Optical imaging of soft biological tissue is highly desirable since it is nonionizing and provides sensitive contrast information which enables the detection of physiological functions and abnormalities, including potentially early cancer detection. However, due to the diffusive nature of light in soft biological tissue, it is difficult to achieve simultaneously good spatial resolution and good imaging depth with pure optical imaging modalities. This work focuses on the ultrasound-modulated optical tomography (UOT): a hybrid technique which combines the advantages of ultrasonic resolution and optical contrast. In this technique, focused ultrasound and optical radiation of high temporal coherence are simultaneously applied to soft biological tissue. The intensity of the sideband, or ultrasound ‗tagged‘ photons depends on the optical absorption in the region of interest where the ultrasound is focused. Demodulation of the optical speckle pattern yields the intensity of tagged photons for each location of the ultrasonic focal spot. Thus UOT yields an image with spatial resolution of the focused ultrasound — typically submillimeter — whose contrast is related to local optical absorption and the diffusive properties of light in the organ. Thus it extends all the advantages of optical imaging deep into highly scattering tissue. However lack of efficient tagged light detection techniques has so far prevented ultrasound-modulated optical tomography from achieving maturity. The signal-to-noise ratio (SNR) and imaging speed are two of the most important figures of merit and need further improvement for UOT to become widely applicable. In the first part of this work, nonlinear optics detection methods have been implemented to demodulate the ―tagged‖ photons. The most common of these is photorefractive (PR) two wave mixing (TWM) interferometry, which is a time-domain filtering technique. When used for UOT, it is found that this approach extracts not only optical properties but also mechanical properties for the area of interest. To improve on TWM, PR four wave mixing (FWM) experiments were performed to read out only the modulated light and at the same time strongly suppressing the ‗untagged‘ light. Spectral-hole burning (SHB) in a rare-earth-ion-doped crystal has been developed for UOT more recently. Experiments in Tm3 :Y3Al5O12 (Tm:YAG) show the outstanding features of SHB: large angle acceptance (etendue), light speckle processing in parallel (insensitive to the diffusive light nature) and real-time signal collection (immune to light speckle decorrelation). With the help of advanced laser stabilization techniques, two orders of magnitude improvement of SNR have been achieved in a persistent SHB material (Pr^3 :Y2SiO5) compared to Tm:YAG. Also slow light with PSHB further reduces noise in Pr:YSO UOT that is caused by polarization leakage by performing time-domain filtering.

The synchronously pumped femtosecond optical parametric oscillator (OPO) based on was periodically poled 5-mol.% MgO-doped lithuium niobate was demonstrated by means of non-critical quasi phase matching. The femtosecond OPO is cable of operating at room temperature and shows no photorefractive damage. The spectrum can be tuned by varying the cavity length up to 70 £gm, the temperature of the nonlinear crystal from room temperature to 150¢J, and the grating periods. The cavity was designed to resonate at 1.33 £gm with bandwidth of 100 nm. The maximum output intensity of the signal is 43 mW with TEM00 mode. The signal slope efficiency is 11%. The spectrum range of the idler is tunable from 1.8 to 2.8 £gm.

Optics has the inherent advantages of parallelism and wide bandwidths in processing information. However, the need to interface with electronics creates a bottleneck that eliminates many of these advantages. The proposed research explores novel optical devices and techniques to overcome some of these bottlenecks. To address parallelism issues we take a specific example of a content-addressable memory that can recognize images. Image recognition is an important task that in principle can be done rapidly using the natural parallelism of optics. However in practice, when presented with incomplete or erroneous information, image recognition often fails to give the correct answer. To address this problem we examine a scheme based on free-space interconnects implemented with diffractive optics. For bandwidth issues, we study possible ways to eliminate the electronic conversion bottleneck by exploring all-optical buffer memories and all-optical processing elements. For buffer memories we examine the specific example of slow light delay lines. Although this is currently a popular research topic, there are fundamental issues of the delay-time-bandwidth product that must be solved before slow light delay lines can find practical applications. For all-optical processing we examine the feasibility of constructing circuit elements that operate directly at optical frequencies to perform simple processing tasks. Here we concentrate on the simplest element, a sub-wavelength optical wire, along with a grating coupler to interface with conventional optical elements such as lenses and fibers. Even such a simple element as a wire has numerous potential applications. In conclusion, information processing by all-optical devices are demonstrated with an associative memory using diffractive optics, an all-optical delay line using room temperature slow light in photorefractive crystals, and a subwavelength optical circuit by surface plasmon effects.

