bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Study of Gas Permeabilities and Breakthrough
Pressures in Clays
Authors: Tanai K. , Kanno T. , Gallé C. 
Published: September 2012

ABSTRACTIn this study, gas migration experiments in unsaturated and saturated states
were carried out to clarify the fundamental gas migration characteristics in
compacted bentonite to be used for the geological disposal of high-level
radioactive waste. In unsaturated experiments, the gas permeability for
Japanese bentonite (Kunigel VI) as a function of degree of saturation was
measured to examine the applicability of conventional two-phase flow models
to compacted bentonite. The intrinsic permeability obtained in this study
was about five orders of magnitude larger than that obtained in water
permeation tests with the same density. The difference seems to originate
from the change of pore structure due to the swelling phenomenon of the
bentonite. Since these effects have not been evaluated quantitatively yet,
various relative gas permeability functions of conventional two-phase flow
models were applied as a first approximation.Saturated experiments designed to simulate the gas migration phenomenon in a
repository for the waste were carried out to obtain relationship between
breakthrough and swelling pressures using Kunigel VI and French Fo-Ca clay
in saturation state. The reproducibility of the breakthrough pressure was
also examined for Kunigel VI bentonite. The breakthrough pressure was almost
the same as swelling pressure irrespective of the type of clay. As to the
reproducibility of breakthrough pressure, it was observed that first and
second breakthrough pressures were almost the same for Kunigel VI specimens
with the dry densities of 1.7 and 1.8 g/cm3.
Photoinduced intermolecular Charge-Transfer Systems for Optical Limiting
Authors: Wu X.-L. , Heikal A. A. , Lee I.-Y. S. , Bohorquez M. , Perry J. W. 
Published: September 2012

AbstractPhotoinduced intermolecular charge transfer (PICT) in donor/acceptor systems has been investigated as an approach to the design of new optical limiting (OL) materials. Solution of cyanines or porphyrins (as sensitizers) and viologen derivatives (as electron acceptors) were used in these studies. Picosecond time-resolved fluorescence measurements were carried out to estimate the charge-transfer rate in these donor/acceptor systems. The radical-ion absorption bands were identified using spectroelectrochemistry. Nonlinear transmission measurements with picosecond and nanosecond laser pulses were utilized to determine the effective photo-induced to ground-state absorption cross-section ratio of the sensitizers alone and the sensitizer/acceptor systems. Our studies are consistent with optical limiting by PICT in solution and indicate a substantial radical-ion yield in the systems examined.
Spectroscopy and Nonlinear Absorption of α, ω-dithienyi Polyenes
Authors: Natarajan L. V. , Sowards Laura A. , Spangler C. W. , Tang N. , Fleitz P. A. , Sutherland R. L. , Cooper T. M. 
Published: September 2012

AbstractThe photophysics and nonlinear absorption behaviour of a series of α, ω-dithienyl polyenes were studied in chloroform and n-octane solutions. Steady state fluorescence, fluorescence lifetime and quantum yield measurements were made. The fluorescence quantum yields were significantly lower than those of the corresponding ax,o-diphenyl polyenes. Among the dithienyl polyenes, 3,3′-substituted polyenes exhibited stronger fluorescence than those of the 2,2′-substituted. Nonlinear optical absorption experiments showed evidence of two photon absorption.
Photorefractive Effect in CdSSe:V Crystals
Authors: Morgan Steven H. , Davis Michelle , Pan Zhengda , Chen Kuo-Tong , Chen Henry , Davis Swanson L. , Burger Arnold 
Published: September 2012

AbstractWe present two-wave mixing results obtained with CdSSe:V crystals. A large photorefractive gain of 0.24 cm-1 was observed at 633 nm with an optical intensity of 60 mW/cm2 and a grating period of 1.6 μrm. At this wavelength, we measured the photorefractive gain as a function of the grating period and incident optical intensity. To our knowledge, this is the first observation of the photorefractive effect in vanadium doped CdSSe crystals. The CdSSe crystals were grown by physical vapor transport (PVT) and doped with 150 ppm (nominal) vanadium for creating trap centers. The grown crystal has a large crystal size, good optical quality and a medium resistivity of 10-5 - 108 Ω-cm. Room temperature absorption and low temperature photoluminescence spectroscopy measurements are also discussed. With a significant photorefractive effect, the CdSSe:V crystals are promising for many device applications based on photorefractive effect, including optical limiting devices in the visible region.
Infrared Liquid Crystal Tunable Filters
Authors: Wu Shin-Tson , Wu Chiung-Sheng 
Published: September 2012

