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DIRECT MEASUREMENT OF HUMAN-CONE-PHOTORECEPTOR ALIGNMENT

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 1995年第10期12卷 2329-2338页

作者： BURNS, SA WU, S DELORI, F ELSNER, AE []The Schepens Eye Research Institute 20 Staniford Street Boston Massachusetts 02114

We have developed an imaging reflectometer to measure cone-photoreceptor alignment. One makes measurements by bleaching the cone photopigment and imaging the distribution of light returning from the retina, which is illuminated from a small source imaged in the plane df the eye's pupil. If the source is near the optimal entry pupil position as determined psychophysically, the distribution of light returning from the retina is peaked, and the magnitude of the peak depends on the location of the source in the pupil. of the eye. If the source is far from the optimal entry pupil position, then there is no measurable peak. The location of the peak varies across individuals and coincides with the reported location of best visibility of the measuring light and with previous psychophysical and reflectometric measurements of the Stiles-Crawford peak. The source of this directionality must arise either from the photoreceptors or from behind the photoreceptors because the peak is not present if measurements are made when the cone photopigments have high optical density.

关键词： PHOTORECEPTORS COLOR VISION wave-guides VISUAL SENSITIVITY STILES-CRAWFORD EFFECT

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Inverse potential scattering in duct acoustics

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2006年第1期119卷 65-73页

作者： Forbes, BJ Pike, ER Sharp, DB Aktosun, T Phonol Ltd London NW2 1DJ England Kings Coll London Dept Phys London WC2R 2LS England Open Univ Dept Mech & Environm Engn Milton Keynes MK7 6AA Bucks England Mississippi State Univ Dept Math & Stat Mississippi State MS 39762 USA

The inverse problem of the noninvasive measurement of the shape of an acoustical duct in which one-dimensional wave propagation can be assumed is examined within the theoretical framework of the governing Klein-Gordon equation. Previous deterministic methods developed over the last 40 years have all required direct measurement of the reflectance or input impedance but now, by application of the methods of inverse quantum scattering to the acoustical system, it is shown that the reflectance can be algorithmically derived from the radiated wave. The potential and area functions of the duct can subsequently be reconstructed. The results are discussed with particular reference to acoustic pulse reflectometry. (c) 2006 Acoustical Society of America.

关键词： VARYING CROSS-SECTION VOCAL-TRACT SHAPE PULSE REFLECTOMETRY FORMANTFREQUENCIES wave-guides RESONANCE FREQUENCIES MODEL PROPAGATION CONVERSION GEOMETRY

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Frequency-resolved optical gating in the 1.55 μm band via cascaded _χ⁽²⁾ processes

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2005年第9期22卷 1985-1993页

作者： Prawiharjo, J Gallo, K Broderick, NGR Richardson, DJ Univ Southampton Optoelect Res Ctr Southampton SO17 1BJ Hants England

We investigate ultrashort-pulse interactions based on cascaded second-harmonic generation and difference-frequency generation and propose their use for frequency-resolved optical gating (FROG) at telecom wavelengths in a waveguide configuration. We show how a chi((2))-chi((2)) FROG device could allow the efficient characterization of ultrashort pulses, with time resolutions well beyond the limits normally imposed by walk-off effects on single-step chi((2)) FROG devices. (C) 2005 Optical Society of America.

关键词： ULTRASHORT LASER-PULSES POLED LITHIUM-NIOBATE wave-guides 2ND-HARMONICGENERATION PHASE CHARACTERIZATION AMPLIFICATION NONLINEARITY TRANSMISSION COMPRESSION AMPLITUDE

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Study of femtosecond-laser-written waveguides in glasses

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2002年第10期19卷 2496-2504页

作者： Streltsov, AM Borrelli, NF Corning Inc Corning NY 14831 USA

Mechanisms of the femtosecond-laser-induced refractive-index change (Deltan) were investigated for fused silica and a borosilicate glass. Experiments were based on two exposure situations: (a) high repetition rate and low pulse energy and (b) low repetition rate and high pulse energy. The calculated temperature rise based on model (b) was above 1000 degreesC, whereas for situation (a) it was negligible. The results do not support a thermal origin of the induced Deltan;rather, heat may limit the magnitude of the change. Correlation between color-center formation and Deltan in both glasses suggests that defects contribute substantially to the index increase. However, annealing studies have shown that the induced An persisted beyond the disappearance of the color centers. Analysis of the induced stress showed that densification plays a small role in this change. (C) 2002 Optical Society of America.

