Changes in the Refractive Index of the Stroma and Its Extrafibrillar Matrix When the Cornea Swells

PubMed Central

Meek, Keith M.; Dennis, Sally; Khan, Shukria

2003-01-01

The transparency of the corneal stroma is critically dependent on the hydration of the tissue; if the cornea swells, light scattering increases. Although this scattering has been ascribed to the disruption caused to the arrangement of the collagen fibrils, theory predicts that light scattering could increase if there is an increased mismatch in the refractive indices of the collagen fibrils and the material between them. The purpose of this article is to use Gladstone and Dale's law of mixtures to calculate volume fractions for a number of different constituents in the stroma, and use these to show how the refractive indices of the stroma and its constituent extrafibrillar material would be expected to change as more solvent enters the tissue. Our calculations predict that solvent entering the extrafibrillar space causes a reduction in its refractive index, and hence a reduction in the overall refractive index of the bovine stroma according to the equation n′s = 1.335 + 0.04/(0.22 + 0.24 H′), where n′s is the refractive index and H′ is the hydration of the swollen stroma. This expression is in reasonable agreement with our experimental measurements of refractive index versus hydration in bovine corneas. When the hydration of the stroma increases from H = 3.2 to H = 8.0, we predict that the ratio of the refractive index of the collagen fibrils to that of the material between them increases from 1.041 to 1.052. This change would be expected to make only a small contribution to the large increase in light scattering observed when the cornea swells to H = 8. PMID:14507686

Improving axial resolution in confocal microscopy with new high refractive index mounting media.

PubMed

Fouquet, Coralie; Gilles, Jean-François; Heck, Nicolas; Dos Santos, Marc; Schwartzmann, Richard; Cannaya, Vidjeacoumary; Morel, Marie-Pierre; Davidson, Robert Stephen; Trembleau, Alain; Bolte, Susanne

2015-01-01

Resolution, high signal intensity and elevated signal to noise ratio (SNR) are key issues for biologists who aim at studying the localisation of biological structures at the cellular and subcellular levels using confocal microscopy. The resolution required to separate sub-cellular biological structures is often near to the resolving power of the microscope. When optimally used, confocal microscopes may reach resolutions of 180 nm laterally and 500 nm axially, however, axial resolution in depth is often impaired by spherical aberration that may occur due to refractive index mismatches. Spherical aberration results in broadening of the point-spread function (PSF), a decrease in peak signal intensity when imaging in depth and a focal shift that leads to the distortion of the image along the z-axis and thus in a scaling error. In this study, we use the novel mounting medium CFM3 (Citifluor Ltd., UK) with a refractive index of 1.518 to minimize the effects of spherical aberration. This mounting medium is compatible with most common fluorochromes and fluorescent proteins. We compare its performance with established mounting media, harbouring refractive indices below 1.500, by estimating lateral and axial resolution with sub-resolution fluorescent beads. We show furthermore that the use of the high refractive index media renders the tissue transparent and improves considerably the axial resolution and imaging depth in immuno-labelled or fluorescent protein labelled fixed mouse brain tissue. We thus propose to use those novel high refractive index mounting media, whenever optimal axial resolution is required.

Automatic and adaptive heterogeneous refractive index compensation for light-sheet microscopy.

PubMed

Ryan, Duncan P; Gould, Elizabeth A; Seedorf, Gregory J; Masihzadeh, Omid; Abman, Steven H; Vijayaraghavan, Sukumar; Macklin, Wendy B; Restrepo, Diego; Shepherd, Douglas P

2017-09-20

Optical tissue clearing has revolutionized researchers' ability to perform fluorescent measurements of molecules, cells, and structures within intact tissue. One common complication to all optically cleared tissue is a spatially heterogeneous refractive index, leading to light scattering and first-order defocus. We designed C-DSLM (cleared tissue digital scanned light-sheet microscopy) as a low-cost method intended to automatically generate in-focus images of cleared tissue. We demonstrate the flexibility and power of C-DSLM by quantifying fluorescent features in tissue from multiple animal models using refractive index matched and mismatched microscope objectives. This includes a unique measurement of myelin tracks within intact tissue using an endogenous fluorescent reporter where typical clearing approaches render such structures difficult to image. For all measurements, we provide independent verification using standard serial tissue sectioning and quantification methods. Paired with advancements in volumetric image processing, C-DSLM provides a robust methodology to quantify sub-micron features within large tissue sections.Optical clearing of tissue has enabled optical imaging deeper into tissue due to significantly reduced light scattering. Here, Ryan et al. tackle first-order defocus, an artefact of a non-uniform refractive index, extending light-sheet microscopy to partially cleared samples.

Photon migration through a turbid slab described by a model based on diffusion approximation. II. Comparison with Monte Carlo results.

PubMed

Martelli, F; Contini, D; Taddeucci, A; Zaccanti, G

1997-07-01

In our companion paper we presented a model to describe photon migration through a diffusing slab. The model, developed for a homogeneous slab, is based on the diffusion approximation and is able to take into account reflection at the boundaries resulting from the refractive index mismatch. In this paper the predictions of the model are compared with solutions of the radiative transfer equation obtained by Monte Carlo simulations in order to determine the applicability limits of the approximated theory in different physical conditions. A fitting procedure, carried out with the optical properties as fitting parameters, is used to check the application of the model to the inverse problem. The results show that significant errors can be made if the effect of the refractive index mismatch is not properly taken into account. Errors are more important when measurements of transmittance are used. The effects of using a receiver with a limited angular field of view and the angular distribution of the radiation that emerges from the slab have also been investigated.

Amorphous silicon as high index photonic material

NASA Astrophysics Data System (ADS)

Lipka, T.; Harke, A.; Horn, O.; Amthor, J.; Müller, J.

2009-05-01

Silicon-on-Insulator (SOI) photonics has become an attractive research topic within the area of integrated optics. This paper aims to fabricate SOI-structures for optical communication applications with lower costs compared to standard fabrication processes as well as to provide a higher flexibility with respect to waveguide and substrate material choice. Amorphous silicon is deposited on thermal oxidized silicon wafers with plasma-enhanced chemical vapor deposition (PECVD). The material is optimized in terms of optical light transmission and refractive index. Different a-Si:H waveguides with low propagation losses are presented. The waveguides were processed with CMOS-compatible fabrication technologies and standard DUV-lithography enabling high volume production. To overcome the large mode-field diameter mismatch between incoupling fiber and sub-μm waveguides three dimensional, amorphous silicon tapers were fabricated with a KOH etched shadow mask for patterning. Using ellipsometric and Raman spectroscopic measurements the material properties as refractive index, layer thickness, crystallinity and material composition were analyzed. Rapid thermal annealing (RTA) experiments of amorphous thin films and rib waveguides were performed aiming to tune the refractive index of the deposited a-Si:H waveguide core layer after deposition.

Improving Axial Resolution in Confocal Microscopy with New High Refractive Index Mounting Media

PubMed Central

Fouquet, Coralie; Gilles, Jean-François; Heck, Nicolas; Dos Santos, Marc; Schwartzmann, Richard; Cannaya, Vidjeacoumary; Morel, Marie-Pierre; Davidson, Robert Stephen; Trembleau, Alain; Bolte, Susanne

2015-01-01

Resolution, high signal intensity and elevated signal to noise ratio (SNR) are key issues for biologists who aim at studying the localisation of biological structures at the cellular and subcellular levels using confocal microscopy. The resolution required to separate sub-cellular biological structures is often near to the resolving power of the microscope. When optimally used, confocal microscopes may reach resolutions of 180 nm laterally and 500 nm axially, however, axial resolution in depth is often impaired by spherical aberration that may occur due to refractive index mismatches. Spherical aberration results in broadening of the point-spread function (PSF), a decrease in peak signal intensity when imaging in depth and a focal shift that leads to the distortion of the image along the z-axis and thus in a scaling error. In this study, we use the novel mounting medium CFM3 (Citifluor Ltd., UK) with a refractive index of 1.518 to minimize the effects of spherical aberration. This mounting medium is compatible with most common fluorochromes and fluorescent proteins. We compare its performance with established mounting media, harbouring refractive indices below 1.500, by estimating lateral and axial resolution with sub-resolution fluorescent beads. We show furthermore that the use of the high refractive index media renders the tissue transparent and improves considerably the axial resolution and imaging depth in immuno-labelled or fluorescent protein labelled fixed mouse brain tissue. We thus propose to use those novel high refractive index mounting media, whenever optimal axial resolution is required. PMID:25822785

Index mismatch aberration correction over long working distances using spatial light modulation.

PubMed

Gjonaj, Bergin; Johnson, Patrick; Bonn, Mischa; Domke, Katrin F

2012-11-20

For many microscopy applications, millimeters-long free working distances (LWD) are required. However, the high resolution and contrast of LWD objectives operated in air are lost when introducing glass and/or liquid with the sample. We propose to use spatial light modulation to correct for such beam aberrations caused by refractive index mismatches. Focusing a monochromatic laser beam with a 10 mm working distance air objective (50×, 0.5 NA) through air, glass, and water, we manage to restore a sharp, intense focus (FWHM<2λ) by adaptive beam phase shaping. Our approach offers a practical and cost-effective route to high resolution and contrast microscopy using LWD air objectives, extending their usage beyond applications in air.

Surrogate immiscible liquid pairs with refractive indexes matchable over a wide range of density and viscosity ratios

NASA Astrophysics Data System (ADS)

Saksena, Rajat; Christensen, Kenneth T.; Pearlstein, Arne J.

2015-08-01

In liquid-liquid flows, use of optical diagnostics is limited by interphase refractive index mismatch, which leads to optical distortion and complicates data interpretation, and sometimes also by opacity. Both problems can be eliminated using a surrogate pair of immiscible index-matched transparent liquids, whose density and viscosity ratios match corresponding ratios for the original liquid pair. We show that a wide range of density and viscosity ratios is accessible using aqueous solutions of 1,2-propanediol and CsBr (for which index, density, and viscosity are available), and solutions of light and heavy silicone oils and 1-bromooctane (for which we measured the same properties at 119 compositions). For each liquid phase, polynomials in the composition variables, least-squares fitted to index and density and to the logarithm of kinematic viscosity, were used to determine accessible density and viscosity ratios for each matchable index. Index-matched solution pairs can be prepared with density and viscosity ratios equal to those for water-liquid CO2 at 0 °C over a range of pressure (allowing water-liquid CO2 behavior at inconveniently high pressure to be simulated by 1-bar experiments), and for water-crude oil and water-trichloroethylene (avoiding opacity and toxicity problems, respectively), each over a range of temperature. For representative index-matched solutions, equilibration changes index, density, and viscosity only slightly, and mass spectrometry and elemental analysis show that no component of either phase has significant interphase solubility. Finally, procedures are described for iteratively reducing the residual index mismatch in surrogate solution pairs prepared on the basis of approximate polynomial fits to experimental data, and for systematically dealing with nonzero interphase solubility.

Optical coherence tomography angiography offers comprehensive evaluation of skin optical clearing in vivo by quantifying optical properties and blood flow imaging simultaneously

NASA Astrophysics Data System (ADS)

Guo, Li; Shi, Rui; Zhang, Chao; Zhu, Dan; Ding, Zhihua; Li, Peng

2016-08-01

Tissue optical clearing (TOC) is helpful for reducing scattering and enhancing the penetration depth of light, and shows promising potential in optimizing optical imaging performances. A mixture of fructose with PEG-400 and thiazone (FPT) is used as an optical clearing agent in mouse dorsal skin and evaluated with OCT angiography (Angio-OCT) by quantifying optical properties and blood flow imaging simultaneously. It is observed that FPT leads to an improved imaging performance for the deeper tissues. The imaging performance improvement is most likely caused by the FPT-induced dehydration of skin, and the reduction of scattering coefficient (more than ˜40.5%) and refractive-index mismatching (more than ˜25.3%) in the superficial (epidermal, dermal, and hypodermal) layers. A high correlation (up to ˜90%) between the relative changes in refractive-index mismatching and Angio-OCT signal strength is measured. The optical clearing rate is ˜5.83×10-5 cm/s. In addition, Angio-OCT demonstrates enhanced performance in imaging cutaneous hemodynamics with satisfactory spatiotemporal resolution and contrast when combined with TOC, which exhibits a powerful practical application in studying microcirculation.

Geometrical tuning art for entirely subwavelength grating waveguide based integrated photonics circuits

DOE PAGES

Wang, Zheng; Xu, Xiaochuan; Fan, Donglei; ...

2016-05-05

Here, subwavelength grating (SWG) waveguide is an intriguing alternative to conventional optical waveguides due to the extra degree of freedom it offers in tuning a few important waveguide properties, such as dispersion and refractive index. Devices based on SWG waveguides have demonstrated impressive performances compared to conventional waveguides. However, the high loss of SWG waveguide bends jeopardizes their applications in integrated photonic circuits. In this work, we propose a geometrical tuning art, which realizes a pre-distorted refractive index profile in SWG waveguide bends. The pre-distorted refractive index profile can effectively reduce the mode mismatch and radiation loss simultaneously, thus significantlymore » reduce the bend loss. This geometry tuning art has been numerically optimized and experimentally demonstrated in present study. Through such tuning, the average insertion loss of a 5 μm SWG waveguide bend is reduced drastically from 5.43 dB to 1.10 dB per 90° bend for quasi-TE polarization. In the future, the proposed scheme will be utilized to enhance performance of a wide range of SWG waveguide based photonics devices.« less

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

Wang, Zheng; Xu, Xiaochuan; Fan, Donglei

Here, subwavelength grating (SWG) waveguide is an intriguing alternative to conventional optical waveguides due to the extra degree of freedom it offers in tuning a few important waveguide properties, such as dispersion and refractive index. Devices based on SWG waveguides have demonstrated impressive performances compared to conventional waveguides. However, the high loss of SWG waveguide bends jeopardizes their applications in integrated photonic circuits. In this work, we propose a geometrical tuning art, which realizes a pre-distorted refractive index profile in SWG waveguide bends. The pre-distorted refractive index profile can effectively reduce the mode mismatch and radiation loss simultaneously, thus significantlymore » reduce the bend loss. This geometry tuning art has been numerically optimized and experimentally demonstrated in present study. Through such tuning, the average insertion loss of a 5 μm SWG waveguide bend is reduced drastically from 5.43 dB to 1.10 dB per 90° bend for quasi-TE polarization. In the future, the proposed scheme will be utilized to enhance performance of a wide range of SWG waveguide based photonics devices.« less

Geometrical tuning art for entirely subwavelength grating waveguide based integrated photonics circuits

PubMed Central

Wang, Zheng; Xu, Xiaochuan; Fan, Donglei; Wang, Yaguo; Subbaraman, Harish; Chen, Ray T.

2016-01-01

Subwavelength grating (SWG) waveguide is an intriguing alternative to conventional optical waveguides due to the extra degree of freedom it offers in tuning a few important waveguide properties, such as dispersion and refractive index. Devices based on SWG waveguides have demonstrated impressive performances compared to conventional waveguides. However, the high loss of SWG waveguide bends jeopardizes their applications in integrated photonic circuits. In this work, we propose a geometrical tuning art, which realizes a pre-distorted refractive index profile in SWG waveguide bends. The pre-distorted refractive index profile can effectively reduce the mode mismatch and radiation loss simultaneously, thus significantly reduce the bend loss. This geometry tuning art has been numerically optimized and experimentally demonstrated in present study. Through such tuning, the average insertion loss of a 5 μm SWG waveguide bend is reduced drastically from 5.43 dB to 1.10 dB per 90° bend for quasi-TE polarization. In the future, the proposed scheme will be utilized to enhance performance of a wide range of SWG waveguide based photonics devices. PMID:27145872

Geometrical tuning art for entirely subwavelength grating waveguide based integrated photonics circuits.

PubMed

Wang, Zheng; Xu, Xiaochuan; Fan, Donglei; Wang, Yaguo; Subbaraman, Harish; Chen, Ray T

2016-05-05

Subwavelength grating (SWG) waveguide is an intriguing alternative to conventional optical waveguides due to the extra degree of freedom it offers in tuning a few important waveguide properties, such as dispersion and refractive index. Devices based on SWG waveguides have demonstrated impressive performances compared to conventional waveguides. However, the high loss of SWG waveguide bends jeopardizes their applications in integrated photonic circuits. In this work, we propose a geometrical tuning art, which realizes a pre-distorted refractive index profile in SWG waveguide bends. The pre-distorted refractive index profile can effectively reduce the mode mismatch and radiation loss simultaneously, thus significantly reduce the bend loss. This geometry tuning art has been numerically optimized and experimentally demonstrated in present study. Through such tuning, the average insertion loss of a 5 μm SWG waveguide bend is reduced drastically from 5.43 dB to 1.10 dB per 90° bend for quasi-TE polarization. In the future, the proposed scheme will be utilized to enhance performance of a wide range of SWG waveguide based photonics devices.

Effective holographic recordings in the photopolymer nanocomposites with functionalized silica nanoparticle and polyurethane matrix

NASA Astrophysics Data System (ADS)

Han, Samsook; Lee, Muncheul; Kim, Byung Kyu

2011-11-01

Effective holographic nanocomposites were developed by the surface-functionalized silica nanoparticles and two acrylate monomers/polyurethane (PU) matrix polymer. The functionalization was done with silane compounds carrying long alkyl chain or vinyl group. We evaluated the holographic nanocomposite films by the diffraction efficiency, volume shrinkage, optical loss, and the film morphology. It was found that acrylate monomers/PU system gave higher diffraction efficiency than those of two monomers due to the high refractive index mismatch between the acrylate-rich and PU-rich regions. With the modification of silica particle, up to 35% of particle loading was possible to give a maximum diffraction efficiency of 93.6% for a film of 20 μm in thickness, along with improved refractive index modulation and the sensitivity.

Linear and nonlinear magneto-optical properties of an off-center single dopant in a spherical core/shell quantum dot

NASA Astrophysics Data System (ADS)

Feddi, E.; Talbi, A.; Mora-Ramos, M. E.; El Haouari, M.; Dujardin, F.; Duque, C. A.

2017-11-01

Using the effective mass approximation and a variational procedure, we have investigated the nonlinear optical absorption coefficient and the relative refractive index changes associated to a single dopant confined in core/shell quantum dots considering the influences of the core/shell dimensions, externally applied magnetic field, and dielectric mismatch. The results show that the optical absorption coefficient and the coefficients of relative refractive index change depend strongly on the core/shell sizes and they are blue shifted when the spatial confinement increases so this effect is magnified by higher structural dimensions. Additionally, it is obtained that both studied optical properties are sensitive to the dielectric environment in such a way that their amplitudes are very affected by the local field corrections.

Modeling of light propagation in the human neck for diagnoses of thyroid cancers by diffuse optical tomography.

PubMed

Fujii, H; Yamada, Y; Kobayashi, K; Watanabe, M; Hoshi, Y

2017-05-01

Diffuse optical tomography using near-infrared light in a wavelength range from 700 to 1000 nm has the potential to enable non-invasive diagnoses of thyroid cancers; some of which are difficult to detect by conventional methods such as ultrasound tomography. Diffuse optical tomography needs to be based on a physically accurate model of light propagation in the neck, because it reconstructs tomographic images of the optical properties in the human neck by inverse analysis. Our objective here was to investigate the effects of three factors on light propagation in the neck using the 2D time-dependent radiative transfer equation: (1) the presence of the trachea, (2) the refractive-index mismatch at the trachea-tissue interface, and (3) the effect of neck organs other than the trachea (spine, spinal cord, and blood vessels). There was a significant influence of reflection and refraction at the trachea-tissue interface on the light intensities in the region between the trachea and the front of the neck surface. Organs other than the trachea showed little effect on the light intensities measured at the front of the neck surface although these organs affected the light intensities locally. These results indicated the necessity of modeling the refractive-index mismatch at the trachea-tissue interface and the possibility of modeling other neck organs simply as a homogeneous medium when the source and detectors were far from large blood vessels. Copyright © 2016 John Wiley & Sons, Ltd.

Hidden Gratings in Holographic Liquid Crystal Polymer-Dispersed Liquid Crystal Films.

PubMed

De Sio, Luciano; Lloyd, Pamela F; Tabiryan, Nelson V; Bunning, Timothy J

2018-04-18

Dynamic diffraction gratings that are hidden in the field-off state are fabricated utilizing a room-temperature photocurable liquid crystal (LC) monomer and nematic LC (NLC) using holographic photopolymerization techniques. These holographic LC polymer-dispersed LCs (HLCPDLCs) are hidden because of the refractive index matching between the LC polymer and the NLC regions in the as-formed state (no E-field applied). Application of a moderate E-field (5 V/μm) generates a refractive index mismatch because of the NLC reorientation (along the E-field) generating high-diffraction efficiency transmission gratings. These dynamic gratings are characterized by morphological, optical, and electrooptical techniques. They exhibit a morphology made of oriented LC polymer regions (containing residual NLC) alternating with a two-phase region of an NLC and LC polymer. Unlike classic holographic polymer-dispersed LC gratings formed with a nonmesogenic monomer, there is index matching between the as-formed alternating regions of the grating. These HLCPDLCs exhibit broad band and high diffraction efficiency (≈90%) at the Bragg angle, are transparent to white light across the visible range because of the refractive index matching, and exhibit fast response times (1 ms). The ability of HLCPDLCs not to consume electrical power in the off state opens new possibilities for the realization of energy-efficient switchable photonic devices.

Best fit refractive index of matching liquid for 3D NIPAM gel dosimeters using optical CT

NASA Astrophysics Data System (ADS)

Chen, Chin-Hsing; Wu, Jay; Hsieh, Bor-Tsung; Chen, De-Shiou; Wang, Tzu-Hwei; Chien, Sou-Hsin; Chang, Yuan-Jen

2014-11-01

The accuracy of an optical computed tomography (CT)-based dosimeter is significantly affected by the refractive index (RI) of the matching liquid. Mismatched RI induces reflection and refraction as the laser beam passes through the gel phantom. Moreover, the unwanted light rays collected by the photodetector produce image artifacts after image reconstruction from the collected data. To obtain the best image quality, this study investigates the best-fit RI of the matching liquid for a 3D NIPAM gel dosimeter. The three recipes of NIPAM polymer gel used in this study consisted of 5% gelatin, 5% NIPAM and 3% N,N'-methylene bisacrylamide, which were combined with three compositions (5, 10, and 20 mM) of Tetrakis (hydroxymethyl) phosphonium chloride. Results were evaluated using a quantitative evaluation method of the gamma evaluation technique. Results showed that the best-fit RI for the non-irradiated NIPAM gel ranges from 1.340 to 1.346 for various NIPAM recipes with sensitivities ranging from 0.0113 to 0.0227. The greatest pass rate of 88.00% is achieved using best-fit RI=1.346 of the matching liquid. The adoption of mismatching RI decreases the gamma pass rate by 2.63% to 16.75% for all three recipes of NIPAM gel dosimeters. In addition, the maximum average deviation is less than 0.1% for the red and transparent matching liquids. Thus, the color of the matching liquid does not affect the measurement accuracy of the NIPAM gel dosimeter, as measured by optical CT.

Surrogate Immiscible Liquid Solution Pairs with Refractive Indexes Matchable Over a Wide Range of Density and Viscosity Ratios

NASA Astrophysics Data System (ADS)

Saksena, Rajat; Christensen, Kenneth T.; Pearlstein, Arne J.

2014-11-01

Use of laser diagnostics in liquid-liquid flows is limited by refractive index mismatch. This can be avoided using a surrogate pair of immiscible index-matched liquids, with density and viscosity ratios matching those of the original liquid pair. We demonstrate that a wide range of density and viscosity ratios is accessible using aqueous solutions of 1,2-propanediol and CsBr (for which index, density, and viscosity are available), and solutions of light and heavy silicone oils and 1-bromooctane (for which we measured the same properties at 119 compositions). For each liquid phase, polynomials in the composition variables were fitted to index and density and to the logarithm of kinematic viscosity, and the fits were used to determine accessible density and viscosity ratios for each matchable index. Index-matched solution pairs can be prepared with density and viscosity ratios equal to those for water-liquid CO2 at 0oC over a range of pressure, and for water-crude oil and water-trichloroethylene, each over a range of temperature. For representative index-matched solutions, equilibration changes index, density, and viscosity only slightly, and chemical analysis show that no component of either solution has significant interphase solubility. Partially supported by Intl. Inst. for Carbon-Neutral Energy Research.

Enhancement of white light OLED efficiency by combining both internal and external light extraction structures

NASA Astrophysics Data System (ADS)

Kao, I.-Ling; Ku, Chun-Neng; Chen, Yi-Ping; Lin, Ding-Zheng

2012-09-01

We proposed an internal nanostructure with a high reflective index planarization layer to solve the optical loss due to the reflective index mismatch between ITO and glass substrate. In our experiments, we found the electrical property of OLED device was significantly influenced by the internal nanostructures without planarization layer. Moreover, the internal extraction structure (IES) is not necessarily beneficial for light extraction. Therefore, we proposed a new substrate combine both internal and external extraction structure (EES) to extract trapping light. We successfully developed a high refractive index (N 1.7) planarization material with flat surface (RMS roughness < 2 nm), and improved about 70% device efficiency compared to traditional glass substrate.

Making the invisible visible: a microfluidic chip using a low refractive index polymer.

PubMed

Hanada, Yasutaka; Ogawa, Tatsuya; Koike, Kazuhiko; Sugioka, Koji

2016-07-07

Microfluidic frameworks known as micro-total-analysis-systems or lab-on-a-chip have become versatile tools in cell biology research, since functional biochips are able to streamline dynamic observations of various cells. Glass or polymers are generally used as the substrate due to their high transparency, chemical stability and cost-effectiveness. However, these materials are not well suited for the microscopic observation of cell migration at the fluid boundary due to the refractive index mismatch between the medium and the biochip material. For this reason, we have developed a new method of fabricating three-dimensional (3D) microfluidic chips made of the low refractive index fluoric polymer CYTOP. This novel fabrication procedure involves the use of a femtosecond laser for direct writing, followed by wet etching with a dilute fluorinated solvent and annealing, to create high-quality 3D microfluidic chips inside a polymer substrate. A microfluidic chip made in this manner enabled us to more clearly observe the flagellum motion of a Dinoflagellate moving in circles near the fluid surface compared to the observations possible using conventional microfluidic chips. We believe that CYTOP microfluidic chips made using this new method may allow more detailed analysis of various cell migrations near solid boundaries.

Optical study of hydrogen-irradiated GaAsN/GaAs heterostructures

NASA Astrophysics Data System (ADS)

Geddo, M.; Patrini, M.; Guizzetti, G.; Galli, M.; Trotta, R.; Polimeni, A.; Capizzi, M.; Martelli, F.; Rubini, S.

2011-06-01

The effect of hydrogen irradiation on the optical properties of GaAs1-xNx/GaAs heterostructures was investigated using photoreflectance and reflectance techniques. Systematic measurements performed on both as-grown and hydrogenated samples for N-concentrations ranging from 0.0% to 3.5% and for H-implanted doses from 3 × 1018 to 6 × 1018 ions/cm2 have shown that (a) the H-induced widening of the energy gap is accompanied by a decrease of the refractive index of the H-treated samples with respect to the as-grown ones, resulting in an index mismatch that can be as large as 2% in the subgap spectral region; and (b) the presence of compressive strain in fully passivated GaAsN determines a decrease of the refractive index even below that of GaAs that can be eliminated via moderate thermal annealing. These findings are promising for the development of heterostructures with planar geometry, in which the simultaneous confinement of both carriers and photons, even on a nanometric scale, can be obtained in a single step process.

Optical transillumination tomography with tolerance against refraction mismatch.

PubMed

Haidekker, Mark A

2005-12-01

Optical transillumination tomography (OT) is a laser-based imaging modality where ballistic photons are used for projection generation. Image reconstruction is therefore similar to X-ray computed tomography. This modality promises fast image acquisition, good resolution and contrast, and inexpensive instrumentation for imaging of weakly scattering objects, such as for example tissue-engineered constructs. In spite of its advantages, OT is not widely used. One reason is its sensitivity towards changes in material refractive index along the light path. Beam refraction artefacts cause areas of overestimated tissue density and blur geometric details. A spatial filter, introduced into the beam path to eliminate scattered photons, will also remove refracted photons from the projections. In the projections, zones affected by refraction can be detected by thresholding. By using algebraic reconstruction techniques (ART) in conjunction with suitable interpolation algorithms, reconstruction artefacts can be partly avoided. Reconstructions from a test image were performed. Standard filtered backprojection (FBP) showed a round mean square (RMS) deviation from the original image of 9.9. RMS deviation with refraction-tolerant ART reconstruction was 0.33 and 0.24, depending on the algorithm, compared to 0.57 (FBP) and 0.06 (ART) in a non-refracting case. In addition, modified ART reconstruction allowed detection of small geometric details that were invisible in standard reconstructions. Refraction-tolerant ART may be the key to eliminating one of the major challenges of OT.

Ultrasensitive plasmonic sensing in air using optical fibre spectral combs

PubMed Central

Caucheteur, Christophe; Guo, Tuan; Liu, Fu; Guan, Bai-Ou; Albert, Jacques

2016-01-01

Surface plasmon polaritons (SPP) can be excited on metal-coated optical fibres, enabling the accurate monitoring of refractive index changes. Configurations reported so far mainly operate in liquids but not in air because of a mismatch between permittivities of guided light modes and the surrounding medium. Here we demonstrate a plasmonic optical fibre platform that overcomes this limitation. The underpinning of our work is a grating architecture—a gold-coated highly tilted Bragg grating—that excites a spectral comb of narrowband-cladding modes with effective indices near 1.0 and below. Using conventional spectral interrogation, we measure shifts of the SPP-matched resonances in response to static atmospheric pressure changes. A dynamic experiment conducted using a laser lined-up with an SPP-matched resonance demonstrates the ability to detect an acoustic wave with a resolution of 10−8 refractive index unit (RIU). We believe that this configuration opens research directions for highly sensitive plasmonic sensing in gas. PMID:27834366

Effect of glucose on the optical properties of arterial blood using Mie theory simulations

NASA Astrophysics Data System (ADS)

Clancy, Neil T.; Leahy, Martin J.

2005-08-01

The glucose concentration in arterial plasma has immediate effects on the optical properties of blood-bearing tissue due primarily to the alteration of refractive index mismatch between the scattering particles (red blood cells) and the medium (plasma). The influence of these effects on pulse oximetry is investigated using a numerical model based on Mie theory. The objective is to determine whether or not physiological fluctuations in blood glucose levels could sufficiently vary the optical properties to shift the calibration curve of a commercial pulse oximeter significantly.

Transparent bulk-size nanocomposites with high inorganic loading

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

Chen, Shi; Gaume, Romain, E-mail: gaume@ucf.edu; Department of Materials Science and Engineering, University of Central Florida, Orlando, Florida 32816

2015-12-14

With relatively high nanoparticle loading in polymer matrices, hybrid nanocomposites made by colloidal dispersion routes suffer from severe inhomogeneous agglomeration, a phenomenon that deteriorates light transmission even when the refractive indices of the inorganic and organic phases are closely matched. The dispersion of particles in a matrix is of paramount importance to obtain composites of high optical quality. Here, we describe an innovative, yet straightforward method to fabricate monolithic transparent hybrid nanocomposites with very high particle loading and high refractive index mismatch tolerance between the inorganic and organic constituents. We demonstrate 77% transmission at 800 nm in a 2 mm-thick acrylate polymermore » nanocomposite containing 61 vol. % CaF{sub 2} nanoparticles. Modeling shows that similar performance could easily be obtained with various inorganic phases relevant to a number of photonic applications.« less

Investigations into the feasibility of optical-CT 3D dosimetry with minimal use of refractively matched fluids

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

Chisholm, Kelsey; Miles, Devin; Rankine, Leith

Purpose: In optical-CT, the use of a refractively matched polyurethane solid-tank in place of a fluid bath has the potential to greatly increase practical convenience, reduce cost, and possibly improve the efficacy of flood corrections. This work investigates the feasibility of solid-tank optical-CT imaging for 3D dosimetry through computer simulation. Methods: A MATLAB ray-tracing simulation platform, ScanSim, was used to model a parallel-source telecentric optical-CT imaging system through a polyurethane solid-tank containing a central cylindrical hollow into which PRESAGE radiochromic dosimeters can be placed. A small amount of fluid fills the 1–5 mm gap between the dosimeter and the wallsmore » of the tank. The use of the solid-tank reduces the required amount of fluid by approximately 97%. To characterize the efficacy of solid-tank, optical-CT scanning simulations investigated sensitivity to refractive index (RI) mismatches between dosimeter, solid-tank, and fluid, for a variety of dosimeter (RI = 1.5–1.47) and fluid (RI = 1.55–1.0) combinations. Efficacy was evaluated through the usable radius (r{sub u}) metric, defined as the fraction of the radius of the dosimeter where measured dose is predicted to be within 2% of the ground truth entered into the simulation. Additional simulations examined the effect of increasing gap size (1–5 mm) between the dosimeter and solid-tank well. The effects of changing the lens tolerance (0.5°–5.0°) were also investigated. Results: As the RI mismatch between the dosimeter and solid-tank increased from 0 to 0.02, the usable radius decreased from 97.6% to 50.2%. The optimal fluid RI decreased nonlinearly from 1.5 to 1.34 as the mismatch increased and was up to 9% lower than the tank. Media mismatches between the dosimeter and solid-tank also exacerbate the effects of changing the gap size, with no easily quantifiable relationship with usable radius. Generally, the optimal fluid RI value increases as gap size increases and is closely matched to the dosimeter at large gap sizes (>3 mm). Increasing the telecentric lens tolerance increases the usable radius for all refractive media combinations and improves the maximum usable radius of mismatched media to that of perfectly matched media for tolerances >5.0°. The maximum usable radius can be improved up to a factor of 2 when lens tolerances are small (<1.0°). Conclusions: Dry solid-tank optical-CT imaging in a telecentric system is feasible if the dosimeter RI is a close match with the solid-tank (<0.01 difference), providing accurate dose measurements within ±2% of true dose to over 80% of the dosimeter volume. In order to achieve accurate measurements over 96% of the dosimeter volume (representing out to 2 mm from the dosimeter edge), the dosimeter-tank RI mismatch must be less than 0.005. Optimal results occur when the RI of the dosimeter and tank is the same, in which case the fluid will have the same RI. If mismatches between the tank and dosimeter RI occur, the RI of the matching fluid needs to be fine tuned to achieve the highest usable radius.« less

Investigations into the feasibility of optical-CT 3D dosimetry with minimal use of refractively matched fluids.

PubMed

Chisholm, Kelsey; Miles, Devin; Rankine, Leith; Oldham, Mark

2015-05-01

In optical-CT, the use of a refractively matched polyurethane solid-tank in place of a fluid bath has the potential to greatly increase practical convenience, reduce cost, and possibly improve the efficacy of flood corrections. This work investigates the feasibility of solid-tank optical-CT imaging for 3D dosimetry through computer simulation. A matlab ray-tracing simulation platform, ScanSim, was used to model a parallel-source telecentric optical-CT imaging system through a polyurethane solid-tank containing a central cylindrical hollow into which PRESAGE radiochromic dosimeters can be placed. A small amount of fluid fills the 1-5 mm gap between the dosimeter and the walls of the tank. The use of the solid-tank reduces the required amount of fluid by approximately 97%. To characterize the efficacy of solid-tank, optical-CT scanning simulations investigated sensitivity to refractive index (RI) mismatches between dosimeter, solid-tank, and fluid, for a variety of dosimeter (RI = 1.5-1.47) and fluid (RI = 1.55-1.0) combinations. Efficacy was evaluated through the usable radius (ru) metric, defined as the fraction of the radius of the dosimeter where measured dose is predicted to be within 2% of the ground truth entered into the simulation. Additional simulations examined the effect of increasing gap size (1-5 mm) between the dosimeter and solid-tank well. The effects of changing the lens tolerance (0.5°-5.0°) were also investigated. As the RI mismatch between the dosimeter and solid-tank increased from 0 to 0.02, the usable radius decreased from 97.6% to 50.2%. The optimal fluid RI decreased nonlinearly from 1.5 to 1.34 as the mismatch increased and was up to 9% lower than the tank. Media mismatches between the dosimeter and solid-tank also exacerbate the effects of changing the gap size, with no easily quantifiable relationship with usable radius. Generally, the optimal fluid RI value increases as gap size increases and is closely matched to the dosimeter at large gap sizes (> 3 mm). Increasing the telecentric lens tolerance increases the usable radius for all refractive media combinations and improves the maximum usable radius of mismatched media to that of perfectly matched media for tolerances > 5.0°. The maximum usable radius can be improved up to a factor of 2 when lens tolerances are small (< 1.0°). Dry solid-tank optical-CT imaging in a telecentric system is feasible if the dosimeter RI is a close match with the solid-tank (< 0.01 difference), providing accurate dose measurements within ± 2% of true dose to over 80% of the dosimeter volume. In order to achieve accurate measurements over 96% of the dosimeter volume (representing out to 2 mm from the dosimeter edge), the dosimeter-tank RI mismatch must be less than 0.005. Optimal results occur when the RI of the dosimeter and tank is the same, in which case the fluid will have the same RI. If mismatches between the tank and dosimeter RI occur, the RI of the matching fluid needs to be fine tuned to achieve the highest usable radius.

Optical effects induced by epitaxial tension in lead titanate

NASA Astrophysics Data System (ADS)

Dejneka, A.; Chvostova, D.; Pacherova, O.; Kocourek, T.; Jelinek, M.; Tyunina, M.

2018-01-01

Single-crystal-type epitaxial films of perovskite oxide ferroelectrics are attractive for integrated photonic applications because of the remarkable optical properties and effects in ferroelectrics. The properties of the films may be influenced by epitaxial strain arising from the film-substrate mismatch. Here, dramatic strain-induced changes of the absorption and refraction are experimentally detected by spectroscopic ellipsometry in epitaxial films of archetypical ferroelectric PbTiO3. Comparison of the properties of a tensile-strained film with those of reference films and crystals reveals that epitaxial tension produces blueshifts of the primary above-bandgap absorption peaks by 1 eV and a decrease in the refractive index by 0.5 in the transparent spectral range. The obtained quadratic electrooptic and effective elastooptic coefficients exceed the bulk values by orders of magnitude. The experimental observations prove that epitaxy is a powerful tool for engineering unprecedented optical properties that may enable future photonics innovations.

[Peripheral refraction and retinal contour in children with myopia by results of refractometry and partial coherence interferometry].

PubMed

Tarutta, E P; Milash, S V; Tarasova, N A; Romanova, L I; Markosian, G A; Epishina, M V

2014-01-01

To determine the posterior pole contour of the eye based on the relative peripheral refractive error and relative eye length. A parallel study was performed, which enrolled 38 children (76 eyes) with myopia from -1.25 to -10.82 diopters. The patients underwent peripheral refraction assessment with WR-5100K Binocular Auto Refractometer ("Grand Seiko", Japan) and partial coherence tomography with IOLMaster ("Carl Zeiss", Germany) for the relative eye length in areas located 15 and 30 degrees nasal and temporal from the central fovea along the horizontal meridian. In general, refractometry and interferometry showed high coincidence of defocus signs and values for the areas located 15 and 30 degrees nasal as well as 15 degrees temporal from the fovea. However, in 41% of patients defocus signs determined by the two methods mismatched in one or more areas. Most of the mismatch cases were mild myopia. We suppose that such a mismatch is caused by optical peculiarities of the anterior eye segment that have an impact on refractometry results.

Integrated Optical Mach-Zehnder Interferometer Based on Organic-Inorganic Hybrids for Photonics-on-a-Chip Biosensing Applications.

PubMed

Bastos, Ana R; Vicente, Carlos M S; Oliveira-Silva, Rui; Silva, Nuno J O; Tacão, Marta; Costa, João P da; Lima, Mário; André, Paulo S; Ferreira, Rute A S

2018-03-12

The development of portable low-cost integrated optics-based biosensors for photonics-on-a-chip devices for real-time diagnosis are of great interest, offering significant advantages over current analytical methods. We report the fabrication and characterization of an optical sensor based on a Mach-Zehnder interferometer to monitor the growing concentration of bacteria in a liquid medium. The device pattern was imprinted on transparent self-patternable organic-inorganic di-ureasil hybrid films by direct UV-laser, reducing the complexity and cost production compared with lithographic techniques or three-dimensional (3D) patterning using femtosecond lasers. The sensor performance was evaluated using, as an illustrative example, E. coli cell growth in an aqueous medium. The measured sensitivity (2 × 10 -4 RIU) and limit of detection (LOD = 2 × 10 -4 ) are among the best values known for low-refractive index contrast sensors. Furthermore, the di-ureasil hybrid used to produce this biosensor has additional advantages, such as mechanical flexibility, thermal stability, and low insertion losses due to fiber-device refractive index mismatch (~1.49). Therefore, the proposed sensor constitutes a direct, compact, fast, and cost-effective solution for monitoring the concentration of lived-cells.

Temperature nonuniformity occurring during the cooling process of a KDP crystal and its effects on second-harmonic generation.

PubMed

Liang, Yingchun; Su, Ruifeng; Lu, Lihua; Liu, Haitao

2014-08-10

The temperature nonuniformity occurring during the cooling process of a KDP crystal is studied, along with its effects on the second-harmonic generation (SHG) of a high-average-power laser. A comprehensive model is proposed incorporating principles of thermodynamics, mechanics, and optics, and it is applied to investigate the temperature nonuniformity and its effects. The temperature rise caused by linear absorption is calculated, while the temperature nonuniformity occurring during the cooling process is analyzed using the finite-element method (FEM). The stress induced by the nonuniformity is then studied using the FEM, and the trend of its change is determined. Moreover, the changes in refractive index caused by the stress are calculated, the results of which are used to determine the variations in the induced phase mismatch. The SHG efficiency considering the phase mismatch is eventually obtained by solving the coupling wave equations. The results demonstrate that the temperature nonuniformity has negative effects on the SHG efficiency.

Three-dimensional imaging of threading dislocations in GaN crystals using two-photon excitation photoluminescence

NASA Astrophysics Data System (ADS)

Tanikawa, Tomoyuki; Ohnishi, Kazuki; Kanoh, Masaya; Mukai, Takashi; Matsuoka, Takashi

2018-03-01

The three-dimensional imaging of threading dislocations in GaN films was demonstrated using two-photon excitation photoluminescence. The threading dislocations were shown as dark lines. The spatial resolutions near the surface were about 0.32 and 3.2 µm for the in-plane and depth directions, respectively. The threading dislocations with a density less than 108 cm-2 were resolved, although the aberration induced by the refractive index mismatch was observed. The decrease in threading dislocation density was clearly observed by increasing the GaN film thickness. This can be considered a novel method for characterizing threading dislocations in GaN films without any destructive preparations.

The refractive index of human hemoglobin in the visible range.

PubMed

Zhernovaya, O; Sydoruk, O; Tuchin, V; Douplik, A

2011-07-07

Because the refractive index of hemoglobin in the visible range is sensitive to the hemoglobin concentration, optical investigations of hemoglobin are important for medical diagnostics and treatment. Direct measurements of the refractive index are, however, challenging; few such measurements have previously been reported, especially in a wide wavelength range. We directly measured the refractive index of human deoxygenated and oxygenated hemoglobin for nine wavelengths between 400 and 700 nm for the hemoglobin concentrations up to 140 g l(-1). This paper analyzes the results and suggests a set of model functions to calculate the refractive index depending on the concentration. At all wavelengths, the measured values of the refractive index depended on the concentration linearly. Analyzing the slope of the lines, we determined the specific refraction increments, derived a set of model functions for the refractive index depending on the concentration, and compared our results with those available in the literature. Based on the model functions, we further calculated the refractive index at the physiological concentration within the erythrocytes of 320 g l(-1). The results can be used to calculate the refractive index in the visible range for arbitrary concentrations provided that the refractive indices depend on the concentration linearly.

Plasmonic nanoshell functionalized etched fiber Bragg gratings for highly sensitive refractive index measurements.

PubMed

Burgmeier, Jörg; Feizpour, Amin; Schade, Wolfgang; Reinhard, Björn M

2015-02-15

A novel fiber optical refractive index sensor based on gold nanoshells immobilized on the surface of an etched single-mode fiber including a Bragg grating is demonstrated. The nanoparticle coating induces refractive index dependent waveguide losses, because of the variation of the evanescently guided part of the light. Hence the amplitude of the Bragg reflection is highly sensitive to refractive index changes of the surrounding medium. The nanoshell functionalized fiber optical refractive index sensor works in reflectance mode, is suitable for chemical and biochemical sensing, and shows an intensity dependency of 4400% per refractive index unit in the refractive index range between 1.333 and 1.346. Furthermore, the physical length of the sensor is smaller than 3 mm with a diameter of 6 μm, and therefore offers the possibility of a localized refractive index measurement.

