O objetivo desse estudo foi avaliar in vitro e in situ a efetividade de irradiação dos lasers Er:YAG, Nd:YAG e CO2 no aumento da resistência ácida do esmalte em regiões de sulcos e fissuras. Para o estudo in vitro foram utilizados molares humanos em fragmentos da porção oclusal de 8mmx4mm divididos em 3 grupos de acordo com o tipo de tratamento : Grupo 1 - Er:YAG; Grupo 2 - Nd:YAG; Grupo 3 - CO2 (n=15). O tratamento de superfície foi feito apenas em metade da área do fragmento, sendo que a outra metade foi considerada controle. As áreas expostas ao desafio cariogênico (14mm2) foram submetidas a ciclagens de pH. Para o testede microdureza os espécimes foram seccionados ao meio e a parede da secção é que sofreu o teste, a outra metade foi utilizada para análise em microscopia de luz polarizada para a medição da área da lesão de desmineralização e análise em MEV para verificar as alterações na morfologia do tecido dentário. As análises dos dados de microdureza (HKN) e área das lesões (mm2) foram feitas com o teste de Wilcoxon para a comparação interna de cada grupo com o seu controle e a comparação entre os grupos utilizou ANOVA para as áreas das lesões e Kruskal Wallis para a microdureza (&alpha; = 5%). Foi observada apenas diferença estatística significante para as amostras do grupo irradiado com laser CO2 entre as partes controle e experimental. Os demais grupos não apresentaram diferença estatisticamente significante com sua área controle. Na análise das medidas de lesão foram observadas diferença estatística significante para as amostras do grupo irradiado com os lasers CO2 e Nd:YAG com suas partes controles, sendo as medidas de área de lesão apresentadas pela área irradiada inferiores a área controle. Na análise em MEV o grupo irradiado com laser CO2 mostrou ausência de exposição dos prismas de esmalte e modificação de superfície na área irradiada. Para o estudo in situ foram utilizados molares humanos em fragmentos da porção oclusal de 4mmx4mm tratados com os 3 diferentes tipos de laser: Grupo 1 - controle (sem tratamento); Grupo 2 - Er:YAG; Grupo 3 - Nd:YAG; Grupo 4 - CO2 (n=15). Os espécimes foram adaptados a um dispositivo intrabucal que foi utilizado pelos voluntários durante 14 dias. Para o desafio cariogênico gotejou-se solução de sacarose 20% sobre os espécimes. Assim como no estudo in vitro, foram realizados o teste de microdureza, análise em microscópio de luz polarizada e análise em MEV. Para a análise dos dados de microdureza (HKN) foi utilizada ANOVA e teste de Fisher LSD (&alpha;= 5%). Foi observada diferença estatística significante para as amostras do grupo irradiado com laser CO2 e Nd:YAG, que apresentaram maiores valores de microdureza do que o grupo controle e não foram diferentes estatisticamente entre si. Os valores de microdureza observados em profundidade foram maiores proporcionalmente a distância da superfície, ou seja, 20&micro;m <30&micro;m <40&micro;m <50&micro;m. Na análise em microscopia de luz polarizada a análise foi feita com teste de Wilcoxon e todos os grupos apresentaram semelhança estatística. Considerando os resultados obtidos nos dois estudo pode-se concluir que os lasers CO2 e Nd:YAG foram capazes de promover aumento de resistência ácida no esmalte dental localizado nas superfície de sulcos e fissuras. / The aim of this study was to assess in vitro and in situ the lasers Er:YAG, Nd:YAG e CO2 in preventing enamel demineralization on the pits and fissures surface. For the in vitro study 45 occlusal enamel blocks were randomly divided into 3 groups in according with the treatment: G1 - Er:YAG; G2 - Nd:YAG; G3 - CO2. Treatments were made only on a half of the specimen and the remaining part was considered as a control. The samples were submitted to an in vitro pH cycles. For the microhardness test the specimens were seccioned in the middle and the seccioned wall received the test. The other halves were analyzed using polarized light microscopy for the measurement of the caries-lesion areas and morphological SEM analyses. Wilcoxon test were performed for the statistical analysis of the data obtained from the microhardness test (KHN) and caries-lesion area