Le développement de matériaux vitreux magnéto-optiques présentant un effet Faraday élevé répond à un besoin grandissant dans l'industrie des isolateurs de Faraday. Ceux présent sur le marché actuellement sont des monocristaux de Tb₃Ga₅O₁₂ avec une concentration en Tb élevée et un procédé de fabrication coûteux. Dans ce sens, l'objectif de cette thèse est de réaliser des verres et fibres optiques fortement concentrés en terbium. La première approche est basée sur l'élaboration dite « conventionnelle » de verre par la méthode fusion-trempe. Des verres de fluorophosphate suivant la loi de composition (100-x)(70 NaPO₃ ­ 30 BaF₂) x TbF₃ avec x = 35, 40, 45 et 50 mol.% ont été explorés et a permis l'obtention de verre massif présentant une constante de Verdet à 650 nm de -78 rad.T⁻¹.m⁻¹ pour la composition optimale avec x = 50 mol.% en TbF₃. Cette valeur de constante de Verdet est la plus élevée rapportée pour un verre de fluorophosphate. Ensuite, la seconde approche consiste à amplifier la réponse magnéto-optique du terbium en l'associant à une autre terre-rare via le co-dopage. À partir de la composition des verres co-dopés suivant la composition (en mol.%) 35 NaPO₃ - 15 BaF₂ - 0,5 ((100-x) TbF₃ - x REF₃) avec les niveaux de substitution x = 0, 1, 2, 3, 4, 5, 10, 25, 50 et 100 où RE = Pr, Dy et Ho ont été explorés. Des constantes de verdet à 600 nm de -84,2, -84,5 et -84,5 rad.T⁻¹.m⁻¹ ont été rapportées pour les verres co-dopés respectivement avec du praséodyme, de l'holmium et du dysprosium comparativement à une constante de Verdet de -81,9 rad.T⁻¹.m⁻¹ pour le verre correspondant non co-dopé. Il s'agit à notre connaissance de la première démonstration de l'augmentation de l'effet Faraday par co-dopage dans des matériaux vitreux. L'influence de la géométrie de l'environnement des ions lanthanides sur l'effet associé au co-dopage a été réalisée dans des vitrocéramiques élaborées à partir des verres co-dopés de composition 35 NaPO₃ - 15 BaF₂ - 0,5 ((100-x) TbF₃ - x PrF₃) avec x = 0, 1, 2, 3, 4 et 5. Ceci a permis d'observer une augmentation de l'effet Faraday par co-dopage de 7,5% pour une matrice cristalline comparativement à une augmentation de 3,7% dans une matrice vitreuse. L'interaction de super-échange associé au co-dopage est alors optimisée dans le cadre d'un environnement cristallin en raison du meilleur recouvrement orbitalaire associé. Une approche « non-conventionnelle » pour outrepasser les limites de solubilité du terbium dans une matrice vitreuse est explorée. Elle consiste en l'élaboration de verre par lévitation aérodynamique permettant d'éliminer la cristallisation induite par l'interface liquide-creuset. Des compositions binaires 50 SiO₂ - 50 Tb₂O₃ et 60 Al₂O₃ - 40 Tb₂O₃ en mol.% sont explorés et des constantes de Verdet respectives de -152 et -160 rad.T⁻¹.m⁻¹ à 632 nm sont rapportées. L'exploration de compositions binaires permet également de mettre en évidence l'influence de la matrice sur l'effet Faraday. Enfin, la dernière approche vise à obtenir une fibre optique de silice à partir du procédé MCVD fonctionnalisée par l'incorporation de nanoparticules de Tb₂O₃. L'optimisation de la dispersion ex-situ de nanoparticules via le système MCVD a permis d'obtenir 4 km de fibre optique présentant une concentration de 0,1 at.% en terbium dans le cœur. Cette fibre de silice présente une constante de Verdet à 660 nm de -7,06 rad.T⁻¹.m⁻¹ pour une atténuation variant de 1,34 à 0,13 dB.m⁻¹ de 700 à 1100 nm. Cette valeur de constante de Verdet est la plus élevée rapportée pour une fibre de silice élaboré par MCVD. / The development of magneto-optical glassy materials with a high Faraday effect meets a growing need in the Faraday insulator industry. Those currently on the market are single crystals of Tb₃Ga₅O₁₂ with a high concentration of Tb and an expensive fabrication process. In this sense, the objective of this thesis is to realize glasses and optical fibers highly concentrated in terbium. The first approach is based on the so-called "conventional" elaboration of glass by the melt-quenching method. Fluorophosphate glasses following the composition law (100-x)(70 NaPO₃ - 30 BaF₂) x TbF₃ with x = 35, 40, 45 and 50 mol.% have been explored and allowed to obtain a bulk glass presenting a Verdet constant at 650 nm of -78 rad.T⁻¹.m⁻¹ for the optimal composition with x = 50 mol.% in TbF₃. This value of Verdet constant is the highest reported for a fluorophosphate glass. Then, the second approach consists in amplifying the magneto-optical response of terbium by associating it with another rare-earth via co-doping. From the composition of the co-doped glasses following the composition (in mol.