for propagated power densities for which free carrier generation effects can be neglected. Above such a threshold, the peculiarities of the nonlinear propagation of elliptical beams enable acquiring an instantaneous picture of the deposition of energy inside the material realistic enough to estimate the effective nonlinear refractive index and nonlinear absorption coefficients that can be used for predicting the spatial distribution of energy deposition inside the material and controlling the beam in the writing process.

Refraction-Assisted Solar Thermoelectric Generator based on Phase-Change Lens

PubMed Central

Kim, Myoung-Soo; Kim, Min-Ki; Jo, Sung-Eun; Joo, Chulmin; Kim, Yong-Jun

2016-01-01

Solar thermoelectric generators (STEGs), which are used for various applications, (particularly small size electronic devices), have optical concentration systems for high energy conversion efficiency. In this study, a refraction-assisted STEG (R-STEG) is designed based on phase-change materials. As the phase-change material (PCM) changes phase from solid to liquid, its refractive index and transmittance also change, resulting in changes in the refraction of the sunlight transmitted through it, and concentration of solar energy in the phase-change lens. This innovative design facilitates double focusing the solar energy through the optical lens and a phase-change lens. This mechanism resulted in the peak energy conversion efficiencies of the R-STEG being 60% and 86% higher than those of the typical STEG at solar intensities of 1 kW m−2 and 1.5 kW m−2, respectively. In addition, the energy stored in PCM can help to generate steady electrical energy when the solar energy was removed. This work presents significant progress regarding the optical characteristic of PCM and optical concentration systems of STEGs. PMID:27283350

Refraction-Assisted Solar Thermoelectric Generator based on Phase-Change Lens.

PubMed

Kim, Myoung-Soo; Kim, Min-Ki; Jo, Sung-Eun; Joo, Chulmin; Kim, Yong-Jun

2016-06-10

Solar thermoelectric generators (STEGs), which are used for various applications, (particularly small size electronic devices), have optical concentration systems for high energy conversion efficiency. In this study, a refraction-assisted STEG (R-STEG) is designed based on phase-change materials. As the phase-change material (PCM) changes phase from solid to liquid, its refractive index and transmittance also change, resulting in changes in the refraction of the sunlight transmitted through it, and concentration of solar energy in the phase-change lens. This innovative design facilitates double focusing the solar energy through the optical lens and a phase-change lens. This mechanism resulted in the peak energy conversion efficiencies of the R-STEG being 60% and 86% higher than those of the typical STEG at solar intensities of 1 kW m(-2) and 1.5 kW m(-2), respectively. In addition, the energy stored in PCM can help to generate steady electrical energy when the solar energy was removed. This work presents significant progress regarding the optical characteristic of PCM and optical concentration systems of STEGs.

Measurement of wavelength-dependent refractive indices of liquid scintillation cocktails.

PubMed

Kossert, Karsten

2013-12-01

Refractive indices of several commercial liquid scintillation cocktails were measured by means of an automatic critical-angle dispersion refractometer in the wavelength range from 404.7 nm to 706.5 nm. The results are needed for various applications. In particular, detailed Monte Carlo simulations of liquid scintillation counters that include the computation of optical light require these data. In addition, the refractive index is an important parameter for studies of micelle sizes by means of dynamic light scattering. In this work, the refractive indices were determined for Ultima Gold™, Ultima Gold™ F, Ultima Gold™ LLT, Ultima Gold™ AB, Hionic Fluor™, Permafluor(®)E+, Mineral Oil Scintillator, Insta-Gel Plus, OptiPhase HiSafe 2, OptiPhase HiSafe 3, Ultima Gold™ XR, Insta-Gel Plus, AquaLight, MaxiLight and Ultima Gold™ MV at 16°C, 18°C, 20°C and 22°C. The carbon dioxide absorber Carbo-Sorb(®)E was also analyzed. For some scintillators, various batches were compared and mixtures with water or nitromethane were studied. © 2013 Published by Elsevier Ltd.

Fabrication Localized Surface Plasmon Resonance sensor chip of gold nanoparticles and detection lipase-osmolytes interaction

NASA Astrophysics Data System (ADS)

Ghodselahi, T.; Hoornam, S.; Vesaghi, M. A.; Ranjbar, B.; Azizi, A.; Mobasheri, H.

2014-09-01

Co-deposition of RF-sputtering and RF-PECVD from acetylene gas and Au target were used to prepare sensor chip of gold nanoparticles (Au NPs). Deposition conditions were optimized to reach a Localized Surface Plasmon Resonance (LSPR) sensor chip of Au NPs with particle size less than 10 nm. The RF power was set at 180 W and the initial gas pressure was set at 0.035 mbar. Transmission Electron Microscopy (TEM) images and Atomic Force Microscopy (AFM) data were used to investigate particles size and surface morphology of LSPR sensor chip. The Au and C content of the LSPR sensor chip of Au NPs was obtained from X-ray photoelectron spectroscopy (XPS). The hydrogenated amorphous carbon (a-C:H) thin film was used as intermediate material to immobilize Au NPs on the SiO2 substrate. The interaction between two types of osmolytes, i.e. sorbitol and trehalose, with Pseudomonas cepacia lipase (PCL) were detected by the prepared LSPR biosensor chip. The detection mechanism is based on LSPR spectroscopy in which the wavelength of absorption peak is sensitive to the refractive index of the environment of the Au NPs. This mechanism eliminates the use of a probe or immobilization of PCL on the Au NPs of LSPR sensor chip. The interaction between PCL and osmolytes can change refractive index of the mixture or solution. We found that unlike to trehalose, sorbitol interacts with the PCL. This interaction increases refractive index of the PCL and sorbitol mixture. Refractive index of PCL in the presence of different concentration of sorbitol was obtained by Mie theory modeling of LSPR peaks. This modeling stated that the present LSPR sensor chip has sensitivity as high as wavelength shift of 175 nm per refractive index. Moreover, the detection of such weakly interaction between bio-molecules cannot be achieved by other analysis.