Refractive index sensor based on the leaky radiation of a microfiber.

PubMed

Gao, F; Liu, H; Sheng, C; Zhu, C; Zhu, S N

2014-05-19

In this work we present a refractive index sensor based on the leaky radiation of a microfiber. The 5.3um diameter microfiber is fabricated by drawing a commercial optical fiber. When the microfiber is immersed into a liquid with larger refractive index than the effective index of fiber mode, the light will leak out through the leaky radiation process. The variation of refractive index of liquid can be monitored by measuring radiation angle of light. The refractive index sensitivity can be over 400 degree/RIU in theory. In the experiment, the variation value 0.001 of refractive index of liquid around this microfiber can be detected through this technique. This work provides a simple and sensitive method for refractive index sensing application.

Optical Limiting Based on Liquid-Liquid Immiscibility

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

Exarhos, Gregory J.; Ferris, Kim F.; Samuels, William D.

A nonionic surfactant is used to stabilize a dispersed droplet phase in a continuous liquid phase when two immiscible liquids are mixed. As both liquid phases approach the index matched condition, interfacial scattering is suppressed, and the mixture takes on the characteristics of a Christiansen-Shelyubskii filter. If, in addition, one of the liquids exhibits a substantial nonlinear optical response, then interfacial light scattering can be reversibly turned on when a laser beam incident upon the filter exceeds a critical fluence. To demonstrate this effect, an organic phase (dichloroethane) was dispersed in an aqueous phase containing sodium thiocyanate (NaSCN) using anmore » alkyl end-capped polyethylene glycol ether. The salt concentration was adjusted so that the index-matched mixture exhibited a large pass band. Marked optical limiting was observed through this transparent medium under conditions where the focused second-harmonic output of a Q-Switched Nd:YAG laser was on the order of about 50 mJ/cm2. An open-aperture Z-scan technique was used to quantify the limiting behavior. Since the thiocyanate anion is both isostructural and isoelectronic with carbon disulfide which exhibits a large optical nonlinearity, the mechanism of optical limiting is thought to be a nonlinear shift in the aqueous fluid index of refraction, resulting in an index mismatch between the disparate phases at high laser fluence. Index mismatch between the two phases leads to multiple reflections, loss of coherence, and a significant transmission decrease due to Mie scattering. The presence of many boundaries significantly amplifies the effect. Experiments also were conducted on the phase-inverted system (aqueous phase in organic liquid). Fundamental studies of such systems are used to verify theoretical predictions of the limiting effect, and aid in the design and development of improved limiters based upon this optical deflection approach.« less

Integrated Optical Mach-Zehnder Interferometer Based on Organic-Inorganic Hybrids for Photonics-on-a-Chip Biosensing Applications

PubMed Central

Oliveira-Silva, Rui; Silva, Nuno J. O.; André, Paulo S.; Ferreira, Rute A. S.

2018-01-01

The development of portable low-cost integrated optics-based biosensors for photonics-on-a-chip devices for real-time diagnosis are of great interest, offering significant advantages over current analytical methods. We report the fabrication and characterization of an optical sensor based on a Mach-Zehnder interferometer to monitor the growing concentration of bacteria in a liquid medium. The device pattern was imprinted on transparent self-patternable organic-inorganic di-ureasil hybrid films by direct UV-laser, reducing the complexity and cost production compared with lithographic techniques or three-dimensional (3D) patterning using femtosecond lasers. The sensor performance was evaluated using, as an illustrative example, E. coli cell growth in an aqueous medium. The measured sensitivity (2 × 10−4 RIU) and limit of detection (LOD = 2 × 10−4) are among the best values known for low-refractive index contrast sensors. Furthermore, the di-ureasil hybrid used to produce this biosensor has additional advantages, such as mechanical flexibility, thermal stability, and low insertion losses due to fiber-device refractive index mismatch (~1.49). Therefore, the proposed sensor constitutes a direct, compact, fast, and cost-effective solution for monitoring the concentration of lived-cells. PMID:29534514

High refractive index and temperature sensitivity LPGs for high temperature operation

NASA Astrophysics Data System (ADS)

Nascimento, I. M.; Gouveia, C.; Jana, Surnimal; Bera, Susanta; Baptista, J. M.; Moreira, Paulo; Biwas, Palas; Bandyopadhyay, Somnath; Jorge, Pedro A. S.

2013-11-01

A fiber optic sensor for high sensitivity refractive index and temperature measurement able to withstand temperature up to 450 °C is reported. Two identical LPG gratings were fabricated, whereas one was coated with a high refractive index (~1.78) sol-gel thin film in order to increase its sensitivity to the external refractive index. The two sensors were characterized and compared in refractive index and temperature. Sensitivities of 1063 nm/RIU (1.338 - 1.348) and 260 pm/°C were achieved for refractive index and temperature, respectively.

Measurement of the Microwave Refractive Index of Materials Based on Parallel Plate Waveguides

NASA Astrophysics Data System (ADS)

Zhao, F.; Pei, J.; Kan, J. S.; Zhao, Q.

2017-12-01

An electrical field scanning apparatus based on a parallel plate waveguide method is constructed, which collects the amplitude and phase matrices as a function of the relative position. On the basis of such data, a method for calculating the refractive index of the measured wedge samples is proposed in this paper. The measurement and calculation results of different PTFE samples reveal that the refractive index measured by the apparatus is substantially consistent with the refractive index inferred with the permittivity of the sample. The proposed refractive index calculation method proposed in this paper is a competitive method for the characterization of the refractive index of materials with positive refractive index. Since the apparatus and method can be used to measure and calculate arbitrary direction of the microwave propagation, it is believed that both of them can be applied to the negative refractive index materials, such as metamaterials or “left-handed” materials.

Denaturation process of laccase in various media by refractive index measurements.

PubMed

Saoudi, O; Ghaouar, N; Ben Salah, S; Othman, T

2017-09-01

In this work, we are interested in the denaturation process of a laccase from Tramates versicolor via the determination of the refractive index, the refractive index increment and the specific volume in various media. The measurements were carried out using an Abbe refractometer. We have shown that the refractive index increment values obtained from the slope of the variation of the refractive index vs. Concentration are outside the range refractive index increments of proteins. To correct the results, we have followed the theoretical predictions based on the knowledge of the protein refractive index from its amino acids composition. The denaturation process was studied by calculating the specific volume variation where its determination was related to the Gladstone-Dale and the Lorentz-Lorentz models.

Patient age, refractive index of the corneal stroma, and outcomes of uneventful laser in situ keratomileusis.

PubMed

Patel, Sudi; Alió, Jorge L; Walewska, Anna; Amparo, Francisco; Artola, Alberto

2013-03-01

To determine the influence of age and the corneal stromal refractive index on the difference between the predicted and actual postoperative refractive error after laser in situ keratomileusis (LASIK) and whether the precision of outcomes could be improved by considering age and the refractive index. Vissum Instituto Oftalmologico de Alicante, Alicante, Spain. Case series. Flaps were created using a mechanical microkeratome. The stromal refractive index was measured using a VCH-1 refractometer after flap lifting. Refractive data were obtained 1, 3, and 6 months postoperatively. Uneventful LASIK was performed in 133 eyes. The mean age, refractive index, and applied corrections were 33.4 years ± 9.49 (SD), 1.368 ± 0.006, and -2.43 ± 3.36 diopters (D), respectively. The difference between the predicted and actual postoperative refractive error = 2.315-0.021 age-1.106 refractive index (F = 3.647, r = 0.254, P=.029; n = 109) at 1 month and = 11.820-0.023 age-7.976 refractive index (F = 3.392, r = 0.261, P=.022, n = 106) at 3 months. A correlation between the actual and calculated postoperative refraction improved from r = -0.178 (P=.064; n = 75) to r = -0.418 (P<.001) after considering the true refractive index 6 months postoperatively. The predicted outcomes of LASIK can be improved by inputting the refractive index of the individual corneal stroma. Unexpected outcomes (>0.50 D) of LASIK could be avoided by considering patient age and the refractive index and by adjusting the applied correction accordingly. Copyright © 2012 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

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

PubMed

Charman, W Neil; Adnan; Atchison, David A

2012-12-01

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

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

PubMed Central

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

2012-01-01

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

Tunable natural nano-arrays: controlling surface properties and light reflectance

NASA Astrophysics Data System (ADS)

Watson, Jolanta A.; Myhra, Sverre; Watson, Gregory S.

2006-01-01

The general principles of optical design based on the theories of reflection, refraction and diffraction have been rigorously developed and optimized over the last three centuries. Of increasing importance has been the ability to predict and devise new optical technologies designed for specific functions. A key design feature of many of today's optical materials is the control of reflection and light transmittance through the medium. A sudden transition or impedance mismatch from one optical medium to another can result in unwanted reflections from the surface plane. Modification of a surface by creation of a gradual change in refractive index over a significant portion of a wavelength range will result in a reduction in reflection. An alternative surface modification to the multi layered stack coating (gradient index coating) is to produce a surface with structures having a period and height shorter than the light wavelength. These structures act like a pseudo-gradient index coating and can be described by the effective medium theory. Bernhard and Miller some forty years ago were the first to observe such structures found on the surface of insects. These were found in the form of hexagonally close packed nanometre sized protrusions on the corneal surface of certain moths. In this study we report on similar structures which we have found on certain species of cicada wings demonstrating that the reflective/transmission properties of these natural nano-structures can be tuned by controlled removal of the structure height using Atomic Force Microscopy (AFM).

Surface transmission enhancement of ZnS via continuous-wave laser microstructuring

NASA Astrophysics Data System (ADS)

Major, Kevin J.; Florea, Catalin M.; Poutous, Menelaos K.; Busse, Lynda E.; Sanghera, Jasbinder S.; Aggarwal, Ishwar D.

2014-03-01

Fresnel reflectivity at dielectric boundaries between optical components, lenses, and windows is a major issue for the optics community. The most common method to reduce the index mismatch and subsequent surface reflection is to apply a thin film or films of intermediate indices to the optical materials. More recently, surface texturing or roughening has been shown to approximate a stepwise refractive index thin-film structure, with a gradient index of refraction transition from the bulk material to the surrounding medium. Short-pulse laser ablation is a recently-utilized method to produce such random anti-reflective structured surfaces (rARSS). Typically, high-energy femtosecond pulsed lasers are focused on the surface of the desired optical material to produce periodic or quasi-periodic assemblies of nanostructures which provide reduced surface reflection. This technique is being explored to generate a variety of structures across multiple optical materials. However, femtosecond laser systems are relatively expensive and more difficult to maintain. We present here a low power and low-cost alternative to femtosecond laser ablation, demonstrating random antireflective structures on the surface of Cleartran ZnS windows produced with a continuous-wave laser. In particular, we find that irradiation with a low-powered (<10 mW), defocused, CW 325nm-wavelength laser produces a random surface with significant roughness on ZnS substrates. The transmission through the structured ZnS windows is shown to increase by up to 9% across a broad wavelength range from the visible to the near-infrared.

Optofluidic two-dimensional grating volume refractive index sensor.

PubMed

Sarkar, Anirban; Shivakiran Bhaktha, B N; Khastgir, Sugata Pratik

2016-09-10

We present an optofluidic reservoir with a two-dimensional grating for a lab-on-a-chip volume refractive index sensor. The observed diffraction pattern from the device resembles the analytically obtained fringe pattern. The change in the diffraction pattern has been monitored in the far-field for fluids with different refractive indices. Reliable measurements of refractive index variations, with an accuracy of 6×10^-3 refractive index units, for different fluids establishes the optofluidic device as a potential on-chip tool for monitoring dynamic refractive index changes.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

Refractive index measurements in absorbing media with white light spectral interferometry.

PubMed

Arosa, Yago; Lago, Elena López; de la Fuente, Raúl

2018-03-19

White light spectral interferometry is applied to measure the refractive index in absorbing liquids in the spectral range of 400-1000 nm. We analyze the influence of absorption on the visibility of interferometric fringes and, accordingly, on the measurement of the refractive index. Further, we show that the refractive index in the absorption band can be retrieved by a two-step process. The procedure requires the use of two samples of different thickness, the thicker one to retrieve the refractive index in the transparent region and the thinnest to obtain the data in the absorption region. First, the refractive index values are retrieved with good accuracy in the transparent region of the material for 1-mm-thick samples. Second, these refractive index values serve also to precisely calculate the thickness of a thinner sample (~150 µm) since the accuracy of the methods depends strongly on the thickness of the sample. Finally, the refractive index is recovered for the entire spectral range.

3-D photo-patterning of refractive index structures in photosensitive thin film materials

DOEpatents

Potter, Jr., Barrett George; Potter, Kelly Simmons

2002-01-01

A method of making a three-dimensional refractive index structure in a photosensitive material using photo-patterning. The wavelengths at which a photosensitive material exhibits a change in refractive index upon exposure to optical radiation is first determined and then a portion of the surface of the photosensitive material is optically irradiated at a wavelength at which the photosensitive material exhibits a change in refractive index using a designed illumination system to produce a three-dimensional refractive index structure. The illumination system can be a micro-lenslet array, a macroscopic refractive lens array, or a binary optic phase mask. The method is a single-step, direct-write procedure to produce a designed refractive index structure.

Determination of the refractive index of microparticles by utilizing light dispersion properties of the particle and an immersion liquid.

PubMed

Niskanen, I; Räty, J; Peiponen, K E

2013-10-15

The knowledge of the refractive index of a particle is important in sensing and imaging applications, e.g., in biology, medicine and process industry. The refractive index of tiny solid particles such as microsize particles can be determined by the so-called liquid immersion technique. This study deals with three different types of interrogation methods to get the refractive index of a particle in a liquid matrix. These methods utilize thermo-optical properties and wavelength-dependent refractive index of the particle and the immersion liquids, as well as, the classical method using a set of in advance prepared set of immersion liquids with different refractive indices. The emphasis is on a method to get especially the wavelength-dependent refractive index of microparticles and exploiting different wavelength-dependences of immersion liquid and a solid particle because identification of a particle is more reliable if the refractive index of the particle is known at several wavelengths. In this study glycerol-water mixtures served as immersion liquids to obtain the refractive index of CaF2 at several discrete wavelengths in the spectral range 200-500 nm. The idea is to find the maximum value of light transmission of suspension by scanning the wavelength of a commercial spectrophotometer. The light dispersion-based method is suggested as a relatively easy, economic and fast method to determine the refractive index of a particle by a spectrophotometer at several wavelengths of light. The accuracy of the detection of the refractive index is suggested to be better than ± 0.005 refractive index units. © 2013 Elsevier B.V. All rights reserved.

Monte Carlo simulations of coherent backscatter for identification of the optical coefficients of biological tissues in vivo

NASA Astrophysics Data System (ADS)

Eddowes, M. H.; Mills, T. N.; Delpy, D. T.

1995-05-01

A Monte Carlo model of light backscattered from turbid media has been used to simulate the effects of weak localization in biological tissues. A validation technique is used that implies that for the scattering and absorption coefficients and for refractive index mismatches found in tissues, the Monte Carlo method is likely to provide more accurate results than the methods previously used. The model also has the ability to simulate the effects of various illumination profiles and other laboratory-imposed conditions. A curve-fitting routine has been developed that might be used to extract the optical coefficients from the angular intensity profiles seen in experiments on turbid biological tissues, data that could be obtained in vivo.

Light dosimetry for focused and defocused beam irradiation in multi-layered tissue models

NASA Astrophysics Data System (ADS)

Petrova, Kremena S.; Stoykova, Elena V.

2006-09-01

Treatment of acupuncture points, trigger points, joint inflammations in low level laser therapy as well as various applications of lasers for treatment of soft tissues in dental medicine, require irradiation by a narrow converging laser beam. The aim of this study is to compare light delivery produced by focused or defocused narrow beam irradiation in a multi-layered skin tissue model at increasing depth of the target. The task is solved by 3-D Monte-Carlo simulation for matched and mismatched refractive indices at the tissue/ambient medium interface. The modeled light beams have a circular cross-section at the tissue entrance with uniform or Gaussian intensity distribution. Three are the tissue models used in simulation : i) a bloodless skin layer; ii) a bloodless skin layer with embedded scattering object; iii) a skin layer with small blood vessels of varying size, which are modeled as infinite cylinders parallel to the tissue surface located at different depths. Optical properties (absorption coefficient, scattering coefficient, anisotropy factor, g, and index of refraction) of different tissue constituents are chosen from the literature.

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

PubMed

Stritzel, Jenny; Rahlves, Maik; Roth, Bernhard

2015-12-01

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

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.

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

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

In-fiber refractive index sensor based on single eccentric hole-assisted dual-core fiber.

PubMed

Yang, Jing; Guan, Chunying; Tian, Peixuan; Yuan, Tingting; Zhu, Zheng; Li, Ping; Shi, Jinhui; Yang, Jun; Yuan, Libo

2017-11-01

We propose a novel and simple in-fiber refractive index sensor based on resonant coupling, constructed by a short section of single eccentric hole-assisted dual-core fiber (SEHADCF) spliced between two single-mode fibers. The coupling characteristics of the SEHADCF are calculated numerically. The strong resonant coupling occurs when the fundamental mode of the center core phase-matches to that of the suspended core in the air hole. The effective refractive index of the fundamental mode of the suspended core can be obviously changed by injecting solution into the air hole. The responses of the proposed devices to the refractive index and temperature are experimentally measured. The refractive index sensitivity is 627.5 nm/refractive index unit in the refractive index range of 1.335-1.385. The sensor without solution filling is insensitive to temperature in the range of 30-90°C. The proposed refractive index sensor has outstanding advantages, such as simple fabrication, good mechanical strength, and excellent microfluidic channel, and will be of importance in biological detection, chemical analysis, and environment monitoring.

Design of embedded system to determine liquid refractive index based on ultrasonic sensor using an ATMega328

NASA Astrophysics Data System (ADS)

Radiyonoa, Y.; Surantoro, S.; Pujayanto, P.; Budiharti, R.; Respati, Y. S.; Saputro, D. E.

2018-05-01

The occurrence of the broken pencil shadow into a glass of water becomes an interesting matter to be learned. The students of senior high school still find difficulty in determining liquid refractive index. To overcome this problem, it needs to develop an experimental tool to determine liquid refractive index by utilizing the newest technology. It is expected to be useful for students. This study is aimed to (1) make the design of physics learning experimental tool determinant of a liquid refractive index assisted by microcontroller based on ultrasonic sensors ATMega328 (2) explain the working principle and experimental result of liquid refractive indexing instrument assisted with ATMega328 microcontroller based ultrasonic sensor. This research used the experimental method. The result of the research shows design of physics learning experimental tool determinant of a liquid refractive index assisted by microcontroller based on ultrasonic sensors ATMega328 that has relative counting mistake of 0.36% on the measurement of aquades liquid refractive index, relative mistake of 0.18% on the 5% NaCl measurement, 0.24% on 5% glucose, and relative mistake of 0.50% on the measurement of 5 % fructose liquid refractive index. It has been created a proper device to be used in determining liquid refractive index.

Spatial Frequency Multiplexing of Fiber-Optic Interferometric Refractive Index Sensors Based on Graded-Index Multimode Fibers

PubMed Central

Liu, Li; Gong, Yuan; Wu, Yu; Zhao, Tian; Wu, Hui-Juan; Rao, Yun-Jiang

2012-01-01

Fiber-optic interferometric sensors based on graded-index multimode fibers have very high refractive-index sensitivity, as we previously demonstrated. In this paper, spatial-frequency multiplexing of this type of fiber-optic refractive index sensors is investigated. It is estimated that multiplexing of more than 10 such sensors is possible. In the multiplexing scheme, one of the sensors is used to investigate the refractive index and temperature responses. The fast Fourier transform (FFT) of the combined reflective spectra is analyzed. The intensity of the FFT spectra is linearly related with the refractive index and is not sensitive to the temperature.

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

PubMed

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

2009-02-01

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

Terahertz metasurfaces with a high refractive index enhanced by the strong nearest neighbor coupling.

PubMed

Tan, Siyu; Yan, Fengping; Singh, Leena; Cao, Wei; Xu, Ningning; Hu, Xiang; Singh, Ranjan; Wang, Mingwei; Zhang, Weili

2015-11-02

The realization of high refractive index is of significant interest in optical imaging with enhanced resolution. Strongly coupled subwavelength resonators were proposed and demonstrated at both optical and terahertz frequencies to enhance the refractive index due to large induced dipole moment in meta-atoms. Here, we report an alternative design for flexible free-standing terahertz metasurface in the strong coupling regime where we experimentally achieve a peak refractive index value of 14.36. We also investigate the impact of the nearest neighbor coupling in the form of frequency tuning and enhancement of the peak refractive index. We provide an analytical circuit model to explain the impact of geometrical parameters and coupling on the effective refractive index of the metasurface. The proposed meta-atom structure enables tailoring of the peak refractive index based on nearest neighbor coupling and this property offers tremendous design flexibility for transformation optics and other index-gradient devices at terahertz frequencies.

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.

A phoswich detector design for improved spatial sampling in PET

NASA Astrophysics Data System (ADS)

Thiessen, Jonathan D.; Koschan, Merry A.; Melcher, Charles L.; Meng, Fang; Schellenberg, Graham; Goertzen, Andrew L.

2018-02-01

Block detector designs, utilizing a pixelated scintillator array coupled to a photosensor array in a light-sharing design, are commonly used for positron emission tomography (PET) imaging applications. In practice, the spatial sampling of these designs is limited by the crystal pitch, which must be large enough for individual crystals to be resolved in the detector flood image. Replacing the conventional 2D scintillator array with an array of phoswich elements, each consisting of an optically coupled side-by-side scintillator pair, may improve spatial sampling in one direction of the array without requiring resolving smaller crystal elements. To test the feasibility of this design, a 4 × 4 phoswich array was constructed, with each phoswich element consisting of two optically coupled, 3 . 17 × 1 . 58 × 10mm3 LSO crystals co-doped with cerium and calcium. The amount of calcium doping was varied to create a 'fast' LSO crystal with decay time of 32.9 ns and a 'slow' LSO crystal with decay time of 41.2 ns. Using a Hamamatsu R8900U-00-C12 position-sensitive photomultiplier tube (PS-PMT) and a CAEN V1720 250 MS/s waveform digitizer, we were able to show effective discrimination of the fast and slow LSO crystals in the phoswich array. Although a side-by-side phoswich array is feasible, reflections at the crystal boundary due to a mismatch between the refractive index of the optical adhesive (n = 1 . 5) and LSO (n = 1 . 82) caused it to behave optically as an 8 × 4 array rather than a 4 × 4 array. Direct coupling of each phoswich element to individual photodetector elements may be necessary with the current phoswich array design. Alternatively, in order to implement this phoswich design with a conventional light sharing PET block detector, a high refractive index optical adhesive is necessary to closely match the refractive index of LSO.

Long period grating refractive-index sensor: optimal design for single wavelength interrogation.

PubMed

Kapoor, Amita; Sharma, Enakshi K

2009-11-01

We report the design criteria for the use of long period gratings (LPGs) as refractive-index sensors with output power at a single interrogating wavelength as the measurement parameter. The design gives maximum sensitivity in a given refractive-index range when the interrogating wavelength is fixed. Use of the design criteria is illustrated by the design of refractive-index sensors for specific application to refractive-index variation of a sugar solution with a concentration and detection of mole fraction of xylene in heptane (paraffin).

Roughened glass slides and a spectrophotometer for the detection of the wavelength-dependent refractive index of transparent liquids.

PubMed

Niskanen, Ilpo; Räty, Jukka; Myllylä, Risto; Sutinen, Veijo; Matsuda, Kiyofumi; Homma, Kazuhiro; Silfsten, Pertti; Peiponen, Kai-Erik

2012-07-01

We describe a method to determine the wavelength-dependent refractive index of liquids by measurement of light transmittance with a spectrophotometer. The method is based on using roughened glass slides with different a priori known refractive indices and immersing the slides into the transparent liquid with unknown refractive index. Using the dispersion data on the glass material it is possible to find the index match between the liquid and the glass slide, and hence the refractive index of the liquid.

Compact eccentric long period grating with improved sensitivity in low refractive index region.

PubMed

Shen, Fangcheng; Zhou, Kaiming; Gordon, Neil; Zhang, Lin; Shu, Xuewen

2017-07-10

We demonstrate a compact eccentric long period grating with enhanced sensitivity in low refractive index region. With a period designed at 15 µm for coupling light to high order cladding modes, the grating is more sensitive to surrounding refractive index in low refractive index region. The intrinsically low coupling coefficients for those high order cladding modes are significantly improved with the eccentric localized inscription induced by the femtosecond laser. The fabricated grating is compact with a length of 4.05 mm, and exhibits an average sensitivity of ~505 nm/RIU in low refractive index region (1.3328-1.3544). The proposed principle can also work in other refractive index region with a proper choice of the resonant cladding modes.

Decoupling the refractive index from the electrical properties of transparent conducting oxides via periodic superlattices.

PubMed

Caffrey, David; Norton, Emma; Coileáin, Cormac Ó; Smith, Christopher M; Bulfin, Brendan; Farrell, Leo; Shvets, Igor V; Fleischer, Karsten

2016-09-13

We demonstrate an alternative approach to tuning the refractive index of materials. Current methodologies for tuning the refractive index of a material often result in undesirable changes to the structural or optoelectronic properties. By artificially layering a transparent conducting oxide with a lower refractive index material the overall film retains a desirable conductivity and mobility while acting optically as an effective medium with a modified refractive index. Calculations indicate that, with our refractive index change of 0.2, a significant reduction of reflective losses could be obtained by the utilisation of these structures in optoelectronic devices. Beyond this, periodic superlattice structures present a solution to decouple physical properties where the underlying electronic interaction is governed by different length scales.

Reflection based Extraordinary Optical Transmission Fiber Optic Probe for Refractive Index Sensing.

PubMed

Lan, Xinwei; Cheng, Baokai; Yang, Qingbo; Huang, Jie; Wang, Hanzheng; Ma, Yinfa; Shi, Honglan; Xiao, Hai

2014-03-31

Fiber optic probes for chemical sensing based on the extraordinary optical transmission (EOT) phenomenon are designed and fabricated by perforating subwavelength hole arrays on the gold film coated optical fiber endface. The device exhibits a red shift in response to the surrounding refractive index increases with high sensitivity, enabling a reflection-based refractive index sensor with a compact and simple configuration. By choosing the period of hole arrays, the sensor can be designed to operate in the near infrared telecommunication wavelength range, where the abundant source and detectors are available for easy instrumentation. The new sensor probe is demonstrated for refractive index measurement using refractive index matching fluids. The sensitivity reaches 573 nm/RIU in the 1.333~1.430 refractive index range.

Sensing dynamic cytoplasm refractive index changes of adherent cells with quantitative phase microscopy using incorporated microspheres as optical probes.

PubMed

Przibilla, Sabine; Dartmann, Sebastian; Vollmer, Angelika; Ketelhut, Steffi; Greve, Burkhard; von Bally, Gert; Kemper, Björn

2012-09-01

The intracellular refractive index is an important parameter that describes the optical density of the cytoplasm and the concentration of the intracellular solutes. The refractive index of adherently grown cells is difficult to access. We present a method in which silica microspheres in living cells are used to determine the cytoplasm refractive index with quantitative phase microscopy. The reliability of our approach for refractive index retrieval is shown by data from a comparative study on osmotically stimulated adherent and suspended human pancreatic tumor cells. Results from adherent human fibro sarcoma cells demonstrate the capability of the method for sensing of dynamic refractive index changes and its usage with microfluidics.

Refractive index dependence of L3 photonic crystal nano-cavities.

PubMed

Adawi, A M; Chalcraft, A R; Whittaker, D M; Lidzey, D G

2007-10-29

We model the optical properties of L3 photonic crystal nano-cavities as a function of the photonic crystal membrane refractive index n using a guided mode expansion method. Band structure calculations revealed that a TE-like full band-gap exists for materials of refractive index as low as 1.6. The Q-factor of such cavities showed a super-linear increase with refractive index. By adjusting the relative position of the cavity side holes, the Q-factor was optimised as a function of the photonic crystal membrane refractive index n over the range 1.6 to 3.4. Q-factors in the range 3000-8000 were predicted from absorption free materials in the visible range with refractive index between 2.45 and 2.8.

Refractometers for different refractive index range by surface plasmon resonance sensors in multimode optical fibers with different metals

NASA Astrophysics Data System (ADS)

Zuppella, P.; Corso, Alain J.; Pelizzo, Maria G.; Cennamo, N.; Zeni, L.

2016-09-01

We have realized a plasmonic sensor based on Au/Pd metal bilayer in a multimode plastic optical fiber. This metal bilayer, based on a metal with high imaginary part of the refractive index and gold, shows interesting properties in terms of sensitivity and performances, in different refractive index ranges. The development of highly sensitive platforms for high refractive index detection (higher than 1.38) is interesting for chemical applications based on molecularly imprinted polymer as receptors, while the aqueous medium is the refractive index range of biosensors based on bio-receptors. In this work we have presented an Au/Pd metal bilayer optimized for 1.38-1.42 refractive index range.

Regional variation in the refractive-index of the bovine and human cornea.

PubMed

Vasudevan, Balamurali; Simpson, Trefford L; Sivak, Jacob G

2008-10-01

Given the refractive importance of the human cornea, surprisingly little attention has been directed to the study of local variation in corneal refractive-index. This in vitro and in vivo study measures the refractive-index of different portions of the bovine and human cornea. Fifty fresh bovine corneas (obtained from an abattoir) and 10 human subjects were used for the study. The refractive-index of the central, nasal, and temporal corneal epithelium was measured with a bench-top Abbe refractometer in the case of bovine corneas and with a hand-held refractometer with humans. The mean (+/-standard deviation) refractive-indices of the central, nasal, and temporal bovine corneal epithelium were 1.3760 (+/-0.003), 1.3757 (+/-0.002), and 1.3746 (+/-0.002), respectively. Refractive-indices of the anterior and posterior bovine corneal stroma were 1.3731 (+/-0.002) and 1.3708 (+/-0.004), respectively. The mean (+/-standard deviation) refractive-index in the central, nasal, and temporal periphery of the human cornea epithelium were 1.3970 (+/-0.001), 1.3946 (+/-0.001), and 1.3940 (+/-0.001), respectively. There are small local differences in the refractive-index of the bovine and human corneal epithelium and the refractive-index of the epithelium is higher than that of the anterior and posterior stroma of the bovine cornea.

Ray trace visualization of negative refraction of light in two-dimensional air-bridged silicon photonic crystal slabs at 1.55 microm.

PubMed

Gan, Lin; Liu, Ya-Zhao; Li, Jiang-Yan; Zhang, Ze-Bo; Zhang, Dao-Zhong; Li, Zhi-Yuan

2009-06-08

We demonstrate design, fabrication, and ray trace observation of negative refraction of near-infrared light in a two-dimensional square lattice of air holes etched into an air-bridged silicon slab. Special surface morphologies are designed to reduce the impedance mismatch when light refracts from a homogeneous silicon slab into the photonic crystal slab. We clearly observed negative refraction of infrared light for TE-like modes in a broad wavelength range by using scanning near-field optical microscopy technology. The experimental results are in good agreement with finite-difference time-domain simulations. The results indicate the designed photonic crystal structure can serve as polarization beam splitter.

Influence of stromal refractive index and hydration on corneal laser refractive surgery.

PubMed

de Ortueta, Diego; von Rüden, Dennis; Magnago, Thomas; Arba Mosquera, Samuel

2014-06-01

To evaluate the influence of the stromal refractive index and hydration on postoperative outcomes in eyes that had corneal laser refractive surgery using the Amaris laser system. Augenzentrum Recklinghausen, Recklinghausen, Germany. Comparative case series. At the 6-month follow-up, right eyes were retrospectively analyzed. The effect of the stromal refractive index and hydration on refractive outcomes was assessed using univariate linear and multilinear correlations. Sixty eyes were analyzed. Univariate linear analyses showed that the stromal refractive index and hydration were correlated with the thickness of the preoperative exposed stroma and was statistically different for laser in situ keratomileusis and laser-assisted subepithelial keratectomy treatments. Univariate multilinear analyses showed that the spherical equivalent (SE) was correlated with the attempted SE and stromal refractive index (or hydration). Analyses suggest overcorrections for higher stromal refractive index values and for lower hydration values. The stromal refractive index and hydration affected postoperative outcomes in a subtle, yet significant manner. An adjustment toward greater attempted correction in highly hydrated corneas and less intended correction in low hydrated corneas might help optimize refractive outcomes. Mr. Magnago and Dr. Arba-Mosquera are employees of and Dr. Diego de Ortueta is a consultant to Schwind eye-tech-solutions GmbH & Co. KG. Mr. Rüden has no financial or proprietary interest in any material or method mentioned. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Fabrication of refractive index distributions in polymer using a photochemical reaction

NASA Astrophysics Data System (ADS)

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

2000-01-01

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

Highly tunable refractive index visible-light metasurface from block copolymer self-assembly.

PubMed

Kim, Ju Young; Kim, Hyowook; Kim, Bong Hoon; Chang, Taeyong; Lim, Joonwon; Jin, Hyeong Min; Mun, Jeong Ho; Choi, Young Joo; Chung, Kyungjae; Shin, Jonghwa; Fan, Shanhui; Kim, Sang Ouk

2016-09-29

The refractive index of natural transparent materials is limited to 2-3 throughout the visible wavelength range. Wider controllability of the refractive index is desired for novel optical applications such as nanoimaging and integrated photonics. We report that metamaterials consisting of period and symmetry-tunable self-assembled nanopatterns can provide a controllable refractive index medium for a broad wavelength range, including the visible region. Our approach exploits the independent control of permeability and permittivity with nanoscale objects smaller than the skin depth. The precise manipulation of the interobject distance in block copolymer nanopatterns via pattern shrinkage increased the effective refractive index up to 5.10. The effective refractive index remains above 3.0 over more than 1,000 nm wavelength bandwidth. Spatially graded and anisotropic refractive indices are also obtained with the design of transitional and rotational symmetry modification.

Highly tunable refractive index visible-light metasurface from block copolymer self-assembly

PubMed Central

Kim, Ju Young; Kim, Hyowook; Kim, Bong Hoon; Chang, Taeyong; Lim, Joonwon; Jin, Hyeong Min; Mun, Jeong Ho; Choi, Young Joo; Chung, Kyungjae; Shin, Jonghwa; Fan, Shanhui; Kim, Sang Ouk

2016-01-01

The refractive index of natural transparent materials is limited to 2–3 throughout the visible wavelength range. Wider controllability of the refractive index is desired for novel optical applications such as nanoimaging and integrated photonics. We report that metamaterials consisting of period and symmetry-tunable self-assembled nanopatterns can provide a controllable refractive index medium for a broad wavelength range, including the visible region. Our approach exploits the independent control of permeability and permittivity with nanoscale objects smaller than the skin depth. The precise manipulation of the interobject distance in block copolymer nanopatterns via pattern shrinkage increased the effective refractive index up to 5.10. The effective refractive index remains above 3.0 over more than 1,000 nm wavelength bandwidth. Spatially graded and anisotropic refractive indices are also obtained with the design of transitional and rotational symmetry modification. PMID:27683077

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

Hidayat, Arif, E-mail: arif.hidayat.fmipa@um.ac.id; Latifah, Eny; Kurniati, Diana

This study investigated the influence of refraction index strength on the light propagation in refraction index-varied dielectric material. This dielectric material served as photonic lattice. The behavior of light propagation influenced by variation of refraction index in photonic lattice was investigated. Modes of the guiding light were determined numerically using squared-operator iteration method. It was found that the greater the strength of refraction index, the smaller the guiding modes.

Cell refractive index for cell biology and disease diagnosis: past, present and future.

PubMed

Liu, P Y; Chin, L K; Ser, W; Chen, H F; Hsieh, C-M; Lee, C-H; Sung, K-B; Ayi, T C; Yap, P H; Liedberg, B; Wang, K; Bourouina, T; Leprince-Wang, Y

2016-02-21

Cell refractive index is a key biophysical parameter, which has been extensively studied. It is correlated with other cell biophysical properties including mechanical, electrical and optical properties, and not only represents the intracellular mass and concentration of a cell, but also provides important insight for various biological models. Measurement techniques developed earlier only measure the effective refractive index of a cell or a cell suspension, providing only limited information on cell refractive index and hence hindering its in-depth analysis and correlation. Recently, the emergence of microfluidic, photonic and imaging technologies has enabled the manipulation of a single cell and the 3D refractive index of a single cell down to sub-micron resolution, providing powerful tools to study cells based on refractive index. In this review, we provide an overview of cell refractive index models and measurement techniques including microfluidic chip-based techniques for the last 50 years, present the applications and significance of cell refractive index in cell biology, hematology, and pathology, and discuss future research trends in the field, including 3D imaging methods, integration with microfluidics and potential applications in new and breakthrough research areas.

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

Refraction index sensor based on phase resonances in a subwavelength structure with double period.

PubMed

Skigin, Diana C; Lester, Marcelo

2016-10-01

In this paper, we numerically demonstrate a refraction index sensor based on phase resonance excitation in a subwavelength-slit structure with a double period. The sensor consists of a metal layer with subwavelength slots arranged in a bi-periodic form, separated from a high refraction index medium. Between the metallic structure and the incident medium, a dielectric waveguide is formed whose refraction index is going to be determined. Variations in the refraction index of the waveguide are detected as shifts in the peaks of transmitted intensity originated by resonant modes supported by the compound metallic structure. At normal incidence, the spectral position of these resonant peaks exhibits a linear or a quadratic dependence with the refraction index, which permits us to obtain the unknown refraction index value with a high precision for a wide range of wavelengths. Since the operating principle of the sensor is due to the morphological resonances of the slits' structure, this device can be scaled to operate in different wavelength ranges while keeping similar characteristics.

Demonstration of versatile whispering-gallery micro-lasers for remote refractive index sensing.

PubMed

Wan, Lei; Chandrahalim, Hengky; Zhou, Jian; Li, Zhaohui; Chen, Cong; Cho, Sangha; Zhang, Hui; Mei, Ting; Tian, Huiping; Oki, Yuji; Nishimura, Naoya; Fan, Xudong; Guo, L Jay

2018-03-05

We developed chip-scale remote refractive index sensors based on Rhodamine 6G (R6G)-doped polymer micro-ring lasers. The chemical, temperature, and mechanical sturdiness of the fused-silica host guaranteed a flexible deployment of dye-doped polymers for refractive index sensing. The introduction of the dye as gain medium demonstrated the feasibility of remote sensing based on the free-space optics measurement setup. Compared to the R6G-doped TZ-001, the lasing behavior of R6G-doped SU-8 polymer micro-ring laser under an aqueous environment had a narrower spectrum linewidth, producing the minimum detectable refractive index change of 4 × 10 -4 RIU. The maximum bulk refractive index sensitivity (BRIS) of 75 nm/RIU was obtained for SU-8 laser-based refractive index sensors. The economical, rapid, and simple realization of polymeric micro-scale whispering-gallery-mode (WGM) laser-based refractive index sensors will further expand pathways of static and dynamic remote environmental, chemical, biological, and bio-chemical sensing.

Design of a compact and high sensitive refractive index sensor base on metal-insulator-metal plasmonic Bragg grating.

PubMed

Binfeng, Yun; Guohua, Hu; Ruohu, Zhang; Yiping, Cui

2014-11-17

A nanometric and high sensitive refractive index sensor based on the metal-insulator-metal plasmonic Bragg grating is proposed. The wavelength encoded sensing characteristics of the refractive index sensor were investigated by analyzing its transmission spectrum. The numerical results show that a good linear relationship between the Bragg wavelength and the refractive index of the sensing material can be obtained, which is in accordance with the analytical results very well. A high refractive index sensitivity of 1,488 nm/RIU around Bragg resonance wavelength of 1,550 nm was obtained. Besides, the simulation results show that the sensitivity is depended on the Bragg resonance wavelength and the longer the Bragg resonance wavelength, the higher sensitivity can be obtained. Furthermore, the figure of merit of the refractive index sensor can be greatly increased by introducing a nano-cavity in the proposed plasmonic Bragg grating structure. This work pave the way for high sensitive nanometric refractive index sensor design and application.

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.

Age-dependence of the average and equivalent refractive indices of the crystalline lens

PubMed Central

Charman, W. Neil; Atchison, David A.

2013-01-01

Lens average and equivalent refractive indices are required for purposes such as lens thickness estimation and optical modeling. We modeled the refractive index gradient as a power function of the normalized distance from lens center. Average index along the lens axis was estimated by integration. Equivalent index was estimated by raytracing through a model eye to establish ocular refraction, and then backward raytracing to determine the constant refractive index yielding the same refraction. Assuming center and edge indices remained constant with age, at 1.415 and 1.37 respectively, average axial refractive index increased (1.408 to 1.411) and equivalent index decreased (1.425 to 1.420) with age increase from 20 to 70 years. These values agree well with experimental estimates based on different techniques, although the latter show considerable scatter. The simple model of index gradient gives reasonable estimates of average and equivalent lens indices, although refinements in modeling and measurements are required. PMID:24466474

Holographic Optical Elements with Ultra-High Spatial Frequencies.

DTIC Science & Technology

1983-01-01

optical film thickness is equal to one-quarter of the wavelength of the incident radiation and the film’s index of refraction is...Am amount of photoresist material removed by developer N diffractive order number n index of refraction nx index of refraction -- x direction ny index ...since a material with the required index of refraction is usually hard to find4 7 . For example, there is no inorganic material available for

Decoupling the refractive index from the electrical properties of transparent conducting oxides via periodic superlattices

PubMed Central

Caffrey, David; Norton, Emma; Coileáin, Cormac Ó; Smith, Christopher M.; Bulfin, Brendan; Farrell, Leo; Shvets, Igor V.; Fleischer, Karsten

2016-01-01

We demonstrate an alternative approach to tuning the refractive index of materials. Current methodologies for tuning the refractive index of a material often result in undesirable changes to the structural or optoelectronic properties. By artificially layering a transparent conducting oxide with a lower refractive index material the overall film retains a desirable conductivity and mobility while acting optically as an effective medium with a modified refractive index. Calculations indicate that, with our refractive index change of 0.2, a significant reduction of reflective losses could be obtained by the utilisation of these structures in optoelectronic devices. Beyond this, periodic superlattice structures present a solution to decouple physical properties where the underlying electronic interaction is governed by different length scales. PMID:27623228

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

PubMed

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

2017-01-23

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

3-dimensional dark traps for low refractive index bio-cells using a single optical fiber Bessel beam.

PubMed

Zhang, Yu; Tang, Xiaoyun; Zhang, Yaxun; Su, Wenjie; Liu, Zhihai; Yang, Xinghua; Zhang, Jianzhong; Yang, Jun; Oh, Kyunghwan; Yuan, Libo

2018-06-15

We proposed and experimentally demonstrated 3-dimensional dark traps for low refractive index bio-cells using a single optical fiber Bessel beam. The Bessel beam was produced by concatenating single-mode fiber and a step index multimode fiber, which was then focused by a high refractive index glass microsphere integrated on the fiber end facet. The focused Bessel beam provided two dark fields along the axial direction, where stable trapping of low refractive index bio-cells was realized in a high refractive index liquid bath. The all-fiber and seamlessly integrated structure of the proposed scheme can find ample potential as a micro-optical probe in in situ characterization and manipulation of multiple bio-cells with refractive indices lower than that of the liquid bath.

Fiber-optic epoxy composite cure sensor. I. Dependence of refractive index of an autocatalytic reaction epoxy system at 850 nm on temperature and extent of cure

NASA Astrophysics Data System (ADS)

Lam, Kai-Yuen; Afromowitz, Martin A.

1995-09-01

We discuss the behavior of the refractive index of a typical epoxy-aromatic diamine system. Near 850 nm the index of refraction is found to be largely controlled by the density of the epoxy. Models are derived to describe its dependence on temperature and extent of cure. Within the range of temperatures studied, the refractive index decreases linearly with increasing temperature. In addition, as the epoxy is cured, the refractive index increases linearly with conversion to the gel point. >From then on, shrinkage in the volume of the epoxy is restricted by local viscosity. Therefore the linear relationship between the refractive index and the extent of cure does not hold beyond the gel point.

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

PubMed

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

2009-10-10

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

Change in refractive index of muscle tissue during laser-induced interstitial thermotherapy.

PubMed

Chen, Na; Chen, Meimei; Liu, Shupeng; Guo, Qiang; Chen, Zhenyi; Wang, Tingyun

2014-01-01

This paper presents a long-period fiber-grating (LPG) based Michelson interferometric refractometry to monitor the change in refractive index of porcine muscle during laser-induced interstitial thermotherapy (LITT). As the wavelength of RI interferometer alters with the change in refractive index around the probe, the LPG based refractometry is combined with LITT system to measure the change in refractive index of porcine muscle when irradiated by laser. The experimental results show the denaturation of tissue alters the refractive index significantly and the LPG sensor can be applied to monitor the tissue state during the LITT.

