Proceedings Volume 4104

Organic Photorefractives, Photoreceptors, and Nanocomposites

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Proceedings Volume 4104

Organic Photorefractives, Photoreceptors, and Nanocomposites

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Volume Details

Date Published: 13 November 2000
Contents: 5 Sessions, 18 Papers, 0 Presentations
Conference: International Symposium on Optical Science and Technology 2000
Volume Number: 4104

Table of Contents

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Table of Contents

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  • Section
  • Materials I
  • Generation and Transport
  • Materials II
  • Devices
  • Section
Section
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Embedded triboluminescent structural damage sensors
Ian Sage, Lisa Humberstone, I. Oswald, et al.
Triboluminescent materials offer a viable route to real-time structural damage sensing. The sensors can be externally attached to the surface of metals or composites, or embedded within composites. In-situ monitoring of structural damage in composites is particularly relevant since severe internal damage can exist with little indication of this damage on the composite surface. The main issue related to embedding triboluminescent sensors within composites is how to access efficiently the optical signal generated upon structural damage and how to guide efficiently this optical damage signal to a remote detector. Earlier work relied on side-coupling of the triboluminescent light into a curved conventional silica fibre and/or end-coupling into the silica fibre, if the damage to the host structure had also broken the fibre. Both these light collection methods are, of course, inefficient and resulted in an optical damage signal with a very poor S/N ratio. By using novel photoluminescent polymeric and silica fibres, we have shown that it is possible to efficiently capture and guide the optical damage signal from an embedded triboluminescent sensor to a remote detector. These fibres resulted in a signal with a S/N ratio that was orders of magnitude larger than that achieved using the conventional silica fibre. Futhermore, we have shown that the light collection/guiding technique can be used effectively with triboluminescent sensors embedded within black CFRP composites. Finally, we have demonstrated that for resins and GFRP composites, triboluminescent sensors act as truly global damage sensors, wehreas for CFRP composites, the damage sensing is localised to areas close to the embedded photoluminescent fibre.
Nanodispersed liquid crystal polymer composites for optically tunable filters
Keith L. Lewis, Ian Robert Mason, Ian Sage, et al.
Nano-phase polymer dispersed liquid crystal composites (n-PDLCs) have shown significant potential for use as in voltage tunable optical devices. In such composites, the dimensional scale of the liquid crystal droplets is such that optical scattering effects can be minimised in the visible and near infrared spectrum. The nanoscopic scale also allows the material to be described as a single homogeneous medium using effective medium approximations. The average refractive index of the material can be changed as electric field is applied and it is possible to effect spectral shifts in transmission bands when the material is incorporated into resonant filter structures. The paper summarises recent developments in such composite materials emphasizing the role of different co-polymer formulations for the matrix phase, and the useof different surfactant species to reduce the effects of pinning of the liquid crystal molecules at the droplet walls.
Two-photon photochromism of a photorefractive organic material for holographic recording
Kevin D. Belfield, David J. Hagan, Yong Liu, et al.
We report the two-photon induced photoisomerization of 3-[1-(1,2- dimethyl-1H-indol-3-yl)-ethylidene]-4-isopropylidene-dihydro-furan- 2,5-dione (1), a photochromic compound with (lambda) maxequals385nm, using 775 fs pulses. The resulting photoisomer has a (lambda) maxequals582 nm. The kinectic rate contant for the isomerization reaction w as measured at two different intensities (two different powers), showing a quadratic dependence with respect to the pump intensity. Results of pump-probe solution phase experiments and guest/host polymer thin film interferometric imaging studies are shown. A two-photon absorption molecular cross-section (sigma) 2equals10.3 x 10- 45 cm4 s/photon was measured using Z-scan, supporting a two photon induced isomerization process.
Optical actuators based on photorefractive materials controlled by moving holographic gratings
Michael J. Curley, Aisha Fields, Sergey S. Sarkisov, et al.