measurements (mm2) (&alpha;= 5%) when each groups was compared with its control. Variance analysis were performed for the difference in means of microhardness data and Kruskal Wallis test were performed for the difference in means of caries-lesion area measurements (&alpha;= 5%). For the microhardness data the G3 was statically different from its control area and the others groups presented statistical similarity among the experimental and control areas. For the caries-lesion area measurements statistical difference was observed for the groups G2 and G3 presenting smaller caries-lesion area when compared with their respective control areas. In the SEM analysis the G3 showed uniform surface without enamel-prism exposure. For the in situ study 60 occlusal enamel blocks were randomly divided into 4 groups in according with the treatment: G1 - Control (no treatment); G2 - Er:YAG; G3 - Nd:YAG; G4 - CO2 (n=15). The specimens were fixed in intra oral appliances and worn by the volunteers for 14d. Sucrose solution (20%) was applied to each specimen 6 times/d. As the in vitro study the samples were removed, sectioned and examined for microhardness, caries-lesion area measurements on the polarized light microcopy and morphological analyses on SEM. Variance analysis and the Fisher test were performed for the statistical analysis of the data obtained from the microhardness test (KHN) (&alpha;= 5%). The control group was statically different from G3 and G4, which present higher microhardness values and were statistical similar between them. The data of microhardness from the depth of surface were greater in proportion of distance from the surface, as 20&micro;m <30&micro;m <40&micro;m <50&micro;m. Wilcoxon test were performed for the statistical analysis of the data obtained from the caries-lesion area measurements (mm2) (= 5%) and all the groups were statically similar. Considering the results obtained from the both of studies can be concluded that the laser CO2 and Nd:YAG were able to increase the enamel acid resistance on the surface of pits and fissures.

O objetivo desse estudo foi avaliar in vitro e in situ a efetividade de irradiação dos lasers Er:YAG, Nd:YAG e CO2 no aumento da resistência ácida do esmalte em regiões de sulcos e fissuras. Para o estudo in vitro foram utilizados molares humanos em fragmentos da porção oclusal de 8mmx4mm divididos em 3 grupos de acordo com o tipo de tratamento : Grupo 1 - Er:YAG; Grupo 2 - Nd:YAG; Grupo 3 - CO2 (n=15). O tratamento de superfície foi feito apenas em metade da área do fragmento, sendo que a outra metade foi considerada controle. As áreas expostas ao desafio cariogênico (14mm2) foram submetidas a ciclagens de pH. Para o testede microdureza os espécimes foram seccionados ao meio e a parede da secção é que sofreu o teste, a outra metade foi utilizada para análise em microscopia de luz polarizada para a medição da área da lesão de desmineralização e análise em MEV para verificar as alterações na morfologia do tecido dentário. As análises dos dados de microdureza (HKN) e área das lesões (mm2) foram feitas com o teste de Wilcoxon para a comparação interna de cada grupo com o seu controle e a comparação entre os grupos utilizou ANOVA para as áreas das lesões e Kruskal Wallis para a microdureza (&alpha; = 5%). Foi observada apenas diferença estatística significante para as amostras do grupo irradiado com laser CO2 entre as partes controle e experimental. Os demais grupos não apresentaram diferença estatisticamente significante com sua área controle. Na análise das medidas de lesão foram observadas diferença estatística significante para as amostras do grupo irradiado com os lasers CO2 e Nd:YAG com suas partes controles, sendo as medidas de área de lesão apresentadas pela área irradiada inferiores a área controle. Na análise em MEV o grupo irradiado com laser CO2 mostrou ausência de exposição dos prismas de esmalte e modificação de superfície na área irradiada. Para o estudo in situ foram utilizados molares humanos em fragmentos da porção oclusal de 4mmx4mm tratados com os 3 diferentes tipos de laser: Grupo 1 - controle (sem tratamento); Grupo 2 - Er:YAG; Grupo 