Dissertations / Theses: 'Nd-YAG lasers'

1

De, Kock Trevor Neil. "The development and evaluation of a Nd:YAG laser incorporating an unstable resonator." Thesis, Rhodes University, 1986. http://hdl.handle.net/10962/d1008566.

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Introduction: For approximately the last eight years the Laser Section of the National Physical Research Laboratory (NPRL) has been interested in inter alia, pulsed solid-state lasers and in particular, Nd:YAG. Investigations of various resonator types were undertaken with a view to the improvement of the laser parameters such as output energy, pulse width, beam quality and sensitivity to mirror misalignment. In 1980 a Nd: YAG laser employing a rotating prism Q-switch was constructed (Preussler (1980)). It involves rotating one of the two cavity reflectors so that they are parallel for only a brief instant in time. Typically the prism must rotate at a speed of 20 000 r.p.m. to ensure a single pulse output. Such lasers suffer from the tendency to emit multiple pulses, they are very noisy and they require frequent maintenance because of the short lifetime of the bearings. A resonator employing conventional curved mirrors and an electro-optical Q-switch was constructed in 1980 (Robertson & Preussler (1982)). In 1981 an electro-optically Q-swi tched laser making use of a crossed Porro-prism resonator was investigated due to its relative insensitivity to misalignment of the reflectors compared with the conventional mirror resonator (Nortier (1981)). Improvements in terms of output power, beam divergence and beam quality can be achieved by making use of a so-called unstable resonator. Such a laser has been investigated and is reported on in this study. Chapter 2 provides some background into laser theory and operation while chapter 3 deals with the theory of the unstable resonator. Chapter 4 provides details of the experimental equipment and techniques used in the work and chapter 5 discusses the evaluation of the project and results obtained.

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Zarour, Hassane. "Lasers et malformations vasculaires superficielles : mise au point : etude preliminaire sur un nouveau type de laser (le laser yag dedouble en frequence)." Aix-Marseille 2, 1991. http://www.theses.fr/1991AIX20819.

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Martial, Igor. "Systèmes laser pompés par diode à fibres cristallines : oscillateurs Er : yAG, amplificateurs Nd : yAG." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00705198.

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Au cours de cette thèse, nous nous intéressons à deux applications nécessitant des sources laser impulsionnelles : l'imagerie active et l'usinage laser. L'imagerie active nécessite des sources laser efficaces émettant dans la gamme de sécurité oculaire (entre 1,5 µm et 1,7 µm) à des cadence de l'ordre du kilohertz et produisant des énergies par impulsion de plusieurs millijoules. Les sources efficaces émettant dans la gamme de sécurité oculaire utilisent l'ion erbium. Cependant la structure électronique complexe de l'ion erbium entraîne de nombreux effets parasites qui limitent fortement l'énergie accessible lors d'un fonctionnement à haute cadence. Pour diminuer l'influence de ces effets parasites nous avons utilisé le concept de fibres cristallines dans le cadre d'une collaboration entre le Laboratoire Charles Fabry et l'entreprise Fibercryst. La géométrie des fibres cristallines, combinant les propriétés des cristaux massifs et les avantages des fibres en verre nous a permis de dépasser les limites des sources actuelles. L'usinage de matériaux requière des sources laser impulsionnelles émettant dans le proche infrarouge (1 µm) et alliant forte énergie, forte puissance crête et forte puissance moyenne. Pour réaliser de telles sources, il est nécessaire d'utiliser des milieux à gain permettant de limiter les phénomènes thermiques et les effets induit par la puissance crête (effets non-linéaires). Pour cela nous avons utilisé à nouveau le concept de fibre cristalline, dopée cette fois ci par l'ion néodyme. Ces fibres cristallines ont été utilisées comme amplificateur de puissance pour amplifier des micro-lasers fonctionnant à haute cadence (de 1 à 100 kHz) et produisant des impulsions courtes (< 1 ns).

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Hill, Timothy J. "Interference of intensity noise in a multimode Nd:YAG laser." Title page, abstract and contents only, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phh6484.pdf.

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Includes bibliographical references (leaves 151-163). Investigates the behaviour of the intensity noise in a multimode Nd:YAG laser. The collective modes of oscillation are excited by broadband ambient noise. Because the phase of the excitation is unknown, a cross spectral technique to measure the antiphase dynamics directly and form a picture of the intensity noise interference for two to five mode operation is developed. For three mode operation, the contributions of the longitudinal modes to collective modes is measured.

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Mondin, Linda. "Stabilisation de fréquence de laser Nd-YAG pour applications spatiales." Nice, 2005. http://www.theses.fr/2005NICE4046.

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Les lasers stabilisés à long terme sont utilisés dans de nombreux domaines en métrologie et constituent la base de toute la recherche expérimentale en spectroscopie à très haute résolution. Ce mémoire décrit mon travail de thèse sur les lasers à Nd:YAG stabilisés en vue d'applications spatiales (missions de physique fondamentale ou géodésie). Les montages doivent satisfaire critères de compacité, stabilité mécanique, robustesse et fiabilité. On traite les références utilisables pour le long (moléculaire) et le court (mécanique) terme ainsi que leurs limitations principales. L'analyse et le choix de ces références de stabilisation seront couplés avec le choix des techniques de stabilisation (PDH, Tilt-Locking, Modulation Transfer). Dans les techniques de stabilisation, celle de Pound-Drever-Hall (PDH) est devenue un classique car elle donne les meilleurs performances connues à ce jour surtout à court terme. Pour réduire le nombre de composants actifs, nous avons aussi implanté une technique dite de Tilt-Locking, que je compare avec celle de PDH dans le cas d'une référence Fabry-Perot monolithique. Les performances théoriques sur le long terme et les efficacités quantiques sont inter-comparées. On présente les montages expérimentaux et les résultats obtenus (lasers stabilisés sur Fabry-Perot et Iode moléculaire). On a calibrer les dérives de fréquence du Fabry-Perot, ce qui permettra de présenter des solutions obtenues analytiquement et numériquement pour l'asservissement en longueur de cette référence mécanique. Des suggestions de prolongation de ces travaux sont suggérés en conclusion et, en appendices, les détails de dimensionnement des bruits de LISA, le rappel théorique des ondes de gravitation, ainsi que divers simulations de calculs effectués, sont présentées
Long term stabilised lasers are used in a multitude of metrological applications and are the basis of experimental research in very high resolution spectroscopy. This document describes my thesis work on stabilised Nd:YAG lasers in view of space applications (for fundamental physics experiments and geodesy). All experiments must satisfy criteria of compactness, mechanical stability, robustness and reliability. I will describe the possible references for the long (molecules) and the short (resonators) term time intervals with their principal limitations. The discussion leading to their choice is actually connected to the stabilisation techniques to be adequately implemented (PDH, Tilt-Locking, Modulation transfer). Among the stabilisation techniques, the Pound-Drever-Hall (PDH) technique is now a classic as it produces the best performance in short term, so far. To reduce active components, we have also implemented a DC technique called Tilt-Locking and I will compare with PDH in the case of a monolithic Fabry-Perot reference. Theoretical performances on the long term and quantum efficiencies will be compared for different techniques. The schematic principles of the experiences and the results I have obtained for stabilised lasers on Fabry-Perot and molecular iodine are presented. We calibrated the Fabry-Perot drifts, this allows me to point out analytical and numerical solutions to control the length of this mechanical reference. Finally suggestions for further work will be approached and, in the appendices, details about noise order of magnitudes for LISA, a theoretical overview of gravitational waves as well as different simulations and calculations are presented

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Delen, Xavier. "Amplificateurs laser à cristaux massifs pompés par diode : fibres cristallines Yb : YAG et cristaux Nd : YVO4." Phd thesis, Palaiseau, Institut d'optique théorique et appliquée, 2013. http://pastel.archives-ouvertes.fr/pastel-00996931.

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Un grand nombre d'applications réclament des sources laser en régime impulsionnel toujours plus puissantes et énergétiques. Les progrès continus des technologies laser permettent non seulement d'améliorer les performances de l'outil laser mais aussi d'ouvrir la voie à de nouvelles applications. Cependant, l'augmentation de la puissance des sources laser est aussi accompagnée par une complexification des systèmes. Cette thèse porte sur l'étude d'amplificateurs laser de puissances qui se distinguent par la simplicité de leurs architectures : avec un ou deux passages dans le milieu laser. Dans la première partie, nous étudions le potentiel de la fibre cristalline Yb: YAG pompée par diode en tant qu'amplificateur. Les effets de confinement de l'intensité de pompe au centre de la fibre cristalline par guidage sont étudies théoriquement et expérimentalement. Deux expériences démontrent ensuite l'intérêt de la fibre cristalline Yb:YAG en tant qu'amplificateur de puissance de sources laser à fibres, l'une en régime femtoseconde et l'autre avec un laser mono-fréquence. Par ailleurs, nous explorons le potentiel de notre concept en régime de forte puissance. Une puissance de 250 W en oscillateur et une extraction de 100 W en amplificateur ont été obtenues avec une diode de pompe de 600 W. La deuxième partie traite de l'étude d'amplificateurs à base de cristaux de Nd:YVO4. Le dimensionnement de notre système est réalisé en s'appuyant sur une étude des propriétés du Nd:YVO4. L'amplificateur ainsi obtenu affiche des performances inédites qui se caractérisent par un très fort gain optique (40-60 dB) couplé à une forte extraction de puissance moyenne (10 à 15 W).

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Rotger, Maud. "Contribution à l'étude d'un laser Nd-YAG industriel de puissance : réalisation d'un lambdamètre pour lasers impulsionnels." Dijon, 1990. http://www.theses.fr/1990DIJOS013.

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La première partie de ce mémoire est consacrée à l'étude de nouvelles cavités résonnantes pour des lasers Nd-YAG industriels de puissance. Une cavité instable SFUR en anneau n'a pas donné expérimentalement les résultats escomptés, tant du point de vue de la puissance de sortie que de celui de la qualité du faisceau. Une cavité plane, en anneau symétrique, donne un bon facteur de qualité et ne présente qu'une seule et grande zone de stabilité, allant du fonctionnement tir-a-tir du laser jusqu'a sa puissance nominale. De plus, la position toujours fixe du beam-waist quel que soit le pompage doit éviter aux utilisateurs tout réajustement vertical de leur plan de travail. Cette cavité nous semble sous différents aspects le meilleur choix dans le domaine des cavités stables. La seconde partie, concerne la réalisation d'un lambdamètre performant pour lasers impulsionnels monomodes en vue notamment de mesurer avec précision la longueur d'onde d'un laser nd-yag injecté. Une étude théorique préalable a permis, compte tenu de l'objectif fixe, d'opter pour la réalisation d'un dispositif optique constitue d'interféromètres de Fabry-Pérot plans. Cet appareil, associé à un système d'acquisition en temps réel et à un logiciel de traitement des données en langage C, travaille à une cadence de 10 Hz avec une résolution de 20 mhz

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Cecchini, Silvia Cristina Mafra. ""Desinfecção da Dentina Radicular pela Irradiação dos Lasers de Nd: YAG e Er: YAG: um Modelo "in vitro""." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/23/23135/tde-30082001-094604/.

