1 |
Análise dos sistemas vítreos ternários Bi-Ge-B, Bi-Ge-Ga e um estudo de cristalização da fase Bi4Ge3O12 / Analysis of ternary glassy system Bi-Ge-B, Bi-Ge-Ga and a study of Bi4Ge3O12 phase crystallizationSouza, Nara Cristina de 20 November 1998 (has links)
Há um crescente interesse científico e tecnológico voltado para compostos cristalinos de óxido de bismuto com óxidos de germânio, silício ou titânio, por exibirem propriedades eletro e magnetoópticas, fotocondutivas e piezoelétricas. Sistemas vítreos com propriedades similares a estes compostos são de alto interesse, devido ao baixo custo e facilidade no procedimento de preparação em relação aos monocristais. Este trabalho teve como finalidade analisar o efeito de adição de óxidos de boro e gálio, ao sistema binário composto por óxido de bismuto com óxidos de germânio. A amostra vítrea de composição 45BiO1.5:40BO1.5:15GeO2 (BBG-8), apresentou alta reprodutibilidade e estabilidade térmica (ΔT=132, Hr=0.34 e S=26.74), sendo assim, selecionada para o estudo da cristalização. As fases cristalizadas nesta amostra, durante tratamento térmico, foram determinadas por análises de difração de raios-X e medidas composicionais. Foram cristalizadas as fases Bi6B10O24 e Bi4Ge3O12, sendo a última, a fase de interesse para nosso estudo. Métodos térmicos foram utilizados no estudo da cristalização da fase Bi4Ge3O12, possibilitando a verificação da energia de ativação (≈ 54Kcal/mol) pelos métodos de Ozawa e Chen, e a direcionalidade do crescimento dos cristais (nmédio=1.12). A fim de obtermos mais informações a respeito de cristalização utilizamos óptica eletrônica. / The sillenite crystals, Bi12MO20 (M = Ge, Si, Ti), are interesting for applications such as optical memories, holography or optical phase conjugating devices. The eulytite crystals, Bi4M3O12, have been studied for their electro-optical, electromechanical and luminescence properties. These crystals am used as scintillators or, when doped with rare-earth elements, as laser materials. The study of glass systems, having properties similar to those crystals, is of high interest because of the lower cost and easier preparation procedures with respect to single crystals. The purpose of this work is the study of interaction of B2O3 and Ga2O3 with binary system Bi2O3-GeO2. The glassy sample BBG-8 (45BiO1.5:40BO1.5:15GeO2), was chosen far crystallition study, due to its high reproducibility and thermal stability. The presence of crystalline phases (Bi6B10O24 and Bi4Ge3O12), obtained after heat treatment, was investigated by powder X-ray diffraction and compositional analysis. The crystalline eulytite phase (Bi4Ge3O12) is an interest of our study. Thermal methods were used on the study of Bi4Ge3O12crystallization process of the sample BBG-8, and the value obtained, by means of Ozawa and Chen methods, was approximately 54Kcal/mol, and the directionality of crystal growth (n average) was equal to 1.12. To obtain further information on the crystallization mechanism we also performed microphotographic analysis.