关键词： Fused-silica Induced breakdown wave-guides Pulses Densification Dielectrics Fabrication fabrication Dielectrics color centers pulse energy Repetition rate induced stress waveguide Device Component Fused silica Densification

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Reducing Insertion Loss of Photonic Crystal Couplers by Suppressing the Remained Power

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Chinese Physics Letters 2007年第2期24卷 454-457页

作者：毛晓宇王建锋黄翊东张巍彭江得 Department of Electronics Engineering Tsinghua University Beijing 100084

We find that the increasing coupling strength can lead to a decreasing density of power inside the waveguide of a photonic crystal waveguide （PC-WG） directional coupler, which is called the mode power remaining phenomenon. This phenomenon is detrimental to achieving low insertion loss of the coupler. An improved structure of the PC- WG directional coupler is proposed by simply increasing the radii of air holes in the post coupling region. The simulation results demonstrate that the insertion loss can be reduced dramatically by suppressing the remained power, and therefore both the short coupling length （8μm） and low insertion loss （lower than 0.5dB） can be obtained.

关键词： wave-guides

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waveguides in three-dimensional layer-by-layer photonic crystals

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2003年第5期20卷 801-809页

作者： Li, ZY Ho, KM Iowa State Univ Ames Lab Ames IA 50011 USA Iowa State Univ Dept Phys & Astron Ames IA 50011 USA

A photonic crystal waveguide network can form in a three-dimensional layer-by-layer photonic crystal along three orthogonal directions. We investigate guided-mode band structures for different waveguide configurations by numerical calculations that combine a plane-wave expansion method with a supercell technique. The in-plane waveguide network composed of waveguides along the (100) and (010) directions of the crystal is located in a single layer of the photonic crystal. This structural design is easy to achieve experimentally. One can create these in-plane waveguides either by removing one single rod or by breaking a segment in each of an array of parallel rods. One produces the off-plane waveguide by removing some segments of rods along the (001) stacking direction of the crystal. Single-mode operation of a waveguide can be achieved by appropriate adjustment of geometrical parameters such as the location and the size of the waveguide. Intrinsic lattice symmetries in these photonic crystal waveguides have been fully employed to reduce the complexity of the numerical solution of guided-mode band structures significantly. (C) 2003 Optical Society of America.

关键词： wave-guides Band-gaps Electromagnetic-waves Infrared wavelengths Bends Transmission Emission Defect Light Slabs

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Structural analysis of hybrid titania-based mesostructured composites

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JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 2005年第27期127卷 9721-9730页

作者： Boettcher, SW Bartl, MH Hu, JG Stucky, GD Univ Calif Santa Barbara CNSI Dept Chem & Biochem Santa Barbara CA 93106 USA Univ Calif Santa Barbara Mat Res Lab Santa Barbara CA 93106 USA

High-optical-quality titania-based mesostructured films with cubic or 2D-hexagonal symmetry were fabricated by combining trifluoroacetate (TFA)-modified titanium precursors with amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide) -poly(ethylene oxide) (PEO-PPO-PEO) copolymers. The distribution, dynamics, and local environments of the TFA-modified titania, PEO, and PPO components of the hybrid were investigated. IR/Raman spectroscopy, in situ small-angle X-ray scattering, and transmission electron microscopy studies indicate that TFA coordinates the titanium center and forms a stable complex that is subsequently organized by the block copolymer species into ordered mesostructures. Solid-state NMR F-19 -> H-1 cross-polarization, C-13{H-1} two-dimensional heteronuclear correlation, and H-1 relaxation techniques were used to determine that PEO is predominantly incorporated within the TFA-modified titania, and that PPO environments encompass both microphase separated regions and interfacial regions composed of mixed PPO and TFA-modified titania. NMR F-19 multiple-quantum spin counting measurements suggest that -CF3 groups of the trifluoroacetate ligands do not form clusters but instead randomly distribute within the inorganic component of the hybrid.