%) 35 NaPO₃ - 15 BaF₂ - 0.5 ((100-x) TbF₃ x REF₃) with substitution levels x = 0, 1, 2, 3, 4, 5, 10, 25, 50 and 100 where RE = Pr, Dy and Ho were explored. Verdet constants at 600 nm of -84.2, -84.5 and -84.5 rad.T⁻¹.m⁻¹ were reported for the glasses co-doped with praseodymium, holmium and dysprosium respectively compared to a Verdet constant of -81.9 rad.T⁻¹.m⁻¹ for the corresponding non-co-doped glass. To our knowledge, this is the first demonstration of the enhancement of the Faraday effect by co-doping in glassy materials. The influence of the geometry of the lanthanide ion environment on the effect associated with co-doping was carried out in glass-ceramics developed from co-doped glasses of composition 35 NaPO₃ - 15 BaF₂ - 0.5 ((100-x) TbF₃ - x PrF₃) with x = 0, 1, 2, 3, 4 and 5. This resulted in an increase in Faraday effect by co-doping of 7.5% for a crystalline matrix compared to an increase of 3.7% in a glassy matrix. The super exchange interaction associated with co-doping is then optimized in the context of a crystalline environment due to the better associated orbital overlap. An "unconventional" approach to overcome the solubility limits of terbium in a glass matrix is explored. It consists in the elaboration of glass by aerodynamic levitation allowing to eliminate the crystallization induced by the liquid-crucible interface. Binary compositions 50 SiO₂ - 50 Tb₂O₃ and 60 Al₂O₃ - 40 Tb₂O₃ in mol.% are explored and respective Verdet constants of -152 and -160 rad.T⁻¹.m⁻¹ at 632 nm are reported. The exploration of binary compositions also allows to highlight the influence of the matrix on the Faraday effect. Finally, the last approach aims at obtaining a silica optical fiber, from the MCVD process, functionalized by the incorporation of Tb₂O₃ nanoparticles. The optimization of the ex-situ dispersion of nanoparticles via the MCVD system allowed to obtain 4 km of optical fiber with a concentration of 0.1 at.% of terbium in the core. This silica fiber presents a Verdet constant at 660 nm of -7.06 rad.T⁻¹.m⁻¹ for an attenuation varying from 1.34 to 0.13 dB.m⁻¹ from 700 to 1100 nm. This value of Verdet constant is the highest reported for a silica fiber processed by MCVD.

Le développement de matériaux vitreux magnéto-optiques présentant un effet Faraday élevé répond à un besoin grandissant dans l'industrie des isolateurs de Faraday. Ceux présent sur le marché actuellement sont des monocristaux de Tb₃Ga₅O₁₂ avec une concentration en Tb élevée et un procédé de fabrication coûteux. Dans ce sens, l'objectif de cette thèse est de réaliser des verres et fibres optiques fortement concentrés en terbium. La première approche est basée sur l'élaboration dite « conventionnelle » de verre par la méthode fusion-trempe. Des verres de fluorophosphate suivant la loi de composition (100-x)(70 NaPO₃ ­ 30 BaF₂) x TbF₃ avec x = 35, 40, 45 et 50 mol.% ont été explorés et a permis l'obtention de verre massif présentant une constante de Verdet à 650 nm de -78 rad.T⁻¹.m⁻¹ pour la composition optimale avec x = 50 mol.% en TbF₃. Cette valeur de constante de Verdet est la plus élevée rapportée pour un verre de fluorophosphate. Ensuite, la seconde approche consiste à amplifier la réponse magnéto-optique du terbium en l'associant à une autre terre-rare via le co-dopage. À partir de la composition des verres co-dopés suivant la composition (en mol.%) 35 NaPO₃ - 15 BaF₂ - 0,5 ((100-x) TbF₃ - x REF₃) avec les niveaux de substitution x = 0, 1, 2, 3, 4, 5, 10, 25, 50 et 100 où RE = Pr, Dy et Ho ont été explorés. Des constantes de verdet à 600 nm de -84,2, -84,5 et -84,5 rad.T⁻¹.m⁻¹ ont été rapportées pour les verres co-dopés respectivement avec du praséodyme, de l'holmium et du dysprosium comparativement à une constante de Verdet de -81,9 rad.T⁻¹.m⁻¹ pour le verre correspondant non co-dopé. Il s'agit à notre connaissance de la première démonstration de l'augmentation de l'effet Faraday par co-dopage dans des matériaux vitreux. L'influence de la géométrie de l'environnement des ions lanthanides sur l'effet associé au co-dopage a été réalisée dans des vitrocéramiques élaborées à partir des verres co-dopés de composition 35 NaPO₃ - 15 BaF₂ - 0,5 ((100-x) TbF₃ - x PrF₃) avec x = 0, 1, 2, 3, 4 et 5. Ceci a permis d'observer une augmentation de l'effet Faraday par co-dopage de 7,5% pour une matrice cristalline comparativement à une augmentation de 3,7% dans une matrice vitreuse. L'interaction de super-échange associé au co-dopage est alors optimisée dans le cadre d'un environnement cristallin en raison du meilleur recouvrement orbitalaire associé. Une approche « non-conventionnelle » pour outrepasser les limites de solubilité du terbium dans une matrice vitreuse est explorée. Elle consiste en l'élaboration de verre par lévitation aérodynamique permettant d'éliminer la cristallisation induite par l'interface liquide-creuset. Des compositions binaires 50 SiO₂ - 50 Tb₂O₃ et 60 Al₂O₃ - 40 Tb₂O₃ en mol.