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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Impact des défauts d'aspect sur la propagation d'un laser de puissance / Visual defect impact on high power laser beam propagation

Tournemenne, Florian 18 October 2019 (has links)
Chaque faisceau d'un laser de puissance, tel que le Laser MégaJoule, est mis en forme et voit son énergie amplifiée à l’aide d’une centaine de composants optiques tels que des plaques de verre amplificateur, des lentilles, des miroirs, des lames de phase, des réseaux... 'Evidemment ces composants ne sont pas parfaitement réalisés et ils présentent à leurs surfaces des défauts de fabrication. Ces imperfections peuvent être dues aux outils de polissage des composants, aux dépôts antireflet ou même apparaitre au cours de la phase d’exploitation ou de remédiation du composant. Ces défauts contribuent à une baisse des performances du Laser MégaJoule que ce soit au niveau de l’énergie déposée au centre de la chambre d’expériences ou à l’endommagement accéléré des composants optiques placés en aval. Actuellement la norme ISO 10110-7 est utilisée pour spécifier les défauts d’aspect. Cependant elle manque de justification pour les besoins d’une chaine laser de puissance. Dans le cadre de la thèse nous nous intéressons exclusivement à l’endommagement fratricide local des composants optiques. Un défaut présent à la surface du composant module l’onde lumineuse par phénomène de diffraction. Un << point chaud >> peut apparaitre dans le faisceau laser augmentant alors la densité locale surfacique d’énergie appliquée aux composants suivants. La loi d’endommagement prédit une augmentation de la probabilité d’endommagement puisque la densité d’énergie est modifiée. Une première étude, fondée sur les équations de Fresnel, met en évidence les paramètres intéressants à spécifier pour prédire les intensifications engendrées par des défauts typiques. Le lien entre paramètres du défaut et intensifications diffractées est, ensuite, validité expérimentalement sur des cas réels de défauts. Une seconde étude établit un seuil exprimé en puissance en deçà duquel l'hypothèse d'une propagation linéaire, selon les équations de Fresnel, est valide. La cohérence des résultats donnés par le seuil en puissance et par la simulation numérique renforce l’idée voulant que la propagation d’un << point chaud >> en présence d'effet Kerr soit sensiblement différente de celle d’un faisceau gaussien. Fort de ces deux résultats nous sommes en capacité d'établir une spécification des défauts d’aspect en ayant une meilleure compréhension de l’endommagement fratricide local. / Each beam of a high power laser facility, such as the Laser MégaJoule, is shaped and amplified thanks to hundreds optical components such as amplifier slabs at Brewster’s angle, lenses, mirrors, phase plates, diffraction gratings... Of course, all these components cannot be perfect; there are some defects on their surface. These imperfections appear at each stage of the life of the component, during polishing, coating, or mitigation process or when the component is used on the facility. They have a huge impact on the energy losses delivered on the target and they decrease the resistance of downstream components to intense light. The ISO 10110-7 standard is currently used to specify the visual defects. However, this standard is poorly justified and do not fit a high power laser needs. In this thesis, we are focused on the fratricide effect. Light propagates through a defect, then, some intensity modulations appear along the propagation. The damage law states that high energy density leads to an increase of the damage probability. Firstly, we investigate the characteristic parameters of the defect morphology linked to the formation of downstream << hot spots >>. Then, the link between these typical parameters and the high intensifications are confirmed by experiments on real defects. Secondly, a power criterion is demonstrated to guarantee the linear propagation hypothesis. This criterion is compared to numerical simulations and it is shown how the nonlinear propagation, induced by Kerr effect, can be different between the << hot spot >> formed by a defect and a Gaussian beam. Finally, the results are used to improve the visual defect specification thanks to a better understanding of the fratricide effect.
22

Développement de procédés de gravure plasma sans dommages pour l'intégration de l'InGaAs comme canal tridimensionnel de transistor nMOS non-planaire / Development of damage free plasma etching processes for the integration of InGaAs as non-planar nMOS transistor tridimensional channel