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).

Light propagation with phase discontinuities: generalized laws of reflection and refraction.

PubMed

Yu, Nanfang; Genevet, Patrice; Kats, Mikhail A; Aieta, Francesco; Tetienne, Jean-Philippe; Capasso, Federico; Gaburro, Zeno

2011-10-21

Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat's principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.

Reconfigurable and responsive droplet-based compound micro-lenses.

PubMed

Nagelberg, Sara; Zarzar, Lauren D; Nicolas, Natalie; Subramanian, Kaushikaram; Kalow, Julia A; Sresht, Vishnu; Blankschtein, Daniel; Barbastathis, George; Kreysing, Moritz; Swager, Timothy M; Kolle, Mathias

2017-03-07

Micro-scale optical components play a crucial role in imaging and display technology, biosensing, beam shaping, optical switching, wavefront-analysis, and device miniaturization. Herein, we demonstrate liquid compound micro-lenses with dynamically tunable focal lengths. We employ bi-phase emulsion droplets fabricated from immiscible hydrocarbon and fluorocarbon liquids to form responsive micro-lenses that can be reconfigured to focus or scatter light, form real or virtual images, and display variable focal lengths. Experimental demonstrations of dynamic refractive control are complemented by theoretical analysis and wave-optical modelling. Additionally, we provide evidence of the micro-lenses' functionality for two potential applications-integral micro-scale imaging devices and light field display technology-thereby demonstrating both the fundamental characteristics and the promising opportunities for fluid-based dynamic refractive micro-scale compound lenses.

Reconfigurable and responsive droplet-based compound micro-lenses

PubMed Central

Nagelberg, Sara; Zarzar, Lauren D.; Nicolas, Natalie; Subramanian, Kaushikaram; Kalow, Julia A.; Sresht, Vishnu; Blankschtein, Daniel; Barbastathis, George; Kreysing, Moritz; Swager, Timothy M.; Kolle, Mathias

2017-01-01

Micro-scale optical components play a crucial role in imaging and display technology, biosensing, beam shaping, optical switching, wavefront-analysis, and device miniaturization. Herein, we demonstrate liquid compound micro-lenses with dynamically tunable focal lengths. We employ bi-phase emulsion droplets fabricated from immiscible hydrocarbon and fluorocarbon liquids to form responsive micro-lenses that can be reconfigured to focus or scatter light, form real or virtual images, and display variable focal lengths. Experimental demonstrations of dynamic refractive control are complemented by theoretical analysis and wave-optical modelling. Additionally, we provide evidence of the micro-lenses' functionality for two potential applications—integral micro-scale imaging devices and light field display technology—thereby demonstrating both the fundamental characteristics and the promising opportunities for fluid-based dynamic refractive micro-scale compound lenses. PMID:28266505

Semiconductor laser devices having lateral refractive index tailoring

DOEpatents

Ashby, Carol I. H.; Hadley, G. Ronald; Hohimer, John P.; Owyoung, Adelbert

1990-01-01

A broad-area semiconductor laser diode includes an active lasing region interposed between an upper and a lower cladding layer, the laser diode further comprising structure for controllably varying a lateral refractive index profile of the diode to substantially compensate for an effect of junction heating during operation. In embodiments disclosed the controlling structure comprises resistive heating strips or non-radiative linear junctions disposed parallel to the active region. Another embodiment discloses a multi-layered upper cladding region selectively disordered by implanted or diffused dopant impurities. Still another embodiment discloses an upper cladding layer of variable thickness that is convex in shape and symmetrically disposed about a central axis of the active region. The teaching of the invention is also shown to be applicable to arrays of semiconductor laser diodes.

Manipulating femtosecond pulse shape using liquid crystals infiltrated one-dimensional graded index photonic crystal waveguides composed of coupled-cavities

NASA Astrophysics Data System (ADS)

Fathollahi Khalkhali, T.; Bananej, A.

2017-10-01

In this paper, we investigate the transmission of a 10-femtosecond pulse through an ordinary and graded index coupled-cavity waveguide, using finite-difference time-domain and transfer matrix method. The ordinary structure is composed of dielectric/liquid crystal layers in which four defect layers are placed symmetrically. Next, we introduce a graded structure based on the ordinary system in which dielectric refractive index slightly increases with a constant step value from the beginning to the end of the structure while liquid crystal layers are maintained unchanged. Simulation results reveal that by applying an external static electric field and controlling liquid crystal refractive index in graded structure, it is possible to transmit an ultrashort pulse with negligible distortion and attenuation.

Size dependence of second-harmonic generation at the surface of microspheres

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

Viarbitskaya, Sviatlana; Meulen, Peter van der; Hansson, Tony

2010-05-15

The resonance-enhanced surface second-harmonic generation (SHG) from a suspension of polystyrene microspheres was investigated as a function of particle size in a range of the order of the fundamental wavelength for two different second-harmonic-enhancing dyes--malachite green and pyridine 1. The two dyes gave the same strongly modulated pattern of the forward second-harmonic scattering efficiency. Direct comparison to the nonlinear Rayleigh-Gans-Debye (NLRGD) and nonlinear Wentzel-Kramers-Brillouin (NLWKB) model predictions showed that the NLWKB model reproduces the overall trend in the size dependence but fails with respect to the strong modulations. The standard NLRGD model was found to fail altogether in the presentmore » particle size range, which was well beyond the observed upper particle size for which the NLRGD and NLWKB models give comparable results. A generalization of the NLRGD model to allow for dispersion and to use the particle refractive indices instead of those of the surrounding medium extended its applicability range by almost an order of magnitude in particle size. There is a pronounced maximal SHG efficiency for particles with a radius that is close to the fundamental wavelength inside the particle. The optically soft particle approximation is inadequate to describe the SHG in this particle size range, as refraction and reflection of the waves at the particle surface have a decisive influence. Dispersion of the media plays a negligible role for particle sizes up to about twice the optimal one for SHG.« less

An experimental investigation of the effect of boundary layer refraction on the noise from a high-speed propeller

NASA Technical Reports Server (NTRS)

Dittmar, J. H.; Burns, R. J.; Leciejewski, D. J.