Refractive index sensor based on a polymer fiber directional coupler for low index sensing.

PubMed

Lee, Kwang Jo; Liu, Xiaoqi; Vuillemin, Nelly; Lwin, Richard; Leon-Saval, Sergio G; Argyros, Alexander; Kuhlmey, Boris T

2014-07-14

We propose, numerically analyze and experimentally demonstrate a novel refractive index sensor specialized for low index sensing. The device is based on a directional coupler architecture implemented in a single microstructured polymer optical fiber incorporating two waveguides within it: a single-mode core and a satellite waveguide consisting of a hollow high-index ring. This hollow channel is filled with fluid and the refractive index of the fluid is detected through changes to the wavelength at which resonant coupling occurs between the two waveguides. The sensor design was optimized for both higher sensitivity and lower detection limit, with simulations and experiments demonstrating a sensitivity exceeding 1.4 × 10(3) nm per refractive index unit. Simulations indicate a detection limit of ~2 × 10(-6) refractive index units is achievable. We also numerically investigate the performance for refractive index changes localized at the surface of the holes, a case of particular importance for biosensing.

Influence of the apex angle of a hollow prism made from an ordinary commercial glass plate as a simple refractometer to the accuracy of the refractive index measurement of the edible oil

NASA Astrophysics Data System (ADS)

Idris, N.; Maswati; Yusibani, E.

2018-05-01

The influence of the apex angle of a hollow prism used as a simple refractometer to the accuracy of a refractive index measurement of the edible oil samples was studied. The hollow prism was made from an ordinary commercial glass plate with a thickness of 2 mm. The apex angle of the constructed hollow prism was varied. The edible oil sample used in this study was palm oil, namely the packaged, branded oil sample and the bulk oil sample. For measuring the refractive index, the oil sample was filled in the constructed hollow prism, and then a helium-neon laser beam was passed through the oil sample at a certain angle of incidence. The angle of minimum deviation of the transmitted laser He-Ne beam was measured and then was used for calculating the refractive index of the oil sample. The refractive index measurement was made using the hollow prism with different apex angles, ranging from 300 to 600. The measurement accuracy was estimated by comparing the refractive index measured using the hollow prisms to that of obtained using a standard Abbe refractometer. It was found that the refractive index of the edible oil can be measured accurately by using the hollow prism. It was also found that the accuracy of the refractive index measurement significantly changes with the apex angle of the hollow prism. The refractive index values measured using this simple refractometer deviate up to 3,49% from the refractive index value measured using the standard Abbe refractometer, especially when the apex angle of the prism is 30°. The measurement results with high accuracies obtained when using the hollow prisms with apex angles of 450 and 600. The optimum apex angle for the present constructed hollow prism is 450. The refractive index obtained using the hollow prism with the apex angle of 450 is 1,4623 and 1,4438 for the bulk oil and the packed, branded oil samples, respectively. This result suggests that the apex angle of the prism used affects largely the accuracy of the refractive index measurement.

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

NASA Astrophysics Data System (ADS)

Bai, Kunlun; Katz, Joseph

2014-04-01

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

The Use of Index-Matched Beads in Optical Particle Counters

PubMed Central

Hu, Zhishang; Ripple, Dean C

2014-01-01

In this paper, we demonstrate the use of 2-pyridinemethanol (2P) aqueous solutions as a refractive index matching liquid. The high refractive index and low viscosity of 2P-water mixtures enables refractive index matching of beads that cannot be index matched with glycerol-water or sucrose-water solutions, such as silica beads that have the refractive index of bulk fused silica or of polymethylmethacrylate beads. Suspensions of beads in a nearly index-matching liquid are a useful tool to understand the response of particle counting instruments to particles of low optical contrast, such as aggregated protein particles. Data from flow imaging and light obscuration instruments are presented for bead diameters ranging from 6 µm to 69 µm, in a matrix liquid spanning the point of matched refractive index. PMID:26601049

Low-Coherence Reflectometry for Refractive Index Measurements of Cells in Micro-Capillaries.

PubMed

Carpignano, Francesca; Rigamonti, Giulia; Mazzini, Giuliano; Merlo, Sabina

2016-10-11

The refractive index of cells provides insights into their composition, organization and function. Moreover, a good knowledge of the cell refractive index would allow an improvement of optical cytometric and diagnostic systems. Although interferometric techniques undoubtedly represent a good solution for quantifying optical path variation, obtaining the refractive index of a population of cells non-invasively remains challenging because of the variability in the geometrical thickness of the sample. In this paper, we demonstrate the use of infrared low-coherence reflectometry for non-invasively quantifying the average refractive index of cell populations gently confined in rectangular glass micro-capillaries. A suspension of human red blood cells in plasma is tested as a reference. As a use example, we apply this technique to estimate the average refractive index of cell populations belonging to epithelial and hematological families.

High Sensitivity Refractive Index Sensor Based on Dual-Core Photonic Crystal Fiber with Hexagonal Lattice.

PubMed

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

2016-10-08

A refractive index sensor based on dual-core photonic crystal fiber (PCF) with hexagonal lattice is proposed. The effects of geometrical parameters of the PCF on performances of the sensor are investigated by using the finite element method (FEM). Two fiber cores are separated by two air holes filled with the analyte whose refractive index is in the range of 1.33-1.41. Numerical simulation results show that the highest sensitivity can be up to 22,983 nm/RIU(refractive index unit) when the analyte refractive index is 1.41. The lowest sensitivity can reach to 21,679 nm/RIU when the analyte refractive index is 1.33. The sensor we proposed has significant advantages in the field of biomolecule detection as it provides a wide-range of detection with high sensitivity.

High Sensitivity Refractive Index Sensor Based on Dual-Core Photonic Crystal Fiber with Hexagonal Lattice

PubMed Central

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

2016-01-01

A refractive index sensor based on dual-core photonic crystal fiber (PCF) with hexagonal lattice is proposed. The effects of geometrical parameters of the PCF on performances of the sensor are investigated by using the finite element method (FEM). Two fiber cores are separated by two air holes filled with the analyte whose refractive index is in the range of 1.33–1.41. Numerical simulation results show that the highest sensitivity can be up to 22,983 nm/RIU(refractive index unit) when the analyte refractive index is 1.41. The lowest sensitivity can reach to 21,679 nm/RIU when the analyte refractive index is 1.33. The sensor we proposed has significant advantages in the field of biomolecule detection as it provides a wide-range of detection with high sensitivity. PMID:27740607

Low-Coherence Reflectometry for Refractive Index Measurements of Cells in Micro-Capillaries

PubMed Central

Carpignano, Francesca; Rigamonti, Giulia; Mazzini, Giuliano; Merlo, Sabina

2016-01-01

The refractive index of cells provides insights into their composition, organization and function. Moreover, a good knowledge of the cell refractive index would allow an improvement of optical cytometric and diagnostic systems. Although interferometric techniques undoubtedly represent a good solution for quantifying optical path variation, obtaining the refractive index of a population of cells non-invasively remains challenging because of the variability in the geometrical thickness of the sample. In this paper, we demonstrate the use of infrared low-coherence reflectometry for non-invasively quantifying the average refractive index of cell populations gently confined in rectangular glass micro-capillaries. A suspension of human red blood cells in plasma is tested as a reference. As a use example, we apply this technique to estimate the average refractive index of cell populations belonging to epithelial and hematological families. PMID:27727172

Refractive index measurement based on confocal method

NASA Astrophysics Data System (ADS)

An, Zhe; Xu, XiPing; Yang, JinHua; Qiao, Yang; Liu, Yang

2017-10-01

The development of transparent materials is closed to optoelectronic technology. It plays an increasingly important role in various fields. It is not only widely used in optical lens, optical element, optical fiber grating, optoelectronics, but also widely used in the building material, pharmaceutical industry with vessel, aircraft windshield and daily wear glasses.Regard of solving the problem of refractive index measurement in optical transparent materials. We proposed that using the polychromatic confocal method to measuring the refractive index of transparent materials. In this article, we describes the principle of polychromatic confocal method for measuring the refractive index of glass,and sketched the optical system and its optimization. Then we establish the measurement model of the refractive index, and set up the experimental system. In this way, the refractive index of the glass has been calibrated for refractive index experiment. Due to the error in the experimental process, we manipulated the experiment data to compensate the refractive index measurement formula. The experiment taking the quartz glass for instance. The measurement accuracy of the refractive index of the glass is +/-1.8×10-5. This method is more practical and accurate, especially suitable for non-contact measurement occasions, which environmental requirements is not high. Environmental requirements are not high, the ordinary glass production line up to the ambient temperature can be fully adapted. There is no need for the color of the measured object that you can measure the white and a variety of colored glass.

Application of refractometry to quality assurance monitoring of parenteral nutrition solutions.

PubMed

Chang, Wei-Kuo; Chao, You-Chen; Yeh, Ming-Kung

2008-01-01

Parenteral nutrition (PN) solution contains various concentrations of dextrose, amino acids, lipids, vitamins, electrolytes, and trace elements. Incorrect preparation of PN solution could lead to patient death. In this study we used the refractive index as a quality assurance tool to monitor the preparation of PN solution. Refractive indices of single nutrient components and PN solutions consisting of various concentrations of dextrose, amino acids, electrolytes, and lipids were measured. A mathematical equation and its linear plot were generated then used to predict the refractive index of the PN solution. The best-fit refractive index for PN solution (i.e., the predicted refractive index)=0.9798x(% dextrose)+1.2889x(% amino acids)+1.1017x(% lipids)+0.9440x(% sum of the electrolytes)+0.5367 (r2=0.99). This equation was validated by comparing the measured refractive indices of 500 clinical PN solutions to their predicted refractive indices. We found that 2 of the 500 prepared samples (0.4%) had less than the predicted refractive index (<95%). Refractive index can be used as a reliable quality assurance tool for monitoring PN preparation. Such information can be obtained at the bedside and used to confirm the accuracy of the PN solution composition.

Determination of refractive index of a simple negative, positive, or zero power lens using wedged plated interferometer

NASA Technical Reports Server (NTRS)

Shukla, R. P.; Perera, G. M.; George, M. C.; Venkateswarlu, P.

1990-01-01

A nondestructive technique for measuring the refractive index of a negative lens using a wedged plate interferometer is described. The method can be also used for measuring the refractive index of convex or zero power lenses. Schematic diagrams are presented for the use of a wedged plate interferometer for measuring the refractive index of a concave lens and of a convex lens.

Refractive-index profiling of embedded microstructures in optical materials

NASA Astrophysics Data System (ADS)

Dave, Digant P.; Milner, Thomas E.

2002-04-01

We describe use of a phase-sensitive low-coherence reflectometer to measure spatial variation of refractive index in optical materials. The described interferometric technique is demonstrated to be a valuable tool to profile the refractive index of optical elements such as integrated waveguides and photowritten optical microstructures. As an example, a refractive-index profile is mapped of a microstructure written in a microscope glass slide with an ultrashort-pulse laser.

A refractive index sensor based on taper Michelson interferometer in multimode fiber

NASA Astrophysics Data System (ADS)

Fu, Xinghu; Zhang, Jiangpeng; Wang, Siwen; Fu, Guangwei; Liu, Qiang; Jin, Wa; Bi, Weihong

2016-11-01

A refractive index sensor based on taper Michelson interferometer in multimode fiber is proposed. The Hydrofluoric acid corrosion processing is studied in the preparation of single cone multimode optical fiber sensor. The taper Michelson interferometer is fabricated by changing corrosion time. The relationship between fiber sensor feature and corrosion time is analyzed. The experimental results show that the interference spectrum shift in the direction of short wave with the increase of the refractive index. The refractive index sensitivity can reach 115.8008 nm/RIU. Thereby, it can be used in detecting the refractive index in different areas including the environmental protection, health care and food production.

Experimental verification and simulation of negative index of refraction using Snell's law.

PubMed

Parazzoli, C G; Greegor, R B; Li, K; Koltenbah, B E C; Tanielian, M

2003-03-14

We report the results of a Snell's law experiment on a negative index of refraction material in free space from 12.6 to 13.2 GHz. Numerical simulations using Maxwell's equations solvers show good agreement with the experimental results, confirming the existence of negative index of refraction materials. The index of refraction is a function of frequency. At 12.6 GHz we measure and compute the real part of the index of refraction to be -1.05. The measurements and simulations of the electromagnetic field profiles were performed at distances of 14lambda and 28lambda from the sample; the fields were also computed at 100lambda.

Polymer microfiber bridging Bi-tapered refractive index sensor based on evanescent field

NASA Astrophysics Data System (ADS)

Lv, Ri-Qing; Wang, Qi; Wang, Bo-Tao; Liu, Yu; Kong, Lingxin

2018-05-01

A PDMS/graphene enhanced PMMA micro optical waveguide sensor is reported in terms of fabrication method and optical characteristics. The micro optical waveguide with a diameter of 6 μm and a length of 800 μm is used as the sensing probe to realize refractive index (RI) measurement suspended in NaCl solutions with different concentrations. Experimental results show that the refractive index sensing sensitivity can reach 2027.97 nm/RIU within the refractive index ranging from 1.3333-1.3426. Research results show that PMMA/graphene micro optical waveguide doped with PDMS is an excellent high sensitive sensing technology in refractive index detection field.

Highly sensitive refractive index fiber inline Mach-Zehnder interferometer fabricated by femtosecond laser micromachining and chemical etching

NASA Astrophysics Data System (ADS)

Sun, Xiao-Yan; Chu, Dong-Kai; Dong, Xin-Ran; Zhou, Chu; Li, Hai-Tao; Luo-Zhi; Hu, You-Wang; Zhou, Jian-Ying; Cong-Wang; Duan, Ji-An

2016-03-01

A High sensitive refractive index (RI) sensor based on Mach-Zehnder interferometer (MZI) in a conventional single-mode optical fiber is proposed, which is fabricated by femtosecond laser transversal-scanning inscription method and chemical etching. A rectangular cavity structure is formed in part of fiber core and cladding interface. The MZI sensor shows excellent refractive index sensitivity and linearity, which exhibits an extremely high RI sensitivity of -17197 nm/RIU (refractive index unit) with the linearity of 0.9996 within the refractive index range of 1.3371-1.3407. The experimental results are consistent with theoretical analysis.

Investigation of the refractive index repeatability for tantalum pentoxide coatings, prepared by physical vapor film deposition techniques.

PubMed

Stenzel, O; Wilbrandt, S; Wolf, J; Schürmann, M; Kaiser, N; Ristau, D; Ehlers, H; Carstens, F; Schippel, S; Mechold, L; Rauhut, R; Kennedy, M; Bischoff, M; Nowitzki, T; Zöller, A; Hagedorn, H; Reus, H; Hegemann, T; Starke, K; Harhausen, J; Foest, R; Schumacher, J

2017-02-01

Random effects in the repeatability of refractive index and absorption edge position of tantalum pentoxide layers prepared by plasma-ion-assisted electron-beam evaporation, ion beam sputtering, and magnetron sputtering are investigated and quantified. Standard deviations in refractive index between 4*10^-4 and 4*10^-3 have been obtained. Here, lowest standard deviations in refractive index close to our detection threshold could be achieved by both ion beam sputtering and plasma-ion-assisted deposition. In relation to the corresponding mean values, the standard deviations in band-edge position and refractive index are of similar order.

Determination of the refractive index of glucose-ethanol-water mixtures using spectroscopic refractometry near the critical angle.

PubMed

Sobral, H; Peña-Gomar, M

2015-10-01

A spectroscopic refractometer was used to investigate the dispersion curves of ethanol and D-glucose solutions in water near the critical angle; here, the reflectivity was measured using a white source. Dispersion curves were obtained in the 320-1000 nm wavelength range with a resolution better than 10(-4) for the refractive index, n. The differential refractive index is measured as a function of wavelength, and a simple expression is proposed to obtain the refractive index of the glucose-ethanol-water ternary system. Using this expression, combined with the experimental differential refractive index values, the concentrations of individual components can be calculated.

Novel Electrochemical Raman Spectroscopy Enabled by Water Immersion Objective.

PubMed

Zeng, Zhi-Cong; Hu, Shu; Huang, Sheng-Chao; Zhang, Yue-Jiao; Zhao, Wei-Xing; Li, Jian-Feng; Jiang, Chaoyang; Ren, Bin

2016-10-04

Electrochemical Raman spectroscopy is a powerful molecular level diagnostic technique for in situ investigation of adsorption and reactions on various material surfaces. However, there is still a big room to improve the optical path to meet the increasing request of higher detection sensitivity and spatial resolution. Herein, we proposed a novel electrochemical Raman setup based on a water immersion objective. It dramatically reduces mismatch of the refractive index in the light path. Consequently, significant improvement in detection sensitivity and spatial resolution has been achieved from both Zemax simulation and the experimental results. Furthermore, the thickness of electrolyte layer could be expanded to 2 mm without any influence on the signal collection. Such a thick electrolyte layer allows a much normal electrochemical response during the spectroelectrochemical investigations of the methanol oxidation.

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.

Laser interferometry of the hydrolytic changes in protein solutions: the refractive index and hydration shells.

PubMed

Sarimov, R M; Matveyeva, T A; Binhi, V N

2018-05-11

Using an original laser interferometer of enhanced sensitivity, an increase in the refractive index of a protein solution was observed during the reaction of proteolysis catalyzed by pepsin. The increase in the refractive index of the protein solution at a concentration of 4 mg/ml was [Formula: see text] for bovine serum albumin and [Formula: see text] for lysozyme. The observed effect disproves the existing idea that the refractive index of protein solutions is determined only by their amino acid composition and concentration. It is shown that the refractive index also depends on the state of protein fragmentation. A mathematical model of proteolysis and a real-time method for estimating the state of protein hydration based on the measurement of refractive index during the reaction are proposed. A good agreement between the experimental and calculated time dependences of the refractive index shows that the growth of the surface of protein fragments and the change in the number of hydration cavities during proteolysis can be responsible for the observed effect.

Optical negative refraction by four-wave mixing in thin metallic nanostructures.

PubMed

Palomba, Stefano; Zhang, Shuang; Park, Yongshik; Bartal, Guy; Yin, Xiaobo; Zhang, Xiang

2011-10-30

The law of refraction first derived by Snellius and later introduced as the Huygens-Fermat principle, states that the incidence and refracted angles of a light wave at the interface of two different materials are related to the ratio of the refractive indices in each medium. Whereas all natural materials have a positive refractive index and therefore exhibit refraction in the positive direction, artificially engineered negative index metamaterials have been shown capable of bending light waves negatively. Such a negative refractive index is the key to achieving a perfect lens that is capable of imaging well below the diffraction limit. However, negative index metamaterials are typically lossy, narrow band, and require complicated fabrication processes. Recently, an alternative approach to obtain negative refraction from a very thin nonlinear film has been proposed and experimentally demonstrated in the microwave region. However, such approaches use phase conjugation, which makes optical implementations difficult. Here, we report a simple but different scheme to demonstrate experimentally nonlinear negative refraction at optical frequencies using four-wave mixing in nanostructured metal films. The refractive index can be designed at will by simply tuning the wavelengths of the interacting waves, which could have potential impact on many important applications, such as superlens imaging.

Aberration correction considering curved sample surface shape for non-contact two-photon excitation microscopy with spatial light modulator.

PubMed

Matsumoto, Naoya; Konno, Alu; Inoue, Takashi; Okazaki, Shigetoshi

2018-06-18

In this paper, excitation light wavefront modulation is performed considering the curved sample surface shape to demonstrate high-quality deep observation using two-photon excitation microscopy (TPM) with a dry objective lens. A large spherical aberration typically occurs when the refractive index (RI) interface between air and the sample is a plane perpendicular to the optical axis. Moreover, the curved sample surface shape and the RI mismatch cause various aberrations, including spherical ones. Consequently, the fluorescence intensity and resolution of the obtained image are degraded in the deep regions. To improve them, we designed a pre-distortion wavefront for correcting the aberration caused by the curved sample surface shape by using a novel, simple optical path length difference calculation method. The excitation light wavefront is modulated to the pre-distortion wavefront by a spatial light modulator incorporated in the TPM system before passing through the interface, where the RI mismatch occurs. Thus, the excitation light is condensed without aberrations. Blood vessels were thereby observed up to an optical depth of 2,000 μm in a cleared mouse brain by using a dry objective lens.

Image Information Obtained Using a Charge-Coupled Device (CCD) Camera During an Immersion Liquid Evaporation Process for Measuring the Refractive Index of Solid Particles.

PubMed

Niskanen, Ilpo; Sutinen, Veijo; Thungström, Göran; Räty, Jukka

2018-06-01

The refractive index is a fundamental physical property of a medium, which can be used for the identification and purity issues of all media. Here we describe a refractive index measurement technique to determine simultaneously the refractive index of different solid particles by monitoring the transmittance of light from a suspension using a charge-coupled device (CCD) camera. An important feature of the measurement is the liquid evaporation process for the refractive index matching of the solid particle and the immersion liquid; this was realized by using a pair of volatile and non-volatile immersion liquids. In this study, refractive indices of calcium fluoride (CaF 2 ) and barium fluoride (BaF 2 ) were determined using the proposed method.

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

PubMed

Lucy, David; Zadora, Grzegorz

2011-10-10

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

TiO2 surface functionalization of COC based planar waveguide Bragg gratings for refractive index sensing

NASA Astrophysics Data System (ADS)

Rosenberger, M.; Girschikofsky, M.; Förthner, M.; Belle, S.; Rommel, M.; Frey, L.; Schmauss, B.; Hellmann, R.

2018-01-01

We demonstrate the applicability of a planar waveguide Bragg grating in cyclo-olefin copolymer (COC) for refractive index sensing. The polymer planar waveguide Bragg grating fabricated using a single writing step technique is coated with a high-index layer of titanium dioxide (TiO2) leading to a distinct birefringence. This in turn results in the splitting of the Bragg reflection into two distinct Bragg wavelengths, which strongly differ regarding their refractive index sensitivities. Where one wavelength is only slightly affected by the ambient refractive index, the second Bragg peak shows a strong sensitivity. Furthermore, we investigate the temperature behaviour of the functionalized sensor and discuss it with respect to applications in refractive index sensing.

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

PubMed

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

2012-11-19

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

Ultrasensitive Magnetic Field Sensing Based on Refractive-Index-Matched Coupling.

PubMed

Rao, Jie; Pu, Shengli; Yao, Tianjun; Su, Delong

2017-07-07

An ultrasensitive magnetic field sensor is proposed and investigated experimentally. The no-core fiber is fusion-spliced between two pieces of single-mode fibers and then immersed in magnetic fluid with an appropriate value of refractive index. Under the refractive-index-matched coupling condition, the guided mode becomes leaky and a coupling wavelength dip in the transmission spectrum of the structure is observed. The coupling wavelength dip is extremely sensitive to the ambient environment. The excellent sensitivity to the refractive index is measured to be 116.681 μm/RIU (refractive index unit) in the refractive index range of 1.45691-1.45926. For the as-fabricated sensors, the highest magnetic field sensing sensitivities of 6.33 and 1.83 nm/mT are achieved at low and high fields, respectively. The sensitivity is considerably enhanced compared with those of previously designed, similar structures.

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

PubMed

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

2014-12-29

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

Method and apparatus for determining peak temperature along an optical fiber

DOEpatents

Fox, Richard J.

1985-01-01

The invention relates to a new method and new apparatus for determining the hottest temperature or the coldest temperature prevailing along the length of an optical-fiber light guide. The invention is conducted with an optical fiber capable of supporting multidiode propagation of light and comprising a core, a cladding, and a jacket. The core is selected to have (1) a higher refractive index than the core and the cladding and (2) a relatively high negative temperature coefficient of refractive index. A light beam capable of establishing substantially single-mode propagation in the core is launched into an end thereof at an angle to the axis. The angle is increased to effect the onset of light refraction from the core into the cladding. The value of the launch angle corresponding to the onset is determined and then used to establish the refractive index of the core corresponding to the onset angle. The maximum temperature prevailing along the fiber then is determined from the (1) refractive index so determined and (2) the temperature coefficient of refractive index for the core. The invention is based on the finding that the launch angle corresponding to the onset of refraction into the cladding is uniquely determined by the maximum value of the ratio of the core refractive index to the cladding refractive index, which maximum occurs at the hottest point along the fiber.

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

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

NASA Astrophysics Data System (ADS)

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

2006-03-01

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

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.

Equivalent refractive-index structure constant of non-Kolmogorov turbulence.

PubMed

Li, Yujie; Zhu, Wenyue; Wu, Xiaoqing; Rao, Ruizhong

2015-09-07

The relationship between the non-Kolmogorov refractive-index structure constant and the Kolmogorov refractive-index structure constant is derived by using the refractive-index structure function and the variance of refractive-index fluctuations. It shows that the non-Kolmogorov structure constant is proportional to the Kolmogorov structure constant and the scaling factor depends on the outer scale and the spectral power law. For a fixed Kolmogorov structure constant, the non-Kolmogorov structure constant increases with a increasing outer scale for the power law less than 11/3, the trend is opposite for the power law greater than 11/3. This equivalent relation provides a way of obtaining the non-Kolmogorov structure constant by using the Kolmogorov structure constant.

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

PubMed

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

2016-03-15

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

Photo-Induced Self-Condensation, A Technique For Fabricating Organic Lightguide Structures

NASA Astrophysics Data System (ADS)

Franke, H.; Heuer, W.

1986-11-01

Planar lightguides have been fabricated from mixtures of the polymer PMMA with benzoin type photoinitiators. Using conventional UV-photolithography 2 dimensional refractive index patterns were recorded in the polymer films. Thickness and refractive index of the organic lightguides were determined by m-line spectroscopy. The achieved refractive index changes increased with increasing photoinitiator concentrations. For high concentrations (< 70 %) the film refractive index could be increased via UV exposure by Δn = 0.03. Thermal treatment at below 100°C caused the out diffusion of the unexposed photoinitiator and completion of the photochemically induced reaction in the exposed parts of the film. Thus refractive index patterns (Δn < 0.05) could be developed and fixed.

Refractive index sensing by Brillouin scattering in side-polished optical fibers.

PubMed

Bernini, Romeo; Persichetti, Gianluca; Catalano, Ester; Zeni, Luigi; Minardo, Aldo

2018-05-15

In this Letter, we demonstrate the possibility to measure the refractive index of a liquid, using the stimulating Brillouin scattering in a 3-cm-long side-polished optical fiber. In addition, we show that by depositing a high-refractive index layer on the polished surface the sensitivity of the Brillouin frequency shift (BFS) can be increased due to a higher penetration of the evanescent field in the outer medium. Experiments show a maximum BFS change of about 11 MHz when varying the refractive index of the external medium from 1 (air) to 1.402, and a BFS sensitivity to refractive index of about 293 MHz/RIU around 1.40.

Fiber-integrated refractive index sensor based on a diced Fabry-Perot micro-resonator.

PubMed

Suntsov, Sergiy; Rüter, Christian E; Schipkowski, Tom; Kip, Detlef

2017-11-20

We report on a fiber-integrated refractive index sensor based on a Fabry-Perot micro-resonator fabricated using simple diamond blade dicing of a single-mode step-index fiber. The performance of the device has been tested for the refractive index measurements of sucrose solutions as well as in air. The device shows a sensitivity of 1160 nm/RIU (refractive index unit) at a wavelength of 1.55 μm and a temperature cross-sensitivity of less than 10 -7   RIU/°C. Based on evaluation of the broadband reflection spectra, refractive index steps of 10 -5 of the solutions were accurately measured. The conducted coating of the resonator sidewalls with layers of a high-index material with real-time reflection spectrum monitoring could help to significantly improve the sensor performance.

Formation of bulk refractive index structures

DOEpatents

Potter, Jr., Barrett George; Potter, Kelly Simmons; Wheeler, David R.; Jamison, Gregory M.

2003-07-15

A method of making a stacked three-dimensional refractive index structure in photosensitive materials using photo-patterning where first determined is the wavelength at which a photosensitive material film exhibits a change in refractive index upon exposure to optical radiation, a portion of the surfaces of the photosensitive material film is optically irradiated, the film is marked to produce a registry mark. Multiple films are produced and aligned using the registry marks to form a stacked three-dimensional refractive index structure.

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

NASA Astrophysics Data System (ADS)

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

2007-05-01

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

Improved retroreflection method for measuring the refractive index of liquids.

PubMed

Shao, Duo; Tian, Linghao; Chen, Jingfei; Chen, Xianfeng

2010-06-01

We propose a new method for measuring the refractive index of liquids with high precision; the method is based on use of the optical fiber end face. As an example, we investigated the refractive index of sugar solution under varying conditions tens of times. The results show that this method has the advantage of higher stability and repeatability. The concentration and the temperature-dependent refractive index of the sugar solution is also experimentally studied.

Nonscanning Moiré deflectometry for measurement of nonlinear refractive index and absorption coefficient of liquids.

PubMed

Farahani, Shahrzad Shahrabi; Madanipour, Khosro; Koohian, Ata

2017-05-01

In this work, a nonscanning measurement technique is presented for determining the nonlinear refractive index and absorption coefficient of liquid media based on Moiré deflectometry. In the proposed method two lasers are used: a low power, wide beam as probe and a high power with specific wavelength as a pump. Interaction of the pump laser beam with the nonlinear sample changes the refractive index, which leads to change in convergence/divergence of the collimated incident probe laser beam. The induced deflection is monitored by Moiré deflectometry. If the pump laser has a Gaussian intensity profile, the refractive index profile of the sample is Gaussian, too. Measuring the deflection angle of the probe beam by Moiré fringes deflection, and by using the inverse Abel transform integral, the refractive index profile and nonlinear refractive index can be determined. This method is fast, easy, and insensitive to environmental noise and allows real-time measurement. Also, the refractive index profile of the interacted medium with pump laser can be achieved by this technique. As a liquid sample, a DCJ dye in water solution was studied. The value of nonlinear refractive index, n₂, and absorption coefficient, α, were obtained -2.54×10^-4  cm² w^-1 and 1.368  cm^-1, respectively.

Estimation of the refractive index of rigid contact lenses on the basis of back vertex power measurements.

PubMed

Pearson, Richard

2011-03-01

To assess the possibility of estimating the refractive index of rigid contact lenses on the basis of measurements of their back vertex power (BVP) in air and when immersed in liquid. First, a spreadsheet model was used to quantify the magnitude of errors arising from simulated inaccuracies in the variables required to calculate refractive index. Then, refractive index was calculated from in-air and in-liquid measurements of BVP of 21 lenses that had been made in three negative BVPs from materials with seven different nominal refractive index values. The power measurements were made by two operators on two occasions. Intraobserver reliability showed a mean difference of 0.0033±0.0061 (t = 0.544, P = 0.59), interobserver reliability showed a mean difference of 0.0043±0.0061 (t = 0.707, P = 0.48), and the mean difference between the nominal and calculated refractive index values was -0.0010±0.0111 (t = -0.093, P = 0.93). The spreadsheet prediction that low-powered lenses might be subject to greater errors in the calculated values of refractive index was substantiated by the experimental results. This method shows good intra and interobserver reliabilities and can be used easily in a clinical setting to provide an estimate of the refractive index of rigid contact lenses having a BVP of 3 D or more.

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.

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

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

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

2003-08-01

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

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

PubMed

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

2018-04-30

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

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.

Temperature independent refractive index measurement using a fiber Bragg grating on abrupt tapered tip

NASA Astrophysics Data System (ADS)

Gomes, André D.; Silveira, Beatriz; Warren-Smith, Stephen C.; Becker, Martin; Rothhardt, Manfred; Frazão, Orlando

2018-05-01

A fiber Bragg grating was inscribed in an abrupt fiber taper using a femtosecond laser and phase-mask interferometer. The abrupt taper transition allows to excite a broad range of guided modes with different effective refractive indices that are reflected at different wavelengths according to Bragg's law. The multimode-Bragg reflection expands over 30 nm in the telecom-C-band. This corresponds to a mode-field overlap of up to 30% outside of the fiber, making the device suitable for evanescent field sensing. Refractive index and temperature measurements are performed for different reflection peaks. Temperature independent refractive index measurements are achieved by considering the difference between the wavelength shifts of two measured reflection peaks. A minimum refractive index sensitivity of 16 ± 1 nm/RIU was obtained in a low refractive index regime (1.3475-1.3720) with low influence of temperature (-0.32 ± 0.06 pm/°C). The cross sensitivity for this structure is 2.0 × 10-5 RIU/°C. The potential for simultaneous measurement of refractive index and temperature is also studied.

Finite element approximation of the radiative transport equation in a medium with piece-wise constant refractive index

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

Lehtikangas, O., E-mail: Ossi.Lehtikangas@uef.fi; Tarvainen, T.; Department of Computer Science, University College London, Gower Street, London WC1E 6BT

2015-02-01

The radiative transport equation can be used as a light transport model in a medium with scattering particles, such as biological tissues. In the radiative transport equation, the refractive index is assumed to be constant within the medium. However, in biomedical media, changes in the refractive index can occur between different tissue types. In this work, light propagation in a medium with piece-wise constant refractive index is considered. Light propagation in each sub-domain with a constant refractive index is modeled using the radiative transport equation and the equations are coupled using boundary conditions describing Fresnel reflection and refraction phenomena onmore » the interfaces between the sub-domains. The resulting coupled system of radiative transport equations is numerically solved using a finite element method. The approach is tested with simulations. The results show that this coupled system describes light propagation accurately through comparison with the Monte Carlo method. It is also shown that neglecting the internal changes of the refractive index can lead to erroneous boundary measurements of scattered light.« less

REFRACTOMETRY AS A TOOL IN DIABETIC STUDIES

PubMed Central

Kavitha, S.; Murthy, V.R.

2006-01-01

The refractive index as well as molar refraction, is the true index of purity of substance and plays a vital role in solution chemistry. A small addition of a foreign substance either in solid state of liquid form is going to effect the refractive index. As such the variation of refractive indices in pure glucose solution as a function of concentration is studied in detail and this principle is extended to the study of the refractive indices of urine solution of diabetic patients. The refractive indices are measured by spectrometry and abbe refractometry. A detailed study of variation of refractive indices of urine samples containing different sugar concentrations, of patients of different age groups revealed that the increase in refractive index follows a linear scale and can be explained by the equation, n=no [l+0.00251og (a s)1/4] [l+0.031og0.011C]. These study provided an opportunity to project refractometry as an effective tool in diagnosing the diabetic level of a patient by making use of a simple calibration curve of increment in refractive index ‘Δn, as a function of level of the disease. PMID:22557211

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.

Iodine insertion and dispersion of refractive index in organic single crystal semiconductor.

PubMed

Kwon, Seonho; Bae, Junwan; Lee, I J

2018-02-20

Insertion of halogens such as bromine or iodine affects the electronic polarizability of ions and the local field inside the medium, and thus modifies the refractive index. Acquiring precise knowledge of the dispersion of refractive index and ultimately tailoring conventional semiconductors for wide-range refractive index control have been a vital issue to resolve before realizing advanced organic optoelectronic devices. In this report, dispersions of the refractive index of a single crystal tetramethyltetraselenafulvalene [C 10 H 12 Se 4 ] (TMTSF) are thoroughly studied from broadband interference modulations of photoluminescence (PL) spectra at various temperatures and doping levels. A large enhancement of the refractive index, more than 20% of the intrinsic value, is achieved with inclusion of a small composition of iodide ions, while the structural and optical properties remain mostly intact. Nearly temperature independent dispersion of the refractive index suggests that, unlike most polymers in which the thermal expansion coefficient dominates over the change of polarizability with temperature, the latter enhances significantly and may become more or less comparable to the thermal expansion coefficient given by 1.71 × 10 -4 /K, when single crystal TMTSF is doped by iodine.

[Modeling and Simulation of Spectral Polarimetric BRDF].

PubMed

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

2016-01-01

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

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.

Refractive index sensor based on optical fiber end face using pulse reference-based compensation technique

NASA Astrophysics Data System (ADS)

Bian, Qiang; Song, Zhangqi; Zhang, Xueliang; Yu, Yang; Chen, Yuzhong

2018-03-01

We proposed a refractive index sensor based on optical fiber end face using pulse reference-based compensation technique. With good compensation effect of this compensation technique, the power fluctuation of light source, the change of optic components transmission loss and coupler splitting ratio can be compensated, which largely reduces the background noise. The refractive index resolutions can achieve 3.8 × 10-6 RIU and1.6 × 10-6 RIU in different refractive index regions.

Optical Properties of Si, Ge, GaAs, GaSb, InAs, and InP at Elevated Temperatures

DTIC Science & Technology

2010-03-01

transmitted, and an absorbed (or scattered) component. The reflectance can be defined in terms of the index of refraction of the media on either side...of the interface. If the index of refraction of the material is n and the material is surrounded by air (nair ≈ 1), then the reflectance for near...the absorption coefficient and t is the sample thickness. 9 Since R depends on the refractive index and the refractive index depends on the

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

PubMed

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

2018-06-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-03-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-05-01

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

Refractive index inversion based on Mueller matrix method

NASA Astrophysics Data System (ADS)

Fan, Huaxi; Wu, Wenyuan; Huang, Yanhua; Li, Zhaozhao

2016-03-01

Based on Stokes vector and Jones vector, the correlation between Mueller matrix elements and refractive index was studied with the result simplified, and through Mueller matrix way, the expression of refractive index inversion was deduced. The Mueller matrix elements, under different incident angle, are simulated through the expression of specular reflection so as to analyze the influence of the angle of incidence and refractive index on it, which is verified through the measure of the Mueller matrix elements of polished metal surface. Research shows that, under the condition of specular reflection, the result of Mueller matrix inversion is consistent with the experiment and can be used as an index of refraction of inversion method, and it provides a new way for target detection and recognition technology.

Study of optical nonlinearities in Se-Te-Bi thin films

NASA Astrophysics Data System (ADS)

Sharma, Ambika; Yadav, Preeti; Kumari, Anshu

2014-04-01

The present work reports the nonlinear refractive index of Se85-xTe15Bix thin films calculated by Ticha and Tichy relation. The nonlinear refractive index of Chalcogenide amorphous semiconductor is well correlated with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system. The density of the system is calculated theoretical as well as experimentally by using Archimedes principle. The linear refractive index and WDD parameters are calculated using single transmission spectra in the spectral range of 400-1500 nm. It is observed that linear as well as nonlinear refractive index increases with Bi content. The results are analyzed on the basis of increasing polarizability due to larger radii of Bi.

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 average refractive index of spin coated DCG films for HOE fabrication

NASA Technical Reports Server (NTRS)

Kim, T. J.; Campbell, Eugene W.; Kostuk, Raymond K.

1993-01-01

The refractive index of holographic emulsions is an important parameter needed for designing holographic optical elements (HOE's). Theoretical calculations of the accuracy required for the refractive index and thickness of emulsions needed to meet predetermined Bragg angle conditions are presented. A modified interferometric method is used to find average refractive index of the unexposed and the developed dichromated gelatin holographic films. Slanted transmission HOE's are designed considering the index and thickness variations, and used to verify the index measurement results. The Brewster angle method is used to measure surface index of the unexposed and the developed films. The differences between average index and surface index are discussed. Theoretical calculation of the effects of index variation on diffraction efficiency, and experimental results for index modulation variation caused by process changes are also presented.

Measurement of Refractive Index Using a Michelson Interferometer.

ERIC Educational Resources Information Center

Fendley, J. J.

1982-01-01

Describes a novel and simple method of measuring the refractive index of transparent plates using a Michelson interferometer. Since it is necessary to use a computer program when determining the refractive index, undergraduates could be given the opportunity of writing their own programs. (Author/JN)

String and Sticky Tape Experiments: Refractive Index of Liquids.

ERIC Educational Resources Information Center

Edge, R. D., Ed.

1979-01-01

Describes a simple method of measuring the refractive index of a liquid using a paper cup, a liquid, a pencil, and a ruler. Uses the ratio between the actual depth and the apparent depth of the cup to calculate the refractive index. (GA)

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.

Long range surface plasmon resonance (LRSPR) based highly sensitive refractive index sensor using Kretschmann prism coupling arrangement

NASA Astrophysics Data System (ADS)

Paliwal, Ayushi; Sharma, Anjali; Tomar, Monika; Gupta, Vinay

2016-04-01

Long range surface plasmon resonance (LRSPR) when exploited for sensing purpose exhibit less losses in comparison to the sensors based on conventional SPR technique leading to the development of highly sensitive refractive index sensor. In order to excite long range surface plasmon (LRSP) mode, a high refractive index prism is used as coupler and a thin metal layer is sandwiched between a dielectric having similar refractive index with that of another semi-infinite dielectric. LRSP mode has been excited in symmetric configuration where metal (Au) layer is sandwiched between the two similar refractive index dielectrics (LiF thin film and a fixed concentration of sugar solution) for realization of a refractive index sensor. When the concentration of sugar solution is slightly increased from 30% to 40%, the LRSPR angle increases from 64.6° to 67.9° and the sensor is found to be highly sensitive with sensitivity of 0.0911 °/(mg/dl).

Effect of temperature rise and hydrostatic pressure on microbending loss and refractive index change in double-coated optical fiber

NASA Astrophysics Data System (ADS)

Seraji, Faramarz E.; Toutian, Golnoosh

This paper presents an analysis of the effect of temperature rise and hydrostatic pressure on microbending loss, refractive index change, and stress components of a double-coated optical fiber by considering coating material parameters such as Young's modulus and the Poisson ratio. It is shown that, when temperature rises, the microbending loss and refractive index changes would decrease with increase of thickness of primary coating layer and will increase after passing through a minima. Increase of thickness of secondary coating layer causes the microbending loss and refractive index changes to decrease. We have shown that the temperature rise affecting the fiber makes the microbending loss and refractive index decrease, linearly. At a particular temperature, the microbending loss takes negative values, due to tensile pressure applied on the fiber. The increase of Young's modulus and the Poisson ratio of primary coating would lower the microbending loss and refractive index change whereas in the secondary coating layer, the condition reverses.

Frequency comb calibrated frequency-sweeping interferometry for absolute group refractive index measurement of air.

PubMed

Yang, Lijun; Wu, Xuejian; Wei, Haoyun; Li, Yan

2017-04-10

The absolute group refractive index of air at 194061.02 GHz is measured in real time using frequency-sweeping interferometry calibrated by an optical frequency comb. The group refractive index of air is calculated from the calibration peaks of the laser frequency variation and the interference signal of the two beams passing through the inner and outer regions of a vacuum cell when the frequency of a tunable external cavity diode laser is scanned. We continuously measure the refractive index of air for 2 h, which shows that the difference between measured results and Ciddor's equation is less than 9.6×10^-8, and the standard deviation of that difference is 5.9×10^-8. The relative uncertainty of the measured refractive index of air is estimated to be 8.6×10^-8. The data update rate is 0.2 Hz, making it applicable under conditions in which air refractive index fluctuates fast.

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.

Figure of Merit Enhancement of a Surface Plasmon Resonance Sensor Using a Low-Refractive-Index Porous Silica Film

PubMed Central

Meng, Qing-Qing; Zhao, Xin; Lin, Cheng-You; Chen, Shu-Jing; Ding, Ying-Chun; Chen, Zhao-Yang

2017-01-01

In this paper; the surface plasmon resonance (SPR) sensor with a porous silica film was studied. The effect of the thickness and porosity of the porous silica film on the performance of the sensor was analyzed. The results indicated that the figure of merit (FOM) of an SPR sensor can be enhanced by using a porous silica film with a low-refractive-index. Particularly; the FOM of an SPR sensor with 40 nm thick 90% porosity porous silica film; whose refractive index is 1.04 was improved by 311% when compared with that of a traditional SPR sensor. Furthermore; it was found that the decrease in the refractive index or the increase in the thickness of the low-refractive-index porous silica film can enlarge the FOM enhancement. It is believed that the proposed SPR sensor with a low-refractive-index porous silica film will be helpful for high-performance SPR sensors development. PMID:28796155

Figure of Merit Enhancement of a Surface Plasmon Resonance Sensor Using a Low-Refractive-Index Porous Silica Film.

PubMed

Meng, Qing-Qing; Zhao, Xin; Lin, Cheng-You; Chen, Shu-Jing; Ding, Ying-Chun; Chen, Zhao-Yang

2017-08-10

In this paper; the surface plasmon resonance (SPR) sensor with a porous silica film was studied. The effect of the thickness and porosity of the porous silica film on the performance of the sensor was analyzed. The results indicated that the figure of merit (FOM) of an SPR sensor can be enhanced by using a porous silica film with a low-refractive-index. Particularly; the FOM of an SPR sensor with 40 nm thick 90% porosity porous silica film; whose refractive index is 1.04 was improved by 311% when compared with that of a traditional SPR sensor. Furthermore; it was found that the decrease in the refractive index or the increase in the thickness of the low-refractive-index porous silica film can enlarge the FOM enhancement. It is believed that the proposed SPR sensor with a low-refractive-index porous silica film will be helpful for high-performance SPR sensors development.