Bizouerne, Maxime 20 April 2018 (has links)
L’augmentation des performances des dispositifs de la microélectronique repose encore pour une dizaine d’années sur une miniaturisation des circuits intégrés. Cette miniaturisation s’accompagne inévitablement d’une complexification des architectures et des empilements de matériaux utilisés. Au début de cette thèse, une des voies envisagées pour poursuivre la miniaturisation était de remplacer, dans une architecture finFET, le canal en silicium par un semi-conducteur à plus forte mobilité électronique, tel que l’In0,53Ga0,47As pour les transistors nMOS. Une étape essentielle à maitriser dans la fabrication des transistors finFET à base d’InGaAs est celle de la gravure plasma qui permet d’élaborer l’architecture du canal. En effet, pour assurer un fonctionnement optimal du transitor, il est primordial que les procédés de gravure ne génèrent pas de défauts sur les flancs du canal tels que la création de rugosité ou une perte de stœchiométrie. L’objectif principal de cette thèse est ainsi de réaliser la structuration du canal 3D d’InGaAs par gravure plasma en générant un minimum de défaut sur les flancs. Pour cela, nous avons évalué trois stratégies de gravure. Des premières études ont visé le développement de procédés de gravure en plasmas halogénés à température ambiante (55°C). De tels procédés conduisent à des profils pentus et rugueux du fait de redépôts InClx peu volatils sur les flancs des motifs. Dans un second temps, des procédés de gravure en plasma Cl2/CH4 à haute température (200°C) ont été étudiés et développés. Des motifs anisotropes et moins rugueux ont pu être obtenus, grâce à la volatilité des produits InClx et à la présence d’une passivation des flancs de type SiOx. Enfin, un concept de gravure par couche atomique, qui consiste à alterner deux étapes de procédé au caractère autolimité, a été étudié. Une première étape d’implantation en plasma He/O2 qui permet une modification de l’InGaAs sur une épaisseur définie suivie d’une étape de retrait humide en HF. Pour ces trois stratégies de gravure, une méthodologie permettant de caractériser de manière systématique les défauts engendrés sur les flancs a été mise en place. La spectroscopie Auger a permis d’accéder à la stœchiométrie des flancs tandis que la rugosité a été mesurée par AFM. Les résultats issus de la caractérisation des flancs des motifs gravés ont alors montré la nécessité de mettre en œuvre des procédés de restauration de surface. Un procédé combinant une étape d’oxydation par plasma de la surface d’InGaAs suivi d’un retrait par voie humide de la couche oxydée a ainsi été proposé. Ce traitement permet effectivement de diminuer la rugosité des flancs des motifs mais a accentué un enrichissement en arsenic déjà présent après les procédés de gravure. / Increasing the performance of transistors for the next decade still relies on transistor downscaling which is inevitably accompanied by an increasing complexity of the architectures and materials involved. At the beginning of this thesis, one strategy to pursue the downscaling was to replace, in a finFET architecture, the silicon channel with high-mobility semiconductor, such as In0,53Ga0,47As for the nMOS transistors. The patterning of the channel architecture by plasma etching is an essential step to overcome in the fabrication of InGaAs-based finFET transistors. Indeed, to ensure optimal performances of the device, it is crucial that the plasma etching process do not generate defects on the channel sidewalls such as a loss of stoichiometry and roughness formation. Thus, the major aim of this thesis is to pattern the 3D InGaAs channel by plasma etching with minimal sidewalls damage. For this, we investigated three plasma etching strategies. First, this work focused on the development of plasma etches process with halogen chemistries at ambient temperature (60°C). Such process leads to sloped and rough patterns due to the redeposit of low volatile InClx etch by products. Secondly, Cl2/CH4 plasma etching processes at high temperature (200°C) have been studied and developed. Anisotropic and relatively smooth patterns can be obtained using such plasma process thanks to enhanced volatility of InClx products and a SiOx sidewall passivation formation. Finally, an atomic layer etching concept has been investigated to pattern InGaAs with minimal damage. This concept consists in alternating two self-limited steps: first, an implantation step using He/O2 plasma modifies the InGaAs surface to a limited thickness. Then, the modified layer is removed by HF wet. For all these etching strategies, a methodology was implemented to perform a systematic characterization of the damage generated on the sidewalls. The Auger spectroscopy was used to determine the sidewall stoichiometry while the sidewall roughness is measured by AFM. The results from the sidewall characterizations revealed the necessity to implement a surface restoration process. It consists in oxidizing the InGaAs sidewalls with O2 plasma and to removed the oxidized layer with a HF step. This process was efficient to smooth the InGaAs pattern sidewalls but enhances an arsenic enrichment which was already present after the etching processes.
23