|
2 |
Análise dos sistemas vítreos ternários Bi-Ge-B, Bi-Ge-Ga e um estudo de cristalização da fase Bi4Ge3O12 / Analysis of ternary glassy system Bi-Ge-B, Bi-Ge-Ga and a study of Bi4Ge3O12 phase crystallizationNara Cristina de Souza 20 November 1998 (has links)
Há um crescente interesse científico e tecnológico voltado para compostos cristalinos de óxido de bismuto com óxidos de germânio, silício ou titânio, por exibirem propriedades eletro e magnetoópticas, fotocondutivas e piezoelétricas. Sistemas vítreos com propriedades similares a estes compostos são de alto interesse, devido ao baixo custo e facilidade no procedimento de preparação em relação aos monocristais. Este trabalho teve como finalidade analisar o efeito de adição de óxidos de boro e gálio, ao sistema binário composto por óxido de bismuto com óxidos de germânio. A amostra vítrea de composição 45BiO1.5:40BO1.5:15GeO2 (BBG-8), apresentou alta reprodutibilidade e estabilidade térmica (ΔT=132, Hr=0.34 e S=26.74), sendo assim, selecionada para o estudo da cristalização. As fases cristalizadas nesta amostra, durante tratamento térmico, foram determinadas por análises de difração de raios-X e medidas composicionais. Foram cristalizadas as fases Bi6B10O24 e Bi4Ge3O12, sendo a última, a fase de interesse para nosso estudo. Métodos térmicos foram utilizados no estudo da cristalização da fase Bi4Ge3O12, possibilitando a verificação da energia de ativação (≈ 54Kcal/mol) pelos métodos de Ozawa e Chen, e a direcionalidade do crescimento dos cristais (nmédio=1.12). A fim de obtermos mais informações a respeito de cristalização utilizamos óptica eletrônica. / The sillenite crystals, Bi12MO20 (M = Ge, Si, Ti), are interesting for applications such as optical memories, holography or optical phase conjugating devices. The eulytite crystals, Bi4M3O12, have been studied for their electro-optical, electromechanical and luminescence properties. These crystals am used as scintillators or, when doped with rare-earth elements, as laser materials. The study of glass systems, having properties similar to those crystals, is of high interest because of the lower cost and easier preparation procedures with respect to single crystals. The purpose of this work is the study of interaction of B2O3 and Ga2O3 with binary system Bi2O3-GeO2. The glassy sample BBG-8 (45BiO1.5:40BO1.5:15GeO2), was chosen far crystallition study, due to its high reproducibility and thermal stability. The presence of crystalline phases (Bi6B10O24 and Bi4Ge3O12), obtained after heat treatment, was investigated by powder X-ray diffraction and compositional analysis. The crystalline eulytite phase (Bi4Ge3O12) is an interest of our study. Thermal methods were used on the study of Bi4Ge3O12crystallization process of the sample BBG-8, and the value obtained, by means of Ozawa and Chen methods, was approximately 54Kcal/mol, and the directionality of crystal growth (n average) was equal to 1.12. To obtain further information on the crystallization mechanism we also performed microphotographic analysis.
|
3 |
Structure et cristallisation de verres d'oxydes simples riches en bore et en terres rares / Structure and crystallization of boron and rare-earth rich oxide glassesTrégouët, Hélène 26 January 2016 (has links)
Ce travail de thèse s'intéresse à la structure de verres d'oxydes simples, riches en bore et en terre rare (TR). Cette famille de verres trouve des applications dans différents domaines, de l'optique au confinement des déchets nucléaires. Ici, nous étudions la structure de verres du système le plus simple regroupant ces deux oxydes, à savoir le binaire B2O3-TR2O3. Un intérêt particulier est porté à la composition métaborate de terre rare TRB3O6, à fusion congruente. Cette étude structurale est menée au moyen de différentes techniques spectroscopiques, notamment la RMN du solide sur les noyaux 11B et 17O, l'absorption optique de Nd3+ et la diffusion des neutrons et des rayons X, associée à de la modélisation par RMC. Nous obtenons ainsi des informations sur la structure du réseau vitreux (nature des groupements structuraux, connectivité du réseau¿) et l'environnement des ions TR3+. La tendance à la cristallisation de ces verres binaires est également étudiée, par ATD, DRX et MEB. Le second volet de ces travaux concerne le système ternaire SiO2-B2O3-TR2O3. Tout d'abord, l'étendue du domaine vitrifiable est déterminée, pour nos conditions d'élaboration, puis certains verres homogènes et transparents obtenus font l'objet d'une étude structurale, de manière analogue aux verres du système binaire. Les premiers résultats concernant la tendance à la cristallisation de ces verres sont obtenus. / This work focuses on the structure of boron and rare earth (RE) rich simple oxide glasses. This family of glasses finds applications in various fields, from optical materials to nuclear waste storage. Here, we study the glass structure of the simplest system combining these two oxides, namely the binary system B2O3-RE2O3. Particular attention is paid to the rare earth metaborate composition REB3O6, which exhibits a congruent melting. This structural study combines different spectroscopic techniques, such as solid state NMR on 17O and 11B nuclei, optical absorption (Nd3+) and neutron and X-rays scattering, coupled with RMC simulation. Information concerning the glassy network (nature of the structural units, network connectivity…) and the rare earth environment is gathered. The tendency towards crystallization of these binary glasses is also studied, using DTA, XRD and SEM. The second part of this work deals with the ternary system SiO2-B2O3-TR2O3. First, the extension of the domain where homogeneous and transparent glasses can be obtained (in our experimental conditions) is determined. Then, some of the glassy samples obtained undergo a structural study, analogously to the glasses of the binary system. The first results about the crystallization tendency of these glasses are obtained.
