Laser welding was investigated as a potential joining technology for alumina ceramic substrates. The objective of this study was to develop a method to preheat the ceramic using a single defocused laser beam prior to welding. Engineering ceramics are employed in a variety of systems and environments due to their unique properties. Joining technologies must be developed to facilitate the manufacture of complex or large ceramic components. Laser welding is advantageous as it forms joints rapidly, and does not introduce intermediate materials to form the bond, which can have deleterious effects. The Laser Machining System (LMS) at Queen’s University was adapted for this study. A defocused far-infrared (FIR) laser beam was positioned to overlay a focused near-infrared (NIR) laser beam; the defocused FIR beam preheated the ceramic substrate and the focused NIR beam formed the weld. A finite element model was developed in COMSOL MultiPhysics to simulate the preheating processes and to develop a preheating protocol. The protocol was implemented using the FIR beam and adjusted to achieve preheating temperatures of 1450, 1525, and 1600degC. Welds were performed on 1 mm thick alumina plates using the preheating protocols and NIR beam powers of 25, 50, and 75 W. Weld speed was held constant throughout the study at 0.5 mm/s. The preheating protocols were successful at achieving near-constant preheating temperatures, with standard deviations below 32 degrees. Partially penetrating welds were formed with the NIR beam at 25 W, and fully penetrating welds at 50 and 75 W. Large pores were present in the 25 W and 50 W welds. Minimal porosity was observed in the welds formed at 75 W. All of the welded plates experienced a transverse fracture that extended perpendicular to weld, and a longitudinal fracture extending parallel to the weld. This study shows that a fixed defocused laser beam can successfully preheat alumina substrates to the high temperatures required for welding; however, non-homogenous cooling results in fracture. Increasing the preheating beam diameter or introducing an auxiliary means to provide a controlled cool-down cycle may mitigate these effects. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-04-29 17:59:57.43

O objetivo deste estudo foi avaliar in vitro o efeito do ácido clorídrico, na forma líquida e gasosa na superfície do esmalte, além de avaliar diferentes tratamentos preventivos e avaliar in situ a influência da Doença do Refluxo Gastroesofágico (DRGE) sobre o esmalte dental e avaliar a eficiência de tratamentos preventivos contra a erosão dental em ambiente bucal. A fase in situ do estudo foi totalmente dependente dos resultados da fase in vitro, ou seja, os tratamentos realizados in situ foram selecionados de acordo coma fase in vitro. Para a fase in vitro, foram obtidos 234 espécimes de esmalte (4X4 mm) a partir de incisivos bovinos, os mesmos foram isolados com resina composta, exceto pela metade da superfície de esmalte a qual foi exposta aos tratamentos preventivos e/ou desafios erosivos. Esta etapa do estudo foi fatorial 3 X 3, tendo como fatores de estudo: Tratamento superficial em 3 níveis: ausência de tratamento (C), laser de CO2 (CO) e laser Nd:YAG (Nd); e a associação à fluoretos em 3 níveis: sem associação (SA), associado ao flúor gel (AF) e associado ao verniz fluoretado (AVF). Os desafios erosivos foram realizados de duas formas, HCl líquido e HCl gasoso. Foram selecionados 180 espécimes tratados (n=10) e distribuídos aleatoriamente. O desafio erosivo com HCl líquido foi realizado sob pH=2, à 37 °C, 6 X ao dia, durante 20s e por 5 dias; o desafio com HCl gasoso foi realizado sob pH=2, à 37 °C, 8 X ao dia, durante 3 min e por 12 dias. A análise foi em função do perfil de desgaste, degrau, perda de volume e rugosidade de superfície. Para a análise das alterações químicas e morfológicas da superfície foram selecionados 54 espécimes divididos