% sont explorés et des constantes de Verdet respectives de -152 et -160 rad.T⁻¹.m⁻¹ à 632 nm sont rapportées. L'exploration de compositions binaires permet également de mettre en évidence l'influence de la matrice sur l'effet Faraday. Enfin, la dernière approche vise à obtenir une fibre optique de silice à partir du procédé MCVD fonctionnalisée par l'incorporation de nanoparticules de Tb₂O₃. L'optimisation de la dispersion ex-situ de nanoparticules via le système MCVD a permis d'obtenir 4 km de fibre optique présentant une concentration de 0,1 at.% en terbium dans le cœur. Cette fibre de silice présente une constante de Verdet à 660 nm de -7,06 rad.T⁻¹.m⁻¹ pour une atténuation variant de 1,34 à 0,13 dB.m⁻¹ de 700 à 1100 nm. Cette valeur de constante de Verdet est la plus élevée rapportée pour une fibre de silice élaboré par MCVD. / The development of magneto-optical glassy materials with a high Faraday effect meets a growing need in the Faraday insulator industry. Those currently on the market are single crystals of Tb₃Ga₅O₁₂ with a high concentration of Tb and an expensive fabrication process. In this sense, the objective of this thesis is to realize glasses and optical fibers highly concentrated in terbium. The first approach is based on the so-called "conventional" elaboration of glass by the melt-quenching method. Fluorophosphate glasses following the composition law (100-x)(70 NaPO₃ - 30 BaF₂) x TbF₃ with x = 35, 40, 45 and 50 mol.% have been explored and allowed to obtain a bulk glass presenting a Verdet constant at 650 nm of -78 rad.T⁻¹.m⁻¹ for the optimal composition with x = 50 mol.% in TbF₃. This value of Verdet constant is the highest reported for a fluorophosphate glass. Then, the second approach consists in amplifying the magneto-optical response of terbium by associating it with another rare-earth via co-doping. From the composition of the co-doped glasses following the composition (in mol.%) 35 NaPO₃ - 15 BaF₂ - 0.5 ((100-x) TbF₃ x REF₃) with substitution levels x = 0, 1, 2, 3, 4, 5, 10, 25, 50 and 100 where RE = Pr, Dy and Ho were explored. Verdet constants at 600 nm of -84.2, -84.5 and -84.5 rad.T⁻¹.m⁻¹ were reported for the glasses co-doped with praseodymium, holmium and dysprosium respectively compared to a Verdet constant of -81.9 rad.T⁻¹.m⁻¹ for the corresponding non-co-doped glass. To our knowledge, this is the first demonstration of the enhancement of the Faraday effect by co-doping in glassy materials. The influence of the geometry of the lanthanide ion environment on the effect associated with co-doping was carried out in glass-ceramics developed from co-doped glasses of composition 35 NaPO₃ - 15 BaF₂ - 0.5 ((100-x) TbF₃ - x PrF₃) with x = 0, 1, 2, 3, 4 and 5. This resulted in an increase in Faraday effect by co-doping of 7.5% for a crystalline matrix compared to an increase of 3.7% in a glassy matrix. The super exchange interaction associated with co-doping is then optimized in the context of a crystalline environment due to the better associated orbital overlap. An "unconventional" approach to overcome the solubility limits of terbium in a glass matrix is explored. It consists in the elaboration of glass by aerodynamic levitation allowing to eliminate the crystallization induced by the liquid-crucible interface. Binary compositions 50 SiO₂ - 50 Tb₂O₃ and 60 Al₂O₃ - 40 Tb₂O₃ in mol.% are explored and respective Verdet constants of -152 and -160 rad.T⁻¹.m⁻¹ at 632 nm are reported. The exploration of binary compositions also allows to highlight the influence of the matrix on the Faraday effect. Finally, the last approach aims at obtaining a silica optical fiber, from the MCVD process, functionalized by the incorporation of Tb₂O₃ nanoparticles. The optimization of the ex-situ dispersion of nanoparticles via the MCVD system allowed to obtain 4 km of optical fiber with a concentration of 0.1 at.% of terbium in the core. This silica fiber presents a Verdet constant at 660 nm of -7.06 rad.T⁻¹.m⁻¹ for an attenuation varying from 1.34 to 0.13 dB.m⁻¹ from 700 to 1100 nm. This value of Verdet constant is the highest reported for a silica fiber processed by MCVD.

