Histology has long recognized the intimate link between structure and function. Over centuries histologists have utilized an assortment of optical microscopy techniques to elucidate functional attributes of tissues through investigating tissue architecture. This thesis includes developments in the field of nonlinear optical microscopy for use in histology and pathology. The main contributions focused on the study of fibrillar collagen in the extracellular matrix (ECM) with polarization-dependent second harmonic generation (P-SHG) microscopy and the study of harmonophore-stained cellular nuclei with third harmonic generation (THG) microscopy. The P-SHG microscopy technique, “polarization-in, polarization-out” (PIPO), was developed to accurately determine the second-order polarization properties of thin tissue sections. The polarization instrumentation was implemented into a nonlinear optical microscope and a custom fitting algorithm extracted ratios of the second-order nonlinear susceptibility elements at every pixel of an obtained image. Hierarchical organization, at every level of structure, can contribute significantly to the macroscopic second-order polarization properties of fibrillar collagen in the ECM and quantifiable differences between the various tissue architectures were observed. A framework was developed, based on the collagen hierarchical organization, to interpret the submicron polarization properties of various tissues. Complimentary to the P-SHG study of connective tissue, the structure of hematoxylin and eosin (H&E) stained nuclei was revealed by THG microscopy. Imaging the 3D organization of nuclei was possible using the inherent optical sectioning provided by nonlinear microscopy. The origin of THG was investigated with spectrally- and temporally-resolved measurements, as well as the THG ratio method. A rather complex situation involving multiple dye complexes was revealed. The structure of dye aggregates was investigated with THG PIPO microscopy. The techniques of PIPO and harmonophore-stained harmonic generation microscopy show great potential for ultimately furthering understanding of tissue structure and function. H&E stained tissue investigations with THG microscopy has applications as a tool for cancer diagnostics. PIPO can elucidate the symmetry and organization of materials beyond tissues, including starch, nanowires, and protein crystals. In pathology, the developed collagen framework has strong implications, as collagen is recognized as playing a more active role in a number of diseases including idiopathic pulmonary fibrosis, wound repair, and tumour development and progression.

Histology has long recognized the intimate link between structure and function. Over centuries histologists have utilized an assortment of optical microscopy techniques to elucidate functional attributes of tissues through investigating tissue architecture. This thesis includes developments in the field of nonlinear optical microscopy for use in histology and pathology. The main contributions focused on the study of fibrillar collagen in the extracellular matrix (ECM) with polarization-dependent second harmonic generation (P-SHG) microscopy and the study of harmonophore-stained cellular nuclei with third harmonic generation (THG) microscopy. The P-SHG microscopy technique, “polarization-in, polarization-out” (PIPO), was developed to accurately determine the second-order polarization properties of thin tissue sections. The polarization instrumentation was implemented into a nonlinear optical microscope and a custom fitting algorithm extracted ratios of the second-order nonlinear susceptibility elements at every pixel of an obtained image. Hierarchical organization, at every level of structure, can contribute significantly to the macroscopic second-order polarization properties of fibrillar collagen in the ECM and quantifiable differences between the various tissue architectures were observed. A framework was developed, based on the collagen hierarchical organization, to interpret the submicron polarization properties of various tissues. Complimentary to the P-SHG study of connective tissue, the structure of hematoxylin and eosin (H&E) stained nuclei was revealed by THG microscopy. Imaging the 3D organization of nuclei was possible using the inherent optical sectioning provided by nonlinear microscopy. The origin of THG was investigated with spectrally- and temporally-resolved measurements, as well as the THG ratio method. A rather complex situation involving multiple dye complexes was revealed. The structure of dye aggregates was investigated with THG PIPO microscopy. The techniques of PIPO and harmonophore-stained harmonic generation microscopy show great potential for ultimately furthering understanding of tissue structure and function. H&E stained tissue investigations with THG microscopy has applications as a tool for cancer diagnostics. PIPO can elucidate the symmetry and organization of materials beyond tissues, including starch, nanowires, and protein crystals. In pathology, the developed collagen framework has strong implications, as collagen is recognized as playing a more active role in a number of diseases including idiopathic pulmonary fibrosis, wound repair, and tumour development and progression.

