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Focusing of an intense Gaussian laser beam in a radially inhomogeneous medium

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2005年第6期22卷 1268-1275页

作者： Prakash, G Sharma, A Verma, MP Sodha, MS Univ Lucknow Dept Sci & Technol Project Inst Adv Studies Educ Lucknow 226007 Uttar Pradesh India

The steady-state focusing-defocusing of a laser beam in a medium characterized by built-in radial inhomogeneity and nonlinearity of a saturating nature has been investigated in the paraxial approximation. By use of the parabolic equation for wave propagation and a complex eikonal, coupled differential equations for the beam-width parameter, absorption parameter, and nonlinearity parameter have been obtained. The numerical solution of these equations for a typical set of parameters yields the dependence of the beam width and axial irradiance on distance of propagation. A discussion of the results follows. The situations for which the analysis may be applicable are indicated in the introduction. (C) 2005 Optical Society of America.

关键词： wave-guides PROPAGATION PLASMAS PULSES LIGHT

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Development of a polarization-preserving optical-fiber probe for near-field scanning optical microscopy and the influences of bending and squeezing on the polarization properties

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REVIEW OF SCIENTIFIC INSTRUMENTS 2005年第4期76卷 043703-1-043703页

作者： Mitsui, T Natl Inst Mat Sci Nanomat Lab Tsukuba Ibaraki 3050044 Japan

We have characterized the optical properties of a polarization-preserving near-field scanning optical microscopy (NSOM) optical fiber probe, and evaluated the influence of probe fabrication processes, such as melting-pulling and bending, on those properties. We found that the extinction ratio always decreases on the linearly polarized light parallel to the slow axis, and that the decrease is independent of the direction in which the probe is bent. The most probable cause of the low extinction ratio is the isotropic compression stress occurring when the fiber is squeezed;such stress cancels out the tensile stress applied to the core by stress applicators. Using the polarization-preserving NSOM probe, we observed the optical properties of the propagation light within a polymeric optical waveguide in guide-collection mode, and investigated those properties with various polarization conditions of incident light and probe collection. (C) American Institute of Physics.

关键词： SINGLE QUANTUM DOTS wave-guides CDS NANOCRYSTALS PHOTOLUMINESCENCE PROPAGATION LIGHT

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One-dimensional assemblies of nanoparticles: Preparation, properties, and promise

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ADVANCED MATERIALS 2005年第8期17卷 951-962页

作者： Tang, ZY Kotov, NA Univ Michigan Dept Chem Engn Ann Arbor MI 48109 USA Univ Michigan Dept Mat Sci Ann Arbor MI 48109 USA Univ Michigan Dept Biomed Engn Ann Arbor MI 48109 USA

Nanoparticle (NP) assemblies are of considerable interest for both fundamental research and applications, since they provide direct bridges between nanometer-scale objects and the macroscale world. Unlike two-dimensional or three-dimensional NP assemblies, which have been extensively studied and reviewed, reports on one-dimensional (1D) NP assemblies are rather rare, even though these assemblies are likely to play critical roles in the improvement of the efficiencies of various electronic, optoelectronic, magnetic, and other devices based on single NPs or their composites. Additionally, 1D assemblies of NPs, i.e., chains, can significantly help in the understanding of a number of biological processes and fundamental quantum mechanics of nanometer-scale systems. The difficulties are very evident when one wants to realize anisotropic 1D assemblies from presumably isotropic, zero-dimensional NPs. In this context, the authors present a systemic review of current research on 1D NP assemblies. Their preparation methods are classified and novel characteristics of NP chains, such as collective properties and directional transfer of photons, electrons, spins, etc., are elucidated. Current problems underlying the fundamental research and practical applications of 1D NP assemblies are also addressed.

关键词： WALLED CARBON NANOTUBES TOBACCO-MOSAIC-VIRUS POLYMER-CONTROLLEDCRYSTALLIZATION ELECTROMAGNETIC ENERGY-TRANSPORT MOLECULAR-DYNAMICS SIMULATION CDSE NANOCRYSTALS METAL NANOPARTICLES SILVER NANOWIRES QUANTUM DOTS wave-guides

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Propagation effects on the ultrafast cross-gain modulation in semiconductor optical amplifiers

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OPTICS COMMUNICATIONS 2005年第1-3期248卷 267-280页