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RESUMO Desinfecção da dentina radicular pela irradiação dos lasers de ND:YAG, HO:YAG e ER:YAG: um modelo in vitro A provável causa do insucesso da terapia endodôntica é a persistência de microrganismos colonizando os túbulos dentinários. Para reduzir o risco de insucesso e, se possível, o tempo despendido no tratamento endodôntico, novos equipamentos e materiais são constantemente desenvolvidos. O objetivo desta investigação foi estudar o efeito da irradiação laser intracanal na desinfecção dos túbulos dentinários de dentes bovinos recém-extraídos, utilizando-se um modelo in vitro. Os grupos irradiados pelos vários lasers foram comparados ao tratamento com hidróxido de cálcio, freqüentemente utilizado como medicação intracanal. O cemento radicular foi removido, o canal preparado e os dentes, cortados, resultando em 180 corpos de prova padronizados. Para promover a colonização bacteriana, os corpos de prova foram incubados, a 37 o C, em frascos contendo caldo de tripticase de soja e Enterococcus faecalis, o qual continha um plasmídeo que permitiu o seu crescimento em um meio seletivo com cloranfenicol. Os corpos de prova foram divididos em cinco grupos experimentais e três grupos-controle. Para irradiação foram utilizados os lasers pulsados de: Ho:YAG a 2,1 µm; Nd:YAG (1,06 µm); e Er:YAG (2,94 µm) com e sem refrigeração ar/água. Os grupos tratados receberam três parâmetros diferentes de irradiação com cada tipo de laser: energia abaixo do limiar de modificação física (physical modification threshold - ½ do PMT) por 60s; no limiar (PMT) por 60s; e, acima do limiar (120s). O Grupo 5 recebeu sete dias de tratamento com hidróxido de cálcio. Como controles, três espécimes para cada grupo receberam água estéril (controle negativo), três receberam KI3, após exposição à bactéria (controle negativo) e três não receberam tratamento após exposição à bactéria (controle positivo). A quantidade de bactérias foi estimada mediante a contagem de unidades formadoras de colônias (u.f.c.). De modo a avaliar, paralelamente, se os comprimentos de onda laser utilizados no experimento poderiam ser absorvidos pelo E. faecalis, foram obtidos espectros de absorção no UV, VIS e IR, por meio de espectroscopia. A análise estatística mostrou uma redução bacteriana como segue: Ho:YAG > hidróxido de cálcio > Nd:YAG > Er:YAG com refrigeração ar/água > Er:YAG sem refrigeração ar/água. Houve uma significativa redução bacteriana no grupo irradiado pelo Ho:YAG no limiar de modificação PMT (50 mJ, 10 Hz, 66 J/cm 2 , por 120s), seguida pelo Ho:YAG a 50 mJ, 10 Hz, 33J/cm 2 , por 60s e pelo grupo que recebeu hidróxido de cálcio. Os dois últimos grupos não apresentaram diferenças estatísticas significativas. O espectro de absorção pelas bactérias (E. faecalis) nas faixas dos comprimentos de onda do UV e VIS apresentou picos de absorção em 361 nm e em 377 nm (UV). Já o infravermelho próximo revelou uma baixa absorção pelo microrganismo testado.
SUMMARY Disinfection of intracanal dentin by Nd:YAG, Ho:YAG and Er:YAG laser irradiation: an in vitro model A possible cause for root canal failure is the persistence of bacteria that have colonized dentinal tubules. To reduce this risk and, if possible, to also shorten the time-consuming endodontic therapy, new equipment and materials are constantly being introduced. The aim of the present investigation was to study the effect of disinfection of dentinal tubules by intracanal laser irradiation using an in vitro model. The groups irradiated by various lasers were compared with calcium hydroxide, a material frequently used as intracanal medication between appointments. Freshly extracted, intact bovine incisors were used. The root cementum was removed and the teeth cut to produce 180 standardized specimens. For bacterial colonization, specimens were incubated at 37 o C in test tubes with Tryptic Soy Broth and Enterococcus faecalis, which carried a plasmid that allowed the growth in a selective medium containing chloramphenicol. The specimens were divided in five treatment groups and three control groups. For irradiation, pulsed delivered Ho:YAG laser at 2.1 µm, Nd:YAG laser (1.06 µm), and Er:YAG and Er:YAG laser (2.94µm) with and without air/water coolant, were used. Lasers groups received three different laser settings for treatment: output energy below the physical modification threshold (½ of PMT) for 60 sec, at the PMT for 60 sec and above the PMT (120 sec). Group 5 received a seven-day treatment with calcium hydroxide. As controls, three specimens for each treatment group received sterile water instead of bacteria (negative control), three received iodine potassium-iodide after bacterial exposure (negative control), and three did not receive treatment after bacterial exposure (positive control). The number of bacteria was estimated by counting CFU. In order to evaluate whether the lasers used in the experiment could be absorbed by the bacteria E. faecalis, an UV, VIS and NIR spectra were obtained using a spectrophotometer. Statistical analysis showed the bacterial reduction as follow: Ho:YAG laser > hidróxido de cálcio> Nd:YAG laser > Er:YAG laser with air/water coolant > Er:YAG laser without air/water coolant. There was a significantly higher bacterial reduction in the group irradiated by the Ho:YAG at the PMT (50mJ, 10 Hz, 66 J/cm 2 for 120 sec), followed by Ho:YAG irradiated at 50mJ, 10 Hz, 33 J/cm 2 for 60 sec, and the group that received calcium hydroxide. The latter two groups were not significantly different. The UV and VIS absorbance spectrum presented two absorbance peaks at 361nm and 337nm (UV). The NIR spectrum revealed a very low absorbance by the E. faecalis.

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Bjurshagen, Stefan. "Diode-pumped Nd : YAG lasers for generation of blue light by frequency doubling." Licentiate thesis, KTH, Physics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1795.

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Quasi-three-level lasers in neodymium-doped crystals such asNd:YAG, Nd:YLF and Nd:YVO₄have received a great deal of interest becausethey allow generation of blue light by frequency doubling. Forsolid-state blue laser sources, there exist numerousapplications as in high-density optical data storage, colourdisplays, submarine communication and biologicalapplications.

Efficient lasing on quasi-three-level transitions at 900-950nm in Nd-doped crystals is considerably more difficult toachieve than on the stronger four-level transitions at 1-1.1µm. The problems with these quasi-three-level transitionsare a significant reabsorption loss at room temperature and avery small stimulated emission cross section. This requires atight focusing of the pump light, which is achieved byend-pumping with high-intensity diode lasers.

n this thesis, progress in diode-pumped solid-state lasersfor generation of blue light by frequency doubling has beenmade. Nd:YAG lasers at the 946 nm transition have been builtand a maximum power of 7.0 W was obtained. By inserting a thinquartz etalon in the laser cavity, the938.5 nm laser linecould be selected. An output power of 3.9 W was obtained.

By using nonlinear crystals, frequency-doubling of laserlight at both 946 nm and 938.5 nm by second harmonic generation(SHG) was achieved. SHG of the 946 nm transition gives bluelight at 473 nm. Efficient generation of blue light has beenachieved in periodically poled KTP, both in single-passextra-cavity and intracavity configurations. More than 0.5 Wwas obtained at 473 nm by intracavity doubling. Intracavity SHGof the 938.5 nm transition gave slightly more than 200 mW at469 nm.

The influence of energy-transfer upconversion (ETU) is adetrimental effect in Nd-doped lasers. An analytical model hasbeen developed for continuous wave quasi-three-level lasersincluding the influence of ETU. The results of the generaloutput modelling are applied to a laser with Gaussian beams,and rigorous numerical calculations have been done to study theinfluence of ETU on threshold, output power, spatialdistribution of population-inversion density and fractionalthermal loading. The model is applied to a laser operating at946 nm in Nd:YAG, where thermal lensing and the dependency oflaser-beam size are investigated in particular. A simple modelfor the degradation of laser beam quality from a transversallyvarying saturated gain is also proposed, which is in very goodagreement with measurements of the laser in a plane-planecavity.

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Faria, Irval Cardoso de. "Geração de pulsos laser ultracurtos por auto injeção no laser de Nd : YAG." [s.n.], 1986. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277323.

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Orientadores: Antonio G. J. Balbin Villaverde, Carlos Henrique de Brito Cruz
Dissertação (mestrado) - Universidade Estadual de Campinas. Instituto de Fisica Gleb Wataghin
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Abstract: Not informed.
Mestrado
Física
Mestre em Física

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11

Charton, Stephane. "Contribution à l'étude du contrôle en ligne des opérations de soudage par laser ND : Yag impulsionnel." Dijon, 1999. http://www.theses.fr/1999DIJOS047.

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Cette thèse est consacrée à l'étude d'un système de contrôle en ligne des assemblages par laser Nd 3 : YAG pulsé. Lors d'une opération de soudage, l'interaction laser-matière est à l'origine de l'émission de signaux (optiques, acoustiques, électriques, thermiques), caractéristiques de son comportement. Le contrôle en ligne est basé sur l'hypothèse que leurs évolutions, mesurées par des capteurs tels que des photodiodes ou des microphones, doivent être corrélées aux défauts de soudure. Le contrôle qualité d'un assemblage par faisceau laser peut être assuré par la qualification préalable de la machine, et par le suivi en ligne de l'opération de soudage proprement dite. La similitude des signaux issus des lasers pulsés (machine et interaction), nous a conduits à développer un système spécifique d'acquisition et de traitement de données. L'utilisation d'outils de traitement du signal (transformation de Fourier, transformation en ondelettes) associés à des techniques de classification de données (polytopes de contraintes), introduit une approche innovante du contrôle en ligne. La détermination des paramètres discriminants (corrélation signaux/défauts) devient ainsi automatique et non subjective. Le prototype réalisé peut être utilisé pour la détection de tout type de défaut, puisque l'opérateur de classification retenu est supervise et repose donc sur une phase d'apprentissage. Il a été validé sur des défauts de soudure simples à maitriser, pour être finalement appliqué à un problème de contrôle de fabrication au département fabrications et technologies nucléaires du centre d'études de Valduc du Commissariat à l'energie atomique.

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Ayyalasomayajula, Narasimha Rao. "Nd:YAG mini slab laser hybrid integration and Raman sensor application /." Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10437.

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Thesis (Ph. D.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains xiv, 170 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 159-164).

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Medeiros, Júnior Rui. "Avaliação Clínica de Pacientes Submetidos à Frenectomias Labiais com Laser de Nd:YAG e Cirurgia Convencional." Universidade Federal de Pernambuco, 2012. https://repositorio.ufpe.br/handle/123456789/12609.

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O objetivo do estudo foi comparar resultados clínicos pré, trans e pós-operatórios relacionados às frenectomias labiais realizadas pela técnica convencional e com laser de Nd:YAG. Quarenta pacientes foram distribuídos em 2 grupos: G1 - cirurgia pela técnica convencional (n=22) e G2 – cirurgia com laser de Nd:YAG (n=18). O tipo de inserção do frênulo, sangramento, tempo cirúrgico, necessidade de sutura, medo pré-operatório e desconforto pós-operatório foram avaliados. A maioria dos frênulos (90%) foi classificado como de inserção papilar ou transpapilar e não houve diferença relacionada ao medo pré-operatório entre os grupos (p=0,593). Os pacientes do G2 não necessitaram de sutura (p<0,001) e apresentaram ausência de sangramento trans-operatório na maioria dos casos (p<0,001), acarretando em uma redução do tempo cirúrgico (p<0,001). Este estudo revelou algumas vantagens da terapia realizada com laser de Nd:YAG relacionadas ao ato operatório, entretanto não foi observada uma superioridade nos resultados clínicos pós-operatórios de dor e função oral.

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CANUTO, Thais Sayonara Romão. "Avaliação comparativa do uso do laser de Nd:YAG ou cirurgia convencional no tratamento de hiperplasia fibrosa inflamatória." Universidade Federal de Pernambuco, 2017. https://repositorio.ufpe.br/handle/123456789/26360.

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O objetivo desse estudo preliminar foi avaliar e comparar resultados clínicos pré, trans e pós-operatórios relacionados às exéreses de lesões diagnosticadas como hiperplasia fibrosa realizadas pela técnica convencional e com laser de Nd:YAG. Vinte pacientes foram distribuídos em dois grupos: G1 - cirurgia com laser de Nd:YAG (n=10) e G2 – cirurgia pela técnica convencional (n=10). O tamanho da lesão de hiperplasia fibrosa, consistência, tipo de inserção, medo pré-operatório, quantidade de tubetes anestésicos, intensidade de sangramento, tempo cirúrgico, necessidade de sutura e desconforto pós-operatório foram avaliados. Os dados obtidos foram avaliados com valor de significância de 5% (p < 0,05). Não houve diferença relacionada ao medo pré-operatório entre os grupos (p=0,485). Do ponto de vista transcirúrgico foi observado um tempo médio de 2,7 minutos para o procedimento a laser contra 7,8 minutos no procedimento convencional (p=0,037). Os pacientes do grupo G1 apresentaram menor intensidade de sangramento (p=0,001), não necessitaram de sutura (p<0,001) e menor uso de analgésico no pós-cirúrgico (p=0,05). A presente pesquisa aponta vantagens nos resultados clínicos trans e pós-operatórios em tratamentos de hiperplasias fibrosas realizadas com laser de Nd:YAG, quando comparados com a cirurgia convencional. Estudos adicionais com um maior número de pacientes são necessários para melhor elucidar as vantagens da cirurgia a laser.
The aim of the study was to compare pre, trans and post surgery clinical results related to the exeresis of lesions diagnosed as imflammatory fibrous hyperplasia performed by the conventional technique compared to Nd: YAG laser. Twenty patients were divided into 2 groups: G1 - Nd: YAG laser surgery (n = 10) and G2 - conventional surgery (n = 10). The data were evaluated with a significance level of 5% (p <0.05). From the transsurgical point of view, an average time of 2.7 minutes was observed for the laser procedure versus 7.8 minutes in the conventional procedure (p = <0.05). Patients in the G1 group had less bleeding (p = <0.05), discomfort only in the first hour after the surgical procedure and need for analgesics in only 10% of the patients, in the first 6 days after the procedure. Regarding the G2 group, there was a need for suture in all the exesions (p> 0.05), a greater bleeding and 50% of the patients used analgesics until eight days after surgery. The results of the present study indicate advantages in the accomplishment of exéreses of IFH lesions with the use of Nd:YAG laser when compared to conventional surgery. Additional studies with a greater number of patients are needed to better elucidate the advantages of laser therapy.

