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Das Ziel der vorliegenden Arbeit bestand in der Integration einer Technologie zur Erzeugung zeitlich alternierender (gepulster) Gasströme auf dem Gebiet der Laserfügetechnik. Für die technische Realisierung implizierte dies spezifische Anpassungen der drei Systemkernelemente (Stelleinheit, Messstrecke, Regelung) bzw. eine vollständige Neukonzeption des Technologieaufbaus. Die somit dem Anwender zur Verfügung stehenden neuen Parameter ermöglichten eine positive Beeinflussung des Fügeprozesses bzw. der Schweißergebnisse. Über die zeitliche Steuerung des Gasvolumenstroms in Korrespondenz zum Laserstrahlschweißprozess gelang es, mit Schutzgaspulsen eine Krafteinwirkung auf die Schmelze hervorzurufen und dadurch eine Verbesserung in Hinblick auf die Einschweißcharakteristik von lasergeschweißten Nähten zu realisieren. / The present study focuses on the integration of a technology for generating temporally alternating (pulsed) gas flows in the field of laser welding. The technical realization required the specific adaptation of the three core elements of the system (valve, section of measurements, control system) or rather a completely new concept of the technological setup. The new parameters allow for a positive influence on the joining process and on the results of welding, respectively. By means of temporal control of the gas volume flow in combination with a laser welding process, it was possible to produce a force effect on the molten.

The demand for high energy battery assemblies is growing in sectors such as transportation. Alongwith it is the need for reliable, efficient and cost-effective ways to electrically connect the batteries toensure their performance. Battery cells are most often put into modules or packs when produced forelectrically driven vehicles. The variable of greatest influence when welding battery packs is thecontact resistance between the cell and the connection tab. It is crucial to minimize this variable asmuch as possible to prevent energy loss in the form of heat generation. The purpose of this project is to conduct a comparative literature study of different weldingtechniques for welding batteries. The compared techniques are resistance spot welding, laser beamwelding and ultrasonic welding. The performance was evaluated in terms of numerous factors such asproduction cost, degree of automation and weld quality. All three methods are tried and proven to function in the production of battery applications. Eachmethod has separate strengths and limitations which makes them complement each other. Thus, it isimportant to look at several factors when deciding which welding technique is the most suitable forthe desired application. The scale of production, economical aspects as well as battery cell geometrywere concluded to be the most important in making this decision.

After nearly 100 years of particle acceleration, particle accelerator experiments continue providing results within the field of high energy physics. Particle acceleration is used worldwide in practical applications such as radiation therapy and materials science research. Unfortunately, these accelerators are large and expensive. Dielectric Laser Acceleration (DLA) is a promising technique for accelerating particles with high acceleration gradients, without requiring large-scale accelerators. DLA utilizes the electric field of a high energy laser to accelerate electrons in the proximity of a nanostructured dielectric surface.The aim of this project was limited to laser beam routing and imaging techniques for a DLA experiment. The goal was to design the laser beam pathway between the laser and the dielectric sample, and testing a proposed imaging system for aiming the laser. This goal was achieved in a test setup using a low-energy laser. In the main setup including a femtosecond laser, the result indicated lack of focus. For a full experimental setup, a correction of this focus is essential and the beam path would need to be combined with a Scanning Electron Microscope (SEM) as an electron source.