3 - Nd:YAG; Grupo 4 - CO2 (n=15). Os espécimes foram adaptados a um dispositivo intrabucal que foi utilizado pelos voluntários durante 14 dias. Para o desafio cariogênico gotejou-se solução de sacarose 20% sobre os espécimes. Assim como no estudo in vitro, foram realizados o teste de microdureza, análise em microscópio de luz polarizada e análise em MEV. Para a análise dos dados de microdureza (HKN) foi utilizada ANOVA e teste de Fisher LSD (&alpha;= 5%). Foi observada diferença estatística significante para as amostras do grupo irradiado com laser CO2 e Nd:YAG, que apresentaram maiores valores de microdureza do que o grupo controle e não foram diferentes estatisticamente entre si. Os valores de microdureza observados em profundidade foram maiores proporcionalmente a distância da superfície, ou seja, 20&micro;m <30&micro;m <40&micro;m <50&micro;m. Na análise em microscopia de luz polarizada a análise foi feita com teste de Wilcoxon e todos os grupos apresentaram semelhança estatística. Considerando os resultados obtidos nos dois estudo pode-se concluir que os lasers CO2 e Nd:YAG foram capazes de promover aumento de resistência ácida no esmalte dental localizado nas superfície de sulcos e fissuras. / The aim of this study was to assess in vitro and in situ the lasers Er:YAG, Nd:YAG e CO2 in preventing enamel demineralization on the pits and fissures surface. For the in vitro study 45 occlusal enamel blocks were randomly divided into 3 groups in according with the treatment: G1 - Er:YAG; G2 - Nd:YAG; G3 - CO2. Treatments were made only on a half of the specimen and the remaining part was considered as a control. The samples were submitted to an in vitro pH cycles. For the microhardness test the specimens were seccioned in the middle and the seccioned wall received the test. The other halves were analyzed using polarized light microscopy for the measurement of the caries-lesion areas and morphological SEM analyses. Wilcoxon test were performed for the statistical analysis of the data obtained from the microhardness test (KHN) and caries-lesion area measurements (mm2) (&alpha;= 5%) when each groups was compared with its control. Variance analysis were performed for the difference in means of microhardness data and Kruskal Wallis test were performed for the difference in means of caries-lesion area measurements (&alpha;= 5%). For the microhardness data the G3 was statically different from its control area and the others groups presented statistical similarity among the experimental and control areas. For the caries-lesion area measurements statistical difference was observed for the groups G2 and G3 presenting smaller caries-lesion area when compared with their respective control areas. In the SEM analysis the G3 showed uniform surface without enamel-prism exposure. For the in situ study 60 occlusal enamel blocks were randomly divided into 4 groups in according with the treatment: G1 - Control (no treatment); G2 - Er:YAG; G3 - Nd:YAG; G4 - CO2 (n=15). The specimens were fixed in intra oral appliances and worn by the volunteers for 14d. Sucrose solution (20%) was applied to each specimen 6 times/d. As the in vitro study the samples were removed, sectioned and examined for microhardness, caries-lesion area measurements on the polarized light microcopy and morphological analyses on SEM. Variance analysis and the Fisher test were performed for the statistical analysis of the data obtained from the microhardness test (KHN) (&alpha;= 5%). The control group was statically different from G3 and G4, which present higher microhardness values and were statistical similar between them. The data of microhardness from the depth of surface were greater in proportion of distance from the surface, as 20&micro;m <30&micro;m <40&micro;m <50&micro;m. Wilcoxon test were performed for the statistical analysis of the data obtained from the caries-lesion area measurements (mm2) (= 5%) and all the groups were statically similar. Considering the results obtained from the both of studies can be concluded that the laser CO2 and Nd:YAG were able to increase the enamel acid resistance on the surface of pits and fissures.

