Neste trabalho estudamos as propriedades térmicas e óticas de íons emissores usando as técnicas de lente térmica e z-scan, resolvidas no tempo. Foram obtidos o espectro fototérmico de lente térmica de amostras dopadas com Yb3+ e diversos outros parâmetros fototérmicos. Foi também realizado um estudo dos efeitos da saturação da não linearidade ótica sobre a determinação das propriedades eletrônicas em sólidos dopados com Cr3+, utilizando a técnica de z-scan. A seguir a mesma técnica foi aplicada na obtenção do parâmetro de upconversion em materiais dopados com Nd3+ e Cr3+ (com excitação ressonante e não ressonante ao nível laser emissor). Empregando a integral de difração foram investigados os efeitos do processo de upconversion Auger sobre a refração não linear. Os resultados experimentais e numéricos mostraram uma excelente concordância. Também foi investigado o comportamento temporal da população do nível emissor na fase de excitação, demonstrando assim uma forma alternativa de obter o parâmetro de upconversion. Finalmente, usando a técnica de z-scan obtivemos a forma de linha da não linearidade ótica de uma amostra dopada com Yb3+ onde demonstramos que a contribuição mais importante para a não linearidade do íon advém de transições no UV, mesmo estando o íon sob excitação ressonante ao nível emissor. / In this work we have studied the thermal and optical properties of emitters ions by using the thermal lens and z-scan time resolved techniques. It was obtained the thermal lens photothermal spectra of Yb3+ doped samples, and several other photothermal parameters. Also, it was done a study on the optical nonlinearity saturation effects over the determination of the optical properties in Cr3+ doped solids, using the z-scan technique. In the sequence the same technique was used in order to obtain the upconversion parameter in Nd3+ and Cr3+ doped materials (with excitation resonant and non resonant to the emitter level). Employing the diffraction integral, the effects of Auger upconversion process on the nonlinear refraction were investigated. The experimental and numerical results agree very well. It was also investigated the temporal behavior of the emitter level population during the excitation process, showing an alternative way to obtain the upconvertion parameter. Finally, by using the z-scan technique we have obtained the optical nonlinear lineshape of a Yb3+ doped sample, and demonstrated that the major contribution to the optical non linearity arises from the UV transitions, even when the emitter level of the ion is under resonant excitation.

As técnicas de lente térmica (LT) e \"Z-scan\" foram usadas para estudar as propriedades termo-óticas (difusividade térmica, condutividade térmica, taxa de variação do caminho ótico em função da temperatura e eficiência quântica de fluorescência) e não-lineares (partes real e imaginária do índice de refração não-linear, diferença de polarizabilidade e da seção de choque de absorção entre os estados excitado e fundamental, respectivamente) de sólidos dopados com Neodímio e Cromo. Uma nova extensão da técnica de LT foi proposta para determinar a eficiência quântica de fluorescência sem necessitar de amostra referência, como é feito na maioria dos métodos fototérmicos. Além disso, ambas técnicas foram usadas como espectroscopia, ou seja, a LT foi usada para estudar a forma de linha do calor gerado no material quando a excitação é feita próximo da banda de absorção do material, possibilitando assim a determinação da eficiência de transferência entre a matriz e o íon dopante, e a técnica \"Z-scan\" foi adaptada para medir a forma de linha do índice de refração não-linear próximo das linhas de emissão laser nos cristais dopados com Cromo. / The Thermal Lens (TL) and Z-scan technique were used to study the thermo-optical (thermal diffusivity, thermal conductivity, temperature coefficient of the optical path length change and fluorescence quantum efficiency) and nonlinear optical (parts real and imaginary of the refractive index, polarizability difference and absorption cross section between the excited and ground states, respectively) properties of Neodymium and Chromium doped solids. A new extension of the TL technique was proposed to determine the fluorescence quantum efficiency without measuring a reference sample, as done by any photothermal method Moreover, both techniques were used as an spectroscopy one, i. e., the TL was used to study the line shape of the heat created in material when the excitation is done near at the host absorption band, allowing the determination of the energy transfer efficiency between the host and the dopant ion, and the 2-scan technique was adapted to measure the line shape of the nonlinear refractive index near the laser lines in Chromium doped crystals.