Orientador: Edson Bim / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-06T11:16:01Z (GMT). No. of bitstreams: 1 Bertonha_LeandroCorrea_M.pdf: 4817108 bytes, checksum: 7377641ea7817b2bac41b6c4870c60b2 (MD5) Previous issue date: 2006 / Resumo: Neste trabalho é apresentada a implementação de uma estratégia de controle escalar V/f que mantém o fluxo de entreferro constante em seu valor nominal a partir do controle da relação entre a tensão de terceira harmônica, do estator, presente devido à saturação magnética, e da freqüência elétrica. No caso das bobinas de estator estarem conectadas em Y, a terceira harmônica de tensão é obtida a partir da soma das tensões de fase do estator. Na. presente proposta não é necessário saber a magnitude do fluxo, mas apenas o valor da terceira harmônica de tensão quando o motor opera na sua condição nominal. O método proposto é simples de ser implementado, computacionalmente leve e insensível aos parâmetros do motor. Esta última característica é especialmente atrativa, pois boa parte cios acionamentos elétricos propostos na literatura com controle escalar tem seu desempenho insatisfatório devido à influência da variação da resistência de estator, principalmente quando o motor opera em baixas velocidades. Resultados experimentais mostram que a técnica implementada tem um excelente desempenho em regime permanente, ainda que com carga mecânica, e bom desempenho nos transitórios / Abstract: In this work it is presented the implementation of scalar control V/f technique. It keeps the air gap flux constant in its rated value by the control of the relation between third harmonic voltage, due to saturation, and electric frequency. When the coils are conected in Y. the third harmonic is obtained by the sum of staler phase voltage. We propose that it is not necessary to know the air gap flux magnitude, but only the third harmonic value when the induction motor operates in rated condition. The proposed method is easy to implement, has a light coputational processing and it is not sensitive to motor parameters. This last caracteristic is attractive, because many electric drivers have low performance due to the influence of stator resistence variation, mainly when, the motor operates in reduced speed. Experimental results show the high performance of system in steady state, with applied load, and good performance in dynamic situation / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Les semi-conducteurs nitrures d'éléments III type GaN, AlN sont des matériaux extrêmement intéressants pour la photonique intégrée sur silicium. Ils sont transparents sur une gamme très étendue et possèdent des susceptibilités non linéaires non nulles, ce qui rend possible les expériences non linéaires d'ordre deux et d'ordre trois. Dans ce contexte, cette thèse a été consacrée à l'étude de circuits photoniques avec des micro-résonateurs tels que les cristaux photoniques et les microdisques en matériau GaN/AlN épitaxiés sur Si. Le dessin des microcavités et des procédés de fabrication ont été optimisés afin d’obtenir un mode résonant dans le proche infrarouge avec un facteur de qualité jusqu'à 34000 pour les cristaux photoniques et 80000 pour les microdisques. J’ai étudié sur ces circuits photoniques les propriétés de conversion harmonique telles que la génération de seconde harmonique (SHG) et la génération de troisième harmonique (THG). En utilisant les propriétés de la THG, en combinant simplement un objectif optique et une caméra CCD, j'ai effectué l'imagerie des modes de cristaux photoniques du proche infrarouge avec une résolution spatiale sub-longueur d'onde (300 nm). J'ai également effectué l'imagerie de SHG sur des microdisques avec une excitation optique en résonance avec un mode de galerie pour le laser pompe. La dernière partie porte sur l'étude de la SHG en accord de phase entre les modes TM-0-0-X et TM-0-2-2X en variant le diamètre du disque avec un pas extrêmement faible (8 nm). Cela a été effectué pour des modes résonants de facteurs de qualité autour de 10000. Ces résultats montrent le potentiel des semi-conducteurs de III-nitrures pour la réalisation de circuits optiques sur silicium à deux dimensions. / Nitride semiconductors are extremely interesting for integrated photonics on silicon. They have a large transparent window and dispose of non zero nonlinear susceptibilities which enable second and third order nonlinear experiments. In this context, this thesis has been devoted to integrated photonic circuits with microresonators such as photonic crystals and microdisks. The microcavity design and the fabrication process have been optimized in order to obtain a near infrared resonant mode with a quality factor up to 34000 for photonic crystals and 80000 for microdisks. I carried out harmonic conversion experiments such as second harmonic generation (SHG) and third harmonic generation (THG). With THG, by combining simply an optical objective and a CCD camera, I carried out near infrared photonic crystal modes imaging with a subwavelength spatial resolution (300 nm). I also did SHG imaging on microdisks with an optical excitation in resonance with the gallery mode for the pump laser. The last part of the work is dedicated to the demonstration of phase-matched SHG in microdisk photonic circuits between the TM-0-0-X and TM-0-2-2X modes by varying the microdisk diameter with a very small step (8 nm). These experiments have been done for resonant modes with quality factors around 10000.These demonstrations show the potential of III-nitride semiconductors for the realization of two dimensional optical circuits on silicon.