aleatoriamente de acordo os tratamentos preventivos propostos e de acordo com as seguintes análises (n=3): DRX e MEV-EDS. Os dados foram submetidos ao teste estatística de análise de variância (ANOVA) a dois critérios, os dados referentes ao DRX e EDS foi avaliado de forma descritiva, as imagens da MEV foram avaliadas qualitativamente. Resultados HCl líquido - observa-se que a associação VF aumentou o perfil de desgaste (médias e desvio padrão: 0,82±0,17) em relação ao C (0,66±0,14), na interação dos fatores C/AVF e Nd/AVF aumentou o perfil de desgaste (0,84±0,21; 0,86±0,12), C (0,70±0,10); a associação VF aumentou a rugosidade (0,26±0,06), C (0,22±0,07), entretanto na interação dos fatores os tratamentos CO e C/AF foram melhores (0,19±0,07; 0,18±0,03), C (0,21±0,07); para o degrau e perda de volume não houve diferença estatística. Resultados HCl gasoso - observou-se que o Nd (1,3±0,08) proporcionou menor perfil de desgaste e Nd/AF(1,8±0,51) maior desgaste, C (1,4±0,16); a associação F e VF proporcionou menor degrau (6,6±4,9; 8,9±3,8), rugosidade (0,35±0,07; 0,37±0,05) e perda de volume (6,0±3,3; 8,3±3,6), C (11,86±4,3; 0,41±0,04; 11,05±4,7; respectivamente). Na análise de EDS houve diminuição do conteúdo de flúor nos tratamentos C, C/AFC/AVF, CO/AVF, Nd/AF e Nd/AVF, proporção Ca/P não foi alterada; para o DRX não observou-se alteração no contudo de flúor. Não observou-se em MEV alteração morfológica. Conclui-se que o ácido clorídrico, na forma líquida e gasosa, causa erosão dental, com comportamentos distintos, para o HCl líquido o tratamento CO/AF produziu menor desgaste, para o HCl gasoso a associação ao F e VF diminuíram o desgaste, os tratamentos não levaram ao aumento do conteúdo de flúor na superfície. A fase in situ contou com a participação de 44 voluntários divididos nos seguintes grupos: Controle- saudável; Suspeita- com erosão dental e sintomas de DRGE; DRGE- diagnosticados com a doença. Foram obtidos 264 espécimes de esmalte bovino (2x2x2 mm), os quais foram impermeabilizados com resina composta, exceto pela metade da superfície de esmalte que foi submetida aos tratamentos preventivos e expostas ao meio bucal. O estudo foi fatorial de 3X2, sendo: Tratamento Superficial em 3 níveis: ausência de tratamento (C), laser de CO2 (CO) e laser Nd:YAG (Nd); e a associação à fluoretos em 2 níveis: sem associação (SA), associado ao flúor gel (AF), em 2 fases de 30 dias com intervalo de 7 dias entre cada fase. Os dados foram submetidos ao teste estatística de análise de variância (ANOVA) a dois critérios. Os resultados foram nulos (0) para o perfil, degrau, perda de volume rugosidade, o grupo CO quando exposto na cavidade bucal levou à formação de trincas na superfície. Conclui-se que o período de 30 dias em meio bucal de pacientes portadores de DRGE são insuficientes para causar erosão no esmalte, os estudos in vitro e in situ apresentam resultados divergentes entre si, sendo necessário mais estudos na área. / The aim of this in vitro study was to evaluated hydrochloric acid liquid and gaseous effect on enamel surface and preventive treatments, to evaluated in situ gatroesophageos reflux disease (GERD) effect on dental enamel and prevenvtive treatments. The in situ study was totally dependent on the in vitro results, ie the superficial treatments performed in situ were selected according to the in vitro results. To in vitro study 234 enamel samples (4x4 mm) were obtained from bovine incisors and isolated with the compound resin except half of the enamel surface which was exposed to preventative treatments and erosive challenges. This study was 3 X 3 factorial, study factor: Superficial treatment in 3 levels: no treatment (C), CO2 laser (CO) and Nd:YAG laser (Nd); and fluoride assiciation in 3 levels: swithout (WA), fluoride gel association (FA) and fluoride narnish association (FVA). Erosive challenges were performed using HCl liquid and gaseous. 