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Superlinear photovoltaic currents in LiNbO₃:: analyses under the two-center model

APPLIED PHYSICS B-LASERS AND OPTICS 2004年第3期79卷 351-358页

作者： Carnicero, J Caballero, O Carrascosa, M Cabrera, JM Univ Autonoma Madrid Fac Ciencias Dept Fis Mat C4 E-28049 Madrid Spain

Superlinear photovoltaic currents in LiNbO3 are theoretically studied by using a two active center model, with Fe2+/Fe3+ as primary center and Nb-Li(4+)/Nb-Li(5+) as secondary center. Analytical instead of numerical results are provided, including close-form expressions for most common experimental situations. Recent photovoltaic parameters obtained for alpha-phase proton-exchanged LiNbO3 waveguides (very similar to the substrate) are used for applying the model and comparing with published experimental results. Thoroughly studied aspects are: the redistribution of donor/acceptor states for each species as a function of the light intensity, their contribution to the photovoltaic current density, the effect of the temperature, and the role of the center concentrations and their reduction state. This provides a detailed understanding of the photovoltaic current function shapes versus light intensity, predicts new features of interest for experimentalists and suggests further experiments to better determine the material parameters. Photovoltaic measurements and modeling appear a simpler and safer way of understanding the role of the two-center photovoltaic effect in photorefractive phenomena as well as for determining important photorefractive parameters.

关键词： HIGH LIGHT INTENSITIES BENZOIC-ACID VAPOR wave-guides LITHIUM-NIOBATE PHOTOREFRACTIVE MATERIALS CRYSTALS ERASURE High intensity light PHOTOVOLTAIC PHOTOVOLTAIC EFFECT Supralinearity Lithium niobate crystals waveguide Device Component Light intensity

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Prism coupling technique investigation of elasto-optical properties of thin polymer films

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JOURNAL OF APPLIED PHYSICS 2004年第12期96卷 7147-7153页

作者： Ay, F Kocabas, A Kocabas, C Aydinli, A Agan, S Bilkent Univ Dept Phys TR-06800 Ankara Turkey Kirikkale Univ Dept Phys TR-71450 Kirikkale Turkey

The use of thin polymer films in optical planar integrated optical circuits is rapidly increasing. Much interest, therefore, has been devoted to characterizing the optical and mechanical properties of thin polymer films. This study focuses on measuring the elasto-optical properties of three different polymers;polystyrene, polymethyl-methacrylate, and benzocyclobutane. The out-of-plane elastic modulus, refractive index, film thickness, and birefringence of thin polymer films were determined by means of the prism coupling technique. The effect of the applied stress on the refractive index and birefringence of the films was investigated. Three-dimensional finite element method analysis was used so as to obtain the principal stresses for each polymer system, and combining them with the stress dependent refractive index measurements, the elasto-optic coefficients of the polymer films were determined. It was found that the applied stress in the out-of-plane direction of the thin films investigated leads to negative elasto-optic coefficients, as observed for all the three thin polymer films. (C) 2004 American Institute of Physics.

关键词： THROUGH-PLANE MODULUS wave-guides PHOTOELASTIC PROPERTIES THERMAL-EXPANSION GLASSY STATE PMDA-ODA BENZOCYCLOBUTENE POLYSTYRENE ORIENTATION ANISOTROPY

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wavelength- and temperature-dependent measurement of refractive indices

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2004年第4期21卷 729-738页

作者： Jasny, I Nickel, B Borowicz, AP Polish Acad Sci Inst Phys Chem PL-01224 Warsaw Poland Max Planck Inst Biophys Chem D-37077 Gottingen Germany

A new method for determination of the refractive index of any transparent solvent or glass was developed and tested for use at temperatures of 133-293 K in the ultraviolet and visible spectral ranges. The wavelength and temperature dependencies of the refractive indices of several solvents and of fused silica are reported. The data obtained for tetrachloromethane and fused silica are compared with those available in the literature. The advantages and limitations of the method are discussed, based on the accuracy of the data presented. Knowing the values of refractive indices of organic solvents should be useful in luminescence spectroscopy. (C) 2004 Optical Society of America.