O objetivo do trabalho foi avaliar a resistência ao cisalhamento de bráquetes ortodônticos cerâmicos com base de retenção química e mecânica, colados com diferentes compósitos e irradiados com laser de CO2. Foram utilizados 120 pré-molares humanos hígidos, suas coroas foram incluídas em resina acrílica e as faces vestibulares planificadas e polidas com lixas d\'água até exposição de 5mm esmalte. Posteriormente, as raízes dos dentes foram incluídas em tubos de PVC também com resina acrílica de forma que a face vestibular ficasse perpendicular à base do tubo. Os 120 corpos de prova foram divididos em 8 grupos (n=15), sendo 2 controles e 6 experimentais. Nos grupos 1 e 2 (controles) o compósito utilizado para colagem foi o Transbond XT, sendo que no grupo 1 foi colado o bráquete cerâmico Mystique (retenção mecânica) e no grupo 2 o bráquete cerâmico Fascination (retenção química). Nos grupos experimentais 3, 4 e 5 foi colado o bráquete Mystique com os compósitos Transbond XT, Concise e Z250, respectivamente. Nos grupos 6, 7 e 8 foi colado o bráquete Fascination com os mesmos compósitos dos grupos 3, 4 e 5, na mesma sequência. Nos grupos experimentais, após a colagem, os bráquetes foram irradiados com laser de CO2 com 10W de potência por 3 segundos e pulso de 0,01 segundo. Imediatamente após a irradiação foi realizado o teste de resistência ao cisalhamento da colagem em máquina universal de ensaios mecânicos (Emic DL 500) à velocidade de 0,5 mm/minuto. Após o teste, as superfícies avaliadas por meio do Índice de Remanescente Adesivo (IRA) e submetidas à Microscopia Eletrônica de Varredura (MEV) para investigação de eventuais fraturas. Os dados de resistência ao cisalhamento foram submetidos à Análise de Variância ANOVA e posteriormente teste de Tukey. O teste de Mann-Whitney foi utilizado para a avaliação do IRA. Os resultados mostraram que os grupos experimentais apresentaram valores de resistência ao cisalhamento menores quando comparados aos controle (p 0,05). O bráquete Mystique (retenção mecânica) apresentou valores maiores de resistência ao cisalhamento e o compósito Z 250 foi o que apresentou menor força de adesão após irradiação com laser de CO2. Os grupos 5 e 8 foram os que apresentaram maior média do IRA e para todas as superfícies avaliadas o modo de fratura mais prevalente foi a fratura adesiva . Concluiu-se que o laser de CO2 foi eficaz como auxiliar na descolagem de bráquetes cerâmicos de retenção química e mecânica. / The objective of this study was to evaluate the shear strength of the ceramic orthodontic brackets based in chemical and mechanical restraint, bonded with different composites and irradiated with CO2 laser was evaluated. Healthy human premolars (120) were used and their crowns were embedded in acrylic resin and the buccal surfaces flattened and polished with sandpaper until exposure of 5 mm of enamel. Subsequently, the roots of the teeth were included in PVC pipes also with acrylic resin so that the labial surface was perpendicular to the base of the pipe. The 120 samples were divided into 8 groups (n = 15), 2 being the control groups and 6, the experimental groups. In groups 1 and 2 (controls) the composite used for bonding was Transbond XT. Group 1 was glued to the ceramic bracket Mystique (by mechanical retention) and the group 2, with ceramic bracket Fascination (by chemical restraint). In the experimental groups 3, 4 and 5 Mystique brackets were glued with Transbond XT, Concise and Z250, respectively. In groups 6, 7 and 8 the Fascination bracket were glued with the same composites of groups 3, 4 and 5 and in the same sequence. In the experimental groups, after bonding, the brackets were irradiated with CO2 laser with 10W of power for 3 seconds and per pulse 0.01 seconds. Immediately after irradiation shear strength tests were performed on shear bonding with mechanical universal testing machines (Emic DL 500) at a speed of 0.5 mm/minute. After testing, the surfaces were evaluated using the Adhesive Remnant Index (ARI) and submitted to scanning electron microscopy (SEM) to investigate possible fractures. The shear strength data were subjected to analysis of variance with ANOVA and Tukey test later. The Mann-Whitney test was used to evaluate the ARI. The results showed that experimental groups showed lower shear strength values, comparing to the control groups (p 0.05). The bracket Mystique (mechanical retention) showed higher shear strength values and the Z 250 composite showed the lowest adhesion strength after irradiation with CO2 laser. Groups 5 and 8 presented the highest average of IRA and for all the surfaces that were evaluated the most prevalent fracture mode was the adhesive one. It was concluded that the CO2 laser was effective as an aid in bracket debonding of ceramic with chemical and mechanical retention.