Amélioration de la tenue au flux laser des composants optiques du laser Mégajoules par traitement chimique / Laser-induced damage resistance improvement of fused silica optics by wet etching process.

Pfiffer, Mathilde 17 October 2017 (has links)
Cette thèse porte sur l’amélioration de la résistance au flux laser de la surface descomposants optiques en silice en régime nanoseconde. Ce matériau est utilisé sur lesinstallations de laser de puissance telles que le Laser Mégajoule. Pour augmenter la durée de viedes composants optiques et garantir le fonctionnement nominal de cette installation,l’endommagement laser doit être maîtrisé. Il s’agit d’une dégradation irréversible de la surfacedes composants causée par l’interaction entre le faisceau laser et des défauts précurseurs. Cesderniers sont une conséquence de la synthèse de la silice puis du polissage des composants etleur présence peut être limitée par une action de traitement chimique réalisée à l’issue dupolissage qui consiste à éroder la surface de silice à l’aide d’une solution chimique. Cette érosionne doit cependant pas dégrader la qualité de la surface polie et ses propriétés optiques. Cettethèse se concentre sur la réalisation de cette étape de traitement chimique et se décompose entrois études. La première porte sur la caractérisation de la pollution induite en surface par lepolissage et sa suppression par le traitement chimique. La seconde et la troisième analysentl’impact des traitements chimiques respectivement sur les propriétés optiques de la surface etsur les rayures de polissage. Ces études nous permettent d’évaluer l’influence des différentsparamètres du traitement chimique, tels que la solution, le système de mise en oeuvre etl’épaisseur érodée, sur les performances apportées aux composants optiques. Finalement,l’ensemble de ces connaissances nous conduit à proposer un traitement chimique optimisé quiaméliore la tenue au flux des composants optiques sans dégrader leurs propriétés optiques. / In this thesis, laser-induced damage resistance improvement of fused silica opticsis investigated in the nanosecond regime. This material is used on high power laser facilitiessuch as the Laser Mégajoule. In order to improve the optics life time and to ensure the nominaloperation of this facility, laser induced damage has to be controlled. This phenomenon is anirreversible modification of the components surface because of the interaction between the laserbeam and precursors defects. These defects are a consequence of the synthesis of silica and thepolishing of the optics and their presence can be reduced by a wet etching. This process consistsin an erosion of the surface using a chemical solution however optical properties must remainunchanged. In this thesis, we focus on the wet etching process and we conduct three studies. Thefirst one is about the characterization of the polishing induced contamination and the capabilityof a wet etching to remove it from the surface. The second and the third analyzes are about theimpact of the wet etching respectively on the surface and on the scratches. These studies allowus to evaluate the influence of the wet etching parameters as the chemical solution, the systemused and the deep etched. Finally, the highlights obtained thanks to these studies enable tooptimize the wet etching process and improve the laser induced damage resistance ofcomponents without compromising their optical properties.
24

Efeito in vitro e in vivo da terapia fotodinâmica antimicrobial sobre streptococcus mutans presentes em acessórios metálicos ortodônticos