A presente pesquisa apresenta um estudo do ciclo de palestras intitulado A história química de uma vela, proferido por Michael Faraday como parte das celebrações natalinas de 1860, na Royal Institution, em Londres. Nas palestras, Faraday apresentou uma vela como objeto motivador para o estudo de vários aspectos da ciência contemporânea, e a transcrição da sua fala nos permite observar como o tema detinha a atenção do público do período. Seguindo os preceitos da nova historiografia da ciência, procuramos reconstruir parte do contexto de formação de Faraday, para entender como se consolidaram seus métodos de trabalho como palestrante. Algumas obras de influência sobre sua formação inicial são revisitadas: Conversations on Chemistry, de Jane Marcet (1805) e The Improvement of the Mind, de Isaac Watts (1741). O primeiro texto representa uma introdução à química do século XIX. Escritas sob a forma de diálogos, as conversas de Jane Marcet teriam nutrido o jovem Faraday de \"fatos\" científicos, que o motivaram no aprendizado das ciências naturais e renderam várias manifestações de reconhecimento do posterior filósofo para com a autora. Já a segunda obra se constitui num manual que instrumentaliza o autoaprendizado. Dividido em dois volumes, The improvement of the mind primeiro trata das regras para a aquisição de conhecimentos, amplamente estudadas e defendidas por Faraday em sua formação e, em seguida, das estratégias para a comunicação de conhecimentos, com particular ênfase sobre as palestras. Esta segunda parte da obra de Watts também foi objeto da atenção de Faraday, e os registros primários de ambos os autores nos fornecem critérios contemporâneos para a análise da atuação de Faraday como palestrante. Os resultados da pesquisa apontam para a coerência do trabalho de Faraday em relação aos preceitos que construiu sob a orientação de referências pessoais e textuais, como os palestrantes a que assistiu na juventude, e as obras que estudou em suas etapas de formação. Faraday conciliou e incorporou vários dos aspectos atribuídos por Watts ao bom palestrante, e também promoveu uma visão da química consoante com a divulgada por Jane Marcet em seu livro. Este estudo de caso busca na história da ciência a análise de fatores que contribuem ao êxito de uma iniciativa de divulgação científica. Dentro do seu contexto, o livro de Jane Marcet e as palestras de Faraday se constituíram em duas formas distintas de abordagem, e ambas lograram sucesso ao conseguirem ganhar a atenção do público para tratar das ciências naturais em geral, e da química em particular. Entendendo que nas iniciativas de divulgação científica a demanda por criatividade é atemporal, buscamos neste estudo histórico alguns argumentos que permitam refletir sobre essa prática em qualquer tempo. / This work presents a study on Michael Faraday\"s six-lecture course entitled The chemical history of a candle, delivered as part of the 1860 Christmas celebrations at the Royal Institution, London. In the lectures, Faraday departed from an ordinary candle to motivate the study of several current scientific issues. The transcription of his speech allows us to investigate how science attracted general public attention at the time. In order to understand how Faraday achieved the maturity of his work as a lecturer, we considered the precepts of the new historiography of science and followed up on the context of his early intellectual development. Some works of reference are revisited: Conversations on Chemistry, by Jane Marcet (1805) and The Improvement of the Mind, by Isaac Watts (1741). The first book represents an introductory course in chemistry, written in the form of dialogs for the early nineteenth century general public. According to Faraday\"s own reports, such book had nourished him with scientific \"facts\", which stimulated him to pursue a scientific career. The second book consists in a manual aimed to improve self-learning initiatives. The Improvement of the Mind is divided in two volumes, being the first dedicated to the rules for the acquisition of knowledge, and the second to the skills to communicate such knowledge, specially by means of lectures. Both volumes seem to have influenced the young Faraday remarkably, not only by helping him to establish his methods of study but also by instructing him about dealing with knowledge. Moreover, this second volume of the book gives us contemporary criteria to analyze Faraday\"s later work as a lecturer. Our research results point out to the coherence between Faraday\"s work and the precepts he developed under the guidance of both personal and textual references, such as the lecturers he attended to or the books he read during his apprenticeship. Faraday was able to personify many of the attributes of the good lecturer described by Watts, and also promoted a view of chemistry which coincides on several aspects with the one popularized by Jane Marcet in her conversations. This case study focuses on a science popularization initiative, and analyzes the factors which influence its outcome. Within their particular context, Jane Marcet\"s conversations and Faraday\"s lectures represent two different approaches to science popularization, and they both achieved great success in getting the public\"s attention to chemistry, and to science in general. Taking creativity as a timeless requirement for any initiative in science popularization, we hope with this work to promote reflections about such practices at any time.

Dans les systèmes de télécommunications l'isolateur est le seul élément qui n'a pas encore été intégré, en raison du traitement thermique élevé (~ 700 °C) nécessaire à la cristallisation des matériaux magnétiques le constituant. Ce composant autorise le passage de la lumière dans une seule direction, en bloquant la propagation dans le sens retour et évite les risques des dommages ou d’instabilités. Il est basé sur l'effet non-réciproque de la rotation Faraday des matériaux magnéto-optiques. Pour surmonter ce problème de compatibilité tout en exaltant l'effet magnéto-optique, un matériau composite structuré en cristal photonique 3D a été élaboré par imprégnation d’un opale direct de polystyrène avec une solution de précurseurs métalliques dopés avec des nanoparticules magnétiques (CoFe2O4) à basse température en utilisant le procédé sol-gel. Premièrement, nous avons montré par le calcul, que l'utilisation d'un matériau magnétique diluée avec un indice de réfraction relativement faible dans un cristal photonique 1D, peut augmenter le facteur de mérite par rapport à une seule monocouche magnéto-optique. Pour obtenir une rotation Faraday suffisante, la fraction volumique de nanoparticules magnétiques dans la couche composite a tout d’abord été augmentée de quelques pour cent à une valeur aussi importante que 40%. Le résultat principal de cette thèse est enfin que la rotation de Faraday des cristaux magnéto-photoniques réalisés a montré une amélioration