The development and characterization of experimental setups for angle-resolved photoelectron spectroscopy (ARPES) and spin- and angle-resolved photoelectron spectroscopy (SARPES) is described. Subsequently, the two techniques are applied to studies of the electronic band structure in topologically non-trivial materials. The laser-based ARPES setup works at a photon energy of 10.5 eV and a typical repetition rate in the range 200 kHz to 800 kHz. By using a time-of-flight electron energy analyzer electrons emitted from the sample within a solid angle of up to ±15 degrees can be collected and analyzed simultaneously. The SARPES setup is equipped with a traditional hemispherical electron energy analyzer in combination with a mini-Mott electron polarimeter. The system enables software-controlled switching between angle-resolved spin-integrated and spin-resolved measurements, thus providing the possibility to orient the sample by mapping out the electronic band structure using ARPES before performing spin-resolved measurements at selected points in the Brillouin zone. Thin films of the topological insulators (TIs) Bi2Se3, Bi2Te3 and Sb2Te3 are grown using e-beam evaporation and their surface states are observed by means of ARPES. By using a combination of low photon energies and cryogenic sample temperatures the topological states originating from both the vacuum interface (surface) and the substrate interface are observed in Bi2Se3 films and Bi2Se3/Bi2Te3 heterostructures, with total thicknesses in the ultra-thin limit (six to eight quintuple layers), grown on Bi-terminated Si(111) substrates. Band alignment between Si and Bi2Se3 at the interface creates a band bending through the films. The band bending is found to be independent of the Fermi level (EF) position in the bulk of the substrate, suggesting that the surface pinning of EF in the Si(111) substrate remains unaltered after deposition of the TI films. Therefore, the type and level of doping of the substrate does not show any large influence on the size of the band bending. Further, we provide experimental evidence for the realization of a topological crystalline insulator (TCI) phase in the narrow-band semiconductor Pb1−xSnxSe. The TCI phase exists for temperatures below the transition temperature Tc and is characterized by an inverted bulk band gap accompanied by the existence of non-gapped surface states crossing the band gap. Above Tc the material is in a topologically trivial phase where the surface states are gapped. Thus, when lowering the sample temperature across Tc a topological phase transition from a trivial insulator to a TCI is observed. SARPES studies indicate a helical spin structure of the surface states both in the topologically trivial and the TCI phase. / <p>QC 20130507</p>