1984-01-01

Models of supersonic propellers were previously tested for acoustics in the Lewis 8- by 6-Foot Wind Tunnel using pressure transducers mounted in the tunnel ceiling. The boundary layer on the tunnel ceiling is believed to refract some of the propeller noise away from the measurement transducers. Measurements were made on a plate installed in the wind tunnel which had a thinner boundary layer than the ceiling boundary layer. The plate was installed in two locations for comparison with tunnel ceiling noise data and with fuselage data taken on the NASA Dryden Jetstar airplane. Analysis of the data indicates that the refraction increases with: increasing boundary layer thickness; increasing free stream Mach number; increasing frequency; and decreasing sound radiation angle (toward the inlet axis). At aft radiation angles greater than about 100 deg there was little or no refraction. Comparisons with the airplane data indicated that not only is the boundary layer thickness important but also the shape of the velocity profile. Comparisons with an existing two-dimensional theory, using an idealized shear layer to approximate the boundary layer, showed that the theory and data had the same trends. Analysis of the data taken in the tunnel at two different distances from the propeller indicates a decay with distance in the wind tunnel at high Mach numbers but the decay at low Mach numbers is not as clear.

Optical monitoring of thermal effects in RPE during heating

NASA Astrophysics Data System (ADS)

Schuele, G.; Huie, Ph.; Yellachich, D.; Molnar, F. E.; O'Conell-Rodwell, C.; Vitkin, E.; Perelman, L. T.; Palanker, D.

2005-04-01

Fast and non-invasive detection of cellular stress is useful for fundamental research and practical applications in medicine and biology. Using Light Scattering Spectroscopy we extract information about changes in refractive index and size of the cellular organelles. Particle sizes down to 50nm in diameter can be detected using light within the spectral range of 450-850 nm. We monitor the heat-induced sub-cellular structural changes in human RPE cells and, for comparison, in transfected NIH-3T3 cells which express luciferase linked to the heat shock protein (HSP). Using inverse light scattering fitting algorithm, we reconstruct the size distribution of the sub-micron organelles from the light scattering spectrum. The most significant (up to 70%) and rapid (20sec) temperature-related changes can be linked to an increase of refractive index of the 160nm sized mitochondria. The start of this effect coincides with the onset of HSP expression. This technique provides an insight into metabolic processes within organelles larger than 50nm without exogenous staining and opens doors for non-invasive real-time assessment of cellular stress, which can be used for monitoring of retinal laser treatments like transpupillary thermo therapy or PDT.

GLANCING VIEWS OF THE EARTH: FROM A LUNAR ECLIPSE TO AN EXOPLANETARY TRANSIT

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

Garcia Munoz, A.; Barrena, R.; Montanes-Rodriguez, P.

2012-08-20

It has been posited that lunar eclipse observations may help predict the in-transit signature of Earth-like extrasolar planets. However, a comparative analysis of the two phenomena addressing in detail the transport of stellar light through the planet's atmosphere has not yet been presented. Here, we proceed with the investigation of both phenomena by making use of a common formulation. Our starting point is a set of previously unpublished near-infrared spectra collected at various phases during the 2008 August lunar eclipse. We then take the formulation to the limit of an infinitely distant observer in order to investigate the in-transit signaturemore » of the Earth-Sun system as being observed from outside our solar system. The refraction bending of sunlight rays that pass through Earth's atmosphere is a critical factor in the illumination of the eclipsed Moon. Likewise, refraction will have an impact on the in-transit transmission spectrum for specific planet-star systems depending on the refractive properties of the planet's atmosphere, the stellar size, and the planet's orbital distance. For the Earth-Sun system, at mid-transit, refraction prevents the remote observer's access to the lower {approx}12-14 km of the atmosphere and, thus, also to the bulk of the spectroscopically active atmospheric gases. We demonstrate that the effective optical radius of the Earth in-transit is modulated by refraction and varies by {approx}12 km from mid-transit to internal contact. The refractive nature of atmospheres, a property which is rarely accounted for in published investigations, will pose additional challenges to the characterization of Earth-like extrasolar planets. Refraction may have a lesser impact for Earth-like extrasolar planets within the habitable zone of some M-type stars.« less

Relative humidity sensor based on surface plasmon resonance of D-shaped fiber with polyvinyl alcohol embedding Au grating

NASA Astrophysics Data System (ADS)

Yan, Haitao; Han, Daofu; Li, Ming; Lin, Bo

2017-01-01

This paper presents the design, fabrication, and characterization of a D-shaped fiber coated with polyvinyl alcohol (PVA) embedding an Au grating-based relative humidity (RH) sensor. The Au grating is fabricated on a D-shaped fiber to match the wave-vector and excite the surface plasmon, and the PVA is embedded in the Au grating as a sensitive cladding film. The refractive index of PVA changes with the ambient humidity. Measurements in a controlled environment show that the RH sensor can achieve a sensitivity of 5.4 nm per relative humidity unit in the RH range from 0% to 70% RH. Moreover, the surface plasmon resonance can be realized and used for RH sensing at the C band of optical fiber communication instead of the visible light band due to the metallic grating microstructure on the D-shaped fiber.

78 FR 74154 - Draft Guidance for Industry on Size, Shape, and Other Physical Attributes of Generic Tablets and...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-10

...] Draft Guidance for Industry on Size, Shape, and Other Physical Attributes of Generic Tablets and... ``Size, Shape, and Other Physical Attributes of Generic Tablets and Capsules.'' This guidance discusses FDA recommendations for the size, shape, and other physical attributes of generic tablets intended to...

Bidirectional Expression of Metabolic, Structural, and Immune Pathways in Early Myopia and Hyperopia

PubMed Central

Riddell, Nina; Giummarra, Loretta; Hall, Nathan E.; Crewther, Sheila G.