O objetivo do trabalho foi avaliar a resistência ao cisalhamento de bráquetes ortodônticos cerâmicos com base de retenção química e mecânica, colados com diferentes compósitos e irradiados com laser de CO2. Foram utilizados 120 pré-molares humanos hígidos, suas coroas foram incluídas em resina acrílica e as faces vestibulares planificadas e polidas com lixas d\'água até exposição de 5mm esmalte. Posteriormente, as raízes dos dentes foram incluídas em tubos de PVC também com resina acrílica de forma que a face vestibular ficasse perpendicular à base do tubo. Os 120 corpos de prova foram divididos em 8 grupos (n=15), sendo 2 controles e 6 experimentais. Nos grupos 1 e 2 (controles) o compósito utilizado para colagem foi o Transbond XT, sendo que no grupo 1 foi colado o bráquete cerâmico Mystique (retenção mecânica) e no grupo 2 o bráquete cerâmico Fascination (retenção química). Nos grupos experimentais 3, 4 e 5 foi colado o bráquete Mystique com os compósitos Transbond XT, Concise e Z250, respectivamente. Nos grupos 6, 7 e 8 foi colado o bráquete Fascination com os mesmos compósitos dos grupos 3, 4 e 5, na mesma sequência. Nos grupos experimentais, após a colagem, os bráquetes foram irradiados com laser de CO2 com 10W de potência por 3 segundos e pulso de 0,01 segundo. Imediatamente após a irradiação foi realizado o teste de resistência ao cisalhamento da colagem em máquina universal de ensaios mecânicos (Emic DL 500) à velocidade de 0,5 mm/minuto. Após o teste, as superfícies avaliadas por meio do Índice de Remanescente Adesivo (IRA) e submetidas à Microscopia Eletrônica de Varredura (MEV) para investigação de eventuais fraturas. Os dados de resistência ao cisalhamento foram submetidos à Análise de Variância ANOVA e posteriormente teste de Tukey. O teste de Mann-Whitney foi utilizado para a avaliação do IRA. Os resultados mostraram que os grupos experimentais apresentaram valores de resistência ao cisalhamento menores quando comparados aos controle (p 0,05). O bráquete Mystique (retenção mecânica) apresentou valores maiores de resistência ao cisalhamento e o compósito Z 250 foi o que apresentou menor força de adesão após irradiação com laser de CO2. Os grupos 5 e 8 foram os que apresentaram maior média do IRA e para todas as superfícies avaliadas o modo de fratura mais prevalente foi a fratura adesiva . Concluiu-se que o laser de CO2 foi eficaz como auxiliar na descolagem de bráquetes cerâmicos de retenção química e mecânica. / The objective of this study was to evaluate the shear strength of the ceramic orthodontic brackets based in chemical and mechanical restraint, bonded with different composites and irradiated with CO2 laser was evaluated. Healthy human premolars (120) were used and their crowns were embedded in acrylic resin and the buccal surfaces flattened and polished with sandpaper until exposure of 5 mm of enamel. Subsequently, the roots of the teeth were included in PVC pipes also with acrylic resin so that the labial surface was perpendicular to the base of the pipe. The 120 samples were divided into 8 groups (n = 15), 2 being the control groups and 6, the experimental groups. In groups 1 and 2 (controls) the composite used for bonding was Transbond XT. Group 1 was glued to the ceramic bracket Mystique (by mechanical retention) and the group 2, with ceramic bracket Fascination (by chemical restraint). In the experimental groups 3, 4 and 5 Mystique brackets were glued with Transbond XT, Concise and Z250, respectively. In groups 6, 7 and 8 the Fascination bracket were glued with the same composites of groups 3, 4 and 5 and in the same sequence. In the experimental