Generating a moving holographic grating in a slab os photorefractive crystal can turn it into a smart optical material making up an optically driven actuator. Actuation occurs as a result of mechanical deformation of the crystal caused by photogenerated electric charge distribution due to piezoelectric effect. The charge distribution is periodical since it is produced by a holographic grating generated by two interfering coherent laser beams. In case of static grating with oscillating amplitude or grating vibrating near the static position the effect results in appearance of a surface acoustic wave or in bending bulk crystal as has been recently demonstrated for BSO. In this paper we focus ourselves on periodical surface deformation moving synchronously with running holographic grating. This running surface wave of deformation is similar to that being used to push a rotor pressed by its surface against a vibrating stator in so-called ultrasonic motors. It can be potentially used in optically driven actuators, which could be small in size (nanometers), less power consuming, and less affected by FR interference. We report on an appearance of a periodical surface deformation in photorefractive crystals of iron doped lithium niobate that is produced by a holographic grating. The amplitude of the deformation is of the order of 10 nm. We also report light-induced mechanical motion of micron-size particles associated with self- diffraction of weak laser beams in strongly absorbing solutions of phthalocyanines. These results might find some applications in new types of all-optical and electro-optical actuators.
Semiconductor-to-metallic phase transitions in VO2/gold nanocomposite materials
Keith L. Lewis, Andrew M. Pitt, Richard M. Bennett
Vanadium dioxide is well known for its thermochromic characteristics arising from a semiconductor to metallic phase transition at 68 degree(s)C. The optical properties of the material on each side of the phase transition are relatively well established and the change in refractive index as a result of heating allows the exploitation of the material in fast optical switching devices. Whilst switching speeds of the order of a few nanoseconds can be readily achieved, the properties of high temperature phases are less than optimal, due to the imperfect nature of the metallic state. This paper examines the feasibility of enhancing the metallic phase properties through the realisation of a noncomposite formed as a result of the reactive co-sputtering of vanadium and gold in an oxygen environment. The vanandium reacts with oxygen during the reactive sputtering process to produce VO2 whilst the gold is unchanged and appears as a discrete phase in the oxide host.
Optical properties of crystalline tungsten oxide
Michael G. Hutchins, A. John Topping, N. S. Butt, et al.
While designing a thermal control device based upon crystalline tungsten oxide it is vital to have knowledge of both n, the real part of the refractive index and k, the complex part. With this knowledge it is possible to predict the performance of an electrochromic device at different wavelengths of radiation. We performed a series of experiments on crystalline samples of tungsten oxide where both n and k were carefully determined from spectral reflectance and transmittance measurements after set amounts of charge were inserted electrochemically, thus reducing the tungsten oxide. The trends for n and k are different, which has implementations for device performance and design. We also investigated the effect of deposition temperature on the optical properties of crystalline tungsten oxied. This has implications for both the substrate that may be u sed in a device and the construction of the device. The final data we shall present are some electromechanical studies of insertion into crystalline tungsten oxide flake samples and powder samples. The flakes and powder are deposited in a similar way to a graphite paste electrodes used in Li ion battery studies. This is a possible route to a flexible eleectrochromic device based upon crystalline tungsten oxide.
All-solid-state electrochromic window of SnO2/Mo and electrodeposited WO3 film with poly(acrylonitrile) gel electrolyte
Lianyong Su
An all solid-state electrochromic smart window employing SnO2/Mo and electrodeposited WO3 film with poly(acrylonitrile)(PAN) gel electrolyte with high conductivity (5 mS/cm) at room temperature has been fabricated. The smart window has been found excellent electrochromism and memory characteristics.
Electrochemical and optical properties of WO3:X sol-gel coatings (X=Li, Ti, Nb, Ta)
Cesar O. Avellaneda, Luis O. Bulhoes
Electrochromic behavior of amorphous tungsten oxide (formula available in paper)doped films was investigated. The addition of titanium (5 %mol), noibium (5 %mol), tantalum (5 %mol) and lithium salt (15 %mol) to the precursor solutions leads to films with different electrochemical performance. The electrochormic properties of these films were investigated by in situ spectroelectrochemical method exhibiting a blue coloration under Li+ insertion with a reversible variation of the transmittance in the visible and near infrared range between 10% and 90%. The electrochemical and optical responses of the films were obtained from the cyclic voltammetry measurements using propylene carbonate with 0.1M LiC1O4 as electrolyte. The bleaching process in the lithium doped films occurs in a few seconds and faster response for the bleaching was obtained for WO3:Li:Ti film.
Materials I
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Poly(1-vinylindole) and some of its methyl derivatives as substrates for photorefractive materials: their synthesis, optical, and electrical characterization
Arturo Colligiani, Fiorella Brustolin, Valter Castelvetro, et al.