Introdução: O aumento na prevalência das doenças cardiovasculares alerta para a necessidade de estratégias eficazes e de baixo custo como medidas preventivas na redução dos fatores de risco, morbidades e óbitos decorrentes de eventos coronarianos. As modificações no estilo de vida são as primeiras alternativas a serem adotadas. Nesse contexto, a dieta ocupa lugar de destaque e os benefícios dos ácidos graxos poli-insaturados ômega-3 na saúde cardiovascular são amplamente reconhecidos. As doenças cardiovasculares são influenciadas por diversos fatores de risco e o desequilíbrio na concentração plasmática das lipoproteínas é um fator de risco independente no desenvolvimento da doença cardiovascular aterosclerótica. Entretanto, há evidências de que as subfrações lipoproteicas podem influenciar o risco cardiovascular de maneira diferenciada, dependendo das características físico-químicas e funcionalidade de cada partícula. O desenvolvimento de novas técnicas, capazes de identificar esses parâmetros, tem sido foco de grande interesse científico. Objetivo: Avaliar o papel do ômega-3 sobre as características físico-químicas da LDL e HDL e possível associação entre medidas Z-scan e marcadores cardiometabólicos em indivíduos adultos. Metodologia: A partir de uma subamostra do estudo CARDIONUTRI (estudo clínico, randomizado, controlado e duplo cego com seguimento de 8 semanas) foram selecionados 36 indivíduos do Grupo Ômega-3 (3,0g/dia de óleo de peixe - 1,11g de EPA + 0,69g de DHA) e 27 do Grupo Placebo (3,0g/dia de óleo mineral). Foram monitorados o perfil clínico, antecedentes familiares, consumo alimentar, atividade física e antropometria. Amostras de sangue foram coletadas após 12 horas de jejum para avaliação das concentrações plasmáticas de CT, TAG, HDL-C, LDL-C, APOAI, APOB, PON1 e glicose. O tamanho da HDL e LDL foi analisado pelo método padronizado Lipoprint®. O conteúdo de LDL(-) foi determinado por ELISA. As medidas Z-scan foram determinadas por meio da difusividade térmica e absorção linear da LDL (1,0 mg/dL de proteína), isolada por ultracentrifugação. Todos as variáveis do estudo foram avaliadas no momento basal e após 8 semanas de intervenção. A adesão à intervenção foi monitorada pela contagem de cápsulas e percentual dos ácidos graxos plasmáticos. Para avaliar a associação das medidas Z-Scan aos marcadores cardiometabólicos, os dados obtidos no momento basal foram submetidos à Análise de Componentes Principais. Resultados: A idade média dos participantes do estudo foi de 51,5 (10,5) anos. A suplementação com ômega-3 promoveu redução significativa de CT, TAG, não-HDL, HDLPEQUENA e LDL(-), além de aumento significativo de HDL-C e HDLGRANDE. O ômega-3 foi mais eficaz na redução dos TAG (29,2 por cento ) quando comparado ao placebo (2,9 por cento ). O Grupo Ômega-3 apresentou aumento de HDLGRANDE (16,9 por cento ) e redução de HDLPEQUENA (-16,3 por cento ) ao final da intervenção, com diferença significativa quando comparado ao Grupo Placebo que apresentou redução de HDLGRANDE (-4,8 por cento ) e aumento de HDLPEQUENA (17,7 por cento ). Não foram observadas diferenças nas medidas Z-scan após a intervenção, porém as medidas se associaram positivamente a Componentes Principais com padrões cardioprotetores da amostra e negativamente a padrões aterogênicos. Conclusão: O ômega-3 demonstrou efeito positivo no perfil lipídico e propriedades aterogênicas das subfrações lipoproteicas. A suplementação com ômega-3 não modificou as medidas Z-scan, no entanto, a técnica demonstrou ser