groups, after bonding, the brackets were irradiated with CO2 laser with 10W of power for 3 seconds and per pulse 0.01 seconds. Immediately after irradiation shear strength tests were performed on shear bonding with mechanical universal testing machines (Emic DL 500) at a speed of 0.5 mm/minute. After testing, the surfaces were evaluated using the Adhesive Remnant Index (ARI) and submitted to scanning electron microscopy (SEM) to investigate possible fractures. The shear strength data were subjected to analysis of variance with ANOVA and Tukey test later. The Mann-Whitney test was used to evaluate the ARI. The results showed that experimental groups showed lower shear strength values, comparing to the control groups (p 0.05). The bracket Mystique (mechanical retention) showed higher shear strength values and the Z 250 composite showed the lowest adhesion strength after irradiation with CO2 laser. Groups 5 and 8 presented the highest average of IRA and for all the surfaces that were evaluated the most prevalent fracture mode was the adhesive one. It was concluded that the CO2 laser was effective as an aid in bracket debonding of ceramic with chemical and mechanical retention.

Une des limitations du fonctionnement des grandes chaines lasers de puissance telle que le Laser MegaJoule, est la problématique de l’endommagement laser des composants optiques. Différents phénomènes physiques qui dépendent à la fois des propriétés des matériaux, de leurs conditions de fabrication/ préparation et des paramètres d’irradiation laser peuvent conduire à un amorçage de dommages sur la surface ou dans le volume, qui vont croître lors d’irradiations successives. Ce phénomène limite la montée en puissance, affecte la durée de vie des composants optiques et le coût de maintenance des chaînes laser. Il peut également être à l’origine de graves problèmes de sécurité. Pour remédier à cette croissance des dommages et augmenter la durée de vie des composants en silice, un procédé laser dit de «stabilisation » est étudié dans le cadre de cette thèse, l’objectif étant de traiter les dommages pour arrêter leur croissance sous tirs répétés afin de recycler les optiques endommagées. Ce processus consiste en une fusion, suivie d’une évaporation locale, par dépôt d’énergie localisé par un faisceau laser CO2, de la zone fracturée de silice. Nous nous sommes intéressés particulièrement à la stabilisation de dommages laser sur silice par un procédé de micro-usinage par laser CO2 dans le but de traiter des dommages de dimensions millimétriques. Cette technique est basée sur une micro-ablation rapide de la silice durant laquelle le faisceau laser est balayé à la surface du composant afin de former un cratère de forme ajustable (typiquement conique) englobant le site endommagé. Un banc d’expérimentations a ainsi été mis en place à l’Institut Fresnel pour développer et étudier ce procédé. Différents travaux numériques et expérimentaux ont également été menés pour valider et optimiser la technique. Nos travaux ont montré l’efficacité de ce procédé de micro-usinage par laser CO2 pour arrêter la croissance de dommages de plusieurs centaines de microns de largeur et de profondeur. Pour parvenir à cet objectif nous nous sommes appuyés sur la modélisation des phénomènes physiques mis en jeu lors des expériences de stabilisation en utilisant le logiciel de simulation multi-physique COMSOL. D’une part, le modèle thermique, développé au cours de cette thèse, permet de calculer la distribution de température dans le matériau pendant le tir laser avec ou sans mouvement du faisceau. Combinées à une approche thermodynamique, ces