2016-01-01

Myopia (short-sightedness) affects 1.45 billion people worldwide, many of whom will develop sight-threatening secondary disorders. Myopic eyes are characterized by excessive size while hyperopic (long-sighted) eyes are typically small. The biological and genetic mechanisms underpinning the retina's local control of these growth patterns remain unclear. In the present study, we used RNA sequencing to examine gene expression in the retina/RPE/choroid across 3 days of optically-induced myopia and hyperopia induction in chick. Data were analyzed for differential expression of single genes, and Gene Set Enrichment Analysis (GSEA) was used to identify gene sets correlated with ocular axial length and refraction across lens groups. Like previous studies, we found few single genes that were differentially-expressed in a sign-of-defocus dependent manner (only BMP2 at 1 day). Using GSEA, however, we are the first to show that more subtle shifts in structural, metabolic, and immune pathway expression are correlated with the eye size and refractive changes induced by lens defocus. Our findings link gene expression with the morphological characteristics of refractive error, and suggest that physiological stress arising from metabolic and inflammatory pathway activation could increase the vulnerability of myopic eyes to secondary pathologies. PMID:27625591

Potentiation of femtosecond laser intratissue refractive index shaping (IRIS) in the living cornea with sodium fluorescein.

PubMed

Nagy, Lana J; Ding, Li; Xu, Lisen; Knox, Wayne H; Huxlin, Krystel R

2010-02-01

To assess the effectiveness of intratissue refractive index shaping (IRIS) in living corneas and test the hypothesis that it can be enhanced by increasing the two-photon absorption (TPA) of the tissue. Three corneas were removed from adult cats and cut into six pieces, which were placed in preservative (Optisol-GS; Bausch & Lomb, Inc., Irvine, CA) containing 0%, 0.25%, 1%, 1.5%, or 2.5% sodium fluorescein (Na-Fl). An 800-nm Ti:Sapphire femtosecond laser with a 100-fs pulse duration and 80-MHz repetition rate was used to perform IRIS in each piece, creating several refractive index (RI) modification lines at different speeds (between 0.1 and 5 mm/s). The lines were 1 mum wide, 10 microm apart, and approximately 150 microm below the tissue surface. The RI change of each grating was measured using calibrated, differential interference contrast microscopy. TUNEL staining was performed to assess whether IRIS or Na-Fl doping causes cell death. Scanning at 0.1 mm/s changed the RI of undoped, living corneas by 0.005. In doped corneas, RI changes between 0.01 and 0.02 were reliably achieved with higher scanning speeds. The magnitude of RI changes attained was directly proportional to Na-Fl doping concentration and inversely proportional to the scanning speed used to create the gratings. IRIS can be efficiently performed in living corneal tissue. Increasing the TPA of the tissue with Na-Fl increased both the scanning speeds and the magnitude of RI changes in a dose-dependent manner. Ongoing studies are exploring the use of IRIS to alter the optical properties of corneal tissue in situ, over an extended period.

Potentiation of Femtosecond Laser Intratissue Refractive Index Shaping (IRIS) in the Living Cornea with Sodium Fluorescein

PubMed Central

Nagy, Lana J.; Ding, Li; Xu, Lisen; Knox, Wayne H.

2010-01-01

Purpose. To assess the effectiveness of intratissue refractive index shaping (IRIS) in living corneas and test the hypothesis that it can be enhanced by increasing the two-photon absorption (TPA) of the tissue. Methods. Three corneas were removed from adult cats and cut into six pieces, which were placed in preservative (Optisol-GS; Bausch & Lomb, Inc., Irvine, CA) containing 0%, 0.25%, 1%, 1.5%, or 2.5% sodium fluorescein (Na-Fl). An 800-nm Ti:Sapphire femtosecond laser with a 100-fs pulse duration and 80-MHz repetition rate was used to perform IRIS in each piece, creating several refractive index (RI) modification lines at different speeds (between 0.1 and 5 mm/s). The lines were 1 μm wide, 10 μm apart, and ∼150 μm below the tissue surface. The RI change of each grating was measured using calibrated, differential interference contrast microscopy. TUNEL staining was performed to assess whether IRIS or Na-Fl doping causes cell death. Results. Scanning at 0.1 mm/s changed the RI of undoped, living corneas by 0.005. In doped corneas, RI changes between 0.01 and 0.02 were reliably achieved with higher scanning speeds. The magnitude of RI changes attained was directly proportional to Na-Fl doping concentration and inversely proportional to the scanning speed used to create the gratings. Conclusions. IRIS can be efficiently performed in living corneal tissue. Increasing the TPA of the tissue with Na-Fl increased both the scanning speeds and the magnitude of RI changes in a dose-dependent manner. Ongoing studies are exploring the use of IRIS to alter the optical properties of corneal tissue in situ, over an extended period. PMID:19815735

Noninvasive intratissue refractive index shaping (IRIS) of the cornea with blue femtosecond laser light.

PubMed

Xu, Lisen; Knox, Wayne H; DeMagistris, Margaret; Wang, Nadan; Huxlin, Krystel R

2011-10-17

To test the feasibility of intratissue refractive index shaping (IRIS) in living corneas by using 400-nm femtosecond (fs) laser pulses (blue-IRIS). To test the hypothesis that the intrinsic two-photon absorption of the cornea allows blue-IRIS to be performed with greater efficacy than when using 800-nm femtosecond laser pulses. Fresh cat corneas were obtained postmortem and cut into six wedges. Blue laser pulses at 400 nm, with 100-fs pulse duration at 80 MHz were used to micromachine phase gratings into each corneal wedge at scanning speeds from 1 to 15 mm/s. Grating lines were 1 μm wide, 5 μm apart, and 150 μm below the anterior corneal surface. Refractive index (RI) changes in micromachined regions were measured immediately by recording the diffraction efficiency of inscribed gratings. Six hours later, the corneas were processed for histology, and TUNEL staining was performed to assess whether blue-IRIS causes cell death. Scanning at 1 and 2 mm/s caused overt corneal damage in the form of bubbles and burns. At faster scanning speeds (5, 10, and 15 mm/s), phase gratings were created in the corneal stroma, which were shown to be pure RI changes ranging from 0.037 to 0.021 in magnitude. The magnitude of RI change was inversely related to scanning speed. TUNEL staining showed cell death only around bubbles and burns. Blue-IRIS can be performed safely and effectively in living cornea. Compared with near-infrared laser pulses, blue-IRIS enhances both achievable RI change and scanning speed without the need to dope the tissue with two-photon sensitizers, increasing the clinical applicability of this technique.

