Dissertations / Theses on the topic 'Photorefractive materials'
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Jones, David Caradoc. "Wave interactions in photorefractive materials." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257934.
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Ellin, Hannah Catherine. "Aspects of wave interactions in photorefractive materials." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296992.
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Liu, Yafang. "Some properties of photorefractive spatial solitons." Thesis, University of Salford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272774.
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Au, L. B. "Wave propagation and grating formation in photorefractive materials." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235016.
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Farsari, Maria. "Dielectric and optical properties of organic photorefractive materials." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5226/.
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The work presented in this thesis is derived from experimentation in the field of polymeric photorefractive materials. Low T(_g) polymeric composites were prepared, based on the well-known photoconductive polymer PVK (maximum 50% w/w), sensitized with TNF (2% w/w) and C(_60) (0.2% w/w), plasticized with ECZ (maximum 49.3% w/w) and doped with the nonlinear optical materials NPP (50% w/w), DAN (20% w/w), DED (5% w/w), DCNQI (0.5% w/w), ULTRA-DEMI (5% w/w) and DI-DEMI (2% w/w), and their dielectric, linear and non linear optical properties were investigated. All the materials, except DCNQI, exhibited good solubility and sample processibility. The dielectric properties of the composites at 1 KHz and 1 MHz were determined using a parallel-plate capacitance bridge. The dielectric constant and loss at 10 GHz were measured using a novel adaptation of the resonant cavity technique, which was designed for measurements at ambient and elevated temperatures. The method was used to measure of the dielectric constant and loss of two novel, high T(_g), electro-optic polymers at temperatures up to 100 ºC. The dielectric properties measured were typical of polymeric materials. The absorption coefficient and the refractive index at different wavelengths were measured using a spectrophotometer. For the refractive index, an interference fringe analysis was used. The nonlinear measurements consisted of second harmonic generation, to prove the nonhnearity of the composites, two-beam coupling measurements, to prove their photorefractivity and degenerate four-wave mixing to measure their diffraction efficiency. The NPP, DAN, DED and ULTRA-DEMI doped investigated composites exhibited second order nonlinearity with highest the one of ULTRA-DEMI, at 292 pm/V for 19 kV of corona poling field. The photorefractivity of the NPP, DAN and DED doped composites was proven at 632.8 nm, while ULTRA-DEMI doped composites photooxidized before any measurements were possible. The two-beam coupling coefficients measured were lower than 20 cm(^-3), while net gain was observed only in the NPP doped composite. The diffraction efficiencies of the NPP, DAN and DED doped composites were measured at 632.8 nm, and were found to be l0(^-5)-l0(^-6).
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Grunnet-Jepsen, Anders. "Two-wave mixing and subharmonic instability in photorefractive materials." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260761.
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McClelland, Toby Edward. "Beam coupling and space-charge waves in photorefractive materials." Thesis, University of Kent, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309780.
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Montemezzani, Germano Luigi Montemezzani Germano Luigi Montemezzani Germano Luigi. "Optical wave manipulation and signal processing in anisotropic photorefractive materials /." Zürich : Swiss Federal Institute of Technology, Zurich, Institute of Quantum Electronics, 2003. http://e-collection.ethbib.ethz.ch/show?type=habil&nr=14.
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Cottrill, Ethan J. "Photorefractive Liquid Crystalline Materials towards Holographic, 3-D Data Storage." Ohio University Honors Tutorial College / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1367371515.
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Chen, Junfu. "Photorefractive effects in optical fibers grating fabrication and characterization." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/30424.
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Stark, Thomas S. "Picosecond Dynamics of Free-Carrier Populations, Space-Charge Fields, and Photorefractive Nonlinearities in Zincblende Semiconductors." Thesis, University of North Texas, 1999. https://digital.library.unt.edu/ark:/67531/metadc2202/.
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Generally, nonlinear optics studies investigate optically-induced changes in refraction or absorption, and their application to spectroscopy or device fabrication. The photorefractive effect is a nonlinear optical effect that occurs in solids, where transport of an optically-induced free-carrier population results in an internal space-charge field, which produces an index change via the linear electrooptic effect. The photorefractive effect has been widely studied for a variety of materials and device applications, mainly because it allows large index changes to be generated with laser beams having only a few milliwatts of average power.Compound semiconductors are important photorefractive materials because they offer a near-infrared optical response, and because their carrier transport properties allow the index change to be generated quickly and efficiently. While many researchers have attempted to measure the fundamental temporal dynamics of the photorefractive effect in semiconductors using continuous-wave, nanosecond- and picosecond-pulsed laser beams, these investigations have been unsuccessful. However, studies with this goal are of clear relevance because they provide information about the fundamental physical processes that produce this effect, as well as the material's speed and efficiency limitations for device applications.In this dissertation, for the first time, we time-resolve the temporal dynamics of the photorefractive nonlinearities in two zincblende semiconductors, semi-insulating GaAs and undoped CdTe. While CdTe offers a lattice-match to the infrared material HgxCd1-xTe, semi-insulating GaAs has been widely used in optoelectronic and high-speed electronic applications. We use a novel transient-grating experimental method that allows picosecond temporal resolution and high sensitivity. Our results provide a clear and detailed picture of the picosecond photorefractive response of both materials, showing nonlinearities due to hot-carrier transport and the Dember space-charge field, and a long-lived nonlinearity that is due to the EL2 midgap species in GaAs. We numerically model our experimental results using a general set of equations that describe nonlinear diffraction and carrier transport, and obtain excellent agreement with the experimental results in both materials, for a wide variety of experimental conditions.
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Feinleib, Richard Eric 1964. "Adaptive optical learning network with a photorefractive crystal." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276867.
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An optical computer which performs the classification of an input object pattern into one of two learned classes is designed and demonstrated. The classifier is an optical implementation of a neural network model of computation featuring learning, self-organization, and decision-making competition. Neural computation is discussed including models for learning networks and motivation for optical implementation. A discussion of photorefractive crystal holographic storage and adaptation is presented followed by experimental results of writing and erasing gratings in several different crystals. The optical network features a photorefractive crystal to store holographic interconnection weights and an opto-electronic circuit to provide a means of competitive decision making and feedback. Results of the optical learning network and its operation as an associative memory are followed by extensions of the architecture to allow improved performance and greater flexibility.
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Orlov, Sergei S. Yariv Amnon. "Holographic storage dynamics, phase conjugation, and nonlinear optics in photorefractive materials /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-06082005-110714.
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Fuentes-Hernandez, Canek. "Photorefractive polymer composites with improved operational stability and performance." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280699.
