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Made available in DSpace on 2014-10-09T12:53:36Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:47Z (GMT). No. of bitstreams: 0 / Um requisito do processo de manufatura é a necessidade de se obter peças processadas, caracterizadas pela boa qualidade de acabamento superficial, baixa rugosidade e a conservação de suas propriedades metalúrgicas. Essas condições motivaram o desenvolvimento deste estudo, no qual selecionou-se o processamento de materiais a laser para o corte do titânio, unindo uma tecnologia a um metal de recente aplicação. Além disso, a versatilidade e as vantagens, como também a tendência global do setor industrial, tornaram-se fatores preponderantes na utilização do laser como ferramenta de usinagem. Neste presente trabalho foram investigados os efeitos da usinagem por laser pulsado de Nd:YAG sobre a qualidade, como também a formação de fases na superfície de corte e analisados pela aplicação do planejamento experimental. Para isso, chapas de titânio comercialmente puro (grau 2) e da liga Ti-6Al-4V (grau 5), com espessuras de 0,5 e 1,0 milímetros, foram empregadas na realização dos ensaios sob ação do laser. As amostras obtidas foram analisadas por microscopia ótica (MO), microscopia eletrônica por varredura (MEV), ensaios de microdureza e inspeção superficial da rugosidade. Capturaram-se digitalmente as imagens do material ressolidificado, aderido na superfície de corte para determinação da formação de rebarbas. Com base nestes dados construíram-se arranjos fatoriais, por meio da metodologia de planejamento experimental (DOE), a fim de avaliar o grau de influência dos parâmetros e suas possíveis interações e assim averiguar sua significância estatística. Verificou-se um endurecimento superficial na região do corte a laser com nitrogênio, em virtude da formação de nitretos (TiN) sob uma fina camada da zona de ressolidificação. Apesar da complexidade das interações entre os diversos parâmetros envolvidos no processamento a laser, os resultados corroboram que a otimização do processo de corte a laser do titânio pode ser factível. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Orientador: Maria Clara Filippini Ierardi / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T12:12:23Z (GMT). No. of bitstreams: 1 Soares_EvaldoJulioFerreira_D.pdf: 5976897 bytes, checksum: 3a90757d7dedddb93e26e91797b38b52 (MD5) Previous issue date: 2005 / Resumo: A melhoria nas propriedades superficiais dos materiais tem sido buscada incessantemente pelas indústrias de transformação. A utilização do laser para tratamento térmico e refusão, entre outros processos, tem possibilitado grandes avanços nesta área. Muito se tem trabalhado na determinação dos parâmetros operacionais do laser e a resultante destas influências sobre as propriedades dos materiais. Os objetivos deste trabalho são estudar os efeitos destes parâmetros operacionais sobre a profundidade da camada superficial e a caracterização microestrutural das amostras submetidas a tratamento térmico a laser. Foram feitos experimentos usando os aços AISI 1045 e AISI 4340, a partir de amostras recozidas, temperadas e nitretadas. Foi utilizado um laser de CO2, pertencente ao LNLS, com potência nominal de 1 kW, desfocado em 2 mm, velocidade de deslocamento do feixe variando de 3000 a 10000 mm/min. Os resultados confirmam o laser como um instrumento eficaz na aplicação dos tratamentos superficiais. Para o aço AISI 1045, verifica-se que as amostras nitretadas apresentam maior profundidade da poça resultante após tratamento a laser. Já para o aço AISI 4340 as amostras endurecidas são as que se apresentam com maiores profundidades de poça. Para ambos os casos, as amostras recozidas apresentam os menores valores de profundidade da poça. Os ensaios de corrosão demonstram, com exceção das amostras nitretadas, uma tendência de elevação na nobreza do potencial eletroquímico do material. Quanto à resistência ao desgaste, com exceção das amostras nitretadas, do aço AISI 4340, todas as amostras apresentaram melhora após submetidas aos tratamentos propostos / Abstract: The industry development during last decades has allowed significant improvements concerning materials surface properties. Laser application for thermal treatment and remelting has also permitted important advances in this area. A lot of work has been spent in order to understand the influence of the operational laser parameters on the products¿ performance. The main objective of this study is to examine the effects of such parameters on the surface layer depth and on the typical microstructural arrangement of the treated samples. Thus, experiments were carried out using the steels AISI 1045 and AISI 4340, which were annealed, tempered and nitrated. Further, It was used a CO2¿s laser equipment, with nominal power of 1kW (defocusing of 2mm) and scan speed varying from 3000 mm/min to 10000 mm/min. The results confirmed the laser as an effective technique for surface treatments application. For steel AISI 1045, it was verified that nitrated samples presented the deepest liquid pool as consequence of the laser treatment. However, for steel AISI 4340, the hardened samples presented the deepest liquid pool. In both cases the annealed samples presented the lowest values concerning such parameter. The corrosion tests demonstrated that, except for the nitrated samples, a tendency of electrochemical potential increasing could be observed for all other studied conditions. Concerning wear resistance, excepting steel AISI 4340 nitrated samples, the others shown an improvement after the proposed treatment / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

