The properties of two novel random fibre lasers, in which stimulated Brillouin scattering supplies the effective gain mechanism and Rayleigh scattering along the standard telecommunication optical fibre provides random distributed feedback, are characterised. Firstly, ultra-narrow microwave signals with a Dirac delta function profile are successfully created by beating two random-lasing near-Gaussian beams, arising from the synchronization of optical modes from two Stokes signals with random phase accumulated over the ultra-long optical fibre. This finding provides a completely new approach to synthesise high spectral purity microwave signals from Brillouin fibre lasers with randomised feedback. In addition, we also develop a theoretical model of the random fibre Fabry-Pérot resonator based on the fact that the pump depletion effect naturally selects out the effective Rayleigh feedback regions localised in both ends of this long fibre. A narrow random-laser output with the linewidth of ~860 Hz is experimentally demonstrated and is employed to characterise the linewidth of the pump light. Furthermore, the random laser dynamics is studied and one application towards the physical entropy source is eventually achieved.

Les particules de suie émises lors de la combustion d’hydrocarbures ont un impact important sur le réchauffement climatique et sur la santé. La compréhension des mécanismes de formation des particules de suie dans les flammes présente donc un fort intérêt environnemental. Cependant, le mécanisme de formation de ces particules pose toujours de nombreuses questions. En particulier la phase de nucléation, qui conduit à la formation des particules primaires de suie (nuclei) à partir de molécules HAPs (Hydrocarbures Aromatiques Polycycliques) en phase gazeuse, reste incomprise. Au cours de ce travail de thèse, nous avons mis en œuvre deux méthodes expérimentales de diagnostic laser, la Fluorescence Induite par Laser en Jet Froid (JCLIF) et l’Incandescence Induite par Laser (LII), respectivement pour la mesure de HAPs (naphtalène, pyrène et fluoranthène) et des particules de suies formées dans des flammes de CH4/O2/N2 stabilisées à basse-pression et de C2H4/air stabilisées à pression atmosphérique. Les résultats obtenus offrent une base de données expérimentale tout à fait originale pour l’amélioration de la compréhension des voies réactionnelles prépondérantes menant à la formation des particules de suie. Par ailleurs, nous avons également mis en évidence l’existence de flammes de nucléation, i.e des flammes dans lesquelles les particules de suie sont essentiellement formées par nucléation, sans subir de croissance de surface. Dans ce travail de thèse, nous montrons que ces flammes pourraient ainsi constituer un cas test unique et très pertinent pour la compréhension du processus de nucléation. / Soot particles emitted during fuel combustion have an important impact on global warming and health. Therefore, the improvement of the knowledge on soot particle formation mechanisms in flames shows an important environmental interest. However, this mechanism is not fully understood. Indeed, the nucleation step, forming primary particles (nuclei) from gaseous PAHs (Polycyclic Aromatic Hydrocarbons), is still speculative and needs accurate experimental data to be fully understood. In this work, two experimental techniques based on laser diagnostics have been implemented, the Jet-Cooled Laser Induced Fluorescence (JCLIF) and the Laser Induced Incandescence (LII), respectively for the measurement of PAHs (naphthalene, pyrene and fluoranthene) and soot particles formed in low-pressure CH4/O2/N2 flames and atmospheric pressure C2H4/air flames. These results offer an original experimental database for the improvement of the understanding of the main chemical pathways leading to soot particle formation. Besides, we also highlight the possibility of generating nucleation flames, i.e flames in which soot particles are essentially formed by nucleation, without growth by soot surface processes. In this thesis, we show that these specific flame conditions could be a unique test case, very well suited for the understanding of the soot nucleation process.