uma ferramenta capaz de se associar a padrões aterogênicos e antiaterogênicos monitorados no presente estudo / Introduction: The increased of cardiovascular disease prevalence draws attention to the need to adopt effective and inexpensive strategies as preventive measures to reduce risk factors, morbidity and deaths from coronary events. Lifestyle modification is indicated as first alternative to be adopted. In this context the diet stands out and omega-3 polyunsaturated fatty acids benefits on cardiovascular health are largely recognized. Cardiovascular diseases are influenced by several risk factors and the plasma imbalance lipoprotein is considered a crucial independent risk factor. However, there is evidence of the influence of lipoprotein subfractions in cardiovascular risk, based on the physicochemical characteristics of these particles. The development of new techniques able to identify those parameters has been the focus of great scientific interest. Objective: To evaluate the role of omega-3 on HDL and LDL physicochemical characteristics and possible association between Z-scan measurements and cardiometabolic markers in adults. Methods: From a subsample of the study CARDIONUTRI (clinical, randomized, controlled, double blind study with 8-week follow-up) were selected 36 individuals from the Omega-3 Group (3.0g/day of fish oil - 1,11g EPA + 0.69g DHA) and 27 individuals from the Placebo Group (3.0g/day of mineral oil). The clinical profile, family history, dietary intake, physical activity and anthropometry were monitored. Blood samples were collected after 12 hours of fasting to evaluate plasma concentrations of TC, TAG, HDL-C, LDL-C, APOAI, APOB, PON1 and glucose. The HDL and LDL size was analyzed by the standard method Lipoprint®. The levels of LDL (-) was determined by ELISA. The Z-scan measurements were determined by thermal diffusivity and linear absorption of LDL (1.0 mg / dL protein) isolated by ultracentrifugation. All study variables were evaluated at baseline and after 8 weeks of intervention. The intervention accession was monitored by capsule count and percentage of plasma fatty acids. To evaluate the association of the Z-Scan measurements to cardiometabolic markers, the data collected at baseline were subjected to Principal Component Analysis. Results: The average age of individuals were 51.5 (10.5) years. The omega-3 supplementation promoted a significant decreased of TC, TAG, non-HDL, small HDL and LDL(-), and significantly increased HDL-C and large HDL. The omega-3 was more effective in reducing the TAG (29.2 per cent ) when compared to placebo (2.9 per cent ). The Omega-3 Group increased large HDL (16.9 per cent ) and decreased small HDL (-16.3 per cent ) after the intervention, with significant difference when compared to the Placebo Group that decreased large HDL (-4.8 per cent ) and increased small HDL (17.7 per cent ). There were no differences in Z-scan measurements with the interventions, but were observed positively associated the Z-scan measurements with the anti-atherogenic sample patterns and negatively associated with atherogenic sample patterns when the sample was standardized from the Principal Components Analysis. Conclusion: The omega-3 demonstrated positive effect on the lipid profile and atherogenic lipoprotein subfractions. Supplementation with omega-3 did not modify the Z-scan measurements, however, the technique proved to be a tool that can be associated with atherogenic and anti-atherogenic sample patterns monitored in this study.

