O desenvolvimento de materiais nanoestruturados tem se destacado devido a necessidade de miniaturização de dispositivos e a procura por novos efeitos físicos e químicos capazes de gerar novas tecnologias. Um importante composto com aplicações principalmente em óptica é o YAG (Y3Al5O12) presente no sistema cerâmico alumina-ítria (\'AL IND.2\'O IND.3\'-\'Y IND.2\'O IND.3\'). O YAG apresenta estrutura cristalina cúbica, expansão térmica isotrópica e não apresenta efeitos de birrefringência, o que possibilita a produção de cerâmica transparente para uso como material hospedeiro de íons terras-raras para o desenvolvimento de lasers de estado sólido. O ponto de partida em processamento cerâmico começa com o conhecimento das características físico-químicas do pó do composto. Em nosso trabalho, o objetivo foi o desenvolvimento de uma metodologia para a obtenção de nanopós de YAG de tamanhos médios diferenciados. Para isso foram realizados distintos processos químicos de síntese, e também, foram utilizados diferentes processos de separação, como a centrifugação e a sedimentação. Na produção das nanopartículas foram utilizados três métodos de síntese: Método de Pechini, Rota Glicerol e Método de Coprecipitação. No método de Pechini avaliou-se o efeito de diferentes valores de pH (1, 4, 7, 9 e 11) e procurou-se correlacionar com os tamanhos médios das nanopartículas. Após a obtenção do pó precursor foram realizadas medidas de decomposição térmica (DSC e TG), observando as principais transformações físico-químicas do material decorrentes dos diferentes métodos de síntese. A formação da fase cristalina do YAG foi determinada por difração de raios X e uma análise estrutural foi efetuada por espectroscopia de infravermelho. Medidas de área superficial específica (BET) foram usadas para avaliar o tamanho médio das partículas. Nanopós de YAG com diferentes intervalos de tamanhos foram produzidos, e o rendimento para cada intervalo de tamanho definido. / Nanostructured materials has emerged because the intense interest for miniaturization of devices and crescent demand for new physical and chemical effects that can generate new technologies. An important compound with applications mainly in optics is the YAG (Y3Al5O12). It\'s present in the alumina-yttria ceramic system (\'AL IND.2\'O IND.3\'-\'Y IND.2\'O IND.3\'). The YAG has a cubic crystaline structure, isotropic thermal expansion and it has no birefringence effects, which allows the production of transparent ceramics to use as host of solid-state lasers. The starting point in ceramic processing begins with the knowledge of the characteristics and physical and chemical properties of the powder. In our work, the goal was the development of a methodology for obtaining YAG nanopowders of different average sizes. To do this we performed distinct chemical synthesis, and we also used different separation processes such as centrifugation and sedimentation. For production of nanoparticles we used three synthesis methods: Pechini, glycerol route and coprecipitation. In the Pechini method we evaluated the effect of different pH values (1, 4, 7, 9 and 11) and tried to correlate with the average sizes of nanoparticles. After obtain the precursor powders we studied the decomposition thermal (DSC and TG) process, arising from the different synthesis methods. The crystalline phase of YAG was determined by x-ray diffraction and the structural analysis was carried out by infrared spectroscopy. Specific surface area measurements (BET) were used to evaluate the average particle size.YAG nanopowders with different average sizes were produced.