Noninvasive Intratissue Refractive Index Shaping (IRIS) of the Cornea with Blue Femtosecond Laser Light

PubMed Central

Xu, Lisen; Knox, Wayne H.; DeMagistris, Margaret; Wang, Nadan

2011-01-01

Purpose. To test the feasibility of intratissue refractive index shaping (IRIS) in living corneas by using 400-nm femtosecond (fs) laser pulses (blue-IRIS). To test the hypothesis that the intrinsic two-photon absorption of the cornea allows blue-IRIS to be performed with greater efficacy than when using 800-nm femtosecond laser pulses. Methods. Fresh cat corneas were obtained postmortem and cut into six wedges. Blue laser pulses at 400 nm, with 100-fs pulse duration at 80 MHz were used to micromachine phase gratings into each corneal wedge at scanning speeds from 1 to 15 mm/s. Grating lines were 1 μm wide, 5 μm apart, and 150 μm below the anterior corneal surface. Refractive index (RI) changes in micromachined regions were measured immediately by recording the diffraction efficiency of inscribed gratings. Six hours later, the corneas were processed for histology, and TUNEL staining was performed to assess whether blue-IRIS causes cell death. Results. Scanning at 1 and 2 mm/s caused overt corneal damage in the form of bubbles and burns. At faster scanning speeds (5, 10, and 15 mm/s), phase gratings were created in the corneal stroma, which were shown to be pure RI changes ranging from 0.037 to 0.021 in magnitude. The magnitude of RI change was inversely related to scanning speed. TUNEL staining showed cell death only around bubbles and burns. Conclusions. Blue-IRIS can be performed safely and effectively in living cornea. Compared with near-infrared laser pulses, blue-IRIS enhances both achievable RI change and scanning speed without the need to dope the tissue with two-photon sensitizers, increasing the clinical applicability of this technique. PMID:21931133

Refractive Changes Induced by Spherical Aberration in Laser Correction Procedures: An Adaptive Optics Study.

PubMed

Amigó, Alfredo; Martinez-Sorribes, Paula; Recuerda, Margarita

2017-07-01

To study the effect on vision of induced negative and positive spherical aberration within the range of laser vision correction procedures. In 10 eyes (mean age: 35.8 years) under cyclopegic conditions, spherical aberration values from -0.75 to +0.75 µm in 0.25-µm steps were induced by an adaptive optics system. Astigmatism and spherical refraction were corrected, whereas the other natural aberrations remained untouched. Visual acuity, depth of focus defined as the interval of vision for which the target was still perceived acceptable, contrast sensitivity, and change in spherical refraction associated with the variation in pupil diameter from 6 to 2.5 mm were measured. A refractive change of 1.60 D/µm of induced spherical aberration was obtained. Emmetropic eyes became myopic when positive spherical aberration was induced and hyperopic when negative spherical aberration was induced (R 2 = 81%). There were weak correlations between spherical aberration and visual acuity or depth of focus (R 2 = 2% and 3%, respectively). Contrast sensitivity worsened with the increment of spherical aberration (R 2 = 59%). When pupil size decreased, emmetropic eyes became hyperopic when preexisting spherical aberration was positive and myopic when spherical aberration was negative, with an average refractive change of 0.60 D/µm of spherical aberration (R 2 = 54%). An inverse linear correlation exists between the refractive state of the eye and spherical aberration induced within the range of laser vision correction. Small values of spherical aberration do not worsen visual acuity or depth of focus, but positive spherical aberration may induce night myopia. In addition, the changes in spherical refraction when the pupil constricts may worsen near vision when positive spherical aberration is induced or improve it when spherical aberration is negative. [J Refract Surg. 2017;33(7):470-474.]. Copyright 2017, SLACK Incorporated.

Refractive improvements and safety with topography-guided corneal crosslinking for keratoconus: 1-year results.

PubMed

Nordström, Maria; Schiller, Maria; Fredriksson, Anneli; Behndig, Anders

2017-07-01

To assess the refractive improvements and the corneal endothelial safety of an individualised topography-guided regimen for corneal crosslinking in progressive keratoconus. An open-label prospective randomised clinical trial was performed at the Department of Clinical Sciences, Ophthalmology, Umeå University Hospital, Umeå, Sweden. Thirty-seven patients (50 eyes) with progressive keratoconus planned for corneal crosslinking were included. The patients were randomised to topography-guided crosslinking (photorefractive intrastromal crosslinking (PiXL); n=25) or uniform 9 mm crosslinking (corneal collagen crosslinking (CXL); n=25). Visual acuity, refraction, keratometry (K1, K2 and K max ) and corneal endothelial morphometry were assessed preoperatively and at 1, 3, 6 and 12 months postoperatively. The PiXL treatment involved an asymmetrical treatment zone centred on the area of maximum corneal steepness with treatment energies ranging from 7.2 to 15.0 J/cm 2 ; the CXL treatment was a uniform 9 mm 5.4 J/cm 2 pulsed crosslinking. The main outcome measures were changes in refractive errors and corneal endothelial cell density. The spherical refractive errors decreased (p<0.05) and the visual acuity improved (p<0.01) at 3, 6 and 12 months after PiXL, but not after CXL. The between-groups differences, however, were not significant. K2 and K max decreased at 3, 6 and 12 months after PiXL (p<0.01), but not after CXL (p<0.01 when comparing the two treatments). No corneal endothelial cell loss was seen after either treatment. Individualised topography-based crosslinking treatment centred on the ectatic cone has the potential to improve the corneal shape in keratoconus with decreased spherical refractive errors and improved visual acuity, without damage to the corneal endothelium. NCT02514200, Results. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