|
4 |
Approche multi-échelle des verres d’oxyde : évolution structurale sous hautes pressions et processus de relaxation en température / Multi-scale study of oxide glasses : structural evolution under high pressure and temperature induced relaxation processesCornet, Antoine 17 October 2017 (has links)
Les verres d'oxydes sont des matériaux amorphes qui possèdent de nombreuses propriétés fondamentalement et industriellement intéressantes. Parmi elles, on trouve l'aptitude à densifier. En effet, lorsqu'un verre d'oxyde a été soumis à des pressions de l'ordre de la dizaine de gigapascal, il présente une densité plus importante, et une structure vitreuse différente. Cette observation a donné lieu dans les années 1990 et 2000 à la naissance du concept de polyamorphisme. Par analogie avec le polymorphisme des solides cristallins, on considère qu'un même composé chimique peut présenter différentes structures vitreuses, et que des transitions sont possibles entre ces différents états vitreux.Dans ce travail, nous avons cherché à mettre en évidence les changements structuraux associés à un possible polyamorphisme dans les verres d'oxyde. Pour cela, nous avons opté pour deux approches. D'une manière classique, nous avons suivi de manière in-situ la compression différents matériaux vitreux, en explicitant la dépendance de la densification à la température (verre de GeO2) et à la dépolymérisation (verres sodo-silicates). Nous avons également choisi une approche originale, qui consiste à densifier de manière permanente des compositions similaires, et à relaxer ces échantillons à haute température dans un second temps, en suivant de manière in-situ les différents processus.Cette approche novatrice nous a permis de mettre en évidence un état activé lors de la relaxation des verres densifiés vers leur état non-densifié. Cet état transitoire se caractérise par une augmentation du désordre à toutes les échelles de la structure vitreuse, et semble confirmer le concept de polyamorphisme dans les verres d'oxydes / The oxide glasses form a class of materials with many fundamental and industrial interesting properties. Among these particularities we find the capability of such glasses to densify. Indeed, after a compression at pressures up to around ten gigapascal, a typical oxide glass presents an increase in density and several structural changes compared to the non-compressed glass. This observation led to the birth of the polyamophism theory in the decades 1990 and 2000. In the same way that a chemical compound can exist in different crystalline structure, it has been proposed that different amorphous structure exist, and that transitions between these amorphous states are possible.During this work, we tried to evidence the structural changes associated to the possible polyamorphism in oxide glasses. To do so, we followed two different approaches. In the old fashioned way, we probed in-situ the structure of different glasses during the compression, and we determined the dependence of the processes to the temperature (GeO2 glass) and to the polymerization degree (sodo-silicate glasses). In a second time, we compressed several similar glasses to perform permanent densification. Then we relaxed these densified glasses at high temperature, and we monitored in-situ the glassy structure during the transformation.This new approach allowed us to evidence the existence of an activated state during the relaxation of densified glasses to their pristine non-densified state. This transitory state is characterized by an increase of the inhomogeneity of the structure at all length scales, and seems to confirm the polyamorphism theory in oxide glasses
|
5 |
Nonlinear Femtosecond Near Infrared Laser Structuring In Oxide GlassesRoyon, Arnaud 01 January 2009 (has links)