Les procédés de soudage conduisent à des modifications de microstructure et induisent des contraintes et distorsions résiduelles jouant un rôle important sur la tenue mécanique des assemblages. Cette étude a pour objectif la modélisation des phénomènes thermomécaniques liés à l'opération de soudage du TA6V, ce qui implique d'identifier et de modéliser les sollicitations thermiques imposées par le soudage, le comportement métallurgique et thermomécanique du matériau. L'étude thermique et métallurgique a permis de montrer les principales évolutions de phases de l'alliage, durant le soudage laser. Ainsi, en première approximation, nous pouvons considérer que 3 phases distinctes sont à prendre en compte dans le calcul thermomécanique (la phase a, la phase ß et la phase a'). Afin de caractériser les phases ou mélange de phase en présence, des essais thermomécaniques sont réalisés pour diverses températures et conditions de déformation. Concernant le choix du modèle numérique, on adopte pour chacune des phases un modèle à variables internes de type Lemaître et Chaboche avec écrouissage cinématique non linéaire, un critère de plasticité de type Von Mises et une loi d'écoulement viscoplastique de type Norton, couplé à une loi de transition d'échelle. L'identification de chaque phase se fait par méthode inverse, à partir des essais thermomécaniques, grâce au module d'optimisation de ZSeT/ZMaT. La loi de localisation choisie est basée sur un modèle polycristallin en ß qui permet le passage du comportement microscopique de chaque phase au comportement macroscopique de l'ensemble. La validité de ce modèle décrit précédemment passera par la définition d'un essai expérimental représentatif des différents phénomènes rencontrés lors de l'opération de soudage.

Nichtwäßrige Sol-Gel-Vorstufen, die zu einem Mischgefüge aus Al2O3 und YAG führen (Volumenverhältnis 45 : 55), wurden zu Fasern versponnen, in unterschiedlichen Atmosphären pyrolysiert und abschließend gesintert. Die strukturelle Ent-wicklung während der Pyrolyse der Gel-Fasern wurde in Abhängigkeit von Pyrolysetemperatur (200-850 °C) und -atmosphäre beschrieben. Die Zusammenhänge zwischen den mittels der Pyrolyseparameter variierten amorphen Strukturen und dem daraus resultierenden Kristallisations- und Sinterverhalten sowie den mechanischen Fasereigenschaften wurden gezeigt. Die isotropen Gel-Fasern sind frei von Poren und weisen lokal regelmäßig angeordnete, organische Domänen mit mittleren Abständen von 2 nm innerhalb des anorganischen Matrixgerüsts auf. Während der Pyrolyse auftretende Strukturveränderungen hängen stark von der Atmosphäre und der Temperatur ab. In Luft- und Sauerstoffatmosphäre trat ab 600 °C innerhalb der Fasern lokal eine Kristallisation von YAG und Korund in Form kugeliger Bereiche auf, die zum Bruch der Fasern bereits während der Pyrolyse führten. Die Abgabe organischer Bestandteile erfolgte bei Pyrolyse in Stickstoff im wesentlichen zwischen 300 °C und 500 °C, blieb jedoch auch bei höheren Temperaturen unvollständig. In Wasserdampf-Atmosphäre kam es durch Hydrolysereaktionen zwischen 250 °C und 385 °C zu einer verbesserten Abgabe der organischen Bestandteile. Der Kohlenstoffgehalt sinkt bei 385 °C unter 2 Masse-%. Werden dem Wasserdampf saure Gase wie z.B. Stickoxide zugesetzt, wird um 200 °C die Hydrolyse und Abgabe der Organik zusätzlich verstärkt. Nach Pyrolyse in Stickstoff oder wasserhaltigen Atmosphären blieben die Fasern amorph. Bei Pyrolyse in Stickstoff war die Struktur der Fasern porenfrei, wobei die organischen Pyrolysatreste wie in den Gel-Fasern als regelmäßig angeordnete, isolierte Bereiche innerhalb einer anorganischen Matrix vorlagen. In Wasserdampf bildete sich ab 250 °C aus den organischen Domänen eine geordnete Porenstruktur, die sich mit ansteigender Temperatur vergröberte. Auch in der aus verdampfter Salpetersäure erzeugten Atmosphäre bildeten sich Poren. Die Porendurchmesser und spezifischen Oberflächen der Fasern blieben jedoch geringer als in reinem Wasserdampf. In dem anorganischen Matrixgerüst änderten sich durch die Pyrolyse die Koordinationsverhältnisse der Al-Ionen. Ausgehend von der mehrheitlich 6-fachen Koordination in den Gel-Fasern kam es zunehmend zur Umlagerung in die 4- und 5-fache Koordination. Bei Pyrolyse in reinem Wasserdampf war diese Koordinationsveränderung deutlich schwächer ausgeprägt als in Stickstoff oder der Atmosphäre aus verdampfter Salpetersäure. Während der Sinterung treten