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This dissertation describes advances in the operational stability and performance of polymer composites that used a new hole-transporting polymer matrix, PATPD. Stable operation is achieved when PATPD provides the transport manifold because it prevents the chromophores to act as hole-traps. Operational stability is combined with video-rate compatible response times and large photorefractive nonlinearities, comparable to those obtained with the commonly used hole-transporting polymer PVK. The advances obtained in understanding the impact of chromophore aggregation to the photorefractive properties of such composites will be presented in the framework of a two-trapping site mode. Numerical simulations of the photogenerated current transients and the sensitizer anion build-up will reveal the intricate nature of the trap dynamics when chromophore aggregates can act as hole-traps in a material. Finally, the photorefractive properties of hybrid polymer composites sensitized with CdSe nanoparticles, that currently define the state-of-the-art for the photorefractive performance of this kind of materials, will be presented. The operational stability of hybrid composites is presented for the first time and the limitations to its performance will be analyzed.
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Wiegel, Michaela E. K. (Michaela Emilie Kurt) 1973. "Gravitational effects on defect formation in melt grown photorefractive materials : bismuth silicate." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29626.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (leaves 206-213).
Photorefractivity is the modulation of index of refraction due to nonuniform illumination, and numerous applications have been demonstrated utilizing this nonlinear optical property. However, commercial production is seriously impeded by the inability to produce bulk material with the homogeneity of opto-electronic properties that is required for device applications. Bismuth Silicate, Bi12SiO20, (BSO) is a photorefractive material with outstanding properties including a fast response time and high sensitivity is studied. Its photorefractivity is due to a native defect whose exact nature and origin have not been unambiguously determined. Motivation for current research arose from unexplained optical variations observed in BSO that implicate convective interference as playing a role in native defect formation. Microgravity growth experiments are proposed in order to establish a controlled, convection-free environment to study the origin and nature of the critical native defect. This work aims at resolving critical aspects of performing quantitative microgravity growth experiments that include the interaction of BSO melts with its confinement material; development and characterization of a vertical Bridgman-Stockbarger growth system with a quantifiable, reproducible, and controllable thermal environment; and Bridgman-Stockbarger growth experiments. A comparative analysis of crystals was done in order to establish the relationship between variations in opto-electronic properties as a function of changes in growth conditions. Wetting experiments revealed the sessile drop method to be inappropriate for the BSO-platinum system due to grain boundary pinning. No fundamental difference between the wetting behavior in a terrestrial and a low gravity environment was observed.
(cont.) Results from the comparative analysis indicate a lower defect concentration in Bridgman-Stockbarger material as compared to Czochralski material. The ambient atmosphere during processing and high temperature annealing was found affect material response, including removal of the photochromic response and decrease of carrier lifetime. The lack of the critical defect in hydrothermal BSO, and its existence in all melt grown material indicates that the melt plays a fundamental role in its formation. Clustering in the melt is implicated in the literature from nonlinear melt properties. It is therefore hypothesized that these clusters in the melt act as precursors for native defect formation and subject to gravitationally induced convection. The support of the National Aeronautics and Space Administration is gratefully acknowledged.
by Michaela E.K. Wiegel.
Ph.D.
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Lindsay, Iain. "Optical phase conjugation in photorefractive materials and its application to image processing." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47541.
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Momtahan, Omid. "Analysis and optimization for volume holographic recording." Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-07062006-211943/.
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Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2007.Smith, Glenn, Committee Member ; Trebino, Rick, Committee Member ; Adibi, Ali, Committee Chair ; Gaylord, Thomas, Committee Member ; Buck, John, Committee Member.
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Schunemann, Peter Gerard. "Growth and characterization of high-purity and iron-doped photorefractive barium titanate." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14797.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Vita.
Bibliography: leaves 71-75.
by Peter Gerard Schunemann.
M.S.
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Day, Daniel John, and DDay@groupwise swin edu au. "Three-dimensional bit optical data storage in a photorefractive polymer." Swinburne University of Technology. Centre for Micro-Photonics, 2001. http://adt.lib.swin.edu.au./public/adt-VSWT20050307.112258.
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As the computer industry grows, so will the requirements for data storage. Magnetic memory has been the most stable method in terms of capacity and recording/reading speed. However, we have reached the point where a substantial increase in the capacity cannot be produced without increasing the size of the system. When compact discs (CDs) were introduced in the 1980�s they revolutionized the concept of data storage. While the initial force behind compact discs could easily be said to be the music industry, once recordable and rewritable discs became available they quickly found more use in the computer industry as backup devices. Since their inception, the capacity requirements have far exceeded what is available on a compact disc, and they are now following the same path as magnetic memories. Following this trend, it could be assumed that digital versatile discs or digital video discs (DVDs) have a limited lifetime as a storage medium. In fact it has been noted (Higuchi et al., 1999) that the maximum capacity of digital video discs will be reached in 3 � 5 years. The question then is, what comes next? The efficiency of conventional optical data storage is extremely poor. For an optically thick recording medium, both CDs and DVDs use less than 0.01% of the total volume to store the information. Three-dimensional bit optical data storage endeavors to increase the efficiency by recording information in a volume that is greater than 90% of the total volume. The concept of three-dimensional bit optical data storage was first proposed by Parthenopoulos and Rentzepis in 1989, where they demonstrated that capacities far exceeding that of compact discs could be achieved. Three-dimensional bit optical data storage relies on creating a highly localised chemical or physical change within a recording medium, such that further layers can be recorded without causing interference. Ideally the chemical/physical change in the material should be reversible to enable erasable/rewritable data storage. In order to create a highly localised effect nonlinear excitation can be used; whereby the excitation is limited to a small region around the focal spot. Depending on the material and recording method there are several techniques for reading the information such as transmission imaging or reflection confocal microscopy. However, all the recording and reading methods require focusing to a deep position within a recording medium, such focusing encounters spherical aberration as a result of the difference in the refractive indices between the immersion and recording media. This thesis has concentrated on several areas to understand and develop the concept of three-dimensional bit optical data storage. The photorefractive effect in crystals has been studied for many years and is now widely used in optoelectronic devices. The use of photorefractive polymers is a relatively new and exciting development in optical data storage. Until now they have been used solely in the area of holographic data storage. The research in this thesis was conducted