180 treated specimens were selected (n=10) and randomized. Erosive challenge using HCl liquid - pH=2, 37 °C, 6 times/day, during 20s, for 5 days; erosive challenge using HCl gaseous - pH=2, 37 °C, 8 times/day, during 3 min, for 12 days. It was evaluated wear depth (perfilometer), degree, volume loss and roughness. Chemical and morphological surface analysis was performed, thus 54 specimens were selected randomly divided according preventive treatments (n=3): XRD and SEM-EDS. Data were analyzed by two-way ANOVA, XRD and EDS was performed descriptive data analysis, SEM was analyzed qualitatively. HCl liquid results - FV association presented higher wear depth (menos and standard deviation: 0.82±0.17) compared to C (0.66±0.14), in the interaction between factors C/FVA and Nd/FVA increased wear depth (0.84±0.21; 0.86±0.12), C (0.70±0.10); the association FV increased roughness (0.26±0.06), C (0.22±0.07), the interaction between factors CO and C/FA were better (0.19±0.07; 0.18±0,03), C (0.21±0.07); For degree and volume loss are not significantly different. HCl gaseous results - Nd presented less wear depth (1.3±0.08) and Nd/FA higher wear depth (1.8±0.51), C (1.4±0.16); F and VF association presented less degree (6.6±4.9; 8.9±3.8), roughness (0.35±0.07; 0.37±0.05) and volume loss (6.0±3.3; 8.3±3.6), C (11.86±4.3; 0.41±0.04; 11.05±4.7; respectively). For EDS analysis there was decrease fluoride content after the treatmentos C, C/FA, C/FVA, CO/FVA, Nd/FA e Nd/FVA, ratio Ca/P was not altered; For XRD was not observed fluoride content changes. Was not observed morphological change by SEM. It can be concluded that hydrochloric acid liquid and gaseous promoted dental erosion, for HCl liquid CO/FA promoted less wear depth, for HCl gaseous F and VF association decreased wear depth, the treatments do not alter fluoride contente on enamel surface. For in situ study, 44 volunteers were selectioned and divided into groups: Control- healthy; Suspect- dental erosion and GERD symptoms; GERD- with disease diagnosis. Were obtained 264 specimens from bovine incisors (2x2x2 mm), which were isolated with the compound resin except half of the enamel surface which was exposed to preventative treatments and oral cavity exposed. The study was factorial 3X2: Superficial treatments in 3 levels: no treatment (C), CO2 laser (CO) and Nd:YAG laser (Nd); and fluoride association in 2 evels: without association (WA) and fluoride gel association (FA),in 2 phases of 30 days and 7-day interval between each phase. Data were analyzed by two-way ANOVA. The results were null (0) foro wear depth, degree, volume loss and roughness, the CO group exposed to oral cavity promoted superficial cracks. It can be concluded that 30-day period in the oral environment are insufficient to cause enamel erosion in GERD patients, in vitro studies and in situ show divergent results among themselves, more studies are needed.

<p>This study is concerned with investigating the effects of warm laser shock peening (wLSP) on the enhancement of mechanical performance of laser welded joints. A 3-D finite element model is presented which predicts the surface indentation geometry and in-depth compressive residual stresses generated by wLSP. To define the LSP pressure on the surface of the material, a 1-D confined plasma model is implemented to predict plasma pressure generated by laser-coating interaction in an oil confinement regime. Residual stresses predicted by the finite element model for wLSP reveal higher magnitude and depth of compressive residual stresses than room temperature laser shock peening. A novel dual laser wLSP experimental setup is developed for simultaneous heating of the sample, to a prescribed temperature, and to perform wLSP. The heating laser power is tuned to achieve a predefined temperature in the material through predictive analysis with a 3-D transient laser heating model.