intermediär gamma-Al2O3 und hexagonales YAlO3 als metastabile Phasen vor der Kristallisation von YAG auf. Mit der Kristallisation von Korund schließt die Phasenbildung der Al2O3-YAG-Fasern je nach vorangegangener Pyrolysebehandlung zwischen 1275 °C und 1315 °C ab. Die Abweichungen in der Kristallisationstemperatur bzw. Keimbildungsdichte von Korund und im Sinterverhalten ließen sich auf die Unterschiede in den amorphen Strukturen der pyrolysierten Fasern zurückführen. Hohe Anteile 6-fach koordinierter Al-Ionen und eine zu hohen spezifischen Oberflächen führende, feine Porosität erwiesen sich als günstige Strukturmerkmale für pyrolysierte Fasern. Die dabei entstandenen feinkörnigen, homogenen Gefüge konnten dicht gesintert werden und hatten die höchsten Festigkeiten und E-Moduln. Kohlenstoffgehalte bis zu 2 Masse-% wirkten sich in den offenporigen Zwischenprodukten nicht negativ auf das Sinterverhalten aus. In dieser Arbeit wurde gezeigt, daß die Kristallisation der Sol-Gel-abgeleiteten Fasern und damit auch die Ausbildung der keramischen Gefüge in entscheidendem Maße von den Pyrolysebedingungen abhängen. Bei einheitlicher Synthese der Gel-Fasern lassen sich durch die Pyrolysebehandlung unterschiedliche Strukturen in den amorphen Zwischenprodukten einstellen, die durch ihre spezifisches Kristallisations- und Sinterverhalten zu unterschiedlichen keramischen Gefügen in den Fasern führen. Die Optimierung der Gefüge vorstufenabgeleiteter Keramiken durch Zusatz von Keimen ("Seeding") ist seit längerem bekannt. In Ergänzung dazu bietet die gezielte Wahl der Pyrolysebedingungen eine weitere Möglichkeit zur Steuerung der Gefügeausbildung in Sol-Gel-Keramiken. / Ceramic fibers of Al2O3-YAG composition (volume ratio 45 : 55) were prepared by spinning non-aqueous sol-gel precursors to fibers which were then pyrolyzed in various atmospheres and finally sintered. Structural development of the gel fibers upon pyrolysis at temperatures between 200 °C and 850 °C was described for different atmospheres. Variation of pyrolysis conditions lead to different amorphous structures. A correlation between the amorphous structures and their crystallization and sintering behavior as well as mechanical fiber properties could be established. The gel fibers have an isotropic, pore-free structure which is characterized by an inorganic matrix that contains organic domains in a locally ordered arrangement with mean distances of 2 nm. Alteration of this structure strongly depends on the type of atmosphere and temperature during pyrolysis. In air and oxygen above 600 °C local, spherulitic crystallization of YAG and corundum occurs within the fibers and leads to fracture of the fibers. In nitrogen, organic constituents are mainly removed between 300 and 500 °C, but residues remain even at higher temperatures. Water vapor hydrolyses organic constituents and enhances their release at 200-385 °C. Thus carbon contents drops below 2 wt.-% at 385 °C. Additional acceleration of hydrolysis at ~200 °C can be achieved by addition of acidic gases like nitric oxide to the moist atmosphere. The structure of fibers pyrolysed in nitrogen or moist atmospheres remains amorphous. After pyrolysis in nitrogen the fibers are pore-free and the organic residues still appear as locally ordered domains within an inorganic matrix. In water vapor from 250 °C on, the release of organics leads to the formation of ordered micropores that coarsen with further increasing temperature. In the atmosphere of evaporated nitric acid, pores form too, but pore sizes and specific surface areas of the fibers are lower than in pure water vapor. The coordination of Al-ions in the inorganic network is altered by pyrolysis. Gel fibers mainly contain 6-fold coordinated Al-ions. With increasing temperature a rearrangement of part of the octahedrally coordinated Al-ions to 4- and 5-fold coordination was observed. While this rearrangement was only weakly pronounced for fibers pyrolysed in water vapor, in nitrogen or the atmosphere that was derived from evaporated nitric acid a significantly higher proportion of 6-fold coordinated Al-ions rearranged to lower coordination numbers. During the sintering process gamma-Al2O3 and hexagonal YAlO3 are formed as intermediate metastable phases prior to the crystallization of YAG. Formation of crystalline phases in the Al2O3-YAG fibers completes with the crystallization of corundum at 1275 to 1315 °C depending on pyrolysis conditions. Differences in crystallization temperature and nucleation density of corundum were put down the structural features of pyrolysed, amorphous fibers. A high proportion of 6-fold coordinated Al-ions and a high specific surface caused by fine pores revealed as favorable characteristics of low corundum crystallization temperature and high nucleation density. Such fibers could be fully densified resulting in the highest strength and Young's moduli in the ceramic fibers. Carbon contents up to 2 wt.