Database and new models based on a group contribution method to predict the refractive index of ionic liquids.

PubMed

Wang, Xinxin; Lu, Xingmei; Zhou, Qing; Zhao, Yongsheng; Li, Xiaoqian; Zhang, Suojiang

2017-08-02

Refractive index is one of the important physical properties, which is widely used in separation and purification. In this study, the refractive index data of ILs were collected to establish a comprehensive database, which included about 2138 pieces of data from 1996 to 2014. The Group Contribution-Artificial Neural Network (GC-ANN) model and Group Contribution (GC) method were employed to predict the refractive index of ILs at different temperatures from 283.15 K to 368.15 K. Average absolute relative deviations (AARD) of the GC-ANN model and the GC method were 0.179% and 0.628%, respectively. The results showed that a GC-ANN model provided an effective way to estimate the refractive index of ILs, whereas the GC method was simple and extensive. In summary, both of the models were accurate and efficient approaches for estimating refractive indices of ILs.

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

PubMed

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

2009-03-01

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

Determining thickness and refractive index from free-standing ultra-thin polymer films with spectroscopic ellipsometry

DOE PAGES

Hilfiker, James N.; Stadermann, Michael; Sun, Jianing; ...

2016-08-27

It is a well-known challenge to determine refractive index (n) from ultra-thin films where the thickness is less than about 10 nm. In this paper, we discovered an interesting exception to this issue while characterizing spectroscopic ellipsometry (SE) data from isotropic, free-standing polymer films. Ellipsometry analysis shows that both thickness and refractive index can be independently determined for free-standing films as thin as 5 nm. Simulations further confirm an orthogonal separation between thickness and index effects on the experimental SE data. Effects of angle of incidence and wavelength on the data and sensitivity are discussed. Finally, while others have demonstratedmore » methods to determine refractive index from ultra-thin films, our analysis provides the first results to demonstrate high-sensitivity to the refractive index from ultra-thin layers.« less

Method and apparatus for determining peak temperature along an optical fiber

DOEpatents

Fox, R.J.

1982-07-29

The invention relates to a new method and new apparatus for determining the hottest temperature or the coldest temperature prevailing along the length of an optical-fiber light guide. The invention is conducted with an optical fiber capable of supporting multidiode propagation of light and comprising a core, a cladding, and a jacket. The core is selected to have (1) a higher refractive index than the core and the cladding and (2) a relatively high negative temperature coefficient of refractive index. A light beam capable of establishing substantially single-mode propagation in the core is launched into an end thereof at an angle to the axis. The angle is increased to effect the onset of light fraction from the core into the cladding. The value of the launch angle corresponding to the onset is determined and then used to establish the refractive index of the core corresponding to the onset angle. The maximum temperature prevailing along the fiber then is determined from the (1) refractive index so determined and (2) the temperature coefficient of refractive index for the core. The invention is based on the finding that the launch angle corresponding to the onset of refraction into the cladding is uniquely determined by the maximum value of the ratio of the core refractive index to the cladding refractive index, which maximum occurs at the hottest point along the fiber.

High Dynamic Range (Δn) Two-Stage Photopolymers via Enhanced Solubility of a High Refractive Index Acrylate Writing Monomer.

PubMed

Alim, Marvin D; Glugla, David J; Mavila, Sudheendran; Wang, Chen; Nystrom, Philip D; Sullivan, Amy C; McLeod, Robert R; Bowman, Christopher N

2018-01-10

Holographic photopolymers capable of high refractive index modulation (Δn) on the order of 10 -2 are integral for the fabrication of functional holographic optical elements that are useful in a myriad of optical applications. In particular, to address the deficiency of suitable high refractive index writing monomers for use in two-stage holographic formulations, here we report a novel high refractive index writing monomer, 1,3-bis(phenylthio)-2-propyl acrylate (BPTPA), simultaneously possessing enhanced solubility in a low refractive index (n = 1.47) urethane matrix. When examined in comparison to a widely used high refractive index monomer, 2,4,6-tribromophenyl acrylate, BPTPA exhibited superior solubility in a stage 1 urethane matrix of approximately 50% with a 20% higher refractive index increase per unit amount of the writing monomer for stage 2 polymerizations. Formulations with 60 wt % loading of BPTPA exhibit a peak-to-mean holographic Δn ≈ 0.029 without obvious deficiencies in transparency, color, or scatter. To the best of our knowledge, this value is the highest reported in the peer-reviewed literature for a transmission hologram. The capabilities and versatility of BPTPA-based formulations are demonstrated at varying length scales via demonstrative refractive index gradient structure examples including direct laser write, projection mask lithography of a 1″ diameter Fresnel lens, and ∼100% diffraction efficiency volume transmission holograms with a 1 μm fringe spacing in 11 μm thick samples.

Rapid assessment of mid-infrared refractive index anisotropy using a prism coupler: chemical vapor deposited ZnS

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

Qiao, Hong; Lipschultz, Kristen A.; Anheier, Norman C.

2012-04-01

A state-of-the-art mid-infrared prism coupler was used to study the refractive index properties of forward-looking-infrared (FLIR) grade zinc sulfide samples prepared with unique planar grain orientations and locations with respect to the CVD growth axis. This study was motivated by prior photoluminescence and x-ray diffraction measurements that suggested refractive index may vary according to grain orientation. Measurements were conducted to provide optical dispersion and thermal index (dn/dT) data at discrete laser wavelengths between 0.633 and 10.591 {mu}m at two temperature set points (30 C and 90 C). Refractive index measurements between samples exhibited an average standard deviation comparable to themore » uncertainty of the prism coupler measurement (0.0004 refractive index units), suggesting that the variation in refractive index as a function of planar grain orientation and CVD deposition time is negligible, and should have no impact on subsequent optical designs. Measured dispersion data at mid-infrared wavelengths was found to agree well with prior published measurements.« less

Refractive index, molar refraction and comparative refractive index study of propylene carbonate binary liquid mixtures.

PubMed

Wankhede, Dnyaneshwar Shamrao

2012-06-01

Refractive indices (n) have been experimentally determined for the binary liquid-liquid mixtures of Propylene carbonate (PC) (1) with benzene, ethylbenzene, o-xylene and p-xylene (2) at 298.15, 303.15 and 308.15 K over the entire mole fraction range. The experimental values of n are utilised to calculate deviation in refractive index (Δn), molar refraction (R) and deviation in molar refraction (ΔR). A comparative study of Arago-Biot (A-B), Newton (NW), Eyring and John (E-J) equations for determining refractive index of a liquid has been carried out to test their validity for all the binary mixtures over the entire composition range at 298.15 K. Comparison of various mixing relations is represented in terms of average deviation (AVD). The Δn and ΔR values have been fitted to Redlich-Kister equation at 298.15 K and standard deviations have been calculated. The results are discussed in terms of intermolecular interactions present amongst the components.

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.

Method of producing optical quality glass having a selected refractive index

DOEpatents

Poco, John F.; Hrubesh, Lawrence W.

2000-01-01

Optical quality glass having a selected refractive index is produced by a two stage drying process. A gel is produced using sol-gel chemistry techniques and first dried by controlled evaporation until the gel volume reaches a pre-selected value. This pre-selected volume determines the density and refractive index of the finally dried gel. The gel is refilled with solvent in a saturated vapor environment, and then dried again by supercritical extraction of the solvent to form a glass. The glass has a refractive index less than the full density of glass, and the range of achievable refractive indices depends on the composition of the glass. Glasses having different refractive indices chosen from an uninterrupted range of values can be produced from a single precursor solution.

Angularly symmetric splitting of a light beam upon reflection and refraction at an air-dielectric plane boundary: comment.

PubMed

Andersen, Torben B

2016-05-01

In a recent paper, conditions for achieving equal and opposite angular deflections of a light beam by reflection and refraction at an interface between air and a dielectric were determined [J. Opt. Soc. Am. A32, 2436 (2015)JOAOD60740-323210.1364/JOSAA.32.002436]. The paper gives plots of angles of incidence and refraction as a function of the prism refractive index as well as plots of reflectances and incident linear-polarization azimuth angles as functions of the refractive index. We show here that it is possible to express these quantities as simple algebraic functions of the refractive index.

Experimental determination of refractive index of condensed reflectin in squid iridocytes.

PubMed

Ghoshal, Amitabh; DeMartini, Daniel G; Eck, Elizabeth; Morse, Daniel E

2014-06-06

Loliginid squid dynamically tune the structural iridescence of cells in their skin for active camouflage and communication. Bragg reflectors in these cells consist of membrane-bound lamellae periodically alternating with low refractive index extracellular spaces; neuronal signalling induces condensation of the reflectin proteins that fill the lamellae, consequently triggering the expulsion of water. This causes an increase in refractive index within the lamellae, activating reflectance, with the change in lamellar thickness and spacing progressively shifting the wavelength of reflected light. We used micro-spectrophotometry to measure the functionally relevant refractive index of the high-index lamellae of the Bragg reflectors containing the condensed reflectins in chemically fixed dermal iridocytes of the squid, Doryteuthis opalescens. Our high-magnification imaging spectrometer allowed us to obtain normalized spectra of optically distinct sections of the individual, subcellular, multi-layer Bragg stacks. Replacement of the extracellular fluid with liquids of increasing refractive index allowed us to measure the reflectivity of the Bragg stacks as it decreased progressively to 0 when the refractive index of the extracellular medium exactly matched that of the reflectin-filled lamellae, thus allowing us to directly measure the refractive index of the reflectin-filled lamellae as ncondensed lamellae ≈ 1.44. The measured value of the physiologically relevant ncondensed lamellae from these bright iridocytes falls within the range of values that we recently determined by an independent optical method and is significantly lower than values previously reported for dehydrated and air-dried reflectin films. We propose that this directly measured value for the refractive index of the squid's Bragg lamellae containing the condensed reflectins is most appropriate for calculations of reflectivity in similar reflectin-based high-index layers in other molluscs.

Experimental determination of refractive index of condensed reflectin in squid iridocytes

PubMed Central

Ghoshal, Amitabh; DeMartini, Daniel G.; Eck, Elizabeth; Morse, Daniel E.

2014-01-01

Loliginid squid dynamically tune the structural iridescence of cells in their skin for active camouflage and communication. Bragg reflectors in these cells consist of membrane-bound lamellae periodically alternating with low refractive index extracellular spaces; neuronal signalling induces condensation of the reflectin proteins that fill the lamellae, consequently triggering the expulsion of water. This causes an increase in refractive index within the lamellae, activating reflectance, with the change in lamellar thickness and spacing progressively shifting the wavelength of reflected light. We used micro-spectrophotometry to measure the functionally relevant refractive index of the high-index lamellae of the Bragg reflectors containing the condensed reflectins in chemically fixed dermal iridocytes of the squid, Doryteuthis opalescens. Our high-magnification imaging spectrometer allowed us to obtain normalized spectra of optically distinct sections of the individual, subcellular, multi-layer Bragg stacks. Replacement of the extracellular fluid with liquids of increasing refractive index allowed us to measure the reflectivity of the Bragg stacks as it decreased progressively to 0 when the refractive index of the extracellular medium exactly matched that of the reflectin-filled lamellae, thus allowing us to directly measure the refractive index of the reflectin-filled lamellae as ncondensed lamellae ≈ 1.44. The measured value of the physiologically relevant ncondensed lamellae from these bright iridocytes falls within the range of values that we recently determined by an independent optical method and is significantly lower than values previously reported for dehydrated and air-dried reflectin films. We propose that this directly measured value for the refractive index of the squid's Bragg lamellae containing the condensed reflectins is most appropriate for calculations of reflectivity in similar reflectin-based high-index layers in other molluscs. PMID:24694894

Note: Index of refraction measurement using the Fresnel equations.

PubMed

McClymer, J P

2014-08-01

The real part of the refractive index is measured from 1.30 to above 3.00 without the use of index matching fluids. This approach expands upon the Brewster angle technique as both S and P polarized lights are used and the full Fresnel equations fitted to the data to extract the index of refraction using nonlinear curve fitting.

Optofluidic refractive-index sensor in step-index fiber with parallel hollow micro-channel.

PubMed

Lee, H W; Schmidt, M A; Uebel, P; Tyagi, H; Joly, N Y; Scharrer, M; Russell, P St J

2011-04-25

We present a simple refractive index sensor based on a step-index fiber with a hollow micro-channel running parallel to its core. This channel becomes waveguiding when filled with a liquid of index greater than silica, causing sharp dips to appear in the transmission spectrum at wavelengths where the glass-core mode phase-matches to a mode of the liquid-core. The sensitivity of the dip-wavelengths to changes in liquid refractive index is quantified and the results used to study the dynamic flow characteristics of fluids in narrow channels. Potential applications of this fiber microstructure include measuring the optical properties of liquids, refractive index sensing, biophotonics and studies of fluid dynamics on the nanoscale.

Options for refractive index and viscosity matching to study variable density flows

NASA Astrophysics Data System (ADS)

Clément, Simon A.; Guillemain, Anaïs; McCleney, Amy B.; Bardet, Philippe M.

2018-02-01

Variable density flows are often studied by mixing two miscible aqueous solutions of different densities. To perform optical diagnostics in such environments, the refractive index of the fluids must be matched, which can be achieved by carefully choosing the two solutes and the concentration of the solutions. To separate the effects of buoyancy forces and viscosity variations, it is desirable to match the viscosity of the two solutions in addition to their refractive index. In this manuscript, several pairs of index matched fluids are compared in terms of viscosity matching, monetary cost, and practical use. Two fluid pairs are studied in detail, with two aqueous solutions (binary solutions of water and a salt or alcohol) mixed into a ternary solution. In each case: an aqueous solution of isopropanol mixed with an aqueous solution of sodium chloride (NaCl) and an aqueous solution of glycerol mixed with an aqueous solution of sodium sulfate (Na_2SO_4). The first fluid pair allows reaching high-density differences at low cost, but brings a large difference in dynamic viscosity. The second allows matching dynamic viscosity and refractive index simultaneously, at reasonable cost. For each of these four solutes, the density, kinematic viscosity, and refractive index are measured versus concentration and temperature, as well as wavelength for the refractive index. To investigate non-linear effects when two index-matched, binary solutions are mixed, the ternary solutions formed are also analyzed. Results show that density and refractive index follow a linear variation with concentration. However, the viscosity of the isopropanol and NaCl pair deviates from the linear law and has to be considered. Empirical correlations and their coefficients are given to create index-matched fluids at a chosen temperature and wavelength. Finally, the effectiveness of the refractive index matching is illustrated with particle image velocimetry measurements performed for a buoyant jet in a linearly stratified environment. The creation of the index-matched solutions and linear stratification in a large-scale experimental facility are detailed, as well as the practical challenges to obtain precise refractive index matching.

Construction of Lines of Constant Density and Constant Refractive Index for Ternary Liquid Mixtures.

ERIC Educational Resources Information Center

Tasic, Aleksandar Z.; Djordjevic, Bojan D.

1983-01-01

Demonstrates construction of density constant and refractive index constant lines in triangular coordinate system on basis of systematic experimental determinations of density and refractive index for both homogeneous (single-phase) ternary liquid mixtures (of known composition) and the corresponding binary compositions. Background information,…

Plasmas with an index of refraction greater than 1.

PubMed

Nilsen, Joseph; Scofield, James H

2004-11-15

Over the past decade, x-ray lasers in the wavelength range 14-47 nm have been used for interferometry of plasmas. As in optical interferometry of plasmas, the experimental analysis assumed that the index of refraction is due only to free electrons. This makes the index of refraction less than 1. Recent experiments in A1 plasmas have shown fringe lines bending the wrong way as though the electron density were negative. We show how the bound electrons can dominate the index of refraction in many plasmas and make the index greater than 1 or enhance the index such that one would greatly overestimate the density of the plasma using interferometry.

Enhancing intensity and refractive index sensing capability with infrared plasmonic perfect absorbers.

PubMed

Cheng, Fei; Yang, Xiaodong; Gao, Jie

2014-06-01

An infrared refractive index sensor based on plasmonic perfect absorbers for glucose concentration sensing is experimentally demonstrated. Utilizing substantial absorption contrast between a perfect absorber (∼98% at normal incidence) and a non-perfect absorber upon the refractive index change, a maximum value of figure of merit (FOM^*) about 55 and a bulk wavelength sensitivity about 590  nm/RIU are achieved. The demonstrated sensing platform provides great potential in improving the performance of plasmonic refractive index sensors and developing future surface enhanced infrared spectroscopy.

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.

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.

Refractive index modulation in LiNbO3: MgO slab through Lamb wave

NASA Astrophysics Data System (ADS)

Prakash, Suraj; Sharma, Gaurav; Yadav, Gulab Chand; Singh, Vivek

2018-05-01

Present theoretical analysis deals with inducing refractive index contrast in Y-Z LiNbO3:MgO plate via GHz Lamb wave perturbation for photonic applications. Dispersion curves for Lamb wave in plate are plotted by employing displacement potential technique. Selecting wave parameters from dispersion curve, fundamental symmetric Lamb mode (S0) is excited in slab for 6GHz frequency. Produced displacement field by propagating S0 mode and thus developed strain is estimated to calculate refractive index modulation by applying photo-elastic relations. Modulated refractive index is of sinusoidal nature with period of modulation dependence on Lamb's wavelength. This plate having periodically modulated refractive index can be used as photonic crystal for different applications with acoustically tunable photonic band gap.

Methods for prediction of refractive index in glasses for the infrared

NASA Astrophysics Data System (ADS)

McCloy, John S.

2011-06-01

It is often useful to obtain custom glasses that meet particular requirements of refractive index and dispersion for highend optical design and applications. In the case of infrared glasses, limited experimental data are available due to difficulties in processing of these glasses and also measuring refractive indices accurately. This paper proposes methods to estimate refractive index and dispersion as a function of composition for selected infrared-transmitting glasses. Methods for refractive index determination are reviewed and evaluated, including Gladstone-Dale, Wemple- DiDomenico single oscillator, Optical basicity, and Lorentz-Lorenz total polarizability. Various estimates for a set of PbO-Bi2O3-Ga2O3 (heavy metal oxide) and As-S (chalcogenide) glasses will be compared with measured values of index and dispersion.

Simultaneous measurements of absorption spectrum and refractive index in a microfluidic system.

PubMed

Helseth, Lars Egil

2012-02-13

The characterization of dyes in various solvents requires determination of the absorption spectrum of the dye as well as the refractive index of the solvent. Typically, the refractive index of the solvent and the absorption spectrum of the solute are measured using separate experimental setups where significant liquid volumes are required. In this work the first optical measurement system that is able to do simultaneous measurements of the refractive index of the solvent and the spectral properties of the solute in a microscopic volume is presented. The laser dye Rhodamine 6G in glycerol is investigated, and the refractive index of the solution is monitored using the interference pattern of the light scattered off the channel, while its spectral properties is found by monitoring reflected light from the channel.

Refractive index and absorption detector for liquid chromatography based on Fabry-Perot interferometry

DOEpatents

Yeung, E.S.; Woodruff, S.D.

1984-06-19

A refractive index and absorption detector are disclosed for liquid chromatography. It is based in part on a Fabry-Perot interferometer and is used for the improved detection of refractive index and absorption. It includes a Fabry-Perot interferometer having a normally fixed first partially reflecting mirror and a movable second partially reflecting mirror. A chromatographic flow-cell is positioned between the mirrors along the optical axis of a monochromatic laser beam passing through the interferometer. A means for deriving information about the interference fringes coming out of the interferometer is used with a mini-computer to compute the refractive index of the specimen injected into the flow cell. The minicomputer continuously scans the interferometer for continuous refractive index readings and outputs the continuous results of the scans on a chart recorder. The absorption of the specimen can concurrently be scanned by including a second optical path for an excitation laser which will not interfere with the first laser, but will affect the specimen so that absorption properties can be detected. By first scanning for the refractive index of the specimen, and then immediately adding the excitation laser and subsequently scanning for the refractive index again, the absorption of the specimen can be computed and recorded. 10 figs.

Refractive index and absorption detector for liquid chromatography based on Fabry-Perot interferometry

DOEpatents

Yeung, Edward S.; Woodruff, Steven D.

1984-06-19

A refractive index and absorption detector for liquid chromatography. It is based in part on a Fabry-Perot interferometer and is used for the improved detection of refractive index and absorption. It includes a Fabry-Perot interferometer having a normally fixed first partially reflecting mirror and a movable second partially reflecting mirror. A chromatographic flow-cell is positioned between the mirrors along the optical axis of a monochromatic laser beam passing through the interferometer. A means for deriving information about the interference fringes coming out of the interferometer is used with a mini-computer to compute the refractive index of the specimen injected into the flow cell. The minicomputer continuously scans the interferometer for continuous refractive index readings and outputs the continuous results of the scans on a chart recorder. The absorption of the specimen can concurrently be scanned by including a second optical path for an excitation laser which will not interfere with the first laser, but will affect the specimen so that absorption properties can be detected. By first scanning for the refractive index of the specimen, and then immediately adding the excitation laser and subsequently scanning for the refractive index again, the absorption of the specimen can be computed and recorded.

Effect of Refractive Index of Substrate on Fabrication and Optical Properties of Hybrid Au-Ag Triangular Nanoparticle Arrays

PubMed Central

Liu, Jing; Chen, Yushan; Cai, Haoyuan; Chen, Xiaoyi; Li, Changwei; Yang, Cheng-Fu

2015-01-01

In this study, the nanosphere lithography (NSL) method was used to fabricate hybrid Au-Ag triangular periodic nanoparticle arrays. The Au-Ag triangular periodic arrays were grown on different substrates, and the effect of the refractive index of substrates on fabrication and optical properties was systematically investigated. At first, the optical spectrum was simulated by the discrete dipole approximation (DDA) numerical method as a function of refractive indexes of substrates and mediums. Simulation results showed that as the substrates had the refractive indexes of 1.43 (quartz) and 1.68 (SF5 glass), the nanoparticle arrays would have better refractive index sensitivity (RIS) and figure of merit (FOM). Simulation results also showed that the peak wavelength of the extinction spectra had a red shift when the medium’s refractive index n increased. The experimental results also demonstrated that when refractive indexes of substrates were 1.43 and 1.68, the nanoparticle arrays and substrate had better adhesive ability. Meanwhile, we found the nanoparticles formed a large-scale monolayer array with the hexagonally close-packed structure. Finally, the hybrid Au-Ag triangular nanoparticle arrays were fabricated on quartz and SF5 glass substrates and their experiment extinction spectra were compared with the simulated results.

Pressure sensing in high-refractive-index liquids using long-period gratings nanocoated with silicon nitride.

PubMed

Smietana, Mateusz; Bock, Wojtek J; Mikulic, Predrag; Chen, Jiahua

2010-01-01

The paper presents a novel pressure sensor based on a silicon nitride (SiNx) nanocoated long-period grating (LPG). The high-temperature, radio-frequency plasma-enhanced chemical-vapor-deposited (RF PECVD) SiNx nanocoating was applied to tune the sensitivity of the LPG to the external refractive index. The technique allows for deposition of good quality, hard and wear-resistant nanofilms as required for optical sensors. Thanks to the SiNx nanocoating it is possible to overcome a limitation of working in the external-refractive-index range, which for a bare fiber cannot be close to that of the cladding. The nanocoated LPG-based sensing structure we developed is functional in high-refractive-index liquids (nD>1.46) such as oil or gasoline, with pressure sensitivity as high as when water is used as a working liquid. The nanocoating developed for this experiment not only has the highest refractive index ever achieved in LPGs (n>2.2 at λ=1,550 nm), but is also the thinnest (<100 nm) able to tune the external-refractive-index sensitivity of the gratings. To the best of our knowledge, this is the first time a nanocoating has been applied on LPGs that is able to simultaneously tune the refractive-index sensitivity and to enable measurements of other parameters.

Liquid refractive index sensing independent of opacity using an optofluidic diffraction sensor.

PubMed

Xu, Zhida; Han, Kevin; Khan, Ibrahim; Wang, Xinhao; Liu, G Logan

2014-10-15

We have implemented a multifunctional optofluidic sensor that can monitor changes in the refractive index and pressure of biofluid simultaneously and can detect free-solution molecular interaction in situ. In this Letter, we demonstrate two major improvements of this sensor proven by both simulation and experiments. One improvement is the broader measurement range of refractive index by making the diffraction grating with high-index polymer. The other improvement is the separation of refractive index sensing from opacity sensing by using the relative power ratio of diffraction orders. This simple, compact and low-cost multifunctional optofluidic sensor has the potential to be used for in situ biofluid monitoring.

Adaptive Optoelectronic Eyes: Hybrid Sensor/Processor Architectures

DTIC Science & Technology

2006-11-13

corresponding calculated data. The width of the mirror stopband is proportional to the refractive index difference between the high and low index materials ...Silicon VLSI Neuron Unit Arrays 56 Development of a Single-Sided Flip-Chip Bonding Process 65 Development of High Refractive Index Diffractive Optical ...Elements (DOEs) 68 Development of High-Performance Antireflection Coatings for High Refractive Index DOEs 69 Design and Fabrication of Low Threshold

Refractive index degeneration in older lenses: A potential functional correlate to structural changes that underlie cataract formation.

PubMed

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

2015-11-01

A major structure/function relationship in the eye lens is that between the constituent proteins, the crystallins and the optical property of refractive index. Structural breakdown that leads to cataract has been investigated in a number of studies; the concomitant changes in the optics, namely increases in light attenuation have also been well documented. Specific changes in the refractive index gradient that cause such attenuation, however, are not well studied because previous methods of measuring refractive index require transparent samples. The X-ray Talbot interferometric method using synchrotron radiation allows for measurement of fine changes in refractive index through lenses with opacities. The findings of this study on older human lenses show disruptions to the refractive index gradient and in the refractive index contours. These disruptions are linked to location in the lens and occur in polar regions, along or close to the equatorial plane or in lamellar-like formations. The disruptions that are seen in the polar regions manifest branching formations that alter with progression through the lens with some similarity to lens sutures. This study shows how the refractive index gradient, which is needed to maintain image quality of the eye, may be disturbed and that this can occur in a number of distinct ways. These findings offer insight into functional changes to a major optical parameter in older lenses. Further studies are needed to elicit how these may be related to structural degenerations reported in the literature. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

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

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

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

2013-07-15

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

Femtosecond laser-induced refractive index modification in multicomponent glasses

NASA Astrophysics Data System (ADS)

Bhardwaj, V. R.; Simova, E.; Corkum, P. B.; Rayner, D. M.; Hnatovsky, C.; Taylor, R. S.; Schreder, B.; Kluge, M.; Zimmer, J.

2005-04-01

We present a comprehensive study on femtosecond laser-induced refractive index modification in a wide variety of multicomponent glasses grouped as borosilicate, aluminum-silicate, and heavy-metal oxide glasses along with lanthanum-borate and sodium-phosphate glasses. By using high-spatial resolution refractive index profiling techniques, we demonstrate that under a wide range of writing conditions the refractive index modification in multicomponent glasses can be positive, negative, or nonuniform, and exhibits a strong dependence on the glass composition. With the exception of some aluminum-silicate glasses all other glasses exhibited a negative/nonuniform index change. We also demonstrate direct writing of waveguides in photosensitive Foturan® glass with a femtosecond laser without initiating crystallization by thermal treatment. Upon ceramization of lithium-aluminum-silicate glasses such as Foturan®, Zerodur®, and Robax® we observe switching of laser-induced refractive index change from being positive to negative. The measured transmission losses in the waveguides at 1550nm agree with the index profile measurements in alkali-free aluminum-silicate glasses.

Homodyne chiral polarimetry for measuring thermo-optic refractive index variations.

PubMed

Twu, Ruey-Ching; Wang, Jhao-Sheng

2015-10-10

Novel reflection-type homodyne chiral polarimetry is proposed for measuring the refractive index variations of a transparent plate under thermal impact. The experimental results show it is a simple and useful method for providing accurate measurements of refractive index variations. The measurement can reach a resolution of 7×10^-5.

Refractive index of colloidal dispersions of spheroidal particles

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

Meeten, G.H.

1980-09-01

The effect of particle shape on the refractive index of a colloidal dispersion of spheroidal particles is investigated theoretically, using the Rayleigh, Rayleigh- Gans-Debye, and the anomalous diffraction light-scattering approximations. It is shown that departure from particle sphericity modify the dispersion refractive index, both size and shape being of importance.

Photorefractive Nonlinear Optics

DTIC Science & Technology

1991-01-15

conjugate interferometer for the measurement of thin film thickness, refractive index and absorption coefficients. Also, we have investigated...conjugate interferometer for the measurement of thin film thickness, refractive index and absorption coefficients. Also, we have investigated...interaction by considering the refractive index grating as a linear superposition of the gratings from each of the frequency components of the

Femtosecond Z-scan measurements of the nonlinear refractive index of fused silica

NASA Astrophysics Data System (ADS)

Zhang, Lin; Shi, Zhendong; Ma, Hua; Ren, Huan; Yuan, Quan; Ma, Yurong; Feng, Xiaoxuan; Chen, Bo; Yang, Yi

2018-01-01

Z-scan technology is a popular experimental technique for determining the nonlinear refractive index of the material. However, it encounters a great difficulty in measuring the weak nonlinear material like fused silica which is about two orders of magnitude below the nonlinear refractive index of most of the materials studied with the nanosecond and picosecond Z-scan methods. In this case, the change of refractive index introduced by accumulation of thermal effects cannot be neglected. In order to have a reliable measurement of the nonlinear refractive index, a metrology bench based on the femtosecond Z-scan technology is developed. The intensity modulation component and the differential measurement system are applied to guarantee the accuracy of the measuring system. Based on the femtosecond Z-scan theory, the femtosecond laser Z-scan technique is performed on fused silica, and the nonlinear refractive index of Fused silica is determined to be 9.2039×10-14esu for 800nm, 37fs pulse duration at I0=50GW/cm2 with a good repeatability of 6.7%.

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.

Further Studies on the Effect of SiN x Refractive Index and Emitter Sheet Resistance on Potential-Induced Degradation

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

Oh, Jaewon; Dauksher, Bill; Bowden, Stuart

We present the impacts of silicon nitride (SiNx) antireflection coating refractive index and emitter sheet resistance on potential-induced degradation of the shunting type (PID-s). Previously, it has been shown that the cell becomes more PID-s-susceptible as the refractive index decreases or the emitter sheet resistance increases. To verify the effect of refractive index on PID-s, we fabricated cells with varying SiN x refractive index (1.87, 1.94, 2.05) on typical p-type base solar cells with ~60 Ω/sq emitters. However, none of these cells showed output power degradation, regardless of the refractive index. Further investigation of the emitter showed that the PID-smore » was suppressed at ~60 Ω/sq due to the extremely high surface phosphorus concentration (6 x 10 21 cm -3), as measured by secondary ion mass spectrometry. Furthermore, PID-s was observed on cells possessing a high emitter sheet resistance (~80 Ω/sq). In conclusion, the emitter surface phosphorus concentration plays an important role in determining PID-s susceptibility.« less

Further Studies on the Effect of SiN x Refractive Index and Emitter Sheet Resistance on Potential-Induced Degradation

DOE PAGES

Oh, Jaewon; Dauksher, Bill; Bowden, Stuart; ...

2017-01-11

We present the impacts of silicon nitride (SiNx) antireflection coating refractive index and emitter sheet resistance on potential-induced degradation of the shunting type (PID-s). Previously, it has been shown that the cell becomes more PID-s-susceptible as the refractive index decreases or the emitter sheet resistance increases. To verify the effect of refractive index on PID-s, we fabricated cells with varying SiN x refractive index (1.87, 1.94, 2.05) on typical p-type base solar cells with ~60 Ω/sq emitters. However, none of these cells showed output power degradation, regardless of the refractive index. Further investigation of the emitter showed that the PID-smore » was suppressed at ~60 Ω/sq due to the extremely high surface phosphorus concentration (6 x 10 21 cm -3), as measured by secondary ion mass spectrometry. Furthermore, PID-s was observed on cells possessing a high emitter sheet resistance (~80 Ω/sq). In conclusion, the emitter surface phosphorus concentration plays an important role in determining PID-s susceptibility.« less

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.

High sensitivity refractive index sensor based on adiabatic tapered optical fiber deposited with nanofilm by ALD.

PubMed

Zhu, Shan; Pang, Fufei; Huang, Sujuan; Zou, Fang; Dong, Yanhua; Wang, Tingyun

2015-06-01

Atomic layer deposition (ALD) technology is introduced to fabricate a high sensitivity refractive index sensor based on an adiabatic tapered optical fiber. Different thickness of Al₂O₃ nanofilm is coated around fiber taper precisely and uniformly under different deposition cycles. Attributed to the high refractive index of the Al₂O₃ nanofilm, an asymmetry Fabry-Perot like interferometer is constructed along the fiber taper. Based on the ray-optic analysis, total internal reflection happens on the nanofilm-surrounding interface. With the ambient refractive index changing, the phase delay induced by the Goos-Hänchen shift is changed. Correspondingly, the transmission resonant spectrum shifts, which can be utilized for realizing high sensitivity sensor. The high sensitivity sensor with 6008 nm/RIU is demonstrated by depositing 3000 layers Al₂O₃ nanofilm as the ambient refractive index is close to 1.33. This high sensitivity refractive index sensor is expected to have wide applications in biochemical sensors.

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

PubMed

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

2017-05-31

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

High refractive index immersion liquid for superresolution 3D imaging using sapphire-based aplanatic numerical aperture increasing lens optics.

PubMed

Laskar, Junaid M; Shravan Kumar, P; Herminghaus, Stephan; Daniels, Karen E; Schröter, Matthias

2016-04-20

Optically transparent immersion liquids with refractive index (n∼1.77) to match the sapphire-based aplanatic numerical aperture increasing lens (aNAIL) are necessary for achieving deep 3D imaging with high spatial resolution. We report that antimony tribromide (SbBr₃) salt dissolved in liquid diiodomethane (CH₂I₂) provides a new high refractive index immersion liquid for optics applications. The refractive index is tunable from n=1.74 (pure) to n=1.873 (saturated), by adjusting either salt concentration or temperature; this allows it to match (or even exceed) the refractive index of sapphire. Importantly, the solution gives excellent light transmittance in the ultraviolet to near-infrared range, an improvement over commercially available immersion liquids. This refractive-index-matched immersion liquid formulation has enabled us to develop a sapphire-based aNAIL objective that has both high numerical aperture (NA=1.17) and long working distance (WD=12  mm). This opens up new possibilities for deep 3D imaging with high spatial resolution.

Wave refraction in negative-index media: always positive and very inhomogeneous.

PubMed

Valanju, P M; Walser, R M; Valanju, A P

2002-05-06

We present the first treatment of the refraction of physical electromagnetic waves in newly developed negative index media (NIM), also known as left-handed media (LHM). The NIM dispersion relation implies that group fronts refract positively even when phase fronts refract negatively. This difference results in rapidly dispersing, very inhomogeneous waves. In fact, causality and finite signal speed always prevent negative wave signal (not phase) refraction. Earlier interpretations of phase refraction as "negative light refraction" and "light focusing by plane slabs" are therefore incorrect, and published NIM experiments can be explained without invoking negative signal refraction.

Spatial variation of stratospheric aerosol acidity and model refractive index - Implications of recent results

NASA Technical Reports Server (NTRS)

Russell, P. B.; Hamill, P.

1984-01-01

Recent experimental results indicate that little or no solid ammonium sulfate is present in background stratospheric aerosols. Other results allow straightforward calculation of sulfuric acid/water droplet properties (acidity, specific gravity, refractive index) as functions of stratospheric temperature and humidity. These results are combined with a variety of latitudinal and seasonal temperature and humidity profiles to obtain corresponding profiles of droplet properties. These profiles are used to update a previous model of stratospheric aerosol refractive index. The new model retains the simplifying approximation of vertically constant refractive index in the inner stratosphere, but has sulfuric acid/water refractive index values that significantly exceed the previously used room temperature values. Mean conversion ratios (e.g., extinction-to-number, backscatter-to-volume) obtained using Mie scattering calculations with the new refractive indices are very similar to those obtained for the old indices, because the effects of deleting ammonium sulfate and increasing acid indices tend to cancel each other.

Tunable Liquid Gradient Refractive Index (L-GRIN) lens with two degrees of freedom.

PubMed

Mao, Xiaole; Lin, Sz-Chin Steven; Lapsley, Michael Ian; Shi, Jinjie; Juluri, Bala Krishna; Huang, Tony Jun

2009-07-21

We report a tunable optofluidic microlens configuration named the Liquid Gradient Refractive Index (L-GRIN) lens for focusing light within a microfluidic device. The focusing of light was achieved through the gradient refractive index (GRIN) within the liquid medium, rather than via curved refractive lens surfaces. The diffusion of solute (CaCl(2)) between side-by-side co-injected microfluidic laminar flows was utilized to establish a hyperbolic secant (HS) refractive index profile to focus light. Tailoring the refractive index profile by adjusting the flow conditions enables not only tuning of the focal distance (translation mode), but also shifting of the output light direction (swing mode), a second degree of freedom that to our knowledge has yet to be accomplished for in-plane tunable microlenses. Advantages of the L-GRIN lens also include a low fluid consumption rate, competitive focusing performance, and high compatibility with existing microfluidic devices. This work provides a new strategy for developing integrative tunable microlenses for a variety of lab-on-a-chip applications.

Measurement of the refractive index dispersion of As2Se3 bulk glass and thin films prior to and after laser irradiation and annealing using prism coupling in the near- and mid-infrared spectral range

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

Carlie, Nathan; Anheier, Norman C.; Qiao, Hong

2011-05-01

The prism coupling technique has been utilized to measure the refractive index in the near- and mid-IR spectral region of chalcogenide glasses in bulk and thin film form. A commercial system (Metricon model 2010) has been modified with additional laser sources, detectors, and a new GaP prism to allow the measurement of refractive index dispersion over the 1.5–10.6 μm range. The instrumental error was found to be ±0.001 refractive index units across the entire wavelength region examined. Measurements on thermally evaporated AMTIR2 thin films confirmed that (i) the film deposition process provides thin films with reduced index compared to thatmore » of the bulk glass used as a target, (ii) annealing of the films increases the refractive index of the film to the level of the bulk glass used as a target to create it, and (iii) it is possible to locally increase the refractive index of the chalcogenide glass using laser exposure at 632.8 nm.« less

Measurement of the refractive index dispersion of As{sub 2}Se{sub 3} bulk glass and thin films prior to and after laser irradiation and annealing using prism coupling in the near- and mid-infrared spectral range

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

Carlie, N.; Petit, L.; Musgraves, J. D.

2011-05-15

The prism coupling technique has been utilized to measure the refractive index in the near- and mid-IR spectral region of chalcogenide glasses in bulk and thin film form. A commercial system (Metricon model 2010) has been modified with additional laser sources, detectors, and a new GaP prism to allow the measurement of refractive index dispersion over the 1.5-10.6 {mu}m range. The instrumental error was found to be {+-}0.001 refractive index units across the entire wavelength region examined. Measurements on thermally evaporated AMTIR2 thin films confirmed that (i) the film deposition process provides thin films with reduced index compared to thatmore » of the bulk glass used as a target, (ii) annealing of the films increases the refractive index of the film to the level of the bulk glass used as a target to create it, and (iii) it is possible to locally increase the refractive index of the chalcogenide glass using laser exposure at 632.8 nm.« less

Is the nuclear refractive index lower than cytoplasm? Validation of phase measurements and implications for light scattering technologies.

PubMed

Steelman, Zachary A; Eldridge, Will J; Weintraub, Jacob B; Wax, Adam

2017-12-01

The refractive index (RI) of biological materials is a fundamental parameter for the optical characterization of living systems. Numerous light scattering technologies are grounded in a quantitative knowledge of the refractive index at cellular and subcellular scales. Recent work in quantitative phase microscopy (QPM) has called into question the widely held assumption that the index of the cell nucleus is greater than that of the cytoplasm, a result which disagrees with much of the current literature. In this work, we critically examine the measurement of the nuclear and whole-cell refractive index using QPM, validating that nuclear refractive index is lower than that of cytoplasm in four diverse cell lines and their corresponding isolated nuclei. We further examine Mie scattering and phase-wrapping as potential sources of error in these measurements, finding they have minimal impact. Finally, we use simulation to examine the effects of incorrect RI assumptions on nuclear morphology measurements using angle-resolved scattering information. Despite an erroneous assumption of the nuclear refractive index, accurate measurement of nuclear morphology was maintained, suggesting that light scattering modalities remain effective. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Refractive index engineering of high performance coupler for compact photonic integrated circuits

NASA Astrophysics Data System (ADS)

Liu, Lu; Zhou, Zhiping

2017-04-01

High performance couplers are highly desired in many applications, but the design is limited by nearly unchangeable material refractive index. To tackle this issue, refractive index engineering method is investigated, which can be realized by subwavelength grating. Subwavelength gratings are periodical structures with pitches small enough to locally synthesize the refractive index of photonic waveguides, which allows direct control of optical profile as well as easier fabrication process. This review provides an introduction to the basics of subwavelength structures and pay special attention to the design strategies of some representative examples of subwavelength grating devices, including: edge couplers, fiber-chip grating couplers, directional couplers and multimode interference couplers. Benefited from the subwavelength grating which can engineer the refractive index as well as birefringence and dispersion, these devices show better performance when compared to their conventional counterparts.

Improve the refractive index sensitivity of coaxial-cable type gold nanostructure: the effect of dielectric polarization from the separate layer

NASA Astrophysics Data System (ADS)

Zhu, Jian; Li, Jian-Jun; Zhao, Jun-Wu

2013-06-01

The separate layer refractive index sensitivity of a coaxial-cable type three-layered gold nanotube has been studied. Theoretical calculation results based on quasi-static model show that the coaxial-cable type gold nanostructure has higher refractive index sensitivity than that of single-layered gold nanotube. This sensitivity could be improved by increasing the inner wire radius or decreasing the total radius of the tube, and the maximum sensitivity may exceed 1,000 nm per refractive index unit. The physical origin was also investigated based on the coupling of the dielectric media induced polarizations and the local electric fields in separate layer and outer surrounding. These separate layer refractive index sensing properties of coaxial-cable type gold nanostructure present well potential for plasmonic biosensing applications.

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.

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.

Methods for Prediction of Refractive Index in Glasses for the Infrared

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

McCloy, John S.

It is often useful to obtain custom glasses that meet particular requirements of refractive index and dispersion for high-end optical design and applications. In the case of infrared glasses, limited experimental data are available due to difficulties in processing of these glasses and also measuring refractive indices accurately. This paper proposes methods to estimate refractive index and dispersion as a function of composition for selected infrared-transmitting glasses. Methods for refractive index determination are reviewed and evaluated, including Gladstone-Dale, Wemple-DiDomenico single oscillator, Optical basicity, and Lorentz-Lorenz total polarizability. Various estimates for a set of PbO-Bi2O3-Ga2O3 (heavy metal oxide) and As-S (chalcogenide)more » glasses will be compared with measured values of index and dispersion.« less

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

PubMed Central

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

2013-01-01

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

Frequency modulation and compression of optical pulses in an optical fibre with a travelling refractive-index wave

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

Zolotovskii, I O; Lapin, V A; Sementsov, D I

2016-01-31

We have studied the conditions for spectral broadening, frequency modulation and compression (both temporal and spectral) of Gaussian pulses propagating in a fibre with a travelling refractive-index wave. Analytical expressions have been derived for the dependences of pulse duration, chirp and spectral width on the distance travelled through the fibre, parameters of the fibre and radiation launched into it. Based on the numerical analysis we have studied the behaviour of these characteristics by changing the coefficient of the refractive-index modulation and other parameters of the travelling refractive-index wave. (nonlinear optical phenomena)

Refractive index sensor based on combination of tilted fiber Bragg grating and waist-enlarged fusion bitaper

NASA Astrophysics Data System (ADS)

Liu, Xiaohang; Zheng, Jie; Yang, Jingyi; Li, Yi; Dong, Xinyong

2015-12-01

Refractive index measurement by using the combination of a tilted fiber Bragg grating (TFBG) and a waist-enlarged fusion bitaper (WEFBT) is proposed and demonstrated. The both devices can couple light between core and cladding modes with coupling coefficients depending on ambient refractive index. It is found that the proposed refractive index sensor offers two measurement ranges respectively from 1.333 to 1.428 and from 1.383 to 1.453 when different sensing segment is used, in addition to advantages of reflection operation mode and intensity-modulated measurement.