AbstractComputer simulations on Fabry-Perot liquid crystal tunable filters are performed in the 3–5 and 8–12 μm bands and some discrete laser lines. Effects of transmittance, contrast ratio and response time on liquid crystal birefringence, layer thickness, absorption coefficient and reflectivity of mirrors are analyzed. Absorption spectra and responsible mechanisms of liquid crystals in the 2.5–20 μm region are studied. The fluorinated tolane and diphenyl-diacetylenes and dialkyl diphenyldiacetylenes are found to possess low absorption in the mid-IR range. Mixtures of these compounds will find useful applications for the proposed IR tunable filters.
Liquid Crystals for Fast Infrared Laser Switching and Optical Limiting Application
Authors: Khoo I. C. , Wood M. V. , Guenther Brett D. 
Published: September 2012

AbstractThe nonlinear optical effects of chlorophyll ‘a’ have been determined using an array of measurement techniques. Regions of spectral interest exhibiting induced excited state absorption were identified with transient absorption spectroscopy measurements. At specific wavelengths within these regions, the dye was characterised using the Z-scan technique. Additional measurements were made to complement the latter results including a focused aperture experiment in which thermal defocusing and scattering mechanisms were identified.
Optical Limiting in Phthalocyanine Solutions and in Pure Liquid Phthalocyanines
Authors: Flom Steven R. , Pong Richard G. S. , Shirk James S. , Bartoli F. J. , Cozzens R. F. , Boyle Michael E. , Snow Arthur W. 
Published: September 2012

AbstractOptical limiting, degenerate four-wave mixing and transient absorption experiments have been performed on a neat liquid lead substituted phthalocyanine. The photophysical mechanisms responsible for the good optical limiting observed in other phthalocyanine solutions are maintained in this pure liquid despite its different peripheral substitution pattern. The liquid is shown to have excited state absorption cross sections that exceed those of the ground state through much of the visible spectrum. Hybrid absorptive/refractive nonlinear response is demonstrated to contribute to both the four-wave mixing and optical limiting response. The mechanism and states responsible are discussed.
Nonlinear Optical Fiber Core Materials For Optical Limiting Application
Authors: Khoo I. C. , Wood M. V. , Guenther Brett. D. 
Published: September 2012

AbstractSeveral liquid phase liquid crystals and liquids are found to possess broadband nonlinear absorption characteristics suitable for optical limiting applications. Using these liquids as fiber waveguiding cores, we have developed fiber arrays that provide excellent limiting performance characteristics against frequency agile visible laser pulses in the nanosecond - picosecond time scale. These fiber arrays are compact, low cost/weight, and are capable of transmitting high quality images throughout the entire visible spectrum.
Shadowgraphic Imaging of Dilute Carbon and Mo2Ag4S8,[PPh3]4 Suspensions
Authors: Goedert Robert , Becker Roger , Clements Andrew , Whittaker Thomas 
Published: September 2012

AbstractTime-resolved imagery is presented showing the changes that occur in the focal volume of dilute liquid/particle suspensions following the arrival of single, Q-switched, frequency-doubled, Nd:YAG laser pulses. Limiting data and corresponding imagery at 21, 84, 244, 790, and 2900 nanoseconds following the laser pulse are presented for a carbon particle suspension consisting of used (carbonized) 1OW-15 motor oil and for a suspension of the inorganic metallic cluster molecule Mo2Ag4S8 [PPh3]4. The images in conjunction with the accompanying limiting data show that the reduction in transmission, observed as the input pulse energy is increased, results from scattering from bubbles augmented by plasma absorption. Keywords: laser induced breakdown, plasma, suspension, bubble, nonlinear materials, shadowgraph, imagery
Non-Linear Optical Characteristics of Novel Porphyrin Dye Media
Authors: McEwan K. J. , Robertson J. M. , Wylie A. P. , Anderson H. L. 
Published: September 2012

AbstractMeasurements of sensitive RSA phenonema in new porphyrin dyes are presented. Both the linear and non-linear optical properties are shown to depend strongly on the molecular structure. A detailed analysis of two of the porphyrins reveals that inter-systems crossing rate and the excited state absorption profile are strongly influenced by substitution of a heavy atom into the central atom position. It is shown that by appropriate choice of wavelength values in excess of 30 can be achieved for the material parameter σex / σgr. This value compares well with previously reported results and is achieved in conjunction with excited state lifetimes on the order of 300 ns.
Nonlinear Mechanisms in Carbon-Black Suspension in a Limiting Geometry
Authors: Fougeanet Francois , Fabre Jean-Claude 
Published: September 2012