Effects of Iris Surface Curvature on Iris Recognition

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

Thompson, Joseph T; Flynn, Patrick J; Bowyer, Kevin W

To focus on objects at various distances, the lens of the eye must change shape to adjust its refractive power. This change in lens shape causes a change in the shape of the iris surface which can be measured by examining the curvature of the iris. This work isolates the variable of iris curvature in the recognition process and shows that differences in iris curvature degrade matching ability. To our knowledge, no other work has examined the effects of varying iris curvature on matching ability. To examine this degradation, we conduct a matching experiment across pairs of images with varyingmore » degrees of iris curvature differences. The results show a statistically signi cant degradation in matching ability. Finally, the real world impact of these ndings is discussed« less

Nonlocal nonlinear refractive index of gold nanoparticles synthesized by ascorbic acid reduction: comparison of fitting models.

PubMed

Balbuena Ortega, A; Arroyo Carrasco, M L; Méndez Otero, M M; Gayou, V L; Delgado Macuil, R; Martínez Gutiérrez, H; Iturbe Castillo, M D

2014-12-12

In this paper, the nonlinear refractive index of colloidal gold nanoparticles under continuous wave illumination is investigated with the z -scan technique. Gold nanoparticles were synthesized using ascorbic acid as reductant, phosphates as stabilizer and cetyltrimethylammonium chloride (CTAC) as surfactant agent. The nanoparticle size was controlled with the CTAC concentration. Experiments changing incident power and sample concentration were done. The experimental z -scan results were fitted with three models: thermal lens, aberrant thermal lens and the nonlocal model. It is shown that the nonlocal model reproduces with exceptionally good agreement; the obtained experimental behaviour.

X-ray phase contrast imaging of objects with subpixel-size inhomogeneities: a geometrical optics model.

PubMed

Gasilov, Sergei V; Coan, Paola

2012-09-01

Several x-ray phase contrast extraction algorithms use a set of images acquired along the rocking curve of a perfect flat analyzer crystal to study the internal structure of objects. By measuring the angular shift of the rocking curve peak, one can determine the local deflections of the x-ray beam propagated through a sample. Additionally, some objects determine a broadening of the crystal rocking curve, which can be explained in terms of multiple refraction of x rays by many subpixel-size inhomogeneities contained in the sample. This fact may allow us to differentiate between materials and features characterized by different refraction properties. In the present work we derive an expression for the beam broadening in the form of a linear integral of the quantity related to statistical properties of the dielectric susceptibility distribution function of the object.

Aircraft vortex marking program

NASA Technical Reports Server (NTRS)

Pompa, M. F.

1979-01-01

A simple, reliable device for identifying atmospheric vortices, principally as generated by in-flight aircraft and with emphasis on the use of nonpolluting aerosols for marking by injection into such vortex (-ices) is presented. The refractive index and droplet size were determined from an analysis of aerosol optical and transport properties as the most significant parameters in effecting vortex optimum light scattering (for visual sighting) and visual persistency of at least 300 sec. The analysis also showed that a steam-ejected tetraethylene glycol aerosol with droplet size near 1 micron and refractive index of approximately 1.45 could be a promising candidate for vortex marking. A marking aerosol was successfully generated with the steam-tetraethylene glycol mixture from breadboard system hardware. A compact 25 lb/f thrust (nominal) H2O2 rocket chamber was the key component of the system which produced the required steam by catalytic decomposition of the supplied H2O2.

Composition measurements of binary mixture droplets by rainbow refractometry.

PubMed

Wilms, J; Weigand, B

2007-04-10

So far, refractive index measurements by rainbow refractometry have been used to determine the temperature of single droplets and ensembles of droplets. Rainbow refractometry is, for the first time, to the best of our knowledge, applied to measure composition histories of evaporating, binary mixture droplets. An evaluation method is presented that makes use of Airy theory and the simultaneous size measurement by Mie scattering imaging. The method further includes an empirical correction function for a certain diameter and refractive index range. The measurement uncertainty was investigated by numerical simulations with Lorenz-Mie theory. For the experiments, an optical levitation setup was used allowing for long measurement periods. Temperature measurements of single-component droplets at different temperature levels are shown to demonstrate the accuracy of rainbow refractometry. Measurements of size and composition histories of binary mixture droplets are presented for two different mixtures. Experimental results show good agreement with numerical results using a rapid-mixing model.

Determination of the aerosol size distribution by analytic inversion of the extinction spectrum in the complex anomalous diffraction approximation.

PubMed

Franssens, G; De Maziére, M; Fonteyn, D

2000-08-20

A new derivation is presented for the analytical inversion of aerosol spectral extinction data to size distributions. It is based on the complex analytic extension of the anomalous diffraction approximation (ADA). We derive inverse formulas that are applicable to homogeneous nonabsorbing and absorbing spherical particles. Our method simplifies, generalizes, and unifies a number of results obtained previously in the literature. In particular, we clarify the connection between the ADA transform and the Fourier and Laplace transforms. Also, the effect of the particle refractive-index dispersion on the inversion is examined. It is shown that, when Lorentz's model is used for this dispersion, the continuous ADA inverse transform is mathematically well posed, whereas with a constant refractive index it is ill posed. Further, a condition is given, in terms of Lorentz parameters, for which the continuous inverse operator does not amplify the error.

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.