Refractive index modulation in polymer film doped with diazo Meldrum's acid

NASA Astrophysics Data System (ADS)

Zanutta, Alessio; Villa, Filippo; Bertarelli, Chiara; Bianco, Andrea

2016-08-01

Diazo Meldrum's acid undergoes a photoreaction induced by UV light and it is used as photosensitizer in photoresists. Upon photoreaction, a change in refractive index occurs, which makes this system interesting for volume holography. We report on the sublimation effect at room temperature and the effect of photoirradiation on the refractive index in thin films of CAB (Cellulose acetate butyrate) doped with different amount of diazo Meldrum's acid. A net modulation of the refractive index of 0.01 is achieved with 40% of doping ratio together with a reduction of the film thickness.

Analyzing refractive index changes and differential bending in microcantilever arrays.

PubMed

Huber, François; Lang, Hans Peter; Hegner, Martin; Despont, Michel; Drechsler, Ute; Gerber, Christoph

2008-08-01

A new microcantilever array design is investigated comprising eight flexible microcantilevers introducing two solid bars, enabling to subtract contributions from differences in refractive index in an optical laser read out system. Changes in the refractive index do not contribute undesirably to bending signals at picomolar to micromolar DNA or protein concentrations. However, measurements of samples with high salt concentrations or serum are affected, requiring corrections for refractive index artifacts. Moreover, to obtain a deeper understanding of molecular stress formation, the differential curvature of cantilevers is analyzed by positioning the laser spots along the surface of the levers during pH experiments.

Theoretical study of polarization dependence of carrier-induced refractive index change of quantum dot.

PubMed

Miao, Qingyuan; Yang, Ziyi; Dong, Jianji; He, Ping-An; Huang, Dexiu

2018-02-05

The influences of dot material component, barrier material component, aspect ratio and carrier density on the refractive index changes of TE mode and TM mode of columnar quantum dot are analyzed, and a multiparameter adjustment method is proposed to realize low polarization dependence of refractive index change. Then the quantum dots with low polarization dependence of refractive index change (<1.5%) within C-band (1530 nm - 1565 nm) are designed, and it shows that quantum dots with different material parameters are anticipated to have similar characteristics of low polarization dependence.

Refractive index measurement of the mouse crystalline lens using optical coherence tomography

PubMed Central

Chakraborty, Ranjay; Lacy, Kip D.; Tan, Christopher C.; Park, Han na; Pardue, Machelle T.

2014-01-01

In recent years, there has been a growing interest for using mouse models in refractive development and myopia research. The crystalline lens is a critical optical component of the mouse eye that occupies greater than 50% of the ocular space, and significant increases in thickness with age. However, changes in refractive index of the mouse crystalline lens are less known. In this study, we examined the changes in thickness and refractive index of the mouse crystalline lens for two different strains, wild-type (WT) and a nyx mutant (nob) over the course of normal visual development or after form deprivation. Refractive index and lens thickness measurements were made on ex vivo lens using spectral domain optical coherence tomography (SD-OCT). Comparison of refractive index measurements on 5 standard ball lenses using the SD-OCT and their known refractive indices (manufacturer provided) indicated good precision (intra-class correlation coefficient, 0.998 and Bland-Altman coefficient of repeatability, 0.116) of the SD-OCT to calculate mouse lens refractive index ex vivo. During normal visual development, lens thickness increased significantly with age for three different cohorts of mice, aged 4 (average thickness from both eyes; WT: 1.78 ± 0.03, nob: 1.79 ± 0.08 mm), 10 (WT: 2.02 ± 0.05, nob: 2.01 ± 0.04 mm) and 16 weeks (WT: 2.12 ± 0.06, nob: 2.09 ± 0.06 mm, p<0.001). Lens thickness was not significantly different between the two strains at any age (p=0.557). For mice with normal vision, refractive index for isolated crystalline lenses in nob mice was significantly greater than WT mice (mean for all ages; WT: 1.42 ± 0.01, nob: 1.44 ± 0.001, p<0.001). After 4 weeks of form deprivation to the right eye using a skull-mounted goggling apparatus, a thinning of the crystalline lens was observed in both right and left eyes of goggled animals compared to their naïve controls (average from both the right and the left eye) for both strains (p=0.052). In form deprived mice, lens refractive index was significantly different between the goggled animals and non-goggled naïve controls in nob mice, but not in WT mice (p=0.009). Both eyes of goggled nob mice had significantly greater lens refractive index (goggled, 1.49 ± 0.01; opposite, 1.47 ± 0.03) compared to their naïve controls (1.45 ± 0.02, p<0.05). The results presented here suggest that there are genetic differences in the crystalline lens refractive index of the mouse eye, and that the lens refractive index in mice significantly increase with form deprivation. Research applications requiring precise optical measurements of the mouse eye should take these lens refractive indices into account when interpreting SD-OCT data. PMID:24939747

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.

Evaluation of a quantitative structure-property relationship (QSPR) for predicting mid-visible refractive index of secondary organic aerosol (SOA).

PubMed

Redmond, Haley; Thompson, Jonathan E

2011-04-21

In this work we describe and evaluate a simple scheme by which the refractive index (λ = 589 nm) of non-absorbing components common to secondary organic aerosols (SOA) may be predicted from molecular formula and density (g cm(-3)). The QSPR approach described is based on three parameters linked to refractive index-molecular polarizability, the ratio of mass density to molecular weight, and degree of unsaturation. After computing these quantities for a training set of 111 compounds common to atmospheric aerosols, multi-linear regression analysis was conducted to establish a quantitative relationship between the parameters and accepted value of refractive index. The resulting quantitative relationship can often estimate refractive index to ±0.01 when averaged across a variety of compound classes. A notable exception is for alcohols for which the model consistently underestimates refractive index. Homogenous internal mixtures can conceivably be addressed through use of either the volume or mole fraction mixing rules commonly used in the aerosol community. Predicted refractive indices reconstructed from chemical composition data presented in the literature generally agree with previous reports of SOA refractive index. Additionally, the predicted refractive indices lie near measured values we report for λ = 532 nm for SOA generated from vapors of α-pinene (R.I. 1.49-1.51) and toluene (R.I. 1.49-1.50). We envision the QSPR method may find use in reconstructing optical scattering of organic aerosols if mass composition data is known. Alternatively, the method described could be incorporated into in models of organic aerosol formation/phase partitioning to better constrain organic aerosol optical properties.

Pressure Sensing in High-Refractive-Index Liquids Using Long-Period Gratings Nanocoated with Silicon Nitride

PubMed Central

Smietana, Mateusz; Bock, Wojtek J.; Mikulic, Predrag; Chen, Jiahua

2010-01-01

The paper presents a novel pressure sensor based on a silicon nitride (SiNx) nanocoated long-period grating (LPG). The high-temperature, radio-frequency plasma-enhanced chemical-vapor-deposited (RF PECVD) SiNx nanocoating was applied to tune the sensitivity of the LPG to the external refractive index. The technique allows for deposition of good quality, hard and wear-resistant nanofilms as required for optical sensors. Thanks to the SiNx nanocoating it is possible to overcome a limitation of working in the external-refractive-index range, which for a bare fiber cannot be close to that of the cladding. The nanocoated LPG-based sensing structure we developed is functional in high-refractive-index liquids (nd > 1.46) such as oil or gasoline, with pressure sensitivity as high as when water is used as a working liquid. The nanocoating developed for this experiment not only has the highest refractive index ever achieved in LPGs (n > 2.2 at λ = 1,550 nm), but is also the thinnest (<100 nm) able to tune the external-refractive-index sensitivity of the gratings. To the best of our knowledge, this is the first time a nanocoating has been applied on LPGs that is able to simultaneously tune the refractive-index sensitivity and to enable measurements of other parameters. PMID:22163527

Refractive-index-sensing fiber comb using intracavity multi-mode interference fiber sensor

NASA Astrophysics Data System (ADS)

Oe, Ryo; Minamikawa, Takeo; Taue, Shuji; Fukano, Hideki; Nakajima, Yoshiaki; Minoshima, Kaoru; Yasui, Takeshi

2018-02-01

Refractive index measurement is important for evaluation of liquid materials, optical components, and bio sensing. One promising approach for such measurement is use of optical fiber sensors such as surface plasmonic resonance or multi-mode interference (MMI), which measure the change of optical spectrum resulting from the refractive index change. However, the precision of refractive index measurement is limited by the performance of optical spectrum analyzer. If such the refractive index measurement can be performed in radio frequency (RF) region in place of optical region, the measurement precision will be further improved by the frequency-standard-based RF measurement. To this end, we focus on the disturbance-to-RF conversion in a fiber optical frequency comb (OFC) cavity. Since frequency spacing frep of OFC depends on an optical cavity length nL, frep sensitively reflects the external disturbance interacted with nL. Although we previously demonstrated the precise strain measurement based on the frep measurement, the measurable physical quantity is limited to strain or temperature, which directly interacts with the fiber cavity itself. If a functional fiber sensor can be installed into the fiber OFC cavity, the measurable physical quantity will be largely expanded. In this paper, we introduce a MMI fiber sensor into a ring-type fiber OFC cavity for refractive index measurement. We confirmed the refractive-index-dependent frep shift.

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.

Nonintrusive measurement of the liquid refractive index by using properties of the cuvette wall.

PubMed

Xu, Ming; Ren, Junpeng; Miao, Runcai; Zhang, Zongquan

2016-10-01

We present a method of nonintrusive measurement of the refractive index of a liquid in a glass cuvette, which uses some optical properties of the cuvette wall and the principle of total internal reflection. By coating a transmission-scattering paint layer on the outer surface of the cuvette, we transform an incident laser beam into a transmitted scattered light. When the transmitted scattered light reaches the interface between the container wall and the liquid inside, the light beams satisfying the condition of total internal reflection are reflected to the coating layer, automatically forming a circular dark pattern that is related to the refractive index of the liquid. Based on an analytic relation between the diameter of the circular dark pattern and the refractive index of the liquid, we devised a method of in situ nonintrusive refractive index measurement. We tested the effect of several parameters on the measuring accuracy and found that the optimal thickness of the transmission-scattering layer is in the range of 50-70 μm, and the aperture of the diaphragm should be in the range of 0.7-1.0 mm. We measured the refractive indices of ethanol, Coca Cola, and red wine, and achieved an accuracy of ±3×10^-4  RIU (refractive index unit).

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

PubMed Central

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

2016-01-01

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

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

PubMed

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

2016-08-25

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

Modulation of polymer refractive indices with diamond nanoparticles for metal-free multilayer film mirrors.

PubMed

Ogata, Tomonari; Yagi, Ryohei; Nakamura, Nozomi; Kuwahara, Yutaka; Kurihara, Seiji

2012-08-01

Modulation of the refractive index of a polymer was achieved by combining it with diamond nanoparticles (NDs). The increase in the refractive index was controlled by the amount of NDs added, according to the Lorentz-Lorenz equation. The refractive index of poly(vinyl alcohol) (PVA), which was used as the base polymer, increased from 1.52 to 1.88. A multilayer film consisting of alternating layers of ND-PVA composite and poly(methyl methacrylate) exhibited ca. 80% reflectance with 10 bilayers.

A FORTRAN Program for Computing Refractive Index Using the Double Variation Method.

ERIC Educational Resources Information Center

Blanchard, Frank N.

1984-01-01

Describes a computer program which calculates a best estimate of refractive index and dispersion from a large number of observations using the double variation method of measuring refractive index along with Sellmeier constants of the immersion oils. Program listing with examples will be provided on written request to the author. (Author/JM)

Functional photonic crystal fiber sensing devices

NASA Astrophysics Data System (ADS)

Villatoro, Joel; Finazzi, Vittoria; Pruneri, Valerio

2011-12-01

We report on a functional, highly reproducible and cost effective sensing platform based on photonic crystal fibers (PCFs). The platform consists of a centimeter-length segment of an index-guiding PCF fusion spliced to standard single mode fibers (SMFs). The voids of the PCF are intentionally sealed over an adequate length in the PCF-SMF interfaces. A microscopic collapsed region in the PCF induces a mode field mismatch which combined with the axial symmetry of the structure allow the efficient excitation and recombination or overlapping of azimuthal symmetric modes in the PCF. The transmission or reflection spectrum of the devices exhibits a high-visibility interference pattern or a single, profound and narrow notch. The interference pattern or the notch position shifts when the length of the PCF experiences microelongations or when liquids or coatings are present on the PCF surface. Thus, the platform here proposed can be useful for sensing diverse parameters such as strain, vibration, pressure, humidity, refractive index, gases, etc. Unlike other PCF-based sensing platforms the multiplexing of the devices here proposed is simple for which it is possible to implement PCF-based sensor arrays or networks.

Determination of the refractive index of insoluble organic extracts from atmospheric aerosol over the visible wavelength range using optical tweezers

NASA Astrophysics Data System (ADS)

Shepherd, Rosalie H.; King, Martin D.; Marks, Amelia A.; Brough, Neil; Ward, Andrew D.

2018-04-01

Optical trapping combined with Mie spectroscopy is a new technique used to record the refractive index of insoluble organic material extracted from atmospheric aerosol samples over a wide wavelength range. The refractive index of the insoluble organic extracts was shown to follow a Cauchy equation between 460 and 700 nm for organic aerosol extracts collected from urban (London) and remote (Antarctica) locations. Cauchy coefficients for the remote sample were for the Austral summer and gave the Cauchy coefficients of A = 1.467 and B = 1000 nm2 with a real refractive index of 1.489 at a wavelength of 589 nm. Cauchy coefficients for the urban samples varied with season, with extracts collected during summer having Cauchy coefficients of A = 1.465 ± 0.005 and B = 4625 ± 1200 nm2 with a representative real refractive index of 1.478 at a wavelength of 589 nm, whilst samples extracted during autumn had larger Cauchy coefficients of A = 1.505 and B = 600 nm2 with a representative real refractive index of 1.522 at a wavelength of 589 nm. The refractive index of absorbing aerosol was also recorded. The absorption Ångström exponent was determined for woodsmoke and humic acid aerosol extract. Typical values of the Cauchy coefficient for the woodsmoke aerosol extract were A = 1.541 ± 0.03 and B = 14 800 ± 2900 nm2, resulting in a real refractive index of 1.584 ± 0.007 at a wavelength of 589 nm and an absorption Ångström exponent of 8.0. The measured values of refractive index compare well with previous monochromatic or very small wavelength range measurements of refractive index. In general, the real component of the refractive index increases from remote to urban to woodsmoke. A one-dimensional radiative-transfer calculation of the top-of-the-atmosphere albedo was applied to model an atmosphere containing a 3 km thick layer of aerosol comprising pure water, pure insoluble organic aerosol, or an aerosol consisting of an aqueous core with an insoluble organic shell. The calculation demonstrated that the top-of-the-atmosphere albedo increases by 0.01 to 0.04 for pure organic particles relative to water particles of the same size and that the top-of-the-atmosphere albedo increases by 0.03 for aqueous core-shell particles as volume fraction of the shell material increases to 25 %.

A Simple Method to Determine the Refractive Index of Glass.

ERIC Educational Resources Information Center

Mak, Se-yuen

1988-01-01

Describes an experiment for determining the refractive index. Discusses the experiment procedure and mathematical expression for calculating the index. Provides two geometrical diagrams and a graph for determining the index with a typical data. (YP)

High Accuracy, Absolute, Cryogenic Refractive Index Measurements of Infrared Lens Materials for JWST NIRCam using CHARMS

NASA Technical Reports Server (NTRS)

Leviton, Douglas; Frey, Bradley

2005-01-01

The current refractive optical design of the James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) uses three infrared materials in its lenses: LiF, BaF2, and ZnSe. In order to provide the instrument s optical designers with accurate, heretofore unavailable data for absolute refractive index based on actual cryogenic measurements, two prismatic samples of each material were measured using the cryogenic, high accuracy, refraction measuring system (CHARMS) at NASA GSFC, densely covering the temperature range from 15 to 320 K and wavelength range from 0.4 to 5.6 microns. Measurement methods are discussed and graphical and tabulated data for absolute refractive index, dispersion, and thermo-optic coefficient for these three materials are presented along with estimates of uncertainty. Coefficients for second order polynomial fits of measured index to temperature are provided for many wavelengths to allow accurate interpolation of index to other wavelengths and temperatures.

Prediction and observation of tin and silver plasmas with index of refraction greater than one in the soft x-ray range.

PubMed

Filevich, Jorge; Grava, Jonathan; Purvis, Mike; Marconi, Mario C; Rocca, Jorge J; Nilsen, Joseph; Dunn, James; Johnson, Walter R

2006-07-01

We present the calculated prediction and the experimental confirmation that doubly ionized Ag and Sn plasmas can have an index of refraction greater than one for soft x-ray wavelengths. Interferometry experiments conducted using a capillary discharge soft x-ray laser operating at a wavelength of confirm that in few times ionized laser-created plasmas of these elements the anomalous dispersion from bound electrons can dominate the free electron contribution, making the index of refraction greater than one. The results confirm that bound electrons can strongly influence the index of refraction of numerous plasmas over a broad range of soft x-ray wavelengths confirming recent observations. The understanding of index of refraction at short wavelengths will become even more essential during the next decade as x-ray free electron lasers will become available to probe a wider variety of plasmas at higher densities and shorter wavelengths.

Group refractive index quantification using a Fourier domain short coherence Sagnac interferometer.

PubMed

Montonen, Risto; Kassamakov, Ivan; Lehmann, Peter; Österberg, Kenneth; Hæggström, Edward

2018-02-15

The group refractive index is important in length calibration of Fourier domain interferometers by transparent transfer standards. We demonstrate accurate group refractive index quantification using a Fourier domain short coherence Sagnac interferometer. Because of a justified linear length calibration function, the calibration constants cancel out in the evaluation of the group refractive index, which is then obtained accurately from two uncalibrated lengths. Measurements of two standard thickness coverslips revealed group indices of 1.5426±0.0042 and 1.5434±0.0046, with accuracies quoted at the 95% confidence level. This agreed with the dispersion data of the coverslip manufacturer and therefore validates our method. Our method provides a sample specific and accurate group refractive index quantification using the same Fourier domain interferometer that is to be calibrated for the length. This reduces significantly the requirements of the calibration transfer standard.

The refractive index in electron microscopy and the errors of its approximations.

PubMed

Lentzen, M

2017-05-01

In numerical calculations for electron diffraction often a simplified form of the electron-optical refractive index, linear in the electric potential, is used. In recent years improved calculation schemes have been proposed, aiming at higher accuracy by including higher-order terms of the electric potential. These schemes start from the relativistically corrected Schrödinger equation, and use a second simplified form, now for the refractive index squared, being linear in the electric potential. The second and higher-order corrections thus determined have, however, a large error, compared to those derived from the relativistically correct refractive index. The impact of the two simplifications on electron diffraction calculations is assessed through numerical comparison of the refractive index at high-angle Coulomb scattering and of cross-sections for a wide range of scattering angles, kinetic energies, and atomic numbers. Copyright © 2016 Elsevier B.V. All rights reserved.

Manipulating Refractive Index in Organic Light-Emitting Diodes.

PubMed

Salehi, Amin; Chen, Ying; Fu, Xiangyu; Peng, Cheng; So, Franky

2018-03-21

In a conventional organic light-emitting diode (OLED), only a fraction of light can escape to the glass substrate and air. Most radiation is lost to two major channels: waveguide modes and surface plasmon polaritons. It is known that reducing the refractive indices of the constituent layers in an OLED can enhance light extraction. Among all of the layers, the refractive index of the electron transport layer (ETL) has the largest impact on light extraction because it is the layer adjacent to the metallic cathode. Oblique angle deposition (OAD) provides a way to manipulate the refractive index of a thin film by creating an ordered columnar void structure. In this work, using OAD, the refractive index of tris(8-hydroxyquinoline)aluminum (Alq3) can be tuned from 1.75 to 1.45. With this low-index ETL deposited by OAD, the resulting phosphorescent OLED shows nearly 30% increase in light extraction efficiency.

Investigation of a pressure-dependent refractive index of germanium film with an optical fiber film sensor.

PubMed

Yuan, Dongxu; Gao, Hongyun; Chen, Hao; Li, Min

2018-02-01

The refractive index of Ge is found in decline with applied pressure at a specific wavelength in the absorption region below 1900 nm, where the absorption coefficient rises dramatically with decreased wavelength. In this paper, we use a Ge-coated fiber optic probe to demonstrate quantitatively that the downward trend in the refractive index to increasing pressure matches the theoretically simulated optical properties of Ge with a measurement error of 1.03×10 -3 in the refractive index, which is further calculated within the framework of density functional theory with local density approximation. For the first time, to the best of our knowledge, both theoretical and experimental results prove that the refractive index reduces linearly with a gradient of -3.30×10 -4 /MPa as the pressure increases from 0 to 20 MPa.

New method to determine the refractive index and the absorption coefficient of organic nonlinear crystals in the ultra-wideband THz region.

PubMed

Ohno, Seigo; Miyamoto, Katsuhiko; Minamide, Hiroaki; Ito, Hiromasa

2010-08-02

A method for simultaneously measuring the refractive index and absorption coefficient of nonlinear optical crystals in the ultra-wideband terahertz (THz) region is described. This method is based on the analysis of a collinear difference frequency generation (DFG) process using a tunable, dual-wavelength, optical parametric oscillator. The refractive index and the absorption coefficient in the organic nonlinear crystal DAST were experimentally determined in the frequency range 2.5-26.2 THz by measuring the THz-wave output using DFG. The resultant refractive index in the x-direction was approximately 2.3, while the absorption spectrum was in good agreement with FT-IR measurements. The output of the DAST-DFG THz-wave source was optimized to the phase-matching condition using the measured refractive index spectrum in THz region, which resulted in an improvement in the output power of up to a factor of nine.

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

PubMed Central

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

2013-01-01

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

Refractive index of r-cut sapphire under shock pressure range 5 to 65 GPa

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

Cao, Xiuxia; Li, Jiabo; Li, Jun

2014-09-07

High-pressure refractive index of optical window materials not only can provide information on electronic polarizability and band-gap structure, but also is important for velocity correction in particle-velocity measurement with laser interferometers. In this work, the refractive index of r-cut sapphire window at 1550 nm wavelength was measured under shock pressures of 5–65 GPa. The refractive index (n) decreases linearly with increasing shock density (ρ) for shock stress above the Hugoniot elastic limit (HEL): n = 2.0485 (± 0.0197) − 0.0729 (± 0.0043)ρ, while n remains nearly a constant for elastic shocks. This behavior is attributed to the transition from elastic (below HEL) to heterogeneous plastic deformationmore » (above HEL). Based on the obtained refractive index-density relationship, polarizability of the shocked sapphire was also obtained.« less

High precision refractometry based on Fresnel diffraction from phase plates.

PubMed

Tavassoly, M Taghi; Naraghi, Roxana Rezvani; Nahal, Arashmid; Hassani, Khosrow

2012-05-01

When a transparent plane-parallel plate is illuminated at a boundary region by a monochromatic parallel beam of light, Fresnel diffraction occurs because of the abrupt change in phase imposed by the finite change in refractive index at the plate boundary. The visibility of the diffraction fringes varies periodically with changes in incident angle. The visibility period depends on the plate thickness and the refractive indices of the plate and the surrounding medium. Plotting the phase change versus incident angle or counting the visibility repetition in an incident-angle interval provides, for a given plate thickness, the refractive index of the plate very accurately. It is shown here that the refractive index of a plate can be determined without knowing the plate thickness. Therefore, the technique can be utilized for measuring plate thickness with high precision. In addition, by installing a plate with known refractive index in a rectangular cell filled with a liquid and following the described procedures, the refractive index of the liquid is obtained. The technique is applied to measure the refractive indices of a glass slide, distilled water, and ethanol. The potential and merits of the technique are also discussed.

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.

Measuring the Index of Refraction.

ERIC Educational Resources Information Center

Phelps, F. M., III; Jacobson, B. S.

1980-01-01

Presents two methods for measuring the index of refraction of glass or lucite. These two methods, used in the freshman laboratory, are based on the fact that a ray of light inside a block will be refracted parallel to the surface. (HM)

Combined Theoretical and Experimental Study of Refractive Indices of Water-Acetonitrile-Salt Systems.

PubMed

An, Ni; Zhuang, Bilin; Li, Minglun; Lu, Yuyuan; Wang, Zhen-Gang

2015-08-20

We propose a simple theoretical formula for describing the refractive indices in binary liquid mixtures containing salt ions. Our theory is based on the Clausius-Mossotti equation; it gives the refractive index of the mixture in terms of the refractive indices of the pure liquids and the polarizability of the ionic species, by properly accounting for the volume change upon mixing. The theoretical predictions are tested by extensive experimental measurements of the refractive indices for water-acetonitrile-salt systems for several liquid compositions, different salt species, and a range of salt concentrations. Excellent agreement is obtained in all cases, especially at low salt concentrations, with no fitting parameters. A simplified expression of the refractive index for low salt concentration is also given, which can be the theoretical basis for determination of salt concentration using refractive index measurements.

Refractive index of plant cell walls

NASA Technical Reports Server (NTRS)

Gausman, H. W.; Allen, W. A.; Escobar, D. E.

1974-01-01

Air was replaced with media of higher refractive indices by vacuum infiltration in leaves of cucumber, blackeye pea, tomato, and string bean plants, and reflectance of noninfiltrated and infiltrated leaves was spectrophotometrically measured. Infiltrated leaves reflected less light than noninfiltrated leaves over the 500-2500-nm wavelength interval because cell wall-air interfaces were partly eliminated. Minimal reflectance should occur when the average refractive index of plant cell walls was matched by the infiltrating fluid. Although refractive indices that resulted in minimal reflectance differed among the four plant genera, an average value of 1.425 approximates the refractive index of plant cell walls for the four plant genera.

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.

Silicon Nitride Antireflection Coatings for Photovoltaic Cells

NASA Technical Reports Server (NTRS)

Johnson, C.; Wydeven, T.; Donohoe, K.

1984-01-01

Chemical-vapor deposition adapted to yield graded index of refraction. Silicon nitride deposited in layers, refractive index of which decreases with distance away from cell/coating interface. Changing index of refraction allows adjustment of spectral transmittance for wavelengths which cell is most effective at converting light to electric current. Average conversion efficiency of solar cells increased from 8.84 percent to 12.63 percent.

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

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

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1992-01-01

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

Sensitivity enhancement in optical micro-tube resonator sensors via mode coupling

NASA Astrophysics Data System (ADS)

Ling, Tao; Guo, L. Jay

2013-07-01

A liquid filled, silica micro-tube with a low refractive index material inner-coating has been proposed and theoretically studied as a coupled micro-resonator sensor to greatly enhance biochemical sensor sensitivity. Its unique coupling phenomenon has been analyzed and utilized to boost the device's refractive index sensitivity to 967 nm/Refractive Index Unit (RIU). Through optimization of the coupling strength between the two micro-resonators, further improvement in refractive index sensitivity up to 1100 nm/RIU has been predicted. This mode coupling strategy allows us to design robust, thick-walled micro-tube sensors with ultra-high sensitivity which is useful in practical biochemical sensing applications.

Anomalous behavior of nonlinear refractive indexes of CO2 and Xe in supercritical states.

PubMed

Mareev, Evgenii; Aleshkevich, Victor; Potemkin, Fedor; Bagratashvili, Victor; Minaev, Nikita; Gordienko, Vyacheslav

2018-05-14

Direct measurement of pressure dependent nonlinear refractive index of CO 2 and Xe in subcritical and supercritical states are reported. In the vicinity of the ridge (or the Widom line), corresponding to the maximum density fluctuations, the nonlinear refractive index reaches a maximum value (up to 4.8*10 -20 m 2 /W in CO 2 and 3.5*10 -20 m 2 /W in Xe). Anomalous behavior of the nonlinear refractive index in the vicinity of a ridge is caused by the cluster formation. That corresponds to the results of our theoretical assumption based on the modified Langevin theory.

Optical fiber Fabry-Perot interferometer cavity fabricated by femtosecond laser micromachining and fusion splicing for refractive index sensing.

PubMed

Liao, C R; Hu, T Y; Wang, D N

2012-09-24

We demonstrate a fiber in-line Fabry-Perot interferometer cavity sensor for refractive index measurement. The interferometer cavity is formed by drilling a micro-hole at the cleaved fiber end facet, followed by fusion splicing. A micro-channel is inscribed by femtosecond laser micromachining to vertically cross the cavity to allow liquid to flow in. The refractive index sensitivity obtained is ~994 nm/RIU (refractive index unit). Such a device is simple in configuration, easy for fabrication and reliable in operation due to extremely low temperature cross sensitivity of ~4.8 × 10(-6) RIU/°C.

Tapered-fiber-based refractive index sensor at an air/solution interface.

PubMed

Lu, Ping; Harris, Jeremie; Wang, Xiaozhen; Lin, Ganbin; Chen, Liang; Bao, Xiaoyi

2012-10-20

An approach to achieve refractive index sensing at an air and aqueous glycerol solution interface is proposed using a tapered-fiber-based microfiber Mach-Zehnder interferometer (MFMZI). Compared to a surrounding uniform medium of air or solutions, the spectral interference visibility of the MFMZI at the air/solution interface is significantly reduced due to a weak coupling between the fundamental cladding mode and high-order asymmetric cladding modes, which are extremely sensitive to the external refractive index. The MFMZI is experimentally demonstrated as an evanescent wave refractive index sensor to measure concentrations of glycerol solutions by monitoring average power attenuation of the tapered fiber.

Development and characterization of high refractive index and high scattering acrylate polymer layers

NASA Astrophysics Data System (ADS)

Eiselt, Thomas; Gomard, Guillaume; Preinfalk, Jan; Gleissner, Uwe; Lemmer, Uli; Hanemann, Thomas

2016-04-01

The aim is to develop a polymer layer which has the ability to diffuse light homogeneously and exhibit a high refractive index. The mixtures are containing an acrylate casting resin, benzylmethacrylate, phenanthrene and other additives. Phenanthrene is employed to increase the refractive index. The mixtures are first rheologically characterized and then polymerized with heat and UV radiation. For the refractive index measurements the polymerized samples require a planar surface without air bubbles. To produce flat samples a special construction consisting of a glass plate, a teflon sheet, a silicone ring (PDMS mold), another teflon sheet and another glass plate is developed. Glue clamps are used to fix this construction together. Selected samples have a refractive index of 1.585 at 20°C at a wavelength of 589nm. A master mixture with a high refractive index is taken for further experiments. Nano scaled titanium dioxide is added and dispersed into the master mixture and then spin coated on a glass substrate. These layers are optically characterized. The specular transmission and the overall transmission are measured to investigate the degree of scattering, which is defined as the haze. Most of the presented layers express the expected haze of over 50%.

Analysis of interferograms of refractive index inhomogeneities produced in optical materials

NASA Astrophysics Data System (ADS)

Tarjányi, N.

2014-12-01

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

Development and characterization of high refractive index and high scattering acrylate polymer layers

NASA Astrophysics Data System (ADS)

Eiselt, Thomas; Gomard, Guillaume; Preinfalk, Jan; Gleißner, Uwe; Lemmer, Uli; Hanemann, Thomas

2016-11-01

In this work, we develop a wet-processable scattering layer exhibiting a high refractive index that can be used in organic light-emitting diodes for light outcoupling purposes. The composite layers contain an acrylate casting resin, benzylmethacrylate, and phenanthrene, which is employed to increase the refractive index. The mixtures are first rheologically characterized and then polymerized with heat and UV radiation. For the refractive index measurements, the polymerized samples require a planar surface without air bubbles. To produce flat samples, a special construction consisting of a glass plate, a teflon sheet, a silicone ring (PDMS mold), another teflon sheet, and another glass plate is developed. Glue clamps are used to hold the construction together. The refractive index of the samples can be increased from 1.565 to 1.585 at 20°C at a wavelength of 589 nm following the addition of 20 wt% phenanthrene. A master mixture with a high refractive index is taken for further experiments. Nanoscaled titanium dioxide is added and dispersed into the master mixture and then spin coated on a glass substrate. These layers are optically characterized. Most of the presented layers present the expected haze of over 50%.

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.

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.

Plasmonic Waveguide Coupled Ring Cavity for a Non-Resonant Type Refractive Index Sensor.

PubMed

Kwon, Soon-Hong

2017-11-03

Sensitive refractive index sensors with small footprints have been studied to allow the integration of a large number of sensors into a tiny chip for bio/chemical applications. In particular, resonant-type index sensors based on various micro/nanocavities, which use a resonant wavelength dependence on the refractive index of the analyte, have been developed. However, the spectral linewidth of the resonance, which becomes the resolution limit, is considerably large in plasmonic cavities due to the large absorption loss of metals. Therefore, there is demand for a new type of plasmonic refractive index sensor that is not limited by the linewidth of the cavity. We propose a new type of plasmonic index sensors consisting of a channel waveguide and a ring cavity. Two emissions from the ring cavity in both directions of the waveguide couple with a reflection phase difference depending on the length of a closed right arm with a reflecting boundary. Therefore, the output power dramatically and sensitively changes as a function of the refractive index of the analyte filling the waveguide.

Plasmonic Waveguide Coupled Ring Cavity for a Non-Resonant Type Refractive Index Sensor

PubMed Central

Kwon, Soon-Hong

2017-01-01

Sensitive refractive index sensors with small footprints have been studied to allow the integration of a large number of sensors into a tiny chip for bio/chemical applications. In particular, resonant-type index sensors based on various micro/nanocavities, which use a resonant wavelength dependence on the refractive index of the analyte, have been developed. However, the spectral linewidth of the resonance, which becomes the resolution limit, is considerably large in plasmonic cavities due to the large absorption loss of metals. Therefore, there is demand for a new type of plasmonic refractive index sensor that is not limited by the linewidth of the cavity. We propose a new type of plasmonic index sensors consisting of a channel waveguide and a ring cavity. Two emissions from the ring cavity in both directions of the waveguide couple with a reflection phase difference depending on the length of a closed right arm with a reflecting boundary. Therefore, the output power dramatically and sensitively changes as a function of the refractive index of the analyte filling the waveguide. PMID:29099740

Refractive Index Imaging of Cells with Variable-Angle Near-Total Internal Reflection (TIR) Microscopy.

PubMed

Bohannon, Kevin P; Holz, Ronald W; Axelrod, Daniel

2017-10-01

The refractive index in the interior of single cells affects the evanescent field depth in quantitative studies using total internal reflection (TIR) fluorescence, but often that index is not well known. We here present method to measure and spatially map the absolute index of refraction in a microscopic sample, by imaging a collimated light beam reflected from the substrate/buffer/cell interference at variable angles of incidence. Above the TIR critical angle (which is a strong function of refractive index), the reflection is 100%, but in the immediate sub-critical angle zone, the reflection intensity is a very strong ascending function of incidence angle. By analyzing the angular position of that edge at each location in the field of view, the local refractive index can be estimated. In addition, by analyzing the steepness of the edge, the distance-to-substrate can be determined. We apply the technique to liquid calibration samples, silica beads, cultured Chinese hamster ovary cells, and primary culture chromaffin cells. The optical technique suffers from decremented lateral resolution, scattering, and interference artifacts. However, it still provides reasonable results for both refractive index (~1.38) and for distance-to-substrate (~150 nm) for the cells, as well as a lateral resolution to about 1 µm.

Lithographically-Scribed Planar Holographic Optical CDMA Devices and Systems

DTIC Science & Technology

2007-02-15

operate with quite high refractive index contrast (order 0.5). Thin -filn filter devices are viewed as relatively low in chromatic dispersion. We have...stack consists of planar interfaces between materials of refractive index n, and n,. Let An = In2 - nil and n = (n, - n1)/2. The planar interfaces are... index ). It may be desirable to have a relatively large refractive index differential when diffractive elements are formed from cladding material at a

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.

Uniform refraction in negative refractive index materials.

PubMed

Gutiérrez, Cristian E; Stachura, Eric

2015-11-01

We study the problem of constructing an optical surface separating two homogeneous, isotropic media, one of which has a negative refractive index. In doing so, we develop a vector form of Snell's law, which is used to study surfaces possessing a certain uniform refraction property, in both the near- and far-field cases. In the near-field problem, unlike the case when both materials have positive refractive indices, we show that the resulting surfaces can be neither convex nor concave.

Refractive index measurement of the mouse crystalline lens using optical coherence tomography.

PubMed

Chakraborty, Ranjay; Lacy, Kip D; Tan, Christopher C; Park, Han Na; Pardue, Machelle T

2014-08-01

In recent years, there has been a growing interest for using mouse models in refractive development and myopia research. The crystalline lens is a critical optical component of the mouse eye that occupies greater than 50% of the ocular space, and significant increases in thickness with age. However, changes in refractive index of the mouse crystalline lens are less known. In this study, we examined the changes in thickness and refractive index of the mouse crystalline lens for two different strains, wild-type (WT) and a nyx mutant (nob) over the course of normal visual development or after form deprivation. Refractive index and lens thickness measurements were made on ex vivo lenses using spectral domain optical coherence tomography (SD-OCT). Comparison of refractive index measurements on 5 standard ball lenses using the SD-OCT and their known refractive indices (manufacturer provided) indicated good precision (intra-class correlation coefficient, 0.998 and Bland-Altman coefficient of repeatability, 0.116) of the SD-OCT to calculate mouse lens refractive index ex vivo. During normal visual development, lens thickness increased significantly with age for three different cohorts of mice, aged 4 (average thickness from both eyes; WT: 1.78 ± 0.03, nob: 1.79 ± 0.08 mm), 10 (WT: 2.02 ± 0.05, nob: 2.01 ± 0.04 mm) and 16 weeks (WT: 2.12 ± 0.06, nob: 2.09 ± 0.06 mm, p < 0.001). Lens thickness was not significantly different between the two strains at any age (p = 0.557). For mice with normal vision, refractive index for isolated crystalline lenses in nob mice was significantly greater than WT mice (mean for all ages; WT: 1.42 ± 0.01, nob: 1.44 ± 0.001, p < 0.001). After 4 weeks of form deprivation to the right eye using a skull-mounted goggling apparatus, a thinning of the crystalline lens was observed in both right and left eyes of goggled animals compared to their naïve controls (average from both the right and the left eye) for both strains (p = 0.052). In form deprived mice, lens refractive index was significantly different between the goggled animals and non-goggled naïve controls in nob mice, but not in WT mice (p = 0.009). Both eyes of goggled nob mice had significantly greater lens refractive index (goggled, 1.49 ± 0.01; opposite, 1.47 ± 0.03) compared to their naïve controls (1.45 ± 0.02, p < 0.05). The results presented here suggest that there are genetic differences in the crystalline lens refractive index of the mouse eye, and that the lens refractive index in mice significantly increase with form deprivation. Research applications requiring precise optical measurements of the mouse eye should take these lens refractive indices into account when interpreting SD-OCT data. Published by Elsevier Ltd.

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.;

Observation of acoustic Dirac-like cone and double zero refractive index

PubMed Central

Dubois, Marc; Shi, Chengzhi; Zhu, Xuefeng; Wang, Yuan; Zhang, Xiang

2017-01-01

Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre. PMID:28317927

Slot-waveguide biochemical sensor.

PubMed

Barrios, Carlos A; Gylfason, Kristinn B; Sánchez, Benito; Griol, Amadeu; Sohlström, H; Holgado, M; Casquel, R

2007-11-01

We report an experimental demonstration of an integrated biochemical sensor based on a slot-waveguide microring resonator. The microresonator is fabricated on a Si3N4-SiO2 platform and operates at a wavelength of 1.3 microm. The transmission spectrum of the sensor is measured with different ambient refractive indices ranging from n=1.33 to 1.42. A linear shift of the resonant wavelength with increasing ambient refractive index of 212 nm/refractive index units (RIU) is observed. The sensor detects a minimal refractive index variation of 2x10(-4) RIU.

High purity silica reflecting heat shield development

NASA Technical Reports Server (NTRS)

Congdon, W.

1974-01-01

A reflecting heat shield composed of fused silica in which the scattering results from the refractive index mismatch between silica particles and the voids introduced during the fabrication process is developed. Major considerations and conclusions of the development are: the best material to use is Type A, which is capable of ultra-high-purity and which does not show the 0.243 micrometer absorption band; the reflection efficiency of fused silica is decreased at higher temperatures due to the bathochromic shift of the ultraviolet cut-off; for a given silica material, over the wavelength region and particle sizes tested, the monodisperse particle size configurations produce higher reflectances than continuous particle size configurations; and the smaller monodisperse particle size configurations give higher reflectance than the larger ones. A reflecting silica configuration that is an efficient reflector of shock layer radiation at high ablation temperatures is achieved by tailoring the matrix for optimum scattering and using an ultra-high-purity material.

The Predictive Power of Electronic Polarizability for Tailoring the Refractivity of High Index Glasses Optical Basicity Versus the Single Oscillator Model

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

McCloy, John S.; Riley, Brian J.; Johnson, Bradley R.

Four compositions of high density (~8 g/cm3) heavy metal oxide glasses composed of PbO, Bi2O3, and Ga2O3 were produced and refractivity parameters (refractive index and density) were computed and measured. Optical basicity was computed using three different models – average electronegativity, ionic-covalent parameter, and energy gap – and the basicity results were used to compute oxygen polarizability and subsequently refractive index. Refractive indices were measured in the visible and infrared at 0.633 μm, 1.55 μm, 3.39 μm, 5.35 μm, 9.29 μm, and 10.59 μm using a unique prism coupler setup, and data were fitted to the Sellmeier expression to obtainmore » an equation of the dispersion of refractive index with wavelength. Using this dispersion relation, single oscillator energy, dispersion energy, and lattice energy were determined. Oscillator parameters were also calculated for the various glasses from their oxide values as an additional means of predicting index. Calculated dispersion parameters from oxides underestimate the index by 3 to 4%. Predicted glass index from optical basicity, based on component oxide energy gaps, underpredicts the index at 0.633 μm by only 2%, while other basicity scales are less accurate. The predicted energy gap of the glasses based on this optical basicity overpredicts the Tauc optical gap as determined by transmission measurements by 6 to 10%. These results show that for this system, density, refractive index in the visible, and energy gap can be reasonably predicted using only composition, optical basicity values for the constituent oxides, and partial molar volume coefficients. Calculations such as these are useful for a priori prediction of optical properties of glasses.« less

Interferometric measurement of refractive index modification in a single mode microfiber

NASA Astrophysics Data System (ADS)

Ahmed, Farid; Ahsani, Vahid; Jun, Martin B. G.

2017-02-01

Efficient and cost effective measurement of the refractive index profile in an optical fiber is a significant technical job to design and manufacture in-fiber photonic devices and communication systems. For instance, to design fiber gratings, it is required to estimate the refractive index modulation to be inscribed by the fabrication apparatus such as ultraviolet or infrared lasers. Mach-Zehnder interferometer (MZI) based quantification of refractive index change written in single mode microfiber by femtosecond laser radiation is presented in this study. The MZI is constructed by splicing a microfiber (core diameter: 3.75 μm, cladding diameter: 40 μm) between standard single mode fibers. To measure the RI inscribed by infrared femtosecond laser, 200 μm length of the core within the MZI was scanned with laser radiation. As the higher index was written within 200 μm length of the core, the transmission spectrum of the interferometer displayed a corresponding red shift. The observed spectral shift was used to calculate the amount of refractive index change inscribed by the femtosecond irradiation. For the MZI length of 3.25 mm, and spectral shift of 0.8 nm, the calculated refractive index was found to be 0.00022. The reported results display excellent agreement between theory and experimental findings. Demonstrated method provides simple yet very effective on-site measurement of index change in optical fibers. Since the MZI can be constructed in diverse fiber types, this technique offers flexibility to quantify index change in various optical fibers.