AbstractAlthough Carbon-Black suspensions (CBS) have been studied extensively for optical limiting applications, the microscopic mechanisms responsible for their limiting behavior still remain unclear. To study the mechanisms leading to the nonlinearity, we have performed a pump-probe experiment coupled with plasma emission measurements. Time resolved probe transmission have permitted to differentiate bubbles from plasma effects in the case of Carbon-Black in CS2. Other effects are discussed in terms of limiting performance.
Reverse Saturable Absorption and Induced Thermal Effects in Chlorophyll ‘A’
Authors: Robertson J. M. , Bourhill G. 
Published: September 2012

AbstractThe nonlinear optical effects of chlorophyll ‘a’ have been determined using an array of measurement techniques. Regions of spectral interest exhibiting induced excited state absorption were identified with transient absorption spectroscopy measurements. At specific wavelengths within these regions, the dye was characterised using the Z-scan technique. Additional measurements were made to complement the latter results including a focused aperture experiment in which thermal defocusing and scattering mechanisms were identified.
DFT Study of Alkynyl Porphyrin Dimers and Brominated Tetraphenyl Porphyrins
Authors: Wang Zhiqiang , Day Paul , Pachter Ruth , McLean Daniel G. 
Published: September 2012

AbstractGeometry optimizations and electronic structure calculations using Density Functional Theory (DFT) are reported for tetra-acetylene porphyrins (TAP), their dimers, and octabromotetraphenyl porphyrins (OBP). The acetylene group contributes to the π-electron conjugation along the porphyrin ring for the HOMO and LUMO, and reduces significantly the HOMO-LUMO gap. The gap is further reduced in dimers. The planar geometry of the TAP dimer has a lower energy than the non-planar one. The geometry of H2OBP is found to be non-planar, and the distortion of porphyrin ring is shown to be closely related to the HOMO-LUMO gap.
Nonlinear optical Properties of Pentaazadentate Expanded Porphyrins and Application in Optical Limiting
Authors: Wang Duoyuan , Sun Wenfang , Dong Shiming , Si Jinhai , Li Chunfei 
Published: September 2012

AbstractNonlinear optical properties of asymmetric pentaazadentate expanded porphyrin metal complexes are investigated. The transmittance dependence of the target compounds on the incident laser intensity generates different nonlinear optical effects in the excited states. The reverse saturable absorption at 532 nm in the ns pulses and the saturable absorption for the pspulses at high fluences are observed in solutions. The nonlinear refractive indices n2 aremeasured by the Z-scan technique. The optical limiting based on the RSA and transverse refraction are demonstrated for ns and continuous laser. An optical limiter based on the RSA and self-refraction is performed, in which the limitating threshold and amplitude of output energy are reduced.
The design of Optical Limiters Based on the Formation of Bipolaron-Like Dications
Authors: Spangler Charles W. , He Mingqian 
Published: September 2012

AbstractDuring the past decade, there has been considerable effort in the design of new materials with greatly enhanced nonlinear absorption characteristics. In recent years, it has been shown that incorporation of bipolaronic charges in the pi-electron sequence in conjugated polymers or copolymers leads to enhanced third-order nonlinear optical properties. In this current study a design strategy for the synthesis of optical power limiting copolymers is presented whose properties are based on the photogeneration of stable bipolaron-like dications.
Optical Limiting in Fullerene Materials
Authors: Tang B. Z. , Peng H. , Leung S. M. , Yu N.-T. , Hiraoka H. , Fok W. 
Published: September 2012

AbstractFullerene chemistry is booming, but how the chemical reactions affect fullerene's materials properties has seldom been studied. We have investigated optical limiting behavior of a series of fullerene derivatives, polymers, and glasses and have observed the following structure-property relationships for optical limiting in the fullerene materials: (i) The fullerene polymers with aromatic and chlorine moieties, i.e., C60-containing polycarbonate (C60-PC), polystyrene (C60- PS), and poly(vinyl chloride) (C60-PVC), limit the 8-ns pulses of 532-nm laser light more effectively than does the parent C60; (ii) the fullerene polymers with carbonyl groups, i.e., C60- containing CR-39 (C60-CR-39) and poly(methyl methacrylate), (C60-PMMA), do not enhance C60's limiting power; and (iii) the aminated fullerene derivatives, i.e., HxC60 (NHR)x [R = -(CH2CH2O)2H (1), x = 11; -(CH2)6OH (2), x = 7; -cyclo-C6H11 (3), x = 11; -(CH2)3Si(OC2H5)3 (4), x = 4], and their sol-gel glasses, i.e., 1–3/SiO2 (physical blending) and 4-SiO2 (chemical bonding), show complex limiting responses, with 4(-SiO2) performing consistently better than 1-3(/SiO2). The fullerene glasses are optically stable and their optical limiting properties remainunchanged after being subjected to continuous attack by the strong laser pulses for ca. 1 h.
Non-Linear Effects in Thin Film Fullerene Structures
Authors: Lewis Keith , Blacker Richard S , Bourhill Grant , Robertson John M 
Published: September 2012