High-speed optical networks will require all-optical signalprocessing to avoid bottleneck due to optical-to-electrical (O/E)and electrical-to-optical (E/O) conversion. Enabling of opticalprocessing tasks such as optical buffering and data synchronizationwill require large tunable delay. Recently, slow-light physics gotwide attention to generate tunable delay. However, for a slow-lightsystem large delay comes at the expense of increased distortion.This dissertation presents a study of the slow-light systems andquantifies the limitations imposed on delay due to distortion andsystem resource constraints. Optimal designs for two- and three-lineBrillouin slow-light systems showed fractional pulse delay of up to1.7 compared to a single-line gain system. Optimal designs forbroadband Brillouin gain system showed upto 100\% delay improvementcompared to the Gaussian pump. Wavelength conversion and dispersionbased tunable delay systems showed bit delay of 15 bits. An opticalbuffer based on photorefractive medium for real-time data storagewas demonstrated by storing and retrieving a 7-bit data sequence.

The aim of this project was to develop a passive optical compensating arrangement that would allow the formation and continued stability of interference patterns over a long timescale and also to investigate optical wave scattering in thick gratings at extreme angles of scattering. A novel passive arrangement based on a Sagnac interferometer is described that produces interference patterns more stable than those produced by a conventional arrangement. An analysis of the arrangement is presented that shows it to be an order of magnitude more stable than an equivalent conventional approach. The excellent fringe stability allowed holographic gratings with small periods (~ 0.5 μm) to be written in photorefractive lithium niobate with low intensity writing fields (~mW/cm2) produced by a He:Ne laser, despite long grating fabrication times (~ 1000 s). This was possible because the optical arrangement compensated for phase shifts introduced by translational and rotational mirror motion caused by environmental perturbations. It was shown that the rapid introduction of a phase shift in one of the writing fields can change the direction of energy flow in the two-wave mixing process. It was found that the improvement in stability of the modified Sagnac arrangement over a conventional interferometer decreased when the crossing angle was increased and that the point about which the mirrors are rotated greatly affects the stability of the arrangement. For a crossing angle of 12 degrees, the modified Sagnac arrangement is more than twice as stable when the mirrors are rotated about their midpoints, rather than their endpoints. Investigations into scattering in the extremely asymmetrical scattering (EAS) geometry were undertaken by scattering light from a 532nm Nd:YAG laser off gratings written in photorefractive barium titanate and lithium niobate. Despite the difficulties posed by background noise, there was very good agreement between the observed scattered field and that predicted by a previously established theoretical model. Thus, this work represents the first experimental observation of EAS in the optical part of the spectrum.

Orientador: Prof. Dr. Marcos Roberto da Rocha Gesualdi / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2017. / Sistemas de instrumentação cientíca vem sendo poderosas ferramentas para viabiliza- ção e comprovação de modelos em física teórica, bem como, para geração de produtos tecnológicos. Nesse sentido, as técnicas de Interferometria e Microscopia Holográca se mostram como poderosos métodos ópticos para observação de fenômenos perturbativos, na análise da fase de frentes de onda ópticas, em ensaios não destrutivos de análise de superfícies e aferição de sistemas ópticos. Particularmente, as técnicas holográcas em tempo real se apresentam favoráveis em relação às técnicas convencionais de análise de superfícies e frentes de onda, pois permitem a análise, visualização e monitoramento in situ dos sistemas estudados com