sur les bords de la bande interdite photonique en comparaison à la seule monocouche / For telecommunication systems the isolator is the only element, which has not been integrated yet, because of the high temperature (~700 °C) annealing process which is required for the crystallization of magnetic materials. Due to the non-reciprocal behavior of the magneto-optical effects, this device assures that the transmitted light passes in one direction, but it blocks the backward propagation into the laser and avoids damage risk or instabilities. To overcome this compatibility problem and increase the magneto-optical effect, a composite material arranged as 3D photonic crystal has been elaborated by impregnating polystyrene direct opals with magnetic nanoparticles(CoFe2O4) doped metallic precursor solution using low temperature sol-gel process. Firstly, we have shown by calculation, that the use of a dilute magnetic material with a relatively low refractive index in a 1D photonic crystal can increase the merit factor compared to a single magnetic monolayer. To obtain a sufficient Faraday rotation, the volume fiaction of magnetic nanoparticles had to be increased. We managed to reach 40%, whereas this rate was only a few percent at the beginning of this work. The main result of this thesis is that the Faraday rotation of the realized magneto-photonic crystals showed an enhancement at the edges of the photonic band gap comparing to the single monolayer

A presente pesquisa apresenta um estudo do ciclo de palestras intitulado A história química de uma vela, proferido por Michael Faraday como parte das celebrações natalinas de 1860, na Royal Institution, em Londres. Nas palestras, Faraday apresentou uma vela como objeto motivador para o estudo de vários aspectos da ciência contemporânea, e a transcrição da sua fala nos permite observar como o tema detinha a atenção do público do período. Seguindo os preceitos da nova historiografia da ciência, procuramos reconstruir parte do contexto de formação de Faraday, para entender como se consolidaram seus métodos de trabalho como palestrante. Algumas obras de influência sobre sua formação inicial são revisitadas: Conversations on Chemistry, de Jane Marcet (1805) e The Improvement of the Mind, de Isaac Watts (1741). O primeiro texto representa uma introdução à química do século XIX. Escritas sob a forma de diálogos, as conversas de Jane Marcet teriam nutrido o jovem Faraday de \"fatos\" científicos, que o motivaram no aprendizado das ciências naturais e renderam várias manifestações de reconhecimento do posterior filósofo para com a autora. Já a segunda obra se constitui num manual que instrumentaliza o autoaprendizado. Dividido em dois volumes, The improvement of the mind primeiro trata das regras para a aquisição de conhecimentos, amplamente estudadas e defendidas por Faraday em sua formação e, em seguida, das estratégias para a comunicação de conhecimentos, com particular ênfase sobre as palestras. Esta segunda parte da obra de Watts também foi objeto da atenção de Faraday, e os registros primários de ambos os autores nos fornecem critérios contemporâneos para a análise da atuação de Faraday como palestrante. Os resultados da pesquisa apontam para a coerência do trabalho de Faraday em relação aos preceitos que construiu sob a orientação de referências pessoais e textuais, como os palestrantes a que assistiu na juventude, e as obras que estudou em suas etapas de formação. Faraday conciliou e incorporou vários dos aspectos atribuídos por Watts ao bom palestrante, e também promoveu uma visão da química consoante com a divulgada por Jane Marcet em seu livro. Este estudo de caso busca na história da ciência a análise de fatores que contribuem ao êxito de uma iniciativa de divulgação científica. Dentro do seu contexto, o livro de Jane Marcet e as palestras de Faraday se constituíram em duas formas distintas de abordagem, e ambas lograram sucesso ao conseguirem ganhar a atenção do público para tratar das ciências naturais em geral, e da química em particular. Entendendo que nas iniciativas de divulgação científica a demanda por criatividade é atemporal, buscamos neste estudo histórico alguns argumentos que permitam refletir sobre essa prática em qualquer tempo. / This work presents a study on Michael Faraday\"s six-lecture course entitled The chemical history of a candle, delivered as part of the 1860 Christmas celebrations at the Royal Institution, London. In the lectures, Faraday departed from an ordinary candle to motivate the study of several current scientific issues. The transcription of his speech allows us to investigate how science attracted general public attention at the time. In order to understand how Faraday achieved the maturity of his work as a lecturer, we considered the precepts of the new historiography of science and followed up on the context of his early intellectual development. Some works of reference are revisited: Conversations on Chemistry, by Jane Marcet (1805) and The Improvement of the Mind, by Isaac Watts (1741). The first book represents an introductory course in chemistry, written in the form of dialogs for the early nineteenth century general public. According to Faraday\"s own reports, such book had nourished him with scientific \"facts\", which stimulated him to pursue a scientific career. The second book consists in a manual aimed to improve self-learning initiatives. The Improvement of the Mind is divided in two volumes, being the first dedicated to the rules for the acquisition of knowledge, and the second to the skills to communicate such knowledge, specially by means of lectures. Both volumes seem to have influenced the young Faraday remarkably, not only by helping him to establish his methods of study but also by instructing him about dealing with knowledge. Moreover, this second volume of the book gives us contemporary criteria to analyze Faraday\"s later work as a lecturer. Our research results point out to the coherence between Faraday\"s work and the precepts he developed under the guidance of both personal and textual references, such as the lecturers he attended to or the books he read during his apprenticeship. Faraday was able to personify many of the attributes of the good lecturer described by Watts, and also promoted a view of chemistry which coincides on several aspects with the one popularized by Jane Marcet in her conversations. This case study focuses on a science popularization initiative, and analyzes the factors which influence its outcome. Within their particular context, Jane Marcet\"s conversations and Faraday\"s lectures represent two different approaches to science popularization, and they both achieved great success in getting the public\"s attention to chemistry, and to science in general. Taking creativity as a timeless requirement for any initiative in science popularization, we hope with this work to promote reflections about such practices at any time.