Drilling is an industrial process in which holes are produced by removal of material. This process is relatively well established for macroscale machining. However, microscale mechanical drilling is a more challenging process, especially in parts made of difficult-to-cut materials such as nickel-based superalloys. Although laser drilling and electrical discharge machining (EDM) have been reported as alternatives, mechanical drilling continues to be widely used for industrial macroscale drilling. However, mechanical microdrilling suffers from premature drill breakage due to the fragile nature of the microdrill. Furthermore, mechanical-drilled holes are inherently associated with geometry and metallurgy defects such as burr and subsurface damage, respectively. In laser percussion drilling, the challenge is how to improve the quality of the hole by minimising taper, recast layer, and heat affected zone formation. In addition, drilling hollow parts such as airfoil blades without introducing damage to the back wall is a major challenge in laser drilling. In drilling, the accuracy of the process and the quality of the surface finish are of great importance for both the manufacturer and the customer. Hybrid machining has been identified as a promising process which combines the benefits of different machining processes especially when applied to machining of superalloys. This Thesis presents a novel method to microdrill an Inconel 718 alloy, at both normal and inclined angles to the surface, using laser followed by mechanical drilling (sequential drilling). The method was aimed at extending the twist drill life and improving the quality of the hole when compared with existing techniques. The effect of laser predrilled-hole geometry on the quality of the produced hole were studied and evaluated. Continuous wave (CW) fibre and pulsed Nd:YAG lasers were used to produce holes with different geometry (blind, positive and negative tapered holes) as a pilot hole for mechanical drilling. CW fibre and Nd:YAG laser microdrilling of Inconel 718 alloy were implemented and evaluated before conducting the sequential drilling process. Taguchi methods were employed to design the experiments and analyse the results to establish the optimum set of parameters that yields an acceptable level of the response target. The standard commercial statistical software package MINITAB was used to evaluate the results. Initial experiments on the use of CW fibre laser drilling showed a great improvement in the quality of the hole and drilling speed. Those encouraging results inspired more experimental work and further evaluation of microdrilling of an Inconel 718 alloy. This unprecedented work was aimed at establishing the optimum conditions of laser and process parameters for hole taper, recast layer, and machining time. The results proved that the CW fibre laser drilling mechanism could be considered as a keyhole laser welding before material breakthrough. Furthermore, the process gas must be used to push away the molten material through the hole exit. The results also showed that a near zero tapered hole with very small recast layer and free of micro-cracks could be achieved with air process gas. This would have huge economical and environmental impacts since air is cheap and also an abundant resource. In the case of Nd:YAG laser microdrilling, the results proved that using assisted gas in laser drilling would not always increase the drilling speed or improve the quality of the hole. It was also found that the quality of the holes produced by air process gas is sufficient to meet the requirements for mechanical finishing. The sequential laser mechanical technique reduced the width of cut compared to mechanical drilling and relieved the load on the drill point resulting in a decrease in the thermal and mechanical stresses on the cutting tool. When compared with pure mechanical microdrilling, mechanical finishing of near zero laser drilled hole resulted in 100-330% increase in the tool life, up to 75% reduction in burr height, and significant improvement in surface integrity. In addition, the sequential laser and mechanical drilling of laser blind holes would be an effective technique for decreasing burr size and avoiding the back-wall problem in laser drilling of hollow parts especially when the exit surface of the components to be drilled has a closed cavity or is hard to access. It was also found that a smaller predrilled hole provided stability to the twist drill at the entry stage. However, burr size at the exit side decreased when the size of the predrilled hole was increased. Therefore, the mechanical finishing of negative tapered hole technique was developed to maintain the stability of the drill, extend the drill life, improve the burr size and surface integrity. The burr size for the mechanical finishing of negatively tapered laser predrilled holes was measured to be 6 times smaller than that of pure mechanical drilling. Finally, the results proved that the new technique alleviated the indentation and secondary cutting edge action. This would enable manufacturers to grind drills to thicker web thickness, which in turn, will increase the drill strength.

Shock waves generated by laser-driven ablation in solids have provided a great opportunity for the study of dense plasmas. The work presented in this thesis include measurements of Hugoniot curves and the reflectivity of shocked aluminum. In these experiments, planar aluminum targets were irradiated with a 0.53µm, 2ns (FWHM) laser pulse at irradiances up to ~ 10¹⁴/cm². Temporally and spectrally resolved measurements of the target rear surface luminous emission have yielded the shock speed and temperature Hugoniot curve which showed good agreement with equation of state predictions. In addition, temporally resolved reflectivity measurements of the shocked target rear surface compared well with a theoretical model for the electrical conductivity of a dense plasma. For copper and molybdenum targets, both the luminescence and the reflectivity measurements indicated that the heating of the dense target material was dominated by radiation transport from the coronal plasma rather than shock heating. An analysis of the molybdenum results indicate that x-ray shine-through may be the dominant energy transport mechanism to the target rear surface, whereas for the copper targets the transport process appears to be much more complex. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