simulations thermiques permettent de décrire les transformations de la silice lors de l’irradiation afin de prédire la morphologie des cratères formés dans le verre. D’autre part, la partie mécanique du modèle permet de simuler la position et la valeur des contraintes résiduelles, générées dans le matériau autour du cratère CO2, lors de l’élévation de température suivie du refroidissement rapide. D’autres expériences concernant le traitement de fractures liées au polissage, ou des défauts de fabrication de réseaux de silice sont également traités dans ce manuscrit. / One limitation of the operation of large power lasers chains such as Laser MegaJoule, is the issue of laser damage of optical components. Different physical phenomena which depend on both the properties of materials, their conditions of manufacture / preparation and laser irradiation parameters can lead to damage initiation on the surface or in the volume, which will grow under successive irradiation. This effect limits the output power, affects the lifetime of the optical components and the maintenance cost of the laser. It can also cause serious safety problems. To address this issue and increase the lifetime of fused silica components, a laser process called "stabilization" is studied in this thesis, the aim being to treat the damage sites to stop their growth under repeated pulses for recycling damaged optics. This process consists of melting, followed by local evaporation by localized energy deposition by a CO2 laser beam of the damage site. We focused particularly on the stabilization of silica components by a micromachining process using a CO2 laser in order to treat millimeter size damages. This technique is based on fast micro-ablation of the silica during which the laser beam is scanned on the component surface to form an adjustable form of crater (typically conical) including the damaged site. A bench of experiments has been set up at the Fresnel Institute to develop and study this process. Various numerical and experimental works were also conducted to validate and optimize the technique. Our work has shown the efficiency of this micro-machining process by CO2 laser to stop the growth of damage to several hundred microns wide and deep. To achieve this goal we relied on modeling of physical phenomena involved in stabilization experiments using the COMSOL Multiphysics simulation software. First, the thermal model developed in this thesis is used to calculate the temperature distribution in the material during laser irradiation with or without movement of the beam. Combined with a thermodynamic approach, these thermal simulations can describe the transformation of silica during irradiation and predict the morphology of craters formed in the glass. Secondly, the mechanical part of the model can simulate the position and value of residual stress generated in the material around the crater after the temperature rise followed by rapid cooling. Other experiments on the treatment of fractures related to polishing on silica surfaces, or manufacturing defects on silica gratings are covered in this manuscript.

The project compares the technology of welding of CO2 laser and fiber laser in terms of engineering study, the welds will be made by same welding conditions on two materials (S235JRG2 a X5CrNi 18-10), by using different protective gases (Helium and Argon). In the terms of literal background research both the technologies and questions of laser welding are described. The geometry of welds is carried out in the experimental part. The final results of the experiment are concluded at the end of the diploma thesis.