A detailed characterization of the Saharan dust collected during the Fennec campaign in 2011: in situ ground-based and laboratory measurements

NASA Astrophysics Data System (ADS)

Rocha-Lima, Adriana; Vanderlei Martins, J.; Remer, Lorraine A.; Todd, Martin; Marsham, John H.; Engelstaedter, Sebastian; Ryder, Claire L.; Cavazos-Guerra, Carolina; Artaxo, Paulo; Colarco, Peter; Washington, Richard

2018-01-01

Millions of tons of mineral dust are lifted by the wind from arid surfaces and transported around the globe every year. The physical and chemical properties of the mineral dust are needed to better constrain remote sensing observations and are of fundamental importance for the understanding of dust atmospheric processes. Ground-based in situ measurements and in situ filter collection of Saharan dust were obtained during the Fennec campaign in the central Sahara in 2011. This paper presents results of the absorption and scattering coefficients, and hence single scattering albedo (SSA), of the Saharan dust measured in real time during the last period of the campaign and subsequent laboratory analysis of the dust samples collected in two supersites, SS1 and SS2, in Algeria and in Mauritania, respectively. The samples were taken to the laboratory, where their size and aspect ratio distributions, mean chemical composition, spectral mass absorption efficiency, and spectral imaginary refractive index were obtained from the ultraviolet (UV) to the near-infrared (NIR) wavelengths. At SS1 in Algeria, the time series of the scattering coefficients during the period of the campaign show dust events exceeding 3500 Mm-1, and a relatively high mean SSA of 0.995 at 670 nm was observed at this site. The laboratory results show for the fine particle size distributions (particles diameter  < 5µm and mode diameter at 2-3 µm) in both sites a spectral dependence of the imaginary part of the refractive index Im(m) with a bow-like shape, with increased absorption in UV as well as in the shortwave infrared. The same signature was not observed, however, in the mixed particle size distribution (particle diameter < 10 µm and mode diameter at 4 µm) in Algeria. Im(m) was found to range from 0.011 to 0.001i for dust collected in Algeria and 0.008 to 0.002i for dust collected in Mauritania over the wavelength range of 350-2500 nm. Differences in the mean elemental composition of the dust collected in the supersites in Algeria and in Mauritania and between fine and mixed particle size distributions were observed from EDXRF measurements, although those differences cannot be used to explain the optical properties variability between the samples. Finally, particles with low-density typically larger than 10 µm in diameter were found in some of the samples collected at the supersite in Mauritania, but these low-density particles were not observed in Algeria.

Analysis and design of optical systems by use of sensitivity analysis of skew ray tracing

NASA Astrophysics Data System (ADS)

Lin, Psang Dain; Lu, Chia-Hung

2004-02-01

Optical systems are conventionally evaluated by ray-tracing techniques that extract performance quantities such as aberration and spot size. Current optical analysis software does not provide satisfactory analytical evaluation functions for the sensitivity of an optical system. Furthermore, when functions oscillate strongly, the results are of low accuracy. Thus this work extends our earlier research on an advanced treatment of reflected or refracted rays, referred to as sensitivity analysis, in which differential changes of reflected or refracted rays are expressed in terms of differential changes of incident rays. The proposed sensitivity analysis methodology for skew ray tracing of reflected or refracted rays that cross spherical or flat boundaries is demonstrated and validated by the application of a cat's eye retroreflector to the design and by the image orientation of a system with noncoplanar optical axes. The proposed sensitivity analysis is projected as the nucleus of other geometrical optical computations.

Analysis and Design of Optical Systems by Use of Sensitivity Analysis of Skew Ray Tracing

NASA Astrophysics Data System (ADS)

Dain Lin, Psang; Lu, Chia-Hung

2004-02-01

Optical systems are conventionally evaluated by ray-tracing techniques that extract performance quantities such as aberration and spot size. Current optical analysis software does not provide satisfactory analytical evaluation functions for the sensitivity of an optical system. Furthermore, when functions oscillate strongly, the results are of low accuracy. Thus this work extends our earlier research on an advanced treatment of reflected or refracted rays, referred to as sensitivity analysis, in which differential changes of reflected or refracted rays are expressed in terms of differential changes of incident rays. The proposed sensitivity analysis methodology for skew ray tracing of reflected or refracted rays that cross spherical or flat boundaries is demonstrated and validated by the application of a cat ?s eye retroreflector to the design and by the image orientation of a system with noncoplanar optical axes. The proposed sensitivity analysis is projected as the nucleus of other geometrical optical computations.

Spatial Frequency Responses of Anisotropic Refractive Index Gratings Formed in Holographic Polymer Dispersed Liquid Crystals

PubMed Central

Fukuda, Yoshiaki; Tomita, Yasuo

2016-01-01

We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs). We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of radical mediated chain-growth polymerizations and the other with thiol-ene monomer capable of step-growth polymerizations. It was found that the photopolymerization kinetics of the two HPDLC materials could be well explained by the autocatalytic model. We also measured grating-spacing dependences of anisotropic refractive index gratings at a recording wavelength of 532 nm. It was found that the HPDLC material with the thiol-ene monomer gave higher spatial frequency responses than that with the acrylate monomer. Statistical thermodynamic simulation suggested that such a spatial frequency dependence was attributed primarily to a difference in the size of formed liquid crystal droplets due to different photopolymerization mechanisms. PMID:28773314

Spatial Frequency Responses of Anisotropic Refractive Index Gratings Formed in Holographic Polymer Dispersed Liquid Crystals.

PubMed

Fukuda, Yoshiaki; Tomita, Yasuo

2016-03-10

We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs). We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of radical mediated chain-growth polymerizations and the other with thiol-ene monomer capable of step-growth polymerizations. It was found that the photopolymerization kinetics of the two HPDLC materials could be well explained by the autocatalytic model. We also measured grating-spacing dependences of anisotropic refractive index gratings at a recording wavelength of 532 nm. It was found that the HPDLC material with the thiol-ene monomer gave higher spatial frequency responses than that with the acrylate monomer. Statistical thermodynamic simulation suggested that such a spatial frequency dependence was attributed primarily to a difference in the size of formed liquid crystal droplets due to different photopolymerization mechanisms.

Anomalous Surface Wave Launching by Handedness Phase Control.