Three-dimensional femtosecond laser structuring has a growing interest because of its ease of implementation and the numerous possible applications in the domain of photonic components. Structures such as waveguides, diffraction gratings, optical memories or photonic crystals can be fabricated thanks to this technique. Its use with oxide glasses is promising because of several advantages; they are resistant to flux and ageing, their chemical composition can easily be changed to fit the well-defined requirements of an application. They can already be found in Raman amplifiers, optical fibers, fiber lasers, and other devices. This thesis is based on two axes. The first axis consists in characterizing the linear and nonlinear optical properties of bulk vitreous materials in order to optimize their composition with a particular application in view. Within this context, the nonlinear optical properties, their physical origins (electronic and nuclear) as well as their characteristic response times (from a few femtoseconds to a few hundreds of picoseconds) are described within the Born-Oppenheimer approximation. Fused silica and several sodium-borophosphate glasses containing different concentrations in niobium oxide have been studied. Results show that the nonlinear optical properties of fused silica are mainly from electronic origin, whereas in the sodium-borophosphate glasses, the contribution from nuclear origin becomes predominant when the concentration of niobium oxide exceeds 30%. The second axis is based on the structuring of materials. Three commercially available fused silica samples presenting different fabrication conditions (therefore distinct impurity levels) and irradiated with a near infrared femtosecond laser have been studied. The laser induced defects have been identified by means of several spectroscopic techniques. They show the formation of color centers as well as a densification inside the irradiated area. Their linear refractive index and nonlinear third-order susceptibility properties have been measured. Moreover, the structuring of fused silica at the subwavelength scale into "nanogratings" is observed and the form of birefringence induced by these structures is discussed. In addition to the fused silica samples, several oxide glasses presenting very distinct chemical compositions have been studied. A sodium-borophosphate glass containing niobium oxide exhibits micro-cracks and nano-crystallites following irradiation. A silicate glass with or without a silver component reveals fluorescent rings or "nanograting" structures. A zinc phosphate glass containing silver also presents fluorescent ring structures, with a size of the order of 80 nm, well below the diffraction limit. Pump-probe microscope techniques have been performed on this glass to investigate the laser-glass interaction. The absorption mechanism is determined to be four-photon absorption. The generated free electron density is ~ 1017 cm-3, which suggests the conclusion that an electron gas rather than a plasma is formed during the laser irradiation.
|
6 |
Influência de PbF2 nas propriedades físicas e estruturais de vidros boratos contendo óxidos de metais pesados / Influence of PbF2 in physical and structural properties in heavy metal oxides borate glassesFernandes, Roger Gomes 26 July 2012 (has links)
Vidros nas composições 26,66\'B IND.2\'O IND.3\'-16\'GE\'O IND.2\'-4\'BI IND.2\'O IND.3\'-(53,33-x)\'PB\'O\'-x\'PB\'F IND.2\' com x até 30% mol foram sintetizados e caracterizados com respeito as suas propriedades térmicas e espectroscópicas. A substituição de \'PB\'O\' por \'PB\'F IND.2\' desloca a janela de transmissão óptica no ultravioleta para maiores energia. Os espectros Raman e Infravermelho foram interpretados em conjunto, e a partir desta análise identificou-se a ocorrência de uma leve conversão de unidades \'BO IND.3\' a unidades \'BO IND.4\', concomitante com o aumento da concentração de \'PB\'F IND.2\'. Utilizando RMN de alta resolução em sólidos dos núcleos \'ANTPOT. 11 B\' e \'ANTPOT. 19 F\', e diferentes técnicas de dupla ressonância \'ANTPOT. 