using photorefractive materials that were fabricated in two polymer matrices, poly(N-vinylcarbazole) (PVK) and poly(Methyl Methacrylate) (PMMA). The recording samples also consisted of the following compounds in various proportions, 2,5-dimethyl-4-(p-nirtophenylazo)anisole (DMNPAA), 2,4,7-trinitro-9-fluorenone (TNF) and N-ethylcarbazole (ECZ). In this project two-photon excitation was used as the recording mechanism to achieve erasable/rewritable data storage in a photorefractive polymer. As a result of two-photon excitation, the quadratic dependence of excitation on the incident intensity produces an excitation volume that is confined to the focal region in both the transverse and axial directions. Therefore, focusing the laser beam above or below its previous position provides a method by which layers of information can be recorded in the depth direction of a material, without causing interference from neighbouring layers. The feasibility of two-photon excitation in photorefractive polymers is demonstrated in this thesis. The quadratic relationship between excitation and incident light in two-photon excitation requires high photon density to ensure efficient excitation. The use of ultra-short pulsed lasers, while effective, is not a practical solution for an optical data storage system. This thesis demonstrates the ability to produce three-dimensional erasable/rewritable data storage in a photorefractive polymer using continuous wave illumination. Using this technology it has been possible to achieve a density of 88 Gbits/cm3, which corresponds to a capacity of 670 Gbytes on a compact disc sized recording medium. This is an increase of 1000 times the capacity of a CD and 130 times the capacity of current DVDs. While erasable optical data storage is an exciting prospect there are problems associated with the deterioration of the information. For long term information storage a permanent recording process would be more practical. It is demonstrated that there is a point after which further increases in the recording power result in the formation of a micro-cavity. While two-photon excitation is the recording method for erasable data storage, the increase in power results in an increase in ultra-violet absorption such that multi-photon excitation may occur. This thesis demonstrates the ability to record multi-layered arrays of micro-cavities. The change in refractive index associated with an erasable bit is less than 1%. As a result only phase sensitive reading methods (transmission imaging or differential interference contrast (DIC) microscopy) can be used to image a recorded bit. Both transmission and DIC imaging systems have poor axial resolution and therefore limit the density of the recording system, as well as being large optical systems. The introduction of a split or quadrant detector reduces the size of the optical reading system and is demonstrated to be sensitive enough to detect the phase changes of a recorded bit. However, the change in refractive index across a micro-cavity is large enough that reflection confocal microscopy can be used to detect a bit. It is demonstrated in this thesis that multi-layered micro-cavity arrays can be read using reflection confocal microscopy.
Focusing of light to deep positions within an optical thick recording medium has the effect of increasing spherical aberration resulting from the refractive index mismatching between the immersion and recording media. The work in this thesis illustrates the effect of spherical aberration on the performance of both the recording and reading systems. The work conducted in this thesis shows the ability to record multi-layered erasable/rewritable information in a photorefractive polymer using pulsed and continuous wave two-photon excitation. It has also been demonstrated that through multi-photon excitation multi-layered micro-cavity arrays can be fabricated. It has also been illustrated that while spherical aberration deteriorates the performance of the recording and reading systems it is possible to achieve a density of greater than 88 Gbits/cm3.
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Rodgers, John Scott. "Multimode interference in a Kerr nonlinear material." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/13365.
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Parshall, Elaine Ruth. "A numerical model of optical beam propagation in photorefractive crystals and comparisons with experiment /." Thesis, Connect to Dissertations & Theses @ Tufts University, 1995.
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Thesis (Ph.D.)--Tufts University, 1995.Adviser: M. Cronin-Golomb. Submitted to the Dept. of Electrical Engineering. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;
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Kota, Akash. "Spectral Analysis of Bragg and Non-Bragg Orders in Dynamic Holography Using Photorefractive Materials." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1470323121.
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Wilson, Daniel W. "Optical waveguiding in photorefractive crystals : photoinduced polarization conversion and electron waveguiding in semiconductor nanostructures : modes, directional coupling, and discontinuities." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/14934.
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Lin, Haibo Yu Ping. "Speckle mechanism in holographic optical coherence imaging." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6184.
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Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 15, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Ping Yu. Vita. Includes bibliographical references.
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Sayano, Koichi Yariv Amnon. "Photorefractive properties of ferroelectric materials for optical phase conjugation, two-beam coupling, and holographic storage /." Diss., Pasadena, Calif. : California Institute of Technology, 1990. http://resolver.caltech.edu/CaltechETD:etd-11072006-135048.
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Momtahan, Omid. "Analysis and Optimization for Volume Holographic Recrording." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/16183.
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Methods for analysis and optimization of volume holographic recording are presented for two main groups of applications. In the first group of applications (mainly storage systems), the designs and the techniques of volume holography are well known and the main optimization effort is finding the proper material to store the holograms. One of the results of this research is complete global optimization of dynamic range and sensitivity in two-center recording that is the best technique for persistent rewritable storage. For this purpose, a complete theoretical analysis as well as experimental demonstration is presented. Also, other effects and processes such as electron tunneling and recording at high temperature are considered for possible improvement of the dynamic range of the material. For the second group of applications (mainly holographic optical elements), the focus of this research is on analysis and optimization of the design of the volume holograms in contrast to material optimization. A new method (multi-grating method) is developed for the analysis of an arbitrary hologram that is based on the representation of the hologram as the superposition of several plane wave gratings. Based on this method, a new class of optical devices that integrates the functionalities of different optical elements into a simple volume hologram is introduced and analyzed. As a result, very compact, low cost, and easy to use devices such as portable spectrometers can be made with particular applications in biological and environmental sensing.
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Tziraki, Maria. "The development of photorefractive holography through turbid media for application to biomedical imaging." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341934.
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Abeywickrema, Haburugala Vithanage Ujitha A. "Applications of Induced Gratings in Nonlinear Media." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1429985534.
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Peereboom, Nick C. (Nicolaas Christopher) Carleton University Dissertation Engineering Electrical. "Optical two-wave mixing in iron-doped indium phosphide." Ottawa, 1992.
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Kumamoto, Rodrigo Eduardo Fraga. "Estudo de força fotoeletromotriz de um padrão luminoso oscilante de speckle e suas aplicações." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277974.