PubMed

Zhang, Xueqian; Xu, Yuehong; Yue, Weisheng; Tian, Zhen; Gu, Jianqiang; Li, Yanfeng; Singh, Ranjan; Zhang, Shuang; Han, Jiaguang; Zhang, Weili

2015-11-25

Anomalous launch of a surface wave with different handedness phase control is achieved in a terahertz metasurface based on phase discontinuities. The polarity of the phase profile of the surface waves is found to be strongly correlated to the polarization handedness, promising polarization-controllable wavefront shaping, polarization sensing, and environmental refractive-index sensing. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The role of cloud contamination, aerosol layer height and aerosol model in the assessment of the OMI near-UV retrievals over the ocean

NASA Astrophysics Data System (ADS)

Gassó, Santiago; Torres, Omar

2016-07-01

Retrievals of aerosol optical depth (AOD) at 388 nm over the ocean from the Ozone Monitoring Instrument (OMI) two-channel near-UV algorithm (OMAERUV) have been compared with independent AOD measurements. The analysis was carried out over the open ocean (OMI and MODerate-resolution Imaging Spectrometer (MODIS) AOD comparisons) and over coastal and island sites (OMI and AERONET, the AErosol RObotic NETwork). Additionally, a research version of the retrieval algorithm (using MODIS and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) information as constraints) was utilized to evaluate the sensitivity of the retrieval to different assumed aerosol properties. Overall, the comparison resulted in differences (OMI minus independent measurements) within the expected levels of uncertainty for the OMI AOD retrievals (0.1 for AOD < 0.3, 30 % for AOD > 0.3). Using examples from case studies with outliers, the reasons that led to the observed differences were examined with specific purpose to determine whether they are related to instrument limitations (i.e., pixel size, calibration) or algorithm assumptions (such as aerosol shape, aerosol height). The analysis confirms that OMAERUV does an adequate job at rejecting cloudy scenes within the instrument's capabilities. There is a residual cloud contamination in OMI pixels with quality flag 0 (the best conditions for aerosol retrieval according to the algorithm), resulting in a bias towards high AODs in OMAERUV. This bias is more pronounced at low concentrations of absorbing aerosols (AOD 388 nm ˜ < 0.5). For higher aerosol loadings, the bias remains within OMI's AOD uncertainties. In pixels where OMAERUV assigned a dust aerosol model, a fraction of them (< 20 %) had retrieved AODs significantly lower than AERONET and MODIS AODs. In a case study, a detailed examination of the aerosol height from CALIOP and the AODs from MODIS, along with sensitivity tests, was carried out by varying the different assumed parameters in the retrieval (imaginary index of refraction, size distribution, aerosol height, particle shape). It was found that the spherical shape assumption for dust in the current retrieval is the main cause of the underestimate. In addition, it is demonstrated in an example how an incorrect assumption of the aerosol height can lead to an underestimate. Nevertheless, this is not as significant as the effect of particle shape. These findings will be incorporated in a future version of the retrieval algorithm.

Pupil size in Jewish theological seminary students.

PubMed

Shemesh, G; Kesler, A; Lazar, M; Rothkoff, L

2004-01-01

To investigate the authors' clinical impression that pupil size among myopic Jewish theological seminary students is different from pupil size of similar secular subjects. This cross-sectional study was conducted on 28 male Jewish theological seminary students and 28 secular students or workers who were matched for age and refraction. All participants were consecutively enrolled. Scotopic and photopic pupil size was measured by means of a Colvard pupillometer. Comparisons of various parameters between the groups were performed using the two-sample t-test, Fisher exact test, a paired-sample t-test, a two-way analysis of variance, and Pearson correlation coefficients as appropriate. The two groups were statistically matched for age, refraction, and visual acuity. The seminary students were undercorrected by an average of 2.35 diopters (D), while the secular subjects were undercorrected by only 0.65 D (p<0.01). The average pupil size was larger in the religious group under both scotopic and photopic luminance. This difference was maintained when the two groups were compared according to iris color under both conditions, reaching a level of statistical significance (p<0.0001). There was a significant difference in photopic pupil size between dark and light irises (p=0.049), but this difference was not maintained under scotopic conditions. The average pupil size of young ultraorthodox seminary students was significantly larger than that of matched secular subjects. Whether this is the result of intensive close-up work or of apparently characteristic undercorrection of the myopia is undetermined.

The use of WaveLight® Contoura to create a uniform cornea: the LYRA Protocol. Part 3: the results of 50 treated eyes.

PubMed

Motwani, Manoj

2017-01-01

To demonstrate how using the Wavelight Contoura measured astigmatism and axis eliminates corneal astigmatism and creates uniformly shaped corneas. A retrospective analysis was conducted of the first 50 eyes to have bilateral full WaveLight ® Contoura LASIK correction of measured astigmatism and axis (vs conventional manifest refraction), using the Layer Yolked Reduction of Astigmatism Protocol in all cases. All patients had astigmatism corrected, and had at least 1 week of follow-up. Accuracy to desired refractive goal was assessed by postoperative refraction, aberration reduction via calculation of polynomials, and postoperative visions were analyzed as a secondary goal. The average difference of astigmatic power from manifest to measured was 0.5462D (with a range of 0-1.69D), and the average difference of axis was 14.94° (with a range of 0°-89°). Forty-seven of 50 eyes had a goal of plano, 3 had a monovision goal. Astigmatism was fully eliminated from all but 2 eyes, and 1 eye had regression with astigmatism. Of the eyes with plano as the goal, 80.85% were 20/15 or better, and 100% were 20/20 or better. Polynomial analysis postoperatively showed that at 6.5 mm, the average C3 was reduced by 86.5% and the average C5 by 85.14%. Using WaveLight ® Contoura measured astigmatism and axis removes higher order aberrations and allows for the creation of a more uniform cornea with accurate removal of astigmatism, and reduction of aberration polynomials. WaveLight ® Contoura successfully links the refractive correction layer and aberration repair layer using the Layer Yolked Reduction of Astigmatism Protocol to demonstrate how aberration removal can affect refractive correction.