11 B\'/\'ANTPOT. 19 F\' (REDOR, CPMAS e 2D-CPMAS), foi possível realizar uma análise estrutural quantitativa desses materiais. A fração encontrada de unidades estruturais \'BO IND.4\' é moderadamente maior comparada com vidros que apresentam a mesma razão de \'Pb\'O\'/\'B IND.2\'O IND.3\', quando \'PB\'F IND.2\' é acrescido no sistema, sugerindo a participação de \'PB\'F IND.2\' no processo de transformação da rede. Essa sugestão é confirmada a partir dos espectros de RMN de \'ANTPOT. 19 F\'. A maior parte dos íons fluoretos encontra-se na sua forma iônica, mas aproximadamente 20% atua como modificador de rede, resultando na formação de unidades \'BO IND.3/2\'F POT.-\'. Essas unidades foram identificadas por experimentos REDOR \'ANTPOT.19 F\' . Esses resultados fornecem as primeiras evidências das ligações B-F em sistemas vítreos modificados por \'PB\'F IND.2\'. Além disso, verifica-se que a maioria dos íons fluoretos é encontrada em um ambiente dominado por chumbo. As medidas de segundo momento dipolar homonuclear \'ANTPOT. 19 F\'-\'ANTPOT. 19 F\' a partir de experimentos por espectroscopia de decaimento de eco de spin são quantitativamente consistentes com um modelo no qual esses íons estão aleatoriamente distribuídos no interior de um subdomínio constituído de \'PB\'O\', \'BI IND.2\'O IND.3\' and \'PB\'F IND.2\'. Este modelo, que implica na coordenação dos átomos de flúor às espécies formadoras da rede borato em adição ao surgimento de íons de flúor, com certo grau de agregação, é consistente com todas as observações experimentais. / A series of heavy metal oxide (HMOG) glasses with composition 26,66\'B IND.2\'O IND.3\'-16\'GE\'O IND.2\'-4\'BI IND.2\'O IND.3\'-(53,33-x)\'PB\'O\'-x\'PB\'F IND.2\' with x until 40% mol, has been prepared and characterized with respect to their bulk (glass transition and crystallization temperature, densities, molar volumes) and spectroscopic properties. Homogeneous glasses are formed up to x = 30, while crystallization of \'beta\'- \'PB\'F IND.2\' takes place at higher contents. Substitution of \'PB\'O\' by \'PB\'F IND.2\' shifts the optical band gap towards higher energies, thereby extending the UV transmission window significantly towards higher frequencies. Raman and infrared absorption spectra can be interpreted in conjunction with published reference data. Using \'ANTPOT. 11 B\' and \'ANTPOT. 19 F\' high-resolution solid state NMR as well as \'ANTPOT. 11 B\'/\'ANTPOT. 19 F\' double resonance methodologies, we developed a quantitative structural description of this material. The fraction of four-coordinated boron is found to be moderately higher compared to that in glasses with the same \'PB\'O\'/\'B IND.2\'O IND.3\' ratios, suggesting some participation of \'PB\'F IND.2\' in the network transformation process. This suggestion is confirmed by the \'ANTPOT. 19 F\' NMR spectra. While the majority of the fluoride ions is present as ionic fluoride, approximately 20% of the fluorine inventory acts as a network modifier, resulting in the formation of four-coordinate \'BO IND.3/2\'F POT.-\' units. These units can be identified by \'ANTPOT. 19 F\' rotational echo double resonance and \'ANTPOT. 11 B\' cross-polarization magic angle spinning (CPMAS) data. These results provide the first unambiguous evidence of B-F bonding in a \'PB\'F IND.2\'-modified glass system. The majority of the fluoride ions are found in a lead-dominated environment. \'ANTPOT. 19 F\'-\'ANTPOT. 19 F\' homonuclear dipolar second moments measured by spin echo decay spectroscopy are quantitatively consistent with a model in which these ions are randomly distributed within the network modifier subdomain consisting of \'PB\'O\', \'BI IND.2\'O IND.3\' and \'PB\'F IND.2\'. This model, which implies both the features of atomic scale mixing with the network former borate species and some degree of fluoride ion clustering is consistent with all of the experimental data obtained on these glasses.