</p><p>Laser welded joints of AA6061-T6 and TZM alloy in bead-on-plate (BOP) and overlap configurations, created by laser welding with a high power fiber laser, were post processed with wLSP. To evaluate the strength of the welded joints pre- and post-processing, tensile testing and tensile-shear testing were carried out. To understand the failure modes in tensile-shear testing of the samples, a 3-D finite element model of the welded joint was developed with weld regions’ material strength properties defined through microhardness testing. The stress concentration regions predicted by the finite element model clearly explain the failure regions in the experimental tensile testing analysis. The tensile tests and tensile-shear tests carried out on wLSP processed AA6061-T6 samples demonstrate an enhancement in the joint strength by about 20% and ductility improvement of about 33% over as-welded samples. The BOP welds of TZM alloy processed with wLSP demonstrated an enhancement in strength by about 30% and lap welds demonstrated an increase in joint strength by 22%.<br></p><p></p>

by Iu Chun-ho. / Bibliography: leaves 80-81 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985

Dans le cadre de cette thèse, nous présentons l’optimisation du transfert du spin électronique à la polarisation d’un laser à semi-conducteur (SC) à émission par la surface en cavité externe (VECSEL). Un spin-laser pourrait constituer une rupture technologique dans le domaine des communications en répondant à l’augmentation du débit de données tout en apportant des fonctionnalités supplémentaires (cryptage de l’information…). Afin de développer un tel composant, deux approches complémentaires ont été explorées. La première a pour objectif d’appréhender les effets d’injection de spin dans un VECSEL, ainsi que comprendre les paramètres du laser, tels que la biréfringence de phase et le dichroïsme de gain linéaires, qui figent la polarisation à un état linéaire. En réduisant le dichroïsme d’un facteur 50 et en compensant la biréfringence résiduelle de la cavité jusqu’à 0,1 mrad (soit une diminution d’un facteur 40), une augmentation de l’ellipticité de 1° à 35° a été rendue possible. L’injection de porteurs polarisés en spin par pompage optique dans le milieu actif du laser compensé a permis d’obtenir un basculement de l’état de polarisation entre deux états elliptiques ( 35 ↔ +35°). La seconde approche concerne l’étude de l’injection de spin par pompage électrique, point clé du développement d’un dispositif compact. Pour cela, un injecteur ferromagnétique répondant aux contraintes du transport du spin électronique de l’électron vers le SC est inséré dans la cavité optique. Malgré l’utilisation d’une structure anti-résonante, qui permet de limiter l’absorption de l’injecteur intra-cavité, nous démontrons des effets d’électroluminescence dont le profil spatial est compatible avec une émission laser. Enfin, nous apportons les éléments permettant d’améliorer le procédé de fabrication du spin-laser dans l’optique d’obtenir un effet laser. / Optimisation of the spin transport to the polarization of a vertical cavity semiconductor laser

Orientador: Helmut Karl Bockelmann / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-09-26T18:11:12Z (GMT). No. of bitstreams: 1 Mirage_Armando_M.pdf: 783495 bytes, checksum: 34a5e9df84fb9e2adddb5d72a477a031 (MD5) Previous issue date: 1978 / Resumo: Foi construido um sistema para produção de plasma através de descargas de um laser pulsado de rubi, cuja potência de radiação atingiu um valor de até 150 MW. A ionização foi feita nos gases oxigênio e argônio, sob pressões de 1, 2 e 3 atmosferas. O sistema de diagnóstico constituiu-se de um interferômetro de Mach-Zehnder funcionando com um laser de He - Ne, o qual forneceu curvas da densidade eletrônica em função do tempo para uma posição fixa no espaço, além da velocidade de expansão das partículas / Abstract: Not informed / Mestrado / Física / Mestre em Física

No description available.