-% were not deleterious to the densification of pyrolysed fibers with an open porous structure. The results presented in this study show that crystallization and microstructural evolution of sol-gel derived ceramic fibers critically depend on pyrolysis conditions. Different amorphous structures that lead to altered ceramic microstructures can be obtained from uniformly synthesized gel fibers by variation of pyrolysis conditions. Seeding is a well known process for the microstructural optimization of precursor derived ceramics. As a supplement the choice of suitable pyrolysis conditions is a further tool for the microstructure control in sol-gel ceramics.

A adaptação dos cimentos endodônticos, Ketac-Endo, AH Plus e Endomethásone, à dentina radicular submetida à ação prévia dos agentes de limpeza final laser de Er:YAG, EDTA a 17% e Solução Salina Fisiológica a 0,9% foi estudada pelas microscopias óptica e eletrônica de varredura. Foram empregados 90 caninos humanos extraídos, que após instrumentação pela técnica escalonada de memória e irrigação com hipoclorito de sódio a 1%, foram divididos em três grupos de 30, de acordo com o agente de limpeza final empregado. No grupo A, empregou-se o laser de Er:YAG intracanal, com parâmetros de 100mJ (energia real de 44mJ), 10pps, durante dez segundos, sob refrigeração a ar, com movimentos circulares no sentido apicocoronário, seguido de irrigação com 20ml de solução salina fisiológica a 0,9%. No grupo B, empregaram-se 5ml de EDTA a 17% durante cinco minutos, seguido de irrigação com solução salina fisiolólgica a 0,9%. No grupo C, empregaram-se 20ml de Solução Salina Fisiológica a 0,9%. Após secagem, os canais radiculares foram armazenados em solução salina fisiológica a 0,9% durante 48 horas. Cada grupo foi então dividido em três subgrupos de dez,de acordo com o cimento endodôntico. Os 90 canais radiculares foram obturados pela técnica clássica, seguida da condensação lateral ativa da guta-percha. Após comprovação radiográfica da obturação os canais foram vedados com Cimpat no terço cervical e forame apical, e as raízes armazenadas em solução salina fisiológica a 0,9% em umidade de 100% a 37oC, durante 30 dias. Em seguida, foram seccionadas transversalmente a 5mm do ápice radicular, fotografadas com aumento de quatro vezes e submetidas à análise em microscopia óptica. Para a análise em microscopia eletrônica de varredura, as secções apicais foram moldadas em silicona Aquasil e os moldes obtidos foram metalizados e fotografados em aumentos que variaram de 50 a 200 vezes. As fotos obtidas pelas microscopias foram escaneadas e transferidas para um programa de medida de área (SigmaScan) para mensuração das áreas preenchidas pelos materiais obturadores e das possíveis fendas entre material obturador e parede do canal radicular. Diante dos resultados obtidos com a metodologia empregada e da discussão apresentada pudemos concluir que: 1- Os agentes de limpeza final empregados exerceram efeito diferenciado na adaptação dos cimentos testados. O laser de Er:YAG interferiu na adaptação de todos os cimentos, o EDTA melhorou a adaptação do Endomethásone e do AH Plus em relação ao laser de Er:YAG e à solução salina fisiológica a 0,9% e a solução salina fisiológica melhorou a adaptação do Ketac-Endo, em ambas microscopias empregadas. 2- O Endomethásone apresentou a pior adaptação entre os cimentos e o AH Plus apresentou a melhor adaptação com EDTA na microscopia eletrônica de varredura. 3- A associação das microscopias óptica e eletrônica de varredura mostrou ser um método confiável na detecção das fendas, sendo que a microscopia eletrônica de varredura propiciou melhor visualização. 