|
7 |
Influência de PbF2 nas propriedades físicas e estruturais de vidros boratos contendo óxidos de metais pesados / Influence of PbF2 in physical and structural properties in heavy metal oxides borate glassesRoger Gomes Fernandes 26 July 2012 (has links)
Vidros nas composições 26,66\'B IND.2\'O IND.3\'-16\'GE\'O IND.2\'-4\'BI IND.2\'O IND.3\'-(53,33-x)\'PB\'O\'-x\'PB\'F IND.2\' com x até 30% mol foram sintetizados e caracterizados com respeito as suas propriedades térmicas e espectroscópicas. A substituição de \'PB\'O\' por \'PB\'F IND.2\' desloca a janela de transmissão óptica no ultravioleta para maiores energia. Os espectros Raman e Infravermelho foram interpretados em conjunto, e a partir desta análise identificou-se a ocorrência de uma leve conversão de unidades \'BO IND.3\' a unidades \'BO IND.4\', concomitante com o aumento da concentração de \'PB\'F IND.2\'. Utilizando RMN de alta resolução em sólidos dos núcleos \'ANTPOT. 11 B\' e \'ANTPOT. 19 F\', e diferentes técnicas de dupla ressonância \'ANTPOT. 11 B\'/\'ANTPOT. 19 F\' (REDOR, CPMAS e 2D-CPMAS), foi possível realizar uma análise estrutural quantitativa desses materiais. A fração encontrada de unidades estruturais \'BO IND.4\' é moderadamente maior comparada com vidros que apresentam a mesma razão de \'Pb\'O\'/\'B IND.2\'O IND.3\', quando \'PB\'F IND.2\' é acrescido no sistema, sugerindo a participação de \'PB\'F IND.2\' no processo de transformação da rede. Essa sugestão é confirmada a partir dos espectros de RMN de \'ANTPOT. 19 F\'. A maior parte dos íons fluoretos encontra-se na sua forma iônica, mas aproximadamente 20% atua como modificador de rede, resultando na formação de unidades \'BO IND.3/2\'F POT.-\'. Essas unidades foram identificadas por experimentos REDOR \'ANTPOT.19 F\' . Esses resultados fornecem as primeiras evidências das ligações B-F em sistemas vítreos modificados por \'PB\'F IND.2\'. Além disso, verifica-se que a maioria dos íons fluoretos é encontrada em um ambiente dominado por chumbo. As medidas de segundo momento dipolar homonuclear \'ANTPOT. 19 F\'-\'ANTPOT. 19 F\' a partir de experimentos por espectroscopia de decaimento de eco de spin são quantitativamente consistentes com um modelo no qual esses íons estão aleatoriamente distribuídos no interior de um subdomínio constituído de \'PB\'O\', \'BI IND.2\'O IND.3\' and \'PB\'F IND.2\'. Este modelo, que implica na coordenação dos átomos de flúor às espécies formadoras da rede borato em adição ao surgimento de íons de flúor, com certo grau de agregação, é consistente com todas as observações experimentais. / A series of heavy metal oxide (HMOG) glasses with composition 26,66\'B IND.2\'O IND.3\'-16\'GE\'O IND.2\'-4\'BI IND.2\'O IND.3\'-(53,33-x)\'PB\'O\'-x\'PB\'F IND.2\' with x until 40% mol, has been prepared and characterized with respect to their bulk (glass transition and crystallization temperature, densities, molar volumes) and spectroscopic properties. Homogeneous glasses are formed up to x = 30, while crystallization of \'beta\'- \'PB\'F IND.2\' takes place at higher contents. Substitution of \'PB\'O\' by \'PB\'F IND.2\' shifts the optical band gap towards higher energies, thereby extending the UV transmission window significantly towards higher frequencies. Raman and infrared absorption spectra can be interpreted in conjunction with published reference data. Using \'ANTPOT. 11 B\' and \'ANTPOT. 19 F\' high-resolution solid state NMR as well as \'ANTPOT. 11 B\'/\'ANTPOT. 19 F\' double resonance methodologies, we developed a quantitative structural description of this material. The fraction of four-coordinated boron is found to be moderately higher compared to that in glasses with the same \'PB\'O\'/\'B IND.2\'O IND.3\' ratios, suggesting some participation of \'PB\'F IND.2\' in the network transformation process. This suggestion is confirmed by the \'ANTPOT. 19 F\' NMR spectra. While the majority of the fluoride ions is present as ionic fluoride, approximately 20% of the fluorine inventory acts as a network modifier, resulting in the formation of four-coordinate \'BO IND.3/2\'F POT.