L’ABS est un copolymère de Acrylonitrile-Butadiène-Styrène utilisé industriellement et dont la surface peut être recouverte para un dépôt métallique. Le processus traditionnel pour déposer des films métalliques de manière auto catalytique est connu comme « Electroless ». Cependant, ce processus utilise un mélange sulfochromique dans l’étape de traitement préliminaire de la surface, contenant du Cr (VI), qui est dans la liste des contaminants toxiques qui doivent être substitués. Il est donc primordial de développer de nouveaux procédés de modification de surface de faible impact sur l’environnement. Dans ce travail de thèse, nous avons développé trois nouvelles techniques de modifications de la surface d’ABS. Les deux premières permettent une modification générale de la surface et la troisième une modification spécifique. La première méthode, par voie sèche basée sur l’application en alternance de décharges Corona et radiations ultra-violet, est appelée « Traitement Optophysique ». La deuxième méthode appelée « Traitement Photocatalytique » correspond à l’application des propriétés photocatalytiques de nanoparticules de TiO2 (30nm) en suspension sur la surface du polymère et soumis à une radiation ultra-violet. La troisième méthode appelée « Traitement Optothermique » permettant une modification sélective, est réalisée par ablation thermique laser» à partir d’une sensibilisation de la surface avec des nanoparticules de Palladium et des particules d’Argent. Postérieur à l’étape de traitement « Traitement Optophysique » ou « Traitement Photocatalytique », les substrats ont été pré-métallisés soit par le procédé « Electroless », soit par le procédé de «Dépôt Chimique Dynamique » (DCP). A différence du procédé « Electroless », le procédé « DCP » ne nécessite pas d’une étape antérieure d’activation de sites superficielles avec des ions palladium. Le dépôt métallique final est réalisé par voie électrolytique conventionnelle. Les surfaces prétraitées ont été analysées par des Mesures d’Angle de Contact et les techniques de spectroscopie FT-IR et XPS. La présence de charges superficielles a été évaluée par la Mesure de Potentielle de Surface et de Radiométrie des Photoporteurs. La morphologie des surfaces a été observée et mesurée par les techniques de SEM, AFM et AFAM. Les analyses de rugosité ont été faites par Senseur Mécanique, par Optique Interférentielle et par AFM. L’adhérence des dépôts métalliques a été mesurée par la méthode de la Bande Adhésive sur Coupe Croisée (ASTM D-3359), les essais Pull Off. (ASTM D4541-02) et Peel Off (ASTM B533 A). Les dépôts les plus adhérents ont été obtenus avec un prétraitement « Optophysique » et une pré-métallisation par « DCP ». Les valeurs d’adhérence obtenues sont supérieures à celle des dépôts obtenus para le procédé traditionnelle « Electroless ». Le « Traitement Optothermique » a permis une gravure sélective de la surface de l’ABS en utilisant des lasers de faible puissance. / The ABS is a copolymer formed by Acrylonitrile-Butadiene-Styrene used in industry whose surface can be coated with a metallic deposit. The traditional process for depositing metallic films in an auto-catalytic way is know as “Electroless”, However, this process uses a sulfo-chromic mixture in the preliminary stage of the surface treatment containing Cr (VI) which is a toxic, polluting agent that needs to be replaced. Therefore, it is necessary to develop new surface modification procedures with a lower environmental impact. Three new techniques for ABS surface modification have been developed in this study. The first two allow a general surface modification and the third one a specific surface modification. The first method, using a dry system, is based on alternating a corona discharge with ultraviolet radiation and is called the “Optophysique Treatment”. The second method involves the application of the photocatalytic properties of TiO2 nanoparticles in a suspension on the polymer surface under ultraviolet radiation and is called “Photocatalytic Treatment”. The third method allows a selective modification using thermal laser ablation which is accomplished with the ABS sensibilization with