Orientador: Oseas Valente de Avilez Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica / Made available in DSpace on 2018-07-13T23:59:26Z (GMT). No. of bitstreams: 1 Santos_WaldomiroNogueirados_M.pdf: 2855702 bytes, checksum: f043ad2dfbc824c87b3d96e475b07970 (MD5) Previous issue date: 1991 / Resumo: Não informado / Abstract: Not informed. / Mestrado / Mestre em Engenharia Elétrica

The Stark field perturbed spectra of near infrared vibrational overtones of hydrogen fluoride and acetylene have been measured with a high resolution molecular beam laser spectrometer. A high performance laser power build-up cavity (optical resonator) was constructed to measured the weak ro-vibrational transitions of the v₂ + 3v₃ vibrational combination band of acetylene. The measured gain of the build-up cavity was found to be at least 300 out of a potential 2000. The primary reason for the lower than expected gain was attributed to losses induced by the extreme heat build-up on the mirror surfaces. The electric dipole moment for the v = 3 vibrational overtone of hydrogen fluoride was determined to be 1.9614 ± 0.0021 Debye. This result was compared with predictions from the available theoretical models and some theoretical constants were revised based on the current contribution to dipole moment function of hydrogen fluoride. The Stark field perturbed spectra of the v₁ + 3v₃ and v₂ + 3v₃ vibrational combination bands of acetylene were analysed for their polarisability tensors. In order to complete the study, the ground electronic state static polarisability and anisotropy of the polarisability were also determined. They were found to be 3.96A³ and 1.071 ± 0.014A³, respectively. The |1030⁰0⁰> state (v₁ + 3v₃) was observed to be coupled with the |0040⁰0⁰> infrared forbidden state (4v₃) in the presence of the Stark electric field. The resultant analysis produced values of 4.62 ± 0.09A³ for the polarisability and 1.15 ± 0.03A³ for the polarisability anisotropy of the |1030⁰0⁰> state. The difference in energy between |1030⁰0⁰> and |0040⁰0⁰> was determined to be 4.133 cm⁻¹, which compares well with local mode calculations. The measurements of the v₂ + 3v₃ band indicated that the |0130⁰0⁰> state was strongly coupled with another infrared allowed, unidentified (rogue), state in the absence of the Stark field as well as with the infrared forbidden, |1120⁰0⁰> state in the presence of the Stark field. The previously unobserved J = 5 ← 4 transition of the infrared allowed rogue state was recorded here for the first time. The Stark field perturbed spectra of the R(3) and R(5) ro-vibrational transitions of the v₂ + 3v₃ band also showed evidence of rogue transitions. The ensuing analysis determined that the |0130°0°) state has a polarisability of 3.5 ± 0.3A³ and a polarisability anisotropy of 5.6 ± 1.8A³. The Stark field perturbed spectra of the R(3) and R(5) transitions were fit to a non-crossing model and the energy levels of the rogue J = 4 and J = 6 states were determined. The energy level difference between |0130°0°) and |1120°0°) was determined to be -11.88±0.22 cm⁻¹. This does not compare well with local mode calculations and it is possible that the perturbations due to the presence of the rogue state impeded the accurate determination of the energy level difference. The identity of the rogue vibrational state could not be determined from the data presented in this thesis alone. However, collaborative work with another research group suggests that the rogue vibrational state is |0306°3¹) (see Chapter 7). / Graduate

Laser detonators offer several advantages over traditional electrical detonators, such as exploding bridgewire and slapper detonators, in terms of both safety and performance. Laser detonators remove the electrical conduction path to the energetic material, providing immunity from threats such as electrostatic discharge and lightning. A larger separation between the initiating energy source and the explosive devices is possible, up to several tens of metres, compared to a few metres for electrical slapper detonators. A laser detonator system has been developed, with laser-driven flyer plates used to shock initiate the explosive. All aspects of the system, including coupling into an optical fibre, used to transmit the laser energy to the detonator, the optical fibre, the flyer plate launch and acceleration and subsquent shock into the explosive, and the explosive initiation have been investigated, with an understanding of the underlying principles and processes developed. Shock initiation of two secondary explosives, hexanitrostilbene and pentaerythritol tetranitrate, has been studied at extremely high shock pressures, comparable to the detonation pressure, and the critical energy fluence required for initiation established. The laser detonator system is robust and optimised, with design tools developed to enable efficient design of future system / © Cranfield University, 2014

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.