4- Todos os cimentos testados apresentaram alteração dimensional, verificando-se contração para o Ketac-Endo, expansão para o Endomethásone e AH-Plus, sendo que o AH Plus mostrou-se mais próximo da estabilidade dimensional. / The adaptation of endodontic sealers, Ketac-Endo, AH Plus and Endomethásone to dentinal root submitted to the previous action of final Er:YAG laser cleaning agents, EDTA at 17% and a saline solution at 0.9% was studied by Optical and Scanning Electron Microscopy. Ninety extracted human canines were employed, and following the step back technique preparation and irrigation with sodium hypochlorite solution they were divided into three groups with thirty teeth each, according to the final cleaning agent used. In group A, Er:YAG laser was used intracanal, with the following parameters: 100mJ (real energy 44mJ), 10pps, for 10 seconds under air cooling with circular movements in apicocervical direction and the canals were irrigated with 20ml saline solution at 0.9%. In group B, 5ml of EDTA at 17% irrigated the root canals for 5 minutes, followed by a saline solution at 0.9%. In group C, a saline solution at 0.9% was employed to irrigate the root canals. After drying, the roots were stored in a saline solution at 0.9% for 48 hours. Each group was divided into three subgroups of ten, according to the selected endodontic sealer. The ninety root canals were filled through standard technique, followed by gutta-percha lateral condensation. Following radiographic filling proof, the root canals were sealed with Cimpat in the cervical third and at the apical foramen, and the roots stored in a 0.9% saline solution at 37oC and 100% humidity for 30 days. Afterwards, they were transversally secctioned at 5mm to the root apex, and photographed with a 4x magnification, and submitted to optical microscopic analysis. Before the Scanning Electron Microscopic analysis, the apical root sections were molded with Aquasil and the obtained replicas metallized and photographed with 50x and 200x magnifications. The resulting images, in both microscopies, were scanned and transferred to the area measurement software program (SigmaScan) to measure the areas filled by endodontic materials and the failed areas between the endodontic material and the root canal walls. Through the results with the selected methodology and by means of the presented discussion, we could conclude that: 1- The final cleaning agents employed in the root canals presented different effects in the adaptation of the endodontic sealers. The Er:YAG laser was harmful to the adaptation of all the endodontic sealers; the EDTA improved the adaptation of Endomethásone and AH Plus and the 0.9% saline solution improved the adaptation of Ketac-Endo in both microscopies. 2- Endomethásone presented the worst adaptation compared to the other sealers and AH Plus presented the best adaptation with EDTA by Scanning Electron Microscopic analysis. 3- The Optical Microscopy associated with the Scanning Electron Microscopy proved to be a safe method in detecting filling failures, being, the Scanning Electron Microscopy the best. 4- All endodontic sealers presented dimensional alterations, Ketac-Endo presented contraction, Endomethásone and AH Plus presented expansion, being, AH Plus closer to dimensional stability.

Nos últimos anos tem-se observado um grande crescimento em tecnologia para modificação de superfícies de implantes que reduza ou elimine o tempo de espera pela cicatrização óssea. A textura da superfície é uma característica fundamental na promoção da osseointegração. Os estudos da topografia de superfície implantada e no comportamento celular mostram que a estrutura óssea deposita-se indistintamente em superfícies porosas ou lisas, seja em implantes de cerâmica, titânio ou em ampla variedade de superfícies. A porosidade, portanto, não é condição necessária para que ocorra a aposição óssea, entretanto, desempenha um papel preponderante no percentual de aposição óssea sobre a superfície do implante, assim como na velocidade em que essa deposição ocorre. O objetivo deste trabalho é investigar a influência da rugosidade superficial obtida com a tecnologia de jateamento abrasivo mecânico e a do laser Nd-YAG na osseointegração, através de ensaio de torque de extração de corpos-de-prova de titânio, implantados em tíbias de coelhos. Os resultados demonstram que a rugosidade superficial dos corpos-de-prova tratados proporciona uma osseointegração mais rápida e de melhor qualidade, no período de quatro semanas, quando comparados com corpos-de-prova do grupo controle, sem tratamento superficial, sendo possível evidenciá-los pelos dados de torque de extração. Esta característica da superfície do titânio é fundamental para otimizar o procedimento.