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

PubMed

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

2007-01-21

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

Synthesis and Characterization of Functional Mesostructures Using Colloidal Crystal Templating

DTIC Science & Technology

2004-01-01

fluorescent probes in aqueous polymer solutions . Khoury and co-workers measured the diffusion coefficient of several fluorescein-labeled proteins in...diffraction naq refractive index of the aqueous solution phase xvii ni refractive index of component i ngel refractive index of the hydrogel...phase Tg glass transition temperature α angle of diffraction φaq volume fraction of the aqueous solution phase φi volume fraction of

Chemical Sensing Sensitivity of Long-Period Grating Sensor Enhanced by Colloidal Gold Nanoparticles

PubMed Central

Tang, Jaw-Luen; Wang, Jien-Neng

2008-01-01

A simple and effective method is proposed to improve spectral sensitivity and detection limit of long period gratings for refractive index or chemical sensing, where the grating surface is modified by a monolayer of colloidal gold nanoparticles. The transmission spectra and optical properties of gold nanospheres vary with the different refractive index of the environment near the surface of gold nanospheres. The sensor response of gold colloids increases linearly with solvents of increasing refractive index. The results for the measurement of sucrose and sodium chloride solutions are reported, which show that this type of sensor can provide a limiting resolution of ∼10-3 to ∼10-4 for refractive indices in the range of 1.34 to 1.39 and a noticeable increase in detection limit of refractive index to external medium. PMID:27879701

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

PubMed

Wakamatsu, Takashi; Watanabe, Keita; Saito, Kazuhiro

2005-02-20

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

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

NASA Astrophysics Data System (ADS)

Wakamatsu, Takashi; Watanabe, Keita; Saito, Kazuhiro

2005-02-01

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

Optical Super-Resolution by High-Index Liquid-Immersed Microspheres

DTIC Science & Technology

2012-01-01

the BD without liquid can be achieved using microspheres with small-to-moderate index of refraction such as borosilicate glass (n 1.47), soda lime ...titanate glass microspheres with diameters (D) in the range 2–220 lm and with high refractive index (n 1.9–2.1) can be used for super-resolution...achieving optical super-resolution. It has been demonstrated10 that silica spheres with refractive index (n) about 1.46 and with diame- ters (D) in the

Effects of Source Correlations on the Spectrum of Radiated Fields

DTIC Science & Technology

1990-09-01

media. When the refractive index n(co) is nearly constant over the source spectral width, the medium acts as a non- dispersive homogeneous medium of...constant refractive index no = n(w0 ), where o is the central frequency of the source spectrum. We will consider the non- dispersive case first. It is...in free space (a), for propagation in a homogeneous medium of an index of refraction n((o) = 1.5 (b) and for propagation in a medium of index of

Silicon-nanocrystal Optoelectronic Kerr Effect for Complementary Metal-oxide Semiconductor (CMOS) Compatible Optical Switching

DTIC Science & Technology

2011-04-01

changes the material’s index of refraction via dispersion . This absorption requires carrier transport and, in present implementations, suffers from slow...designed to take advantage of the large Kerr effect that has been reported in Si-nanocrystals imbedded in oxide (Si-nc). The expected refractive index ...estimate of the expected refractive index change versus applied voltage. An index change of ~2 x 10–4 is enough to modulate the light, corresponding to a

Stochastic digital holography for visualizing inside strongly refracting transparent objects.

PubMed

Desse, Jean-Michel; Picart, Pascal

2015-01-01

This paper presents a digital holographic method to visualize and measure refractive index variations, convection currents, or thermal gradients, occurring inside a transparent and refracting object. The proof of principle is provided through the visualization of refractive index variation inside a lighting bulb. Comparison with transmission and reflection holography is also provided. A very good agreement is obtained, thus validating the proposed approach.

On-fiber plasmonic interferometer for multi-parameter sensing

DOE PAGES

Zhang, Zhijian; Chen, Yongyao; Liu, Haijun; ...

2015-01-01

We demonstrate a novel miniature multi-parameter sensing device based on a plasmonic interferometer fabricated on a fiber facet in the optical communication wavelength range. This device enables the coupling between surface plasmon resonance and plasmonic interference in the structure, which are the two essential mechanisms for multi-parameter sensing. We experimentally show that these two mechanisms have distinctive responses to temperature and refractive index, rendering the device the capability of simultaneous temperature and refractive index measurement on an ultra-miniature form factor. A high refractive index sensitivity of 220 nm per refractive index unit (RIU) and a high temperature sensitivity of –60more » pm/ °C is achieved with our device.« less

Index of Refraction Measurements and Window Corrections for PMMA under Shock Compression

NASA Astrophysics Data System (ADS)

Chapman, David; Eakins, Daniel; Williamson, David; Proud, William

2011-06-01

Symmetric plate impact experiments were performed to investigate the change in the refractive index of PMMA under shock loading. Flyer and target geometries allowed the measurement of shock velocity, particle velocity, and refractive index in the shocked state, using the simultaneous application of VISAR (532 nm) and Het-V (1550 nm). The change in refractive index of PMMA as a function of density is generally considered to be well described by the Gladstone-Dale relationship, meaning that the ``apparent'' velocity measured by a laser velocity interferometer is the ``true'' velocity, and hence there is no window correction. The results presented characterise the accuracy of this assumption at peak stresses up to 2 GPa.

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

PubMed Central

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

2015-01-01

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

Preparation of MgF2-SiO2 thin films with a low refractive index by a solgel process.

PubMed

Ishizawa, Hitoshi; Niisaka, Shunsuke; Murata, Tsuyoshi; Tanaka, Akira

2008-05-01

Porous MgF(2)-SiO(2) thin films consisting of MgF(2) particles connected by an amorphous SiO(2) binder are prepared by a solgel process. The films have a low refractive index of 1.26, sufficient strength to withstand wiping by a cloth, and a high environmental resistance. The refractive index of the film can be controlled by changing the processing conditions. Films can be uniformly formed on curved substrates and at relatively low temperatures, such as 100 degrees C. The low refractive index of the film, which cannot be achieved by conventional dry processes, is effective in improving the performance of antireflective coatings.

Enhancement of graphene visibility on transparent substrates by refractive index optimization.

PubMed

Gonçalves, Hugo; Alves, Luís; Moura, Cacilda; Belsley, Michael; Stauber, Tobias; Schellenberg, Peter

2013-05-20

Optical reflection microscopy is one of the main imaging tools to visualize graphene microstructures. Here is reported a novel method that employs refractive index optimization in an optical reflection microscope, which greatly improves the visibility of graphene flakes. To this end, an immersion liquid with a refractive index that is close to that of the glass support is used in-between the microscope lens and the support improving the contrast and resolution of the sample image. Results show that the contrast of single and few layer graphene crystals and structures can be enhanced by a factor of 4 compared to values commonly achieved with transparent substrates using optical reflection microscopy lacking refractive index optimization.

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.

A naked eye refractive index sensor with a visible multiple peak metamaterial absorber.

PubMed

Ma, Heli; Song, Kun; Zhou, Liang; Zhao, Xiaopeng

2015-03-26

We report a naked eye refractive index sensor with a visible metamaterial absorber. The visible metamaterial absorber consisting of a silver dendritic/dielectric/metal structure shows multiple absorption peaks. By incorporating a gain material (rhodamine B) into the dielectric layer, the maximal magnitude of the absorption peak can be improved by about 30%. As the metamaterial absorber is sensitive to the refractive index of glucose solutions, it can function as a sensor that quickly responds to variations of the refractive index of the liquid. Meanwhile, since the response is presented via color changes, it can be clearly observed by the naked eyes. Further experiments have confirmed that the sensor can be used repeatedly.

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

Hilfiker, James N.; Stadermann, Michael; Sun, Jianing

It is a well-known challenge to determine refractive index (n) from ultra-thin films where the thickness is less than about 10 nm. In this paper, we discovered an interesting exception to this issue while characterizing spectroscopic ellipsometry (SE) data from isotropic, free-standing polymer films. Ellipsometry analysis shows that both thickness and refractive index can be independently determined for free-standing films as thin as 5 nm. Simulations further confirm an orthogonal separation between thickness and index effects on the experimental SE data. Effects of angle of incidence and wavelength on the data and sensitivity are discussed. Finally, while others have demonstratedmore » methods to determine refractive index from ultra-thin films, our analysis provides the first results to demonstrate high-sensitivity to the refractive index from ultra-thin layers.« less

Gradient Refractive Index Lenses.

ERIC Educational Resources Information Center

Morton, N.

1984-01-01

Describes the nature of gradient refractive index (GRIN) lenses, focusing on refraction in these materials, focal length of a thin Wood lens, and on manufacturing of such lenses. Indicates that GRIN lenses of small cross section are in limited production with applications suggested for optical communication and photocopying fields. (JN)

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

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

Correct consideration of the index of refraction using blackbody radiation.

PubMed

Hartmann, Jurgen

2006-09-04

The correct consideration of the index of refraction when using blackbody radiators as standard sources for optical radiation is derived and discussed. It is shown that simply using the index of refraction of air at laboratory conditions is not sufficient. A combination of the index of refraction of the media used inside the blackbody radiator and for the optical path between blackbody and detector has to be used instead. A worst case approximation for the introduced error when neglecting these effects is presented, showing that the error is below 0.1 % for wavelengths above 200 nm. Nevertheless, for the determination of the spectral radiance for the purpose of radiation temperature measurements the correct consideration of the refractive index is mandatory. The worst case estimation reveals that the introduced error in temperature at a blackbody temperature of 3000 degrees C can be as high as 400 mk at a wavelength of 650 nm and even higher at longer wavelengths.

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

PubMed

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

2017-02-01

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

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

Absolute distance measurement with correction of air refractive index by using two-color dispersive interferometry.

PubMed

Wu, Hanzhong; Zhang, Fumin; Liu, Tingyang; Li, Jianshuang; Qu, Xinghua

2016-10-17

Two-color interferometry is powerful for the correction of the air refractive index especially in the turbulent air over long distance, since the empirical equations could introduce considerable measurement uncertainty if the environmental parameters cannot be measured with sufficient precision. In this paper, we demonstrate a method for absolute distance measurement with high-accuracy correction of air refractive index using two-color dispersive interferometry. The distances corresponding to the two wavelengths can be measured via the spectrograms captured by a CCD camera pair in real time. In the long-term experiment of the correction of air refractive index, the experimental results show a standard deviation of 3.3 × 10^-8 for 12-h continuous measurement without the precise knowledge of the environmental conditions, while the variation of the air refractive index is about 2 × 10^-6. In the case of absolute distance measurement, the comparison with the fringe counting interferometer shows an agreement within 2.5 μm in 12 m range.

Measurement of refractive index of photopolymer for holographic gratings

NASA Astrophysics Data System (ADS)

Watanabe, Eriko; Mizuno, Jun; Fujikawa, Chiemi; Kodate, Kashiko

2007-02-01

We have made attempts to measure directly the small-scale variation of optical path lengths in photopolymer samples. For those with uniform thickness, the measured quantity is supposed to be proportional to the refractive index of the photopolymer. The system is based on a Mach-Zehnder interferometer using phase-locking technique and measures the change in optical path length during the sample is scanned across the optical axis. The spatial resolution is estimated to be 2μm, which is limited by the sample thickness. The path length resolution is estimated to be 6nm, which corresponds to the change in refractive index less than 10 -3 for the sample of 10μm thick. The measurement results showed clearly that the refractive index of photopolymer is not simply proportional to the exposure energy, contrary to the conventional photosensitive materials such as silver halide emulsion and dichromated gelatine. They also revealed the refractive index fluctuation in uniformly exposed photopolymer sample, which explains the milky appearance that sometimes observed in thick samples.

Photogeneration of refractive-index patterns in doped polyimide films.

PubMed

Chakravorty, K K

1993-05-01

A photosensitive benzophenone tetracarboxylic dianhyride-alkylated diamine polyimide formulation has been evaluated for application in an optical interconnection area. The refractive-index patterns in this material were optically recorded by UV-assisted photodoping of sensitizers. The polyimide films were selectively doped with benzoin-type photosensitizers such as benzildimethylketal and benzoin ethyl ether, which cause a decrease in the refractive index. High-dose UV irradiation that causes cross linking of the polyimide chains was also employed for augmenting the refractive-index difference to 0.017 between the doped and undoped regions. Refractive-index variations and lightguiding properties were investigated as a function of doping concentrations and other processing conditions. The author utilized this technique for the fabrication of embedded polyimide channel waveguides. The two photosensitizers have different effects on the waveguiding characteristics of the polyimide films. Losses for benzoin ethyl ether remained low whereas doping with benzildimethylketal caused significant increase in the waveguiding loss at high doping concentrations. Near-field imaging of the output from such waveguides shows good confinement of 815-nm light.

Plasma Parameters From Reentry Signal Attenuation

DOE PAGES

Statom, T. K.

2018-02-27

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

An investigation into dispersion upon switching between solvents within a microfluidic system using a chemically resistant integrated optical refractive index sensor.

PubMed

Parker, Richard M; Gates, James C; Wales, Dominic J; Smith, Peter G R; Grossel, Martin C

2013-02-07

A planar Bragg grating device has been developed that is capable of detecting changes in the refractive index of a wide range of fluids including solvents, acids and bases. The integration of this high precision refractive index sensor within a chemically resistant microfluidic flow system has enabled the investigation of diverse fluid interactions. By cycling between different solvents, both miscible and immiscible, within the microfluidic system it is shown that the previous solvent determines the nature of the refractive index profile across the transition in composition. This solvent dispersion effect is investigated with particular attention to the methanol-water transition, where transients in refractive index are observed that are an order of magnitude larger in amplitude than the difference between the bulk fluids. The potential complications of such phenomenon are discussed together with an example of a device that exploits this effect for the unambiguous composition measurement of a binary solvent system.

Refractive index of solutions of human hemoglobin from the near-infrared to the ultraviolet range: Kramers-Kronig analysis.

PubMed

Sydoruk, Oleksiy; Zhernovaya, Olga; Tuchin, Valery; Douplik, Alexandre

2012-11-01

Because direct measurements of the refractive index of hemoglobin over a large wavelength range are challenging, indirect methods deserve particular attention. Among them, the Kramers-Kronig relations are a powerful tool often used to derive the real part of a refractive index from its imaginary part. However, previous attempts to apply the relations to solutions of human hemoglobin have been somewhat controversial, resulting in disagreement between several studies. We show that this controversy can be resolved when careful attention is paid not only to the absorption of hemoglobin but also to the dispersion of the refractive index of the nonabsorbing solvent. We present a Kramers-Kroning analysis taking both contributions into account and compare the results with the data from several studies. Good agreement with experiments is found across the visible and parts of near-infrared and ultraviolet regions. These results reinstate the use of the Kramers-Kronig relations for hemoglobin solutions and provide an additional source of information about their refractive index.

Photogeneration of refractive-index patterns in doped polyimide films

NASA Astrophysics Data System (ADS)

Chakravorty, K. K.

1993-05-01

A photosensitive benzophenone tetracarboxylic dianhyride-alkylated diamine polyimide formulation has been evaluated for application in an optical interconnection area. The refractive-index patterns in this material were optically recorded by UV-assisted photodoping of sensitizers. The polyimide films were selectively doped with benzoin-type photosensitizers such as benzildimethylketal and benzoin ethyl ether, which cause a decrease in the refractive index. High-dose UV irradiation that causes cross linking of the polyimide chains was also employed for augmenting the refractive-index difference to 0.017 between the doped and undoped regions. Refractive-index variations and lightguiding properties were investigated as a function of doping concentrations and other processing conditions. The author utilized this technique for the fabrication of embedded polyimide channel waveguides. The two photosensitizers have different effects on the waveguiding characteristics of the polyimide films. Losses for benzoin ethyl ether remained low whereas doping with benzildimethylketal caused significant increase in the waveguiding loss at high doping concentrations. Near-field imaging of the output from such waveguides shows good confinement of 815-nm light.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

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

Antireflective coatings with adjustable refractive index and porosity synthesized by micelle-templated deposition of MgF2 sol particles.

PubMed

Bernsmeier, Denis; Polte, Jörg; Ortel, Erik; Krahl, Thoralf; Kemnitz, Erhard; Kraehnert, Ralph

2014-11-26

Minimizing efficiency losses caused by unwanted light reflection at the interface between lenses, optical instruments and solar cells with the surrounding medium requires antireflective coatings with adequate refractive index and coating thickness. We describe a new type of antireflective coating material with easily and independently tailorable refractive index and coating thickness based on the deposition of colloidal MgF2 nanoparticles. The material synthesis employs micelles of amphiphilic block copolymers as structure directing agent to introduce controlled mesoporosity into MgF2 film. The coatings thickness can be easily adjusted by the applied coating conditions. The coatings refractive index is determined by the materials porosity, which is controlled by the amount of employed pore template. The refractive index can be precisely tuned between 1.23 and 1.11, i.e., in a range that is not accessible to nonporous inorganic materials. Hence, zero reflectance conditions can be established for a wide range of substrate materials.

Plasma Parameters From Reentry Signal Attenuation

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

Statom, T. K.

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

Index of refraction engineering in five-level dressed interacting ground states atoms.

PubMed

Sagona-Stophel, Steven A; Weatherall, James Owen; Search, Christopher P

2011-08-15

We present a five-level atomic system in which the index of refraction of a probe laser can be enhanced or reduced below unity with vanishing absorption in the region between pairs of absorption and gain lines formed by dressing of the atoms with a control laser and rf/microwave fields. By weak incoherent pumping of the population into a single metastable state, one can create several narrow amplifying resonances. At frequencies between these gain lines and additional absorption lines, there exist regions of vanishing absorption but resonantly enhanced index of refraction. In Rb vapors with density N in units of cm(-3), we predict an index of refraction up to n≈√(1+1.2×10(-14)N) for the D1 line, which is more than an order of magnitude larger than other proposals for index of refraction enhancement. Furthermore, the index can be readily reduced below 1 by simply changing the sign of the probe or rf field detunings. This enhancement is robust with respect to homogeneous and inhomogeneous broadening. © 2011 Optical Society of America

Refractive Index of Sodium Iodide

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

Jellison Jr, Gerald Earle; Boatner, Lynn A; Ramey, Joanne Oxendine

2012-01-01

The refractive index of sodium iodide, an important scintillator material that is widely used for radiation detection, is based on a single measurement made by Spangenberg at one wavelength using the index-matching liquid immersion method (Z. Kristallogr., 57, 494-534 (1923)). In the present paper, we present new results for the refractive index of sodium iodide as measured by the minimum deviation technique at six wavelengths between 436 nm (n=1.839 0.002) and 633 nm (n=1.786 0.002). These 6 measurements can be fit to a Sellmeier model, resulting in a 2 of 1.02, indicating a good fit to the data. In addition,more » we report on ellipsometry measurements, which suggest that the near-surface region of the air sensitive NaI crystal seriously degrades, even in a moisture-free environment, resulting in a significantly lower value of the refractive index near the surface. First-principles theoretical calculations of the NaI refractive index that agree with the measured values within 0.025-0.045 are also presented and discussed.« less

Refractive index and viscosity: dual sensing with plastic fibre gratings

NASA Astrophysics Data System (ADS)

Ferreira, Ricardo; Bilro, Lúcia; Marques, Carlos; Oliveira, Ricardo; Nogueira, Rogério

2014-05-01

A refractive index and viscosity sensor based on FBGs in mPOF is reported for the first time. The refractive index was measured with a sensitivity of -10:98nm=RIU and a resolution of 1 - 10-4RIU. Viscosity measurements were performed with acousto-optic modulation, obtaining a sensitivity of -94:42%=mPa • s and a resolution of 0:06mPa • s.

Selenium Interlayer for High-Efficiency Multijunction Solar Cell

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A (Inventor)

2015-01-01

A multi junction solar cell is provided and includes multiple semiconducting layers and an interface layer disposed between the multiple semiconducting layers. The interface layer is made from an interface bonding material that has a refractive index such that a ratio of a refractive index of each of the multiple semiconducting layers to the refractive index of the interface bonding material is less than or equal to 1.5.

Selenium Interlayer for High-Efficiency Multijunction Solar Cell

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A. (Inventor)

2016-01-01

A multi-junction solar cell is provided and includes multiple semiconducting layers and an interface layer disposed between the multiple semiconducting layers. The interface layer is made from an interface bonding material that has a refractive index such that a ratio of a refractive index of each of the multiple semiconducting layers to the refractive index of the interface bonding material is less than or equal to 1.5.

Development of 1.0- to 1.4-Micrometer Heterojunction LEDs.

DTIC Science & Technology

1980-04-01

dispersion of silica fibers decreases with increasing wavelength (2]. This is due to the wavelength dependence of the refractive index , which predicts...shown here is sufficient to provide strong electron confine- ment in the low-energy material (InGaAs). A similar difference in refractive index for these...bandgap and refractive - index steps discussed above form the basis of fabricating heterojunction emitters (both edge-emitting LEDs and lasers

Patient-prosthesis mismatch in aortic valve replacement: really tolerable?

PubMed

Fuster, Rafael García; Montero Argudo, José A; Albarova, Oscar Gil; Sos, Fernando Hornero; López, Sergio Cánovas; Codoñer, María Bueno; Buendía Miñano, José A; Albarran, Ignacio Rodríguez

2005-03-01

Several studies have demonstrated favorable results despite patient-prosthesis mismatch after aortic valve replacement with the use of third generation prostheses. Our aim was to determine whether this mismatch is always tolerable. A clinical-echocardiographic study has been performed in 339 consecutive patients who underwent aortic valve replacement because of aortic stenosis. In-hospital outcome and left ventricular mass index regression (1st month-1st year) were analyzed in the presence or absence of mismatch (indexed effective orifice area < or =0.85cm(2)/m(2)). The influence of high degrees of preoperative left ventricular mass on in-hospital mortality has also been evaluated. Left ventricular mass index was considered increased if the calculated value was over the superior quartile of the frequency distribution of all the values observed in both sexes. Mismatch was found in 38% of the patients. In the absence of mismatch, the absolute mass regression was proportional to the preoperative left ventricular mass. This regression was higher in patients with increased left ventricular mass indexed (vs not increased): -38.0+/-7.8 vs -8.8+/-4.7g/m(2), p<0.01 (1st month) and -67.7+/-16.9vs -23.5+/-6.7g/m(2), p<0.05 (1st year). Mass regression was impaired in the presence of mismatch, particularly, in patients with previously increased left ventricular mass: -8.2+/-11.6 vs -5.6+/-6.3g/m(2) (p=0.83) and -24.6+/-12.6 vs -11.7+/-10.5g/m(2) (p=0.54). This worse regression was reflected on a 100% incidence of residual hypertrophy at follow-up (1st month-1st year). In the presence of mismatch, increased ventricular mass was associated with higher mortality: 14.7% vs 2.1% (p<0.01). In the absence of mismatch, ventricular mass was not associated with mortality: 4.1 vs 2.5% (p=0.55). In patients with severe ventricular hypertrophy it may be important to elude patient-prosthesis mismatch to avoid a significant increase in mortality and improve ventricular mass regression. Mismatch may be tolerable in those patients with lesser degree of hypertrophy.

Modeling of a Single-Notch Microfiber Coupler for High-Sensitivity and Low Detection-Limit Refractive Index Sensing.

PubMed

Zhang, Jiali; Shi, Lei; Zhu, Song; Xu, Xinbiao; Zhang, Xinliang

2016-05-11

A highly sensitive refractive index sensor with low detection limit based on an asymmetric optical microfiber coupler is proposed. It is composed of a silica optical microfiber and an As₂Se₃ optical microfiber. Due to the asymmetry of the microfiber materials, a single-notch transmission spectrum is demonstrated by the large refractive index difference between the two optical microfibers. Compared with the symmetric coupler, the bandwidth of the asymmetric structure is over one order of magnitude narrower than that of the former. Therefore, the asymmetric optical microfiber coupler based sensor can reach over one order of magnitude smaller detection limit, which is defined as the minimal detectable refractive index change caused by the surrounding analyte. With the advantage of large evanescent field, the results also show that a sensitivity of up to 3212 nm per refractive index unit with a bandwidth of 12 nm is achieved with the asymmetric optical microfiber coupler. Furthermore, a maximum sensitivity of 4549 nm per refractive index unit can be reached while the radii of the silica optical microfiber and As₂Se₃ optical microfiber are 0.5 μm and a 0.128 μm, respectively. This sensor component may have important potential for low detection-limit physical and biochemical sensing applications.

Refractive index measurement for biomaterial samples by total internal reflection.

PubMed

Jin, Y L; Chen, J Y; Xu, L; Wang, P N

2006-10-21

The refractive index of biological tissue is a fundamental parameter in applications of optical diagnosis and laser treatments. In the present work, the refractive indices and thermo-optic coefficients of some basic biomaterials, such as blood plasma, haemoglobin solution and lipid membrane, were studied by the method of total internal reflection at the wavelengths of 532 and 632.8 nm that are the most frequently used laser wavelengths in the biomedical field. The effects of the sample concentration and the temperature on refractive index were measured, and empirical relationships were summarized, accompanied by a theoretical explanation based on molecular polarization theory. The results provide some fundamental data for the refractive indices of these biomaterials under variant conditions, and also demonstrate that the total internal reflection method is a feasible and reliable way to measure the refractive indices of biological samples.

Optical diffusion property of chicken tissue

NASA Astrophysics Data System (ADS)

Schneider, Patricia S.; Flamholz, Alex; Wong, Peter K.; Lieberman, David H.; Cheung, Tak D.; Itoka, Harriet; Minott, Troy; Quizhpi, Janie; Rodriguez, Jacquelin

2004-11-01

Chicken tissue acts as a turbid medium in optical wavelength. Optical characterization data of fresh chicken dark and white meat were studied using the theory of light diffusion. The gaussian-like transmission profile was used to determine the transport mean free path and absorption. The refractive index, a fundamental parameter, was extracted via transmission correlation function analysis without using index-matching fluid. The variation in refractive index also produced various small shifts in the oscillatory feature of the intensity spatial correlation function at distance shorter than the transport mean free path. The optical system was calibrated with porous silicate slabs containing different water contents and also with a solid alumina slab. The result suggested that the selective scattering/absorption of myoglobin and mitochondria in the dark tissues is consistent with the transmission data. The refractive index was similar for dark and white tissues at the He-Ne wavelength and suggested that the index could serve as a marker for quality control. Application to chicken lunchmeat samples revealed that higher protein and lower carbohydrate would shift the correlation toward smaller distance. The pure fat refractive index was different from that of the meat tissue. Application of refractive index as a fat marker is also discussed

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

Highly Sensitive Refractive Index Sensor Based on Adiabatically Tapered Microfiber Long Period Gratings

PubMed Central

Ji, Wen Bin; Tjin, Swee Chuan; Lin, Bo; Ng, Choong Leng

2013-01-01

We demonstrate a refractive index sensor based on a long period grating (LPG) inscribed in a special photosensitive microfiber with double-clad profile. The fiber is tapered gradually enough to ensure the adiabaticity of the fiber taper. In other words, the resulting insertion loss is sufficiently small. The boron and germanium co-doped inner cladding makes it suitable for inscribing gratings into its tapered form. The manner of wavelength shift for refractive indices (RIs) differs from conventional LPG, and the refractive index detection limit is 1.67 × 10−5. PMID:24141267

Highly sensitive refractive index sensor based on adiabatically tapered microfiber long period gratings.

PubMed

Ji, Wen Bin; Tjin, Swee Chuan; Lin, Bo; Ng, Choong Leng

2013-10-17

We demonstrate a refractive index sensor based on a long period grating (LPG) inscribed in a special photosensitive microfiber with double-clad profile. The fiber is tapered gradually enough to ensure the adiabaticity of the fiber taper. In other words, the resulting insertion loss is sufficiently small. The boron and germanium co-doped inner cladding makes it suitable for inscribing gratings into its tapered form. The manner of wavelength shift for refractive indices (RIs) differs from conventional LPG, and the refractive index detection limit is 1.67 × 10⁻⁵.

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

PubMed

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

2015-01-01

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

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

PubMed

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

2018-04-15

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

Real-Time and In-Flow Sensing Using a High Sensitivity Porous Silicon Microcavity-Based Sensor.

PubMed

Caroselli, Raffaele; Martín Sánchez, David; Ponce Alcántara, Salvador; Prats Quilez, Francisco; Torrijos Morán, Luis; García-Rupérez, Jaime

2017-12-05

Porous silicon seems to be an appropriate material platform for the development of high-sensitivity and low-cost optical sensors, as their porous nature increases the interaction with the target substances, and their fabrication process is very simple and inexpensive. In this paper, we present the experimental development of a porous silicon microcavity sensor and its use for real-time in-flow sensing application. A high-sensitivity configuration was designed and then fabricated, by electrochemically etching a silicon wafer. Refractive index sensing experiments were realized by flowing several dilutions with decreasing refractive indices, and measuring the spectral shift in real-time. The porous silicon microcavity sensor showed a very linear response over a wide refractive index range, with a sensitivity around 1000 nm/refractive index unit (RIU), which allowed us to directly detect refractive index variations in the 10 -7 RIU range.

Surface plasmon resonance optical cavity enhanced refractive index sensing.

PubMed

Giorgini, A; Avino, S; Malara, P; Gagliardi, G; Casalino, M; Coppola, G; Iodice, M; Adam, P; Chadt, K; Homola, J; De Natale, P

2013-06-01

We report on a method for surface plasmon resonance (SPR) refractive index sensing based on direct time-domain measurements. An optical resonator is built around an SPR sensor, and its photon lifetime is measured as a function of loss induced by refractive index variations. The method does not rely on any spectroscopic analysis or direct intensity measurement. Time-domain measurements are practically immune to light intensity fluctuations and thus lead to high resolution. A proof of concept experiment is carried out in which a sensor response to liquid samples of different refractive indices is measured. A refractive index resolution of the current system, extrapolated from the reproducibility of cavity-decay time determinations over 133 s, is found to be about 10(-5) RIU. The possibility of long-term averaging suggests that measurements with a resolution better than 10(-7) RIU/√Hz are within reach.

Measuring Variable Refractive Indices Using Digital Photos

ERIC Educational Resources Information Center

Lombardi, S.; Monroy, G.; Testa, I.; Sassi, E.

2010-01-01

A new procedure for performing quantitative measurements in teaching optics is presented. Application of the procedure to accurately measure the rate of change of the variable refractive index of a water-denatured alcohol mixture is described. The procedure can also be usefully exploited for measuring the constant refractive index of distilled…

Temperature-Dependent Refractive Index of Cleartran® ZnS to Cryogenic Temperatures

NASA Technical Reports Server (NTRS)

Leviton, Doug; Frey, Brad

2013-01-01

First, let's talk about the CHARMS facility at NASA's Goddard Space Flight Center: Cryogenic, High-Accuracy Refraction Measuring System (CHARMS); design features for highest accuracy and precision; technologies we rely on; data products and examples; optical materials for which we've measured cryogenic refractive index.

Measurement of Refractive Index Gradients by Deflection of a Laser Beam

ERIC Educational Resources Information Center

Barnard, A. J.; Ahlborn, B.

1975-01-01

In this simple experiment for an undergraduate laboratory a laser beam is passed through the mixing zone of two liquids with different refractive indices. The spatial variation of the refractive index, at different times during the mixing, can be determined from the observed deflection of the beam. (Author)

Cryogenic refractive index of Heraeus homosil glass

NASA Astrophysics Data System (ADS)

Miller, Kevin H.; Quijada, Manuel A.; Leviton, Douglas B.

2017-08-01

This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.34—3.16 μm and temperature range of 120—335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASA's Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a fieldwidened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitive performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dn/dT) and dispersion relation (dn/dλ) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in the literature.

Cryogenic Refractive Index of Heraeus Homosil Glass

NASA Technical Reports Server (NTRS)

Miller, Kevin H.; Quijada, Manuel A.; Leviton, Douglas B.

2017-01-01

This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.343.16 m and temperature range of 120335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASAs Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a field-widened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitivity performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dndT) and dispersion relation (dnd) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in literature.

Empirical modelling to predict the refractive index of human blood.

PubMed

Yahya, M; Saghir, M Z

2016-02-21

Optical techniques used for the measurement of the optical properties of blood are of great interest in clinical diagnostics. Blood analysis is a routine procedure used in medical diagnostics to confirm a patient's condition. Measuring the optical properties of blood is difficult due to the non-homogenous nature of the blood itself. In addition, there is a lot of variation in the refractive indices reported in the literature. These are the reasons that motivated the researchers to develop a mathematical model that can be used to predict the refractive index of human blood as a function of concentration, temperature and wavelength. The experimental measurements were conducted on mimicking phantom hemoglobin samples using the Abbemat Refractometer. The results analysis revealed a linear relationship between the refractive index and concentration as well as temperature, and a non-linear relationship between refractive index and wavelength. These results are in agreement with those found in the literature. In addition, a new formula was developed based on empirical modelling which suggests that temperature and wavelength coefficients be added to the Barer formula. The verification of this correlation confirmed its ability to determine refractive index and/or blood hematocrit values with appropriate clinical accuracy.

Cryogenic Refractive Index of Heraeus Homosil Glass

NASA Technical Reports Server (NTRS)

Miller, Kevin H.; Quijada, Manuel A.; Leviton, Douglas B.

2017-01-01

This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.34-3.16 microns and temperature range of 120-335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASAs Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a field-widened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitivity performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dn/dT) and dispersion relation (dn/d(lamda)) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in literature.

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

Prakash, Deo; Shaaban, E.R., E-mail: esam_ramadan2008@yahoo.com; Shapaan, M.

Highlights: • Combined experimental and theoretical researches on ZnSe Thin Films. • The film thickness and refractive index were determined using envelope method. • The absorption coefficient and the energy gap were calculated. • Dispersion parameters were determined using Wemple-DiDomenico relation. • The third order susceptibility and nonlinear refractive index were calculated. - Abstract: Zinc selenide (ZnSe) thin films with different thicknesses were evaporated onto glass substrates using the thermal evaporation technique. X-ray diffraction analysis confirmed that both the film and powder have cubic zinc-blende structure. The fundamental optical parameters like absorption coefficient, extinction coefficient and band gap were evaluatedmore » in transparent region of transmittance and reflectance spectrum. The optical transition of the films was found to be allowed, where the energy gap increased from 2.576 to 2.702 eV with increasing film thickness. Also, the refractive index value increase with increasing film thickness. The refractive indices evaluated through envelope method were extrapolated by Cauchy dispersion relationship over the whole spectra range. Additionally, the dispersion of refractive index was determined in terms of Wemple-DiDomenico single oscillator model. Third order susceptibility and nonlinear refractive index were determined for different thickness of ZnSe thin films.« less

Tunable two-dimensional liquid gradient refractive index (L-GRIN) lens for variable light focusing.

PubMed

Huang, Hua; Mao, Xiaole; Lin, Sz-Chin Steven; Kiraly, Brian; Huang, Yiping; Huang, Tony Jun

2010-09-21

We report a two-dimensional (2D) tunable liquid gradient refractive index (L-GRIN) lens for variable focusing of light in the out-of-plane direction. This lens focuses a light beam through a liquid medium with a 2D hyperbolic secant (HS) refractive index gradient. The refractive index gradient is established in a microfluidic chamber through the diffusion between two fluids with different refractive indices, i.e. CaCl(2) solution and deionized (DI) water. The 2D HS refractive index profile and subsequently the focal length of the L-GRIN lens can be tuned by changing the ratio of the flow rates of the CaCl(2) solution and DI water. The focusing effect is experimentally characterized through side-view and top-view image analysis, and the experimental data match well with the results from ray-tracing optical simulations. Advantages of the 2D L-GRIN lens include simple device fabrication procedure, low fluid consumption rate, convenient lens-tuning mechanism, and compatibility with existing microfluidic devices. We expect that with further optimizations, this 2D L-GRIN lens can be used in many optics-based lab-on-a-chip applications.

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.

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.

The effect of UV irradiation on the refractive index modulation in photo-thermo-refractive glasses: Mechanisms and application

NASA Astrophysics Data System (ADS)

Chernakov, Dmitry I.; Sidorov, Alexander I.; Stolyarchuk, Maxim V.; Kozlova, Darya A.; Krykova, Victoria A.; Nikonorov, Nikolay V.

2018-02-01

It is shown experimentally that in photo-thermo-refractive glasses the transformation of charged silver subnanosized molecular clusters to neutral state by UV irradiation results in the increase of glass refractive index. The increment of the refractive index reaches Δn = 0.76·10-4. Computer simulation has shown that the polarizability of neutral molecular clusters is by 20-40% larger than of charged ones. The reason of this is the increase of electron density and volume of electron density surfaces during the transformation of molecular cluster to the neutral state. The transition molecular cluster from the ground state to the excited state also results in the increase of its polarizability.

Phase and group refractive indices of air calculation by fitting of phase difference measured using a combination of laser and low-coherence interferometry

NASA Astrophysics Data System (ADS)

Pikálek, Tomáš; Šarbort, Martin; Číp, Ondřej; Pham, Minh Tuan; Lešundák, Adam; Pravdová, Lenka; Buchta, Zdeněk.

2017-06-01

The air refractive index is an important parameter in interferometric length measurements, since it substantially affects the measurement accuracy. We present a refractive index of air measurement method based on monitoring the phase difference between the ambient air and vacuum inside a permanently evacuated double-spaced cell. The cell is placed in one arm of the Michelson interferometer equipped with two light sources—red LED and HeNe laser, while the low-coherence and laser interference signals are measured separately. Both phase and group refractive indices of air can be calculated from the measured signals. The method was experimentally verified by comparing the obtained refractive index values with two different techniques.

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.

Measurement of the refractive index of air in a low-pressure regime and the applicability of traditional empirical formulae

NASA Astrophysics Data System (ADS)

Schödel, René; Walkov, Alexander; Voigt, Michael; Bartl, Guido

2018-06-01

The refractive index of air is a major limiting factor in length measurements by interferometry, which are mostly performed under atmospheric conditions. Therefore, especially in the last century, measurement and description of the air refractive index was a key point in order to achieve accuracy in the realisation of the length by interferometry. Nevertheless, interferometric length measurements performed in vacuum are much more accurate since the wavelength of the light is not affected by the air refractive index. However, compared with thermal conditions in air, in high vacuum heat conduction is missing. In such a situation, dependent on the radiative thermal equilibrium, a temperature distribution can be very inhomogeneous. Using a so-called contact gas instead of high vacuum is a very effective way to enable heat conduction on nearly the same level as under atmospheric pressure conditions whereby keeping the effect of the air refractive index on a small level. As physics predicts, and as we have demonstrated previously, helium seems like the optimal contact gas because of its large heat conduction and its refractive index that can be calculated from precisely known parameters. On the other hand, helium gas situated in a vacuum chamber could easily be contaminated, e.g. by air leakage from outside. Above the boiling point of oxygen (‑183 °C) it is therefore beneficial to use dry air as a contact gas. In such an approach, the air refractive index could be calculated based on measured quantities for pressure and temperature. However, existing formulas for the air refractive index are not valid in the low-pressure regime. Although it seems reasonable that the refractivity (n  ‑  1) of dry air simply downscales with the pressure, to our knowledge there is no experimental evidence for the applicability of any empirical formula. This evidence is given in the present paper which reports on highly accurate measurements of the air refractive index for the wavelengths 532 nm, 633 nm and 780 nm in the low-pressure regime from 0 Pa to 1300 Pa. In our approach, using a vacuum cell, n  ‑  1 is obtained from the comparison of optical path lengths in vacuum and air along the same path by imaging interferometry. These measured values are compared with the ones obtained from Bönsch’s formula. An agreement of  ±10‑9 is found in the low-pressure regime. Accordingly, this formula could be applied for the accurate determination of the refractive index of dry air even at low pressures, provided that the pressure is measured with high accuracy.

Temperature-dependent Absolute Refractive Index Measurements of Synthetic Fused Silica

NASA Technical Reports Server (NTRS)

Leviton, Douglas B.; Frey, Bradley J.

2006-01-01

Using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, we have measured the absolute refractive index of five specimens taken from a very large boule of Corning 7980 fused silica from temperatures ranging from 30 to 310 K at wavelengths from 0.4 to 2.6 microns with an absolute uncertainty of plus or minus 1 x 10 (exp -5). Statistical variations in derived values of the thermo-optic coefficient (dn/dT) are at the plus or minus 2 x 10 (exp -8)/K level. Graphical and tabulated data for absolute refractive index, dispersion, and thermo-optic coefficient are presented for selected wavelengths and temperatures along with estimates of uncertainty in index. Coefficients for temperature-dependent Sellmeier fits of measured refractive index are also presented to allow accurate interpolation of index to other wavelengths and temperatures. We compare our results to those from an independent investigation (which used an interferometric technique for measuring index changes as a function of temperature) whose samples were prepared from the same slugs of material from which our prisms were prepared in support of the Kepler mission. We also compare our results with sparse cryogenic index data from measurements of this material from the literature.

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

PubMed

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

2014-03-01

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

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.

Optical coatings of variable refractive index and high laser-resistance from physical-vapor-deposited perfluorinated amorphous polymer

DOEpatents

Chow, Robert; Loomis, Gary E.; Thomas, Ian M.

1999-01-01

Variable index optical single-layers, optical multilayer, and laser-resistant coatings were made from a perfluorinated amorphous polymer material by physical vapor deposition. This was accomplished by physically vapor depositing a polymer material, such as bulk Teflon AF2400, for example, to form thin layers that have a very low refractive index (.about.1.10-1.31) and are highly transparent from the ultra-violet through the near infrared regime, and maintain the low refractive index of the bulk material. The refractive index can be varied by simply varying one process parameter, either the deposition rate or the substrate temperature. The thus forming coatings may be utilized in anti-reflectors and graded anti-reflection coatings, as well as in optical layers for laser-resistant coatings at optical wavelengths of less than about 2000 nm.

Direct-patterned optical waveguides on amorphous silicon films

DOEpatents

Vernon, Steve; Bond, Tiziana C.; Bond, Steven W.; Pocha, Michael D.; Hau-Riege, Stefan

2005-08-02

An optical waveguide structure is formed by embedding a core material within a medium of lower refractive index, i.e. the cladding. The optical index of refraction of amorphous silicon (a-Si) and polycrystalline silicon (p-Si), in the wavelength range between about 1.2 and about 1.6 micrometers, differ by up to about 20%, with the amorphous phase having the larger index. Spatially selective laser crystallization of amorphous silicon provides a mechanism for controlling the spatial variation of the refractive index and for surrounding the amorphous regions with crystalline material. In cases where an amorphous silicon film is interposed between layers of low refractive index, for example, a structure comprised of a SiO.sub.2 substrate, a Si film and an SiO.sub.2 film, the formation of guided wave structures is particularly simple.

New infrared transmitting material via inverse vulcanization of elemental sulfur to prepare high refractive index polymers.

PubMed

Griebel, Jared J; Namnabat, Soha; Kim, Eui Tae; Himmelhuber, Roland; Moronta, Dominic H; Chung, Woo Jin; Simmonds, Adam G; Kim, Kyung-Jo; van der Laan, John; Nguyen, Ngoc A; Dereniak, Eustace L; Mackay, Michael E; Char, Kookheon; Glass, Richard S; Norwood, Robert A; Pyun, Jeffrey

2014-05-21

Polymers for IR imaging: The preparation of high refractive index polymers (n = 1.75 to 1.86) via the inverse vulcanization of elemental sulfur is reported. High quality imaging in the near (1.5 μm) and mid-IR (3-5 μm) regions using high refractive index polymeric lenses from these sulfur materials was demonstrated. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quality control analytical methods: refractive index.

PubMed

Allen, Loyd V

2015-01-01

There are numerous analytical methods that can be utilized in a compounding pharmacy for a quality-assurance program. Since the index of refraction of a liquid/solution is a physical constant, it can be used to assist in identification of a substance, establish its purity, and, in some instances, to determine the concentration of an analyte in solution. This article serves as an introduction to refractive index and some applications of its use in a compounding program.

Measuring refractive index and volume of liquid under high pressure with optical coherence tomography and light microscopy.

PubMed

Wang, Donglin; Yang, Kun; Zhou, Yin

2016-03-20

Measuring the refractive index and volume of liquid under high pressure simultaneously is a big challenge. This paper proposed an alternative solution by combing optical coherence tomography with microscopy. An experiment for a feasibility study was carried out on polydimethylsiloxane liquid in a diamond anvil cell. The refractive index of the sample increased dramatically with pressure loaded, and the curve of pressure volume was also obtained.

Method of determining dispersion dependence of refractive index of nanospheres building opals

NASA Astrophysics Data System (ADS)

Kępińska, Mirosława; Starczewska, Anna; Duka, Piotr

2017-11-01

The method of determining dispersion dependence of refractive index of nanospheres building opals is presented. In this method basing on angular dependences of the spectral positions of Bragg diffraction minima on transmission spectra for opal series of known spheres diameter, the spectrum of effective refractive index for opals and then refractive index for material building opal's spheres is determined. The described procedure is used for determination of neff(λ) for opals and nsph(λ) for material which spheres building investigated opals are made of. The obtained results are compared with literature data of nSiO2(λ) considered in the analysis and interpretation of extremes related to the light diffraction at (hkl) SiO2 opal planes.

Surface relief and refractive index gratings patterned in chalcogenide glasses and studied by off-axis digital holography.

PubMed

Cazac, V; Meshalkin, A; Achimova, E; Abashkin, V; Katkovnik, V; Shevkunov, I; Claus, D; Pedrini, G

2018-01-20

Surface relief gratings and refractive index gratings are formed by direct holographic recording in amorphous chalcogenide nanomultilayer structures As 2 S 3 -Se and thin films As 2 S 3 . The evolution of the grating parameters, such as the modulation of refractive index and relief depth in dependence of the holographic exposure, is investigated. Off-axis digital holographic microscopy is applied for the measurement of the photoinduced phase gratings. For the high-accuracy reconstruction of the wavefront (amplitude and phase) transmitted by the fabricated gratings, we used a computational technique based on the sparse modeling of phase and amplitude. Both topography and refractive index maps of recorded gratings are revealed. Their separated contribution in diffraction efficiency is estimated.