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Chan, Ambrose. "Neodymium:yag laser induced pulpal anaesthesia : a study investigating clinical efficacy and effects in teeth." Thesis, The University of Sydney, 1997. http://hdl.handle.net/2123/4634.

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Silva, André César da. "Desenvolvimento de um laser pulsado de Nd : YAG de alta radiância para aplicações em óptica não-linear." Instituto Tecnológico de Aeronáutica, 1988. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=1883.

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Foi projetada uma cavidade óptica estável incorporando um telescópio de magniticação 3, para a obtenção de um laser pulsado de Nd:YAG de alta radiância. São verificadas as seguintes vantagens deste tipo de cavidade sobre as cavidades usuais: 1) a potência do laser é menos sensível ao alinhamento dos espelhos; 2) permite o casamento do volume do modo fundamental transversal com o volume do meio ativo, possibilitando a extracação de máxima energia neste modo; 3) o fator de estabilidade pode ser ajustado pela defocagem do telescópio para a condição de máxima estabilidade; 4) as caracteristicas do feixe são insensíveis às flutuações da lente térmica, às distância e ao arranjo dos componentes na região do feixe expandido; 5) oferece alta reprodutibilidade dospulsos de laser em termos de qualidade óptica, independente da taxa de repetição ou da energia de bombeamento.

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Crespo, Gillian da Silva [UNESP]. "Influência da potência de laser Nd: YAG na soldagem do aço inoxidável duplex UNS S32205." Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/113854.

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Conduziu-se um estudo da soldagem laser na condição “bead on plate” no aço inoxidável duplex UNS S 32205 na forma de chapas com 3,0 x 20 x 45 mm (A x L x P). Realizou-se 12 soldas em atmosfera de gás argônio com fluxo de gás de 15 l/min, diâmetro de feixe de 0,2 mm, ângulo de 90º, taxa de repetição de 9 Hz, velocidade de soldagem de 150 mm/min, profundidades de foco iguais a 1,0; 1,5 e 2,0 mm abaixo da superfície da peça e energia do pulso (Ep) fixada em 6,0 J. A variação de potência foi obtida variando as larguras temporais (Lt) em valores de 4, 6, 8 e 10 ms. Os resultados foram analisados com base na relação entre potência, geometria do cordão de solda, balanço de fases ferrita/austenita, dureza Vickers e análise química. Para revelação dos metais de solda utilizou-se reagentes Behara modificado e eletrolítico com solução oxálica 10%. As medidas de geometria (largura e profundidade) dos cordões de solda foram realizadas através de imagens obtidas através de câmera digital em um microscópio óptico comum. O processamento das imagens foi realizado através do programa “Image J”, um software de edição de imagens de domínio público pautado na plataforma Java. Os maiores valores de largura e profundidade foram encontrados nos maiores valores de potência e o aumento do valor da posição focal acarretou em um aumento da variabilidade da média desses parâmetros geométricos. O valor do balanço ferrita/austenita para o metal base e metal de solda foi de 52/48 % e 70/30 % respectivamente. O valor médio da dureza para o metal base foi igual a 286 HV. Nos metais de solda e nas ZTAs a posição focal -1,5 mm apresentou os menores valores de dureza, independente da potência utilizada. A composição química dos elementos de liga não apresentou grandes variações entre os dados de fábrica e os obtidos para o metal base e o metal de solda
We carried out a study of laser welding provided bead on plate in duplex stainless steel UNS S 32205 in the form of plates with 3,0 x 20 x 45 mm (H x W x D). 12 welds was performed in argon gas flow of 15 l/min, beam diameter 0,2 mm, angle of 90°, repetition rate of 9 Hz, welding speed of 150 mm / min, gas depths focus equal to 1,0; 1,5 and 2,0 mm below the surface of the workpiece and the pulse energy (Ep) set at 6,0 J. The power variation was obtained by varying the time width (Lt) at values of 4, 6, 8 and 10 ms. The results were analyzed based on the relationship between power, weld bead geometry, balance ferrite/austenite phases, Vickers hardness and chemical analysis. For structure revelation of the weld metals used both Behara modified and electrolyte with 10% oxalic solution reagents. Measures of geometry (width and depth) of the weld beads were made using images taken by digital camera on an ordinary optical microscope. Image processing was performed using the Image J program, a graphics editing software in the public domain lined on Java platform. The highest values of width and depth were found in higher values of power and increasing the value of the focal position resulted in an increase in the variability of the mean of these geometrical parameters. The balance sheet value of the ferrite/austenite for the base metal and weld metal was 52/48 % and 70/30% respectively. The average hardness for the base metal was equal to 286 HV. In weld metals and the ZTAs focal position -1.5 mm had the lowest hardness values, regardless of power used. The chemical composition of alloying elements did not show large variations between factory data and those obtained for the base metal and the weld metal

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Crespo, Gillian da Silva. "Influência da potência de laser Nd: YAG na soldagem do aço inoxidável duplex UNS S32205 /." Ilha Solteira, 2014. http://hdl.handle.net/11449/113854.

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Orientador: Vicente Afonso Ventrella
Co-orientador: Ruís Camargo Tokimatsu
Banca: Wyser José Yamakami
Banca: Angelo Caporalli Filho
Resumo: Conduziu-se um estudo da soldagem laser na condição "bead on plate" no aço inoxidável duplex UNS S 32205 na forma de chapas com 3,0 x 20 x 45 mm (A x L x P). Realizou-se 12 soldas em atmosfera de gás argônio com fluxo de gás de 15 l/min, diâmetro de feixe de 0,2 mm, ângulo de 90º, taxa de repetição de 9 Hz, velocidade de soldagem de 150 mm/min, profundidades de foco iguais a 1,0; 1,5 e 2,0 mm abaixo da superfície da peça e energia do pulso (Ep) fixada em 6,0 J. A variação de potência foi obtida variando as larguras temporais (Lt) em valores de 4, 6, 8 e 10 ms. Os resultados foram analisados com base na relação entre potência, geometria do cordão de solda, balanço de fases ferrita/austenita, dureza Vickers e análise química. Para revelação dos metais de solda utilizou-se reagentes Behara modificado e eletrolítico com solução oxálica 10%. As medidas de geometria (largura e profundidade) dos cordões de solda foram realizadas através de imagens obtidas através de câmera digital em um microscópio óptico comum. O processamento das imagens foi realizado através do programa "Image J", um software de edição de imagens de domínio público pautado na plataforma Java. Os maiores valores de largura e profundidade foram encontrados nos maiores valores de potência e o aumento do valor da posição focal acarretou em um aumento da variabilidade da média desses parâmetros geométricos. O valor do balanço ferrita/austenita para o metal base e metal de solda foi de 52/48 % e 70/30 % respectivamente. O valor médio da dureza para o metal base foi igual a 286 HV. Nos metais de solda e nas ZTAs a posição focal -1,5 mm apresentou os menores valores de dureza, independente da potência utilizada. A composição química dos elementos de liga não apresentou grandes variações entre os dados de fábrica e os obtidos para o metal base e o metal de solda
Abstract: We carried out a study of laser welding provided "bead on plate" in duplex stainless steel UNS S 32205 in the form of plates with 3,0 x 20 x 45 mm (H x W x D). 12 welds was performed in argon gas flow of 15 l/min, beam diameter 0,2 mm, angle of 90°, repetition rate of 9 Hz, welding speed of 150 mm / min, gas depths focus equal to 1,0; 1,5 and 2,0 mm below the surface of the workpiece and the pulse energy (Ep) set at 6,0 J. The power variation was obtained by varying the time width (Lt) at values of 4, 6, 8 and 10 ms. The results were analyzed based on the relationship between power, weld bead geometry, balance ferrite/austenite phases, Vickers hardness and chemical analysis. For structure revelation of the weld metals used both Behara modified and electrolyte with 10% oxalic solution reagents. Measures of geometry (width and depth) of the weld beads were made using images taken by digital camera on an ordinary optical microscope. Image processing was performed using the "Image J" program, a graphics editing software in the public domain lined on Java platform. The highest values of width and depth were found in higher values of power and increasing the value of the focal position resulted in an increase in the variability of the mean of these geometrical parameters. The balance sheet value of the ferrite/austenite for the base metal and weld metal was 52/48 % and 70/30% respectively. The average hardness for the base metal was equal to 286 HV. In weld metals and the ZTAs focal position -1.5 mm had the lowest hardness values, regardless of power used. The chemical composition of alloying elements did not show large variations between factory data and those obtained for the base metal and the weld metal
Mestre

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Shori, Ramesh K. "A Study of Spiking and Relaxation Oscillations in Nd:YAG Laser Using Measured Laser Parameters." PDXScholar, 1993. https://pdxscholar.library.pdx.edu/open_access_etds/4641.

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It was shown analytically and experimentally that when the cavity losses are perturbed, the output intensity experiences an amplitude modulation or becomes a regular train of spikes, with the frequency depending on both the frequency of perturbation as well as pump power. Coupled nonlinear rate equations including the cavity perturbation term, are solved numerically by a Runga-Kutta method using experimentally-measured parameter values for Nd: Y AG laser. A continuously pumped Nd: Y AG laser was used to verify this theory.

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Lopes, Angélica Marquezim. "Influência de aplicações do "laser" érbio:YAG sobre a viabilidade microbiana, sua resistência a drogas e atividade hemolítica /." Araçatuba, 2003. http://hdl.handle.net/11449/96168.

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Resumo: A atividade antimicrobiana do laser Er:YAG foi avaliada sobre biofilme bacteriano constituído por Escherichia coli ATCC 8739, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 e 3 cepas de Fusobacterium nucleatum e sobre biofilme de microrganismos salivares. Os biofilmes foram submetidos à ação do laser a 1,2 W e 10 Hz por 5, 10, 15, 20, 30 e 60 s e fez-se a avaliação da microbiota residual em ágar sangue, em anaerobiose. O biofilme salivar se mostrou mais sensível nos primeiros tempos de irradiação. A redução microbiana em relação ao controle foi estatisticamente significativa entre todos os tempos testados. Avaliou-se também a ação do laser Er:YAG sobre 7 cepas de Fusobacterium nucleatum inoculadas sobre a superfície de corpos-de-prova (5mmX4mm) de dentes extraídos. Fez-se a aplicação do laser nos mesmos parâmetros físicos mencionados anteriormente, durante 15 s, levando à eliminação total do conteúdo séptico. O estudo avaliou também a irradiação do laser de Er:YAG durante tempos subinibitórios sobre a atividade hemolítica e susceptibilidade de 9 cepas de Fusobacterium nucleatum a amoxicilina, eritromicina, metronidazol e tetraciclina. Após a irradiação do laser, determinou-se a concentração inibitória mínima (CIM) para as drogas através do método de diluição em ágar. A ação do laser sobre a atividade hemolítica foi determinada em sangue humano. Verificou-se que o laser Er:YAG não afetou a atividade hemolítica de Fusobacterium nucleatum, que se mostrou α-hemolítica, tampouco a susceptibilidade a drogas dos isolados testados.
Abstract: Antimicrobial activity of Er:YAG laser was evaluated on a bacterial biofilm constituted by Escherichia coli ATCC 8739, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 and 3 strains of Fusobacterium nucleatum and on biofilm produced by salivary microorganisms. Biofilms were irradiated by Er:YAG laser, 1,2 W and 10 Hz, for 5, 10, 15, 20, 30, and 60 s and the evaluation of residual contamination was performed on blood agar, under anaerobiosis. It was verified that salivary biofilm showed to be more susceptibility to the Er:YAG laser in shorter periods of laser irradiation. Bacterial reduction was significative in all tested periods of irradiation. The activity of Er:YAG laser was also evaluated on 7 strains of Fusobacterium nucleatum inoculated on samples of human dentin (5mm X 4mm), obtained from extracted teeth. The laser was used following the same physical parameters, as previously described, for 15 s, leading to complete elimination of their septic content. The study also evaluated the effects of subinibitory irradiation of Er:YAG laser on bacterial susceptibility of 9 strains of Fusobacterium nucleatum to antimicrobial drugs (amoxicillin, erythromycin, metronidazole, tetracycline) and hemolysis. Thus, after laser irradiation, the minimal inhibitory concentration of antimicrobial drugs was determined by using an agar dilution method. The influence of laser on hemolysis was carried out on human blood. It was verified that Er:YAG laser did not produce any measurable effect on hemolytic activity and the microbial susceptibility to tested antimicrobial drugs.
Orientador: José Ricardo Kina
Coorientador: Elerson Gaetti Jardim Júnior
Mestre

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Feitosa, Fernanda Alves [UNESP]. "Efeitos de lasers de alta potência na superfície de cerâmicas vítreas de dissilicato de lítio e sua resistência de união à dentina humana." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/139434.