[pt] Atualmente, os lasers de alta potência estão sendo testados pela indústria de petróleo como ferramentas de perfuração. Isto ocorre visando dois objetivos fundamentais: (i) aumentar a eficiência na perfuração de poços (maior taxa de penetração) e (ii) melhorar o controle da geometria do corte de revestimento no processo de canhoneio de poço. Este trabalho tem como objetivo contribuir para a tecnologia de canhoneio a laser em rochas carbonáticas através do desenvolvimento de técnicas para aumentar o volume de rocha removida por unidade de tempo. Estudou-se o comportamento termomecânico das rochas carbonáticas quando um laser é utilizado como ferramenta de perfuração no processo de canhoneio. Este conhecimento, obtido através de experimentos e simulações, forneceu dados para a otimização dos parâmetros de perfuração. Foram investigadas as condições de perfuração estática (não há movimentação do feixe do laser) e dinâmica (o feixe do laser percorre uma trajetória espiral). Além disso, foram investigados os resultados da perfuração sob pressão atmosférica e também utilizando uma câmara de pressão projetada para emular a pressão confinante do reservatório. Foram realizados testes experimentais de perfuração a laser com corpos de prova feitos a partir da rocha Bege Bahia. O Bege Bahia é um afloramento utilizado para simular as rochas encontradas nos reservatórios do Pré-sal. A análise destes corpos de prova foi feita através de inspeção e da caracterização por microtomografia, permitindo observar e caracterizar as propriedades da rocha, além da zona termicamente afetada (ZTA), características geométricas do furo, e valores da energia específica da perfuração. Estes resultados foram comparados com resultados obtidos através de simulações. Na modelagem numérica, o processo de canhoneio foi simulado pelo método de elementos finitos através de um modelo termomecânico elástico transiente axissimétrico que verificou as condições de perfuração. O modelo numérico permitiu observar o comportamento das tensões e temperaturas nos testes que envolvem altas temperaturas e altas pressões. Estas grandezas são usualmente difíceis de serem medidas em ensaios experimentais e, portanto, não foram observadas nos ensaios experimentais discutidos nesta tese. Também foram obtidos através da modelagem numérica valores para propriedades da rocha e da zona termicamente afetada (ZTA), características geométricas do furo, e valores da energia específica da perfuração. Os resultados numéricos obtidos foram comparados com resultados dos ensaios experimentais. Os resultados obtidos mostraram que a condição de perfuração dinâmica consegue remover uma quantidade maior de material e produzir uma ZTA maior em Comparação com o teste estático, gerando uma melhor relação tempo x potência. Os testes estáticos e dinâmicos permitiram se chegar às condições de canhoneio mais eficientes para a perfuração da rocha. A análise de tensões do modelo mostrou uma correlação compatível com o perfil do dano encontrado nos ensaios experimentais. / [en] Currently, the petroleum industry is testing high power lasers as drilling tools. The use of these lasers for this application has two main reasons: (i) to increase the efficiency of well drilling (higher penetration rate) and (ii) to improve the control of the geometry of the hole in the casing during the perforation process of the well. The present thesis has the purpose of contributing to the laser perforation technology in carbonate rocks by developing techniques to increase the volume of rock removed by unit of time. The thermo-mechanical behavior of the carbonate rocks was studied when a laser is used as the drilling tool in the perforation process. This knowledge, obtained through experiments and simulations, supplied data for the optimization of the drilling parameters. Both static (the laser beam does not move) and dynamic (the laser beam moves in a spiral trajectory) drilling conditions were investigated. Also investigated were drilling conditions under atmospheric pressure and under high pressure, where a pressure chamber designed to emulate pressure conditions of reservoirs was used. Experimental tests were performed by laser drilling samples made of Bege Bahia rock. This rock is used to simulate rocks found in pre-salt reservoirs. The analysis of these samples was performed through inspection and microtomography characterization, allowing the observation of properties of the rocks and of the heat affected zone (HAZ), geometric characteristics of the hole, and values of the drilling specific energy. These results were compared to the results obtained by simulations. In the numerical modeling, the perforation process was simulated with the finite element method through a transient axisymmetric thermo-mechanical elastic model that verified the drilling conditions. The numerical model allowed the observation of the behavior of the tensions and temperatures in tests involving high temperatures and pressures. These properties are usually difficult to measure in experimental tests and, therefore, were not measured during the experimental tests discussed in this thesis. Also obtained by numeric modeling were: properties of the rock and of the HAZ, geometric characteristics of the hole, and values of the drilling specific energy. The numeric results obtained were compared to the experimental results. The results obtained showed that the dynamic drilling condition is able to remove a larger amount of material and produce a larger HAZ, compared to the static condition, thus generating a better time x power relation. The static and dynamic tests allowed reaching more efficient conditions for rock drilling. The analysis of the tension of the model showed a compatible correlation with the damage profile found in the experimental tests.

Os Medidores de Distância por Triangulação a Laser são sistemas optoeletrônicos destinados à medição de pequenas distâncias ou deslocamentos, sem contato físico direto. Estes equipamentos possuem um grande campo de aplicações industriais. Este trabalho descreve as diversas configurações que este equipamento pode se apresentar, discutindo suas vantagens relativas. São estudadas também as suas partes e os componentes mais indicados. O projeto detalhado de um medidor usando sensor tipo CCD, e apresentado. Algumas aplicações industriais deste modelo são relatadas e diversos métodos e sugestões de uso são apresentadas, com base nas experiências realizadas pelo autor. / Laser Triangulation Rangefinders are non-contact, optoelectronic devices for measurement of small displacements or distances. These devices offer a broad range of industrial applications. This work explains common configurations, parts and main components, comparing their advantages. A detailed project on a CCD based Laser Rangefinder is presented. Some industrial applications for that project are related, discussing practical aspects based on authors experience. Some potential applications are also suggested.