Notre étude concerne la mesure du déphasage optique non linéaire (NL) d’ordre trois. Deux catégories de procédés seront abordées : i) la technique interférométrique à décalage de phase qui permet la caractérisation de la phase avec une bonne résolution spatiale, ce qui est crucial pour un faisceau focalisé dans le milieu non linéaire. Cette technique utilise le critère des moindres carrés associé à plusieurs interférogrammes. Mise en œuvre à l'aide d'un modulateur spatial de lumière, elle fournit un calibrage pratique pour chaque déphasage considéré. La fiabilité de la méthode proposée est vérifiée par comparaison directe avec la méthode de transformation de Fourier ; ii) les méthodes innovantes de type Z-scan combinées avec un montage imageur. Elles seront ici appliquées aux mesures des coefficients NL d’ordre trois et d’ordres supérieurs. Nous montrerons que la flexibilité d’emploi d'une caméra CCD permet un meilleur pointage et suivi en temps réel du faisceau. Enfin nous nous intéresserons au montage Dark-field Z-scan bénéficiant des avantages de la microscopie à champ sombre à fort contraste. Ces améliorations ouvrent potentiellement un nouveau champ d’exploration microscopique pour l’investigation et la cartographie des effets non linéaires. / Our study concerns the measurement of the nonlinear (NL) optical phase shift of order three. Two categories of methods will be addressed: i) the phaseshift interferometric technique that allows phase characterization with good spatial resolution, which is crucial for a focused beam in the non-linear medium. This technique uses the least squares criterion associated with several interferograms. Implemented using a spatial light modulator, it provides a practical calibration for each phase shift considered. The reliability of the proposed method is verified by direct comparison with the Fourier transformation method; ii) innovative Z-scan methods combined with an imager assembly. They will be applied here to measurements of the NL coefficients of order three and higher. We will show that the flexibility of using a CCD camera allows for better pointing and real-time tracking of the beam. Finally, we will focus on the Dark-field Z-scan setup, which benefits from the advantages of high contrast dark field microscopy. These improvements potentially open up a new field of microscopic exploration for the investigation and mapping of non-linear effects.

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.

Materiais dopados com o íon trivalente Tb apresentam intensa emissão no verde (5D4 → 7Fj, j = 3, 4, 5 e 6) e fraca na região UV-azul (5D3 → 7Fj , j = 4, 5 e 6). A emissão azul pode ocorrer a partir de excitação direta no UV (emissão Stokes) ou por upconversion (emissão anti-Stokes), após a excitação em 488 nm (excitação ressonante no nível 5D4 a partir do estado fundamental). Nesta dissertação analisamos as propriedades da luminescência do Tb3+ em vidros aluminosilicato de cálcio com baixa concentração de sílica. Para excitação em 325nm, verificou-se que a intensidade da luminescência verde aumenta linearmente com a concentração, enquanto a emissão azul é fortemente reduzida com o aumento da concentração de Tb3+ de 0,5 para 15,0% (% em peso). No caso da excitação em 488 nm, observou-se uma forte saturação das emissões verdes, para intensidades duas ordens de grandeza menores que o esperado. Por meio de um sistema de equações de taxa, mostramos que esse comportamento pode ser explicado pelo mecanismo de absorção do estado excitado (AEE) e, por uma seção de choque de absorção (5D4 → 5D3) aproximadamente duas ordens de magnitude maior do que a do estado fundamental (7F6 → 5D4). Nossos resultados sugerem que a relaxação cruzada envolvendo os níveis 5D4 e 5D3 não é o único mecanismo responsável pela depopulação do nível 5D3 , como tipicamente descrito na literatura. Processos de upconversion por luminescência cooperativa entre íons excitados (5D3: 5D3 ou 5D3: 5D4) e outros mecanismos que envolvem transferência de energia para níveis excitados superiores (4f5d, banda de transferência de carga, matriz hospedeira, defeitos, etc) podem desempenhar um papel significativo neste sistema. Medidas de Z-scan resolvidas no tempo com excitação em 488 nm foram realizadas e não-linearidades de altas ordens foram observadas (n2, n4, etc.). A partir do n2, valores de Δαp e Δσ da ordem de 10-25 cm3 e 10-20cm2 foram calculados, respectivamente. Este valor de Δαp é o mais alto já reportado em materiais dopados com TR, provavelmente devido à baixa energia dos níveis 4f5d para o íon Tb3+. / Trivalent Tb-doped materials exhibit strong emission in the green (5D4 → 7Fj, j = 3, 4, 5 e 6) and weak in the UV-blue (5D3 → 7Fj , j = 4,5 e 6). The blue emission can occur from direct UV excitation (Stokes emission) or by upconversion (anti-Stokes emission) through 488 nm excitation (resonant pump of 5D4 metastable level from the ground state). In this dissertation the luminescence properties of Tb3+ doped low silica calcium aluminosilicate glasses are reported and analyzed. The intensity of green luminescence increases proportionally to the concentration while the blue luminescence is strongly reduced with the increase of Tb3+ concentration from 0.5 up to 15.0 wt%. In the case of 488 nm excitation, a saturation behavior of the green emission is observed at intensities two orders of magnitude smaller than expected for bleaching of the ground state population. Using a rate equation model, we show that this behavior can be explained by an excited state absorption (ESA) from 5D4 to upper levels, with an absorption cross section two orders of magnitude larger than the ground state absorption. The effect of ESA could also be observed by the shortening of the green emission risetime with the increase of pump intensity. We infer that the CR is not the only loss mechanism responsible for the 5D3 depopulation. Cooperative upconversion from a pair of excited ions (5D3:5D3 or 5D3:5D4) and other mechanisms involving upper lying states (4f5d, charge transfer, host matrix, defects, etc.) may play a significant role. Time-resolved Z-scan measurements were also performed at 488 nm high order nonlinearities were observed (n2, n4, etc.). From n2, Δαp and Δσ of the order of 10-25 cm3 and 10-20cm2, respectively, were obtained. This Δαp value is the highest ever reported for a RE doped material, it seems to be due to the low energy value of the 4f5d state in Tb3+.

O índice de refração não-linear n2 é o parâmetro chave da não-linearidade de terceira ordem em materiais ópticos. Um método simples, direto e sensível para medição do índice de refração não-linear (n2) é a técnica Z-scan proposta Sheik-Bahae et al 1. Nesse trabalho, um estudo sistemático quanto a esta técnica foi realizado. Utilizando a integral de difração de Fresnel-Kirchhoff, foi possível analisar a técnica investigando a influência do raio de abertura da íris. Foram obtidas expressões analíticas inéditas quando consideramos baixas não-linearidades induzidas por amostras finas. Esses resultados mostraram que o valor de n2 obtido é aproximadamente 36% maior do que n2 obtido por Sheik-Bahae para abertura linear de S=0,5, por exemplo.Extensões da técnica foram feitas, onde simulações para testar a viabilidade de medidas Z-scan no campo próximo e com dois feixes foram realizadas, de onde também foi possível encontrar resultados analíticos inéditos. Esses resultados teóricos foram testados tanto para feixe único quanto duplo em alguns experimentos, sendo obtido um bom acordo. Por fim, um novo método para medição do índice de refração não-linear não-degenerado foi proposto, em que é possível obter n2 no comprimento de onda do feixe de prova, num experimento com dois feixes. Esse resultado é importante uma vez que, em muitos casos, não é possível a realização de uma medida Z-scan convencional, devido ao fato da amostra não absorver o comprimento de onda do feixe de prova. Um resultado de n2 para rubi em 633nm foi obtido em bom acordo com resultados prévios da literatura, em que foram utilizadas técnicas de maior complexidade experimental. / The nonlinear refractive index n2 is the key parameter of the third order nonlinearity of optical materials. A simple, direct and sensitive measurement of nonlinear refractive index n2 is so-called Z-scan technique proposed by Sheik Bahae et al 1. In this work, a systematic study on this technique was performed. Based on Fresnel-Kirchhoff diffraction integral formula, it was possible to analyze the technique in order to investigate the influence of the apertures radius. We obtained unpublished analytical expressions when we consider small nonlinearities induced by thin samples. These results showed that the value of n2 obtained is about 36% larger than n2 obtained by Sheik-Bahae when the linear opening is 50%, for example.Extensions about the technique were made. Simulations were performed in order to test the feasibility of near-field Z-scan and two-color Z-scan measurements. Again it was also possible to find unpublished analytical results. The theoretical results were tested in some experiments and good agreement was found. Finally, a new method for measuring the nondegenerate refractive index was proposed. So, there is the possibility to obtain n2 at the wavelength of the probe beam in a two-color Z-scan experiment. This result is important since in many cases is impossible to perform a conventional z-scan measurement, due to the fact that the sample does not absorb the wavelength of the probe beam. A result of n2 for ruby at 633nm was obtained in good agreement with previous studies.