De rapides avancées technologiques ont autorisé depuis le début des années 1980 un développement important des lasers de puissance et ont ouvert la voie aux régimes d’interaction laser-matière relativiste. L’accès aux intensités lumineuses supérieures à 1.1018 W.cm-2 a ainsi donné la possibilité à la communauté scientifique d’explorer une nouvelle physique riche d’applications. Bien que le principal moteur ait historiquement été constitué par les recherche sur la fusion par confinement inertiel, l’astrophysique de laboratoire, la génération de rayonnement (harmoniques, bétatron, X) ou la génération de particules énergétiques (électrons, ions) élargissent de plus en plus ce domaine d’étude.En effet, les très bonnes qualités des sources lumineuses et des sources d’ions créées par laser laissent fortement envisager qu’elles viendront un jour remplacer les sources conventionnelles comme les synchrotrons ou les accélérateurs qui sont des machines très coûteuses.Dans le cadre de cette thèse, une attention toute particulière a été portée à l’accélération d’ions qui a déjà montré son fort potentiel en termes de qualité des faisceaux accélérés. Malheureusement, ses applications sont encore limitées (radiographie, chauffage isochorique) à cause de paramètres limitants comme la divergence du faisceau, le spectre large ou l’énergie maximale atteinte par ces faisceaux. Au cours de ce travail de thèse, l’accent a plus particulièrement été mis sur l’augmentation de l’énergie maximale des faisceaux de protons dans le cadre des régimes à ultra haute intensité (supérieur à 1.1019W.cm-2). Cette recherche s’est orientée suivant deux axes principaux (impulsions longue et courtes), qui ont donné lieu à de nombreux échanges et au renforcement de la collaboration entre les laboratoires du LULI à l’École Polytechnique (France) et l’INRS-EMT (Canada).Dans le cadre des recherches menées au sein du LULI, des techniques innovantes ont pu être explorées afin de poursuivre la compréhension des mécanismes et d’améliorer les qualités de l’accélération d’ions à partir d’impulsion “longues” (entre 300 fs et 1,5 ps). Nous avons montré que l’utilisation de cibles ayant des dimensions transverses réduites permettait le confinement géométrique des électrons dans la zone d’impact du laser et augmentait ainsi significativement le taux de conversion de l’énergie laser vers les protons et l’énergie maximale atteinte par le faisceau. Par ailleurs, l’utilisation originale d’une optique plasma refocalisante a démontré son efficacité quant à réduire fortement la surface de focalisation du laser, conduisant à augmenter son intensité et donc l’énergie de coupure des faisceaux d’ions accélérés. Enfin, l’utilisation de deux impulsions laser a mis en évidence qu’une interaction entre les électrons accélérés par chaque impulsion était possible et qu’elle permet de modifier l’énergie et la typologie des faisceaux de protons.Les expériences réalisées au sein de l’INRS-EMT visaient quant à elle à améliorer la compréhension des régimes d’accélération femtoseconde, où peu d’études à ultrahaute intensité existaient au début de cette thèse, et à valider ou non la pertinence de ces régimes. Les nombreuses expériences menées ont clairement établi l’importance du contraste laser et la nécessité que ce derniers soit important pour que l’accélération de protons soit efficace dans ces régimes ultracourts. L’analyse systématique des faisceaux accélérés en face avant et en face arrière d’une cible mince montre que le processus d’accélération manifeste une certaine symétrie et prouve, qu’à énergie laser constante,l’accélération d’ions par laser n’est pas la plus efficace pour la plus courte durée d’impulsion. / Technological improvements since the 1980s have allowed for important developments in the field of high power lasers, thus paving the way for relativistic laser-matter interactions. With laser intensities higher than 1.1018 W.cm-2, the scientific community could explore a new physics, full of promising applications. Historically, laser–plasma interaction research initially aimed at exploring fusion by inertial confinement, but, with the breakthrough of ultra-high power lasers, the scope of research could now be broadened to laboratory astrophysics, radiation generation (harmonics, betatron, X) and the production of high energy particles (electrons, ions). Regarding the latter, radiation and ion sources are of such excellent quality that they might in the future replace current conventional sources like synchrotrons or accelerators, which require very expensive facilities. This thesis focuses particularly on laser-driven ion acceleration, whose accelerated beams have already demonstrated strong potential, e.g. in ultrafast imaging or warm dense matter generation.Within this domain, the present work focused on strategies developed to increase the ion beam energy in the ultrahigh intensity regime (higher than 1.1019 W.cm-2), exploiting as well moderate (400 fs) and short (25 fs) pulses facilities available as a result of the collaboration between the LULI laboratory in France and the INRS-EMT in Quebec. Innovative acceleration techniques have been explored at the LULI laboratory