La fabrication de tissus biologiques a été largement étudiée pour ses applications dans la recherche, la transplantation d'organes et le dépistage de drogues. Bien que des tissus minces ou avasculaires aient été fabriqués avec succès auparavant, le maintien de la viabilité des tissus épais nécessite la présence d'un réseau capillaire tout au long de la construction pour permettre l'apport de nutriments et l'élimination des déchets cellulaires par le sang. En plus des cellules endothéliales, l'incorporation de types de cellules de soutien dans le réseau capillaire est nécessaire pour favoriser la survie et la maturation. Comparée à d'autres méthodes de biofabrication, la bioimpression est une technologie prometteuse qui permet la fabrication précise de motifs 3D complexes à haute résolution spatiale. Nous avons conçu de nouveau notre procédé technique de bio-impression laser nommé LIST (de l'anglais \textit{laser-induced side transfer}) dans laquelle la bioencre de la suspension cellulaire passe à travers un capillaire horizontal avec un orifice face à l'échafaudage. Lorsque le laser frappe la bioencre, une bulle se forme qui propulse une gouttelette à travers l'orifice. Nous avons mené une étude détaillée pour caractériser cette bio-impression technique et validé sa cytocompatibilité par l'évaluation de la viabilité de HUVECs imprimés grâce à LIST. Nous avons incorporé des fibroblastes et des péricytes dans nos échantillons et observé le recrutement progressif de ces cellules par les structures de type capillaire HUVEC imprimées sur Matrigel. Des images fluorescentes ont été analysées pour quantifier le recrutement de fibroblastes/péricytes au fil du temps. / The fabrication of biological tissues in laboratory settings has been widely investigated for its applications in research, organ transplantation, and drug screening. Although several previous attempts to generate avascular or thin tissues have been successful, there remains the challenge to create thick functional tissues. Maintaining the viability of thick tissues requires the presence of a capillary network throughout the construct to allow the intake of nutrients and the discard of cellular waste through blood. In addition to endothelial cells, the incorporation of supporting cell types is necessary to promote survival, maturation, and acquire in vivo-like functionality. Compared to other biofabrication methods, bioprinting is a promising technology that enables the precise fabrication of complex 3D patterns at high spatial resolution. We have come up with a new configuration of our in-house laser-based bioprinting technique called laser-induced side transfer (LIST) in which the bioink passes through a horizontal glass capillary with an orifice facing the receiving substrate. When the laser beam causes bubble formation in the bioink, a liquid jet exits through the orifice that will eventually form a droplet. We have conducted a detailed study to characterize this bioprinting technique and validated its cytocompatibility through viability assessment of LIST-printed human umbilical vein endothelial cells (HUVECs). In an effort to generate physiological blood vessels, we incorporated fibroblasts and pericytes in our samples and observed the gradual recruitment of these cells by the printed HUVEC capillary-like structures on Matrigel. Fluorescent images were taken and analyzed to quantify the fibroblast/pericyte recruitment over time.

No description available.

L'utilisation de techniques de spectroscopie cohérente comme la diffusion Raman anti-Stokes cohérente (DRASC) sont communément utilisées pour l'analyse quantitative de milieux réactifs.Dans le cadre des progrès récents des sources lasers et des détecteurs, ce travail de thèse propose une adaptation de la technique de mesure de température au régime des impulsions ultra-courtes (femtoseconde, picoseconde) à haute cadence.Le développement d'un dispositif expérimental de DRASC en régime hybride fs/ps utilisant un laser femtoseconde et un réseau de Bragg en volume a permis de générer une impulsion de sonde de 30 ps. Dans la configuration choisie pour ce travail, la résolution spectrale est de 0,7 cm-1, ce qui réprésente l'état de l'art. Ce dispositif est appliqué à la spectroscopie ro-vibrationnelle de plusieurs espèces moléculaires.Pour décrire l'interaction dans ce régime temporel, un modèle de simulation des spectres DRASC est implémenté. Cette modélisation prend notamment en compte le profil en amplitude et phase de la sonde ainsi que son retard par rapport à l'excitation femtoseconde. L'influence des collisions moléculaires est discutée dans le cadre du régime hybride.Les ajustements des spectres calculés sur des spectres expérimentaux enregistrés dans l'air ambiant et dans une flamme de prémélange CH4/air, permettent de valider la modélisation proposée dans ce travail. En particulier, la température est mesurée à froid et à chaud à pression atmosphérique, avec une précision comparable à l'état de l'art dans le régime hybride fs/ps.Ce travail permet d'obtenir des résultats probants, et de valider la pertinence du montage développé pour la thermométrie. Fort de ces résultats, des applications en chambre de combustion réelles sont envisagées à court terme à l'ONERA, notamment par l'extrapolation du modèle à haute pression. / Coherent spectroscopy such as Coherent Anti-Stokes Raman Scattering (CARS) is commonly used for the study of reactive media.Following the recent progress encountered in laser sources and detectors, this thesis work proposes an adaptation of the technique for temperature measurements that exploits the ultra-short pulse regime (femtosecond, picosecond) to operate at high repetition-rate.The developed hybrid fs/ps-CARS setup delivers a 30-ps probe pulse using a femtosecond laser source and a Volume Bragg Grating. The obtained spectral resolution is 0,7 cm-1, which represents, within this pulse generation framework, the state of the art. This setup is applied to ro-vibrational spectroscopy of several molecular species.The interaction in the hybrid regime is described through a CARS simulation model that has been implemented. The modelling takes into account both the amplitude and the phase profiles of the probe pulse, and its delay to the femtosecond excitation. Influence of molecular collisions in the hybrid regime is also discussed.This modelling has been validated by fitting calculated spectra on experimental spectra recorded in ambient air, and in a premixed CH4/air flame. Temperature has been then measured at atmospheric pressure in these media. The precision is similar to the hybrid fs/ps-CARS thermometry state of the art.This work validates our N2 thermometry approach based on both the developed CARS setup and simulation model. Short term perspectives of this work are measurements on real combustion chambers at ONERA, by extrapolating our simulation model at high pressure.