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O objetivo desse estudo foi avaliar a eficiência da irradiação com lasers de alta potência e a influência da aplicação do silano previa ou posteriormente à irradiação com os lasers na resistência de união entre cerâmica vítrea de dissilicato de lítio, cimento resinoso e dentina humana. Foram confeccionados 50 espécimes tronco-cônicos de cerâmica (n=10), divididos aleatoriamente em 5 grupos: 1- Controle- Condicionamento com ácido hidrofluorídrico 10% por 1 min e aplicação do silano; 2- Er:YAG – irradiação com laser Er:YAG (200 mJ e 10 Hz), seguido do condicionamento com ácido hidrofluorídrico 10% por 1 min e aplicação do silano; 3- Silano + Er:YAG – Condicionamento com ácido hidrofluorídrico 10% por 1 min, aplicação do silano e irradiação com laser Er:YAG nos mesmo parâmetros do grupo anterior; 4- Nd:YAG – irradiação com laser Nd:YAG (120 mJ e 10 Hz), seguido de condicionamento com ácido hidrofluorídrico 10% por 1 min e aplicação do silano, 5- Silano + Nd:YAG - Condicionamento com ácido hidrofluorídrico 10% por 1 min, aplicação do silano e irradiação com laser Nd:YAG nos mesmo parâmetros do grupo anterior. Após os tratamentos os espécimes cerâmicos foram cimentados com cimento resinoso de presa dual à superfície de dentina de 50 molares humanos incluídos em resina acrílica ativada quimicamente. Após armazenamento por 24 h foi realizado o ensaio de tração em máquina de ensaios universais com célula de carga de 10 KgF e velocidade constante de 1mm/min. Os dados obtidos foram submetidos à ANOVA 2-fatores e teste de Dunnet (α=5%). A análise dos padrões de fratura foram analisadas em estereomicroscopio. Adicionalmente foram confeccionados 15 espécimes em cerâmica no formato cilíndrico, submetidos aos mesmo tratamentos dos grupos anteriores (n=3) e utilizados para análise do ângulo de contato e análise em microscópio eletrônico de varredura. O teste de Dunnet mostrou diferenças significativas entre o grupo controle (9,42 ± 2,27 MPa) e os grupos Er (19,25 ± 3,7 MPa) e Sil+Er (14,11 ± 4,11 MPa). A análise de variância (p<5%) para os fatores Tipo de Laser (p<0,0001) e Técnica de Silanização (p=0,0002) mostraram diferenças significativas para os dois fatores, porém não para sua interação. Assim, a irradiação com Er:YAG (16,68 MPa) mostrou-se mais eficiente que a irradiação com Nd:YAG (8,19 MPa). A técnica de silanização posterior à irradiação com laser (14,46 MPa) também se mostrou superior à silanização previa (10,41 MPa). Quanto à análise de fraturas, o grupo Controle teve prevalência de falhas adesivas em dentina e em cerâmica; os grupos Nd, Sil + Nd e Sil + Er tiveram prevalência de falhas adesivas em cerâmica, e o grupo Er apresentou predominância de falhas coesivas no cimento. A análise do ângulo de contato foi submetida aos testes ANOVA 1-fator e Tukey, apresentando diferenças significativas entre os grupos (p<0,0001). Os grupos com silanização prévia (Sil + Er = 45,60b graus; Sil + Nd = 52,10b graus) apresentaram ângulos de contato superiores aos demais, e semelhantes entre si. As imagens de Microscopia Eletrônica de Varredura mostram a presença da camada de silano sobre a superfície cerâmica no grupo Sil + Nd, e uma aparente fundição à superfície cerâmica no grupo Sil + Er. Para os Grupos Er e Nd foi possível verificar modificações no padrão normal da estrutura da cerâmica, entremeadas por áreas semelhantes ao padrão convencional do grupo Controle após condicionamento com ácido hidrofluorídrico. Conclui-se que o tratamento com laser de Érbio associado ao condicionamento com ácido hidrofluorídrico a 10% por 1 min apresenta os melhores resultados de resistência de união e ângulo de contato. O tratamento com silano previamente à irradiação melhorou a resistência de união em relação ao grupo Controle apenas quando associado ao laser de Érbio.
The aim of this study was to evaluate the efficiency of irradiation with high-power lasers and the influence of silane application before or after irradiation with lasers on the bond strength between lithium disilicate glass-ceramic, resin cement and human dentin. Fifty truncated-cones ceramic specimens (n=10) were randomly divided into 5 groups: Control- etching with hydrofluoric acid 10% for 1 min and application of silane; 2- Er - Er:YAG laser irradiation (200 mJ and 10 Hz), followed by etching with hydrofluoric acid 10% for 1 min and application of silane; 3- Sil + Er - etching with hydrofluoric acid 10% for 1 min, silane application and irradiation with Er: YAG laser in the same parameters as the previous group; 4- Nd:YAG laser - irradiation with Nd: YAG laser (120 mJ and 10 Hz), followed by etching with hydrofluoric acid 10% for 1 min and application of the silane, 5- Sil + Nd- Etching with hydrofluoric acid 10% for 1 min, silane application and irradiation with Nd: YAG laser on the same parameters as the previous group. After treatment, the ceramic specimens were cemented with dual cure resin cement to the dentin of 50 human molars included in acrylic resin. After storage for 24 h it was submitted to tensile test in a universal testing machine with 10 kgf load cell and constant speed of 1 mm/min. Data were submitted to ANOVA 2-way and Dunnet test (α = 5%). The analysis of fracture patterns were analyzed in stereomicroscope. In addition were made 15 ceramic specimens in cylindrical shape, subjected to the same treatment of the above groups (n = 3) and used for analysis of the contact angle analysis and scanning electron microscope. The Dunnet test showed significant differences between Control group (9.42 ± 2.27 MPa) and Er group (19.25 ± 3.7 MPa) and Sil + Er (14.11 ± 4.11 MPa). ANOVA 2-way (p <5%) for Laser Type (p <0.0001) and Technical of Silanization (p = 0.0002) showed significant differences for both factors, but not for their interaction. Thus, the irradiation with Er:YAG laser (16,68 MPa) was more effective than irradiation with Nd:YAG laser (8,19 MPa). The technique of silanization after laser irradiation was more effective (14,46 MPa) than the previous silanization (10,41 MPa). The analysis of fractures showed a prevalence of adhesive failures on dentin and ceramic for the Control group; Nd, Sil + Nd e Sil + Er had a prevalence of adhesive failures in ceramics, and Er group presented predominance of cohesive failures in cement. The analysis of contact angle was submitted to ANOVA 1-way and Tukey test, with significant differences between the groups (p <0.0001). Groups with silanization previous to laser irradiation (Sil + Er = 45,60b degrees; Sil + Nd = 52,10b degrees) had contact angles greater than the other groups. The Scanning Electron Microscopy images showed the presence of a silane layer on the ceramic surface in Sil + Nd group, and an apparent casting of the ceramic surface in Sil + Er group. For Er and Nd Groups was possible to see changes in the normal pattern of ceramic structure, interspersed with areas similar to conventional standard control group after etching with hydrofluoric acid. It is concluded that treatment with Er:YAG laser associated with etching with hydrofluoric acid at 10% for 1 min gives the highest bond strength results and the lower contact angle, resulting in a recommended treatment. Treatment with silane previously to laser irradiation improved bond strength only when associated with the Er:YAG laser, which probably occurred by the efficiency of Er: YAG laser irradiation, and not due to the silanization technique.

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Senne, Firmani Mello Bento de. "Capsulotomia posterior unilateral : alterações de função e capacidade visual na vida diaria." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/311234.

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Orientador: Edmea Rita Temporini Nastari
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas
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Resumo: Realizou-se um estudo transversal com intervenção com os objetivos de identificar a influência da capsulotomia posterior unilateral com Neodímio: Ítrio-Alumínio-Granada (Nd:YAG) laser na função visual e em relação à percepção de dificuldades nas atividades diárias, e verificar a relação entre as medidas subjetivas e objetivas da função visual após a intervenção. A amostra, prontamente acessível, foi composta por 48 pacientes entre 40 e 80 anos, média de 68 anos, mediana de 70 anos, pseudofácicos uni ou bilaterais, com opacificação de cápsula posterior e acuidade visual menor ou igual a 0,30 (logMAR) em um olho, atendidos consecutivamente em um hospital universitário no Brasil. Todos os pacientes foram submetidos a capsulotomia posterior com Nd:YAG laser. Um questionário, elaborado a partir de estudo exploratório, foi aplicado antes e depois da intervenção. Após a capsulotomia posterior, a acuidade visual e a estereoacuidade melhoraram significativamente. Na percepção dos sujeitos, houve redução das dificuldades relacionadas às atividades diárias ligadas à visão, exceto passar roupas, tomar banho sem ajuda e pentear os cabelos. As medidas objetivas e a auto-avaliação da visão apresentaram congruência de resultados e todos os pacientes declararam ter valido a pena a realização do procedimento laser
Abstract: An interventional survey was conducted to assess the influence of Neodymium: Yttrium-Aluminium-Garnet (Nd: YAG) laser unilateral posterior capsulotomy on visual function and perception of difficulties with vision-related daily life activities, and to verify the association between objective and subjective measures of visual function after intervention. The readily accessible sample comprised 48 patients aged between 40 and 80 years, with uni- or bilateral pseudophakia, posterior capsule opacification and visual acuity equal to or less than 0,30 (logMAR) in one eye, consecutively seen at a Brazilian university hospital. All the patients were submitted to posterior capsulotomy by Nd:YAG laser. Before and after intervention, patients were asked to answer a questionnaire developed from data obtained in an exploratory study. After posterior capsulotomy, visual acuity and stereoacuity improved significantly. According to the subjects' perception, they found less difficulty in vision-related daily activities, except for ironing, bathing without help and combing the hair. Objective measures of visual function and self-rated visual function showed congruent results after intervention. All the subjects interviewed stated that the posterior capsulotomy procedure had been ¿worthwhile¿
Doutorado
Oftalmologia
Doutor em Ciências Médicas

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23

SAINTE-CATHERINE, CLAUDE. "Etude des possibilites d'applications des lasers nd-yag de forte puissance aux traitements de surface." Paris, ENMP, 1990. http://www.theses.fr/1990ENMP0255.