precisão e conabilidade. Por outro lado, as técnicas de Holograa Computacional e Fotorrefrativa, nas quais cristais fotorrefrativos são usados como meio de registro holográco, tem se mostrado promissoras para geração de feixes ópticos especiais. Desta forma, o objetivo deste trabalho foi estudar e aplicar os métodos da Interferometria e Microscopia Holográca (Digital e Fotorrefrativa) para análise de intensidade e fase em feixes ópticos especiais (não-difrativos) e superfícies tridimensionais micro-estruturadas. Desenvolvemos para esses ns, um arranjo de Interferometria Hologr áca Digital e Fotorrefrativa para geração e análise de feixes ópticos e um sistema de Microscopia Holográca Digital e Fotorrefrativa para análise micro-estruturas (retículos e células sanguíneas). Os resultados obtidos estão de acordo com o previsto teoricamente, permitindo excelente perspectiva de aplicações desses sistemas na análise e caracterização de feixes ópticos e superfícies micro e nano-estruturadas. / Scientic instrumentation systems are powerful tools for feasibility and verication of models in theoretical physics, as well as for the generation of technological products. In this sense, Holographic Interferometry and Holographic Microscopy are shown as powerful optical methods for observing perturbative phenomena, in the analysis of the phase of wavefronts, non-destructive testing for surface analysis and optical systems admeasurement. Notably, real-time Holographic techniques are favorable compared to conventional surface analysis techniques, since they allow the analysis, visualization and in situ monitoring of the studied systems with precision and reliability. On the other hand, Computational and Photorefractive Holographic techniques, in which photorefractive materials are used as holographic recording media, are promising techniques for special optical beams generation. Thus, the objective of this research project was to study and apply the methods of Holographic Interferometry and Holographic Microscopy (Digital and Photorefractive) for the analysis of intensity and phase of special optical beams (non-diractive) and micro-structured three-dimensional surfaces. For these purposes, we developed a Digital and Photorefractive Holographic Interferometry arrangement for the generation and analysis of optical beams and a Digital and Photorefractive Holographic Microscopy for micro-structures analysis (resolution targets and blood cells). The obtained results are in agreement with those predicted theoretically, allowing an excellent perspective of applications of these systems in the analysis and characterization of optical beams and micro and nano-structured surfaces.

La thèse présente l’étude de la propagation et de l’auto-focalisation de faisceaux d’Airy dans un milieu photoréfractif. Le faisceau d’Airy est un faisceau dit accélérant qui, dans l’espace libre, présente une trajectoire curviligne, ne se déforme pas et est capable de se régénérer après un obstacle. L’auto-focalisation de faisceaux conventionnels, tels les faisceaux gaussiens, a été étudiée dans des milieux nonlinéaires en particulier pour des applications de routage tout-optique. En propageant des faisceaux optiques à travers de tels milieux photosensibles, il est possible de graver optiquement des guides d’onde retraçant la trajectoire de ces faisceaux. C’est dans ce contexte que le faisceau d’Airy suscite beaucoup d’intérêt, grâce à sa forme et sa trajectoire uniques. Dans ce mémoire nous étudions expérimentalement comme théoriquement les mécanismes d’auto-focalisation du faisceau d’Airy. Durant le régime transitoire de l’effet d’auto-focalisation, nous montrons des dynamiques spatiotemporelles singulières qui suggèrent une analogie avec les interactions gravitationnelles entre un objet massique et une onde se propageant dans l’espace-temps courbe. Dans un second temps, nous ajoutons un faisceau d’Airy se propageant dans la direction opposée au premier afin d’analyser leurs interactions. Ensuite, nous testons ces structures guidantes photoinduites par un ou deux faisceaux