Les composés organiques et organométalliques représentent des matériaux prometteurs pour leurs applications dans divers domaines tels que l'optique non linéaire, l'optoélectronique, la photonique et le stockage des données par voie optique. Dans ce travail,nous avons étudié les propriétés optiques non linéaires(ONL) de deux familles de composés à savoir des molécules organiques à base de BODIPY et des complexes organométalliques à base de ruthénium (II)et de fer (II). Pour cette étude nous avons utilisé un laser pulsé en régime picoseconde qui délivre deux longueurs d'ondes : 1064 nm et 532 nm. Nous avons utilisé 1064nm pour les techniques de la génération de la seconde harmonique (SHG) et la génération de la troisième harmonique (THG) et 532 nm pour celle de Zscan.Les résultats obtenus sont intéressants et originaux et montrent bien que la réponse non linéaire dépend du nombre de groupements donneurs d’électrons pour les molécules organiques à base de BODIPY. Le même comportement a été observé dans le cas des complexes organométalliques à base de ruthénium (II) et de fer (II) mettant en évidence la modulation de la réponse optique non linéaire en fonction de la nature du métal de transition utilisé(Ru(II)ou Fe(II)) et de la nature des ligands auxiliaires autour du fragment organométallique (Ru(II)). / Organic and organometallic compounds represent an important potential in many fields such as optics, optoelectronics, photonics and optical data storage. In this work, we have studied the nonlinear optical properties of two types of compounds; organic molecules based on BODIPY and organometallic complexes based on ruthenium (II) and iron (II). For this, the experimental techniques used were based on SHG, THG and onZ-scan techniques. For this study, we used a pulsed picosecond laser delivering two wavelengths: 1064 nm and 532 nm. 1064 nm for SHG and THG techniques and 532 nm for Z-scantechnique were used, respectively. The results obtained are interesting and original and show that the nonlinear optical response of organic molecules based on BODIPY depends in particular on the number of electron donor groups. The same behavior has been observed in the case of organometallic complexes based on ruthenium (II) and iron (II), highlighting the modulation of the nonlinear optical response as a function of the nature of the transition metal used (Ru ( II) or Fe (II)) and the nature of the ancillary ligands around the organometallic moiety (Ru (II)).

Apresentamos uma série de novos resultados acerca dos vidros aluminosilicato de cálcio com diferentes concentrações de sílica (7,0 e 34,0% em massa) dopados com o íon Tb3+ (Tb4O7 = 0,05 - 15,0% em massa). A partir de medidas de absorção, excitação, emissão e tempos de decaimento; discutimos detalhadamente os mecanismos de emissão verde e azul do Tb3+ neste sistema vítreo. As emissões na região do azul (nível 5D3) foram analisadas tanto pela excitação direta no UV (emissão de Stokes) quanto por conversão ascendente de energia (emissão anti-Stokes), após a excitação em 488 nm (excitação ressonante com o nível 5D4). Para excitação em 325 nm, verificou-se que a intensidade da luminescência verde aumenta linearmente com a concentração, enquanto a emissão azul é fortemente reduzida com o aumento da concentração de Tb3+. No caso da excitação em 488 nm, observou-se uma forte saturação das emissões no verde, para intensidades duas ordens de grandeza menores que o esperado (Isat = 2,3×106 W/cm2). Por meio de um sistema de equações de taxa, mostramos que esse comportamento pode ser explicado pelo mecanismo de absorção do estado excitado e por uma seção de choque de absorção (5D4 → 5D3) aproximadamente duas ordens de magnitude maior do que