Panhóca, Vitor Hugo 07 May 2015 (has links)
Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-09-14T14:14:33Z No. of bitstreams: 1 TeseVHP.pdf: 3273273 bytes, checksum: afe82ad5c25bb61d489c9fcaec24a835 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:20:25Z (GMT) No. of bitstreams: 1 TeseVHP.pdf: 3273273 bytes, checksum: afe82ad5c25bb61d489c9fcaec24a835 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:20:33Z (GMT) No. of bitstreams: 1 TeseVHP.pdf: 3273273 bytes, checksum: afe82ad5c25bb61d489c9fcaec24a835 (MD5) / Made available in DSpace on 2016-09-16T19:20:46Z (GMT). No. of bitstreams: 1 TeseVHP.pdf: 3273273 bytes, checksum: afe82ad5c25bb61d489c9fcaec24a835 (MD5) Previous issue date: 2015-05-07 / Não recebi financiamento / Demineralization and caries are often present in patients with orthodontic braces due to the increased accumulation of dental biofilm containing Streptococcus mutans, which produces acids that attack the tooth surface. The Antimicrobial Photodynamic Therapy (APDT) has been shown as an alternative in microbial inactivation in dentistry. This work, carried out both in vitro and in vivo, aims to evaluate the antimicrobial effect of APDT on Streptococcus mutans present in the dental biofilm accumulated on the metal surface of orthodontic appliances and in patients undergoing orthodontic treatment. The in vitro study evaluated the susceptibility of biofilm formed by S. mutans on the metal surface under the application of orthodontic appliances APDT induced Curcumin diluted surfactant (SDS) and blue light-emitting diode (LED). The samples were treated with the photosensitizer (PS) at a concentration of 1 g/L, 0.1% surfactant and exposed to LED light (455 ± 10 nm, 46mW/cm²), fluence of 30 J/cm². The experimental groups studied were: control group (P-L-S-); light (P-L+S-), surfactant (P-L-S+) and photosensitizer (P+L-S-) groups; surfactant-light (P-L+S+), photosensitizer-surfactant (P+L-S+) and PDT (P+L+S-) groups; and the PDT-surfactant (P+L+S+) group. Each group was named accordingly to the addiction or not of the photosensitizer (P+ or P-), surfactant (S+ or S-) and application or not of light (L+ or L-), respectively. The colonies grown on plates of brain heart infusion (BHI) were counted (CFU / mL) and the results were analyzed by ANOVA and the post hoc Tukey test (p <0.05). The results showed that in this research protocol, the group P+L+S+ was able to promote significant decrease (p<0.001) on the population of S. mutans of 99.999% compared to the control group. In the in vivo study, 24 volunteers were randomly selected in order to evaluate the clinical utility of APDT and the APDT association with the surfactant (SDS) as oral decontamination agents in orthodontic patients. The selected patients (n = 24) were randomly divided into seven groups: G1 - Negative control, G2 - Curcumin mouthwash, G3 - Curcumin mouthwash+SDS, G4 - light irradiation, G5 - APDT, G6 - APDT+SDS and G7 - Positive Control (chlorhexidine 0.12% moutwash). Saliva samples were collected from unstimulated way of each patient in three steps (S) as follows: S1 - initial condition S2 - Treatment with rinsing (water, curcumin or chlorhexidine) and S3 - After APDT. The photosensitiser used was curcumin with concentration of 1 g/L. Two types of blue LED light source emitting in 450±10nm were used in the present study: one emitting with an intensity of 33.54 mW/cm² and other with 212 mW/cm². Evaluation of microbial reduction, and survival fraction in each of the studied levels, was performed using the Kruskal-Wallis ANOVA test. Statistical analysis showed that only G6 and G7 presented