AbstractThe fullerene materials are well known for their non-linear behaviour arising from excited state absorption processes. In solution, the processes can set in at low irradiance levels, although evidence is building that the magnitude of the effects is dependent on the solvent used in the experiments and the role of charge transfer processes. In evaporated films of C60, the solvent is absent and reduced non-linearities are seen as irradiances approach the laser damage threshold of the films. When the chromophor is incorporated into polymer films, non-linear processes are found at the same levels as the solution case provided that some residual solvent remains in the composite. Excited state absorption spectra suggest that some ionisation of the C60 may be occuring.
Polymer Materials Design for Optical Limiting
Authors: Cumpston B. H. , Mansour K. , Heikal A. A. , Perry J. W. 
Published: September 2012

AbstractPhthalocyanines (PC's) containing heavy metal central atoms have recently been recognized as leading candidates for reverse saturable absorption and optical limiting (OL) applications in the visible spectrum. Strong triplet excited state absorption brought about by a large intersystem crossing rate is responsible for the excellent limiting performance of these molecules. Moreover, devices which maximize the excited state population along the light path will demonstrate maximum limiting efficiency. A non-homogeneous distribution of indium tetra(tert-butyl) phthalocyanine chloride (InC1PC) has been shown to be very effective in attenuating 532 nm nanosecond laser pulses. This was accomplished by approximating a hyperbolic distribution of chromophores using discrete elements of fixed dye concentration. Greater OL should be achieved by fabricating materials containing a continuous concentration gradient of chromophore. This paper focuses on issues concerning the preparation of solid polymeric materials that contain such a chromophore gradient. This design is achieved by diffusing chromophore-containing solutions into partially polymerized poly(methyl methacrylate) (PMMA).
Two-Photon Absorbing Organic Chromophores for Optical Limiting
Authors: Ehrlich J. E. , Wu X. L. , Lee I.-Y. S. , Heikal A. A. , Hu Z.-Y. , Röckel H. , Marder S. R. , Perry J. W. 
Published: September 2012

AbstractStrong optical limiting and large two-photon absorptivities are reported for a class of bisdonor diphenylpolyene derivatives with varying polyene bridge lengths. These molecules exhibit strong optical limiting using nanosecond pulses over a broad spectral range. Bis(diphenylamino)stilbene exhibits a 90 nm red shift of its optical limiting band, and only a minimal shift of about 13 nm of its lowest one-photon electronic absorption band relative to bis(di-n-butylamino)stilbene. This suggests a potential for broadband optical limiting with high transparency using mixtures of such compounds. Pulse width dependent nonlinear transmission measurements suggest that two-photon pumped excited-state absorption contributes significantly to the limiting of nanosecond pulses.
Reverse saturable Absorption in Organically Doped Xerogels
Authors: Brunel M. , Chaput F. , Vinogradov S. A. , Campagne B. , Canva M. , Boilot J-P. , Brun A. 
Published: September 2012

AbstractPd and Zn - tetraphenyltetrabenzoporphyrins (PdTPTBP and ZnTPTBP), hexacyanin 3 (HITCI), and substituted phthalocyanines were incorporated in solid-state matrices (xerogels) using a sol-gel process. Nonlinear reverse saturable absorption was observed with those materials when they were illuminated with nanosecond laser pulses at 532 nm, or other wavelengths in the visible spectrum (between 450 nm and 630 nm). PdTPTBP doped xerogels exhibit a nonlinear activation threshold of about 10 mJ/cm , which is much lower than the value of 80 mJ/cm2 obtained under similar conditions with classical Al phthalocyanine chloride, or HITCI molecules. Solid state “red active” reverse saturable absorbers can be obtained with substituted phthalocyanines doped xerogels. The different experimental results are discussed using classical 4- energy level diagrams.
Sructural evolution of GaN during initial stage MOCVD growth
Authors: Kim Chong Cook , Je Jung Ho , Yi Min-Su , Noh Do Young 
Published: September 2012