a observada na transição 7F6 → 5D4. Espectros de excitação e emissão realizados a baixa temperatura (6 K) evidenciaram a presença de emissões atribuídas à matriz hospedeira. Medidas de Z-scan resolvidas no tempo, com excitação em 488 nm também foram realizadas e nos permitiram calcular a variação da polarizabilidade (Δαp) das amostras. A concentração de sílica apresentou forte influência nas propriedades não lineares aferidas. Para a amostra com menor concentração de sílica (7,0% em massa), o valor de Δαp é aproximadamente 10 vezes maior do que para a amostra com maior concentração de sílica (34% em massa). / We present a series of new results concerning Tb+3 (Tb4O7 = 0,05 - 15,0 wt.%) doped calcium aluminosilicate glasses with different silica concentrations (7.0 and 34.0 wt.%). Through optical absorption, excitation spectra, photoluminescence, and fluorescence decay measurements, the blue and green Tb+3 emission are discussed in detail. Emissions in the UV-blue region (5D3 level) were analyzed by direct UV excitation (Stokes emission) and by upconversion (anti-Stokes emission), resonant excitation with level 5D4 level. For the excitation at 325 nm, the intensity of the green luminescence increases linearly with the Tb+3 concentration. In opposite, the blue emission is strongly reduced with increasing the Tb+3 concentration from 0.5 to 15.0% (wt%). In the case of the 488 nm excitation, strong saturation of the green emissions was observed for pump intensity two orders of magnitude lower than expected (Isat = 2,3×106 W/cm2). By means a rate equations system, we explain this behavior by the excited state absorption and by an absorption cross section (5D4 → 5D3) approximately two orders of magnitude larger than 7F6 → 5D4 transition. Excitation and emission spectra were performed at low temperature (6 K) in the Tb doped LSCAS glass. These spectra showed matrix emission bands. Time-resolved Z-scan measurements were performed (at 488 nm). From these measurements, we determine the polarizability change (Δαp) in Tb doped glasses. The silica concentration presents a great influence on the nonlinear properties measured. The Δαp value in low silica calcium aluminosilicate glass (7.0 wt.%) is approximately 10 times higher than the value determined the sample with a higher silica content (34.0 wt.%).

Η εφεύρεση του laser έδωσε την δυνατότητα μελέτης της αλληλεπίδρασης ύλης-φωτός σε υψηλές εντάσεις ακτινοβολίας με αποτέλεσμα να οδηγηθούμε σε φαινόμενα κατά τα οποία οι συνήθεις οπτικές παράμετροι δε μπορούν να θεωρηθούν σταθερές, αλλά εξαρτώνται από την ένταση. Σε αυτή την περίπτωση, η συχνότητα δύναται να μεταβληθεί κατά την διάδοση της ακτινοβολίας σε ένα μέσο, ενώ η αρχή της επαλληλίας κυμάτων παραβιάζεται. Ο κλάδος της μη γραμμικής οπτικής μελετά φαινόμενα αλληλεπίδρασης της ύλης με ακτινοβολίες υψηλής έντασης. Αυτά τα φαινόμενα προέρχονται από την μεταβολή των οπτικών ιδιοτήτων της ύλης λόγω ισχυρών ηλεκτρικών πεδίων και η μη γραμμικότητα αυτών των φαινόμενων έγκειται στο ότι η απόκριση του υλικού είναι μη γραμμική συνάρτηση της έντασης της ακτινοβολίας. Οι θεμελιώδεις φυσικές αρχές που διέπουν τα μη γραμμικά φαινόμενα έχουν πλέον πλήρως αποσαφηνιστεί και το ενδιαφέρον έχει πια στραφεί στην μελέτη των μη γραμμικών οπτικών ιδιοτήτων διαφόρων υλικών. Σκοπός των ερευνών αυτών αποτελεί η εύρεση υλικών με μεγάλη μη γραμμική απόκριση, που θα μπορούσαν να χρησιμοποιηθούν σε διάφορες εφαρμογές στις οπτικές τηλεπικοινωνίες και στην οπτική επεξεργασία της πληροφορίας (π.χ. ως οπτικοί διακόπτες). Σε αυτήν την εργασία λοιπόν μέσω των τεχνικών ΟΚΕ και Z-Scan, ασχοληθήκαμε με την μελέτη της μη γραμμικής απόκρισης μιας σειράς παραγώγων φουλλερενίων, οι οπτικές ιδιότητες των οποίων είναι άμεσα συνδεδεμένες με την δομή τους και τον τρόπο σύνδεσης των επιμέρους ενώσεων από τις οποίες αποτελούνται.