Temperature and refractive index measurement based on a coating-enhanced dual-microspheric fiber sensor

NASA Astrophysics Data System (ADS)

Ju, Yao; Ning, Shougui; Sun, Huijin; Mo, Jun; Yang, Chao; Feng, Guoying; Zhou, Hao; Zhou, Shouhuan

2018-07-01

We propose and demonstrate a coating-enhanced dual-microspheric structure fiber sensor that measures temperature and refractive index simultaneously. The claddings of the two microspheric structured fibers are spliced together and the ends of the fibers are coated with a layer of gold film to increase reflection, thereby forming a dual-microspheric structure sensor head. Our experimental results show that the temperature sensitivity and the refractive index can reach 65.77 pm °C‑1 and  ‑19.7879 nm RIU‑1, respectively. Compared with the uncoated sensor, the refractive index sensitivity is significantly improved by the gold film. This work suggests a low-cost, high-resolution and convenient fiber-based method to achieve multifunctional sensing applications.

Concentration and temperature dependence of the refractive index of ethanol-water mixtures: influence of intermolecular interactions.

PubMed

Riobóo, R J; Philipp, M; Ramos, M A; Krüger, J K

2009-09-01

The temperature and concentration dependence of the refractive index, nD(x, T), in ethanol-water mixtures agrees with previous data in the ethanol-rich concentration range. The refractive index versus concentration x determined at 20 degrees C shows the expected maximum at about 41 mol% water (22 mass% water). The temperature derivative of the refractive index, dnD/dT, shows anomalies at lower water concentrations at about 10 mol% water but no anomaly at 41 mol% water. Both anomalies are related to intermolecular interactions, the one in nD seems to be due to molecular segregation and cluster formation while the origin of the second one in dnD/dT is still not clear.

Estimation of the R134a gas refractive index for use as a Cherenkov radiator, using a high energy charged particle beam

NASA Astrophysics Data System (ADS)

Charitonidis, N.; Karyotakis, Y.; Gatignon, L.

2017-11-01

Gases with relatively high refractive index, n - 1 ≥ 500 ×10-6 at atmospheric pressure, giving a satisfactory photoelectron yield at relatively low pressures (≤ 5 bar) are rare. These gases are often the only practical solution for low momentum particle identification in conventional secondary beam lines. The refractive index of R134a, one of the most common gases available to the physics community, has never been measured or reported. In the present note, the results of a dedicated experiment to estimate the refractive index of R134a, using mixed hadron/electron beams in the range 0.5-10 GeV are presented.

Fiber optic refractive index monitor

DOEpatents

Weiss, Jonathan David

2002-01-01

A sensor for measuring the change in refractive index of a liquid uses the lowest critical angle of a normal fiber optic to achieve sensitivity when the index of the liquid is significantly less than the index of the fiber core. Another embodiment uses a liquid filled core to ensure that its index is approximately the same as the liquid being measured.

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

NASA Astrophysics Data System (ADS)

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

1992-09-01

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

A single-image method for x-ray refractive index CT.

PubMed

Mittone, A; Gasilov, S; Brun, E; Bravin, A; Coan, P

2015-05-07

X-ray refraction-based computer tomography imaging is a well-established method for nondestructive investigations of various objects. In order to perform the 3D reconstruction of the index of refraction, two or more raw computed tomography phase-contrast images are usually acquired and combined to retrieve the refraction map (i.e. differential phase) signal within the sample. We suggest an approximate method to extract the refraction signal, which uses a single raw phase-contrast image. This method, here applied to analyzer-based phase-contrast imaging, is employed to retrieve the index of refraction map of a biological sample. The achieved accuracy in distinguishing the different tissues is comparable with the non-approximated approach. The suggested procedure can be used for precise refraction computer tomography with the advantage of a reduction of at least a factor of two of both the acquisition time and the dose delivered to the sample with respect to any of the other algorithms in the literature.

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.

CHARMS: The Cryogenic, High-Accuracy Refraction Measuring System

NASA Technical Reports Server (NTRS)

Frey, Bradley; Leviton, Douglas

2004-01-01

The success of numerous upcoming NASA infrared (IR) missions will rely critically on accurate knowledge of the IR refractive indices of their constituent optical components at design operating temperatures. To satisfy the demand for such data, we have built a Cryogenic, High-Accuracy Refraction Measuring System (CHARMS), which, for typical 1R materials. can measure the index of refraction accurate to (+ or -) 5 x 10sup -3 . This versatile, one-of-a-kind facility can also measure refractive index over a wide range of wavelengths, from 0.105 um in the far-ultraviolet to 6 um in the IR, and over a wide range of temperatures, from 10 K to 100 degrees C, all with comparable accuracies. We first summarize the technical challenges we faced and engineering solutions we developed during the construction of CHARMS. Next we present our "first light," index of refraction data for fused silica and compare our data to previously published results.

Sequential Infiltration Synthesis for the Design of Low Refractive Index Surface Coatings with Controllable Thickness

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

Berman, Diana; Guha, Supratik; Lee, Byeongdu

Control over refractive index and thickness of surface coatings is central to the design of low refraction films used in applications ranging from optical computing to antireflective coatings. Here, we introduce gas-phase sequential infiltration synthesis (SIS) as a robust, powerful and efficient approach to deposit conformal coatings with very low refractive indices. We demonstrate that the refractive indices of inorganic coatings can be efficiently tuned by the number of cycles used in the SIS process, composition and selective swelling of the of the polymer template. We show that the refractive index of Al 2O 3 can be lowered from 1.76more » down to 1.1 using this method. The thickness of the Al 2O 3 coating can be efficiently controlled by the swelling of the block copolymer template in ethanol at elevated temperature, thereby enabling deposition of both single-layer and graded-index broadband anti-reflective coatings. Using this technique, Fresnel reflections of glass can be reduced to as low as 0.1% under normal illumination over a broad spectral range.« less

Sequential Infiltration Synthesis for the Design of Low Refractive Index Surface Coatings with Controllable Thickness

DOE PAGES

Berman, Diana; Guha, Supratik; Lee, Byeongdu; ...

2017-01-31

Control over refractive index and thickness of surface coatings is central to the design of low refraction films used in applications ranging from optical computing to antireflective coatings. Here, we introduce gas-phase sequential infiltration synthesis (SIS) as a robust, powerful and efficient approach to deposit conformal coatings with very low refractive indices. We demonstrate that the refractive indices of inorganic coatings can be efficiently tuned by the number of cycles used in the SIS process, composition and selective swelling of the of the polymer template. We show that the refractive index of Al 2O 3 can be lowered from 1.76more » down to 1.1 using this method. The thickness of the Al 2O 3 coating can be efficiently controlled by the swelling of the block copolymer template in ethanol at elevated temperature, thereby enabling deposition of both single-layer and graded-index broadband anti-reflective coatings. Using this technique, Fresnel reflections of glass can be reduced to as low as 0.1% under normal illumination over a broad spectral range.« less

Sequential Infiltration Synthesis for the Design of Low Refractive Index Surface Coatings with Controllable Thickness

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

Berman, Diana; Guha, Supratik; Lee, Byeongdu

Control over refractive index and thickness of surface coatings is central to the design of low refraction films used in applications ranging from optical computing to antireflective coatings. Here, we introduce gas-phase sequential infiltration synthesis (SIS) as a robust, powerful, and efficient approach to deposit conformal coatings with very low refractive indices. We demonstrate that the refractive indices of inorganic coatings can be efficiently tuned by the number of cycles used in the SIS process, composition, and selective swelling of the of the polymer template. We show that the refractive index of Al2O3 can be lowered from 1.76 down tomore » 1.1 using this method. The thickness of the Al2O3 coating can be efficiently controlled by the swelling of the block copolymer template in ethanol at elevated temperature, thereby enabling deposition of both single-layer and graded-index broadband antireflective coatings. Using this technique, Fresnel reflections of glass can be reduced to as low as 0.1% under normal illumination over a broad spectral range.« less

Sequential Infiltration Synthesis for the Design of Low Refractive Index Surface Coatings with Controllable Thickness.

PubMed

Berman, Diana; Guha, Supratik; Lee, Byeongdu; Elam, Jeffrey W; Darling, Seth B; Shevchenko, Elena V

2017-03-28

Control over refractive index and thickness of surface coatings is central to the design of low refraction films used in applications ranging from optical computing to antireflective coatings. Here, we introduce gas-phase sequential infiltration synthesis (SIS) as a robust, powerful, and efficient approach to deposit conformal coatings with very low refractive indices. We demonstrate that the refractive indices of inorganic coatings can be efficiently tuned by the number of cycles used in the SIS process, composition, and selective swelling of the of the polymer template. We show that the refractive index of Al 2 O 3 can be lowered from 1.76 down to 1.1 using this method. The thickness of the Al 2 O 3 coating can be efficiently controlled by the swelling of the block copolymer template in ethanol at elevated temperature, thereby enabling deposition of both single-layer and graded-index broadband antireflective coatings. Using this technique, Fresnel reflections of glass can be reduced to as low as 0.1% under normal illumination over a broad spectral range.

Proximity to AGCT sequences dictates MMR-independent versus MMR-dependent mechanisms for AID-induced mutation via UNG2

PubMed Central

Thientosapol, Eddy Sanchai; Sharbeen, George; Lau, K.K. Edwin; Bosnjak, Daniel; Durack, Timothy; Stevanovski, Igor; Weninger, Wolfgang

2017-01-01

Abstract AID deaminates C to U in either strand of Ig genes, exclusively producing C:G/G:C to T:A/A:T transition mutations if U is left unrepaired. Error-prone processing by UNG2 or mismatch repair diversifies mutation, predominantly at C:G or A:T base pairs, respectively. Here, we show that transversions at C:G base pairs occur by two distinct processing pathways that are dictated by sequence context. Within and near AGCT mutation hotspots, transversion mutation at C:G was driven by UNG2 without requirement for mismatch repair. Deaminations in AGCT were refractive both to processing by UNG2 and to high-fidelity base excision repair (BER) downstream of UNG2, regardless of mismatch repair activity. We propose that AGCT sequences resist faithful BER because they bind BER-inhibitory protein(s) and/or because hemi-deaminated AGCT motifs innately form a BER-resistant DNA structure. Distal to AGCT sequences, transversions at G were largely co-dependent on UNG2 and mismatch repair. We propose that AGCT-distal transversions are produced when apyrimidinic sites are exposed in mismatch excision patches, because completion of mismatch repair would require bypass of these sites. PMID:28039326

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

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.

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

Planar optical waveguides for optical panel having gradient refractive index core

DOEpatents

Veligdan, James T.

2001-01-01

An optical panel is disclosed. A plurality of stacked planar optical waveguides are used to guide light from an inlet face to an outlet face of an optical panel. Each of the optical waveguides comprises a planar sheet of core material having a central plane. The core material has an index of refraction which decreases as the distance from the central plane increases. The decrease in the index of refraction occurs gradually and continuously.

Investigation of Refractive Index Profile Induced with Femtosecond Pulses into Neodymium Doped Phosphate Glass for the Purposes of Hybrid Waveguiding Structures Formation

NASA Astrophysics Data System (ADS)

Bukharin, M.; Khudakov, D.; Vartapetov, S.

The technique of writing depressed cladding waveguides into Nd:phosphate glass with relatively large mode field diameter in 2-line geometry was reported for the purposes of waveguiding structures formation. The easy to use and accurate technique of induced refractive index measurement was proposed, and it was shown the inefficiency of widespread indirect (numerical aperture) technique of refractive index measurement for such femtosecond written waveguides.

Planar optical waveguides for optical panel having gradient refractive index core

DOEpatents

Veligdan, James T.

2004-08-24

An optical panel is disclosed. A plurality of stacked planar optical waveguides are used to guide light from an inlet face to an outlet face of an optical panel. Each of the optical waveguides comprises a planar sheet of core material having a central plane. The core material has an index of refraction which decreases as the distance from the central plane increases. The decrease in the index of refraction occurs gradually and continuously.

Estimation of effective refractive index of birefringent particles using a combination of the immersion liquid method and light scattering.

PubMed

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

2008-04-01

A method to detect the effective refractive index and concentration of birefringent pigments is suggested. The method is based on the utilization of the immersion liquid method and a multifunction spectrophotometer for the measurement of back scattered light. The method has applications in the measurement of the effective refractive index of pigments that are used, e.g., in the paper industry to improve the opacity of paper products.

Determination of the complex refractive index and size distribution of atmospheric particulates from bistatic-monostatic lidar and solar radiometer measurements

NASA Technical Reports Server (NTRS)

Reagan, J. A.; Byrne, D. M.; Herman, B. M.; King, M. D.; Spinhirne, J. D.

1980-01-01

A method is presented for inferring both the size distribution and the complex refractive index of atmospheric particulates from combined bistatic-monostatic lidar and solar radiometer observations. The basic input measurements are spectral optical depths at several visible and near-infrared wavelengths as obtained with a solar radiometer and backscatter and angular scatter coefficients as obtained from a biostatic-monostatic lidar. The spectral optical depth measurements obtained from the radiometer are mathematically inverted to infer a columnar particulate size distribution. Advantage is taken of the fact that the shape of the size distribution obtained by inverting the particulate optical depth is relatively insensitive to the particle refractive index assumed in the inversion. Bistatic-monostatic angular scatter and backscatter lidar data are then processed to extract an optimum value for the particle refractive index subject to the constraint that the shape of the particulate size distribution be the same as that inferred from the solar radiometer data. Specifically, the scattering parameters obtained from the bistatic-monostatic lidar data are compared with corresponding theoretical computations made for various assumed refractive index values. That value which yields best agreement, in a weighted least squares sense, is selected as the optimal refractive index estimate. The results of this procedure applied to a set of simulated measurements as well as to measurements collected on two separate days are presented and discussed.

Experimental and numerical study of underwater beam propagation in a Rayleigh-Bénard turbulence tank.

PubMed

Nootz, Gero; Matt, Silvia; Kanaev, Andrey; Judd, Kyle P; Hou, Weilin

2017-08-01

The propagation of a laser beam through Rayleigh-Bénard (RB) turbulence is investigated experimentally and by way of numerical simulation. For the experimental part, a focused laser beam transversed a 5  m×0.5  m×0.5  m water filled tank lengthwise. The tank is heated from the bottom and cooled from the top to produce convective RB turbulence. The effect of the turbulence on the beam is recorded on the exit of the beam from the tank. From the centroid motion of the beam, the index of refraction structure constant Cn2 is determined. For the numerical efforts RB turbulence is simulated for a tank of the same geometry. The simulated temperature fields are converted to the index of refraction distributions, and Cn2 is extracted from the index of refraction structure functions, as well as from the simulated beam wander. To model the effect on beam propagation, the simulated index of refraction fields are converted to discrete index of refraction phase screens. These phase screens are then used in a split-step beam propagation method to investigate the effect of the turbulence on a laser beam. The beam wander as well as the index of refraction structure parameter Cn2 determined from the experiment and simulation are compared and found to be in good agreement.

Refractive Index Sensing Using Visible Electromagnetic Resonances of Supported Cu2O Particles.

PubMed

Susman, Mariano D; Vaskevich, Alexander; Rubinstein, Israel

2017-03-08

Plasmonic metal nanostructures, in colloidal or surface-supported forms, have been extensively studied in the context of metamaterials design and applications, in particular as refractometric sensing platforms. Recently, high refractive index (high-n) dielectric subwavelength structures have been experimentally shown to support strong Mie scattering resonances, predicted to exhibit analogous refractive index sensing capabilities. Here we present the first experimental demonstration of the use of supported high-n dielectric nano/microparticle ensembles as refractive index sensing platforms, using cuprous oxide as a model high-n material. Single-crystalline Cu 2 O particles were deposited on transparent substrates using a chemical deposition scheme, showing well-defined electric and magnetic dipolar resonances (EDR and MDR, respectively) in the visible range, which change in intensity and wavelength upon changing the medium refractive index (n m ). The significant modulation of the MDR intensity when n m is modified appears to be the most valuable empirical sensing parameter. The Mie scattering properties of Cu 2 O particles, particularly the spectral dependence of the MDR on n m , are theoretically modeled to support the experimental observations. MDR extinction changes (i.e., refractive index sensitivity) per particle are >100 times higher compared to localized surface plasmon resonance (LSPR) changes in supported Au nanoislands, encouraging the evaluation of Cu 2 O and other high-n dielectric particles and sensing modes in order to improve the sensitivity in optical (bio)sensing applications.

Heat accumulation regime of femtosecond laser writing in fused silica and Nd:phosphate glass

NASA Astrophysics Data System (ADS)

Bukharin, M. A.; Khudyakov, D. V.; Vartapetov, S. K.

2015-04-01

We investigated refractive index induced by direct femtosecond laser writing inside fused silica and Nd:phosphate glass in heat accumulation regime. Spatial profile and magnitude of induced refractive index were investigated at various pulse repetition rates and translation velocities. It was shown that the magnitude of induced refractive index significantly rises with decreasing in time interval between successive laser pulses below the time for thermal diffusion. Going from nonthermal regime to heat accumulation regime, we achieved induced refractive index growth from 4 × 10-3 up to 6.5 × 10-3 in fused silica and from -6 × 10-3 to -9 × 10-3 in Nd:phosphate glass. Aspect ratio of treated area decreased from 2.1 down to less than 1.5 without correcting optical elements. It was shown that in heat accumulation regime, the treated area was surrounded by region of alternatively changed refractive index with significant magnitude up to -2 × 10-3. Wide regions of decreased refractive index enable fabrication of depressed cladding waveguides. We demonstrated low-loss (0.3 dB/cm) tubular waveguide inside fused silica. For orthogonal polarizations of guiding light, we achieved a small difference between losses as 0.1 dB/cm using highly symmetric written tracks forming the cladding. The desired structure was simulated with the beam propagation method, and the results were in good agreement with experiment data.

Slow-light enhanced subwavelength plasmonic waveguide refractive index sensors.

PubMed

Huang, Yin; Min, Changjun; Dastmalchi, Pouya; Veronis, Georgios

2015-06-01

We introduce slow-light enhanced subwavelength scale refractive index sensors which consist of a plasmonic metal-dielectric-metal (MDM) waveguide based slow-light system sandwiched between two conventional MDM waveguides. We first consider a MDM waveguide with small width structrue for comparison, and then consider two MDM waveguide based slow light systems: a MDM waveguide side-coupled to arrays of stub resonators system and a MDM waveguide side-coupled to arrays of double-stub resonators system. We find that, as the group velocity decreases, the sensitivity of the effective index of the waveguide mode to variations of the refractive index of the fluid filling the sensors as well as the sensitivities of the reflection and transmission coefficients of the waveguide mode increase. The sensing characteristics of the slow-light waveguide based sensor structures are systematically analyzed. We show that the slow-light enhanced sensors lead to not only 3.9 and 3.5 times enhancements in the refractive index sensitivity, and therefore in the minimum detectable refractive index change, but also to 2 and 3 times reductions in the required sensing length, respectively, compared to a sensor using a MDM waveguide with small width structure.

The Cryogenic, High-Accuracy, Refraction Measuring System (CHARMS): A New Facility for Cryogenic Infrared through Vacuum Far-Ultraviolet Refractive Index Measurements

NASA Technical Reports Server (NTRS)

Frey, Bradley J.; Leviton, Douglas B.

2004-01-01

The optical designs of future NASA infrared (IR) missions and instruments, such as the James Webb Space Telescope's (JWST) Near-Mixed Camera (NIRCam), will rely on accurate knowledge of the index of refraction of various IR optical materials at cryogenic temperatures. To meet this need, we have developed a Cryogenic, High-Accuracy Refraction Measuring System (CHARMS). In this paper we discuss the completion of the design and construction of CHARMS as well as the engineering details that constrained the final design and hardware implementation. In addition, we will present our first light, cryogenic, IR index of refraction data for LiF, BaF2, and CaF2, and compare our results to previously published data for these materials.

Manufacturer-provided effective orifice area index charts and the prevention of prosthesis-patient mismatch.

PubMed

House, Chad M; Nelson, William B; Kroshus, Timothy J; Dahiya, Ranjan; Pibarot, Philippe

2012-01-01

Prosthesis-patient mismatch (PPM) occurs when an implanted prosthesis is too small relative to the patient's body surface area (BSA). However, mismatch can often be prevented by indexing the expected effective orifice area (EOA) of a prosthesis to the patient's BSA and then selecting the largest implantable prosthesis to avoid mismatch. Previously, prosthesis manufacturers have attempted to simplify this process by providing charts that include the expected EOA for their prosthesis, already indexed into an array of BSA values. One caveat with these charts is that the expected EOA data must truly be reliable, or the charts will misguide the implanting surgeon. Manufacturer-provided charts could be improved by standardizing the EOA data, with one potential source being the hemodynamic data submitted to the United States Food and Drug Administration. This review discusses PPM, manufacturer-provided EOA charts, and the regulation of EOA data.

Morphology of the scattering targets: Fresnel and turbulent mechanisms, part 2.1A

NASA Technical Reports Server (NTRS)

Royrvik, O.

1984-01-01

Refractive index fluctuations cause coherent scattering and reflection of VHF radio waves from the clear air in the altitude region between 0 and approximately 90 km. Similar echoes from the stratosphere/troposphere and the mesosphere are observed at UHF and MF/HF frequencies, respectively. The nature of the refractive index fluctuations has been studied for many years without producing a clear consensus on what mechanism causes them. It is believed that the irregularities can originate from two different mechanisms: turbulent mixing of the gradient of refractive index, and stable horizontally stratified laminae of sharp gradients in the refractive index. In order to explain observations of volume dependence and aspect sensitivity of the echo power in the MST region, a diversity of submechanisms has been proposed. They include isotropic and anisotropic turbulent scattering, Fresnel scattering and reflection, and diffuse reflection. Isotropic turbulent scattering is believed to cause a majority of the clear air echoes observed by MST radars. The mechanism requires active turbulence mixing of a preexisting gradient in the refractive index profile.

Bioinspired adaptive gradient refractive index distribution lens

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

Photo-oxidation-modulated refractive index in Bi2Te3 thin films

NASA Astrophysics Data System (ADS)

Yue, Zengji; Chen, Qinjun; Sahu, Amit; Wang, Xiaolin; Gu, Min

2017-12-01

We report on an 800 nm femtosecond laser beam induced giant refractive index modulation and enhancement of near-infrared transparency in topological insulator material Bi2Te3 thin films. An ultrahigh refractive index of up to 5.9 was observed in the Bi2Te3 thin film in near-infrared frequency. The refractive index dramatically decreases by a factor of ~3 by an exposure to the 800 nm femtosecond laser beam. Simultaneously, the transmittance of the Bi2Te3 thin films markedly increases to ~96% in the near-infrared frequency. The Raman spectra provides strong evidences that the observed both refractive index modulation and transparency enhancement result from laser beam induced photooxidation effects in the Bi2Te3 thin films. The Bi2Te3 compound transfers into Bi2O3 and TeO2 under the laser beam illumination. These experimental results pave the way towards the design of various optical devices, such as near-infrared flat lenses, waveguide and holograms, based on topological insulator materials.

Refractive index profilometry using the total internally reflected light field.

PubMed

Das, Tania; Bhattacharya, K

2017-11-20

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

On the scattering directionality of a dielectric particle dimer of High Refractive Index.

PubMed

Barreda, Ángela I; Saleh, Hassan; Litman, Amélie; González, Francisco; Geffrin, Jean-Michel; Moreno, Fernando

2018-05-22

Low-losses and directionality effects exhibited by High Refractive Index Dielectric particles make them attractive for applications where radiation direction control is relevant. For instance, isolated metallo-dielectric core-shell particles or aggregates (dimers) of High Refractive Index Dielectric particles have been proposed for building operational switching devices. Also, the possibility of using isolated High Refractive Index Dielectric particles for optimizing solar cells performance has been explored. Here, we present experimental evidence in the microwave range, that a High Refractive Index Dielectric dimer of spherical particles is more efficient for redirecting the incident radiation in the forward direction than the isolated case. In fact, we report two spectral regions in the dipolar spectral range where the incident intensity is mostly scattered in the forward direction. They correspond to the Zero-Backward condition (also observed for isolated particles) and to a new condition, denoted as "near Zero-Backward" condition, which comes from the interaction effects between the particles. The proposed configuration has implications in solar energy harvesting devices and in radiation guiding.

Numerical Approach to Modeling and Characterization of Refractive Index Changes for a Long-Period Fiber Grating Fabricated by Femtosecond Laser

PubMed Central

Saad, Akram; Cho, Yonghyun; Ahmed, Farid; Jun, Martin Byung-Guk

2016-01-01

A 3D finite element model constructed to predict the intensity-dependent refractive index profile induced by femtosecond laser radiation is presented. A fiber core irradiated by a pulsed laser is modeled as a cylinder subject to predefined boundary conditions using COMSOL5.2 Multiphysics commercial package. The numerically obtained refractive index change is used to numerically design and experimentally fabricate long-period fiber grating (LPFG) in pure silica core single-mode fiber employing identical laser conditions. To reduce the high computational requirements, the beam envelope method approach is utilized in the aforementioned numerical models. The number of periods, grating length, and grating period considered in this work are numerically quantified. The numerically obtained spectral growth of the modeled LPFG seems to be consistent with the transmission of the experimentally fabricated LPFG single mode fiber. The sensing capabilities of the modeled LPFG are tested by varying the refractive index of the surrounding medium. The numerically obtained spectrum corresponding to the varied refractive index shows good agreement with the experimental findings. PMID:28774060

Numerical Approach to Modeling and Characterization of Refractive Index Changes for a Long-Period Fiber Grating Fabricated by Femtosecond Laser.

PubMed

Saad, Akram; Cho, Yonghyun; Ahmed, Farid; Jun, Martin Byung-Guk

2016-11-21

A 3D finite element model constructed to predict the intensity-dependent refractive index profile induced by femtosecond laser radiation is presented. A fiber core irradiated by a pulsed laser is modeled as a cylinder subject to predefined boundary conditions using COMSOL5.2 Multiphysics commercial package. The numerically obtained refractive index change is used to numerically design and experimentally fabricate long-period fiber grating (LPFG) in pure silica core single-mode fiber employing identical laser conditions. To reduce the high computational requirements, the beam envelope method approach is utilized in the aforementioned numerical models. The number of periods, grating length, and grating period considered in this work are numerically quantified. The numerically obtained spectral growth of the modeled LPFG seems to be consistent with the transmission of the experimentally fabricated LPFG single mode fiber. The sensing capabilities of the modeled LPFG are tested by varying the refractive index of the surrounding medium. The numerically obtained spectrum corresponding to the varied refractive index shows good agreement with the experimental findings.

Artificial dielectric stepped-refractive-index lens for the terahertz region.

PubMed

Hernandez-Serrano, A I; Mendis, Rajind; Reichel, Kimberly S; Zhang, Wei; Castro-Camus, E; Mittleman, Daniel M

2018-02-05

In this paper we theoretically and experimentally demonstrate a stepped-refractive-index convergent lens made of a parallel stack of metallic plates for terahertz frequencies based on artificial dielectrics. The lens consist of a non-uniformly spaced stack of metallic plates, forming a mirror-symmetric array of parallel-plate waveguides (PPWGs). The operation of the device is based on the TE 1 mode of the PPWG. The effective refractive index of the TE 1 mode is a function of the frequency of operation and the spacing between the plates of the PPWG. By varying the spacing between the plates, we can modify the local refractive index of the structure in every individual PPWG that constitutes the lens producing a stepped refractive index profile across the multi stack structure. The theoretical and experimental results show that this structure is capable of focusing a 1 cm diameter beam to a line focus of less than 4 mm for the design frequency of 0.18 THz. This structure shows that this artificial-dielectric concept is an important technology for the fabrication of next generation terahertz devices.

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.

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.

Investigating the transverse optical structure of spider silk micro-fibers using quantitative optical microscopy

NASA Astrophysics Data System (ADS)

Little, Douglas J.; Kane, Deb M.

2017-01-01

The transverse optical structure of two orb-weaver (family Araneidae) spider dragline silks was investigated using a variant of the inverse-scattering technique. Immersing the silks in a closely refractive index-matched liquid, the minimum achievable image contrast was greater than expected for an optically homogeneous silk, given what is currently known about the optical absorption of these silks. This "excess contrast" indicated the presence of transverse optical structure within the spider silk. Applying electromagnetic scattering theory to a transparent double cylinder, the minimum achievable irradiance contrast for the Plebs eburnus and Argiope keyserlingi dragline silks was determined to be consistent with step index refractive index contrasts of 1-4×10-4 and 6-7×10-4, respectively, supposing outer-layer thicknesses consistent with previous TEM studies (50 nm and 100 nm, respectively). The possibility of graded index refractive index contrasts within the spider silks is also discussed. This is the strongest evidence, to date, that there is a refractive index contrast associated with the layered morphology of spider silks and/or variation of proportion of nanocrystalline components within the spider silk structure. The method is more generally applicable to optical micro-fibers, including those with refractive index variations on a sub-wavelength scale.

[Relationship between the refractive index and specific gravity of the rat urine (author's transl)].

PubMed

Kitagawa, Y F; Takahashi, T; Hayashi, H

1981-07-01

The relationship between the refractive index and specific gravity of urine was studied with specimens from 165 Sprague-Dawley rats, by graphic analysis of the plot of the refractometrically determined index against the specific gravity which was measured with a pycnometer. 1. A linear regression was demonstrated between the refractive index and specific gravity. 2. The nomogram fitted the data of even those samples with high refractive index and specific gravity, irrespective of changes in food or water intake and protein or glucose contents in the urine. 3. The nomogram was in good agreement, in respect of linearity, with the regression line derived from the conversion table of TS meter by the American Optical Corporation and also with the nomogram of the Japanese Society of Clinical Pathology. It approximated more closely to the former than to the latter.

Optical coatings of variable refractive index and high laser-resistance from physical-vapor-deposited perfluorinated amorphous polymer

DOEpatents

Chow, R.; Loomis, G.E.; Thomas, I.M.

1999-03-16

Variable index optical single-layers, optical multilayer, and laser-resistant coatings were made from a perfluorinated amorphous polymer material by physical vapor deposition. This was accomplished by physically vapor depositing a polymer material, such as bulk Teflon AF2400, for example, to form thin layers that have a very low refractive index (ca. 1.10--1.31) and are highly transparent from the ultra-violet through the near infrared regime, and maintain the low refractive index of the bulk material. The refractive index can be varied by simply varying one process parameter, either the deposition rate or the substrate temperature. The thus forming coatings may be utilized in anti-reflectors and graded anti-reflection coatings, as well as in optical layers for laser-resistant coatings at optical wavelengths of less than about 2000 nm. 2 figs.

Optical parameters of the tunable Bragg reflectors in squid.

PubMed

Ghoshal, Amitabh; Demartini, Daniel G; Eck, Elizabeth; Morse, Daniel E

2013-08-06

Cephalopods (e.g. octopus, squid and cuttlefish) dynamically tune the colour and brightness of their skin for camouflage and communication using specialized skin cells called iridocytes. We use high-resolution microspectrophotometry to investigate individual tunable Bragg structures (consisting of alternating reflectin protein-containing, high-refractive index lamellae and low-refractive index inter-lamellar spaces) in live and chemically fixed iridocytes of the California market squid, Doryteuthis opalescens. This subcellular, single-stack microspectrophotometry allows for spectral normalization, permitting use of a transfer-matrix model of Bragg reflectance to calculate all the parameters of the Bragg stack-the refractive indices, dimensions and numbers of the lamellae and inter-lamellar spaces. Results of the fitting analyses show that eight or nine pairs of low- and high-index layers typically contribute to the observed reflectivity in live cells, whereas six or seven pairs of low- and high-index layers typically contribute to the reflectivity in chemically fixed cells. The reflectin-containing, high-index lamellae of live cells have a refractive index proportional to the peak reflectivity, with an average of 1.405 ± 0.012 and a maximum around 1.44, while the reflectin-containing lamellae in fixed tissue have a refractive index of 1.413 ± 0.015 suggesting a slight increase of refractive index in the process of fixation. As expected, incremental changes in refractive index contribute to the greatest incremental changes in reflectivity for those Bragg stacks with the most layers. The excursions in dimensions required to tune the measured reflected wavelength from 675 (red) to 425 nm (blue) are a decrease from ca 150 to 80 nm for the high-index lamellae and from ca 120 to 50 nm for the low-index inter-lamellar spaces. Fixation-induced dimensional changes also are quantified, leading us to suggest that further microspectrophotometric analyses of this iridocyte system can be used as a model system to quantify the effects of various methods of tissue fixation. The microspectrophotometry technique described can be expected to provide deeper insights into the molecular and physical mechanisms governing other biophotonically active cells and structures.

Optical parameters of the tunable Bragg reflectors in squid

PubMed Central

Ghoshal, Amitabh; DeMartini, Daniel G.; Eck, Elizabeth; Morse, Daniel E.

2013-01-01

Cephalopods (e.g. octopus, squid and cuttlefish) dynamically tune the colour and brightness of their skin for camouflage and communication using specialized skin cells called iridocytes. We use high-resolution microspectrophotometry to investigate individual tunable Bragg structures (consisting of alternating reflectin protein-containing, high-refractive index lamellae and low-refractive index inter-lamellar spaces) in live and chemically fixed iridocytes of the California market squid, Doryteuthis opalescens. This subcellular, single-stack microspectrophotometry allows for spectral normalization, permitting use of a transfer-matrix model of Bragg reflectance to calculate all the parameters of the Bragg stack—the refractive indices, dimensions and numbers of the lamellae and inter-lamellar spaces. Results of the fitting analyses show that eight or nine pairs of low- and high-index layers typically contribute to the observed reflectivity in live cells, whereas six or seven pairs of low- and high-index layers typically contribute to the reflectivity in chemically fixed cells. The reflectin-containing, high-index lamellae of live cells have a refractive index proportional to the peak reflectivity, with an average of 1.405 ± 0.012 and a maximum around 1.44, while the reflectin-containing lamellae in fixed tissue have a refractive index of 1.413 ± 0.015 suggesting a slight increase of refractive index in the process of fixation. As expected, incremental changes in refractive index contribute to the greatest incremental changes in reflectivity for those Bragg stacks with the most layers. The excursions in dimensions required to tune the measured reflected wavelength from 675 (red) to 425 nm (blue) are a decrease from ca 150 to 80 nm for the high-index lamellae and from ca 120 to 50 nm for the low-index inter-lamellar spaces. Fixation-induced dimensional changes also are quantified, leading us to suggest that further microspectrophotometric analyses of this iridocyte system can be used as a model system to quantify the effects of various methods of tissue fixation. The microspectrophotometry technique described can be expected to provide deeper insights into the molecular and physical mechanisms governing other biophotonically active cells and structures. PMID:23740489

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.

Index of refraction of GaAs-Al(x)Ga(1-x)As superlattices and multiple quantum wells

NASA Technical Reports Server (NTRS)

Kahen, K. B.; Leburton, J. P.

1987-01-01

A theoretical study of the index of refraction of superlattices and its variation as a function of frequency and the superlattice parameters, i.e., layer width and AlAs composition, is presented. Gamma-region exciton and valence-band mixing effects are included in the model. It is found that these two effects have an important influence on the value of the index of refraction and that superstructure effects rapidly decrease for energies greater than the superlattice potential barriers. Because of the quasi-two-dimensional character of the Gamma-region excitons, the results indicate that the superlattice index of refraction can vary by about two percent at the quantized, bound-exciton, transition energies. Overall, the theoretical results are in good agreement with the experimental data.

Refractive index of B1-xGaxN semiconductors

NASA Astrophysics Data System (ADS)

Vyas, P. S.; Baria, J. K.; Jivani, A. R.; Gajjar, P. N.; Jani, A. R.

2013-06-01

A theoretical procedure is presented for the study of refractive index of ternary alloy B1-xGaxN. The calculations based on the pseudopotential formalism in which local potential coupled with the virtual crystal approximation (VCA) is applied to evaluate energy band gap at point X on the Jones-zone face, refractive index for the entire range of the alloy composition x of the ternary alloy B1-xGaxN. To include exchange and correlation effects, local field correction function due to Nagy is employed. Our results for parent compounds are compared to experiment and other available theoretical findings and showed generally good agreement. During present study it is found that the refractive index of the ternary alloy B1-xGaxN has minimum value at gallium concentration x = 0.4.

Numerical study on refractive index sensor based on hybrid-plasmonic mode

NASA Astrophysics Data System (ADS)

Yun, Jeong-Geun; Kim, Joonsoo; Lee, Kyookeun; Lee, Yohan; Lee, Byoungho

2017-04-01

We propose a highly sensitive hybrid-plasmonic sensor based on thin-gold nanoslit arrays. The transmission characteristics of gold nanoslit arrays are analyzed as changing the thickness of gold layer. The surface plasmon polariton mode excited on the sensing medium, which is sensitive to refractive index change of the sensing medium, is strengthened by reducing the thickness of the gold layer. A design rule is suggested that steeper dispersion curve of the surface plasmon polariton mode leads to higher sensitivity. For the dispersion engineering, hybrid-plasmonic structure, which consists of thin-gold nanoslit arrays, sensing region and high refractive index dielectric space is introduced. The proposed sensor structure with period of 700 nm shows the improved sensitivity up to 1080 nm/RIU (refractive index unit), and the surface sensitivity is extremely enhanced.

Omnidirectional optical waveguide

DOEpatents

Bora, Mihail; Bond, Tiziana C.

2016-08-02

In one embodiment, a system includes a scintillator material; a detector coupled to the scintillator material; and an omnidirectional waveguide coupled to the scintillator material, the omnidirectional waveguide comprising: a plurality of first layers comprising one or more materials having a refractive index in a first range; and a plurality of second layers comprising one or more materials having a refractive index in a second range, the second range being lower than the first range, a plurality of interfaces being defined between alternating ones of the first and second layers. In another embodiment, a method includes depositing alternating layers of a material having a relatively high refractive index and a material having a relatively low refractive index on a substrate to form an omnidirectional waveguide; and coupling the omnidirectional waveguide to at least one surface of a scintillator material.

Emittance of a finite scattering medium with refractive index greater than unity

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

Crosbie, A.L.

1980-01-01

Refractive index and scattering can significantly influence the transfer of radiation in a semitransparent medium such as water, glass, plastics, or ceramics. In a recent article (1979), the author presented exact numerical results for the emittance of a semiinfinite scattering medium with a refractive index greater than unity. The present investigation extends the analysis to a finite medium. The physical situation consists of a finite planar layer. The isothermal layer emits, absorbs, and isotropically scatters thermal radiation. It is characterized by single scattering albedo, optical thickness, refractive index, and temperature. A formula for the directional emittance is derived, the directionalmore » emittance being the emittance of the medium multiplied by the interface transmittance. The ratio of hemispherical to normal emittance is tabulated and discussed.« less

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.

Smart design of a long-period fiber grating refractive index sensor based on dual-peak resonance near the phase-matching turning point.

PubMed

Ling, Qiang; Gu, Zhengtian; Gao, Kan

2018-04-01

This paper presents a smart design way for the long-period fiber grating (LPFG) refractive index sensor, which is based on high sensitivity of LPFG near phase-matching turning point (PMTP) to the surrounding refractive index (SRI). On the basis of the coupled mode theory of LPFG, cladding etching and film coating have opposite effects on the shift of the dual peaks. Therefore, an LPFG can be controlled by the cladding etching and film coating successively, until it operates near PMTP. Experimentally, an LPFG operating near PMTP was fabricated, and the glycerol solution concentration monitoring test was performed. The results show that the sensitivity of this LPFG to the SRI is as high as 5602 nm/refractive index unit.

Zero-order bows in radially inhomogeneous spheres: direct and inverse problems.

PubMed

Adam, John A

2011-10-01

Zero-order ray paths are examined in radially inhomogeneous spheres with differentiable refractive index profiles. It is demonstrated that zero-order and sometimes twin zero-order bows can exist when the gradient of refractive index is sufficiently negative. Abel inversion is used to "recover" the refractive index profiles; it is therefore possible in principle to specify the nature and type of bows and determine the refractive index profile that induces them. This may be of interest in the field of rainbow refractometry and optical fiber studies. This ray-theoretic analysis has direct similarities with the phenomenon of "orbiting" and other phenomena in scattering theory and also in seismological, surface gravity wave, and gravitational "lensing" studies. For completeness these topics are briefly discussed in the appendixes; they may also be of pedagogic interest.

Refractive index sensor based on plastic optical fiber with tapered structure.

PubMed

De-Jun, Feng; Guan-Xiu, Liu; Xi-Lu, Liu; Ming-Shun, Jiang; Qing-Mei, Sui

2014-04-01

This work reports a refractive index sensor made of plastic optical fiber (POF) with tapered structure. Transmission loss is measured when the external environment's refractive index changes from 1.33 to 1.41. Three wavelengths (532, 633, and 780 nm) are used to evaluate the sensitivity of the sensor, and results indicate that 633 nm is the best sensing wavelength due to the increased levels of sensitivity achieved at this wavelength. A biconical sensing structure is designed to enhance the sensitivity of the sensor. A sensitivity of 950 μW/RIU at 633 nm is obtained for a biconical sensing structure when launched power is 1 mW. Due to its sensitivity to the refractive index and simple construction, POF with tapered structure has potential applications in the biosensing field.

Fiber optic refractive index sensor using optofluidic anti-resonant reflecting guidance

NASA Astrophysics Data System (ADS)

Gao, Ran; Lu, Danfeng; Cheng, Jin; Qi, Zhi-mei

2017-10-01

An optofluidic anti-resonant reflecting guidance has been proposed and experimental demonstrated for the measurement of liquid refractive index. Two micro-channels were fabricated for the delivery of the liquid sample in the hollow core photonic crystal fiber by using femtosecond laser micromachining, serving as an inlet and outlet. The refractive index can be detected by using the resonant condition of the Fabry-Perot resonator, which is interrogated through the wavelength shift and of the lossy dip in the transmission spectrum. The experimental results show that the sensitivity of up to 1328 nm/RIU is achieved for the refractive index in the range from 1.345 to 1.363 RIU, respectively. The proposed sensor appears to have potential applications of precise measurement in chemistry, medicine, and biology.

Tilted Fiber Bragg Grating photowritten in microstructured optical fiber for improved refractive index measurement.

PubMed

Phan Huy, Minh Châu; Laffont, Guillaume; Dewynter, Véronique; Ferdinand, Pierre; Labonté, Laurent; Pagnoux, Dominique; Roy, Philippe; Blanc, Wilfried; Dussardier, Bernard

2006-10-30

We report what we believe to be the first Tilted short-period Fiber Bragg Grating photowritten in a microstructured optical fiber for refractive index measurement. We investigate the spectral sensitivity of Tilted Fiber Bragg Grating to refractive index liquid inserted into the holes of a multimode microstructured fiber. We measure the wavelength shift of the first four modes experimentally observed when calibrated oils are inserted into the fiber holes, and thus we determine the refractive index resolution for each of these modes. Moreover, a cross comparison between experimental and simulation results of a modal analysis is performed. Two simulation tools are used, respectively based on the localized functions method and on a finite element method. All results are in very good agreement.

Determination of the refractive index and thickness of holographic silver halide materials by use of polarized reflectances.

PubMed

Beléndez, Augusto; Beléndez, Tarsicio; Neipp, Cristian; Pascual, Inmaculada

2002-11-10

A method to determine the refractive index and thickness of silver halide emulsions used in holography is presented. The emulsions are in the form of a layer of film deposited on a thick glass plate. The experimental reflectances of p-polarized light are measured as a function of the incident angles, and the values of refractive index, thickness, and extinction coefficient of the emulsion are obtained by using the theoretical equation for reflectance. As examples, five commercial holographic silver halide emulsions are analyzed. The procedure to obtain the measurements and the numerical analysis of the experimental data are simple, and agreement of the calculated reflectances, by use of the thickness and refractive index obtained, with the measured reflectances is satisfactory.

Comparative study of quantitative phase imaging techniques for refractometry of optical fibers

NASA Astrophysics Data System (ADS)

de Dorlodot, Bertrand; Bélanger, Erik; Bérubé, Jean-Philippe; Vallée, Réal; Marquet, Pierre

2018-02-01

The refractive index difference profile of optical fibers is the key design parameter because it determines, among other properties, the insertion losses and propagating modes. Therefore, an accurate refractive index profiling method is of paramount importance to their development and optimization. Quantitative phase imaging (QPI) is one of the available tools to retrieve structural characteristics of optical fibers, including the refractive index difference profile. Having the advantage of being non-destructive, several different QPI methods have been developed over the last decades. Here, we present a comparative study of three different available QPI techniques, namely the transport-of-intensity equation, quadriwave lateral shearing interferometry and digital holographic microscopy. To assess the accuracy and precision of those QPI techniques, quantitative phase images of the core of a well-characterized optical fiber have been retrieved for each of them and a robust image processing procedure has been applied in order to retrieve their refractive index difference profiles. As a result, even if the raw images for all the three QPI methods were suffering from different shortcomings, our robust automated image-processing pipeline successfully corrected these. After this treatment, all three QPI techniques yielded accurate, reliable and mutually consistent refractive index difference profiles in agreement with the accuracy and precision of the refracted near-field benchmark measurement.