Due to their inherent BW capacity, optical interconnect (OI) offers a means of replacement to BW limited copper as bottlenecks begin to appear within the various interconnect levels of electronics systems. Low-cost optically enabled printed circuit boards are a key milestone on many electronics roadmaps, e.g. iNEMI. Current OI solutions found in industry are based upon optical fibres and are capable of providing a suitable platform for inter-board applications especially on the backplane. However, to allow component assembly onto high BW interconnects, an integral requirement for intra-board applications, optically enabled printed circuit boards containing waveguides are essential. Major barriers to the deployment of optical printed circuit boards include the compatibility of the technique, the cost of acquiring OI and the optical power budget. The purpose of this PhD research programme is to explore suitable techniques to address these barriers, primarily by means of laser material processing using UV and IR source lasers namely 248 nm KrF Excimer, 355 nm UV Nd:YAG and 10.6 μm IR CO2. The use of these three main lasers, the trio of which dominates most PCB production assembly, provides underpinning drive for the deployment of this technology into the industry at a very low cost without the need for any additional system or system modification. It further provides trade-offs among the suitable candidates in terms of processing speed, cost and quality of waveguides that could be achieved. This thesis presents the context of the research and the underlying governing science, i.e. theoretical analysis, involving laser-matter interactions. Experimental investigation of thermal (or pyrolitic) and bond-breaking (or photolytic) nature of laser ablation was studied in relation to each of the chosen lasers with regression analysis used to explain the experimental results. Optimal parameters necessary for achieving minimum Heat Affected Zone (HAZ) and surface/wall roughness were explored, both of which are key to achieving low loss waveguides. While photochemical dominance - a function of wavelength and pulse duration - is desired in laser ablation of photopolymers, the author has been able to find out that photothermallyprocessed materials, for example at 10.6 μm, can also provide desirable waveguides. Although there are literature information detailing the effect of certain parameters such as fluence, pulse repetition rate, pulse duration and wavelength among others, in relation to the etch rate of different materials, the machining of new materials requires new data to be obtained. In fact various models are available to try to explain the laser-matter interaction in a mathematical way, but these cannot be taken universally as they are deficient to general applications. For this reason, experimental optimisation appears to be the logical way forward at this stage of the research and thus requiring material-system characterisation to be conducted for each case thereby forming an integral achievement of this research. In this work, laser ablation of a single-layer optical polymer (Truemode™) multimode waveguides were successfully demonstrated using the aforementioned chosen lasers, thus providing opportunities for rapid deployment of OI to the PCB manufacturing industry. Truemode™ was chosen as it provides a very low absorption loss value < 0.04 dB/cm at 850 nm datacom wavelength used for VSR interconnections - a key to optical power budget - and its compatibility with current PCB fabrication processes. A wet-Truemode™ formulation was used which required that optical polymer layer on an FR4 substrate be formed using spin coating and then UV-cured in a nitrogen oxygen-free chamber. Layer thickness, chiefly influenced by spinning speed and duration, was studied in order to meet the optical layer thickness requirement for multimode (typically > 9 μm) waveguides. Two alternative polymers, namely polysiloxane-based photopolymer (OE4140 and OE 4141) from Dow Corning and PMMA, were sparingly utilized at some point in the research, mainly during laser machining using UV Nd:YAG and CO2 lasers. While Excimer laser was widely considered for polymer waveguide due to its high quality potential, the successful fabrication at 10.6 μm IR and 355 nm UV wavelengths and at relatively low propagation loss at datacom wavelength of 850 nm (estimated to be < 1.5 dB/cm) were unprecedented. The author considered further reduction in the optical loss by looking at the effect of fluence, power, pulse repetition rate, speed and optical density on the achievable propagation but found no direct relationship between these parameters; it is therefore concluded that process optimisation is the best practice. In addition, a novel in-plane 45-degree coupling mirror fabrication using Excimer laser ablation was demonstrated for the first time, which was considered to be vital for communication between chips (or other suitable components) at board-level.

This work studies discharge plasma in a mixture of gases, similar to that used in the so-called CO2-lasers. This mixture consists of CO2, N2 and He. The effect of the mixture composition and discharge parameters (especially pressure, in the range of 266 Pa - 100 kPa) on the distribution of energy in the vibrational levels of nitrogen was examined. This is important parameter for modelling of the discharge plasma. The effect of the mixture composition on the degree of dissociation of the CO2 molecules was also studied. The relative concentration of CO was applied to find the conditions leading to a minimal dissociation of the carbon dioxide. Measurements of radial profiles were also made. Results from two discharge tubes made from different materials were compared. Two types of discharge were utilized to acquire a wide pressure range - low pressure DC glow discharge in the range of 266 Pa to 1330 Pa and dielectric barrier discharge in the range of 5 kPa to 100 kPa. Both discharges are used in commercial CO2-lasers. We observed a descending dependence of the vibrational temperature on the pressure and a big step caused by increased occurrence of standing ionizing waves in the mixtures with low nitrogen ratio. Vibrational temperature in the DBD was markedly lower than in the DC GD, because of the...