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Le faisceau des lasers nd-yag presente l'avantage par rapport aux co#2 de pouvoir etre transporte par des fibres optiques. Le principal inconvenient de ce type de laser pour le traitement des materiaux etait jusqu'alors les puissances moyennes assez faibles. Le projet eureka eu-226 a justement pour objectif de developper des sources laser nd-yag de forte puissance. L'absorptivite des surfaces metalliques est plus elevee a 1,06 microns (nd-yag) qu'a 10,6. Le transfert d'energie laser-matiere est donc plus important dans le cas d'un laser nd-yag et l'emballement thermique moindre. Cela a ete mis en evidence par des mesures d'absorptivite en fonction de la temperature et par des cycles thermiques calcules. Ces avantages permettent la trempe superficielle des aciers sans revetement ni protection gazeuse donc sans pollution chimique. Les frequences de repetition (superieures a 100 hz) sont suffisamment elevees pour realiser des traitements pseudo continus. Le decoupage d'impulsions (pulse shaping) ne presente un interet que pour des impacts independants. La modelisation fds a permis, pour la trempe superficielle des aciers, de prevoir l'evolution temporelle des phases. L'objectif est de calculer les zones affectees thermiquement mais aussi dans le futur les contraintes residuelles et d'ameliorer les calculs thermiques par une meilleure adequation des variations de chaleur specifique ou de h avec la realite. Les depots par laser hpssl sont tout a fait envisageables si la frequence est suffisamment elevee pour maintenir la zone d'interaction en fusion

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Damião, Alvaro Jose. "Processo de deposição e propriedades de filmes de dióxido de titânio obtidos por "laser ablation"." [s.n.], 2002. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278417.

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Orientador: Mario Antonio Bica de Moraes
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Este trabalho descreve os estudos do processo de deposição a laser de TiO2, assim como algumas propriedades dos alvos utilizados e dos filmes depositados. O objetivo era a obtenção de filmes para serem utilizados como elemento de composição em componentes ópticos de precisão. Foram utilizados três diferentes lasers pulsados: CO2, Nd:YAG e Vapor de Cobre, oscilando nos comprimentos de onda tradicionais, ou seja, sem dobrar freqüências de emissão. A taxa de repetição dos lasers variou de 1 Hz para o laser de CO2 até 18 kHz para o laser de vapor de co-bre. Os lasers e a câmara de evaporação foram desenvolvidos no Instituto de Estudos Avançados IEAv - CTA, onde os trabalhos de deposição foram realizados. A espessura dos filmes depositados foi obtida por três processos diferentes: balança, osci-lador/cristal de quartzo e interferometria, a fim de verificar se havia influência do processo de de-posição no comportamento do cristal de quartzo. Como não houve influência, foram obtidos então os resultados de taxa de deposição, como função do tempo para diferentes condições de deposi-ção. Os alvos foram tratados termicamente, para verificar a influência do material de partida, não tendo sido observadas diferenças nos filmes obtidos. Os filmes foram caracterizados por téc-nicas ópticas (Método do Envelope), difração de raios X, XPS e microscopia eletrônica de varre-dura. Foram obtidos filmes uniformes, aparentemente sem os defeitos normalmente causados pela deposição a laser. Os filmes, como depositados, apresentaram alguma absorção, o que invia-biliza a sua utilização sem tratamento térmico
Abstract: This work presents the results of a laser deposition process of TiO2, target and thin film properties. The aim was to obtain thin films to be part of a multilayer coating for precision optical components. Three different pulsed lasers were used to deposit the films: CO2, Nd:YAG and Copper Vapor Lasers, LVC, all of them oscillating in their natural modes, i.e., without any apparatus to double the emission frequency. The repetition rate of the laser was as low as 1 Hz for CO2 and as high as 18kHz for LVC. The evaporation chamber and the lasers were developed at the Instituto de Estudos Avançados, IEAv-CTA, where the films were deposited. Mass measurement, quartz crystal oscillator and interferometry evaluated the films thick-ness, to check if the deposition process could affect the results obtained by the crystal oscillator. As no influence was detected, the crystal oscillator was used to measure the deposition rate of the films, as function of time, for different deposition conditions. The targets received a thermal treatment, to verify the influence of starting materials on the obtained films. The films were analyzed by Envelop Method (optical properties), X-ray, XPS and SEM. Uniform films were obtained, without the defects normally found when using laser deposi-tion. Films deposited at room temperature (as deposited) presented some absorption, which obliges the use of thermal treatment
Doutorado
Física
Doutor em Ciências

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25

LE, NEVE MARC. "Etude d'un laser nd : yag de forte energie pompe par diodes et declenche par absorbant saturable cr:yag." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10133.

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Nous etudions un laser pompe transversalement par diodes et declenche passivement. L'extraction de fortes energies et la demonstration de rendements eleves sont recherches. Les capacites de differentes matrices dopees neodyme a offrir des rendements d'absorption eleves sont analysees en fonction de leur spectre d'absorption. A cet effet, un code de calcul prealablement qualifie experimentalement, ainsi que les caracterisations effectuees permettent d'acceder a la repartition spatiale de l'energie des diodes dans une section du barreau. Une etude parametree du depot d'energie est effectuee. Nous caracterisons ensuite les absorbants saturables (cr#4#+:yag, colorants bdn) par l'etude de la saturation de l'absorption. La mesure simultanee de la transmission et de l'intensite de fluorescence avec le cr#4#+, nous permet de remettre en cause l'importance de l'absorption dans l'etat excite et de proposer une autre origine a l'absorption residuelle de ces sites aux fortes fluences d'excitation. En declenchement actif, le laser demontre une energie de sortie disponible de 80 mj soit un rendement optique d'environ 10%. Ces resultats sont bien ajustes a l'aide des equations du bilan. Le fonctionnement de ce laser est totalement multimode (longitudinal et transverse). Puis, nous etudions le declenchement passif. Le resonateur plan-concave multimode de base presente un comportement spatio-temporel tres complexe et non reproductible. L'impulsion de sortie comporte plusieurs composantes temporelles distinctes. La repartition d'energie dans le faisceau ne reproduit nullement la carte de depot d'energie. La competition entre les modes transverses est a l'origine de ce comportement. Pour s'en affranchir, il faut tendre vers un oscillateur monomode transverse. Nous y parvenons en definissant des cavites dont le rayon du mode fondamental est eleve. Ainsi, avec une cavite telescopique nous obtenons des impulsions stables temporellement et spatialement, tout en offrant des valeurs de rendement et d'energie interessantes. En declenchement actif et passif, les perspectives d'optimisation du rendement du laser sont egalement quantifiees

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Reda, Claude. "Cyclophotocoagulation transclérale de contact au laser Nd:Yag dans le traitement des glaucomes réfractaires : étude à propos de 47 cas." Montpellier 1, 1992. http://www.theses.fr/1992MON11194.

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FERREIRA, MARCUS V. L. "Estudo in vitro da fusao de hidroxiapatita e esmalte em superficies de esmalte humano pelo laser de Nd: YAG." reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10856.

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Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo

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28

Zhang, Tao. "Laser surface hardening of AISI 1518 alloy steel." Thesis, Nelson Mandela Metropolitan University, 2010. http://hdl.handle.net/10948/723.

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The laser surface hardening process will enhance the hardness profile of automotive components and ensure better process control and predictability of quality as compared to the conventional hardening processes. A 2KW Nd-YAG laser system was used to harden the surface of alloy steel with various process parameters (laser power, focal spot diameter and beam velocity). The results (microhardness, microstructure change and residual stress distribution) were measured and analyzed with Vickers microhardness tester, optical/electron microscope and hole-drilling residual stress equipment. Statistical analyses of the experimental data were used for explaining the relationships between process parameters, microhardness and microstructure. General thermal hardening was applied in the research to show the influence of heating temperature and cooling method on microstructure and mechanical properties. Also, the results were compared with laser surface hardening process from microhardness, microstructure and residual stress to show the advantage of laser surface hardening. Through analysis of the results of the laser surface hardening experiments, a suitable laser power density and interaction time for optimum hardening was obtained. The presented laser surface hardening process can also be applied to other alloy steel surface hardening process.

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Origo, Fabio Dondeo. "Cristalização epitaxial de ligas de SiGe sobre GaAs por laser pulsado." [s.n.], 2004. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278005.

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Orientador: Ivan E. Chambouleyron
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Neste trabalho se estudou pela primeira vez a cristalização e a epitaxia por laser pulsado para a obtenção de filmes de SixG e1-x(x = 0, 0.1, 0,25, 0,5, 0,75 e 1) sobre substratos de GaAs. Foram utilizados pulsos de laser de Nd:Yag ¿ l =532 nm ¿ com duração de 7ns e spot size de 2 a 3 mm. Camadas ou multicamadas amorfas de Ge, Si ou SiGe foram depositadas por , Ion Beam Sputtering sobre substratos epiready e não epiready de GaAs (100) à temperatura de 200 ºC. A espessura total dos filmes depositados era da ordem de 100 nm. Mostramos a eficácia da remoção de óxidos superficiais do GaAs (Ga2O3, As2O3 e As2O5) e contaminantes (C) através do bombardeamento do GaAs por feixe de H2+ (30 eV) após aquecimento a 350ºC. Demonstramos que filmes de a-Si0.1Ge0.9:H depositados com gás Kr são mais compactos que aqueles produzidos com Ar devido ao efeito de bombardeamento por partículas refletidas no alvo e por essa razão todos os filmes preparados para cristalização foram produzidos com Kr. Após irradiação com pulso entre 70 e 170 mJ, os filmes de Ge depositados sobre GaAs foram completamente liquefeitos por intervalo de até 20 ns e foram cristalizados. Dentro da área irradiada, quatro regiões foram identificadas, em ordem crescente da fluência ¿F- do laser: A) material que permaneceu amorfo (F<400 mJ/cm2), B) região policristalina (400 mJ/cm2 Abstract: In this work we studied, for the first time, the pulsed laser crystallization and epitaxy of SixGe1-x films (x = 0, 0.1, 0,25, 0,5, 0,75 and 1) on GaAs substrates. Nd:Yag laser pulses ( g =532 nm), 7 ns wide and 2 to 3 mm spot size, were applied. Amorphous layers and multilayers of Ge, Si or SiGe were deposited, by Ion Beam Sputtering, on epiready and nonepiready GaAs (100) substrates at 200ºC. The total thicknesses are close to 100 nm. We have shown the efficacy of superficial oxide removal (Ga2O3, As2O3 and As2 O5) and contaminants (C) bombarding the substrate surface with H2+ beam (30 eV) after heating at 350ºC. We demonstrated that a-Si0.1Ge0.9:H films deposited with Kr are more compact than those produced with Ar due to the bombardment effect by particles reflected on the target; therefore, all the films prepared for laser crystallization were deposited with Kr. After laser irradiation with 70mJ-170 mJ pulses, the SiGe films were completely liquefied up to 20 ns and crystallized. Inside the irradiated area, four different regions were identified according to the increasing of laser fluency - F: A) amorphous material (F<400 mJ/cm2 ); B) polycrystalline material (400 mJ/cm2 Doutorado
Física
Doutor em Ciências

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30

Abeil, Cécile Caumes. "Le laser ND-YAG dans le traitement du segment antérieur de l'oeil : chirurgie du glaucome et de la cataracte." Montpellier 1, 1988. http://www.theses.fr/1988MON11279.

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Sanitá, Willian Roberto Valicelli. "Análise de juntas soldadas de aço API 5L X-70 com laser Nd : YAG pulsado /." Ilha Solteira, 2017. http://hdl.handle.net/11449/149831.

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Orientador: Vicente Afonso Ventrella
Resumo: We carried out a study of laser welding provided "bead on plate" in micro-alloyed steel ARBL API 5L Gr. X70 in the form of plates with 1,0 x 20 x 120 mm (H x W x D). 12 welds was performed in argonic gas flow of 15 l/min, beam diameter 0,2 mm, angle of 90°, repetition rate of 9, 8, 7, 6 and 5 Hz, welding speed of 1 mm/s, gas depths focus equal to 0,57 mm below the surface of the workpiece and the pulse energy (Ep) set at 10,0 J. The time width (Lt) set at 10 ms. The heat input was varied at 90, 80, 70, 60 and 50 J/mm. The results were analyzed based on the relationship between power, weld bead geometry, corrosion, Vickers hardness, chemical analysis and microstructure. For structure revelation of the weld metals used both Nital 5%. Measures of geometry (width and depth) of the weld beads were made using images taken by digital camera on an ordinary optical microscope. Microscopy tests were carried out using a scanning electron microscope in a backscattered detector (BSD), in order to verify with greater clarity the microstructures of the samples. For verification of mechanical strength was tensile test on samples and base metal without notch insertion. For verification of hardness were analyzed four parameters being three horizontal lines and a vertical line in the center of the weld bead. To verify the corrosion, a potentiostat test was conducted for potentiodynamic polarization test where the polarization curves were analyzed. The greatest values of depth width were found i... (Resumo completo, clicar acesso eletrônico abaixo)
Mestre

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32

Girard, Karen. "Etude de la création de défauts volumiques générés pendant la solidification de soudures réalisées par faisceau laser Nd : YAG impulsionnel - application au soudage du tantale." Dijon, 1999. http://www.theses.fr/1999DIJOS067.