Simultaneous measurements of radar reflectivity and refractive index spectra in clear air convection.

NASA Technical Reports Server (NTRS)

Konrad, T. G.; Robison, F. L.

1972-01-01

Simultaneous measurements of radar reflectivity and radio refractive index at several altitudes in clear air convection have been made. The experimental data were compared with the theoretical relationship which relates the reflectivity to the refractivity spectrum. The agreement between the measurements and the theory is excellent and shows that the radar returns in clear air are the result of, and can be quantitatively described as being from, fine-scale refractivity fluctuations due to turbulent mixing. Further, the data give strong support to the -5/3 spectral decay of the refractivity spectrum in the inertial subrange.

Index of refraction, density, and solubility of ammonium iodide solutions at high pressure.

PubMed

Lamelas, F J

2013-03-07

An asymmetric moissanite anvil cell is used to study aqueous solutions of ammonium iodide at pressures up to 10 kbar. The index of refraction is measured using the rotating Fabry-Perot technique, with an accuracy of approximately 1%. The mass density and molar volume of the solutions are estimated using the measured index values, and the molar volume is used to predict the pressure dependence of the solubility. The solubility derived from the index of refraction measurements is shown to agree with that which is determined by direct observation of the onset of crystallization.

Stressed waveguides with tubular depressed-cladding inscribed in phosphate glasses by femtosecond hollow laser beams.

PubMed

Long, Xuewen; Bai, Jing; Zhao, Wei; Stoian, Razvan; Hui, Rongqing; Cheng, Guanghua

2012-08-01

We report on the single-step fabrication of stressed optical waveguides with tubular depressed-refractive-index cladding in phosphate glasses by the use of focused femtosecond hollow laser beams. Tubelike low index regions appear under direct exposure due to material rarefaction following expansion. Strained compacted zones emerged in domains neighboring the tubular track of lower refractive index, and waveguiding occurs mainly within the tube core fabricated by the engineered femtosecond laser beam. The refractive index profile of the optical waveguide was reconstructed from the measured transmitted near-field intensity.

The relationship between the retinal image quality and the refractive index of defects arising in IOL: numerical analysis

NASA Astrophysics Data System (ADS)

Geniusz, Malwina

2017-09-01

The best treatment for cataract patients, which allows to restore clear vision is implanting an artificial intraocular lens (IOL). The image quality of the lens has a significant impact on the quality of patient's vision. After a long exposure the implant to aqueous environment some defects appear in the artificial lenses. The defects generated in the IOL have different refractive indices. For example, glistening phenomenon is based on light scattering on the oval microvacuoles filled with an aqueous humor which refractive index value is about 1.34. Calcium deposits are another example of lens defects and they can be characterized by the refractive index 1.63. In the presented studies it was calculated how the difference between the refractive indices of the defect and the refractive index of the lens material affects the quality of image. The OpticStudio Professional program (from Radiant Zemax, LLC) was used for the construction of the numerical model of the eye with IOL and to calculate the characteristics of the retinal image. Retinal image quality was described in such characteristics as Point Spread Function (PSF) and the Optical Transfer Function with amplitude and phase. The results show a strong correlation between the refractive indices difference and retinal image quality.

Proposal to Produce Novel, Transparent Radiation Hard Low Refractive Index

DTIC Science & Technology

1994-02-09

or ainy nht.at NX ftU 1.AECY USE a EP....3RFPfT TYP’E AND DATES~ COV-ERED-- 4. TITLE AND SUBTITLE . . FjUNDING NUMBERS PROPOSAL TO PRODUCE NOVEL...cladding use . our research resulted in identifying a radiation hard, low refractive index polymer, poly (heptafluorobutyl methacrylate), P(MFBM) as the best...candidate for a novel ~. cladding material. P(HFB) has a refractive index of 1.387. When used to clada styrene core, the theoretical light propagation

Concentration dependences of the density, viscosity, and refraction index of Cu(NO3)2 · 3H2O solutions in DMSO at 298 K

NASA Astrophysics Data System (ADS)

Mamyrbekova, A. K.

2013-03-01

Physicochemical properties (density, dynamic viscosity, refraction index) of the DMSO-Cu(NO3)2 · 3H2O system are studied in the concentration range of 0.01-2 M at 298 K. The refraction index of a solution of copper(II) nitrate in dimethylsulfoxide (DMSO) is measured at 288-318 K. The excess and partial molar volumes of the solvent and dissolved substance are calculated analytically.

Mach-Zehnder Interferometer Refractive Index Sensor Based on a Plasmonic Channel Waveguide

PubMed Central

Lee, Da Eun; Lee, Young Jin; Shin, Eunso; Kwon, Soon-Hong

2017-01-01

A Mach-Zehnder interferometer based on a plasmonic channel waveguide is proposed for refractive index sensing. The structure, with a small physical footprint of 20 × 120 μm2, achieved a high figure of merit of 294. The cut-off frequency behaviour in the plasmonic channel waveguide resulted in a flat dispersion curve, which induces a 1.8 times larger change of the propagation constant for the given refractive index change compared with previously reported results. PMID:29120381

Optical sensing of concentration and refractive index of pigments in a suspension.

PubMed

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

2010-06-10

We describe an immersion liquid and data analysis method for the simultaneous determination of the refractive index and concentration of pigments by measurement of light transmission of suspensions. A new innovation is that, in the event that two different pigments are simultaneously present in a suspension, it is possible to detect the refractive index of an unknown pigment with the aid of half-width of transmittance and, furthermore, to obtain the concentration of the unknown pigment.

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

PubMed

Friebel, Moritz; Meinke, Martina

2006-04-20

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

Measurement of refractive index of hemoglobin in the visible/NIR spectral range

NASA Astrophysics Data System (ADS)

Lazareva, Ekaterina N.; Tuchin, Valery V.

2018-03-01

This study is focused on the measurements of the refractive index of hemoglobin solutions in the visible/near-infrared (NIR) spectral range at room temperature for characteristic laser wavelengths: 480, 486, 546, 589, 644, 656, 680, 930, 1100, 1300, and 1550 nm. Measurements were performed using the multiwavelength Abbe refractometer. Aqua hemoglobin solutions of different concentrations obtained from human whole blood were investigated. The specific increment of refractive index on hemoglobin concentration and the Sellmeier coefficients were calculated.

Electronic polarizability of light crude oil from optical and dielectric studies

NASA Astrophysics Data System (ADS)

George, A. K.; Singh, R. N.

2017-07-01

In the present paper we report the temperature dependence of density, refractive indices and dielectric constant of three samples of crude oils. The API gravity number estimated from the temperature dependent density studies revealed that the three samples fall in the category of light oil. The measured data of refractive index and the density are used to evaluate the polarizability of these fluids. Molar refractive index and the molar volume are evaluated through Lorentz-Lorenz equation. The function of the refractive index, FRI , divided by the mass density ρ, is a constant approximately equal to one-third and is invariant with temperature for all the samples. The measured values of the dielectric constant decrease linearly with increasing temperature for all the samples. The dielectric constant estimated from the refractive index measurements using Lorentz-Lorentz equation agrees well with the measured values. The results are promising since all the three measured properties complement each other and offer a simple and reliable method for estimating crude oil properties, in the absence of sufficient data.

Simultaneous monitoring the real and imaginary parts of the analyte refractive index using liquid-core photonic bandgap Bragg fibers.

PubMed

Li, Jingwen; Qu, Hang; Skorobogatiy, Maksim

2015-09-07

We demonstrate simultaneous monitoring of the real and imaginary parts of the liquid analyte refractive index by using a hollow-core Bragg fiber. We apply this two-channel fiber sensor to monitor concentrations of various commercial cooling oils. The sensor operates using spectral monitoring of the fiber bandgap center wavelength, as well as monitoring of the fiber transmission amplitude at mid-bandgap position. The sensitivity of the fiber sensor to changes in the real part of the core refractive index is found to be 1460nm/Refractive index unit (RIU). By using spectral modality and effective medium theory, we determine the concentrations of the two commercial fluids from the measured refractive indices with an accuracy of ~0.57% for both low- and high-loss oils. Moreover, using an amplitude-based detection modality allows determination of the oil concentration with accuracy of ~1.64% for low-loss oils and ~2.81% for the high-loss oils.

Negative index effects from a homogeneous positive index prism

NASA Astrophysics Data System (ADS)

Marcus, Sherman W.; Epstein, Ariel

2017-12-01

Cellular structured negative index metamaterials in the form of a right triangular prism have often been tested by observing the refraction of a beam across the prism hypotenuse which is serrated in order to conform to the cell walls. We show that not only can this negative index effect be obtained from a homogeneous dielectric prism having a positive index of refraction, but in addition, for sampling at the walls of the cellular structure, the phase in the material has the illusory appearance of moving in a negative direction. Although many previous reports relied on refraction direction and phase velocity of prism structures to verify negative index design, our investigation indicates that to unambiguously demonstrate material negativity additional empirical evidence is required.

Resonant infrared laser deposition of polymer-nanocomposite materials for optoelectronic applications

NASA Astrophysics Data System (ADS)

Park, Hee K.; Schriver, Kenneth E.; Haglund, Richard F.

2011-11-01

Polymers find a number of potentially useful applications in optoelectronic devices. These include both active layers, such as light-emitting polymers and hole-transport layers, and passive layers, such as polymer barrier coatings and light-management films. This paper reports the experimental results for polymer films deposited by resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) and resonant infrared pulsed laser deposition (RIR-PLD) for commercial optoelectronic device applications. In particular, light-management films, such as anti-reflection coatings, require refractive-index engineering of a material. However, refractive indices of polymers fall within a relatively narrow range, leading to major efforts to develop both low- and high-refractive-index polymers. Polymer nanocomposites can expand the range of refractive indices by incorporating low- or high-refractive-index nanoscale materials. RIR-MAPLE is an excellent technique for depositing polymer-nanocomposite films in multilayer structures, which are essential to light-management coatings. In this paper, we report our efforts to engineer the refractive index of a barrier polymer by combining RIR-MAPLE of nanomaterials (for example, high refractive-index TiO2 nanoparticles) and RIR-PLD of host polymer. In addition, we report on the properties of organic and polymer films deposited by RIR-MAPLE and/or RIR-PLD, such as Alq3 [tris(8-hydroxyquinoline) aluminum] and PEDOT:PSS [poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)]. Finally, the challenges and potential for commercializing RIR-MAPLE/PLD, such as industrial scale-up issues, are discussed.

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.

The gradient index lens of the eye: an opto-biological synchrony.

PubMed

Pierscionek, Barbara K; Regini, Justyn W

2012-07-01

The refractive power of a lens is determined largely by its surface curvatures and the refractive index of its medium. These properties can also be used to control the sharpness of focus and hence the image quality. One of the most effective ways of doing this is with a gradient index. Eye lenses of all species, thus far, measured, are gradient index (GRIN) structures. The index gradation is one that increases from the periphery of the lens to its centre but the steepness of the gradient and the magnitudes of the refractive index vary so that the optics of the lens accords with visual demands. The structural proteins, the crystallins, which create the index gradient, also vary from species to species, in type and relative distribution across the tissue. The crystallin classes do not contribute equally to the refractive index, and this may be related to their structure and amino acid content. This article compares GRIN forms in eye lenses of varying species, the relevance of these forms to visual requirements, and the relationship between refractive index and the structural proteins. Consideration is given to the dynamics of a living lens, potential variations in the GRIN form with physiological changes and the possible link between discontinuities in the gradient and growth. Finally, the property of birefringence and the characteristic polarisation patterns seen in highly ordered crystals that have also been observed in specially prepared eye lenses are described and discussed. Copyright © 2012 Elsevier Ltd. All rights reserved.

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.

Negative refractive index metamaterial with high transmission, low reflection, and low loss in the terahertz waveband.

PubMed

Suzuki, Takehito; Sekiya, Masashi; Sato, Tatsuya; Takebayashi, Yuki

2018-04-02

The refractive index is a basic parameter of materials which it is essential to know for the manipulation of electromagnetic waves. However, there are no naturally occurring materials with negative refractive indices, and high-performance materials with negative refractive indices and low losses are demanded in the terahertz waveband. In this paper, measurements by terahertz time-domain spectroscopy (THz-TDS) demonstrate a metamaterial with a negative refractive index n of -4.2 + j0.17, high transmitted power of 81.5%, low reflected power of 4.3%, and a high figure of merit (FOM = |Re(n)/Im(n)|) of 24.2 at 0.42 THz. The terahertz metamaterial with these unprecedented properties can provide various attractive terahertz applications such as superlenses with resolutions beyond the diffraction limit in terahertz continuous wave imaging.

Bifocal optical coherenc refractometry of turbid media.

PubMed

Alexandrov, Sergey A; Zvyagin, Andrei V; Silva, K K M B Dilusha; Sampson, David D

2003-01-15

We propose and demonstrate a novel technique, which we term bifocal optical coherence refractometry, for the rapid determination of the refractive index of a turbid medium. The technique is based on the simultaneous creation of two closely spaced confocal gates in a sample. The optical path-length difference between the gates is measured by means of low-coherence interferometry and used to determine the refractive index. We present experimental results for the refractive indices of milk solutions and of human skin in vivo. As the axial scan rate determines the acquisition time, which is potentially of the order of tens of milliseconds, the technique has potential for in vivo refractive-index measurements of turbid biological media under dynamic conditions.

In situ measurement method for film thickness using transparency resin sheet with low refractive index under wet condition on chemical mechanical polishing

NASA Astrophysics Data System (ADS)

Oniki, Takahiro; Khajornrungruang, Panart; Suzuki, Keisuke

2017-07-01

We suggest that a transparency resin sheet with low refractive index can be applied to the measurement of a silicon dioxide (SiO2) film on a silicon wafer under wet condition for a film thickness measurement system on chemical mechanical polishing (CMP). By adjusting the refractive indices of the resin sheet and water, stable measurements of the SiO2 film can be expected, irrespective of slurry film thickness fluctuation because it has robustness against the slurry film. This result indicates that the transparency resin sheet with low refractive index is a useful for monitoring system of CMP.

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

PubMed

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

2010-05-01

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

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

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

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

2016-08-15

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

Astigmatism of the Ex Vivo Human Lens: Surface and Gradient Refractive Index Age-Dependent Contributions.

PubMed

Birkenfeld, Judith; de Castro, Alberto; Marcos, Susana

2015-08-01

We estimated the contribution of the gradient refractive index (GRIN) and lens surfaces to lens astigmatism and lens astigmatic angle as a function of age in human donor lenses. Human lenses were imaged, ex vivo, with 3D-spectral optical coherence tomography (OCT) and their back focal length was measured using laser ray tracing. The contribution of lens surfaces and GRIN to lens astigmatism were evaluated by computational ray tracing on the GRIN lens and a homogenous equivalent index lens. Astigmatism magnitude and relative astigmatic angle of and between lens surfaces, GRIN lens, and lens with homogeneous refractive index were evaluated, and all results were correlated with age. The magnitude of astigmatism in the anterior lens surface decreased with age (slope = -0.005 diopters [D]/y; r = 0.397, P = 0.018). Posterior surface astigmatism and lens astigmatism were not age-dependent. Presence of GRIN did not alter significantly the magnitude or axis of the lens astigmatism. The astigmatism of GRIN lens and lens with homogeneous refractive index correlated with anterior lens surface astigmatism (GRIN, P = 3.9E - 6, r = 0.693; equivalent refractive index lens, P = 4.1E - 4, r = 0.565). The astigmatic angle of posterior surface, GRIN lens, and homogeneous refractive index lens did not change significantly with age. The axis of lens astigmatism is close to the astigmatic axis of the anterior lens surface. Age-related changes in lens astigmatism appear to be related to changes in the anterior lens astigmatism. The influence of the GRIN on lens astigmatism and the astigmatic axis is minor.

Determining the Thickness and Refractive Index of a Mirror

ERIC Educational Resources Information Center

Uysal, Ahmet

2010-01-01

When a laser beam reflects from a back surface glass mirror and falls on a screen, a pattern of discrete bright spots is created by partial reflection and refraction of the light at the air-glass interface and reflection at the mirror surface (Fig. 1). This paper explains how this phenomenon can be used to determine the refractive index and the…

An investigation of matched index of refraction technique and its application in optical measurements of fluid flow

NASA Astrophysics Data System (ADS)

Amini, Noushin; Hassan, Yassin A.

2012-12-01

Optical distortions caused by non-uniformities of the refractive index within the measurement volume is a major impediment for all laser diagnostic imaging techniques applied in experimental fluid dynamic studies. Matching the refractive indices of the working fluid and the test section walls and interfaces provides an effective solution to this problem. The experimental set-ups designed to be used along with laser imaging techniques are typically constructed of transparent solid materials. In this investigation, different types of aqueous salt solutions and various organic fluids are studied for refractive index matching with acrylic and fused quartz, which are commonly used in construction of the test sections. One aqueous CaCl2·2H2O solution (63 % by weight) and two organic fluids, Dibutyl Phthalate and P-Cymene, are suggested for refractive index matching with fused quartz and acrylic, respectively. Moreover, the temperature dependence of the refractive indices of these fluids is investigated, and the Thermooptic Constant is calculated for each fluid. Finally, the fluid viscosity for different shear rates is measured as a function of temperature and is applied to characterize the physical behavior of the proposed fluids.

The molecular refractive function of lens γ-crystallins

PubMed Central

Zhao, Huaying; Brown, Patrick H.; Magone, M. Teresa; Schuck, Peter

2011-01-01

γ-crystallins constitute the major protein component in the nucleus of the vertebrate eye lens. Present at very high concentrations, they exhibit extreme solubility and thermodynamic stability to prevent scattering of light and the formation of cataracts. However, functions beyond this structural role have remained mostly unclear. Here, we calculate molecular refractive index increments of crystallins. We show that all lens γ-crystallins have evolved a significantly elevated molecular refractive index increment, which is far above those of most proteins, including non-lens members of the βγ-crystallin family from different species. The same trait has evolved in parallel in crystallins of different phyla, including in the S-crystallins of cephalopods. A high refractive index increment can lower the crystallin concentration required to achieve a suitable refractive power of the lens, and thereby reduce their propensity to aggregate and form cataract. To produce a significant increase of the refractive index increment, a substantial global shift in the amino acid composition is required, which can naturally explain the highly unusual amino acid composition of γ-crystallins and their functional homologues. This function provides a new perspective for interpreting their molecular structure. PMID:21684289

The molecular refractive function of lens γ-Crystallins.

PubMed

Zhao, Huaying; Brown, Patrick H; Magone, M Teresa; Schuck, Peter

2011-08-19

γ-Crystallins constitute the major protein component in the nucleus of the vertebrate eye lens. Present at very high concentrations, they exhibit extreme solubility and thermodynamic stability to prevent scattering of light and formation of cataracts. However, functions beyond this structural role have remained mostly unclear. Here, we calculate molecular refractive index increments of crystallins. We show that all lens γ-crystallins have evolved a significantly elevated molecular refractive index increment, which is far above those of most proteins, including nonlens members of the βγ-crystallin family from different species. The same trait has evolved in parallel in crystallins of different phyla, including S-crystallins of cephalopods. A high refractive index increment can lower the crystallin concentration required to achieve a suitable refractive power of the lens and thereby reduce their propensity to aggregate and form cataracts. To produce a significant increase in the refractive index increment, a substantial global shift in amino acid composition is required, which can naturally explain the highly unusual amino acid composition of γ-crystallins and their functional homologues. This function provides a new perspective for interpreting their molecular structure. Copyright © 2011. Published by Elsevier Ltd.

In vivo measurement of the average refractive index of the human crystalline lens using optical coherence tomography.

PubMed

de Freitas, Carolina; Ruggeri, Marco; Manns, Fabrice; Ho, Arthur; Parel, Jean-Marie

2013-01-15

We present a method for measuring the average group refractive index of the human crystalline lens in vivo using an optical coherence tomography (OCT) system which, allows full-length biometry of the eye. A series of OCT images of the eye including the anterior segment and retina were recorded during accommodation. Optical lengths of the anterior chamber, lens, and vitreous were measured dynamically along the central axis on the OCT images. The group refractive index of the crystalline lens along the central axis was determined using linear regression analysis of the intraocular optical length measurements. Measurements were acquired on three subjects of age 21, 24, and 35 years. The average group refractive index for the three subjects was, respectively, n=1.41, 1.43, and 1.39 at 835 nm.

Retrieval of the thickness and refractive index dispersion of parallel plate from a single interferogram recorded in both spectral and angular domains

NASA Astrophysics Data System (ADS)

Dong, Jingtao; Lu, Rongsheng

2018-04-01

The principle of retrieving the thickness and refractive index dispersion of a parallel glass plate is reported based on single interferogram recording and phase analysis. With the parallel plate illuminated by a convergent light sheet, the transmitted light interfering in both spectral and angular domains is recorded. The phase recovered from the single interferogram by Fourier analysis is used to retrieve the thickness and refractive index dispersion without periodic ambiguity. Experimental results of an optical substrate standard show that the accuracy of refractive index dispersion is less than 2.5 × 10-5 and the relative uncertainty of thickness is 6 × 10-5 (3σ). This method is confirmed to be robust against the intensity noises, indicating the capability of stable and accurate measurement.

Large optical nonlinearity of indium tin oxide in its epsilon-near-zero region.

PubMed

Alam, M Zahirul; De Leon, Israel; Boyd, Robert W

2016-05-13

Nonlinear optical phenomena are crucial for a broad range of applications, such as microscopy, all-optical data processing, and quantum information. However, materials usually exhibit a weak optical nonlinearity even under intense coherent illumination. We report that indium tin oxide can acquire an ultrafast and large intensity-dependent refractive index in the region of the spectrum where the real part of its permittivity vanishes. We observe a change in the real part of the refractive index of 0.72 ± 0.025, corresponding to 170% of the linear refractive index. This change in refractive index is reversible with a recovery time of about 360 femtoseconds. Our results offer the possibility of designing material structures with large ultrafast nonlinearity for applications in nanophotonics. Copyright © 2016, American Association for the Advancement of Science.

Evidence of negative-index refraction in nonlinear chemical waves.

PubMed

Yuan, Xujin; Wang, Hongli; Ouyang, Qi

2011-05-06

The negative index of refraction of nonlinear chemical waves has become a recent focus in nonlinear dynamics researches. Theoretical analysis and computer simulations have predicted that the negative index of refraction can occur on the interface between antiwaves and normal waves in a reaction-diffusion (RD) system. However, no experimental evidence has been found so far. In this Letter, we report our experimental design in searching for such a phenomenon in a chlorite-iodide-malonic acid (CIMA) reaction. Our experimental results demonstrate that competition between waves and antiwaves at their interface determines the fate of the wave interaction. The negative index of refraction was only observed when the oscillation frequency of a normal wave is significantly smaller than that of the antiwave. All experimental results were supported by simulations using the Lengyel-Epstein RD model which describes the CIMA reaction-diffusion system.

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.

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

PubMed

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

2014-08-01

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

Broadband giant-refractive-index material based on mesoscopic space-filling curves

NASA Astrophysics Data System (ADS)

Chang, Taeyong; Kim, Jong Uk; Kang, Seung Kyu; Kim, Hyowook; Kim, Do Kyung; Lee, Yong-Hee; Shin, Jonghwa

2016-08-01

The refractive index is the fundamental property of all optical materials and dictates Snell's law, propagation speed, wavelength, diffraction, energy density, absorption and emission of light in materials. Experimentally realized broadband refractive indices remain <40, even with intricately designed artificial media. Herein, we demonstrate a measured index >1,800 resulting from a mesoscopic crystal with a dielectric constant greater than three million. This gigantic enhancement effect originates from the space-filling curve concept from mathematics. The principle is inherently very broad band, the enhancement being nearly constant from zero up to the frequency of interest. This broadband giant-refractive-index medium promises not only enhanced resolution in imaging and raised fundamental absorption limits in solar energy devices, but also compact, power-efficient components for optical communication and increased performance in many other applications.

Effect of external index of refraction on multimode fiber couplers.

PubMed

Wang, G Z; Murphy, K A; Claus, R O

1995-12-20

The dependence of the performance of fused-taper multimode fiber couplers on the refractive index of the material surrounding the taper region has been investigated both theoretically and experimentally. It has been identified that for a 2 × 2 multimode fiber coupler there is a range of output-power-coupling ratios for which the effect of the external refractive index is negligible. When the coupler is tapered beyond this region, the performance becomes dependent on the external index of refraction and lossy. To analyze the multimode coupler-loss mechanism, we develop a two-dimensional ray-optics model that incorporates trapped cladding-mode loss and core-mode loss through frustrated total internal reflection.

Computer-simulation results support the experimental observations. Related issues such as coupler fabrication and packaging are also discussed.

Dirac directional emission in anisotropic zero refractive index photonic crystals.

PubMed

He, Xin-Tao; Zhong, Yao-Nan; Zhou, You; Zhong, Zhi-Chao; Dong, Jian-Wen

2015-08-14

A certain class of photonic crystals with conical dispersion is known to behave as isotropic zero-refractive-index medium. However, the discrete building blocks in such photonic crystals are limited to construct multidirectional devices, even for high-symmetric photonic crystals. Here, we show multidirectional emission from low-symmetric photonic crystals with semi-Dirac dispersion at the zone center. We demonstrate that such low-symmetric photonic crystal can be considered as an effective anisotropic zero-refractive-index medium, as long as there is only one propagation mode near Dirac frequency. Four kinds of Dirac multidirectional emitters are achieved with the channel numbers of five, seven, eleven, and thirteen, respectively. Spatial power combination for such kind of Dirac directional emitter is also verified even when multiple sources are randomly placed in the anisotropic zero-refractive-index photonic crystal.

Dirac directional emission in anisotropic zero refractive index photonic crystals

PubMed Central

He, Xin-Tao; Zhong, Yao-Nan; Zhou, You; Zhong, Zhi-Chao; Dong, Jian-Wen

2015-01-01

A certain class of photonic crystals with conical dispersion is known to behave as isotropic zero-refractive-index medium. However, the discrete building blocks in such photonic crystals are limited to construct multidirectional devices, even for high-symmetric photonic crystals. Here, we show multidirectional emission from low-symmetric photonic crystals with semi-Dirac dispersion at the zone center. We demonstrate that such low-symmetric photonic crystal can be considered as an effective anisotropic zero-refractive-index medium, as long as there is only one propagation mode near Dirac frequency. Four kinds of Dirac multidirectional emitters are achieved with the channel numbers of five, seven, eleven, and thirteen, respectively. Spatial power combination for such kind of Dirac directional emitter is also verified even when multiple sources are randomly placed in the anisotropic zero-refractive-index photonic crystal. PMID:26271208

Refractive index dispersion sensing using an array of photonic crystal resonant reflectors

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

Hermannsson, Pétur G.; Vannahme, Christoph; Smith, Cameron L. C.

2015-08-10

Refractive index sensing plays a key role in various environmental and biological sensing applications. Here, a method is presented for measuring the absolute refractive index dispersion of liquids using an array of photonic crystal resonant reflectors of varying periods. It is shown that by covering the array with a sample liquid and measuring the resonance wavelength associated with transverse electric polarized quasi guided modes as a function of period, the refractive index dispersion of the liquid can be accurately obtained using an analytical expression. This method is compact, can perform measurements at arbitrary number of wavelengths, and requires only amore » minute sample volume. The ability to sense a material's dispersion profile offers an added dimension of information that may be of benefit to optofluidic lab-on-a-chip applications.« less

Evanescent field-based optical fiber sensing device for measuring the refractive index of liquids in microfluidic channels.

PubMed

Polynkin, PaveL; Polynkin, Alexander; Peyghambarian, N; Mansuripur, Masud

2005-06-01

We report a simple optical sensing device capable of measuring the refractive index of liquids propagating in microfluidic channels. The sensor is based on a single-mode optical fiber that is tapered to submicrometer dimensions and immersed in a transparent curable soft polymer. A channel for liquid analyte is created in the immediate vicinity of the taper waist. Light propagating through the tapered section of the fiber extends into the channel, making the optical loss in the system sensitive to the refractive-index difference between the polymer and the liquid. The fabrication process and testing of the prototype sensing devices are described. The sensor can operate both as a highly responsive on-off device and in the continuous measurement mode, with an estimated accuracy of refractive-index measurement of approximately 5 x 10(-4).

Monitoring of high refractive index edible oils using coated long period fiber grating sensors

NASA Astrophysics Data System (ADS)

Coelho, Luís.; Viegas, Diana; Santos, José Luís.; de Almeida, Jose Manuel M. M.

2015-05-01

Monitoring the quality of high refractive index edible oils is of great importance for the human health. Uncooked edible oils in general are healthy foodstuff, olive oil in particular, however, they are frequently used for baking and cooking. High quality edible oils are made from seeds, nuts or fruits by mechanical processes. Nevertheless, once the mechanical extraction is complete, up to 15% of the oil remains in oil pomace and in the mill wastewater, which can be extracted using organic solvents, often hexane. Optical fiber sensors based on long period fiber gratings (LPFG) have very low wavelength sensitivity when the surround refractive index is higher than the refractive index of the cladding. Titanium dioxide (TiO2) coated LPFG could lead to the realization of high sensitivity chemical sensor for the food industry. In this work LPFG coated with a TiO2 thin film were successfully used for to detect small levels of hexane diluted in edible oils and for real time monitoring the thermal deterioration of edible oils. For a TiO2 coating of 30 nm a wavelength sensitivity of 1361.7 nm/RIU (or 0.97 nm / % V/V) in the 1.4610-1.4670 refractive index range was achieved, corresponding to 0 to 12 % V/V of hexane in olive oil. A sensitivity higher than 638 nm/RIU at 225 ºC was calculated, in the 1.4670-1.4735 refractive index range with a detection limit of thermal deterioration of about 1 minute.

Index of Refraction without Geometry

ERIC Educational Resources Information Center

Farkas, N.; Henriksen, P. N.; Ramsier, R. D.

2006-01-01

This article presents several activities that permit students to determine the index of refraction of transparent solids and liquids using simple equipment without the need for geometrical relationships, special lighting or optical instruments. Graphical analysis of the measured data is shown to be a useful method for determining the index of…

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

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1992-01-01

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

Fabrication of titania inverse opals by multi-cycle dip-infiltration for optical sensing

NASA Astrophysics Data System (ADS)

Chiang, Chun-Chen; Tuyen, Le Dac; Ren, Ching-Rung; Chau, Lai-Kwan; Wu, Cheng Yi; Huang, Ping-Ji; Hsu, Chia Chen

2016-04-01

We have demonstrated a low-cost method to fabricate TiO2 inverse opal photonic crystals with high refractive index skeleton. The TiO2 inverse opal films were fabricated from a polystyrene opal template by multi-cycle dip-infiltration-coating method. The properties of the TiO2 inverse opal films were characterized by scanning electron microscopy and Bragg reflection spectroscopy. The reflection spectroscopic measurements of the TiO2 inverse opal films were compared with theories of photonic band calculations and Bragg law. The agreement between experiment and theory indicates that we can precisely predict the refractive index of the infiltrated liquid sample in the TiO2 inverse opal films from the measurement results. The red-shift of the peak wavelength in the Bragg reflection spectra for both alcohol mixtures and aqueous sucrose solutions of increasing refractive index was observed and respective refractive index sensitivities of 296 and 286 nm/RIU (refractive index unit) were achieved. As the fabrication of the TiO2 inverse opal films and reflection spectroscopic measurement are fairly easy, the TiO2 inverse opal films have potential applications in optical sensing.

Estimation of photonic band gap in the hollow core cylindrical multilayer structure

NASA Astrophysics Data System (ADS)

Chourasia, Ritesh Kumar; Singh, Vivek

2018-04-01

The propagation characteristic of two hollow core cylindrical multilayer structures having high and low refractive index contrast of cladding regions have been studied and compared at two design wavelengths i.e. 1550 nm and 632.8 nm. With the help of transfer matrix method a relation between the incoming light wave and outgoing light wave has been developed using the boundary matching technique. In high refractive index contrast, small numbers of layers are sufficient to provide perfect band gap in both design wavelengths. The spectral position and width of band gap is highly depending on the optical path of incident light in all considered cases. For sensing application, the sensitivity of waveguide can be obtained either by monitoring the width of photonic band gap or by monitoring the spectral shift of photonic band gap. Change in the width of photonic band gap with the core refractive index is larger in high refractive index contrast of cladding materials. However, in the case of monitoring the spectral shift of band gap, the obtained sensitivity is large for low refractive index contrast of cladding materials and further it increases with increase of design wavelength.

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.

Solution of Radiative Transfer Equation with a Continuous and Stochastic Varying Refractive Index by Legendre Transform Method

PubMed Central

Gantri, M.

2014-01-01

The present paper gives a new computational framework within which radiative transfer in a varying refractive index biological tissue can be studied. In our previous works, Legendre transform was used as an innovative view to handle the angular derivative terms in the case of uniform refractive index spherical medium. In biomedical optics, our analysis can be considered as a forward problem solution in a diffuse optical tomography imaging scheme. We consider a rectangular biological tissue-like domain with spatially varying refractive index submitted to a near infrared continuous light source. Interaction of radiation with the biological material into the medium is handled by a radiative transfer model. In the studied situation, the model displays two angular redistribution terms that are treated with Legendre integral transform. The model is used to study a possible detection of abnormalities in a general biological tissue. The effect of the embedded nonhomogeneous objects on the transmitted signal is studied. Particularly, detection of targets of localized heterogeneous inclusions within the tissue is discussed. Results show that models accounting for variation of refractive index can yield useful predictions about the target and the location of abnormal inclusions within the tissue. PMID:25013454

Analytical Modelling of a Refractive Index Sensor Based on an Intrinsic Micro Fabry-Perot Interferometer

PubMed Central

Vargas-Rodriguez, Everardo; Guzman-Chavez, Ana D.; Cano-Contreras, Martin; Gallegos-Arellano, Eloisa; Jauregui-Vazquez, Daniel; Hernández-García, Juan C.; Estudillo-Ayala, Julian M.; Rojas-Laguna, Roberto

2015-01-01

In this work a refractive index sensor based on a combination of the non-dispersive sensing (NDS) and the Tunable Laser Spectroscopy (TLS) principles is presented. Here, in order to have one reference and one measurement channel a single-beam dual-path configuration is used for implementing the NDS principle. These channels are monitored with a couple of identical optical detectors which are correlated to calculate the overall sensor response, called here the depth of modulation. It is shown that this is useful to minimize drifting errors due to source power variations. Furthermore, a comprehensive analysis of a refractive index sensing setup, based on an intrinsic micro Fabry-Perot Interferometer (FPI) is described. Here, the changes over the FPI pattern as the exit refractive index is varied are analytically modelled by using the characteristic matrix method. Additionally, our simulated results are supported by experimental measurements which are also provided. Finally it is shown that by using this principle a simple refractive index sensor with a resolution in the order of 2.15 × 10−4 RIU can be implemented by using a couple of standard and low cost photodetectors. PMID:26501277

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

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.

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

PubMed

Moritake, Yuto; Tanaka, Takuo

2018-02-05

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

Analytical modelling of a refractive index sensor based on an intrinsic micro Fabry-Perot interferometer.

PubMed

Vargas-Rodriguez, Everardo; Guzman-Chavez, Ana D; Cano-Contreras, Martin; Gallegos-Arellano, Eloisa; Jauregui-Vazquez, Daniel; Hernández-García, Juan C; Estudillo-Ayala, Julian M; Rojas-Laguna, Roberto

2015-10-15

In this work a refractive index sensor based on a combination of the non-dispersive sensing (NDS) and the Tunable Laser Spectroscopy (TLS) principles is presented. Here, in order to have one reference and one measurement channel a single-beam dual-path configuration is used for implementing the NDS principle. These channels are monitored with a couple of identical optical detectors which are correlated to calculate the overall sensor response, called here the depth of modulation. It is shown that this is useful to minimize drifting errors due to source power variations. Furthermore, a comprehensive analysis of a refractive index sensing setup, based on an intrinsic micro Fabry-Perot Interferometer (FPI) is described. Here, the changes over the FPI pattern as the exit refractive index is varied are analytically modelled by using the characteristic matrix method. Additionally, our simulated results are supported by experimental measurements which are also provided. Finally it is shown that by using this principle a simple refractive index sensor with a resolution in the order of 2.15 × 10(-4) RIU can be implemented by using a couple of standard and low cost photodetectors.

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.

Optical coherence refractometry.

PubMed

Tomlins, Peter H; Woolliams, Peter; Hart, Christian; Beaumont, Andrew; Tedaldi, Matthew

2008-10-01

We introduce a novel approach to refractometry using a low coherence interferometer at multiple angles of incidence. We show that for plane parallel samples it is possible to measure their phase refractive index rather than the group index that is usually measured by interferometric methods. This is a significant development because it enables bulk refractive index measurement of scattering and soft samples, not relying on surface measurements that can be prone to error. Our technique is also noncontact and compatible with in situ refractive index measurements. Here, we demonstrate this new technique on a pure silica test piece and a highly scattering resin slab, comparing the results with standard critical angle refractometry.

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

PubMed

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

2014-07-14

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

Refractive Index Measurement of Fibers Through Fizeau Interferometry

DTIC Science & Technology

2013-08-01

15. SUBJECT TERMS composite, transparent, refractive index, refractometry , interferometer 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF...transparent fibers has long presented a significant challenge. Abbe refractometry , the typical measurement technique for bulk materials and liquids

Miscibility of ethyl cellulose/copolyamide6/66/1010 blends by viscometry and refractive index method

NASA Astrophysics Data System (ADS)

Zhang, Xiuzhen; Shen, Yuhua; Xie, Anjian; Gao, Sulian; Xing, Zhiying

2011-04-01

The miscibility of ethyl cellulose (EC)/copolyamide6/66/1010 (PA-130) in formic acid is studied by viscometry and refractive index techniques at 25°C. Using viscosity data, the criteria Δ b, Δ b', Δ[η]m, interaction parameter μ, β and thermodynamic parameter α are calculated. These investigations indicate that blend of EC/PA-130 is miscible when the ethyl cellulose content is more than 50 wt % in the blend. Further the result was also confirmed by refractive index measurements.

Spin angular momentum transfer from TEM00 focused Gaussian beams to negative refractive index spherical particles

PubMed Central

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

2011-01-01

We investigate optical torques over absorbent negative refractive index spherical scatterers under the influence of linear and circularly polarized TEM00 focused Gaussian beams, in the framework of the generalized Lorenz-Mie theory with the integral localized approximation. The fundamental differences between optical torques due to spin angular momentum transfer in positive and negative refractive index optical trapping are outlined, revealing the effect of the Mie scattering coefficients in one of the most fundamental properties in optical trapping systems. PMID:21833372

Virtual Excitation and Multiple Scattering Correction Terms to the Neutron Index of Refraction for Hydrogen.

PubMed

Schoen, K; Snow, W M; Kaiser, H; Werner, S A

2005-01-01

The neutron index of refraction is generally derived theoretically in the Fermi approximation. However, the Fermi approximation neglects the effects of the binding of the nuclei of a material as well as multiple scattering. Calculations by Nowak introduced correction terms to the neutron index of refraction that are quadratic in the scattering length and of order 10(-3) fm for hydrogen and deuterium. These correction terms produce a small shift in the final value for the coherent scattering length of H2 in a recent neutron interferometry experiment.

High-Density Near-Field Readout over 50 GB Capacity Using Solid Immersion Lens with High Refractive Index

NASA Astrophysics Data System (ADS)

Shinoda, Masataka; Saito, Kimihiro; Kondo, Takao; Ishimoto, Tsutomu; Nakaoki, Ariyoshi

2003-02-01

We have investigated high-density near-field readout using a solid immersion lens with a high refractive index. By using a glass material with a high refractive index of 2.08, we developed an optical pick-up with the effective numerical aperture of 1.8. We could observe a clear eye pattern for a 50 GB capacity disc in 120 mm diameter. We confirmed that the near-field readout system is promising method of realizing a high-density optical disc system.

Light-driven liquid microlenses

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

Measurement of refractive index of hemoglobin in the visible/NIR spectral range.

PubMed

Lazareva, Ekaterina N; Tuchin, Valery V

2018-03-01

This study is focused on the measurements of the refractive index of hemoglobin solutions in the visible/near-infrared (NIR) spectral range at room temperature for characteristic laser wavelengths: 480, 486, 546, 589, 644, 656, 680, 930, 1100, 1300, and 1550 nm. Measurements were performed using the multiwavelength Abbe refractometer. Aqua hemoglobin solutions of different concentrations obtained from human whole blood were investigated. The specific increment of refractive index on hemoglobin concentration and the Sellmeier coefficients were calculated. (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

Refractive index sensing with Fano resonances in silicon oligomers

PubMed Central

Chong, Katie E.; Orton, Henry W.; Decker, Manuel; Miroshnichenko, Andrey E.; Brener, Igal; Kivshar, Yuri S.

2017-01-01

We demonstrate experimentally refractive index sensing with localized Fano resonances in silicon oligomers, consisting of six disks surrounding a central one of slightly different diameter. Owing to the low absorption and narrow Fano-resonant spectral features appearing as a result of the interference of the modes of the outer and the central disks, we demonstrate refractive index sensitivity of more than 150 nm RIU−1 with a figure of merit of 3.8. This article is part of the themed issue ‘New horizons for nanophotonics’. PMID:28220001

Plasmonic crystal enhanced refractive index sensing

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

Stein, Benedikt; Devaux, Eloïse; Genet, Cyriaque, E-mail: genet@unistra.fr

2014-06-23

We demonstrate experimentally how the local anisotropy of the dispersion relation of surface plasmon modes propagating over periodic metal gratings can lead to an enhancement of the figure of merit of refractive index sensors. Exploiting the possibility to acquire defocused images of the Fourier space of a highly stable leakage radiation microscope, we report a twofold increase in sensing sensitivity close to the band gap of a one-dimensional plasmonic crystal where the anisotropy of the band structure is the most important. A practical sensing resolution of O(10{sup −6}) refractive index units is demonstrated.

Reflection-induced linear polarization rotation and phase modulation between orthogonal waves for refractive index variation measurement.

PubMed

Twu, Ruey-Ching; Wang, Jhao-Sheng

2016-04-01

An optical phase interrogation is proposed to study reflection-induced linear polarization rotation in a common-path homodyne interferometer. This optical methodology can also be applied to the measurement of the refractive index variation of a liquid solution. The performance of the refractive index sensing structure is discussed theoretically, and the experimental results demonstrated a very good ability based on the proposed schemes. Compared with a conventional common-path heterodyne interferometer, the proposed homodyne interferometer with only a single channel reduced the usage of optic elements.

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

PubMed

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

2015-11-20

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

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

NASA Astrophysics Data System (ADS)

Gillespie, James Bryce

1982-03-01

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

High refractive index nanocomposite fluids for immersion lithography.

PubMed

Bremer, L; Tuinier, R; Jahromi, S

2009-02-17

The concept of using dispersions of nanoparticles as high refractive index fluids in immersion lithography is examined both from a theoretical and experimental point of view. In the theoretical part we show that gelation and demixing can be controlled in high solid dispersions, needed to achieve a high (refractive) index, by using short stabilizing brushes. We considered both fluid-fluid demixing by using statistical thermodynamics and percolation, computed using liquid-state approaches. Whenever demixing or percolation takes place, the nanoparticle dispersion is unsuited for immersion lithography. The minimum thickness of the stabilizer layer of a stable suspension is estimated assuming particles plus steric stabilizer to act as hard spheres with van der Waals attraction between the cores. Since the van der Waals attraction can be related to the optical properties of the particles and dispersion medium, it is also possible to estimate the refractive index that can be attained with composite immersion fluids. Using materials that are known to be highly transparent in the bulk at a wavelength of 193 nm, indices above 1.8 can be attained. Other materials with higher indices are expected to be transparent at 193 nm due to a blue shift of the UV absorption and enable much higher indices. In the experiment, we show that it is possible to prepare suspensions with particles of about 4 nm diameter that increase the refractive index of the continuous phase with 0.2 at a wavelength of 193 nm. The refractive index and density of such dispersions are proportional to the volume fraction of the disperse phase, and it is shown that the refractive index of the composite fluid can be predicted very well from the optical properties of the components. Furthermore, successful imaging experiments were performed through a dispersion of silica nanoparticles. These findings lead to the conclusion that immersion lithography using nanoparticle dispersions is indeed possible.