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Orientador: Jaime Frejlich SochaczewskyDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Este trabalho apresenta um estudo sobre o efeito de força fotoeletromotriz produzida por um padrão de speckle espacialmente oscilante quando projetado sobre materiais fotocondutores ou fotorrefrativos. Dentre as contribuições desse trabalho podemos citar o aperfeiçoamento tanto do modelo teórico existente quanto do uso desse fenômeno para medida de vibrações mecânicas transversais. Basicamente, o efeito de força fotoeletromotriz gera uma fotocorrente AC com a mesma frequência do padrão oscilante e uma magnitude que depende da amplitude com que o padrão luminoso oscila espacialmente. A partir de nosso modelo teórico foi possível prever a existência de um máximo valor para a fotocorrente, que ocorreria para uma determinada amplitude de vibração relacionada ao tamanho médio do speckle. Con rmamos experimentalmente a existência desse máximo, embora o valor seja um pouco diferente do esperado teoricamente. Medimos a resposta em frequência da fotocorrente e relacionamos os resultados com as respostas temporais características do material fotocondutor. Para realização das medidas experimentais desenvolvemos um sensor de vibração mecânica baseado no efeito de força fotoeletromotriz, demonstrando a aplicabilidade para medidas de amplitude e de frequência de oscilação de uma superfície vibrante. O sensor é constituído por um cristal fotocondutor e por uma eletônica de amplificação. Um laser é direcionado até um alvo vibrante e a luz retroespalhada, na forma de um padrão de speckle, é focalizada sobre o cristal fotorrefrativo, gerando o efeito speckle-foto-fem. Os cristais utilizados foram o Bi12TiO20 e CdTe:V sob iluminação de 532nm e 1064nm, respectivamente. O sistema mostrou ser interessante tanto para a medida de vibrações mecânicas quanto para a caracterização dos materiais usados como sensores
Abstract: This paper presents a study about photoelectromotive force effect produced by a spatially oscillating \ speckle" pattern when projected onto photoconductive or photorefractive materials. Among the contributions of this paper we can mention the improvement of both the existing theoretical model and use this phenomenon to measure the transverse mechanical vibrations. Basically, the effect of photoelectromotive force generates an AC photocurrent with the same frequency of the oscillating pattern and a magnitude which depends on the amplitude to which the light pattern varies spatially. From our theoretical model, we could predict the existence of a maximum value for the photocurrent, which occurs for a given vibration amplitude related to the average size of the \speckle". We con rmed experimentally the existence of this maximum, but the value is a little different than theoretically expected. We measured the frequency response of the photocurrent and related the results with the temporal response characteristics of the photoconductive material. To perform the experimental measurements we developed a mechanical vibration sensor based on photoelectromotive force effect, demonstrating the applicability for measurements of amplitude and frequency of a vibrating surface. The sensor consists of a photoconductive crystal and an electronic amplification. Light from a laser is directed to a target vibrant and the backscattered light in the form of a speckle pattern is focused on the photoconductive crystal. The crystals used were Bi12TiO20 and CdTe:V under illumination of 532nm and 1064nm, respectively. The system is interesting both for mechanical vibrations measurements and for materials characterization
Mestrado
Física da Matéria Condensada
Mestre em Física
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Pereira, Renata Montenegro. "Estudo de centros fotoativos em materiais fotorrefrativos." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278029.
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Orientador: Jaime Frejlich SochaczewskyTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Utilizamos técnicas holográcas para o estudo dos centros fotoativos em cristais fotorrefrativos da família das sillenitas. Utilizamos uma nova técnica de registro holográco autoestabilizado que permite gerar hologramas estacionários com fases holográcas arbitrárias, o que nos permitiu medir essas fases com maior precisão. A medida dessas fases, assim como da eficiência de difração, em função do campo elétrico aplicado, nos permitiu calcular alguns parâmetros importantes referentes aos centros fotoativos de titanosillenitas (Bi12TiO20) puras e dopadas. Fizemos também um estudo detalhado de um cristal de titanosillenita dopado com Vanádio (BTO:V) e verificamos que, nesse material, a participação de buracos no processo de registro holográco chega a ser igual ou até é maior que a de elétrons
Abstract: We studied photoactive centers in sillenite photorefractive materials using holographic techniques. We used a new technique of self-stabilized holographic recording that allowed us to produce stationary holograms with arbitrary holographic phases, and it allowed us to measure phases with a better accuracy. The measurement of holographic phases and the diffraction efficiency as funcion of the applied eletric field allowed us to find some important parameters related to the photoactive centers of doped and undoped titanosillenite. We also studied vanadium doped Bi12TiO20 (BTO:V) and we showed that in this material the participation of holes in the holographic recording can be as much as or higher than that of electrons
Doutorado
Ótica
Doutora em Ciências
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Amonson, Michael D. "Multiple Charge Carrier Species and Their Effects in Photorefractive Two-Beam Coupling in Potassium Niobate." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1512494096366019.
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Pereira, Renata Montenegro. "Caracterização óptica e elétrica de materiais fotocondutores e fotorrefrativos." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278065.
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Orientador: Jaime Frejlich SochaczewskyDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: O objetivo desta tese foi a caracterização de materiais fotocondutores e fotorrefrativos utilizando técnicas ópticas e elétricas. A propriedade mais importante nestes materiais é a fotocondutividade e por isso nos centramos na medida dessa quantidade. Um dos materiais mais estudados em nosso laboratório, o Bi12TiO20, é pouco fotocondutor e por isso, a técnica clássica, que utiliza uma lâmpada "branca" seguida de um monocromador, para selecionar o comprimento de onda com que a amostra vai ser iluminada, mostrou-se pouco sensível. Para melhorar a sensibilidade da medida, desenvolvemos um sistema baseado num conjunto de LEDs (light-emitting diodes) quase monocromáticos, de diferentes comprimentos de onda, capazes de fornecer maior intensidade de luz do que o sistema clássico. Também propomos uma sistemática diferente para a coleta e processamento dos dados, que leva em consideração, a distribuição exponencial da luz no interior da amostra, devido à absorção¸ característica de cada material. Os resultados mostraram que o novo instrumento e o novo método de processamento de dados permitem obter mais informações sobre os materiais analisados do que seria possível utilizando a técnica clássica. A nova técnica foi aplicada ao estudo de amostras de Bi12TiO20 puro e dopado assim como de Bi12GaO20 e CdTe. Os resultados, junto com outras informações disponíveis por outras técnicas (holografia e fotocorrente modulada), permitiram detectar alguns estados localizados dentro da banda proibida destes materiais, o que é muito importante no estudo da fotocondutividade
Abstract: The objective of this work was the characterization of photoconductive and photo-refractive materials using optical and electrical techniques. The most important property of these materials is photoconductivity so that we concentrated in the measurement of this quantity. One of the most studied materials in our laboratory, Bi12TiO20, is poorly photoconductive and, because of that, the standard technique using a white lamp followed by a monochromator, to select the illumination wavelength on the sample, has shown a very poor sensistivity. In order to improve the measurement we have therefore developed a system based on an array of almost monochromatic LEDs (Light-Emitting Diodes) with different wavelengths, which are able to provide with greater light intensity than with the classical system. We also propose a different system for the data collection and processing, which considers the exponential distribution of light along the sample¿s thickness, due to the characteristic bulk absorption of these materials. Our results have shown that the new instrument and the new data processing method allow us to obtain much more information about the materials under analysis than would be possible with the classical method. The new technique was applied to the study of pure and doped B i12TiO20, as well as Bi12Ga O20 and CdTe. The results, together with further information obtained from other techniques (holography and modulated photocurrent), have allowed us to detect some localized states inside the bandgap of the materials and therefore get a better insight of their structure that is very important for the understanding of their photoconductivity properties
Mestrado
Propriedades Óticas e Espectroscopia da Matéria Condensada
Mestre em Física
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Araujo, William Roberto de 1980. "Sistema para medida de fotocondutividade resolvida em comprimento de onda em materiais fotocondutores." [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267732.