作者： Hessler, TP Selbmann, PE Pleumeekers, JL Dupertuis, MA Deveaud, B Schreieck, R Emery, JY Dagens, B Ecole Polytech Fed Lausanne Inst Photon & Elect Quant CH-1015 Lausanne Switzerland Swiss Fed Inst Technol ETHZ Dept Elect Engn IfE CH-8092 Zurich Switzerland Alcatel Corp Res Ctr Groupement Interet Econ OPTO F-91461 Marcoussis France

We have performed cross-gain modulation experiments on semiconductor optical amplifiers with 100 fs pump pulses. Setting the pump on the high energy side of the gain results in a complex transient for the CW probe that is situated at gain maximum. An important part of this transient is shown to be due to propagation effects. Indeed, the pump pulses, at transparency or in absorption at the entrance, may get out of the amplifier in the gain region. These effects have to be considered, particularly in the potential sub-picosecond wavelength conversion with 100 fs pulses placed at transparency. Simulations based on a microscopic theory, which goes beyond the relaxation time approximation, show that, in such conditions, electron and hole populations can have different temperatures and different evolutions. However these simulations, which neglect propagation effects and consider only one slice of the device, fail to explain some of the experimental curves. In very long amplifiers (more than 2 mm) propagation effects become even more important. We show that they can be distinguished from carrier heating due to the generation of high energy carriers that arises only above an energy per pulse of 40 pJ. (c) 2005 Elsevier B.V. All rights reserved.

关键词： GAALAS LASER-DIODES SUBPICOSECOND GAIN wave-guides DYNAMICS SOA NONLINEARITIES TRANSPARENCY ENHANCEMENT GENERATION LIGHT

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Template-assisted growth of nominally cubic (100)-oriented three-dimensional crack-free photonic crystals

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NANO LETTERS 2005年第12期5卷 2646-2650页

作者： Jin, CJ McLachlan, MA McComb, DW De La Rue, RM Johnson, NP Univ Glasgow Dept Elect & Elect Engn Glasgow G12 8LT Lanark Scotland Univ London Imperial Coll Sci Technol & Med Dept Mat London SW7 2AZ England

Three-dimensional (3D) photonic crystals (PhCs) are now beginning to acquire functionality via the use of dopants and heterostructures. However, the self-organized fabrication of large-area single crystals that are free of cracks and stacking faults has remained a challenge. We demonstrate a technology for the fabrication of (100)-oriented thin film 3D opal PhCs that exhibit no cracks over areas having no intrinsic size limit via a modified template-assisted colloidal self-assembly approach onto a patterned substrate. This technology potentially makes available large area regions of single photonic crystal, which can be used for optoelectronic devices.

关键词： NEAR-INFRARED waveLENGTHS COLLOIDAL CRYSTALS BANDGAP CRYSTALS wave-guides FABRICATION THICKNESS SPHERES CHIP OPAL

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Trimming of microring resonators by photo-oxidation of a plasma-polymerized organosilane cladding material

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OPTICS LETTERS 2005年第17期30卷 2251-2253页

作者： Sparacin, DK Hong, CY Kimerling, LC Michel, J Lock, JP Gleason, KK MIT Dept Mat Sci & Engn Cambridge MA 02139 USA MIT Dept Chem Engn Cambridge MA 02139 USA MIT Inst Soldier Nanotechnol Cambridge MA 02139 USA

As the complexity of microphotonic devices grows, the ability to precisely trim microring resonators becomes increasingly important. Photo-oxidation trimming uses UV irradiation to oxidize a cladding layer composed of polymerized hexamethyldisilane (6M2S) deposited with plasma-enhanced chemical vapor deposition (PECVD). PECVD 6M2S has optical properties that are compatible with microring devices, and its high cross linking renders it insoluble. Photo-oxidation decreases the refractive index of PECVD 6M2S by nearly 4%, permitting large resonance shifts that are not feasible with thermal trimming techniques. Resonance shifts from single-mode, 100 mu m diameter Si3N4 (n=2.2) rings were as large as 12.8 nm for the TE mode and 23.5 nm for the TM mode. (c) 2005 Optical Society of America.

关键词： wave-guides FILTERS FILMS

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Absolute luminescence efficiency and photonic band-gap effect of conjugated polymers with top-deposited distributed Bragg reflectors

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CHEMICAL PHYSICS LETTERS 2005年第4-6期411卷 316-320页

作者： Persano, L Mele, E Camposeo, A Del Carro, P Cingolani, R Pisignano, D Univ Lecce INFM Natl Nanotechnol Lab Dipartimento Ingn Innovazione I-73100 Lecce Italy

We study the effects of the deposition of a photonic crystal (PhC) structure, namely a distributed Bragg reflector, on a light-emitting conjugated polymer. The hybrid organic/PhC system is realised by a novel low-temperature reactive electron beam deposition, suitable for the direct fabrication of high-reflective mirrors onto organic soft matter. We investigated the photoluminescence absolute quantum efficiency of the system, finding a yield of 30% after the mirror deposition. We found evidence for the modulation of the output spectra by the photonic band-gap of the coupled PhC, and for the polarisation splitting (as large as 140 meV) of the emitted light. (c) 2005 Elsevier B.V. All rights reserved.