The best conditions for the synthesis of poly(1-vinylindole) (PVI) and some of its methyl derivatives have been investigated. The aim of the research was to verify if PVI could be used instead of poly(1- vinylcarbazole) (PVK) in polymeric blends having photoconductive and/or photorefractive behavior. All synthesized polymers are characterized by a glass transition temperature that is lower than that of PVK. It has been verified that the indole ring system, inclusive of its methyl substituted derivatives, lacking of the symmetry characteristics of carbazole, possesses an electric dipole moment that is constantly higher than that of PVK. A higher dipole moment can be an advantageous feature to improve the solubility within the polymetric matrix of the optically non-linear molecule, necessary for photorefractivity. Charge-transfer complexes with a fluorenone-like photosensitizer are efficiently formed by both PVI and its derivatives. A direct current measuring apparatus has been assembled by which photocurrents of few picoamperes can be detected and recorded. Preliminary reported results clearly show that PVI is a photoconductive material. Its photoconductivity is compared with that of PVK and of hybrid materials containing mixtures of carbazole and indole moieties, present in the measuring cell as pendant groups on a macromolecular chain, as single molecules, or both.
Amorphous monolithic triphenylamine derivatives with fast holographic response times
Christoph Hohle, Peter Strohriegl, Stephan J. Zilker, et al.
We report on holographic investigations of several organic photorefractive materials based on monolithic low molar mass glasses. The addition of different plasticizing agents and the variation of three NLO-units prove to change the photorefractive performance and the thermal properties of the resulting compounds dramatically. Very fast holographic response times down to 2.5 ms could be reached at refractive index modulations of 6 10- and two-beam coupling gains of up to 140 cm-1.
Generation and Transport
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Transport properties of finite organic matrices containing charged particles: transport layer between metallic electrodes
Sergey Vitalyevich Novikov
Effect of static charges on transport properties of disordered organic materials is considered. Long range mature of Coulomb interaction requires to take into consideration a finite thickness of the transport layer. Presence of conducting electrodes significantly modifies properties of organic medium, removes a long range Coulomb divergence, and makes it possible to calculate in finite form statistical properties of organic medium (with nonzero total charge density), relevant for transport characteristics. A special attention is paid to the particular case of charge induced disorder - a disorder originated from the surface charge located at the rough surface of electrodes. We present also a generalization of 1D model of charge carrier transport ot the case of inhomogeneous energetic disorder that realizes in the case of charge induced disorder.
Variation of the glass transition temperature in organic photorefractive materials: plasticizer versus novel synthetic approaches
Andre Leopold, Uwe Hofmann, M. Grasruck, et al.
Most photorefractive (PR) materials require plasticizers in order to decrease the glass transition temperature, allowing for orientational enhancement by the chromophores. Introduction of the plasticizer, however, alters not only the viscosity but also the photoconductive properties of the material. This can be shown by comparing two different plasticizers which were introduced into a bifunctional low-molecular-weight PR glass and into a polyfluorene guest-host polymer. The latter reaches response times down to 600 microsecond(s) at a writing intensity of 1 W/cm2. We have recently improved the concept of low-molecular-weight PR glasses. A suitable, photoconducting unit allows the synthesis of a bifunctional system with a glass transition of 22.6 degree(s)C. Therefore, no plasticizer is needed. The material is based on a triphenyldiamine (TPD) moiety to which a nonlinear-optical chromophore is directly attached. The system is the first representative of a whole class of TPD molecules and polymers for photorefractive applications.
Materials II
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Photorefractivity in ferroelectric liquid crystals
Gary P. Wiederrecht, Michael R. Wasielewski, Michael J. Fuller
The first observation of photorefractivity in ferroelectric liquid crystals (flcs) is reported. The flcs are doped with the easily oxidized chromophore perylene, which also functions as the sensitizer. The electron acceptor di-buty1-pyromellitimide is added to induce photoconductivity through an efficient intermolecular electron transfer reaction to produce mobile ions. A strong dependence on the orientation of the wavevector of the optical interference pattern and polarization of the writing beams relative to the orientation of the lfc molecules is observed. The results are interpreted as an orientational photorefractive effect in which the net polarization of the flc couples linearly to the space-charge field as opposed to nematic liquid crystals in which the dielectric anisotrophy couples to the square of the space charge field.
Photorefractive polymers for laser-based ultrasound detection
Daniel Wright, Ulrich J. Gubler, Marvin B. Klein, et al.
Photorefractive polymers have recently shown an attractive combination of high two-beam-coupling gain coefficient (approximately equals 200cm-1), low absorption (approximately equals 5-10 cm-1), and fast response (few ms) at 1W/cm2 writing intensity. Such materials show promise as adaptive beamsplitters for homodyne detection of transient phase shifts due to laser-based ultrasound. The performance of a photorefractive polymer composite is explored for this application.