Photo-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%. The conventional method of recording a hologram in PTR glass relies on exposure to continuous-wave ultraviolet laser radiation. In this dissertation the interaction between infrared ultrashort laser pulses and PTR glass is studied. It is shown that photosensitivity in PTR glass can be extended from the UV region to longer wavelengths (near-infrared) by exposure to ultrashort laser pulses. It is found that there exists a focusing geometry and laser pulse intensity interval for which photoionization and refractive index change in PTR glass after thermal development occur without laser-induced optical damage. Photoionization of PTR glass by IR ultrashort laser pulses is explained in terms of strong electric field ionization. This phenomenon is used to fabricate phase optical elements in PTR glass. The interaction between ultrashort laser pulses and volume holograms in PTR glass is studied in two laser intensity regimes. At intensities below ~10^12 W/cm^2 properties such as diffraction efficiency, angular divergence, selectivity, and pulse front tilt are shown to agree with the theory of linear diffraction for broad spectral width lasers. A volume grating pair arrangement is shown to correct the laser pulse distortions arising from pulse front tilt and angular divergence. At higher intensities of irradiation, nonlinear generation and diffraction of third harmonic is observed for three types of interactions: sum-frequency generation, front-surface THG generation, and THG due to phase-matching with a grating formed by modulation of the nonlinear refractive index of PTR glass.

Cette étude est divisée en deux parties: l'analyse des propriétés optiques non linéaires (NLO) de nouveaux dérivés pi-conjugués d’Azobenzène Iminopyridine et les hétérogénéités dynamiques (DH) des mélanges eau/méthanol. La première partie a été réalisée en utilisant la technique Z-scan ainsi que les techniques de génération de deuxième et troisième harmoniques (SHG/THG). Communément, l'optique non linéaire est le domaine de l'optique qui étudie l'interaction de la lumière avec un système matériel et les changements induits dans les propriétés optiques des matériaux parun champ électromagnétique intense. La non-linéarité réside dans le fait que la réponse du matériau ne dépend pas linéairement de l'intensité du champ électrique. Les matériaux qui possèdent une forte réponse non linéaire sont très utiles pour la photonique et l'optoélectronique. Ils peuvent être utilisés comme limiteurs optiques pour protéger les détecteurs de faisceaux laser de haute intensité, également comme commutateurs optiques, portes optiques logiques, etc., avec un objectif ultime qui est le traitement de signal optique et la fabrication d'ordinateurs optiques. La deuxième partie a été réalisée au moyen de calculs informatiques et plus particulièrement de simulations de dynamiques moléculaires dans l'eau, dans le méthanol et dans des mélanges eau/méthanol à différentes températures. La simulation par ordinateur est un outil très approprié pour explorer les liquides, également dans la plage de régime en surfusion, sans les limitations du processus de nucléation qui a lieu dans l'expérience réelle. Lorsque la température diminue les liquides surfondus subissent a minima une augmentation exponentielle de leur viscosité (Arrhenius). Cette grande modification des propriétés detransport apparaît bien que la structure ne change que légèrement avec la température. / This study is divided into two parts: the investigation of the nonlinear optical (NLO) properties of new (pi)- conjugated Azobenzene Iminopyridine derivatives and the Dynamic Heterogeneities (DH) of water/methanol mixtures. The first part was achieved employing Z-scan, Second and Third Harmonic Generation (SHG/THG) techniques. Generally, nonlinear optics is the domain of optics that studies the interaction of light with a material system and the changes resulted in the optical properties of the materials by an intense electromagnetic field. The nonlinearity lies in the fact that the material response does not depend linearly on the intensity of the electric field. Materials with significant nonlinear response are very useful for photonics and optoelectronics. They can be used as optical limiters to protect sensitive detectors of high-intensity laser beams, as well as optical switches, optical logic gates and etc., with an ultimate objective the processing of optical signal and manufacture of optical computers. The second part was done via computer calculationsand more specifically Molecular Dynamic Simulations in water, methanol and water/methanol mixtures at different temperatures. Computer simulation is a very suitable tool for exploring liquids, also in the range of the supercooled regime, without the limitations of the nucleation process, which takes place in the real experiment. Supercooled liquids undergo an exponential (Arrhenius) or even larger increase of their viscosity, when the temperature decreases. This large modification of the transport properties appear while the structure only slightly changes with temperature.