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Orientadores: Rangel Arthur, Jaime FrejlichDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Tecnologia
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Resumo: Neste trabalho foi desenvolvido um instrumento capaz de realizar medidas em materiais fotossensíveis. Para estudar materiais fotossensíveis, por exemplo, o Bi12TO20, que em geral geram correntes muito baixas da ordem de dezenas de picoamperes, fez-se necessário obter um instrumento capaz de medir nessa ordem de grandeza e com baixo ruído. Para identificar estados localizados dentro do band gap de um semicondutor, que são gerados por defeitos estruturais, é necessário ter uma intensidade de luz com energia acima do nível de Fermi que consiga penetrar no semicondutor, e pelos testes realizados não foram facilmente detectados pela técnica convencional, fonte de luz branca seguida de um monocromador. O uso de LED (Light Emitting Diode) se mostrou promissor por ser barato e ter uma intensidade de luz muito maior que a luz monocromática produzida pelo monocromador. O instrumento possui um computador embarcado (Raspberry PI) que realiza o controle do hardware e possui uma interface Ethernet para conexão remota. O hardware é composto de: uma fonte de alimentação para controle da intensidade e modulação para os LEDs, um controle do posicionamento dos LEDs na amostra, um controle da fonte de alta tensão e um sistema de detecção síncrona para melhor coleta dos dados. Os testes realizados com amostra Bi12TO20 se mostrou compatível com resultados já apresentados pela literatura
Abstract: This work aims to an instrument to perform measurements in photosensitive materials. To study photosensitive materials, for example, Bi12TO20, it was necessary to obtain an instrument capable of measuring the scale and with low noise, which generally lead to very low currents on the order of tens of picoamperes. To identify located states within the band gap of a semiconductor, which structural defects are generated, it is necessary to have a light intensity with energy above the Fermi level can penetrate into the semiconductor, and the tests were not easily detected by the technique conventional white light source followed by a monochromator. The use of LED (Light Emitting Diode) has shown promise for being cheap and having a much higher light intensity that monochromatic light produced by the monochromator. The instrument has an embedded computer (Raspberry-PI) that performs hardware the control and an Ethernet interface for remote connection. The hardware is comprised of: a power supply for the control of intensity and modulation for the LED, a control of the positioning of LEDs on the sample, a high voltage supply control and a synchronous detection system for improved data acquisition. The results of performed tests with sample Bi12TO20 were compatible with results have been presented in the literature
Mestrado
Tecnologia e Inovação
Mestre em Tecnologia
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Oliveira, Ivan de 1972. "Fixação de hologramas em Niobato de Lítio." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277998.
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Orientador: Jaime FrejlichTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Neste trabalho foram realizadas contribuições importantes na área de registro holográfico auto-estabilizado em niobato de lítio (LiNbO3:Fe) e do estudo da dinâmica da formação e evolução dos hologramas durante as diferentes etapas da fixação. Outras contribuições importantes neste trabalho referem-se ao desenvolvimento de técnicas mais eficientes e/ou mais simples para a fixação de hologramas. Em termos de registro auto-estabilizado, nosso trabalho permitiu o uso dessas técnicas para obtermos hologramas com alta eficiência de difração e de forma reprodutível. O registro holográfico auto-estabilizado em niobato de lítio já tinha sido utilizado anteriormente. A novidade aqui reside no estudo detalhado da dinâmica do processo, que permitiu uma melhor compreensão das possibilidades e limitações da técnica, incluindo o estudo detalhado do efeito do grau de oxidação (isto é, da relação [Fe3+]/[Fe2+]) do material sobre o comportamento do sistema de estabilização. Em função dos estudos acima referidos que permitiram uma melhor compreensão dos processos, foi possível desenvolver uma técnica de fixação para cristais oxidados que permitiu obter redes fixas com alta eficiência de difração, com valores previzíveis em função das propriedades do cristal e de forma reprodutível. O registro auto-estabilizado foi aplicado com sucesso, pela primeira vez, à técnica de fixação (registro e compensação) a alta temperatura, de forma muito mais simples do que a técnica clássica, e que permitiu obter excelentes resultados mesmo com amostras reduzidas, para as quais o processo clássico não funciona satisfatoriamente. Paralelamente mostramos teórica e experimentalmente os problemas associados à medida da eficiência de difração em hologramas espessos. Mostramos que o uso de um feixe auxiliar (frequentemente utilizado) para este tipo de medida leva a erros consideráveis e para este caso propomos uma forma muito simples de realizar essa medida
Abstract: In this work important contributions to the field and to the self stabilized holographic record in litium niobate were achieved and to the dynamic formation and hologram evolution study during different fixing stages. Other important contributions in this work refer to more efficient technique development and/or simpler ones to hologram fixing. On terms of self stabilized record our work allowed the use of these techniques to obtain some holograms with high efficiency diffractions and in a reproducible form. The self stabilized holographic record in litium niobate had already been used before. The new point here is the detailed study about the process dynamic which allowed a better understanding of the technique possibilities and limitations including the detailed study of the effect of the oxidation degree (thus the relation [Fe3+]/[Fe2+]) of the material about the stabilization system behaviour. According to the referred studies above which permitted a better understanding of the process, it was possible to develop the oxidated crystals fixing technique which permitted to get fixed nets with high diffractions efficience with predictable values according to the crystals properties and in a reproducible form. The self stabilized record was applied sucessfully to the fixing technique (recording and compensation) for the first time to high temperature in a so much simpler form than the classical one which permitted to obtain excellent results even using reduced samples to which the classical process has not worked satisfactionally. Parallel to this, we showed (theoric and experimentally) the associated problems to the diffraction efficience in thick holograms. We showed the use of an auxiliar bin (frequently used) for this kind of measure results in considerable errors and to this case we propose a so much simpler form of achieving this measure
Doutorado
Física da Matéria Condensada
Doutor em Ciências
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Ding, Meisong. "Properties and applications of the photorefractive material Ce:KNSBN." Thesis, Abertay University, 2000. https://rke.abertay.ac.uk/en/studentTheses/10da170f-875b-41b6-8f56-5fb756335ea5.