Toward morphologically stable photorefractive composites: a comparative study of ATOP/PVK-based materials
Erwin Mecher, Francisco Gallego-Gomez, Christoph R. Braeuchle, et al.
For the highly dipolar merocyanine chromophore ATOP, which exhibits a high polarizability anisotropy, material related properties were optimized by substituent variations at four different positions of the pr-conjugated core. Differential scanning calorimetry (DSC) and solubility studies in the model solvent N,N'-dimethylaniline showed a significant influence of the substituents. Thus almost unlimited solubility in N,N'-dimethylaniline and the formation of kinetically stable amorphous glasses was observed for the dye ATOP—4 whereas the parent dye ATOP—5 was a high melting and almost insoluble solid. The more soluble and lower melting derivatives ATOP—3, ATOP—4, ATOP—8 and ATOP—9 all showed a high compatibility with the photoconducting polymer poly(N-vinylcarbazole) which allowed to prepare composites containing up to 50 %wt of the respective dye. For these composites pronounced photorefractive effects were measured with index modulation ofup to zln 7 x iO and gain coefficients ofup to r= 180 cm1 at electrical fields ofonly E —35 V.tm I For the composites of ATOP—4 no evidence for crystallization or phase-separation could be observed over several months, demonstrating that also host-guest systems containing highly dipolar dye molecules may be optimized towards high morphological stability.
Photorefractive properties of TNFM-sensitized PVK-based polymer composites and fully functionalized polymethacrylates
Eric Hendrickx, David Van Steenwinckel, Christiaan Engels, et al.
We have studied the photorefractive properties of (2,4,7-trinitro-9- fluorenylidene)malononitrile (TNFM) sensitized poly(N-vinylcarbazole)/N- ethylcarbazole polymer composites doped with 2-(3,4,4-trimethylhex-2- ene-1-ylidene)-1,3-propanedinitrile and related dyes. Characterization included four-wave mixing experiments, two beam coupling and photoconductivity measurement at a wavelength of 780 nm. At an applied field of 53 V/micrometers , we have observed complete internal diffraction and at 60 V/micrometers a gain coefficient of 230 cm-1. Small alterations in the chromophore donor group substituents were used to tune the ionization potential of the dopant dye by 0.3 eV. They affected the grating build-up time, photorefractive phase shift, and complexation with TNFM. This performance is compared to that of three newly synthesized polymethacrylates functionalized with carbazole, a dodecyl chain as an internal plasticizer and three different dyes. Here we observe net two-beam coupling gain and a diffraction efficiency of 60% at 58 V/micrometers .
Devices
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Synthesis and properties of monolithic photorefractive carbazole-derived calix[4]arenes
Atsushi Gunji, Hiromi Kimura-Suda, Takafumi Sassa, et al.
As a new class of multi-functional compounds, three kinds of calix[4]arene molecules were newly synthesized: calix[4]arenes containing two 3-nitro-N-allyl carbazoles, two N- allyl carbazoles and one of each at the lower rim. These compounds take cone conformation in solution because of the 1,3-di-O-substitution at the lower rim. Those compounds take amorphous state as proved by differential scanning calorimetry and powder X-ray diffraction and they can be made into films without supporting the polymer matrix. Second- harmonic generation signals were observed in the films of the two calix[4]arenes containing nitro groups after electric poling at a temperature above glass transition point. Enhancement of d33 in the calix[4]arene with nitrocarbazole derivatives compared with the calix[4]arene with both carbazole and nitrocarbazole derivatives was observed, which might be attributed partially to some extent to the conformational regulation between the two carbazole chromophores. Using two beam couple experiment, photorefractive effect was observed in the film of the calix[4]arene with both carbazole and nitrocarbazole derivatives doped with 2,4,7-trinitro-9-fluorenone. This is the first report on the photorefractive property of calix[4]arene compound.
Section
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Photochromic properties of chemically modified bacteriorhodopsin films
Bing Liang, Liqian Li, Meiling Li, et al.
The lifetime of M-state in the bacteriorhodopsin photocycle was remarkably prolonged in bR-gelatin film by using 1,4,7,10-tetraoxa-13- azacyclopentadecane (aza-15-crown-5) as chemical additive. Spectral and kinetic measurements were carried out at room temperature. It is observed that the M-state in the film has a long lifetime ((tau) 1/e) of 360s with bR/aza-15-crown-5 weight ratio of 1:3 under room conditions. To investigate the mechanism of aza-15-crown-5 on the photocycle of bR 15-crown-5 was used as chemical additive too. It was suggested that the strong complexing property towards H+ of aza-15- crown-5 played an important role in the prologation. The fitting of the M-state decay kinetics curves corresponded to a sum of three and two exponential components for bR-films using aza-15-crown-5 and 15-crown-5 as chemical additive respectively.