关键词： SEMICONDUCTOR MICROCAVITIES CRYSTAL SLABS wave-guides PHOTOLUMINESCENCE LASER gap effect Organic polymers Laser microresonators electron beam deposition Distributed Bragg reflectors Bragg reflectors Photonic band gap Mirrors waveguide Device Component Polarization Luminous efficacy Quantum efficiency

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3-D molecular assembly of function in titania-based composite material systems

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ACCOUNTS OF CHEMICAL RESEARCH 2005年第4期38卷 263-271页

作者： Bartl, MH Boettcher, SW Frindell, KL Stucky, GD Univ Calif Santa Barbara Dept Chem & Biochem Santa Barbara CA 93106 USA Univ Calif Santa Barbara Calif Nanosyst Inst Santa Barbara CA 93106 USA

Various examples of composite titania-based nanostructured materials exhibiting cooperative functionalities between different active components are presented. The fabrication of these integrated composite materials is based on one-pot supramolecular templating techniques combined with acidic sol-gel chemistry. The defined 3-D nanoscale organization and integration of various functional components results in advanced optoelectronic and photonic applications such as visible light sensitization of mesoporous titania photocatalysts with cadmium sulfide nanocrystals acting as sensitizing integral part of the mesopore wall structure, narrow bandwidth emission from rare earth ion activated nanocrystalline mesoporous titania films, and mirrorless lasing in dye-doped hybrid organic/inorganic mesostructured titania waveguides.

关键词： MESOSTRUCTURED THIN-FILMS MESOPOROUS METAL-OXIDES SOLAR-CELLS wave-guides TIO2 NANOCRYSTALS LUMINESCENCE NANOSTRUCTURES SURFACTANTS CONVERSION

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Emission and detection of terahertz pulses from a metal-tip antenna

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2005年第11期22卷 2357-2365页

作者： Walther, M Chambers, GS Liu, ZG Freeman, MR Hegmann, FA Univ Alberta Dept Phys Edmonton AB T6G 2J1 Canada

We investigate the antenna characteristics of a metal tip coupled to terahertz (THz) pulses generated from a photoconductive switch. Enhanced terahertz pulse emission is observed with the metal tip in contact with one of the electrodes of the photoconductive switch. Measurements of the angular dependence of the emitted THz radiation show that the metal tip acts as a highly directional antenna with radiation patterns well described by the theory for long-wire traveling-wave antennas. Similar behavior is observed for the metal tip acting as a THz pulse receiver, in accordance with the reciprocity principle. Effects related to the broadband nature of the THz pulses are discussed. (c) 2005 Optical Society of America.

关键词： COPLANAR TRANSMISSION-LINES TIME-DOMAIN SPECTROSCOPY NEAR-FIELD wave-guides WHISKER DIODES PROPAGATION GENERATION MICROSCOPY DISPERSION RESOLUTION

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Shaping the radiation field of tilted fiber Bragg gratings

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2005年第5期22卷 962-974页

作者： Walker, RB Mihailov, SJ Lu, P Grobnic, D Commun Res Ctr Ottawa ON K2H 8S2 Canada

Over the past several years polarization-sensitive mode-coupling characteristics of tilted fiber Bragg gratings have been exploited for the development of a number of useful devices, including fiber polarimeters, gain flattening filters, spectrum analyzers, and polarization-dependent-loss compensators. Although a variety of tools are available to model blazed grating responses, to our knowledge a simplified explanation of the parametric dependencies and potential behavior has never been fully presented, making the optimization of these components difficult and elusive at times. We provide a thorough, intuitive discussion of these trends and possibilities as observed through an extensive theoretical and numerical analysis rooted in the volume current method. In addition to a review of the potential limitations and shortcomings of this formulation, some rough guidelines for the manufacture of various devices are also disclosed. © 2005 Optical Society of America.

关键词： VOLUME CURRENT METHOD OPTICAL-FIBER wave-guides MODE EFFICIENT waveguides DISPERSION SCATTERING EXPOSURE FILTER

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