Third-harmonic generation (THG) is a fundamental nonlinear optical process that has been used in different applications such as third-order nonlinear materials characterization and nonlinear microscopy. It is widely employed since the third-order nonlinearity is the most important in isotropic materials and THG occurs in all media regardless of symmetry. In the tightly focused laser beam condition THG is observed only at the materials interfaces, where the focal symmetry is broken due to the presence of two media with different refractive index and/or third-order susceptibilities. Measuring slabs of different types of optical glasses, using femtosecond laser pulses, we could explain the asymmetric THG intensity profile observed at the interfaces. The harmonic generated at the exit interface is systematically stronger than the one generated at the entrance and this phenomenon can be understood by taking into account the presence of self-focusing effects. Basically, the self-focusing reduces the beam waist radius at the exit interface, resulting in greater laser irradiance and, consequently, higher THG. This study was then extended to the interfaces of a cuvette filled with organic solvents. Such systems present four interfaces and a mixture of nonlinear processes contributions since the cuvette walls present only electronic nonlinearity and the solvents present both electronic and orientational ones. In this way, the solvents may present an additional self-focusing contribution and, due to the noninstantaneous nature of the orientational process, the self-focusing from the solvent may be influenced by the pulse duration. In this case, the THG, which is an instantaneous electronic phenomenon, can be indirectly affected by pulse duration by means of the self-focusing effect. Usually, the slow orientational contribution is not considered for materials characterization by THG which may lead to incorrect nonlinear coefficient values, that means our study is important from the fundamental physics point of view and also for applications such as materials characterization. Based on the application of THG in nonlinear microscopy, we also present a microscopy technique which makes use of spatial frequency-modulated imaging (SPIFI) with single element detection. The microscope was developed at Colorado School of Mines (CSM) during an internship. The system uses a spatial light modulator (SLM) to provide the spatial frequency modulation and permits enhanced resolution images. THG SPIFI images are shown for the first time and we also report images obtained by other nonlinear optical process. In summary, the studies presented in this PhD work are of great importance for THG fundamental understanding, materials characterization and nonlinear optical microscopy. / Geração de terceiro harmônico (GTH) é um processo óptico não linear fundamental que tem sido usado em diferentes aplicações, como em caracterização óptica não linear de materiais e microscopia não linear. Ele é amplamente empregado uma vez que a não linearidade de terceira ordem é a mais importante em materiais isotrópicos e GTH ocorre em todos os meios independente da simetria. Na condição de feixe fortemente focalizado a GTH é observada apenas nas interfaces do material, onde a simetria focal é quebrada devido à presença de dois meios com diferentes índices de refração e/ou susceptibilidades de terceira ordem. Medindo lâminas de diferentes tipos de vidros ópticos, com pulsos de laser de femtossegundos, nós explicamos o perfil assimétrico de intensidade de GTH observado nas interfaces. O harmônico gerado na interface de saída é sistematicamente mais intenso do que o gerado na entrada e este fenômeno pode ser entendido levando-se em conta a presença do efeito de autofocalização. Basicamente, a autofocalização reduz a cintura do feixe na interface de saída do material, resultando em uma maior irradiância e, consequentemente, maior GTH. Este estudo foi estendido para o caso de interfaces de uma cubeta preenchida com diferentes solventes orgânicos. Tais sistemas apresentam quatro interfaces e uma mistura na contribuição dos processos não lineares, dado que as paredes da cubeta apresentam apenas não linearidade eletrônica e os solventes podem apresentar não linearidades tanto eletrônicas quanto orientacionais. Neste sentido, os solventes podem apresentar uma contribuição adicional de autofocalização e, devido à natureza não instantânea do processo orientacional, a autofocalização proveniente do solvente pode ser influenciada pela duração do pulso. Neste caso, a GTH, que é um fenômeno eletrônico (instantâneo), pode ser indiretamente afetada pela duração do pulso por meio do efeito de autofocalização. Usualmente, a contribuição orientacional não é considerada na caracterização de materiais por GTH, o que pode levar à valores incorretos para os coeficientes não lineares, o que significa que nosso estudo é importante do ponto de vista de física fundamental como também em aplicações como caracterização de materiais. Por conta da aplicação da GTH em microscopia não linear, apresentamos também nesta tese uma técnica de microscopia, que baseia-se em uma modulação em frequência espacial para imageamento (SPIFI) com uso de um detector de elemento único. O microscópio foi desenvolvido na Colorado School of Mines (CSM) durante um período de estágio. O sistema utiliza um modulador espacial de luz (SLM) para produzir a modulação em frequência espacial e permite obtenção de imagens em alta resolução. Imagens por GTH SPIFI são mostradas pela primeira vez e também apresentamos imagens obtidas por outros processos ópticos não lineares. Em resumo, os estudos apresentados neste trabalho de doutorado são de grande importância para o entendimento fundamental do processo de GTH, caracterização de materiais e microscopia óptica não linear.