results of bacterial inactivation that showed statistically significant differences (p<0.05) compared to those observed in G1. These results indicated that APDT, when combined with SDS surfactant, may be used as an adjunct agent for convenient oral decontamination promoter in vivo. / Desmineralizações e cáries dentais estão comumente presentes em indivíduos portadores de aparelho fixo ortodôntico, isto ocorre devido ao aumento de acúmulo de biofilme dental contendo Streptococcus mutans, os quais produzem ácidos que atacam a superfície dental. A terapia fotodinâmica antimicrobial (TFDA) tem sido mostrada como alternativa em inativação microbiana na Odontologia. Este trabalho, realizado in vitro e in vivo, tem o objetivo de avaliar o efeito antimicrobiano da TFDA sobre Streptococcus mutans em biofilme dental sobre superfície metálica de acessórios ortodônticos e em indivíduos sob tratamento ortodôntico. O estudo in vitro avaliou a susceptilidade de biofilme formado por S. mutans sobre superfície metálica de acessórios ortodônticos sob aplicação de TFDA induzida por Curcumina diluída em surfactante (SDS) e por diodo emissor de luz azul (LED). Nas amostras obtidas de lâminas de bandas ortodônticas foram formados biofilmes e tratadas com fotossensibilizador (FS) com concentração de 1g/L, surfactante a 0,1% e exposto a luz LED (455±10 nm, 46mW/cm²), com fluência de30J/cm2. Os grupos experimentais estudados foram: C- (somente lavagem com solução fisiológica); L+ (aplicação apenas de luz); S+L- (aplicação de surfactante); S+L+ (aplicação de surfactante e luz); F+L- (aplicação de fotossensibilizador sem luz); F+L+ (aplicação de fotossensibilizador e luz); F+L-S+ (aplicação de fotossensibilizador sem luz + surfactante) e F+L+S+ (aplicação de fotossensibilizador e luz + surfactante). As colônias cultivadas em placas com Brain Heart Infusion (BHI) foram contadas (UFC/mL) e os resultados foram analisados por ANOVA e teste Tukey post hoc (p<0.05). Os resultados obtidos demonstraram que no protocolo deste estudo o grupo F+S+L+ foi capaz de promover diminuição significativa(p<0,001) da população de S. mutans em 99,999% comparado ao grupo controle. No estudo in vivo, 24 voluntários foram selecionados aleatoriamente, com o objetivo de avaliar a eficiência clínica da TFDA e da associação da TFDA com o surfactante SDS como agentes de descontaminação bucal em indivíduos ortodônticos. Os indivíduos selecionados foram distribuídos aleatoriamente em sete grupos experimentais: G1 - controle negativo, G2 - bochechos com curcumina, G3 – bochechos com curcumina + SDS, G4 - irradiação com luz apenas, G5 - TFDA, G6 - TFDA + SDS e G7 - Controle Positivo (clorexidina 0,12%). Amostras de saliva foram coletadas de maneira não estimulada de cada um dos indivíduos em três etapas (s), como segue: S1 - Condição inicial, S2 - Tratamento com bochechos (água, clorexidina ou curcumina) e S3 - Após TFDA. O fotossensibilizador usado foi a Curcumina em concentração de 1g/L. Foi utilizado no estudo dois tipos de equipamentos de luz com LED azul (450 ± 10nm, 33.54 mW/cm2 e 212 mW/cm2). A avaliação da redução microbiana, e da fração de sobrevivência em cada um dos níveis estudados, foi realizada utilizando-se o teste ANOVA Kruskal-Wallis. A análise estatística mostrou que apenas os grupos 6 e 7 apresentaram resultados de inativação bacteriana que apresentavam diferenças estatisticamente significantes (p <0,05) em relação aos resultados observados no grupo 1. Estes resultados indicam que a TFDA associada com o surfactante SDS pode ser utilizado como agente auxiliar conveniente para promover a descontaminação bucal.
25