Cet ouvrage présente de nouveaux aspects de l’analogie entre temps et espace pour les ondes, à travers des concepts de contrôle temporel de la propagation des ondes, qui peuvent être interprétés comme la transposition au domaine temporel d’opérations standard du domaine spatial. Toute l’étendue de cette analogie est étudiée dans le cadre deux phénomènes ondulatoires bien connus (dans leurs versions spatiales), et dont nous montrons qu’ils sont étroitement liés : la réflexion des ondes et leur transformation par un cristal. En particulier, il est démontré expérimentalement que l’analogue temporel de la réflexion par un miroir génère une onde retournée temporellement, c’est-à-dire dont l’évolution temporelle est inversée. Une variante monofréquentielle de ce miroir temporel instantané, qui possède des liens étroits avec le concept de conjugaison de phase utilisé pour le retournement temporel d'ondes monochromatiques en optique, est également étudiée. Nous montrons que la modulation temporelle périodique du milieu mise en jeu dans ces expériences constitue l'équivalent temporel d'un cristal pour les ondes et étudions les propriétés générales des ondes dans ces milieux. Nous cherchons naturellement à sonder les limites de ces analogies spatiotemporelles, dont, de toute évidence, le principe de causalité est un élément majeur. Les phénomènes étudiés sont généraux et communs à toutes les ondes classiques, gouvernées en général par l’équation de d’Alembert ou par d’autres équations similaires. Les ondes à la surface d’un liquide sont utilisées comme système ondulatoire modèle dans nos expériences / This work presents new aspects of the analogy between time and space in wave phenomena, through new concepts of time control of wave propagation which can be interpreted as the transposition onto the time domain of standard spatial operations. The depth of this analogy is thoroughly studied in the framework of two well-known wave phenomena: reflection of waves on a mirror and their transformation by a crystal. More precisely, we experimentally demonstrate that the time analog of reflection by a mirror generates a time reverse wave that is whose time evolution is inverted. A monofrequency variant of this instantaneous time mirror, which has strong connections to the concept of wave phase conjugation used for time reversing monochromatic waves in optics, is also studied. We show that the periodic time modulation of the medium involved in the latter experiments constitutes the time equivalent of a crystal for waves and we study the general properties of waves in such media. We address of course the issue of the limits of theses space time analogies, of which, the principle of causality is evidently a major constituent. The phenomena studied here are general and apply to all classical waves (usually governed by d’Alembert’s equation or by similar ones). Waves at the surface of a liquid are used as a model wave system in our experiments / Die Universalitat der klassischen Wellenphanomenen lasst sich weitgehend durch die d’Alembertsche Struktur der Wellengleichungen beschreiben. In letzterer spielen die Zeit- und Raumvariabeln eine ahnliche Rolle. Wir betrachten in diesem Werk diese bekannte Analogie unter einem neuen Licht, indem wir neue Konzepte der Zeitkontrolle von der Wellenpropagation introduzieren, die als Transposition zum Bereich der Zeit von standarden Wellenphanomen des Raumes interpretiert werden konnen, wobei die raumliche Variation der Eigenschaften des Mediums, die sie bestimmen, durch eine zeitliche ersetzt wird. Wir bringen den experimentellen Beweis der Relevanz dieses Ansatzes, wobei wir die Wellen an der Oberflache einer Flussigkeit als Modelwellensystem verwenden und zeigen durch theoretische Erkenntnisse, dass er auf alle Wellensysteme generalisiert werden kann, die durch eine Wellengleichung beschrieben wird, deren 10 Struktur die der d’Alembertschen Gleichung ahnelt. Die ganze Reichweite dieser Analogie wird im Rahmen zweier langst bekannten Wellenphanomenen (in deren raumlichen Version), von denen wir zeigen, dass sie eng verbunden sind : die Spiegelung einer Welle und deren Umwandlung durch einen Kristal. Das Equivalent eines Spiegels fuhrt zur augenblicklichen Erscheinung aus dem gesammten Raum einer zeitumgekehrten Welle, das heist einer Wellenform, derer zeitliche Entwicklung im Vergleich zu der originellen Welle umgekehrt ist. Eine Einzelfrequenzvariante dieses augenblicklichen Zeitspiegels wird auch vorgestellt, die enge Verbindungen mit dem fur die Zeitumkehr monochromatischer Wellen angewendeten Konzept der optischen "Phase Conjugation" (Phasenkonjugierung) besitzt. Wir zeigen, dass die dazugehorige periodische Zeitmodulation des Mediums das zeitliche Equivalent eines Kristals fur die Welle bildet, und wir studieren die generellen Eigenschaften der Wellen in solchen Medien. Wir versuchen, die Grenzen dieser raumzeitlichen Analogien zu erkundigen, in derer Bestimmung selbstverstandlich das Kausalitatsprinzip eine masgebliche Rolle spielt, und die interessanten Unterschiede zwischen den vorgestellten Konzepten und deren raumlichen Pendants offenbaren / La universalidad de los fenomenos ondulatorios clasicos es ampliamente descrita por la estructura de la ecuacion