Neste trabalho fizemos um estudo da geração de terceiro harmônico (GTH) usando pulsos de femtossegundos (fs). A GTH é uma importante técnica que permite estudar propriedades ópticas não lineares de terceira ordem de materiais. Estudamos a GTH aplicando as técnicas de franjas de Maker e a de varredura-Z em diferentes materiais levando em conta as contribuições de suas interfaces. A técnica de franjas de Maker com GTH permite a determinação de propriedades ópticas lineares e não lineares de volume, mas não de interface, portanto, a técnica de varredura-Z na condição de focalização forte foi implementada para estudar a influência da interface na GTH. Estudamos diversos vidros ópticos (sílica, K10, SK11, LLF1 e LLF6) e também diferentes soluções (acetona, clorofórmio, DMSO e tolueno) em uma cubeta. Em termos de número de interfaces, usando uma lâmina de vidro temos duas, no caso de um sanduíche de dois vidros temos três (entrada, meio e saída) e temos quatro interfaces para a cubeta. Observamos que elas contribuem tanto nas intensidades quanto nos espectros dos terceiros harmônicos (TH) gerados. Dependendo do tipo de interface e do sentido de propagação, tanto a intensidade quanto o espectro do TH são diferentes. Observamos que a reflexão de Fresnel atua significativamente nas diferenças de intensidades da GTH nas interfaces entre dois meios com índices de refração lineares diferentes. Uma interferência construtiva ocorre quando o feixe de laser propaga de um material com índice de refração mais alto para outro com índice mais baixo, aumentando a intensidade do laser e, consequentemente, gerando mais TH. Uma interferência destrutiva ocorre numa propagação oposta. Outro efeito interessante observado foi que, além da magnitude da não linearidade do meio, existem as contribuições da propagação e da modulação de fase cruzada no alargamento espectral do TH. Dessa forma, o alargamento espectral depende da não linearidade do meio e também do sentido de propagação no caso de interfaces. Em resumo, esse estudo nos levou a uma melhor compreensão dos fenômenos não lineares de GTH nas interfaces, e também possibilitou o surgimento de um novo método que pode ser usado para a determinação da susceptibilidade de terceira ordem de materiais. / In this work we did a study of the third-harmonic generation (THG) using femtosecond pulses. The THG is an important technique which allows studying thirdorder nonlinear optical properties of materials. We studied the THG by the Maker fringes and the Z-scan techniques in different materials taking into account their interfaces contributions. The Maker fringes technique with THG allows the determination of the bulk linear and the nonlinear properties, but not of the interface. Therefore, the Z-scan technique in the tight focused condition was implemented to study the interface influences on the THG. We studied several optical glasses (silica, K10, SK11, LLF1 and LLF6) and different solutions (acetone, chloroform, DMSO and toluene) in a cuvette. In term of numbers of interfaces, using a glass slab we have two, in the case of two sandwiched optical glasses we have three (input, middle and output) and for the cuvette we have four interfaces. We have observed that they play an important role on the third-harmonic (TH) intensities and spectra. Depending of the interface type and propagation direction, the TH intensity and spectrum are different. We have observed that the Fresnel reflection has a significant effect on the THG intensity differences between two media with different linear refractive indices. A constructive interference occurs when the laser beam propagates from one material with higher refractive index to one with lower refractive index, increasing the laser intensity and, consequently generating more TH. A destructive interference occurs in the opposite propagation case. Another important effect observed was that, beside the materials nonlinearity magnitude, there are propagation and cross-phase modulation contributions to the TH spectrum broadening. In this way, the spectrum broadening depends on the materials nonlinear properties and the propagation direction on the case of interfaces. In summary, this study leads to a better understanding of the TH nonlinear phenomena, and also, has allowed one new method for third-order nonlinear susceptibility determination.