O conjunto de tubos denominado sistema pneumático, tem a função de conduzir o ar quente pressurizado desde o motor até os pontos de utilização pelos sistemas ambientais da aeronave. A ocorrência de falhas em serviço de peças desse sistema soldadas pelo processo TIG (Tungsten Inert Gas), motivou o estudo da substituição desse processo pelo de soldagem a laser. Foi utilizado um laser a fibra de 2 kW de potência e tubos de titânio comercialmente puro grau 2, de 0,5 mm de espessura e 50 mm de diâmetro. Para efeito de comparação foram realizadas soldas pelo processo TIG, semi-automático, cujos parâmetros foram obtidos junto a uma empresa fabricante de aviões. Os tubos de titânio foram soldados em cheio, sem adição de arame, e o argônio foi utilizado como gás de proteção. Os parâmetros de soldagem a laser selecionados foram 200 W e 2000 mm/min e, 250 W e 300 mm/min. Os tubos soldados a laser apresentam cordões com aproximadamente 1 mm de largura e grãos de Ti-CP ?, enquanto que as soldas TIG resultam em cordões de 5 mm e grãos grosseiros serrilhado de Ti-CP ?. O refinamento microestrutural observado nas amostras soldadas a laser, em relação à TIG, deve-se a alta taxa de resfriamento, que no laser foi cerca de 70 vezes maior do que no TIG. Os tubos soldados a laser e TIG foram ciclados na bancada pneumática, 44.000 vezes, a 350 oC, sem fraturarem ou iniciarem uma trinca que comprometesse os testes de pressurização cíclica. Os resultados de fadiga evidenciaram uma maior resistência mecânica da solda a laser na condição de 200 W e 2000 mm/min, quando comparado com as demais condições de soldagem. As avaliações microestruturais e mecânicas dos cordões de solda evidenciaram as vantagens do processo de soldagem a laser para substituir o TIG, em junções do sistema pneumático de aeronaves. / The engine bleed air system, also known as pneumatic system, conducts the pressurized hot air from the engine to the environmental systems of aircrafts. In-service failures of the arc welded pneumatic parts have driven further developments of laser beam welding as an alternative method. Here, a fiber laser with 2 kW power had been employed to weld commercial purity titanium alloy tubes with 0.5 wall thickness and 50 mm diameter. For comparison purposes, semiautomatic TIG welding was realized, based on the previous experience of an aircraft company. All the welds were autogenous, bead-on-plate, and under protective argon atmosphere. The chosen parameters speed and laser powers for laser welding were 200 W - 2000 mm/min and 250 W - 300 mm/min. The laser welded tubes presented 1-mm wide weld beads composed by grained ?-Ti. The TIG welded tubes showed 5-mm wide beads composed by acicular ?-Ti grains. These observed differences had been associated to the cooling rate, which is seventy times higher in the laser case. Both laser and TIG welded tubes were cycled 44.000 times in a pneumatic bench at 350 oC without failures or cracks that could break the internal pressure. The condition 200W-2000mm/min presented superior fatigue resistance values compared to other welding conditions, and being similar to the tubes in the unwelded condition. On the other hand, the condition 250W-3000mm/min presented the highest dispersion for the fatigue lives. The microstructural and mechanical results shown that the current laser technology could replace with advantages the arc welding for the joining of the titanium tubes in the aircrafts pneumatic system.

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.