关键词： FEMTOSECOND LASER TRIPLET-STATE wave-guides GLASSES SILICA MICROPARTICLE ANTHRACENE DISPERSION MOLECULES PYRENE

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Resonant electromagnetism in photonic crystals composed of triangular-arrayed rods with both dielectric constant and magnetic permeability functions

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2004年第2期21卷 413-418页

作者： Yang, SY Hong, CY Drikis, I Horng, HE Yang, HC Da Yeh Univ Dept Mech & Automat Engn Changhua 515 Taiwan Natl Taiwan Normal Univ Inst Electroopt Sci & Technol Dept Phys Taipei 116 Taiwan Natl Taiwan Univ Dept Phys Taipei 106 Taiwan

The modified frequency-domain method was used to simulate the photonic properties of triangular-arrayed rods surrounded by air and possessing nonunity dielectric and magnetic permeability functions. It was found that the photonic bandgap becomes broader for the TE mode when material with higher magnetic permeability and lower dielectric constant is used for rods as compared with that of purely dielectric rods with the same refractive index, whereas the gap is reduced for the TM mode. We further examined the photonic characteristics of the photonic-crystal cavity formed when a point defect is introduced into the rod array. With a fixed refractive index of the rods, the resonant frequency of the TE mode in the first band gap is lower and the electromagnetic energy concentration at the point defect is higher when material with higher magnetic permeability and lower dielectric constant is used for the rods. The opposite was found for the TM mode. (C) 2004 Optical Society of America.

关键词： wave-guides

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Spectra of soft ring graphs

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waveS IN RANDOM MEDIA 2004年第1期14卷 S47-S60页

作者： Exner, P Tater, M Acad Sci Czech Republ Inst Nucl Phys Dept Theoret Phys CZ-25068 Rez Czech Republic Czech Tech Univ Dopper Inst Prague 11519 Czech Republic

We discuss a ring-shaped soft quantum wire modelled by 6 interaction supported by the ring with a generally nonconstant coupling strength. We derive the condition which determines the discrete spectrum of such systems, and analyse the dependence of the eigenvalues and eigenfunctions on the coupling and ring geometry. In particular, we illustrate that a random component in the coupling leads to a localization. The discrete spectrum is also investigated in the situation when the ring is placed into a homogeneous magnetic field or threaded by an Aharonov-Bohm flux and the system exhibits persistent currents.

关键词： Strong delta-interaction Band-gap structure Schrodinger operator Edge states Persistent currents Sphere interactions Acoustic media Hall systems wave-guides Loop Spectra gap structure persistent currents waveguide Device Component discrete spectrum

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Characterization of quasi-phase-matching gratings in quadratic media through double-pass second-harmonic power measurements

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2004年第6期21卷 1137-1145页

作者： Johansen, SKR Baldi, P Univ Nice Lab Phys Mat Condensee F-06108 Nice 2 France Tech Univ Denmark DK-2800 Lyngby Denmark

A new scheme for nondestructive characterization of quasi-phase-matching grating structures and temperature gradients through inverse Fourier theory using second-harmonic-generation experiments is proposed. By inserting a mirror to reflect the signals back through the sample, we show how it is possible to retrieve the relevant information by measuring only the generated second-harmonic power, avoiding more complicated phase measurements. The potential of the scheme is emphasized through theoretical and numerical investigations in the case of periodically poled lithium niobate bulk crystals. (C) 2004 Optical Society of America.

关键词： POLED LITHIUM-NIOBATE wave-guides NONLINEAR-INTERACTIONS BLUE-LIGHT GENERATION SOLITONS FREQUENCY CONVERSION LINBO3 LITAO3

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Design and analysis of a low-threshold polymer circular-grating distributed-feedback laser

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2004年第12期21卷 2142-2150页

作者： Barlow, GF Shore, A Turnbull, GA Samuel, IDW Univ Wales Sch Informat Bangor LL57 4TA Gwynedd Wales Univ St Andrews Sch Phys & Astron St Andrews KY16 9SS Fife Scotland

A transfer-matrix technique is used to calculate the lasing thresholds of second-order circular-grating polymer lasers operating at 630 nm. By use of poly [2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylene] as an example polymer material, it is also shown how known optical properties of polymeric materials may be incorporated into the analysis of both the transverse waveguiding and the distributed feedback in circular-grating distributed-feedback polymer lasers. (C) 2004 Optical Society of America.

关键词： wave-guides DFB EQUATIONS

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Induced focusing of two laser beams in cubic quintic nonlinear media

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PHYSICA SCRIPTA 2004年第6期70卷 354-360页

作者： Jana, S Konar, S Birla Inst Technol Dept Appl Phys Ranchi 835215 Bihar India

This paper presents an investigation of induced focusing of two laser beams (i.e., a pump beam and another probe beam) in a medium possessing cubic quintic nonlinearity. Third and fifth order nonlinear susceptibilities in presence of two interacting waves have been evaluated. These susceptibilities are then employed to derive two coupled nonlinear Schrodinger equations. Variational formalism has been employed to derive relevant equations which govern different characteristics of propagating beams. Extensive numerical simulation has been performed to investigate the influence of the pump beam on the propagation characteristics of the probe beam. Among several important findings. most noteworthy one is that a very weak probe beam can be guided and focused with a pump beam even if its power is well below threshold Value of focusing of the pump beam alone. It has been found that induced focusing of the probe beam is more effective when its wavelength is smaller and initial beam width larger than the corresponding quantities of the pump. The roles of fifth order nonlinear coefficient on induced focusing have been investigated. Particularly. it has been established that even an initially defOCUsing pump can focus a very weak probe.