Depuis plusieurs années, l’étude et le contrôle de la qualité de l’air sont au cœur de toutes les préoccupations. En 2012, la DGA (Direction Générale de l’Armement) met en place le programme ASTRID (Accompagnement Spécifique des Travaux de Recherches et d’Innovation Défense) accompagnant les travaux de recherche duale civile et militaire. Cette thèse s’inscrit dans cette démarche et propose d’étudier la faisabilité du concept de détection et d’identification rapides des microorganismes présents dans un échantillon d’air par microspectroscopie Raman, avec une résolution au niveau de l’espèce. Pour cela, nous construisons un modèle chimiométrique de classification des microorganismes représentatifs de la biodiversité naturelle en acquérant, sans a priori, d’une part les spectres Raman de ces microorganismes après biocollecte et étalement sur la lame d’un microspectromètre Raman, et d’autre part les séquences génomiques codant les ARN 16S de ces mêmes microorganismes.Les travaux de recherche présentés dans cette thèse présentent donc les différentes études mises en œuvre lors du développement d’un nouveau protocole permettant l’analyse des bactéries issues d’aérosols naturels environnementaux. Nous démontrons la nécessité d’optimiser l’acquisition des spectres Raman sur les bactéries et le traitement statistique des données spectrales permettant le développement de modèles de classification présentant des taux de reconnaissance élevés. / For several years, the study and the control of the quality of the air are at the heart of all the concerns. In 2012, the DGA (Direction Générale de l’Armement) employs the ASTRID program (Accompagnement Spécifique des Travaux de Recherches et d’Innovation Défense), to accompany the dual civil and military research work. This thesis is part of this approach and proposes the feasibility study, by Raman microspectroscopy, of the concept of rapid detection and identification of microorganisms present in an air sample, with a resolution at the species level. For this, we construct a chemometric model for the classification of micro-organisms representative of the natural biodiversity. Such a model is built by acquiring, without a priori i) the Raman spectra of these microorganisms after biocollection; and ii) the genomic sequences encoding the 16S RNAs of these same microorganisms. The research presented in this thesis therefore presents the different studies carried out during the development of a new protocol allowing the analysis of bacteria from natural environmental aerosols. We demonstrate the need to optimize the acquisition of Raman spectra on bacteria and the statistical processing of spectral data that allows the development of classification models with high recognition rates.

Les méthodes de combinaison cohérente sont rapidement apparues comme très prometteuses dans la course à la puissance des sources lasers. Cela s’explique par le fait que la puissance autour de l’axe de propagation évolue selon une loi quadratique avec le nombre de faisceaux combinés. Mes premiers travaux ont porté sur la montée en puissance de pompage dans les systèmes de mise en phase passive par auto-organisation. Pour la première fois, nous avons mis en évidence à la fois expérimentalement et numériquement, qu’au-delà du seuil laser, le filtrage spectral intracavité dû à la structure interférométrique du système laser, est un des principaux facteurs limitant l’obtention de qualités de phasage élevées. L’augmentation du nombre d’émetteurs accentue la dégradation de l’efficacité de combinaison avec la montée en puissance, montrant l’incapacité de ce type de méthode à combiner efficacement un grand nombre d’émetteurs lasers de forte puissance. Par la suite, mes travaux ont porté sur l’étude d’une méthode innovante de phasage actif, mise au point à XLIM. Le principe de cette méthode associe un filtrage optique de type contraste de phase, à un algorithme d’optimisation réduisant les écarts de phases entre émetteurs. Les calculs et expériences ont mis en évidence la très faible sensibilité de la méthode au nombre d’émetteurs mis en jeu. Les démonstrations de combinaison cohérente de 7 à 37 émetteurs fibrés délivrant jusqu’à 5W chacun ont été faites. Ce dernier résultat constitue aujourd’hui un record en termes de nombre d’émetteurs combinés de manière active. L’efficacité de combinaison en champ lointain a été estimée à une valeur élevée de 94%, correspondant à une erreur de phase résiduelle d’environ λ/25. Le faible nombre d’itérations d’algorithme nécessaires pour converger a permis de corriger les fluctuations de phase sur une bande d’environ 1kHz. / Coherent laser beam combining techniques rapidly appeared highly promising in the field of ultra-high power laser sources. Indeed, the combined intensity around the propagation axis follows a quadratic law with the number of combined emitters. The first part of my work has been focused on passive phasing techniques, based on self-organization properties of coupled lasers. We have shown, both numerically and experimentally, that the intracavity filtering function due to the interferometric nature of the set-up, is an intrinsic reason for combining efficiency decrease far above laser threshold. The decrease goes steeper when the number of combined laser increases, making that kind of system inappropriate for coherently combining a large number of lasers delivering high power. The second part of my work consisted in studying an innovative active phasing method that associates a phase-contrast like filter with an optimization algorithm reducing phase errors between emitters. Both simulations and experiments showed the weak sensitivity of this method to the number of combined emitters. We demonstrated the phasing of 7 to 37 fiber lasers, delivering up to 5W each. To the best of our knowledge, this last result is the highest number of fiber lasers combined with an active phasing method. The combining efficiency has been estimated around 94%, corresponding to a residual phase error of λ/25. The weak number of algorithm iterations needed to reach the in-phase regime offered a bandwidth of approximately 1kHz.