Doctor of Philosophy / Department of Physics / Kristan L. Corwin / The focus of this research is improving the pulse output energy of a mid-IR pulsed acetylene-filled Hollow-core Optical Fiber Gas LASer (HOFGLAS) system. Pump pulses and acetylene molecules interact with each other inside hollow-core photonic crystal fiber that effectively confines light and allows for strong gain. This results in lasing at 3.11 μm and 3.17 μm lines based on population inversion of acetylene molecules, which are optically pumped at rotational-vibrational overtones near 1.5 μm using 1 ns pulse duration from an optical parametric amplifier (OPA). This acetylene laser operates with no cavity mirrors because of a high gain in a single pass configuration. There are few laser sources in the mid-IR region while there are many applications for having a laser source in this range such as remote sensing, hazardous chemical detection, and breath analysis. This adds to the importance of the acetylene-filled HOFGLAS system. Some of the applications like remote sensing require high power. So, we moved toward power scaling this laser system by optimizing the laser operation through maximizing the OPA alignment to improve its modal content using longer length of fiber to increase the interaction length and improving the beam quality of the mid-IR emissions. The highest pulse energy ever obtained in the 3 µm mid-IR region from the acetylene-filled HOFGLAS after applying the improvements is reported here (1.4 μJ). Higher mid-IR pulse energies can be achieved by improving the pulse energy achievable from the OPA pump source and working with longer pulse duration to decrease the bandwidth of the OPA. This operation demonstrates many novel properties of acetylene-filled pulsed mid-IR hollow-core fiber lasers. The excellent spatial beam quality at highest power and phenomenological scaling of saturation power and efficiency with pressure that we observe point to the promise of power scaling and motivate further development of numerical models of the laser for deeper insight into these effects. M² measurement method was used to examine spatial beam quality and it was found to be fiber-dependent. For the improved setup, M² was investigated at several input pump powers in addition to the reproducibility checks. M² of 1.14 at the maximum output power motivates for beam combining to scale to higher power. The independence of efficiency on pressure is an evidence for reaching higher mid-IR power at a pressure where saturation behavior does not exist. achieving the highest mid-IR power to date, 1.4 μJ, encourages for building higher power OPA to produce high power mid-IR emissions. Taken as a whole, this laser exhibits novel behavior that motivates both numerical/theoretical investigation and further efforts to scale to higher powers.

>Magister Scientiae - MSc / This dissertation consists of two main sections. The first section focuses on generating zero order Bessel beams using axicons. An axicon with an opening angle y = 5⁰ was illuminated with a Gaussian beam of width ω₀ = 1.67 mm from a cw fiber laser with central wavelength λ = 1064 nm to generate zero order Bessel beams with a central spot radius r₀ = 8.3 ± 0.3 μm and propagation distance ½zmax = 20.1 ± 0.5 mm. The central spot size of a Bessel beam changes slightly along the propagation distance. The central spot radius r₀ can be varied by changing the opening angle of the axicon, y, and the wavelength of the beam. The second section focuses on applications of the generated Bessel beams in laser microdrilling. A Ti:Sapphire pulsed femtosecond laser (λ = 775 nm, ω₀ = 2.5 mm, repetition rate kHz, pulse energy mJ, and pulse duration fs) was used to generate the Bessel beams for drilling stainless steel thin sheets of thickness 50 μm and 100 μm and microscopic glass slides 1 mm thick. The central spot radius was r₀ = 15.9 ± 0.3 μm and ½zmax = 65.0 ± 0.5 mm. The effect of the Bessel beam shape on the quality of the holes was analysed and the results were discussed. It was observed that Bessel beams drill holes of better quality on transparent microscopic glass slides than on stainless steel sheet. The holes drilled on stainless steel sheets deviated from being circular on both the top and bottom surface for both thicknesses. However the holes maintained the same shape on both sides of each sample, indicating that the walls are close to being parallel. The holes drilled on the glass slides were circular and their diameters could be measured. The measured diameter (15.4±0.3 μm) of the hole is smaller than the diameter of the central spot (28.2 ± 0.1 μm) of the Bessel beam. Increasing the pulse energy increased the diameter of the drilled hole to a value close to the measured diameter of the central spot.

This diploma thesis deals with the structural and optomechanical design of automatization of focusing laser beam for a remote laser spectroscopy device. The chosen solution uses an active rangefinder and a rotary unit to control the change of the focus plane of the device's optic system. The dependence of the focus plane’s change on the shift of lens in the focus plane was practically measured. For proper control of the rotary unit, this dependency is needed. Structural parts were made based on the created drawing documentation. The structural parts were mounted in the existing assembly of the device together with the purchased components. The proposed solution enables a change of the optical system, for example, in order to obtain a more appropriate range of focal planes.

The aim of this thesis is to quantify the impact of atmospheric turbulence on optical signal used in free space optic communication systems. The first part is associated with atmosphere as transmission medium. Following part deals with interferometry and components of interferometers. Various methods of analysis of trasmission environment for optical beam are introduced theoretically and experimentally. Mathematical apparatus based on Kolmogorov’s cascade theory, Rytov’s variance was used to find value of structural parameter of refraction as a main measure of turbulence intensity. Experimentally obtained data were subjected to statistical analysis. The visualization of interference pattern fluctuations under turbulent conditions is shown in the last section. Interferometric method was realized with Michelson interferometer.