Os sistemas elétricos de potência estão sujeitos a diversos tipos de sobretensões que podem causar desligamentos ou avarias nos equipamentos elétricos que o compõe, comprometendo a continuidade do fornecimento de energia elétrica aos consumidores e impactando negativamente nos índices de qualidade. Um dos dispositivos mais importantes utilizados na proteção destes equipamentos são os pára-raios, os quais podem ser classificados, no sistema elétrico brasileiro, em função de sua tecnologia: a primeira, mais antiga, utiliza carboneto de silício (SiC), a segunda e mais atual utiliza óxido de zinco (ZnO) em seus elementos internos. Os primeiros estão instalados há muitos anos, até mesmo acima de sua vida útil, sendo assim, podem apresentar falhas em campo durante a sua operação. Os pára-raios de SiC estão sendo gradativamente substituídos pelos de ZnO, pois seria economicamente inviável a sua substituição imediata. Por conseguinte, torna-se imprescindível o desenvolvimento de metodologias para avaliação do seu estado de degradação, a fim de evitar-se que estes equipamentos falhem no campo. A medição da corrente de fuga, analisando-se a sua componente de terceira harmônica, mostrou que podem obtidas informações importantes a respeito dos pára-raios de SiC, fornecendo subsídios para a elaboração de um programa de manutenção que priorize a retirada daqueles mais degradados. / Power systems are subject to many types of overvoltages that may provoke interruptions or damage in electrical equipments, compromising the continuity of electrical energy supply to consumers and impacting negatively the power quality indices. One of the most important device used to protect the electric equipments are the surge arresters, which may be classified, in Brazilian power system, by its technology: the first, more antiquated, using gapped silicon-carbide (SiC) surge arrester, and secondly and newer, zinc-oxide (ZnO) surge arrester. The devices of the first type are installed for many years, even above their lifetime, presenting, in such cases, failures in site while operating. The gapped silicon-carbide surge arresters have been substituted gradually by zinc-oxide surge arresters, because it would be economically impracticable to replace them immediately. Therefore, the development of methodologies to evaluate their degradations condition is necessary, in order to avoid the failure of these equipments in site. Measurements of leakage current with third order harmonic analysis showed that important information regarding gapped silicon carbide surge arresters may be obtained, providing subsidies to elaborate a program of maintenance that prioritize the replacement of the most degraded ones.

Os sistemas elétricos de potência estão sujeitos a diversos tipos de sobretensões que podem causar desligamentos ou avarias nos equipamentos elétricos que o compõe, comprometendo a continuidade do fornecimento de energia elétrica aos consumidores e impactando negativamente nos índices de qualidade. Um dos dispositivos mais importantes utilizados na proteção destes equipamentos são os pára-raios, os quais podem ser classificados, no sistema elétrico brasileiro, em função de sua tecnologia: a primeira, mais antiga, utiliza carboneto de silício (SiC), a segunda e mais atual utiliza óxido de zinco (ZnO) em seus elementos internos. Os primeiros estão instalados há muitos anos, até mesmo acima de sua vida útil, sendo assim, podem apresentar falhas em campo durante a sua operação. Os pára-raios de SiC estão sendo gradativamente substituídos pelos de ZnO, pois seria economicamente inviável a sua substituição imediata. Por conseguinte, torna-se imprescindível o desenvolvimento de metodologias para avaliação do seu estado de degradação, a fim de evitar-se que estes equipamentos falhem no campo. A medição da corrente de fuga, analisando-se a sua componente de terceira harmônica, mostrou que podem obtidas informações importantes a respeito dos pára-raios de SiC, fornecendo subsídios para a elaboração de um programa de manutenção que priorize a retirada daqueles mais degradados. / Power systems are subject to many types of overvoltages that may provoke interruptions or damage in electrical equipments, compromising the continuity of electrical energy supply to consumers and impacting negatively the power quality indices. One of the most important device used to protect the electric equipments are the surge arresters, which may be classified, in Brazilian power system, by its technology: the first, more antiquated, using gapped silicon-carbide (SiC) surge arrester, and secondly and newer, zinc-oxide (ZnO) surge arrester. The devices of the first type are installed for many years, even above their lifetime, presenting, in such cases, failures in site while operating. The gapped silicon-carbide surge arresters have been substituted gradually by zinc-oxide surge arresters, because it would be economically impracticable to replace them immediately. Therefore, the development of methodologies to evaluate their degradations condition is necessary, in order to avoid the failure of these equipments in site. Measurements of leakage current with third order harmonic analysis showed that important information regarding gapped silicon carbide surge arresters may be obtained, providing subsidies to elaborate a program of maintenance that prioritize the replacement of the most degraded ones.