O aço de médio carbono e baixa liga SAE 4340 vem sofrendo diversas modificações e neste processo de desenvolvimento surgiu o aço 300M. O presente trabalho visa avaliar e comparar a microestrutura e a resistência mecânica dos aços SAE 4340 e 300M, submetidos ao processo de soldagem autógena a laser e em seguida a duas formas de tratamento: o revenimento pós-soldagem e a nitretação à plasma. Também é avaliado o efeito combinado dos tratamentos de revenimento e nitretação. Após soldagem, as chapas foram divididas nos lotes: como recebido, soldado, soldado e revenido, soldado e tratado superficialmente por nitretação a plasma e soldado, revenido e tratado superficialmente por nitretação a plasma. A partir desses lotes, foram obtidas amostras para análise microestrutural e produzidos corpos-de-prova para ensaios de tração. Os resultados mostraram que a presença de precipitados confere ao aço 300M maior resistência mecânica em relação ao aço 4340. Após a soldagem a laser, a zona fundida e zona termicamente afetada de ambos os materiais apresentaram fases diferentes das fases presentes no metal base, a zona fundida mostrou-se martensítica em sua maioria, e a zona termicamente afetada apresentou-se multifásica. Devido às dimensões reduzidas do cordão de solda, o comportamento em tração dos corpos-deprova soldados não diferiu significativamente dos corpos-de-prova produzidos com os materiais de base. O tratamento térmico de revenimento pós-soldagem promoveu queda na dureza da zona fundida em ambos os aços. Após a nitretação, os aços 4340 e 300M apresentaram aumento de dureza próximo às superfícies. O aço 4340 apresentou aumento na resistência mecânica sem perda significativa de ductilidade. Quando revenido e nitretado após a soldagem, o aço 4340 apresentou ligeira queda na resistência mecânica. A nitretação do aço 300M, com a temperatura e tempo escolhidos, levou à fragilização do material em ambas as situações (com e sem revenimento), resultando em uma piora significativa das propriedades mecânicas, o que indica que os parâmetros de nitretação para este aço devem ser revistos. / The high-strength low-alloy (HSLA) steel SAE 4340 has been modified over time giving raise to the 300M steel. This study intends to evaluate and compare the microstructure and the mechanical behavior of the steels SAE 4340 and 300M, after laser beam welding in one pass, followed by distinct treatment routes: tempering, plasma nitriding and tempering plus plasma nitriding. After welding, the plates were divided into five sets: as welded, welded and tempered, welded and plasma nitrided, welded and tempered and plasma nitrided. The samples for microstructural analyses and tensile tests were taken from these material conditions. The results revealed that the presence of precipitates allow higher mechanical strenght to the 300M steel compared to 4340 steel. The melted zone showed more fases if compared with base material, fase like martensite, and the heat affected zone presented a multiphase in your matrix. The melted zone in both materials suffered a hardness decreasing after tempering, although no microstructural changes were observed. After nitriding the 4340 and 300M steels showed a surface hardness increase. The 4340 steel showed an increase in tensile strenght without significant ductility loss. When tempered and nitrided after welding, the 4340 steel suffered a drop in its mechanical strenght. The 300M steel suffered an embrittlement after nitriding in both situations (with and without tempering), resulting in unsatisfactory mechanical properties. This indicates that improvements are needed in the plasma nitriding parameters for this steel.