d’Airy, qui révèlent des possibilités de guidage uniques, non accessibles avec deux faisceaux conventionnels. Ces faisceaux optiques peuvent permettre de réaliser des fonctions de couplage, routage et multiplexage optique. Par ailleurs, nous étudions les limites de la force de guidage en augmentant la nonlinéarité d’autofocalisation du système. Les dynamiques spatiotemporelles qui en dérivent présentent des comportements et une évolution particuliers suggérant des applications dans le routage tout-optique stationnaire tout comme dynamique. Pour conclure, cette thèse nous permet de démontrer les alternatives prometteuses que nous offre le faisceau d’Airy dans la physique générale et plus particulièrement dans la photonique pour le routage tout-optique / In this thesis we study the propagation and the self-focusing of Airy beams in a photorefractive crystal. The Airy beam is a so-called accelerating beam which propagates in free space along a curved trajectory and with a shape-preserving and self-healing nature. The self-focusing of conventional beams, such as Gaussian beams, has been studied in nonlinear media in particular for all-optical routing solutions. By propagating optical beams in such photosensitive media, one can induce waveguides with the shape of the optical beams’ trajectories. The unique shape and trajectory of the Airy beam however suggest innovative waveguide possibilities. In this manuscript we theoretically and experimentally study the self-focusing mechanisms of the Airy beam. In particular during the transient self-focusing effect, we enlighten peculiar spatiotemporal dynamics suggesting an analogy with the gravitational interactions between a mass and a wave propagating in a curved spacetime. In a second step we add an Airy beam propagating in the opposite direction to analyze their cross-coupling interactions. The guiding structures induced by one or two counterpropagating Airy beams are then tested and show peculiar guiding possibilities that are not achievable using two conventional beams: optical beams can be guided along curved trajectories and eventually split into multiple beams. Furthermore the limits of the waveguiding strength are studied by increasing the self-focusing nonlinearity of the system. The resulting spatiotemporal dynamics present a peculiar behavior and evolution with possible applications in static and dynamical all-optical routing as well as optical computing such as random number generation. Finally with this thesis we demonstrate that the Airy beam offers promising alternatives in general physics and more specifically in photonics for all-optical routing

OBJETIVO: Avaliar a eficácia, estabilidade, previsibilidade e segurança da ceratectomia fotorrefrativa (PRK) guiada pelas frentes de onda corneana para o tratamento da hipermetropia secundária à ceratotomia radial (CR). MÉTODOS: Foram avaliados prospectivamente 61 olhos de 39 pacientes consecutivos, submetidos a PRK personalizado com o laser Esiris-Schwind. A técnica constou de desepitelização mecânica, fotoablação, e utilização de mitomicina C (MMC) 0,02% por 20 ou 40 segundos. A MMC foi aplicada por 40 segundos em 17 olhos (27,9%) que haviam sido submetidos a ablações mais profundas do que 100 ?m ou apresentavam córneas previamente suturadas. As avaliações pós-operatórias foram realizadas após sete dias, um, seis, 12 e 24 meses. Todos os olhos foram avaliados após um ano e dois anos. RESULTADOS: O intervalo médio entre a CR e o PRK foi de 18,8 anos ± 3,8 (DP); o equivalente esférico (EE) médio antes da ceratotomia radial era -4,10 dioptrias (D) ± 1,44. As medidas prévias ao PRK mostraram EE médio de +4,17 D ± 1,97; astigmatismo médio de -1,39 D ± 1,04; AV com correção (AVcc) média de 0,161 ± 0,137 (logMAR); e curvatura corneana média de 35,85 ± 3,60 D. Os resultados encontrados dois anos após a cirurgia foram: EE médio de 0,14 ± 0,99 D (p < 0,001); astigmatismo médio de -1,19 ± 1,02 D (p = 0,627); AV sem correção (AVsc) média de 0,265 ± 0,196 (p < 0,001); AVcc média de 0,072 ± 0,094 (p < 0,001); e curvatura corneana média de 39,01 ± 3,18 D (p < 0,001). AVsc igual ou melhor a 20/25 foi observada em 38% dos olhos e igual ou melhor a 20/40 em 69%. A AVcc melhorou em 62,3% dos olhos, sendo que 21 olhos (34,4%) melhoraram uma linha e outros 17 olhos (27,9%), duas ou mais linhas. Um olho (1,6%) perdeu duas linhas devido ao astigmatismo irregular ocasionado por opacificação corneana periférica. Outro olho perdeu três linhas pelo desenvolvimento de ectasia corneana entre seis e 24 meses, devido ao alargamento progressivo de uma incisão radial inferior, e foi posteriormente submetido à sutura da incisão. Houve 30 olhos (49,2%) entre ± 0,50 D do EE planejado e 45 (73,8%) entre ± 1,00 D. Entre seis e 24 meses, a regressão média do EE foi de +0,39 D (p < 0,05) e cinco olhos (8,3%) sofreram desvio hipermetrópico > 1,00 D. Ocorreu redução estatisticamente significante do coma (p = 0,001), trefoil (p = 0,008), aberração esférica (p < 0,001), astigmatismo secundário (p = 0,001) e quatrefoil (p < 0,001). Não houve mudança estatisticamente significativa da contagem endotelial (p = 0,161). Dois olhos (3,3%) desenvolveram opacificação corneana periférica grau 2 e um, grau 3. CONCLUSÃO: O PRK personalizado pelas frentes de onda corneana coadjuvado pela MMC foi eficaz, previsível e seguro pelo período de dois anos para a redução da hipermetropia após a CR. No pós-operatório observou-se melhora significativa da AVsc, AVcc e das aberrações corneanas. Constatou-se, entretanto, que a hipermetropia consecutiva à CR continua a progredir após o tratamento com o excimer laser. / PURPOSE: To assess the efficacy, stability, predictability and safety of corneal wavefront-guided photorefractive keratectomy (PRK) for correcting hyperopia after radial keratotomy (RK). METHODS: In a prospective study, 61 eyes of 39 consecutive patients were treated with PRK using an Esiris-Schwind excimer laser. Corneal epithelium was mechanically removed, followed by photoablation and use of 0.02% mitomycin C (MMC) for 20 or 40 seconds. MMC was used for 40 seconds in 18 eyes (27.9%) which underwent ablations deeper than 100 micron or had previous corneal sutures. Postoperative evaluations were performed after seven days, six, 12 and 24 months. All patients were followed up for two years. RESULTS: The mean time between RK and PRK was 18.8 years ± 3.8 (SD); mean spherical equivalent (SE) before RK was -4.10 diopters (D) ± 1.44. Before PRK, the mean SE was +4.17 D ± 1.97, mean astigmatism was -1.39 D ± 1.04, the mean best-corrected visual acuity (BCVA) was 0.161 ± 0.137 (logMAR) and the mean corneal curvature was 35.85 ± 3.60 D. At 24 months, mean SE was 0.14 ± 0.99 D (p < 0.001), mean astigmatism was -1.19 ± 1.02 D (p = 0.627), mean UCVA was 0.265 ± 0.196 (p < 0.001), mean BSCVA was 0.072 ± 0.094 (p < 0.001) and the mean corneal curvature was 39.01 ± 3.18 D (p < 0.001). UCVA was 20/25 or better in 38% of eyes and 20/40 or better in 69%. BCVA improved in 62.3% of eyes, with 21 (34.4%) gaining one line and 17 (27.9%), two or more lines. One eye (1.6%) lost two lines due to irregular astigmatism and peripheral haze. Another eye lost three lines due to keratectasia occurring between six and 24 months resulting from widening of an inferior radial incision that was later sutured. Thirty eyes (49.2%) were within ± 0.50 D of intended SE and 45 (73.8%) were within ± 1.00 D. From six to 24 months, the mean SE regression was +0.39 D (p < 0.05) and five eyes (8.3%) had a hyperopic shift > 1.00 D. A significant decrease in coma (p = 0.001), trefoil (p = 0.008), spherical aberration (p < 0.001), secondary astigmatism (p = 0.001) and quatrefoil (p < 0.001) was observed. Endothelial cell counts did not show a statistically significant decrease (p = 0.161). Two eyes (3.3%) developed peripheral haze grade 2 and one, grade 3. CONCLUSION: Corneal wavefront-guided PRK with MMC was effective, predictable and safe after two years for the treatment of hyperopia after RK. A significant improvement in UCVA, BSCVA and corneal aberrations was obtained. However, hyperopic shift after RK continued to progress after excimer laser surgery.