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Ce travail a pour but d'étudier la formation des défauts volumiques apparus au cours de la solidification de points de soudure réalisés par faisceau laser Nd:YAG sur tantale. La fin d'une impulsion laser se caractérise par la phase de solidification pendant laquelle le métal fondu rebouche le capillaire de soudage tout en se refroidissant et en se solidifiant. Selon les conditions opératoires, les modes de remplissage et de refroidissement sont différents et peuvent induire des défauts volumiques dans les soudures. Nous avons étudié ces défauts expérimentalement par microscopie électronique et par radiographie éclair. Ces analyses ont mis en évidence deux catégories de défauts : des porosités et des cavités. Les porosités prennent des formes de petites bulles qui sont piégées dans la matière solidifiée. Les cavités sont des zones sans matière qui sont liées au mode de remplissage du capillaire par le métal fondu qui se refroidit très vite. Nous avons modélisé l'apparition de ces défauts : le piégeage des porosités et la formation des cavités. Le principe du modèle du piégeage des porosités repose sur la comparaison de la durée de solidification de la soudure et de la durée de remontée d'une bulle de dimension connue à la surface du bain fondu. La durée de solidification est calculée grâce à l'équation de diffusion de la chaleur et tient compte d'une loi de remplissage linéaire au cours du temps. Les résultats permettent de prévoir les dimensions des porosités susceptibles d'être piégées dans la zone fondue. La formation des cavités a été modélisée grace à l'étude de l'écoulement du métal fondu à l'intérieur du capillaire avec le logiciel fluent. Les calculs sont basés sur l'équation de Navier-Stokes et tiennent compte des tensions superficielles et de la diffusion de la chaleur. Il apparait que sous l'effet des tensions superficielles, le métal rebouche le dessus du capillaire en emprisonnant une poche gazeuse à l'origine d'une cavité. Les résultats sont corroborés par l'observation in situ de la solidification de soudures de tantale en radiographie X éclair. Cette étude a donc permis de mieux comprendre les phénomènes rapides produits pendant la solidification de soudures et leurs conséquences.

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Mhalla, Taghrid. "Micro-ablation athermique de matériaux transparents par absorption multiphotonique avec une micro-puce laser amplifiée Nd : YAG à impulsions vertes sub-nanosecondes." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY059/document.

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Les microchip lasers à impulsions sub-nanosecondes peuvent être des alternatives intéressantes aux lasers à impulsions femtosecondes pour le micro-usinage des matériaux transparents par absorption multiphotonique. Ces lasers peuvent facilement atteindre les puissances crêtes nécessaires pour déclencher l'ablation de tous les matériaux, y compris les diamants, céramiques, plastiques, et des verres. En outre, ils sont de faible coût, avec un design compact et robuste. Dans cette thèse, un micro-chip laser Nd:YAG amplifié (532 nm, 300 ps) a été utilisé pour la micro-gravure et le marquage de différents types de matériaux transparents, comme le verre borosilicate D263, le verre BK7 et le thermoplastique SBS. L'analyse des résultats a montré un bon accord avec le modèle d'expulsion de matière suite à la génération d'un plasma provoqué par une absorption laser à deux photons. Une résolution sub-micronique de marquage a été obtenue à l'intérieur d'un verre de borosilicate. Des canaux microfluidiques pour capteurs optiques ont été gravés sur verre BK-7 comprenant des guides d'ondes réalisés par échange d'ionique. Des réseaux denses de micro-canaux ont été fabriqués à la surface de matériaux thermoplastiques avec une zone affectée par les effets thermiques limités à quelques micromètres. En conclusion, ce travail de thèse montre que l'utilisation de ce type de laser permet un micro-usinage de très haute résolution avec des effets thermiques limités
Microchip lasers with sub-nanosecond pulses are attractive alternative to femtosecond lasers for micromachining in transparent materials by multiphoton absorption. These lasers can easily reach pulse peak powers that are needed to trigger ablation in all materials, including diamond, ceramics, plastics, and glasses. In addition, they are low cost with compact and rugged design. In this thesis, a microchip laser (532 nm, 300 ps) has been used for micro-engraving and marking different types of transparent materials such as borosilicate D263, BK7, and SBS thermoplastic. Experimental resultsare rationalized by the model of matter explosion following the plasma generation induced by the laser two-photon absorption. Sub-micron resolution embedded marking is demonstrated inside borosilicate glass. Micro fluidic channels for optical sensors are engraved on BK-7 glass with ion-doped waveguides. Arrays of dense micro channels are fabricated at the surface of thermoplastics with a zone affected by thermal effects limited to the micron range. In summary, this thesis demonstrates that this type of laser can be efficiently used for high-resolution micro-machining transparent materials with minimal thermal effects

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LATRACH, LAHOUCINE. "Etude de la synchronisation en phase de deux lasers nd : yag par injection optique. application au laser source de l'interferometre virgo." Paris 11, 1996. http://www.theses.fr/1996PA112220.

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La detection directe des ondes de gravitation est possible a l'aide d'un interferometre de michelson. Pour atteindre la sensibilite requise, la source lumineuse qui illuminera cet interferometre doit etre puissante, stable et fiable. Le but de notre travail dans cette these et de rendre un laser prototype de puissance (laser esclave) stable et monofrequence. La technique utilisee est celle de verrouillage de phase par injection optique, le laser injecte est appele laser maitre. Cette technique a l'avantage de faire la selection des modes axiaux sans perte d'energie. En plus, le laser esclave acquiert toutes les caracteristiques spatiales et spectrales du laser maitre. Ce memoire comporte donc une etude fine de l'injection optique continue d'un laser de puissance. Le deroulement des etudes concernant cette technique a fait l'objet d'une analyse experimentale et d'un modele theorique. L'effet de l'injection optique sur la frequence et l'amplitude du laser est rapporte. Sa modelisation au point de vue de l'asservissement et celle de transfert de differents bruits est aussi au centre de notre discussion

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Conceição, Luciano Fernandes da [UNESP]. "Ocorrência de opacidade de cápsula posterior em cães pós-facoemulsificação, com ou sem a utilização de lente intraocular dobrável e efeitos do Nd: Yag Laser." Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/121864.

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A catarata elenca-se entre as afecções oculares mais freqüentes em cães, sendo a facoemulsificação o método que melhor se adequa à sua terapia. As opacidades de cápsula posterior (OCPs) estão entre as complicações mais comuns e se manifestam em semanas ou meses após a facectomia. Lentes intraoculares (LIOs), empregadas na correção da hipermetropia pós-cirúrgica, são citadas como úteis na prevenção das OCPs, especialmente as acrílicas dobráveis, com bordas truncadas ou quadradas. Entretanto, quando OCPs se estabelecem requerem-se capsulotomias como forma de tratamento. Em pacientes humanos, reconhecem-se os efeitos do Nd:YAG laser como técnica não invasiva e segura frente a tais intercorrências. Para se compararem resultados de olhos de cães que receberam lentes intraoculares acrílicas dobráveis com olhos de cães afácicos, após facoemulsificação, durante um período de 180 dias, utilizaram-se 20 cães de raças diversas, machos ou fêmeas, que variaram de 3 a 7 anos de idade, apresentando catarata juvenil , imatura ou madura (imatura n = 10 , madura n = 10) bilateral. Dois grupos (G1 = com implante de lente intraocular e G2 = sem implante de lente artificial) foram formados aleatoriamente e todos os cães tiveram ambos os olhos operados. Após a cirurgia, os pacientes foram avaliados, semanalmente, quanto a presença ou a ausência de sinéquias, discoria, pressão intraocular, inflamação uveal e presença ou não de opacidade de cápsula posterior durante um período de 180 dias. Aos 60, 90, 120, 150 e 180 dias após a cirurgia, imagens da cápsula posterior foram capturados para avaliação da sua opacidade. Olhos com score 2 ou 3 de opacidade foram submetidos à terapia de capsulotomia pelo Nd:YAG laser. Variáveis categóricas ordinais foram comparadas (G1 X G2) empregando-se o teste de qui-quadrado e o teste exato de Fisher. Variáveis quantitativas foram comparadas empregando-se ANOVA com pós teste de Tukey
Cataracts are among the most common eye diseases in dogs, being the phacoemulsification method the one that best suits in their therapy. The posterior capsule opacification (PCOs) are among the most common complications and manifest themselves in weeks or months after cataract surgery. Intraocular lenses (IOLs) used in the correction of postoperative hyperopia, are mentioned as useful in the prevention of PCOs , especially the foldable acrylic ones with truncated or square edges. However, when PCOs are set up, capsulotomies are required as a treatment. In human patients, the effects of the Nd:YAG laser are recognized as a noninvasive and secure technique against such problems. To compare the results of eyes of dogs that received foldable acrylic intraocular lenses with eyes of aphakic dogs, after phacoemulsification, during a period of 180 days it was used 20 dogs of several breeds, male or female , ranging from 3 to 7 years old , with juvenile, immature or mature (n = 10 immature, mature n = 10) bilateral cataracts . Two groups (G1 = with implantation of intraocular lens and G2 = no artificial lens implant) were randomly formed and all dogs had both eyes operated. After the surgery, the patients were weekly evaluated for the presence or absence of synechiae, discoria, intraocular pressure, uveal inflammation and presence or absence of posterior capsule opacification during a period of 180 days. At 60, 90, 120, 150 and 180 days after surgery, the posterior capsule images were captured for evaluation of their opacity. Eyes with score 2 or 3 of opacity were underwent to capsulotomy by Nd:YAG laser. Ordinal categorical variables were compared (G1 X G2) using the chi-square and Fisher´s exact test. Quantitative variables were compared using ANOVA with Tukey post test. Synechiae were observed in the same frequency in both groups .G2 showed 30 % more discoria when compared to G1 Intraocular pressure did not differ between the groups. The ...

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Conceição, Luciano Fernandes da. "Ocorrência de opacidade de cápsula posterior em cães pós-facoemulsificação, com ou sem a utilização de lente intraocular dobrável e efeitos do Nd: Yag Laser /." Jaboticabal, 2014. http://hdl.handle.net/11449/121864.

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Orientador: José Luiz Laus
Banca: Adriana Morales
Banca: João Antônio Tadeu Pigatto
Banca: Paola Castro Moraes
Banca: Luis Gustavo Gosuen Gonçalves Dias
Resumo: A catarata elenca-se entre as afecções oculares mais freqüentes em cães, sendo a facoemulsificação o método que melhor se adequa à sua terapia. As opacidades de cápsula posterior (OCPs) estão entre as complicações mais comuns e se manifestam em semanas ou meses após a facectomia. Lentes intraoculares (LIOs), empregadas na correção da hipermetropia pós-cirúrgica, são citadas como úteis na prevenção das OCPs, especialmente as acrílicas dobráveis, com bordas truncadas ou quadradas. Entretanto, quando OCPs se estabelecem requerem-se capsulotomias como forma de tratamento. Em pacientes humanos, reconhecem-se os efeitos do Nd:YAG laser como técnica não invasiva e segura frente a tais intercorrências. Para se compararem resultados de olhos de cães que receberam lentes intraoculares acrílicas dobráveis com olhos de cães afácicos, após facoemulsificação, durante um período de 180 dias, utilizaram-se 20 cães de raças diversas, machos ou fêmeas, que variaram de 3 a 7 anos de idade, apresentando catarata juvenil , imatura ou madura (imatura n = 10 , madura n = 10) bilateral. Dois grupos (G1 = com implante de lente intraocular e G2 = sem implante de lente artificial) foram formados aleatoriamente e todos os cães tiveram ambos os olhos operados. Após a cirurgia, os pacientes foram avaliados, semanalmente, quanto a presença ou a ausência de sinéquias, discoria, pressão intraocular, inflamação uveal e presença ou não de opacidade de cápsula posterior durante um período de 180 dias. Aos 60, 90, 120, 150 e 180 dias após a cirurgia, imagens da cápsula posterior foram capturados para avaliação da sua opacidade. Olhos com score 2 ou 3 de opacidade foram submetidos à terapia de capsulotomia pelo Nd:YAG laser. Variáveis categóricas ordinais foram comparadas (G1 X G2) empregando-se o teste de qui-quadrado e o teste exato de Fisher. Variáveis quantitativas foram comparadas empregando-se ANOVA com pós teste de Tukey
Abstract: Cataracts are among the most common eye diseases in dogs, being the phacoemulsification method the one that best suits in their therapy. The posterior capsule opacification (PCOs) are among the most common complications and manifest themselves in weeks or months after cataract surgery. Intraocular lenses (IOLs) used in the correction of postoperative hyperopia, are mentioned as useful in the prevention of PCOs , especially the foldable acrylic ones with truncated or square edges. However, when PCOs are set up, capsulotomies are required as a treatment. In human patients, the effects of the Nd:YAG laser are recognized as a noninvasive and secure technique against such problems. To compare the results of eyes of dogs that received foldable acrylic intraocular lenses with eyes of aphakic dogs, after phacoemulsification, during a period of 180 days it was used 20 dogs of several breeds, male or female , ranging from 3 to 7 years old , with juvenile, immature or mature (n = 10 immature, mature n = 10) bilateral cataracts . Two groups (G1 = with implantation of intraocular lens and G2 = no artificial lens implant) were randomly formed and all dogs had both eyes operated. After the surgery, the patients were weekly evaluated for the presence or absence of synechiae, discoria, intraocular pressure, uveal inflammation and presence or absence of posterior capsule opacification during a period of 180 days. At 60, 90, 120, 150 and 180 days after surgery, the posterior capsule images were captured for evaluation of their opacity. Eyes with score 2 or 3 of opacity were underwent to capsulotomy by Nd:YAG laser. Ordinal categorical variables were compared (G1 X G2) using the chi-square and Fisher's exact test. Quantitative variables were compared using ANOVA with Tukey post test. Synechiae were observed in the same frequency in both groups .G2 showed 30 % more discoria when compared to G1 Intraocular pressure did not differ between the groups. The ...
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Dawkins, Samuel T. "Sapphire room temperature optical frequency reference : design, construction and application." University of Western Australia. School of Physics, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0200.