A pair of high-stability optical frequency references has been developed. The devices are based on room temperature Fabry-Perot cavities with mirrors spaced apart by a hollow single-crystal sapphire element. The sapphire element delivers mechanical sti ness that provides improved immunity to vibrational perturbations compared with the more common spacers made from ultra-low expansion glass. The system is housed in an vacuum chamber designed to provide isolation from environmental perturbations through the use of an active thermal control system, suspension legs and a unique beam alignment system. The dimensional stability of the Fabry-Perot was translated into a highly stable laser frequency by frequency locking a 1064nm Nd:YAG laser to the centre of a mode of the cavity. This frequency lock was implemented by the Pound-Drever-Hall scheme. By careful design, this control system was able to hold the frequency of the laser to within parts in 1016 of the frequency of the fundamental cavity mode. The minimum fractional frequency stability of the laser frequency was measured at 2.1x10[-]14 for integration times of 0.8 s, limited by the residual instability of the Fabry-Perot cavity. The experimental methods used to measure the performance of the system have also been considered in depth. For example, the most common way of characterizing the frequency stability of a frequency standard is the Allan variance. It is demonstrated that, without care, data taken with modern frequency counters can produce erroneous and distorted results when their output is supplied to this algorithm. The method to avoid or account for these errors is also presented. The Fabry-Perot cavity performance is limited on long timescales by residual temperature uctuations, which can be ameliorated in future by enhancing the design of the thermal control system. At short timescales, the system is limited by vibration-induced uctuations together with a white noise source, that is yet to be identi ed, but may relate to fundamental thermodynamic temperature uctuations of the sapphire spacer. This system was used to measure the stability of an optical signal synthesised from a cryogenic microwave sapphire oscillator using an wide-band optical frequency comb. This was the rst demonstration of a multiplication of an ultra-stable signal from the microwave frequency domain into the optical frequency domain, without loss of delity at the level of 2x10[-]14.

Ce travail s'inscrit dans le cadre général de l'étude des mécanismes de couplage entre oscillateurs. Deux aspects sont abordés qui concernent respectivement le couplage par proximité de deux microlasers au sein d'une même galette et les interactions entre modes de polarisation dans les microlasers YAG présentant de faibles anisotropies.<br />L'étude expérimentale du couplage de deux lasers continus a mis en évidence trois régimes dynamiques différents qui apparaissent successivement à mesure que les fréquences propres des cavités des lasers se rapprochent : i) lasers quasi indépendants, ii) instabilités périodiques et chaotiques et iii) verrouillage de phase des lasers.<br />Le modèle développé pour rendre compte des caractéristiques du couplage introduit un coefficient de couplage complexe. Il reproduit de façon remarquable l'ensemble des résultats expérimentaux et de plus a permis de proposer une méthode fiable de mesure du coefficient de couplage. Une étude détaillée du recouvrement entre les modes des lasers et le profil non uniforme du gain et de l'indice de réfraction a permis d'établir une expression analytique reproduisant correctement l'évolution des parties réelle et imaginaire du coefficient de couplage en fonction de la distance entre lasers.<br />La dynamique de polarisation des microlasers YAG, et en particulier des lasers Nd3+,Cr4+:YAG, met en jeu la biréfringence liée aux contraintes locales, l'anisotropie de gain induite par un faisceau de pompe polarisé linéairement et de celle de l'absorbant saturable. Suivant l'importance relative de ces différentes anisotropies, le laser peut émettre dans l'un et/ou l'autre des modes propres de la biréfringence ou avoir une polarisation orientée de façon privilégiée suivant l'un des axes cristallins de l'absorbant. <br />Les observations expérimentales ont pu être reproduites analytiquement et/ou numériquement à l'aide d'un modèle qui rend compte de l'évolution temporelle des composantes du champ selon les axes propres de la biréfringence ainsi que celle de leur phase relative. L'anisotropie du gain est décrite par deux coefficients d'anisotropie respectivement relatifs à la pompe et au laser. L'anisotropie de l'absorbant saturable est prise en compte grâce à l'introduction d'inversions de populations associées à chacun des axes cristallins.