Atomization characteristics of liquid fuel sprays control combustion efficiency and emissions in engines. The present work is motivated by the need to study the atomization and spray structure of vegetable oil biofuels for which no data in the literature exists. In this work, various laser-based diagnostic techniques such as laser shadowgraphy, Particle/Droplet Image Analysis (PDIA) and Laser Sheet Dropsizing (LSD) are applied for studying atomization characteristics, tip penetration, droplet size and liquid volume fraction of Pongamia vegetable oil (SVO) and its blends with diesel. A constant volume high pressure spray visualization chamber is designed and fabricated to study SVO sprays at high gas pressure and temperature conditions. This optical chamber can be used for gas pressures up to 60 bar and temperatures up to 600 K. Optical access inside the chamber is provided through four quartz windows to perform various optical spray diagnostic studies. A high pressure spray injection facility based on components of common rail diesel injection system is designed. This facility can provide an injection pressure of up to 1700 bar with independent control over injection duration and timing. A marked difference is observed between diesel and SVO spray structures under atmospheric gas pressure condition. A very interesting observation related to the behavior of 100% SVO fuel when sprayed into atmospheric pressure is the presence of an intact liquid core even at injection pressure as high as 1600 bar. The presence of liquid core at high injection pressures is attributed to the high viscosity of SVOs and the non-Newtonian behavior of these oils under high pressure and shear. The spray characterization of the oil and its blends at high gas pressure shows that although the atomization is dramatically different from that at atmospheric gas pressure, it is still incomplete even at very high injection pressures. For a gas pressure of 30 bar, it is observed that the Sauter Mean Diameter (SMD) for Pongamia oil is more than twice that of diesel. A new method of simultaneously obtaining two-dimensional droplet size and quantitative liquid volume fraction data in sprays has been developed. Measurements with this method reveal a higher liquid volume fraction at the central axis of spray for Pongamia oil compared to that of diesel indicating potentially poor air-fuel mixing. The experimental data obtained and the spray tip penetration correlations developed for the vegetable oils and blends serve as useful inputs for fuel injection and engine system designers.

Additive manufacturing can bring several advantages in tooling applications especially hot working tooling as high pressure die casting. Printing of conformal cooling channels can lead to improved cooling and faster solidification, which, in turn, can possibly result in better quality of the cast part. However, few studies on advantages of additive manufactured tools in high pressure die casting are published.The aim of this study was to investigate and quantify the effect of conformal cooling on microstructure and mechanical properties of high pressure die cast aluminum alloy. Two tools each consisting of two die inserts were produced with and without conformal channels using additive manufacturing. Both tools were used in die casting of aluminum alloy. Aluminum specimens were then characterized microstructurally in light optical microscope for secondary arm spacing measurements and subjected to tensile and hardness testing. Cooling behavior of different inserts was studied with a thermal camera and by monitoring the temperature change of cooling oil during casting. Surface roughness of die inserts was measured with profilometer before and after casting.Thermal imaging of temperature as a function of time and temperature change of oil during casting cycle indicated that conformal insert had faster cooling and lower temperature compared to conventional insert. However, thermal imaging of temperature after each shot in a certain point of time showed higher maximum and minimum temperature on conformal die surface but no significant difference in normalized temperature gradient compared to the conventional insert.The average secondary dendrite arm spacing values were fairly similar for samples from conventional and conformal inserts, while more specimens from conventional insert demonstrated coarser structure. Slower cooling in conventional insert could result in the coarser secondary dendrite arm spacing.Tensile strength and hardness testing revealed no significant difference in mechanical properties of the specimens cast in conventional and conformal die inserts. However, reduced deviations in hardness was observed for samples cast with conformal insert. This is in agreement with secondary dendrite arm spacing measurements indicating improved cooling with conformal insert.Surface roughness measurement showed small wear of the inserts. More castings are needed to observe a possible difference in wear between the conventional and conformal inserts.Small observed differences in cooling rate and secondary arm spacing did not result in evident difference in mechanical properties of the aluminum alloy but the variation in properties were reduced for samples cast with conformal cooling. Future work may include more accurate measurement of cooling behavior with a thermocouple printed into the die insert, casting of thicker specimen for porosity evaluation and fatigue testing and longer casting series to evaluate the influence of conformal cooling on tool wear.