AbstractThe structural evolution of GaN films during the initial growth process of metalorganic chemical vapor deposition (MOCVD) - low temperature nucleation layer growth, annealing, and high temperature epitaxial growth - was investigated in a synchrotron x-ray scattering experiment. The nucleation layer grown at 560°C that was predominantly cubic GaN consisted of tensile-strained aligned domains and relaxed misaligned domains. The hexagonal GaN, transformed from the cubic GaN during annealing to 1100°C, showed disordered stacking. The atomic layer spacing decreased as the fraction of the hexagonal domains increased. Subsequent growth of epitaxial GaN at 1100°C resulted in the formation of ordered hexagonal GaN domains with rather broad mosaicity.
High-Quality AlxGa1−xN Using Low Temperature-Interlayer and its Application to UV Detector
Authors: Iwaya M. , Terao S. , Hayashi N. , Kashima T. , Detchprohm T. , Amano H. , Akasaki I. , Hirano A. , Pernot C. 
Published: September 2012

AbstractLow-temperature (LT-) AlN interlayer reduces tensile stress during growth of AlxGa1−xN, while simultaneously acts as the dislocation filter, especially for dislocations of which Burger's vector contains [0001] components. UV photodetectors using thus-grown high quality AlxGa1−xN layers were fabricated. The dark current bellow 50 fA at 10 V bias for 10 [.mu]m strip allowing a photocurrent to dark current ratio greater than one even at 40 nW/cm2 have been achieved.
Improved Characteristics of InGaN Multi-Quantum-Well Laser Diodes Grown on Laterally Epitaxially Overgrown GaN on Sapphire
Authors: Hansen Monica , Fini Paul , Zhao Lijie , Abare Amber , Coldren Larry A. , Speck James S. , DenBaars Steven P. 
Published: September 2012

AbstractInGaN multi-quantum-well laser diodes have been fabricated on fully-coalesced laterally epitaxially overgrown (LEO) GaN on sapphire. The laterally overgrown ‘wing’ regions as well as the coalescence fronts contained few or no threading dislocations. Laser diodes fabricated on the low-dislocation-density wing regions showed a reduction in threshold current density from 8 kA/cm2 to 3.7 kA/cm2 compared the those on the high-dislocation ‘window’ regions. Laser diodes also showed a twofold reduction in threshold current density when comparing those on the wing regions to those fabricated on conventional planar GaN on sapphire. The internal quantum efficiency also improved from 3% for laser diodes on conventional GaN on sapphire to 22% for laser diodes on LEO GaN on sapphire.
Spatially Resolved Electroluminescence of InGaN-MQW-LEDs
Authors: Schwegler Veit , Seyboth Matthias , Kirchner Christoph , Scherer Marcus , Kamp Markus , Fischer Peter , Christen Jürgen , Zacharias Margit 
Published: September 2012

AbstractElectroluminescence (EL) is the most significant measure for light-emitting diodes since it probes the most relevant properties of the fully processed device during operation. In addition to the information gained by conventional spectrally resolved EL, scanning micro-EL provides spatially resolved information. The devices under investigation are InGaN/GaN-LEDs with single peak band-band emission at about 400 nm grown by MOVPE on sapphire substrates.The μ-EL-characterization is performed as a function of injection current densities and the emission is investigated from the epitaxial layer as well as from substrate side. Spatially resolved wavelength images reveal emission peaks between 406 nm and 417 nm, corresponding either to In fluctuations of 1%–1.5% or local fluctuations of piezo electric fields. Beside the information on the emission wavelength fluctuations ν-EL is used to determine the temperature distribution in the LEDs and to investigate transparent contacts.
High Reflectance III-Nitride Bragg Reflectors Grown by Molecular Beam Epitaxy
Authors: Ng H. M. , Moustakas T. D. 
Published: September 2012

AbstractDistributed Bragg reflector (DBR) structures based on AlN/GaN have been grown on (0001) sapphire by electron-cyclotron-resonance plasma-assisted molecular-beam epitaxy (ECR-MBE). The design of the structures was predetermined by simulations using the transmission matrix method. A number of structures have been grown with 20.5 – 25.5 periods showing peak reflectance ranging from the near-UV to the green wavelength regions. For the best sample, peak reflectance up to 99% was observed centered at 467 nm with a bandwidth of 45 nm. The experimental reflectance data were compared with the simulations and show excellent agreement with respect to peak reflectance, bandwidth of high reflectance and the locations of the sidelobes.