Rapid development of fiber-optic communications network requirements increasing in recent years, The WDM technology and invention of anhydrous optical fiber open the possibility for optical fiber transmission bands broaden form 1.3 £gm to 1.6 £gm. Chromium doped yttrium aluminum garnet crystal fiber has characteristic of 300 nm broadband. Therefore, it¡¦s strongly desirable to develop a broadband fiber amplifier, laser or other active components for extending the flexibility of system architecture design in optical fiber communication. A few-mode chromium doped yttrium aluminum garnet double-clad crystalline fibers has been demonstrated by employing a modified version of LHPG technique, means using silica-YAG crystal co-drawing and multiple core-tuning process by precisely controlled inter-diffusion between YAG core and silica tube. In this thesis, electron probe x-ray micro-analysis, energy dispersive spectroscopy and transmission electron microscopy were utilized to confirm this fiber structure and composition. This fiber has gross gain about 2.3 dB with dual pumped by few hundred mini Watt. Significantly reduce the pump power threshold. Compared with the last large core size, few-mode (small core size) chromium doped yttrium aluminum garnet double-clad crystalline fibers has lower heat effect and higher power efficiency. To enhance the optical properties towards few modes or even single mode, not only reduce the transmission loss, but improve the device efficiency. Key words: Laser heated pedestal growth, Cr4+:YAG, Double-clad Crystal Fiber, gain

This work deals with the interaction of intense 100 ps laser pulses with double-layer foil targets, consisting of one dielectric (Mylar) layer and one metallic layer. The diagnostics of the evolving plasmas is done by the means of shorttime interferometry, time-resolved X-ray spectroscopy, and methods of ion dosimetry in polymer nuclear track detectors (CR-39). / Die Arbeit beschäftigt sich mit der Wechselwirkung intensiver 100-ps-Laserpulse eines Nd:YAG-Lasersystems mit Zweischicht-Folientargets, die aus einer dielektrischen Schicht (Mylar) und einer metallischen Schicht bestehen. Die entstehenden Plasmen werden mittels Kurzzeitinterferometrie und zeitaufgelöster Röntgenspektroskopie sowie mit Methoden der Ionendosimetrie in Polymer-Kernspurätzdetektoren (CR-39) untersucht.

The main purpose of this research was to investigate new medical applications of femtosecond laser ablation. A near-infrared femtosecond laser was tested and proved to be able to overcome the existing limitations and outperform the conventional long-pulse lasers in the areas of human urinary calculus (kidney stone) lithotripsy and skin treatment. The two primary objectives of my research are: 1) to investigate the feasibility of using femtosecond pulsed laser radiation to ablate urinary calculus of various compositions. The laser-calculus interaction mechanism was characterized using pump probe imaging and fast flash imaging. A novel fiber delivery system was developed to transmit and focus high energy femtosecond pulses for urinary calculus lithotripsy. The successful demonstration of the femtosecond laser lithotripsy provided a promising treatment method better than the existing long-pulse laser lithotripsy in a few different aspects, including less collateral damage to surrounding tissue, small-size debris and more controlled experimental condition. 2) to investigate the depth limitation of femtosecond subsurface ablation in scattering skin sample and develop a prototype tissue optical clearing device to enhance femtosecond beam penetration for deeper subsurface cavitation production in the skin. The successful demonstration of the device has potential benefits to new femtosecond-based therapies for reshaping or removing subcutaneous tissues. / text