O desenvolvimento dos veículos atuais vem sendo impulsionado pela necessidade de redução de massa associada com o aumento da segurança para os passageiros. Na procura de novos materiais e processos para atender estas exigências, os aços bifásicos ferrítico-martensíticos ou DP vêm se destacando entre os aços avançados de alta resistência (AHSS), por apresentar elevada resistência mecânica e boa ductilidade. Da mesma forma, a soldagem a laser vem se mostrando promissora para junção desta classe de materiais. Este processo permite unir os aços DP com boa qualidade metalúrgica sem significativas distorções dimensionais. Embora os aços DP apresentem boa soldabilidade, um amolecimento localizado na zona afetada pelo calor (ZAC) também é observado, especialmente no aço DP1000, que apresenta elevada fração de martensita. Desta forma, esta Tese propõe a soldagem a laser do aço DP1000 de espessura 1,80 mm, seguida de uma sistemática caracterização microestrutural, visando a produção de juntas soldadas suficientemente resistentes. Para isto, foram produzidos cordões numa chapa de aço DP1000, variando a potência nominal de soldagem entre 0,4 e 2,0 kW e a velocidade de soldagem entre 20 e 150 mm/s. A caracterização microestrutural foi conduzida com o auxílio das técnicas de microscopia óptica (MO), microscopia eletrônica de varredura (MEV), difração de raios X (DRX) e difração de elétrons retroespalhados (EBSD). As juntas soldadas mais representativas foram submetidas a ensaios de dureza Vickers e tração uniaxial. Os resultados mostram que é possível produzir juntas soldadas resistentes no aço DP1000. Todavia, é fundamental que a combinação de parâmetros gere soldas com penetração total e mínima largura de ZAC, limitando a quantidade de amolecimento da martensita prévia e a fração volumétrica de austenita retida. Na presente Tese, os melhores resultados foram obtidos para uma potência de 2,0 kW e velocidade de 150 mm/s. / The development of modern vehicles has been driven by the need of mass reduction associated with the increase of the safety of passengers. In the search for new materials and processes to meet these requirements, ferritic-martensitic dual-phase (DP) steels are potential candidates among advanced high-strength steels (AHSS), because of their high mechanical strength and good ductility. In that sense, laser beam welding has been shown promising for joining this class of materials. This process allows joining DP steels with good metallurgical quality without large dimensional distortions. Although DP steels show good weldability, a localized softening in the heat affected zone (HAZ) is also observed, especially in DP1000 steel which contains large amounts of martensite. Thus, laser beam welding has been performed in DP1000 steel with thickness of 1.80 mm, followed by a systematic microstructural characterization, aiming at the production of resistant welded joints. For this, bead-on-plate welds were carried out in DP1000 steel, varying the welding power between 0.4 and 2.0 kW and the welding speed between 20 and 150 mm/s. The microstructural characterization was conducted with the aid of light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD). The most representative welded joints were tested for Vickers hardness and uniaxial tensile test. Results show that it is possible to produce sound and resistant welded joints in DP1000 steel. However, it is critical that the combination of parameters allows the obtainment of welds with full penetration and minimum HAZ width, limiting the amount of softening of prior martensite and the volume fraction of retained austenite. In the present Thesis, this was achieved using a power of 2.0 kW and a welding speed of 150 mm/s.

O aço de médio carbono e baixa liga SAE 4340 vem sofrendo diversas modificações e neste processo de desenvolvimento surgiu o aço 300M. O presente trabalho visa avaliar e comparar a microestrutura e a resistência mecânica dos aços SAE 4340 e 300M, submetidos ao processo de soldagem autógena a laser e em seguida a duas formas de tratamento: o revenimento pós-soldagem e a nitretação à plasma. Também é avaliado o efeito combinado dos tratamentos de revenimento e nitretação. Após soldagem, as chapas foram divididas nos lotes: como recebido, soldado, soldado e revenido, soldado e tratado superficialmente por nitretação a plasma e soldado, revenido e tratado superficialmente por nitretação a plasma. A partir desses lotes, foram obtidas amostras para análise microestrutural e produzidos corpos-de-prova para ensaios de tração. Os resultados mostraram que a presença de precipitados confere ao aço 300M maior resistência mecânica em relação ao aço 4340. Após a soldagem a laser, a zona fundida e zona termicamente afetada de ambos os materiais apresentaram fases diferentes das fases presentes no metal base, a zona fundida mostrou-se martensítica em sua maioria, e a zona termicamente afetada apresentou-se multifásica. Devido às dimensões reduzidas do cordão de solda, o comportamento em tração dos corpos-deprova soldados não diferiu significativamente dos corpos-de-prova produzidos com os materiais de base. O tratamento térmico de revenimento pós-soldagem promoveu queda na dureza da zona fundida em ambos os aços. Após a nitretação, os aços 4340 e 300M apresentaram aumento de dureza próximo às superfícies. O aço 4340 apresentou aumento na resistência mecânica sem perda significativa de ductilidade. Quando revenido e nitretado após a soldagem, o aço 4340 apresentou ligeira queda na resistência mecânica. A nitretação do aço 300M, com a temperatura e tempo escolhidos, levou à fragilização do material em ambas as situações (com e sem revenimento), resultando em uma piora significativa das propriedades mecânicas, o que indica que os parâmetros de nitretação para este aço devem ser revistos. / The high-strength low-alloy (HSLA) steel SAE 4340 has been modified over time giving raise to the 300M steel. This study intends to evaluate and compare the microstructure and the mechanical behavior of the steels SAE 4340 and 300M, after laser beam welding in one pass, followed by distinct treatment routes: tempering, plasma nitriding and tempering plus plasma nitriding. After welding, the plates were divided into five sets: as welded, welded and tempered, welded and plasma nitrided, welded and tempered and plasma nitrided. The samples for microstructural analyses and tensile tests were taken from these material conditions. The results revealed that the presence of precipitates allow higher mechanical strenght to the 300M steel compared to 4340 steel. The melted zone showed more fases if compared with base material, fase like martensite, and the heat affected zone presented a multiphase in your matrix. The melted zone in both materials suffered a hardness decreasing after tempering, although no microstructural changes were observed. After nitriding the 4340 and 300M steels showed a surface hardness increase. The 4340 steel showed an increase in tensile strenght without significant ductility loss. When tempered and nitrided after welding, the 4340 steel suffered a drop in its mechanical strenght. The 300M steel suffered an embrittlement after nitriding in both situations (with and without tempering), resulting in unsatisfactory mechanical properties. This indicates that improvements are needed in the plasma nitriding parameters for this steel.