using moderately short laser pulses (400 fs to a few ps). This has been done first by improving our understanding of acceleration physics. Then, confinement of the laser-driven fast electrons that are at the source of the ion acceleration could be obtained by using reduced size targets. With such targets, electron confinement in the acceleration area could be achieved, inducing improvement of the laser to ions conversion efficiency, the ion beam cut off energy, and the ion beam quality. Another strategy that was exploited was to use refocalizing plasma optics to produce strongly reduced laser focal spot sizes. This induces laser intensity increase and thus improvement of the ion beam cut off energy. Finally, we used the combination of two laser pulses to have the electrons accelerated by each laser pulse interact together. When this was the case, we noted an increase of the ion beam cut off energy along with a modification of the beam typology. Complementarily, the experiments carried out using the 200 TW laser system in Quebec aimed at improving our understanding of femtosecond ion acceleration regimes, as only a fewexperimental studies were yet available, and to confirm the relevance of these regimes for ion acceleration. The results obtained with this laser clearly show the important role of the laser pulse contrast ratio, and the need for it to be extremely high to obtain efficient ion acceleration in this ultrashort regime. The systematic recording of accelerated ion beams has showed that a quasisymmetric acceleration from the target front and rear sides is possible. These results have alsoproved that the highest proton energy is not necessarily obtained with the shortest pulse duration when the laser energy is kept constant. Thus, we demonstrated that the shortest pulses available today (i.e. 25 fs) are not the most efficient to accelerate ion beams.

Mais recentemente foi proposta uma nova técnica para tratamento de doenças relacionadas à retina humana, utilizando descargas laser na retina com seqüência de pulsos da ordem de 200 \'mü\'s, em substituição ao tratamento convencional que utiliza pulsos longos da ordem de 300 ms. A principal vantagem da nova técnica é a preservação (sem morte celular) do tecido exposto ao laser. Esse trabalho apresenta os mecanismos adotados para o desenvolvimento de um sistema eletrônico de controle de uma cavidade laser em 586 nm, para uso oftalmológico, que objetiva atender o protocolo exigido por essa técnica mais recente. O referido protocolo exige a formação de pulsos rápidos de laser, o que torna vital a velocidade do sistema eletrônico de controle da cavidade laser. Para atender os requisitos do projeto foram implementados dois controladores de corrente em malha fechada PI (Proporcional integrative controller) que trabalham em sincronismo, um controlador de potência óptica em malha fechada PI, e circuitos auxiliares de controle térmico da cavidade laser. Em software foram implementados um PI de potência, com objetivo de tornar a malha de controle estável com o tempo de resposta necessário, e o PI de controle térmico dos elementos da cavidade laser. Os testes realizados do protótipo demonstraram que o sistema de controle atendeu as especificações de projeto, principalmente no que se refere a tempo de resposta do pulso rápido, ponto fundamental na obtenção do protocolo clínico (FastPulse), que esse trabalho objetiva atender. Adicionalmente, o protótipo foi submetido a teste clínico em um paciente, e os resultados demonstraram eficácia no tratamento e ausência de marcas (lesões) na retina. / Recently, scientists have proposed a new technique for treating diseases related to the human retina, which is based on retinal laser discharges using pulse sequence around of 200 \'mü\'s, replacing the conventional treatment using long pulses around of 300 ms. The main advantage of the new technique is the conservation (without cell death) of the area exposed to the laser. This work presents the mechanisms adopted for the development of an electronic control system of a laser cavity at 586 nm for ophthalmic use, which aims to meet the protocol required by this recent technique. The protocol requires the formation of rapid pulses of laser, which makes the electronic control system response velocity of the laser cavity vital to the protocol. To meet the project requirements were implemented two current controllers in closed loop PI (proportional integrative controller) working synchronized, an optical power controller in closed loop PI, and auxiliary circuits for temperature control of the laser cavity. Software were implemented for two controls, a PI power, in order to make the control loop stable with the required response time, and a PI thermal control for elements of the laser cavity. Tests showed that the prototype met the design specifications, especially regarding the response time of rapid pulse, key point in obtaining the clinical protocol (FastPulse), that this work aims to meet. Additionally, the prototype was subjected to clinical trial on a patient, and the results demonstrated efficacy and no visible lesions were noticed on retina.

Thesis (M.S.)--Oregon Graduate Center, 1976.