de d’Alembert. En esta ecuacion, las variables espaciales y temporales desempenan un papel similar. En esa obra, revisitamos esta analogia bien conocida a traves de nuevos conceptos de control temporal de la propagacion de las ondas, quienes pueden ser interpretados como transposiciones de fenomenos espaciales estandartes al ambito temporal, en los cuales las variaciones espaciales de las propiedades del medio son reemplazadas por las correspondientes variaciones temporales. Hacemos la prueba, usando ondas a la superficie de un liquido, de la relevancia de este enfoque y mostramos teoreticamente su generalizacion a todo tipo de onda clasica, es decir gobernada por una ecuacion cuya estructura es similar a la de d’Alembert. Toda la extension de esta analogia queda estudiada en el cuadro de los dos fenomenos clasicos (en sus versiones espaciales) que son la reflexion de una onda sobre un espejo y su trasformacion en un cristal. Ademas, mostramos que los dos son intimamente relacionados. El equivalente temporal de un espejo produje instantaneamente desde el medio entero una onda retornada en el tiempo, es decir cuya evolucion temporal es invertida comparado a la onda inicial. Una variante monofrecuencial de este espejo queda estudiada tambien. Posee estrechos vinculos con el concepto de Phase Conjugation (conjugacion de fase), usado en Optica para hacer retornamiento temporal de ondas monocromaticas. Mostramos que la modulacion temporal implicada constituye el equivalente de un cristal para las ondas et estudiamos las caracteristicas generales de ondas en estos medios. Sondeamos los limites de esas analogias espaciotemporales de cuyos obviamente el principio de causalidad es un elemento mayor y que revelan diferencias interesantes entre los conceptos presentados y sus equivalentes espaciales / L’universalita dei fenomeni ondulatori classici e in larga misura descritta dalla struttura dell’equazione di d’Alembert. In quest’equazione, le variabili spaziali e temporali svolgono ruoli analoghi. Nell’opera seguente rivisitiamo questa ben nota analogia introducendo nuovi concetti sul controllo temporale della propagazione delle onde. Questi concetti possono essere interpretati come trasposizione di fenomeni ondulatori spaziali standard nell’ambito temporale, sostituendo le variazioni spaziali delle proprieta del mezzo con le variazioni temporali corrispondenti. Usando delle onde sulla superficie di un liquido come modello fisico, facciamo fede della rilevanza di quell’approccio e mostriamo teoricamente la generalizzazione a tutti i tipi di onde classiche, governate da equazioni simili a quella di d’Alembert. Questa analogia viene studiata nell’ambito di due fenomeni ondulatori ben noti (nella loro versione spaziale) : la riflessione delle onde generata da un specchio e la loro trasformazione generata da un cristallo. Mostriamo inoltre che i due concetti sono intimamente vincolati. L’equivalente temporale di un specchio porta alla generazione in tutto lo spazio di un’onda restituita nel tempo, vale a dire un’onda di cui l’evoluzione temporale e invertita in relazione all’onda originale. In questa tesi viene presentata anche una variante monofrequenziale di questo specchio temporale istantaneo che possiede legami stretti con il concetto di coniugazione di fase usato in ottica per invertire nel tempo onde monocromatiche. Mostriamo in questo lavoro che la modulazione temporale periodica del mezzo in questione costituisce, per le onde, l’equivalente temporale di un cristallo e ne studiamo le proprieta generali. In questa tesi, cerchiamo di sondare i limiti dell’analogia spaziotemporale, di cui il principio di causalita ne e l’essenziale e che rivelano differenze interessanti tra i concetti presentati e i loro equivalenti spaziali

Polarization specific measurements are advancing the capabilities of scientific instruments looking for ever smaller effects and material parameters. For example, the magneto-optical nonlinear Faraday effect can be used to characterize various electric and magnetic polarizability parameters of an individual molecule. Another major application is detection of desired particles in a highly scattering environment, the physical effect of which has been extensively researched, and is being overcome by using time-gated and polarization techniques. The polarimeter sensitivity is limited by the extinction-ratio obtained from polarizers. Of available polarizer materials, naturally occurring Calcite crystals provide the best extinction ratios because of their good optical homogeneity and high birefringence. However, there is a need for polarization determination with higher sensitivities, and thus a necessity to find better polarizing materials and methods. I developed a next-generation polarimeter in an attempt to sensitively detect the second-order Faraday effect, along with a substance s chirality and Verdet constant. Also, I developed a device uniquely able to sensitively detect chiral signatures in the presence of massive depolarizing scattering. In addition, I begun developing a novel type of polarimeter based on the highly-polarization-sensitive nonlinear-optical process of harmonic generation, whose required crystals can be grown with extremely high quality.