关键词： SOLID-STATE-NMR MULTIPLE-QUANTUM NMR MESOPOROUS MOLECULAR-SIEVES THIN-FILMS TRIFLUOROACETIC-ACID METAL-OXIDES POLY(ETHYLENE OXIDE) VIBRATIONAL-SPECTRA CROSS-POLARIZATION wave-guides

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Microstructuring of diamond bulk by IR femtosecond laser pulses

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APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 2008年第4期90卷 645-651页

作者： Kononenko, T. V. Meier, M. Komlenok, M. S. Pimenov, S. M. Romano, V. Pashinin, V. P. Konov, V. I. Inst Gen Phys Moscow 119991 Russia Univ Bern Inst Appl Phys CH-3012 Bern Switzerland

We report the fabrication of graphitic microstructures in the bulk of chemical vapor deposited (CVD) diamond using 120-fs laser pulses at 800-nm wavelength. The nature of the laser-modified region and generation of mechanical stresses in the surrounding diamond is studied with Raman spectroscopy. A spontaneous growth of the laser-modified region from the focal plane towards the laser has been visualized in the process of multipulse irradiation with different pulse energies. The formation of discrete or continuous graphitized structures is revealed depending on the varied local laser intensity. The physical processes governing the appearance of separate graphitic globules and continuous extension of the graphitized region are discussed. Controlling the laser irradiation conditions permits us to fabricate graphitic wires with typical length of 150 mu m and diameter of 1.5 mu m. The longer, 300-ps pulses, as applied to laser microstructuring of the CVD diamond bulk, are found to be inappropriate due to the stronger influence of structural defects on the damage threshold, the noticeable fluctuation of the structure diameter over the length and the pronounced cracking of the surrounding diamond.

关键词： TRANSPARENT MATERIALS wave-guides ABLATION BREAKDOWN DAMAGE GRAPHITIZATION SPECTROSCOPY DIELECTRICS THRESHOLDS DEPOSITION

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Confinement loss in adiabatic photonic crystal fiber tapers

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2006年第9期23卷 1965-1974页

作者： Kuhlmey, Boris T. Nguyen, Hong C. Steel, M. J. Eggleton, Benjamin J. Univ Sydney CUDOS Sydney NSW 2006 Australia Univ Sydney Sch Phys Sydney NSW 2006 Australia RSoft Desing Grp Inc Chippendanle NSW 2008 Australia

We numerically study confinement loss in photonic crystal fiber (PCF) tapers and compare our results with previously published experimental data. Agreement between theory and experiment requires taking into account hole shrinkage during the tapering process, which we measure by using a noninvasive technique. We show that losses are fully explained within the adiabatic approximation and that they are closely linked to the existence of a fundamental core-mode cutoff. This cutoff is equivalent to the core-mode cutoff in depressed-cladding fibers, so that losses in PCF tapers can be obtained semiquantitatively from an equivalent depressed-cladding fiber model. Finally, we discuss the definition of adiabaticity in this open boundary problem. (c) 2006 Optical Society of America.

关键词： MICROSTRUCTURED-OPTICAL-FIBERS SUPERCONTINUUM GENERATION FUNDAMENTAL MODE MULTIPOLE METHOD HOLEY FIBERS wave-guides CUTOFF INDEX

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Microwave properties of Ba_0.5Sr_0.5TiO₃ thin film coplanar phase shifters

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JOURNAL OF APPLIED PHYSICS 2006年第10期99卷 104101.1-104101.7页

作者： Suherman, PM Jackson, TJ Tse, YY Jones, IP Chakalova, RI Lancaster, MJ Porch, A Univ Birmingham Sch Engn Birmingham B15 2TT W Midlands England Cardiff Univ Sch Engn Cardiff CF24 3AA Wales

Coplanar waveguide transmission lines have been used to show that the temperature dependent properties of Ba0.5Sr0.5TiO3 thin films used for microwave phase shifters in the frequency range 45 MHz-50 GHz are correlated strongly with the microstructure of the films. The highest tunability and figure of merit of the phase shifters were obtained for films with the narrowest ferroelectric-paraelectric phase transition range, lowest mosaic spread, and widest columnar microstructure. The study also showed that the operating temperature plays an important role in achieving the optimum phase shift for microwave applications. (c) 2006 American Institute of Physics.

关键词： wave-guides DIELECTRIC-PROPERTIES PERMITTIVITY TEMPERATURE TRANSITION FREQUENCY SUBSTRATE

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