Additive Manufacturing (AM) is on the verge of causing a downfall to conventional manufacturing with its huge potential in part manufacture. With an increase in demand for customized product, on-demand production and sustainable manufacturing, AM is gaining a great deal of attention from different industries in recent years. AM is redefining product design by revolutionizing how products are made. AM is extensively utilized in automotive, aerospace, medical and dental applications for its ability to produce intricate and lightweight structures. Despite their popularity, AM has not fully replaced traditional methods with one of the many reasons being inferior surface quality. Surface texture plays a crucial role in the functionality of a component and can cause serious problems to the manufactured parts if left untreated. Therefore, it is necessary to fully understand the surface behavior concerning the factors affecting it to establish control over the surface quality. The challenge with AM is that it generates surfaces that are different compared to conventional manufacturing techniques and varies with respect to different materials, geometries and process parameters. Therefore, AM surfaces often require novel characterization approaches to fully explain the manufacturing process. Most of the previously published work has been broadly based on two-dimensional parametric measurements. Some researchers have already addressed the AM surfaces with areal surface texture parameters but mostly used average parameters for characterization which is still distant from a full surface and functional interpretation. There has been a continual effort in improving the characterization of AM surfaces using different methods and one such effort is presented in this thesis. The primary focus of this thesis is to get a better understanding of AM surfaces to facilitate process control and optimization. For this purpose, the surface texture of Fused Deposition Modeling (FDM) and Laser-based Powder Bed Fusion of Metals (PBF-LB/M) have been characterized using various tools such as Power Spectral Density (PSD), Scale-sensitive fractal analysis based on area-scale relations, feature-based characterization and quantitative characterization by both profile and areal surface texture parameters. A methodology was developed using a Linear multiple regression and a combination of the above-mentioned characterization techniques to identify the most significant parameters for discriminating different surfaces and also to understand the manufacturing process. The results suggest that the developed approaches can be used as a guideline for AM users who are looking to optimize the process for gaining better surface quality and component functionality, as it works effectively in finding the significant parameters representing the unique signatures of the manufacturing process. Future work involves improving the accuracy of the results by implementing improved statistical models and testing other characterization methods to enhance the quality and function of the parts produced by the AM process.

Human immunodeficiency virus type 1 (HIV-1) still causes a chronic infection that affects millions of individuals worldwide. The infection remains incurable and presents a huge challenge for treatment, as it tends to disable a patient’s immune system. Although the current HIV-1 treatment regime possesses the ability to reduce the viral load to undetectable limits, complete eradication of the virus cannot be achieved while latent HIV-1 reservoirs go unchallenged. These viral reservoirs are established early on during HIV-1 infection and are a major hurdle since they remain unaffected by antiretroviral drugs and have the ability to replenish systemic infections once treatment is interrupted. Further ailments with the highly active antiretroviral therapy (HAART) include issues such as the cumbersome lifelong treatment, development of drug resistant strains of HIV-1 and adverse side effects. Contrarily, early diagnosis of the HIV-1 infection and HIV-1 treatment is a major challenge in resource-limited countries. The current available diagnostic tools for HIV-1 infection have shown to be highly accurate in monitoring CD4+ T lymphocyte count and viral load measurements. However, these tests such as enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) which are highly efficient, are usually very expensive with complex operation, time consuming, require skilled personnel and training that makes them incompatible for the application in resource-limited areas. Therefore, this raises the urgent need for developing an HIV point of care (POC) diagnostic tool that is label-free, highly specific and sensitive as well as therapeutic modalities, which can be used to address the previously mentioned challenges. Much research has been conducted to resolve these problems but to date, there has not been application of laser and/or photonics in HIV research. Therefore, in this thesis a femtosecond laser was used in HIV infected cells for targeted antiretroviral drug delivery while preserving their viability. For the first time according to our knowledge, antiretrovirals (ARVs) that target all the life stages of the HIV-1 life cycle were utilized and they proved to be significant in reducing HIV-1 infection. Furthermore, through the employment of a continuous wave laser at 640 nm, for the first time, surface plasmon resonance was conducted to facilitate label-free detection of HIV-1. Success of these laser based technologies will open doors for incorporation in POC HIV diagnostic tools for the detection and treatment monitoring of HIV in resource-limited settings. / Physics / Ph. D. (Physics)