-\' units. These units can be identified by \'ANTPOT. 19 F\' rotational echo double resonance and \'ANTPOT. 11 B\' cross-polarization magic angle spinning (CPMAS) data. These results provide the first unambiguous evidence of B-F bonding in a \'PB\'F IND.2\'-modified glass system. The majority of the fluoride ions are found in a lead-dominated environment. \'ANTPOT. 19 F\'-\'ANTPOT. 19 F\' homonuclear dipolar second moments measured by spin echo decay spectroscopy are quantitatively consistent with a model in which these ions are randomly distributed within the network modifier subdomain consisting of \'PB\'O\', \'BI IND.2\'O IND.3\' and \'PB\'F IND.2\'. This model, which implies both the features of atomic scale mixing with the network former borate species and some degree of fluoride ion clustering is consistent with all of the experimental data obtained on these glasses.
|
8 |
Beam induced dynamics in oxide glassesTietz, Christoph, Fritz, Thomas, Holzweber, Katharina, Legenstein, Maria, Sepiol, Bogdan 12 July 2022 (has links)
No description available.
|
9 |
New Insights into Topological Phases in (Na2O)x(P2O5)100-x glasses from Enthalpy of Relaxation at Tg from Modulated-DSC and LO- and TO- mode frequency splitting from IR reflectanceGOGI, VAMSHI KIRAN 04 November 2020 (has links)
No description available.
|
10 |
Structuration non-linéaire de verres oxydes par laser femtoseconde dans le proche infrarouge / Nonlinear femtosecond near infrared laser structuring in oxide glassesRoyon, Arnaud 17 June 2009 (has links)
La structuration laser femtoseconde en trois dimensions rencontre un intérêt grandissant du fait de sa facilité de mise en œuvre et des nombreuses applications qu’elle peut couvrir dans le domaine des composants photoniques. Des structures telles que des guides d’onde, des réseaux de diffraction, des mémoires optiques ou des cristaux photoniques peuvent être fabriquées grâce à cette technique. Son emploi sur des verres oxydes est prometteur car ces derniers présentent des avantages certains ; ils sont très résistants au flux et au vieillissement, leur composition chimique peut être changée facilement afin de s’adapter à un cahier des charges précis. On les retrouve déjà dans les amplificateurs Raman, les fibres optiques, les lasers à fibres, etc… Le travail de cette thèse s’articule autour de deux grands axes. Le premier axe consiste à caractériser les propriétés optiques linéaires et non-linéaires de matériaux vitreux massifs afin d’optimiser leur composition en vue d’une application particulière. Dans ce contexte, les propriétés optiques non-linéaires, leurs origines physiques (électronique et nucléaire) ainsi que leurs temps de réponse caractéristiques (de quelques femtosecondes à quelques centaines de picosecondes) sont décrits dans le cadre de l’approximation de Born-Oppenheimer. Ainsi, la silice fondue et plusieurs verres sodo-borophosphates contenant différentes concentrations en oxyde de niobium ont été étudiés. Les résultats montrent que les propriétés optiques non-linéaires dans la silice fondue sont majoritairement d’origine électronique, alors que dans les verres sodo-borophosphates, la contribution d’origine nucléaire peut devenir prépondérante lorsque la concentration en oxyde de niobium dépasse 30%. Le second axe s’articule autour de la structuration des matériaux. Trois échantillons commerciaux de silice fondue présentant des conditions de fabrication différentes (donc des taux d’impuretés distincts) et irradiés avec un laser femtoseconde proche infrarouge ont été étudiés. Les défauts induits par laser ont été identifiés au moyen de plusieurs techniques de spectroscopie. Elles ont montré la formation de centres colorés ainsi qu’une densification au niveau de la zone irradiée. Leurs propriétés optiques linéaire (indice de réfraction) et non-linéaire (susceptibilité du troisième ordre) ont été mesurées. De plus, la structuration de la silice fondue à l’échelle sub-micrométrique sous forme de « nano-réseaux » est observée et la biréfringence de forme induite par ces structures est discutée. En