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CeiKNSBN is a new photorefractive material in the KNSBN family, which has some advantages compared to other crystals. Based on two-wave mixing theory, different methods are used to investigate the photorefractvie properties of the Ce:KNSBN crystal. Most parameters of the CeiKNSBN crystal are in the same orders with those of Cu:KNSBN crystal. The diffraction efficiency from the CeiKNSBN crystal is affected by the applied electric field. The applied field increases the response rate of the grating formation and enhances the diffraction efficiency. There exists an optimum applied field and grating spacing related to the maximum diffraction efficiency, and the history of applied field influences the value of diffraction efficiency. Fanning loss and thermal effects should be considered in the diffraction theory for the CeiKNSBN crystal. The phase conjugate properties of the CeiKNSBN crystal are demonstrated in the four-wave mixing configuration and in the SPPC CAT conjugator. The experimental results agree with the analytical solution under some conditions. The He-Ne laser generates higher SPPC in the CeiKNSBN crystal than that by the argon-ion laser. The Doppler frequency detuning technique is first, to our knowledge, applied in the SPPC CAT configuration. The SPPC reflectivity is enhanced and the uniformity of the reflectivity is improved by this technique.
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Mokhov, Sergiy V. "Theoretical study of beam transformations by volume diffraction." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4986.
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Laser beams can be manipulated by volume diffractive elements in addition to conventional optical elements like mirrors, lenses, and beam splitters. Conventional optical elements can be described by applying the basic laws of reflection and refraction at the surfaces of the elements. Even diffraction by surface gratings utilizes relatively simple mathematics. This is to be contrasted with the volume diffraction, which requires coupled wave theory in the slowly varying envelope approximation (SVEA) to obtain accurate results. Efficient spatially distributed diffraction of laser beams is possible due to the high coherence of laser light, and it occurs at specific resonant Bragg conditions. This research work is inspired and driven by the successful development of recording technology for robust, high-efficiency volume Bragg gratings (VBGs) in photo-thermo-refractive (PTR) glass. Mostly VBGs of the reflective type are discussed in this dissertation. Starting with an analysis of electro-magnetic wave propagation in layered media, we have reformulated Fresnel and volume reflection phenomena in terms of a convenient parameter--strength of reflection. The influence that the different non-uniformities inside a VBG have on its spectral properties has been examined. One important result of this work is the proposal of moire VBG and the derivation of an analytical expression for its bandwidth. A multiplexed VBG used as a coherent combiner is discussed as well. Beam distortion via transmission through and/or reflection by a heated VBG due to residual absorption is analyzed.ID: 030423243; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 114-127).
Ph.D.
Doctorate
Optics and Photonics
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Herlocker, Jon Alan. "Dynamic response and material processing of photorefractive polymer composites." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284284.
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This dissertation describes advances in the photorefractive dynamic response, and in the understanding of response limitations. In a PVK/ECZ based composite using a tolane chromophore and TNFDM sensitization, a photorefractive response time constant of 4 ms was observed at an applied field (Eₐ) of 95 V/μm with a writing fluence of 0.5 W/cm², while the birefringence response time was under a millisecond. This showed that the chromophore orientational response does not limit speed, and suggests further investigation of photogeneration and transport processes to improve dynamic response. Another segment of research investigated performance changes by exposure under working conditions. Photorefractive properties for composites using chromophores of varied ionization potential (I(p)) were characterized as a function of exposure at Eₐ = 80 V/um, up to 10⁴ J/cm² total optical field exposure. The response time and photoconductivity were found to fatigue for all samples, but a higher chromophore I(p) was correlated to greater stability. The four-wave mixing dependence upon E a showed a variation in trap density with exposure which verifies the role of the C₆₀ anion, the ionized sensitizer, as a photorefractive trap. The third segment of research was the proof-of-principle of a photorefractive injection molding process. Photorefractive properties of molded materials were verified by four-wave mixing and two-beam coupling measurements. At Eₐ = 95 V/μm a diffraction efficiency of 25-30% and a gain coefficient near 50 cm⁻¹ was observed. This shows industrial processing potential of these materials and provides a path from hand crafted devices to mass-production techniques, promoting commercial acceptance.
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James, Jemy. "Refractive index engineering using polymer nanocomposites Surface engineering of polystyrene–cerium oxide nanocomposite thin films for refractive index enhancement." Thesis, Lorient, 2019. http://www.theses.fr/2019LORIS552.
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À travers l’histoire, la lumière a suscité le plus vif intérêt chez de nombreuses personnes curieuses, qu’il s’agisse de philosophes questionnant sa nature ou de scientifiques cherchant à interpréter les phénomènes qui lui sont associés. L’optique joue un rôle essentiel dans nombre de nos applications quotidiennes. L’indice de réfraction est l’un des facteurs les plus importants en photonique. Il est possible d’améliorer l’efficacité des dispositifs photoniques, comme les diodes électroluminescentes, les cellules photovoltaïques, etc., en réduisant la disparité des indices de réfraction des matériaux utilisés dans les dispositifs optiques. Cette thèse apporte quelques éclaircissements sur l’adaptation de l’indice de réfraction des matériaux, détaillant des aspects de l’indice de réfraction et de son ingénierie à l’aide de nanocomposites de polymère. Ce chapitre d’introduction évolue vers une discussion plus large sur l’indice de réfraction, ses différentes valeurs, et les avantages potentiels que son ingénierie pourrait générer. De minces films polymères ont été préparés et les nanoparticules ont été introduites de façon à modifier l’indice de réfraction. De la même manière, des films épais ont été préparés en utilisant du PMMA et du polystyrène, ceux-ci ayant été utilisés pour caractériser optiquement et morphologiquement les échantillons préparés. De nombreuses méthodes ont été employées pour préparer les films polymères. Des films polymères ultraminces ont également été préparés en utilisant la technique de revêtement par centrifugation, puis l’épaisseur du film de polystyrène a été modifiée afin d’étudier son impact sur l’indice de réfraction. Il a fallu surmonter plusieurs obstacles lors des recherches, comme la préparation d’un substrat ultra pur, l’uniformité du film polymère mince préparé, l’adhérence du film polymère mince sur les substrats après le coulage au solvant, etc. Tous ces défis ont été relevés grâce aux innovations détaillées dans cette thèseHistorically, light was a centre of interest for numerous inquisitive people: the philosophers who were interested in its nature and the scientists who wanted to interpret its associated phenomena. Optics is playing a pivotal role in many of our day to day applications.The refractive index is one of the most significant parameters in photonics. An increase in the efficiency of the photonic devices, like Light Emitting Diodes, Solar Cells, etc., can be achieved by reducing the refractive index mismatch of materials used in the optical devices.This thesis throws some light into the tailoring the refractive index of materials, by giving detailed aspects of refractive index and engineering of the refractive index using polymer nanocomposite. This introductory chapter evolves into a wider discussion on the refractive index and the types of refractive index and the potential leverage that can be obtained by engineering the refractive index. Polymer thin films were prepared and the nanoparticles were introduced so as to modify the refractive index. Similarly, thick polymer films were prepared using PMMA and Polystyrene and these were utilized to optically and morphologically characterize the prepared samples. Multiple methods have been utilized to prepare the polymer films. Ultra thin polymer films were also prepared using the spin coating technique and later the thickness of the polystyrene film was changed so as to understand its impact on the refractive index. There were multiple challenges to overcome while carrying out the research like the preparation of ultra pure substrate, uniformity in the prepared polymer thin film, adherence of the polymer thin film on to the substrates after solvent casting etc. All the challenges were overcome using the innovations, which are detailed in the thesis
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Rouède, Denis. "Contribution a l'etude des reseaux de phase photoinduits dans un cristal de bi : :(12) si o::(20)." Paris 6, 1987. http://www.theses.fr/1987PA066206.