Mecanismos de ruptura em taludes altos de mineração a céu aberto / Failure mechanisms in high rock slopes at open pit mining

Rolando Enrique Zea Huallanca 14 December 2004 (has links)
Na última década, muitas minas a céu aberto têm alcançado alturas de 600 metros ou mais, algumas com perspectiva em projeto de alcançar mais de 1100 m. A literatura especializada revela que os mecanismos de ruptura para taludes altos ainda não são bem entendidos. Existem dúvidas tanto em relação aos mecanismos de ruptura, como quanto à estimativa da resistência do maciço rochoso em tal escala. Recentemente, há uma tendência crescente da aplicação de análises numéricas para estudar a estabilidade de taludes altos, mas ainda não se consegue reproduzir todos os fenômenos envolvidos. Análises reportadas na literatura consideram apenas a configuração final da cava, sem levar em conta o processo evolutivo da escavação, e o dano induzido ao maciço decorrente deste processo. Este trabalho analisa este efeito e suas conseqüências na avaliação da segurança. Realizaram-se análises bidimensionais de tensão-deformação em taludes de rocha. Tais análises foram realizadas com modelos elástico linear e elasto plástico de amolecimento da coesão e de endurecimento do atrito, considerando a mobilização não simultânea das componentes de resistência no critério de Mohr-Coulomb, e a danificação do maciço rochoso. Avaliação preliminar da segurança de um talude hipotético mostrou que estas considerações são muito importantes. Foram considerados a altura do talude, o ângulo do talude e as tensões in situ. 0 histórico de tensões modifica os parâmetros de resistência do maciço ao longo do talude por danificação. A região do pé do talude, em cada estágio de escavação, está sujeita a concentração de tensões induzidas que geram danificação ao maciço nestas áreas. A danificação em regiões do pé do talude pode explicar o inicio do processo de rupturas do tipo progressivo. / Along the last decade, many open pit mines have reached up to 600 meters or more in height, and some of them are planned to reach more than 1100 meters. The specialized literature shows that the failure mechanisms for high rock slopes are not well understood as yet. Doubts exist in relation to failure mechanisms, as well as to rock mass strength estimation in such scale. In recent years, there is a growing trend for the use of numerical analyses in order to study high rock slope stability, but they are not capable to reproduce all the phenomena involved. Analyses reported in the literature consider only the final configuration of the open pit, without taking into consideration the excavation evolution process, and damage induced to the rock mass resulting from this process. This work analyzes this effect and its consequences on the slope safety evaluation. Two dimensional stress strain analyses in rock slopes are described. Such analyses were conducted with linear elastic model and elasto plastic strain cohesion softening - friction hardening model considering the non-simultaneous mobilization of the strength components in the Mohr-Coulomb criterion, by including the rock mass damage. An approximate safety evaluation of a hypothetical slope shows that these considerations are very important. The stress path modifies the rock mass strength parameters close to the slope face by damage. The regions of the slope toe at each excavation stage are subjected to induced stress concentration causing damage to rock. This damage can explain the beginning of the progressive failure mechanism.
26

Characterization of Post-Plasma Etch Residues and Plasma Induced Damage Evaluation on Patterned Porous Low-K Dielectrics Using MIR-IR Spectroscopy

Rimal, Sirish 05 1900 (has links)
As the miniaturization of functional devices in integrated circuit (IC) continues to scale down to sub-nanometer size, the process complexity increases and makes materials characterization difficult. One of our research effort demonstrates the development and application of novel Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) as a sensitive (sub-5 nm) metrology tool to provide precise chemical bonding information that can effectively guide through the development of more efficient process control. In this work, we investigated the chemical bonding structure of thin fluorocarbon polymer films deposited on low-k dielectric nanostructures, using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Complemented by functional group specific chemical derivatization reactions, fluorocarbon film was established to contain fluorinated alkenes and carbonyl moieties embedded in a highly cross-linked, branched fluorocarbon structure and a model bonding structure was proposed for the first time. In addition, plasma induced damage to high aspect ratio trench low-k structures especially on the trench sidewalls was evaluated both qualitatively and quantitatively. Damage from different plasma processing was correlated with Si-OH formation and breakage of Si-CH3 bonds with increase in C=O functionality. In another endeavor, TiN hard mask defect formation after fluorocarbon plasma etch was characterized and investigated. Finding suggest the presence of water soluble amines that could possibly trigger the formation of TiN surface defect. An effective post etch treatment (PET) methods were applied for etch residue defect removal/suppression.
27

Ultrafast Mid-Infrared Laser-Solid Interactions

Werner, Kevin Thomas 11 July 2019 (has links)
No description available.
28

Measurements of Nonlinear Optical and Damage Properties of Selected Contemporary Semiconductor Materials

Carpenter, Amelia 07 August 2023 (has links)
No description available.
29

Couplage entre auto-focalisation et diffusion Brillouin stimulée pour une impulsion laser nanoseconde dans la silice / Coupling between self-focusing and stimulated Brillouin scattering for nanosecond laser pulses in silica