plus des échantillons de silice fondue, plusieurs verres oxydes présentant des compositions chimiques très distinctes ont été étudiés. Un verre sodo-borophosphate contenant de l’oxyde de niobium exhibe des micro-craquelures et des nano-crystallites après irradiation. Un verre silicate contenant ou non de l’argent dévoile des structures en anneau fluorescentes ou en « nano-réseaux ». Un verre zinc phosphate contenant de l’argent présente lui aussi des structures en anneau fluorescentes, d’une taille de l’ordre de 80 nm, bien inférieure à la limite de diffraction. Des techniques pompe-sonde sous microscope ont été mises en œuvre sur ce dernier verre pour étudier l’interaction laser-verre. Le mécanisme d’absorption de l’énergie lumineuse pour ce verre est l’absorption à quatre photons. La densité d’électrons libres générée est de l’ordre de 1017 cm-3, ce qui permet de conclure qu’un gaz d’électrons plutôt qu’un plasma se forme pendant l’irradiation laser. / Three-dimensional femtosecond laser structuring has a growing interest because of its ease of implementation and the numerous possible applications in the domain of photonic components. Structures such as waveguides, diffraction gratings, optical memories or photonic crystals can be fabricated thanks to this technique. Its use with oxide glasses is promising because of several advantages; they are resistant to flux and ageing, their chemical composition can easily be changed to fit the well-defined requirements of an application. They can already be found in Raman amplifiers, optical fibers, fiber lasers, and other devices. This thesis is based on two axes. The first axis consists in characterizing the linear and nonlinear optical properties of bulk vitreous materials in order to optimize their composition with a particular application in view. Within this context, the nonlinear optical properties, their physical origins (electronic and nuclear) as well as their characteristic response times (from a few femtoseconds to a few hundreds of picoseconds) are described within the Born-Oppenheimer approximation. Fused silica and several sodium-borophosphate glasses containing different concentrations in niobium oxide have been studied. Results show that the nonlinear optical properties of fused silica are mainly from electronic origin, whereas in the sodium-borophosphate glasses, the contribution from nuclear origin becomes predominant when the concentration of niobium oxide exceeds 30%. The second axis is based on the structuring of materials. Three commercially available fused silica samples presenting different fabrication conditions (therefore distinct impurity levels) and irradiated with a near infrared femtosecond laser have been studied. The laser induced defects have been identified by means of several spectroscopic techniques. They show the formation of color centers as well as a densification inside the irradiated area. Their linear refractive index and nonlinear third-order susceptibility properties have been measured. Moreover, the structuring of fused silica at the subwavelength scale into “nanogratings” is observed and the form of birefringence induced by these structures is discussed. In addition to the fused silica samples, several oxide glasses presenting very distinct chemical compositions have been studied. A sodium-borophosphate glass containing niobium oxide exhibits micro-cracks and nano-crystallites following irradiation. A silicate glass with or without a silver component reveals fluorescent rings or “nanograting” structures. A zinc phosphate glass containing silver also presents fluorescent ring structures, with a size of the order of 80 nm, well below the diffraction limit. Pump-probe microscope techniques have been performed on this glass to investigate the laser-glass interaction. The absorption mechanism is determined to be four-photon absorption. The generated free electron density is ~ 1017 cm-3, which suggests the conclusion that an electron gas rather than a plasma is formed during the laser irradiation.
|
Page generated in 0.0788 seconds