palladium and silver particles and is called “Optothermal Treatment”. After the “Optophysique” or “Photocatalytic” treatments, the substrates were treated either by the ¨Electroless¨ method or by the “Dynamic Chemical Deposit” method. Unlike the “Electroless” method, the “DCP” method does not need a preliminary step to activate the surface sites with palladium ions. The final metallic coating is accomplished by a conventional electrolytic method. The pre-treated surfaces were analyzed by Contact Angle Measurements and with the spectroscopy techniques FT-IR and XPS. The presence of surface changes was evaluated by Potential Measurement and Photocarrier Radiometry. The surface morphology was observed and measured by the following techniques: SEM, AFM, and AFAM. The surface roughness analysis was performed by Mechanical Sensors, Optical Interference and AFM. The adherence of the metallic deposits was measured by the Cross Cut Tape test (ASTM D-3359), and the Pull Off test (ASTM D4541-02) and the Peel Off test (ASTM B533 A). The deposits with greater adhesion were obtained with the “Optophysique” treatment using a pre-coating done by “DCP”. The adherence values obtained were higher than those for deposits obtained by the traditional “Electroless” process. The Optothermal treatment allowed the selective etching on the ABS surface using low power lasers. / El ABS es un copolímero formado por Acrilonitrilo-Butadieno-Estireno utilizado industrialmente, cuya superficie puede ser metalizada mediante un depósito metálico. El proceso tradicional para depositar películas metálicas de manera autocatalítica es conocido como “Electroless”. Sin embargo, este proceso utiliza una mezcla sulfocrómica en la etapa de tratamiento preliminar de la superficie, conteniendo Cr (VI), contaminante tóxico que debe ser sustituido. Por lo tanto, es primordial desarrollar nuevos procedimientos de modificación superficial de bajo impacto ambiental. En este trabajo de tesis, se han desarrollado tres nuevas técnicas de modificación de la superficie del ABS. Los dos primeros permiten una modificación general de la superficie y la tercera una modificación específica. El primer método, realizado por vía seca, consiste en la aplicación en alternancia de descargas corona y radiación ultravioleta, este método es llamado “Tratamiento Optofísico”. El segundo método llamado “Tratamiento Fotocatalítico” corresponde a la aplicación de propiedades fotocatalíticas de nanopartículas de TiO2 (30 nm) en suspensión sobre la superficie del polímero y sometidas a una irradiación ultravioleta. El tercer método es llamado “Tratamiento Optotérmico” permite una modificación selectiva y es realizado por “ablación térmica láser” a partir de una sensibilización de partículas de Paladio y Plata. Posterior al tratamiento “Optofísico” o “Fotocatalítico”, los sustratos fueron pre-metalizados ya sea por el método “Electroless”, o por el método de “Depósito Químico Dinámico” (DCP). A diferencia del método “Electroless”, el método “DCP” no necesita de una etapa anterior a la activación de sitios superficiales con iones de Paladio. El depósito metálico final es realizado por vía electrolítica convencional. Las superficies pre-tratadas fueron analizadas por Medición de Ángulo de Contacto y con las técnicas espectroscópicas FT-IR y XPS. Se evaluó la presencia de cargas superficiales por la medición de potencial y radiometría de fotoportadores. La morfología de las superficies fue observada y medida por las técnicas de SEM, AFM y AFAM. Los análisis de rugosidad se hicieron por Sensores Mecánicos, por Interferencia Óptica y por AFM. La adherencia de los depósitos metálicos fue medida por el método de Cinta de Corte Cruzado (ASTM D-3359), la prueba Pull Off (ASTM D4541-02) y Peel Off (ASTM B533 A). Los depósitos de mayor adherencia fueron obtenidos con el tratamiento “Optofísico” y con un pre-metalizado realizado con “DCP”. Los valores de adherencia obtenidos son superiores al de los depósitos obtenidos por el proceso tradicional “Electroless”. El tratamiento Optotérmico permitió realizar un grabado selectivo sobre la superficie del ABS usando láseres de bajas potencias.