Στο πρώτο μέρος αυτής της εργασίας παρατίθενται οι βασικότερες έννοιες της μη γραμμικής οπτικής και περιγράφονται ορισμένα πολύ σημαντικά μη γραμμικά φαινόμενα. Στο δεύτερο μέρος παρουσιάζονται οι τεχνικές ΟΚΕ και Z-Scan οι οποίες χρησιμοποιήθηκαν για την μελέτη των μη γραμμικών οπτικών παραμέτρων των δειγμάτων των παραγώγων των φουλλερενίων στο πειραματικό μέρος της εργασίας αυτής και στη συνέχεια αναλύεται ο τρόπος επεξεργασίας των πειραματικών δεδομένων. Τέλος στο τρίτο μέρος περιγράφονται τα πειράματα που διεξήχθησαν, τα αποτελέσματα καθώς και τα συμπεράσματα που προέκυψαν. / The development of lasers has been a turning point in the history of science. It gave birth to the new field of nonlinear optics (NLO), which is the study of the interaction between intense light radiation and matter. In this regime, the response of matter cannot be considered linearly dependent on the intensity of the applied field, giving rise to significant new types of behavior and a wide spectrum of novel phenomena. Nonlinear optics has now become a rapidly growing field. It is at the forefront of progress in the area of photonics and optoelectronics. This vast development necessitates new materials with large nonlinearities, suitable for NLO applications in the laser and the optical communication technologies (e.g. optical switches). In that context, fullerenes have justifiably attracted considerable interest due to their intriguing physical and chemical properties; the extensive delocalization of their charge, as well as, their small reorganization energy can give rise to fast and high nonlinear optical response. Inevitably, the interest of the scientific community has now turned to the study of sophisticatedly altered fullerene derivatives. Depending on their ability to act as excellent electron acceptors, fullerenes are one of the most prominent chromophores that have been incorporated into multi-component molecular structures. Novel synthetic methods that enable the chemical modification of pristine molecules with electron donating moieties have been developed. This chemical functionalization of fullerenes can result in strong donor-acceptor interactions and photo-induced electron transfer, invigorating their nonlinear optical response. Their potential usage, which can range from photonics and photovoltaics implementations to applications in the biomedical area, is the main driving force of all this research. In the present study, the measurements were performed via the Z-Scan and the Optical Kerr Effect (OKE) techniques. The third order nonlinear susceptibility χ(3) and the second order hyperpolarizability γ of the derivatives were determined employing 4 ns and 35 ps laser pulses respectively, at excitation wavelength of 532 nm. In that respect, the main aim of the current study is threefold. Firstly, to provide a complete overview of the third order nonlinear parameters determined. Secondly, to briefly discuss the linkage between the observed nonlinearities with the molecular structures of the examinant hybrids, as well as, the possible effect of photo-induced charge transfer. Lastly, to shed light upon the role of the different pulse duration in the measurements and the dominant contributing physical processes related. Consequently, the first part of this work provides some basic concepts of nonlinear optics and the physical processes related with it. Then reference will be made to the experimental techniques used, including the fundamental background of the data analysis procedure. Finally, the nonlinearities observed in the picosecond and nanosecond regime are presented.