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Etat de polarisation de l'onde diffractee pour deux configurations transverses 110 et 001. On montre que la configuration 110 est tres bien adaptee au traitement d'images, alors que la configuration 001 est bien adaptee au couplage des ondes
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Jamet, Sophie. "Effet photoréfractif dans l'InP:Fe : étude comparative en fonction de la température à plusieurs longueurs d'onde." Rouen, 1995. http://www.theses.fr/1995ROUES002.
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Cette étude porte sur l'effet photoréfractif dans le phosphure d'indium dopé au fer (InP:Fe). Les gains optiques mesurés en absence de champ électrique appliqué et à la longueur d'onde de 1,06 micromètre sont plus faibles que les valeurs calculées avec un modèle qui tient compte d'un seul niveau d'énergie (celui du fer) dans la bande interdite. Nous contribuons à déterminer l'origine de cette réduction qui est attribuée dans la littérature, soit aux transitions indirectes liées à l'état excité du fer soit à d'autres niveaux superficiels. Dans un premier temps, nous mettons en évidence la nécessité d'effectuer des mesures en fonction de la température et à plusieurs longueurs d'onde (1,06 ; 1,32 et 1,535 micromètre) afin d'établir les rôles respectifs des différents niveaux d'énergie dans les échantillons étudiés où l'effet photoréfractif est dominé par les trous à température ambiante. L'étude de la constante de temps d'effacement du réseau a permis de déterminer les concentrations en ions Fe2+ et Fe3+. Nous comparons ensuite les courbes du gain mesuré pour les trois longueurs d'onde en fonction de la température et du pas avec les simulations effectuées à partir des différents modèles comprenant soit le niveau excité du Fe2+*, soit un second niveau placé près de la bande de conduction puis, près de la bande de valence. Dans les échantillons étudiés, ces différentes comparaisons ont montré qu'à basse température l'effet photoréfractif est influencé par un second niveau situé près de la bande de valence alors qu'à température ambiante il faut à la fois tenir compte du second défaut et de l'état excité du fer
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Martel, Gilles. "Etude de l'effet photoréfractif dans la tellure de cadmium : application à l'interconnexion en espace libre par double miroir à conjugaison de phase." Rouen, 1996. http://www.theses.fr/1996ROUES076.
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Cette thèse traite des propriétés électroniques et optiques, ainsi que des applications en holographie dynamique (photoréfractivité) du tellure de cadmium et de ses alliages à base de zinc. La caractérisation s'est orientée vers l'alliage photoréfractif le plus prometteur : le Cd1-xZnxTe dopé V avec 0x%)4. La croissance retenue pour la réalisation de ces matériaux fut la méthode Bridgman verticale asymétrique. La caractérisation photoréfractive par la technique du mélange à deux ondes nous a permis de sélectionner les matériaux qui autorisent les rendements de diffraction les plus favorables à la conjugaison de phase. Nous avons pu mettre en évidence différents types de comportements photoréfractifs sous champ électrique externe nul, continu ou alternatif (jusqu'à 14 kV/cm). L'existence de ces différents comportements est assujetti à la présence ou non de zinc. Deux modelés considérés comme des extensions de la théorie photoréfractive classique, et dont la limite de validité fut précisément définie par les analyses spectroscopiques des défauts profonds dans un cristal (DLTS, DLOS, PICTS, ODMR, MCD, RPE, effet Hall, photoluminescence et absorption), ont été développés afin de proposer une explication claire des différents processus détectés. Parallèlement à cette étude sur la compréhension du matériau, un démonstrateur de commutateur optique reconfigurable a été développé entre fibres monomodes. Basé sur l'utilisation d'un double miroir à conjugaison de phase (DPCM), ce commutateur a été réalisé à la longueur d'onde de 1. 5 m. Des temps de reconfiguration (cycle effacement-écriture d'un réseau holographique de Bragg photoinscrit) de l'ordre de 10 millisecondes ont été mesurés pour ce démonstrateur à commutation lente. De nombreux problèmes dynamiques (instabilités, franges mobiles) ont été mis en évidence au sein de ce matériau en configuration DPCM et également en configuration miroir à conjugaison de phase en anneau (ring PCM). Une théorie basée sur les ondes couplées a permis de rendre compte de l'aspect fondamental et donc général de la dynamique (franges mobiles) qui existe au sein d'un grand nombre de miroirs à conjugaison de phase.
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Haas, Helge. "Effet Stark quantique dans les puits de CdTe/CdZnTe et développement d'un dispositif photoréfractif." Université Joseph Fourier (Grenoble ; 1971-2015), 1995. http://www.theses.fr/1995GRE10146.