关键词： PARA-TOLUENE SULFONATE OPTICAL FIBERS wave-guides VARIATIONAL APPROACH SOLITARY waveS RING FORMATION PROPAGATION INDEX COLLAPSE PULSES

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Characterization of optically active and photocurable ORMOSIL thin films deposited using the Aerosol process

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JOURNAL OF MATERIALS SCIENCE 2004年第8期39卷 2801-2810页

作者： Trejo-Valdez, M Jenouvrier, P Fick, J Langlet, M Ecole Natl Super Phys Grenoble LMGP F-38402 St Martin Dheres France Univ Grenoble 1 CNRS INPGUMR 5130 ENSERGIMEP F-38016 Grenoble France

Aerosol-gel process is a deposition method based on the sol-gel polymerization of a liquid film produced from an ultrasonically sprayed aerosol. This process offers an attractive alternative for the deposition of photocurable SiO2-TiO2 ORMOSIL films. 3-(trimethoxysilyl) propylmethacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid were used as sol-gel precursors. Doping with a terbium: sulphosalicylic acid complex was also studied to test the deposition of spectroscopically active photocurable films. FTIR spectroscopy has been used to study the precursor solutions and ORMOSIL films. It is shown that titanium precursor incorporation enhances the solution reactivity, which yields optical quality thin films. Photopolymerization and photoluminescence properties of the films are reported and discussed with respect to the experimental parameters. The results allow envisaging the UV-imprinting fabrication of Aerosol-gel-derived active waveguides. (C) 2004 Kluwer Academic Publishers.

关键词： Organic-inorganic nanocomposites 1 55 mu-m wave-guides Complexes Behavior Silicon Cage Gels Sol-gels Optical activity Films waveguide Device Component cages Gels Organic-inorganic hybrid materials thin films precursors

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Polydiacetylene films: a review of recent investigations into chromogenic transitions and nanomechanical properties

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JOURNAL OF PHYSICS-CONDENSED MATTER 2004年第23期16卷 R679-R697页

作者： Carpick, RW Sasaki, DY Marcus, MS Eriksson, MA Burns, AR Univ Wisconsin Dept Engn Phys Madison WI 53704 USA Sandia Natl Labs Biomol Mat & Interfaces Dept Albuquerque NM 87185 USA Univ Wisconsin Dept Phys Madison WI 53704 USA

Polydiacetylenes (PDAs) form a unique class of polymeric materials that couple highly aligned and conjugated backbones with tailorable pendant sidegroups and terminal functionalities. They can be structured in the form of bulk materials, multilayer and monolayer films, polymerized vesicles, and even incorporated into inorganic host matrices to form nanocomposites. The resulting materials exhibit an array of spectacular properties, beginning most notably with dramatic chromogenic transitions that can be activated optically, thermally, chemically, and mechanically. Recent studies have shown that these transitions can even be controlled and observed at the nanometre scale. These transitions have been harnessed for the purpose of chemical and biomolecular sensors, and on a more fundamental level have led to new insights regarding chromogenic phenomena in polymers. Other recent studies have explored how the strong structural anisotropy that these materials possess leads to anisotropic nanomechanical behaviour. These recent advances suggest that PDAs could be considered as a potential component in nanostructured devices due to the large number of tunable properties. In this paper, we provide a succinct review of the latest insights and applications involving PDA. We then focus in more detail on our work concerning ultrathin films, specifically structural properties, mechanochromism, thermochromism, and in-plane mechanical anisotropy of PDA monolayers. Atomic force microscopy (AFM) and fluorescence microscopy confirm that films 1-3 monolayers thick can be organized into highly ordered domains, with the conjugated backbones parallel to the substrate. The number of stable layers is controlled by the head-group functionality. Local mechanical stress applied by AFM and near-field optical probes induces the chromogenic transition in the film at the nanometre scale. The transition involves substantial optical and structural changes in a highly compressed form. Thermochromism is

关键词： ATOMIC-FORCE MICROSCOPY LANGMUIR-BLODGETT-FILMS GAS-WATER INTERFACE ELECTRONIC-STRUCTURE wave-guides SUBSTITUTED POLYDIACETYLENES CONJUGATED POLYMERS PHASE-CONTRAST CD2+ SALTS THERMOCHROMISM

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