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.

In the nanoscale metrology industry, there is a need for low-cost instruments, which have the ability to probe the structrure and elemental composition of thin films. This dissertation, describes the research performed to design and simulate a miniature Cylindrical Mirror Analyzer, (CMA), and Auger Electron Spectrometer, (AES). The CMA includes an integrated coaxial thermionic electron source. Electron optics simulations were performed using the Finite Element Method, (FEM), software COMSOL. To address the large Secondary Electron, (SE), noise, inherent in AES spectra, this research also included experiments to create structures in materials, which were intended to suppress SE backgound noise in the CMA. Laser Beam Machining, (LBM), of copper substrates was used to create copper pillars with very high surface areas, which were designed to supress SE’s. The LBM was performed with a Lumera SUPER RAPID‐HE model Neodymium Vanadate laser. The laser has a peak output power of 30 megawatts, has a 5x lens and a spot size of 16 μm. The laser wavelength is in the infrared at 1064 nm, a pulse width of 15 picoseconds, and pulse repetition rate up to 100 kHz. The spectrometer used in this research is intended for use when performing chemical analysis of the surface of bulk materials and thin films. It is applicable for metrology of thin films, as low as 0.4 nm in thickness, without the need to perform destructive sample thinning, which is required in Scanning Tranmission Electron Microscopy, (STEM). The spectrometer design is based on the well known and widely used coaxial cylinder capacitor design known as the Cylindrical Mirror Analyzer, (CMA). The coaxial tube arrangement of the CMA allows for placing an electron source,which is mounted in the center of the inner cylinder of the spectrometer. Simulation of the electron source with an Einzel Lens was also performed. In addtion, experiments with thin film coatings and Laser Beam Machining to supress Secondary Electron emission noise within the Auger electron spectrum were completed. Design geometry for the miniature CMA were modeled using Computer Aided Design, (CAD). Fixed Boundary Conditions, (BC), were applied and the geometry was then meshed for FEM. The electrostatic potential was then solved using the Poisson equation at each point. Having found the solution to the electrostatic potentials, electron flight simulations were performed and compared with the analytical solution. From several commercially available FEM modeling packages, COMSOL Multiphysics was chosen as the research platform for modeling of the spectrometer design. The CMA in this design was reduced in size by a factor of 4 to 5. This enabled mounting the CMA on a 2 ¾ in flange compared to the commercial PHI model 660 CMA which mounts onto a 10 in flange. Results from the Scanning Electron Microscopy measurements of the Secondary Electron emission characteristics of the LBM electron suppressor will also be presented.

The beam quality and the system efficiency of a diode-pumped solid-state laser source are directly related to the thermal profile inside the laser crystal. The thermal profile in a laser crystal should be made uniform in order to reduce the negative effects of the thermal lens. However, the absorbed pump profile that forms a uniform thermal profile inside the gain medium may adversely affect the system efficiency. In this thesis, a computational and empirical method was developed for designing pumping chambers that results in a suitable thermal profile inside the gain medium, and thus desired laser beam quality was achieved while keeping the system efficiency at an acceptable level. Accomplishment of this thesis work will lead to the design of pumping chambers and resonators in high power laser systems operating at even higher thermal loads.