Mauger, Sarah 29 September 2011 (has links)
Dans le cadre des études sur l’endommagement laser liées au projet Mégajoule, nous analysons le couplage entre l’auto-focalisation induite par effet Kerr et la rétrodiffusion Brillouin stimulée pour des impulsions de durée nanoseconde se propageant dans des échantillons de silice. L’influence de la puissance d’entrée, des modulations de phase ou d’amplitude ainsi que la forme spatiale du faisceau sur la dynamique de filamentation est discutée. Nous montrons qu’une modulation d’amplitude appropriée divisant l’impulsion incidente en train d’impulsions de l’ordre de la dizaine de picosecondes supprime l’effet Brillouin pour toute puissance incidente mais réduit notablement la puissance laser disponible. A l’inverse, des impulsions modulées en phase avec une largeur spectrale comparable peuvent subir de la filamentation multiple et une auto-focalisation à distance plus courte causées par des instabilités modulationnelles. Nous démontrons cependant l’existence d’une largeur spectrale critique à partir de laquelle la rétrodiffusion peut être radicalement inhibée par une modulation de phase, même pour des fortes puissances. Cette observation reste valide pour des faisceaux de forme carrée avec des profils spatiaux plus larges, qui s’auto-focalisent beaucoup plus rapidement et se brisent en filaments multiples sur de courtes distances. L’inclusion de la génération de plasma pour limiter la croissance des ondes pompe et Stokes est finalement abordée. / As part of the studies on laser damage linked to the Megajoule project, we analyze the coupling between the Kerr induce self-focusing and the stimulated Brillouin backscattering pour nanosecond optical pulses propagating in silica samples. The influence of the incident power, phase or amplitude modulations as well as the spatial profile of the pulse of the filamentation dynamic is discussed. We show that an appropriate amplitude modulation dividing the incident pulse in pulse trains of picosecond durations suppresses the Brillouin effect for any incident power but noticeably reduces the available average laser power. On the contrary, phase modulated pulses with a comparable spectral width can undergo multiple filamentation and self-focusing at a shorter distance, caused by modulational instabilities. We demonstrate however the existence of a critical spectral bandwidth from which the backscattering can be radically inhibited by a phase modulation, even for high powers. This conclusion remains valid for spatially broader squared pulses, which self-focus earlier and break into multiple filaments at shorter distances. The inclusion of plasma generation to limit the growth of pump and Stokes waves is finally addressed.
30

Study of Blast-induced Damage in Rock with Potential Application to Open Pit and Underground Mines

Trivino Parra, Leonardo Fabian 31 August 2012 (has links)
A method to estimate blast-induced damage in rock considering both stress waves and gas expansion phases is presented. The method was developed by assuming a strong correlation between blast-induced damage and stress wave amplitudes, and also by adapting a 2D numerical method to estimate damage in a 3D real case. The numerical method is used to determine stress wave damage and provides an indication of zones prone to suffer greater damage by gas expansion. The specific steps carried out in this study are: i) extensive blast monitoring in hard rock at surface and underground test sites; ii) analysis of seismic waveforms in terms of amplitude and frequency and their azimuthal distribution with respect to borehole axis, iii) measurement of blast-induced damage from single-hole blasts; iv) assessment and implementation of method to utilize 2D numerical model to predict blast damage in 3D situation; v) use of experimental and numerical results to estimate relative contribution of stress waves and gas penetration to damage, and vi) monitoring and modeling of full-scale production blasts to apply developed method to estimate blast-induced damage from stress waves. The main findings in this study are: i) both P and S-waves are generated and show comparable amplitudes by blasting in boreholes; ii) amplitude and frequency of seismic waves are strongly dependent on initiation mode and direction of propagation of explosive reaction in borehole; iii) in-situ measurements indicate strongly non-symmetrical damage dependent on confinement conditions and initiation mode, and existing rock structure, and iv) gas penetration seems to be mainly responsible for damage (significant damage extension 2-4 borehole diameters from stress waves; > 22 from gas expansion). The method has the potential for application in regular production blasts for control of over-breaks and dilution in operating mines. The main areas proposed for future work are: i) verification of seismic velocity changes in rock by blast-induced damage from controlled experiments; ii) incorporation of gas expansion phase into numerical models; iii) use of 3D numerical model and verification of crack distribution prediction; iv) further studies on strain rate dependency of material strength parameters, and v) accurate measurements of in-hole pressure function considering various confinement conditions.

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