No description available.

Orientador: Carlos Henrique de Brito Cruz / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-19T02:59:59Z (GMT). No. of bitstreams: 1 Tsuda_Sergio_D.pdf: 11842009 bytes, checksum: 9726ce6253239d01271de132c4389497 (MD5) Previous issue date: 1994 / Resumo: Nesta dissertação serão apresentados os resultados das experiências de espectroscopia diferencial de transmissão resolvida no tempo em amostras de vidros dopados com semicondutor de CdSSe e CdTe. No primeiro tipo de amostras estudamos as mudanças induzidas no espectro de absorção das amostras quando elas são excitadas por um pulso óptico com duração de 60 fs na região acima e abaixo do "gap". No primeiro caso, as alterações do espectro de absorção são causadas por uma não-linearidade relacionada ao efeito de preenchimento de banda e o tempo de resposta é determinado pelo tempo de recombinação dos életrons fotoexcitados. Para a excitação na região de transparência da amostra observmos que o efeito não-linear responsável pelas mudanças é o efeito Stark óptico e a sua resposta é instantânea, isto é, ela dura essencialmente enquanto a excitação está presente. Para a amostra de CdTe, que apresenta efeitos de confinamento quântico sobre os portadores fotoexcitados, observamos a ocorrência da saturação da absorção de uma região do seu espectro de absorção. O efeito correspondente a esse tipo de alteração é conhecido por "hole burning". A dinâmica de relaxação dos portadores fotoexcitados, é inicialmente dominada pela relaxação dos buracos na banda de valência. Esse processo de relaxação ocorre num intervalo de tempo menor do que 100 fs. Posteriormente, a saturação da transição 1S-1S observada se recupera totalmente em menos de 500 fs, possivelmente devido à relaxação dos portadores através de estados de armadilha associados à ligações soltas ("dangling bonds") na interface vidro-semicondutor e/ou defeitos / Abstract: In this thesis the results of time resolved differential transmission spectroscopy in CdSSe and CdTe semiconductor-doped glasses are presented. In the first type of sample we have studied the induced changes in their absorption spectrum when they are excited by 60 fs optical pulses in the region below and above the gap. In the first situation, the spectral absorption changes are due to a nonlineaity related to band filling effect and the time response is determined by the photoexcited electron recombination. For excitation in the transparency region of the sample, we have observed that the nonlinear effect responsible for the changes, we have observed that the nonlinear effect responsible for the changes is the optical Stark effect and its time response is instantaneous, that is, it lasts as long as the excitation is present. For the CdTe sample, which exhibit quantum confinement effects on the photoexcited carriers, we have observed the occurrence of hole burning effects on the absorption spectrum. The relaxation dynamics of the photoexcited carriers is initially dominated by hole relaxation in the valence band. This relaxation process occurs within a time interval shorter than 100 fs. Later on, the observed bleaching of the 1S-1S transition recovers totally in less than 500 fs due to relaxation of the carriers through traps states associated to dangling bonds at the glass-semiconductor interface and/or defects / Doutorado / Física / Doutor em Ciências

BACKGROUND: Complaints of vitreous floaters are not new to veteran ophthalmologists, and many can attest to the reported burden symptomatic floaters have on visual clarity and quality of life. Classic treatment paradigms recommend indefinite observation or, in the case of severely bothersome floaters, pars plana vitrectomy (PPV). Despite the proven efficacy, PPV requires intraocular access and has a side effect profile that warrants severe visual impairment to justify the risks of surgery. Floater laser treatment has the potential to fill the treatment gap as a less invasive alternative using photodisruption to vaporize floaters. Studies have attempted to quantify the efficacy of Nd:YAG laser treatment with moderate success, but the safety profile of the laser floater treatment (LFT) is still limited in duration of follow-up. OBJECTIVE: To analyze the efficacy and safety of Nd:YAG laser vitreolysis performed in-clinic as measured by number of sessions, patients who went on to pursue secondary vitrectomy, and a self-reported survey comparing visual satisfaction before and after LFT. METHODS: In a retrospective study, 32 eyes with a history of symptomatic floaters of varied etiology were treated with the Ellex Nd:YAG laser set to single-shot mode with a maximal pulse energy of 7mJ. The number of treatments each patient underwent until receiving full visual benefit served as an objective measure of the efficacy of the laser. Secondary vitrectomy patients who failed laser vitreolysis were sampled as evidence of inadequate response to treatment. A self-administered survey explored patient satisfaction in terms of overall quality of vision, frequency/severity of floaters, and impact floaters have on activities of daily life (ADLs) before and after the laser, graded on a 4-point scale. RESULTS: Laser Floater Treatment performed in-clinic at Boston Vision/Boston Laser (BVBL) yielded moderate success in resolving symptomatic floaters, as indicated by improved mean patient scores following treatment for quality of vision (+1.13), frequency/severity of floaters (+1.00), and impact floaters have on ADLs (+1.33) when compared to pretreatment scales. The mean number of discrete treatment sessions to gleam full benefit of laser vitreolysis was 2.5 sessions per patient. Approximately 6% (2/32) patients failed vitreolysis and went on to pursue PPV. CONCLUSIONS: Our results showed an improvement of mean patient scores in overall quality of vision, severity of floaters, and floaters’ impact by at least 1 scale point, supporting the efficacy of laser vitreolysis. Patients underwent a mean of 2.5 treatment sessions, and offering multiple sessions likely bolstered the overall efficacy of the procedure. The sample population of 32 yielded only two patients (6%) who went on to pursue secondary vitrectomy, suggesting LFT could potentially serve as another treatment option filling the gap between observation and PPV.

No description available.

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.