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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.

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Lévy, Pierre-Philippe. "Chirurgie des tractions exercées par les brides vitréo-rétiniennes acquises : évaluation des techniques, indications et résultats de la chirurgie conventionnelle et de la photosection au laser Yag." Montpellier 1, 1988. http://www.theses.fr/1988MON11018.

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Rosier, Diallo Laurence. "Etude de l'endothélium cornéen par microscopie spéculaire aprés Q-Switched néodymium : Yag laser." Bordeaux 2, 1990. http://www.theses.fr/1990BOR23087.

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Lopes, Angélica Marquezim [UNESP]. "Influência de aplicações do laser érbio:YAG sobre a viabilidade microbiana, sua resistência a drogas e atividade hemolítica." Universidade Estadual Paulista (UNESP), 2003. http://hdl.handle.net/11449/96168.

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A atividade antimicrobiana do laser Er:YAG foi avaliada sobre biofilme bacteriano constituído por Escherichia coli ATCC 8739, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 e 3 cepas de Fusobacterium nucleatum e sobre biofilme de microrganismos salivares. Os biofilmes foram submetidos à ação do laser a 1,2 W e 10 Hz por 5, 10, 15, 20, 30 e 60 s e fez-se a avaliação da microbiota residual em ágar sangue, em anaerobiose. O biofilme salivar se mostrou mais sensível nos primeiros tempos de irradiação. A redução microbiana em relação ao controle foi estatisticamente significativa entre todos os tempos testados. Avaliou-se também a ação do laser Er:YAG sobre 7 cepas de Fusobacterium nucleatum inoculadas sobre a superfície de corpos-de-prova (5mmX4mm) de dentes extraídos. Fez-se a aplicação do laser nos mesmos parâmetros físicos mencionados anteriormente, durante 15 s, levando à eliminação total do conteúdo séptico. O estudo avaliou também a irradiação do laser de Er:YAG durante tempos subinibitórios sobre a atividade hemolítica e susceptibilidade de 9 cepas de Fusobacterium nucleatum a amoxicilina, eritromicina, metronidazol e tetraciclina. Após a irradiação do laser, determinou-se a concentração inibitória mínima (CIM) para as drogas através do método de diluição em ágar. A ação do laser sobre a atividade hemolítica foi determinada em sangue humano. Verificou-se que o laser Er:YAG não afetou a atividade hemolítica de Fusobacterium nucleatum, que se mostrou α-hemolítica, tampouco a susceptibilidade a drogas dos isolados testados.
Antimicrobial activity of Er:YAG laser was evaluated on a bacterial biofilm constituted by Escherichia coli ATCC 8739, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 and 3 strains of Fusobacterium nucleatum and on biofilm produced by salivary microorganisms. Biofilms were irradiated by Er:YAG laser, 1,2 W and 10 Hz, for 5, 10, 15, 20, 30, and 60 s and the evaluation of residual contamination was performed on blood agar, under anaerobiosis. It was verified that salivary biofilm showed to be more susceptibility to the Er:YAG laser in shorter periods of laser irradiation. Bacterial reduction was significative in all tested periods of irradiation. The activity of Er:YAG laser was also evaluated on 7 strains of Fusobacterium nucleatum inoculated on samples of human dentin (5mm X 4mm), obtained from extracted teeth. The laser was used following the same physical parameters, as previously described, for 15 s, leading to complete elimination of their septic content. The study also evaluated the effects of subinibitory irradiation of Er:YAG laser on bacterial susceptibility of 9 strains of Fusobacterium nucleatum to antimicrobial drugs (amoxicillin, erythromycin, metronidazole, tetracycline) and hemolysis. Thus, after laser irradiation, the minimal inhibitory concentration of antimicrobial drugs was determined by using an agar dilution method. The influence of laser on hemolysis was carried out on human blood. It was verified that Er:YAG laser did not produce any measurable effect on hemolytic activity and the microbial susceptibility to tested antimicrobial drugs.

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Couderc, Vincent. "Laser Nd : YAG pompé par diodes lasers : optimisation du rendement en régime continu, fonctionnement en régime de modes bloqués par miroir non linéaire à cristal doubleur." Limoges, 1995. http://www.theses.fr/1995LIMO0027.

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Les travaux realises sont regroupes en quatre parties distinctes et concernent l'etude de la mise en phase d'un reseau de diodes lasers de puissance et le developpement d'un laser nd:yag pompe par diodes fonctionnant en regime continu et en regime a modes bloques. La premiere partie est consacree a l'etude du fonctionnement unimodal d'un reseau de diodes lasers de puissance. Toutes les methodes utilisees s'appuient sur une retroaction selective externe et ont permis de rassembler soixante dix pour cent de la puissance initiale de la diode dans un diagramme de rayonnement presentant un pic de largeur inferieure a 1,5 fois la divergence minimale permise. Le chapitre deux presente l'optimisation du rendement d'un laser nd:yag pompe par diodes lasers de puissance en regime de fonctionnement continu avec l'utilisation d'un resonateur degenere, en limite de stabilite geometrique, de type afocal autoimageur. Ce genre de cavite optimise automatiquement le rendement de conversion optique. Les performances obtenues se situent au tout premier rang mondial et permettent de confiner la moitie de la puissance de pompe dans un faisceau unimodal de divergence minimale. La troisieme partie des travaux concerne le blocage en phase des modes longitudinaux de la cavite laser. La methode, que j'ai developpee en regime continu, repose sur l'emploi d'un miroir a reflectivite dependant de la puissance. Des impulsions de 10ps avec un taux de repetition de 110 mhz ont ete obtenues. Enfin la derniere partie traite de la realisation d'un laser nd:yag pompe par diode fonctionnant en regime continu et impulsionnel delivrant un rayonnement laser a 1,443 m dans la plage de longueur d'onde dite de securite oculaire avec des impulsions de 450 ns pour des puissances cretes superieures

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Barbosa, Élcio Roberto. "Investigação da influência da rugosidade superficial em implantes odontológicos de titânio, obtidas por jateamento abrasivo e a laser Nd-YAG." Instituto Tecnológico de Aeronáutica, 2009. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=948.

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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.

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Barnier, Vincent. "Etude de l’oxydation de l’aluminium induite par traitement laser Nd :YAG (1064 nm, 10 ns) : conséquences sur les propriétés d’adhérence d’un revêtement d’alumine élaboré par projection thermique." Dijon, 2006. http://www.theses.fr/2006DIJOS045.

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Le procédé PROTAL® permet la combinaison du nettoyage par impulsion laser (10 ns) d’une surface métallique et le dépôt instantané par projection thermique d’un revêtement protecteur. Si la validation technologique est bien avancée, les états physiques et chimiques des surfaces, après décapage et avant dépôt sont encore mal compris. Lors du nettoyage laser d’une surface métallique à l’ambiante, une oxydation liée à l’échauffement transitoire peut se manifester permettant de modifier les propriétés d’adhésion de la surface métallique. L’objectif de cette étude est de mettre en évidence ce phénomène pour un substrat d’aluminium et d’en évaluer l’impact sur l’adhérence d’un revêtement d’Al203 élaboré par projection plasma. Le couplage de plusieurs techniques d’analyses de surface a permis de caractériser les mécanismes d’oxydation induits par l’irradiation laser. Ceux-ci ont été reliés à l’amélioration de l’adhérence du dépôt d’alumine mis en évidence par la méthode « laser-ultrasons »
The PROTAL® allows combining the laser cleaning with short pulses (10 ns) of a metallic surface with a step of thermal spraying. The technology is well advanced but the chemical and physical states of the surface after laser irradiation and before coating are still misunderstood. During laser cleaning of a metallic surface in ambient atmosphere, a limiting oxidation can occur due to transient heating and modify the adhesion properties of this surface. The aim of this study was to highlight this phenomenon and to assess its influence on the adherence of Al2O3 plasma sprayed coating. The oxidation mechanisms induced by laser irradiation were characterized using several surface analysis techniques. These mechanisms were then correlated with adherence improvements of the alumina coating using the “laser-ultrasonic” method

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Ducos, Franck. "Développement d'une chaîne de synthèse de fréquences optiques : application a la mesure de la fréquence absolue d'un laser nd : yag double en fréquence et stabilisé sur une transition de l'iode." Paris, CNAM, 2001. http://www.theses.fr/2001CNAM0401.

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L'objet de ce travail de thèse est le développement d'une chaîne de synthèse de fréquences optiques en vue de mesurer la fréquence d'un laser nd : yag double en fréquence et stabilise sur une transition de l'iode a 563. 2 thz/532 nm. La mesure est basée sur l'utilisation de deux étalons secondaires de fréquence optique co 2/oso 4 et dl/rb opérant a 29 thz/10. 3 m et 385 thz/778 nm respectivement ; ces deux étalons ayant une exactitude de 1. 3 x 10 1 3 (4hz) et 5 x 10 - 1 2 (2 khz). Cette dernière valeur représente l'incertitude ultime du dispositif de mesure que nous avons développé. Nous utilisons deux diodes lasers opérant à 1. 064 m et 1. 551 m respectivement. La différence de fréquences entre ces deux diodes est comparée à l'harmonique 3 de la fréquence de l'étalon co 2/oso 4. Deux doublages de fréquence indépendants permettent de relier ces deux diodes laser aux deux étalons dl/rb et nd : yag/i 2. Des problèmes liés à l'élargissement de battements optiques n'ont pas permis de donner un résultat concluant sur la valeur de cette fréquence. Nous avons donc eu recours a un laser femtoseconde couplé à une fibre en silice à bande interdite photonique. Finalement, la fréquence du laser nd : yag/i 2 ainsi mesurée est : v(nd : yag/i 2) = 563 260 223 511. 6 (1. 2) khz ce résultat est en bon accord avec la recommandation du bureau international des poids et mesures (bipm).

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Chrétien, Lucie. "Relations entre le procédé céramique et les propriétés optiques de céramiques transparentes de type YAG-Nd : rôle des étapes de mise en forme et frittage." Thesis, Limoges, 2014. http://www.theses.fr/2014LIMO0041.