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Nous presentons le developpement et l'etude d'un dispositif photorefractif a puits quantiques ainsi que les mecanismes physiques fondamentaux associes a ce type de composants. La structure de bande de type i pour les trous lourds et de type ii pour les trous legers permet une mesure precise du decalage de bande de valence de cdte/cd#. #7#2zn#0#. #3#8te egal a +11% 2%. Cette situation particuliere produit une degenerescence entre niveaux de trous lourds et trous legers. Dans les puits peu profonds, l'exciton leger est de type i grace au potentiel coulombien exerce par l'electron sur le trou leger. Sous champ electrique, nous mettons en evidence une transition type i-type ii de l'exciton leger. Lorsque l'energie de liaison de l'exciton augmente, la constante dielectrique et l'interaction des excitons avec le reseau diminuent. L'observation de complexes exciton-phonon a basse temperature et leur disparition progressive lorsque l'energie de liaison augmente est favorable a cette interpretation. Une absorption excitonique intense a temperature ambiante est cependant observee lorsque l'energie de liaison est proche ou superieure a l'energie des phonons optiques longitudinaux. En nous fondant sur ces resultats, nous avons developpe un dispositif photorefractif a partir d'une diode schottky et nous avons mesure un rendement de diffraction proche de la valeur theorique. Un maintien du reseau de diffraction inscrit de quelques microsecondes necessite un blocage des porteurs qui ecrantent localement le champ applique. L'introduction de barrieres de potentiel en cdmgznte bloquent efficacement le mouvement perpendiculaire des electrons. Un modele qualitatif et des simulations numeriques permettent de cerner le comportement dynamique du dispositif. La diffusion laterale a l'interface est acceleree par le gradient de potentiel entre zones eclairees et sombres et limite le temps de maintien du reseau. Par des mesures de type pompe-sonde, nous avons determine la diffusion laterale et sa dependance avec le champ applique
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Berteloot-Mazoyer, Valérie. "Cristallogénèse de CdTe : In par T.H.M. (programme EURECA) et de CdTe : V photorefractif par Bridgman : caractérisation physico-chimiques et optiques, influence de la gravité sur l'hydrodynamique de la phase fluide." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1995. http://tel.archives-ouvertes.fr/tel-00158061.
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Pour étudier l'influence de la gravité sur la croissance par T.H.M. du semi-conducteur CdTe dopé indium (programme EURECA), nous avons effectué une analyse comparative d'expérience spatiales et terrestres, complétée par une simulation numérique de l'hydrodynamique de la phase fluide utilisant un code 3D. Notre deuxième objectif a été de prépérer des monocristaux de CdTe dopé vanadium par la technique Bridgman présentant de bonnes propriérés photoréfractives. Pour une meilleure compréhension du mécanisme de l'effet photoréfractif, les matériaux ont été caractérisés par R.P.E., D.C.M. et P.I.C.T.S. afin de déterminer le degré de valence de V et la signature des niveaux vanadium dans la bande interdite. Des mesures optiques (absorption, photoconductivité...) et d'effet photoréfractif ont été effectuées. Enfin, pour évaluer la pertinence spatiale de cette croissance, nous avons étudié par simulation numérique l'influence de la gravité sur la configuration hydrodynamique de la phase fluide.
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McCarthy, Glen William. "Solitons in photorefractive media." Phd thesis, 2006. http://hdl.handle.net/1885/147126.
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Papen, George C. "Transient nonlinear wave mixing in photorefractive materials and plasmas." 1989. http://catalog.hathitrust.org/api/volumes/oclc/22293282.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1989.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
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"Two-wave mixing in photorefractive Cu:KNSBN and Fe:LiNbO3 crystals and bright photovoltaic spatial solitons in photorefractive Fe:LiNbO3 crystals." 2005. http://library.cuhk.edu.hk/record=b5892676.
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Guo Bin = 光折變摻銅鉀鈉鈮酸鍶鋇和摻鐵鈮酸鋰晶體中的二波耦合及摻鐵鈮酸鋰晶體中的亮光伏空間孤子 / 郭斌.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references.
Text in English; abstracts in English and Chinese.
Guo Bin = Guang zhe bian shan tong jia na ni suan si bei he shan tie ni suan li jing ti zhong de er bo ou he ji shan tie ni suan li jing ti zhong de liang guang fu kong jian gu zi / Guo Bin.
Acknowledgements --- p.i
Abstract --- p.ii
Table of Contents --- p.v
Chapter Chapter 1 --- Introduction --- p.1
References --- p.6
Chapter Chapter 2 --- Background --- p.7
Chapter 2.1 --- Photorefractive Effect Based on Band Transport Model --- p.7
Chapter 2.2 --- Photovoltaic Effect --- p.15
Chapter 2.3 --- Surface Charge Recombination in Fe:LiNb〇3 Crystals --- p.17
References --- p.19
Chapter Chapter 3 --- Noise of Two-Wave Mixing in Cu:KNSBN Crystal --- p.20
Chapter 3.1 --- Introduction --- p.20
Chapter 3.2 --- Experimental Setup --- p.22
Chapter 3.3 --- Results and Discussion --- p.23
Chapter 3.4 --- Conclusion --- p.29
References --- p.30
Chapter Chapter 4 --- Bright Photovoltaic Spatial Soliton in Fe:LiNb03 Crystals
Chapter 4.1 --- Introduction --- p.32
Chapter 4.2 --- Theory --- p.33
Chapter 4.3 --- Experimental Setup --- p.36
Chapter 4.4 --- Results and Discussion --- p.39
Chapter 4.5 --- Conclusion --- p.58
References --- p.59
Chapter Chapter 5 --- Two-Wave Mixing of Narrow Laser Beams in a Fe:LiNbO3 Crystal --- p.60
Chapter 5.1 --- Introduction --- p.60
Chapter 5.2 --- Theory of Two-Wave Mixing --- p.62
Chapter 5.3 --- A Simplified Analysis of Two-Wave Mixing of Narrow Beams --- p.66
Chapter 5.4 --- Experimental Setup --- p.70
Chapter 5.5 --- Results and Discussion --- p.71
Chapter 5.6 --- Conclusion --- p.86
References --- p.87
Chapter Chapter 6 --- Two-Wave Mixing of Narrow Laser Beams with an Incoherent Background Beam --- p.89
Chapter 6.1 --- Theory --- p.89
Chapter 6.2 --- Experimental Setup --- p.93
Chapter 6.3 --- Results and Discussion --- p.94
Chapter 6.4 --- Conclusion --- p.105
References --- p.106
Chapter Chapter 7 --- Conclusion and Future Outlook --- p.107
48
Jayanth, P. "Photorefractive Crystals : Optical Phase Conjugation And Phase Conjugate Interferometry." Thesis, 1996. https://etd.iisc.ac.in/handle/2005/1590.
Full text
49
Jayanth, P. "Photorefractive Crystals : Optical Phase Conjugation And Phase Conjugate Interferometry." Thesis, 1996. http://etd.iisc.ernet.in/handle/2005/1590.
Full text
50
Wang, Qing. "Design, synthesis and physical studies of novel organic photonic materials /." 2000. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:9978086.
Full text