Made available in DSpace on 2014-12-17T14:13:40Z (GMT). No. of bitstreams: 1 FranciscoIP_TESE_PARCIAL.pdf: 210737 bytes, checksum: 77c1b45b267230f3fe0cd598e41eee0c (MD5) Previous issue date: 2011-07-01 / The topical corneal application of antimitotic mitomycin-C (MMC) during refractive surgery is still characterized by a lack of standardization and considerable empirism. For this reason the creation of a system capable of reliable drug delivery represents a beneficial innovation for patients submitted to these procedures. Objective: Elaborate a new MMC delivery system during the transoperatory period of photorefractive keratectomy (PRK) followed by patent application. Methods: The project consists of an in vitro experimental study to create an MMC (0.02%) release system. The drug was impregnated in sterile Whatman? 41 paper filter discs with a diameter of 8 mm. After drying, the discs were applied to antibiogram plates seeded with Staphylococcus epidermidis (American Type Culture Collection ATCC 12228), followed by the addition of a drop of sterile water. At the end of 1 minute, the discs were removed and the plates incubated for 48 hours at 35oC. Mean drop volume in the collyrium flasks was measured using analytical balance weighing. The inhibition halo (mm) was correlated with the MMC impregnated into the disc. After completion of the invention design a patent application was lodged at the National Institute of Industrial Property. Results: The correspondence between MMC-produced inhibition halos indicated that a dose of 16?g was ideal for impregnating into the discs. The mean drop volume obtained from the collyrium flasks was 37.7 ?L. A minute after the application of one drop of balanced saline solution, the system released an adequate concentration for PRK surgery. Conclusion: A new MMC delivery system was created for transoperatory application in photorefractive keratectomy (PRK). Publication of the patent application (number PI 0704739-8) gives the authors exclusive intellectual property rights. The study was sponsored by Ophthalmos Ind?stria e Com?rcio de Produtos Farmac?uticos S.A. (S?o Paulo-SP, Brazil) and received the indispensable scientific contribution of researchers from the fields of Pharmacy, Medicine, Biology, Statistics and Law, characterizing the work as multidisciplinary, in accordance with norms established by the Postgraduate Health Sciences Program of the Federal University of Rio Grande do Norte (UFRN) / A aplica??o t?pica corneana do antimit?tico mitomicina C (MMC) durante as cirurgias refrativas ainda ? caracterizada por uma falta de padroniza??o e grande empirismo. Por isso, a cria??o de um sistema capaz de disponibilizar a droga de forma padronizada representa uma inova??o que vem beneficiar os pacientes submetidos ?queles procedimentos. Objetivo: Elaborar um novo sistema de aplica??o da MMC durante o per?odo transoperat?rio da cirurgia de ceratectomia fotorrefrativa (Photorefractive keratectomy- PRK) com posterior dep?sito do Pedido de Patente. M?todos: O projeto representou um estudo experimental in vitro para cria??o de um sistema de libera??o de MMC a 0,02%. A droga foi impregnada em discos est?reis de papel filtro do tipo Whatman? 41 com 8 mm de di?metro. Ap?s o processo de secagem, os discos foram aplicados em placas de antibiograma semeadas com Staphylococcus epidermidis (American Type Culture Collection ATCC 12228), recebendo em seguida uma gota de ?gua est?ril. Decorrido o per?odo de 1 minuto, os discos foram removidos e as placas incubadas por 48 horas a 35oC. O volume m?dio das gotas de frascos de col?rio foi medido pelo m?todo de pesagem em balan?a anal?tica. O halo de inibi??o, em mil?metros, foi correlacionado com a dose da MMC impregnada no disco. Com o delineamento da inven??o, procedeu-se o Dep?sito do Pedido de Patente no Instituto Nacional da Propriedade Industrial. Resultados: A correspond?ncia entre os halos de inibi??o produzidos pela MMC indicou a dose de 16?g como a ideal para ser impregnada nos discos. O volume m?dio de uma gota obtida dos frascos de col?rio foi 37,7 ?L. Com a aplica??o de uma gota de solu??o salina balanceada e ap?s o per?odo de um minuto, o sistema liberou uma concentra??o considerada adequada para a cirurgia de PRK. Conclus?o: Um novo sistema de aplica??o de MMC foi criado para sua aplica??o transoperat?ria na ceratectomia fotorrefrativa (PRK). A publica??o do Pedido de Patente sob o n?mero PI 0704739-8 outorga aos autores a prioridade exclusiva de sua Propriedade Intelectual. A pesquisa teve o patroc?nio da Ophthalmos Ind?stria e Com?rcio de Produtos Farmac?uticos S.A. (S?o Paulo-SP, Brasil) e a indispens?vel contribui??o cient?fica de pesquisadores das ?reas de Farm?cia, Medicina, Biologia, Estat?stica e Direito, revestindo o trabalho de um car?ter multidisciplinar, requisito inerente ?s exig?ncias do Programa de P?s-Gradua??o de Ci?ncias da Sa?de da Universidade Federal do Rio Grande do Norte (UFRN)

Orientador: Jaime Frejlich Sochaczewsky / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-17T17:50:24Z (GMT). No. of bitstreams: 1 Pereira_RenataMontenegro_D.pdf: 11908190 bytes, checksum: a9fa68cda06040da547460ab983bc6e9 (MD5) Previous issue date: 2010 / 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