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Depuis les années 1990, les céramiques transparentes de type YAG:Nd suscitent un vif intérêt pour des applications en tant que milieux amplificateurs de lasers de haute puissance. Les céramiques, contrairement aux monocristaux, actuellement employés pour ces applications, peuvent être fabriquées sous la forme de pièces de grande taille avec des architectures complexes. Toutefois, il apparaît que la transparence et les capacités lasers des céramiques sont fortement affectées par la présence de porosité résiduelle générant de la diffusion de lumière. Dans ce contexte, cette étude s’est attachée dans un premier temps à déterminer les mécanismes contrôlant l’évolution de la porosité des céramiques de YAG:Nd à chaque étape du procédé d’élaboration dans le but de l’éliminer. Ce travail a mis en évidence que la porosité résiduelle pouvait avoir des origines diverses, et provenir notamment des caractéristiques des poudres initiales et/ou de l’étape de frittage-réactif qui peut induire dans des conditions mal maîtrisées à un phénomène de séparation pore/joint de grains. Dans un second temps, cette étude a montré que l’emploi d’une poudre d’alumine fine et peu agglomérée, d’une mise en forme des poudres par coulage sous pression et CIP et au final, le recours à une technique de post-traitement de frittage par pressage isostatique à chaud (post-HIP) permettait d’obtenir des céramiques transparentes de YAG:Nd de microstructure homogène et de qualité laser
Since 90’s, transparent Nd:YAG ceramics have received considerable attention as applications as amplifying media of high-power lasers. Contrary to single crystals, commonly used currently for these applications, ceramics can be fabricated into large size with complicated architectures. However, it appears that the transparency and the laser efficiency of ceramics are strongly affected by residual porosity generating light scattering. In this context, in a first step, this study focused to determine mechanisms controlling porosity evolution of Nd:YAG ceramics at each step of process in order to eliminate this one. This work showed that the residual porosity may have various origins, and result in particular of initial powder characteristics and/or reactive-sintering which can induce under certain conditions at a phenomenon of separation pore/grain boundary. In a second step, this study has shown that the use of a fine and few agglomerate alumina powder, a shaping process with pressure slip-casting and CIP and finally the use of a sinter plus Hot Isostatic Pressing technique achieved Nd:YAG transparent ceramics with homogeneous microstructure and laser quality

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Freitas, Célia Marisa Sampaio. "Tecnologia laser para limpeza de moldes de matriz polimérica." Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/21169.

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Mestrado em Engenharia Física
O presente trabalho teve como objetivo aplicar a tecnologia laser para desenvolver um método alternativo para limpeza da superfície dos moldes de matriz polimérica utilizados no processo de construção de pás eólicas na empresa Ria Blades SA. Tradicionalmente a empresa utiliza um processo de limpeza baseado na remoção e polimento manual dos resíduos. Este método além de moroso e dispendioso em termos de recursos humanos é muito agressivo e compromete a reutilização dos moldes. O método aqui proposto é baseado na tecnologia laser, tendo-se usado para o efeito um laser de Nd:YAG com comprimento de onda de 1064 nm em modo pulsado, acoplado a uma cabeça galvanométrica de forma a permitir um varrimento em linha do feixe laser, sendo o movimento do molde controlado por uma mesa linear motorizada. A primeira fase do trabalho consistiu no estudo da interação laser/molde, tendo sido explorados vários parâmetros de forma a garantir a preservação da superfície do molde, nomeadamente: a intensidade da corrente do laser, a velocidade de varrimento do feixe, a distância focal, a frequência do feixe, o comprimento de varrimento do feixe laser e a velocidade de deslocamento da amostra. Numa segunda fase foi estudada a interação laser/resina/molde com o objetivo de remover a resina preservando a superfície do molde. A caracterização das superfícies foi realizada por várias técnicas, designadamente perfilometria ótica, ângulo de contacto, espetroscopia de Raman, absorção, microscopia eletrónica de varrimento com espectroscopia de dispersão de energia (SEM-EDS). O estudo realizado através da análise elementar EDS e por espectroscopia de Raman permitiu verificar que não existe diferença antes e depois da interação da radiação laser com o substrato, sendo a rugosidade após a remoção da resina epoxy da mesma ordem de grandeza da superfície antes da interação com laser (Sa=0,34 m). A otimização deste estudo permitiu definir um conjunto de parâmetros adequados à limpeza deste tipo de resíduos: comprimento de varrimento do feixe laser de 1 cm; intensidade de corrente de 16A, velocidade de varrimento do feixe de 1000 mm/s, distância focal de 11,5 cm, frequência do feixe laser de 6 kHz e uma velocidade de deslocamento da amostra igual a 5 mm/s. É de salientar que este conjunto de parâmetros permite a remoção da resina por destacamento, isto é, sem promover a sua decomposição, o que é uma grande vantagem pois deste modo evita-se a formação de subprodutos tóxicos. .
The main objective of this work was to apply the laser technology to develop an alternative method to clean the surface of polymeric matrix moulds, used in the building process of wind blade in the Ria Blades SA company. Traditionally, the company use the manual polishing process to remove the materials (waste). This method takes a long time, it is expensive in terms of human resources, is very aggressive and compromises the reuse of moulds. The method proposed is based on laser technology, using a Nd:YAG pulsed laser with a wavelength of 1064 nm coupled to a scan head in a line scan. The movement of the mould is controlled by motorized linear table. The first phase of the work consisted in the study of the laser/mould interaction. Different parameters were explored namely: current intensity of laser, scan speed of pulse laser, focal distance, frequency, laser beam scan distance and speed of mould movement. In a second phase was studied the laser/resin/mould interaction to remove the epoxy resin preserving the surface of the mould. The surfaces were characterized by several techniques such as: optical profilometry, contact angle, Raman spectroscopy, absorption, scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). EDS and Raman spectroscopies allowed to verify no changes after the laser radiation on the substrate. The roughness of mould surface after remove the epoxy resin is the same order of magnitude as before laser interaction (Sa=0,34 m). The study optimization allowed to define optimal parameters to clean this type of waste: 1 cm of laser beam scan distance; 16 A of electrical current intensity, 1000 mm/s scanning speed of beam, 11.5 cm of focal distance, 6 kHz frequency and a sample speed of 5 mm/s. It should be emphasised that these parameters allow to remove epoxy resin without promoting its decomposition, this is a great advantage because it prevents the formation of toxic sub products.

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BERGEON, MURIELE. "Etude et realisation de microlasers declenches et de microlasers balayes en longueur d'onde, compatibles avec un procede de fabrication collectif." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10248.

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Le microlaser est un laser a etat solide miniature (<1mm#3), dont les miroirs de la cavite sont directement deposes sur le milieu a gain. De nombreuses applications demandent un fonctionnement impulsionnel ou balaye en longueur d'onde (telemetrie, detection de gaz, marquage). En inserant un cristal electrooptique a l'interieur de la cavite laser, des microlasers a emission declenchee et des microlasers a emission balayee en longueur d'onde ont ete realises. Les dispositifs concus sont constitues de yag:nd et de tantalate de lithium, ils sont stabilises en temperature et donnent une emission laser a 1,06 m. Le declenchement de ces microlasers a donne des impulsions laser de 0,3 j d'energie, a des frequences de 5 a 10 khz pour un champ electrique appliquee de 0,8 10#6 v/m. De meme, le balayage de la longueur d'onde laser est realise avec un taux de balayage de 10 mhz/v, a des frequences variant du continu jusqu'a 20 khz: des excursions de 10 ghz (0,35 a) ont ete mesurees pour un champ electrique de 10#6 v/m. De maniere a maintenir les qualites de compacite et fiabilite intrinseques au microlaser, un procede de fabrication collectif a ete mis au point

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RASO, PATRICE. "Modelisation et simulation des effets thermiques induits par les lasers nd-yag impulsionnels : application a la determination des degats thermiques et seuil de securite pour la retine et a la determination de parametres de plasma." Paris, ENSAM, 1991. http://www.theses.fr/1991ENAM0017.

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L'emploi des lasers nd-yag impulsionnels dans le domaine de la chirurgie a vu son avenement dans le secteur ophtalmologique, notamment lors de pratiques therapeutiques necessitant une focalisation du faisceau laser. L'apparition d'un plasma protegeant les structures posterieures au point de focalisation joue alors un role preponderant au niveau de la securite. Cependant, il s'avere que de nombreuses complications et lesions peuvent etre creees. De fait, la reconnaissance des effets des laser nd-yag impulsionnels, essentiellement les effets thermique, mecanique et quantique conditionne leur utilisation dans les limites optimales de securite. Nos travaux ont pour objectif de preciser l'amplitude de l'effet thermique des lasers nd-yag impulsionnels au niveau de la retine. D'une part le niveau de temperature d'un tissu retinien soumis a de tels lasers a ete quantifie en volume grace a la methode numerique des differences finies appliquee a l'equation de la chaleur, d'autre part, a partir de criteres de degat thermique, l'amplitude des lesions induites a ete precisee. Des confrontations de simulations numeriques a des experiences ont permis de definir un critere de lesion thermique microscopique et ont confirme les seuils de securite proposes par les praticiens. Parallelement, l'etude de la propagation d'une onde electromagnetique dans un plasma froid couplee au modele de l'explosion ponctuelle instantanee conduit a la determination de la frequence de collisions electron-electron au sein du plasma

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Garnier, Nicolas. "Spectroscopie dans l'état excité des ions terres-rares Nd3+ et Tm3+ et fonctionnement laser multilongueur d'onde du YAG : Nd3+." Saint-Etienne, 1997. http://www.theses.fr/1997STET4020.

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L'ensemble des travaux présentés dans cette thèse a été réalisé dans le cadre du Groupement de recherche matériaux lasers (GDR CNRS n°1148, thème : critère de qualité). Il est issu d'une collaboration entre le Laboratoire Traitement du signal et instrumentation, le Laboratoire Physico-chimie des matériaux luminescents et les entreprises CRISMATEC et BM industrie. Ces travaux ont conduit à la mise en oeuvre de différentes techniques expérimentales permettant la compréhension de divers processus se manifestant par une limitation de l'effet laser dans les cristaux de YAG : Nd3+ (Y3al 5o 1 2 : Nd3+) et YLF : Nd3+ (YLIF4 : Nd3+). Le premier aspect de ces processus est lié à l'ion dopant, ce sont des processus intrinsèques tels que l'absorption dans l'état excité et l'addition de photon par transfert d'énergie conduisant à un dépeuplement du niveau métastable émetteur dans l'infrarouge. Nous avons mis au point différentes expériences à deux faisceaux laser synchronisés (pompe, sonde) permettant l'étude des transitions dans l'état excité tant du point de vue spectral que des sections efficaces. Dans le cas du YLF : Nd3+, ces techniques ont permis la mise en évidence d'un double processus d'addition de photons par transfert d'énergie conduisant à des émissions visibles et ultraviolettes faisant suite à un pompage infrarouge ainsi qu'une double absorption dans l'état excité autour de la longueur d'onde laser (1. 05 m). Nous avons par ailleurs appliqué ces techniques à l'étude de transitions d'absorption dans l'état excité intervenant dans le processus d'avalanche de photons dans l'ion thulium pour différentes matrices (Y3al 5o 1 2, YALO3 et Y2O3). Le second aspect de ces travaux, appliqué au YAG : Nd3+, nous a conduit à envisager l'intervention d'un processus extrinsèque à l'ion dopant lié à la formation de centres colorés après pompage optique. On observe ainsi, après pompage, la diminution d'une bande d'absorption autour de 250 nm n'appartenant pas à l'ion Nd3+, l'apparition d'une bande d'absorption s'étendant depuis le visible jusqu'à l'infrarouge conduisant ainsi à l'augmentation de l'absorption résiduelle à la longueur d'onde laser (1. 064 m), cette absorption résiduelle étant mesurée par une technique interférométrique spécialement développée à cet effet. Le processus envisagé est le changement de Valence d'une impureté (probablement du fer) par piégeage d'un électron libéré dans la matrice YAG sous l'effet du rayonnement ultraviolet des flashes de pompage, processus partiellement réversible, avec la création de centres absorbants sous forte intensité de pompage (phénomène à deux photons) et annihilation (blanchiment) de ces centres sous faible intensité de pompage (phénomène à un photon). L'hypothèse actuelle, quant à la nature de ces centres, serait liée au processus d'oxydo-réduction : Fe3+ + e- Fe2+. Nous avons observé que ces centres colorés avaient une influence sur l'énergie extraite et sur la thermique des barreaux en fonctionnement laser

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Andersson, Martin, and Martin Svensson. "Nd YAG laser welding in Titanium-6242." Thesis, University West, Department of Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-764.

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Dissertations / Theses on the topic 'Nd-YAG lasers'

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