Regarding the higher demand of the total joint replacement (TJR) and revision surgeries in recent years, an implant material should provide much longer lifetime without failure. Nickel titanium (NiTi) is the most popular shape memory alloy in the industry, especially in medical devices due to its unique mechanical properties such as pseudo-elasticity, damping capacity, shape memory and good biocompatibility. However, concerns of nickel ion release of this alloy still exist if it is implanted for a prolonged period of time. Nickel is well known for the possibility of causing allergic response and degeneration of muscle tissue as well as being carcinogenic for the human body beyond a certain threshold. Therefore, drastically improving the surface properties (e.g. wear resistance) of NiTi is a vital step for its adoption as orthopaedic implants. To overcome the above-mentioned risks, different surface treatment techniques have been proposed and investigated, such as Physical Vapour Deposition (PVD), Chemical Vapour Deposition (CVD), ion implantation, plasma spraying, etc. Yet all of these techniques have similar limitations such as high treatment temperature, poor metallurgical bonding between coated film and substrate, and lower flexibility and efficiency. As a result, laser gas nitriding would be an ideal treatment method as it could overcome these drawbacks. Moreover, the shape memory effect and pseudo-elasticity of NiTi from a reversible phase transformation between the martensitic phase and the austenitic phase are very sensitive to heat. Hence, NiTi implant is subjected to the following provisions of the thermo-mechanical treatment process, and this implant provides desired characteristics. It is important to suggest a surface treatment, which would not disturb the original build-in properties. As a result, the low-temperature methods for substrate have to be employed on the surface of NiTi. This present study aims to investigate the feasibility of applying diffusion laser gas nitriding technique to improve the wettability and wear resistance of NiTi as well as establish the optimization technique. The current report summaries the result of laser nitrided NiTi by continuous-wave (CW) fibre laser in nitrogen environment. The microstructure, surface morphology, wettability, wear resistance of the coating layer has been analysed using scanning electron microscopy (SEM), X-ray diffractometry (XRD), sessile drop technique, 3-D profile measurement and reciprocating wear test. The resulting surface layer is free of cracks, and the wetting behaviour is better than the bare NiTi. The wear resistance of the optimised nitride sample with different hatch patterns is also evaluated using reciprocating wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in Hanks’ solution. The results indicate that the wear rates of the nitride samples and the UHMWPE counter-part were both significantly reduced. It is concluded that the diffusion laser gas nitriding is a potential low-temperature treatment technique to improve the surface properties of NiTi. This technique can be applied to a femoral head or a bone fixation plates with relatively large surface area and movable components.

Quel que soit le secteur d’activité, les procédés de fabrication additive pour les matériaux métalliques ont un fort potentiel industriel, spécifiquement pour la production de pièces à haute valeur ajoutée. Le secteur de l’outillage est l’un des utilisateurs de ces procédés, et plus particulièrement du Selective Laser Melting (SLM). Ce procédé permet de diminuer les coûts et les temps de production des outillages, tout en augmentant la complexité des pièces fabriquées. Cependant, pour améliorer la qualité des pièces fabriquées, une meilleure compréhension des mécanismes physiques qui le régissent est nécessaire. Dans ce travail de thèse, consacré à la modélisation du procédé SLM, les approches suivies sont multiphysiques à deux échelles. La première échelle de modélisation, utilisant la méthode Volume Of Fluid, correspond à la fusion d’un lit de poudre par un laser puis sa solidification. Le lit de poudre numérique est produit à partir d’un générateur spécifique basé sur la granulométrie identifiée expérimentalement. Après certaines hypothèses simplificatrices posées sur les phénomènes physiques à modéliser, la tension superficielle a été implémentée et a nécessité l’utilisation de la méthode des « heights functions ». La seconde échelle de modélisation correspond à la construction d’une succession de cordons à l’aide de la méthode des éléments finis. Le modèle thermomécanique utilise la méthode « element birth » pour se rapprocher au plus près des conditions réelles du procédé. Après leur validation par des essais expérimentaux, les simulations ont permis de prédire le champ de température, la largeur de la zone fondue, ainsi que la formation du « keyhole ». / Regardless the industry, additive manufacturing processes for metallic materials have a great industrial potential, especially to product high added value parts. One of the main users of these processes, and more specifically the Selective Laser Melting (SLM), is the tooling industry for plastics processing. It make possible to reduce production costs and manufacturing times while increasing the complexity of manufactured parts. However, in order to improve the quality of the latter and ensure their certifications, a better insight into the related physical phenomena undergone by the material during the process is still needed. In this PhD thesis, the SLM process modeling is multiphysic and concerns two different scales. The first modeling scale uses the Volume Of Fluid method to model the powder bed melting and its ensuing solidification. The numerical powder bed is computed thanks to a specific generator enabling to take account for the experimental granulometry. Once some simplifying assumptions on the physical phenomena stated, the surface tension has been implemented requiring the "heights functions" method use. The second modeling scale corresponds to the building of laser tracks series through the finite element method. The thermomechanical approach uses the element birth method in order to meet as far as possible the experimental conditions. Following its assessment through experiment/simulation face off, model have enable to predict the temperature field and the melted zone width as well as the keyhole formation.

No description available.

No description available.