Time-resolved Faraday rotation (TRFR) is a pulsed laser pump/probe optical measurement used to characterize electron spin dynamics in semiconductor materials. A Mach-Zehnder type interferometer with orthogonally polarized arms is presented as a device for TRFR measurement that is superior to optical bridge detection, the traditional measuring technique, since Faraday rotation can be passively optically amplified via interference. Operation of the interferometer is analyzed under ideal conditions. Corrections to the ideal case stemming from imperfectly aligned optics, finite polarization extinction ratios, and an imperfect recombination optic are analyzed using a matrix transformation approach. The design of the interferometer is presented and chronicled. A description of the single-beam active control system utilized to stabilize the interferometer by continuous corrections to the optical path length of one arm with a piezoelectric actuator is given. Optical amplification by increasing the power in either arm of the interferometer is demonstrated and TRFR measurements taken with the interferometer at ambient temperatures are compared with measurements taken with the optical bridge. We find the interferometer to offer a detection limit on the order of 50 mrad at room temperature, which is five times more sensitive than the optical bridge. Isolation and stabilization of the interferometer were also successful in reducing signal noise to a level comparable with the optical bridge. Our results demonstrate that the interferometer is a better detection device for Faraday rotation under ambient conditions. In the immediate future, improvements to the control system should be made and experiments should be performed with high-quality samples at cryogenic temperatures to confirm that the interferometer performs as favorably under those conditions.

Time-resolved Faraday rotation (TRFR) is a pulsed laser pump/probe optical measurement used to characterize electron spin dynamics in semiconductor materials. A Mach-Zehnder type interferometer with orthogonally polarized arms is presented as a device for TRFR measurement that is superior to optical bridge detection, the traditional measuring technique, since Faraday rotation can be passively optically amplified via interference. Operation of the interferometer is analyzed under ideal conditions. Corrections to the ideal case stemming from imperfectly aligned optics, finite polarization extinction ratios, and an imperfect recombination optic are analyzed using a matrix transformation approach. The design of the interferometer is presented and chronicled. A description of the single-beam active control system utilized to stabilize the interferometer by continuous corrections to the optical path length of one arm with a piezoelectric actuator is given. Optical amplification by increasing the power in either arm of the interferometer is demonstrated and TRFR measurements taken with the interferometer at ambient temperatures are compared with measurements taken with the optical bridge. We find the interferometer to offer a detection limit on the order of 50 mrad at room temperature, which is five times more sensitive than the optical bridge. Isolation and stabilization of the interferometer were also successful in reducing signal noise to a level comparable with the optical bridge. Our results demonstrate that the interferometer is a better detection device for Faraday rotation under ambient conditions. In the immediate future, improvements to the control system should be made and experiments should be performed with high-quality samples at cryogenic temperatures to confirm that the interferometer performs as favorably under those conditions.

Nous avons obtenu des angles de rotation Faraday (RF) allant jusqu'à 19° par orientation optique d'un gaz d'électrons dans GaAs de type n inclus dans une microcavité (Q=19000), sans champ magnétique. Cette forte rotation est obtenue en raison des multiples allers-retours de la lumière dans la cavité. Nous avons également démontré la commutation optique rapide de la RF à l'échelle sub-microseconde en échantillonnant le signal de RF sous excitation impulsionnelle mono-coup. De la dépolarisation de la RF en champ magnétique transverse, nous avons déduit un temps de relaxation de spin de 160 ns. Le concept de section efficace de RF, coefficient de proportionnalité entre l'angle RF, la densité de spin électronique, et le chemin parcouru, a été introduit. La section efficace de RF, qui définit l'efficacité du gaz d'électrons à produire une RF, a été estimée quantitativement, et comparée avec la théorie. Nous avons également démontré la possibilité de mesurer de manière non destructive l'aimantation nucléaire dans GaAs-n, via la RF amplifiée par la cavité. Contrairement aux méthodes existantes, cette détection ne nécessite pas la présence d'électrons hors équilibre. Par cette technique nous avons étudié la dynamique de spin nucléaire dans GaAs-n avec différents dopages. Contrairement à ce qu'on pourrait attendre, le déclin de la RF nucléaire est complexe et consiste en deux composantes ayant des temps de relaxation très différents. Deux effets à l'origine de la RF nucléaire sont identifiés: le splitting de spin de la bande de conduction, et la polarisation en spin des électrons localisés, tous deux induits par le champ Overhauser. Le premier effet domine la RF nucléaire dans les deux échantillons étudiés, tandis que la RF induite par les électrons localisés n'a été observée que dans l'échantillon métallique. / We obtained Faraday rotation (FR) up to 19° by using optical orientation of electron gas in n-doped bulk GaAs confined in a microcavity (Q=19000), in the absence of magnetic field. This strong rotation is achieved because the light makes multiple round trips in the microcavity. We also demonstrated fast optical switching of FR in sub-microsecond time scale by sampling the FR in a one-shot experiment under pulsed excitation. From the depolarization of FR by a transverse magnetic field, we deduce electron spin relaxation time of about 160 ns. A concept of FR cross-section as a proportionality coefficient between FR angle, electron spin density and optical path is introduced. This FR cross-section which defines the efficiency of spin polarized electrons in producing FR was estimated quantitatively and compared with theory. We also demonstrated non-destructive measurement of nuclear magnetization in n-GaAs via cavity enhanced FR. In contrast with the existing optical methods, this detection scheme does not require the presence of detrimental out-of-equilibrium electrons. Using this technique, we studied nuclear spin dynamics in n-GaAs with different doping concentrations. Contrary to simple expectation, the nuclear FR is found to be complex, and consists of two components with vastly different time constants. Two effects at the origin of FR have been identified: the conduction band spin splitting and the localized electron spin polairzation both induced by the Overhauser field. The first effect dominates the FR in both studied samples, while the FR induced by the localized electrons has been observed only in the metallic sample.