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Orientador: Carlos Henrique de Brito Cruz / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-16T09:39:48Z (GMT). No. of bitstreams: 1 Silva_ValeriaLoureiroda_M.pdf: 3530989 bytes, checksum: fb86135bf40c2cda8dff4330b0b3802c (MD5) Previous issue date: 1986 / Resumo: Este trabalho tem como objetivo a construção e estudo de uma chave óptica a semicondutor. Esta chave pode ser usada tanto para gerar pulsos curtos no infravermelho como para estudar o próprio semicondutor. O tempo de resposta da. chave depende das características do semicondutor e do laser usado para controle. Apresentamos aqui os resultados obtidos com uma chave de Ge controlada por laser de N2, NdYag e corante. O tempo de resposta obtido foi de 50 ns, limitado pelo tempo de recombinação do Ge. Obtivemos um aumento na refletividade, em 10,6 mm no Ge, de 7% para 59% quando usamos o laser de N2 para controlar a chave. Apresentamos também um modelo simples para o comportamento das propriedades ópticas do semicondutor que explica bastante bem os resultados encontrados experimentalmente / Abstract: In this work we have studied a semiconductor optical switch. Its main use Is in the generation of short infrared pulses but it can also be used to study the semiconductor. The switch response time depends on the semiconductor and on the control laser characteristics. We show the results obtained using a Ge switch controlled by N2, NdYag and Dye lasers. The response time was 50ns limited by the Ge recombination time. The reflectivity increased from 7% to 59% when we use a N2 laser to control the switch. We als show a simple model for the semiconductor optical properties that explain very well the experimental results / Mestrado / Física / Mestre em Física

Orientador : Chhiu-Tsu Lin / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-07-14T02:59:33Z (GMT). No. of bitstreams: 1 Atvars_TeresaDibZambon_M.pdf: 7603406 bytes, checksum: 9991ade4385dbccc1ee1b57abccd993d (MD5) Previous issue date: 1977 / Mestrado

Orientador: Artemio Scalabrin / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-14T17:37:23Z (GMT). No. of bitstreams: 1 Cruz_CarlosHenriquedeBrito_M.pdf: 4245171 bytes, checksum: 49d1e590d575a998230dc167dc254851 (MD5) Previous issue date: 1980 / Resumo: Não informado / Abstract: Not informed. / Mestrado / Física / Mestre em Física

Orientador: Jorge Humberto Nicola / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T07:42:47Z (GMT). No. of bitstreams: 1 Lima_ErzeliJacquesde_M.pdf: 25666315 bytes, checksum: deea48e89f3649b7e92de81759ba200a (MD5) Previous issue date: 1984 / Resumo: O relacionamento entre a física e a medicina é importante no sentido de que tem um alto interesse social, econômico e político em um país como o Brasil. Social, porque dá oportunidade de que a sociedade desfrute de melhores condições de atendimento clínico, advindo de aplicações geradas da interação entre físicos e médicos. Econômicas porque o desenvolvimento de equipamentos obtidos desta maneira, em geral, são muito mais baratos que os similares importados, e político porque permite que um grupo altamente treinado, como o formado por físicos e médicos, una esforços no sentido de tornar o país independente da tecnologia estrangeira. Este trabalho primeiramente tece considerações sobre os processos tradicionais de cirurgia utilizados pelos médicos. Após isto introduz o uso de lasers em geral como uma ferramenta poderosa nas terapias e tratamentos de desordens orgânicas. Apresenta os parâmetros de mérito para a utilização deste moderno instrumental terapêutico. O laser de CO2 é apresentado com destaque para suas aplicações nas microcirurgias e são consideradas as diversas áreas médicas onde é utilizado. Em seguida, o laser de CO2 é discutido na sua base teórica, onde consideramos o laser em si e destacamos o estudo de molécula de dióxido de carbono, a inversão de população para a ação laser e os mecanismos de relaxação. Passamos então a parte prática do trabalho que é o roteiro da construção de um laser de CO2 nacional e a obtenção dos parâmetros de mérito para a ótima utilização deste aparelho. O sistema por nós construído é seguro e facilmente manipulável por médicos cirurgiões. Tecemos então considerações sobre as aplicações deste laser de CO2 nacional e o acompanhamento cirúrgico em diversas intervenções realizadas com este equipamento / Abstract: In a country like Brasil, with its social, economical and political characteristics, a close interrelation between physics and medicine is highly desirable. This interaction may have a social impact among the population, yelding an improvement of the general health conditions. From the economical point of view, the development of the required equipment by a highly trained group is much less expensive than purchasing foreign similars. In addition, large groups of physicians and physicists working in collaboration will join efforts in the process of making the country independent from foreign technology. In this work we firstly discuss the traditional processes of common use in cirurgy. It follows an introduction of the laser techniques in medicine, showing the laser as a powerful tool in the treatments of organic diseases. The CO2 laser is presented with prominence for use in microcirurgies and the medical areas where the laser is used are considered. After this, we discuss the theoretical basis of the CO2 lasers, specially in relation to the study of the carbondioxide molecule, the population inversion and the relaxation processes. We finally discuss practical aspects of our work, aiming at construction of national CO2 lasers and optimizing the different parameters for best use. The system devised by us is of easy handling for medical personnel with a high standard for safety / Mestrado / Física / Mestre em Física

Aim of this thesis is to investigate the optimum working parameters of a helium-neon laser. Partial pressure ratios, total pressures of the gases and voltage-current characteristics were studied. The analysis of the results includes the minor factors (impurity, volume, etc.) and their effects to main parameters (laser power, voltage, current). Tables, which were formed by measured optical parameters as wavelength and power, converted to graphs and from these graphs optimal working conditions for the laser are obtained.

This thesis reports work extending the scope of a recently developed gas sensing technique, multi-mode absorption spectroscopy (MUMAS). The ability of MUMAS to simultaneously detect multiple species from a mixture is demonstrated for the first time. The technique is subsequently extended to mid-infrared wavelengths, realising large gains in sensitivity. A solid-state, multi-mode laser has been developed to provide a high-performance comb source for use with MUMAS. This in-house constructed, diode-pumped, Er/Yb:glass laser operates on 10 longitudinal modes, separated by 18 GHz and centred close to 1565 nm. The extensive development and prototyping work leading to this final laser design is described. Multi-species detection with MUMAS is reported for the first time, thus demonstrating the ability of this technique to perform multi-gas sensing using a single laser and simple detection scheme. The previously described Er/Yb multi-mode laser was used to record MUMAS signals from a sample containing CO, C₂H₂, and N₂O. The components of the mixture were detected simultaneously by identifying multiple transitions in each of the species. Temperature- and pressure-dependent modelled spectral fits to the data were used to determine the partial pressures of each species in the mixture with an uncertainty better than +/-2%. Multi-mode radiation has been successfully generated at 3.3 μm using quasi phase matched difference frequency generation (QPM-DFG). A mid-infrared laser comb was produced by optically mixing the near-infrared, multi-mode comb produced by the previously developed Er/Yb:glass laser with the single-mode output of a Nd:YAG laser operating at 1064 nm. This multi-frequency laser source was characterised to verify performance, and subsequently used to perform proof-of-principle MUMAS measurements on the strong transitions found in this spectral region. Spectra were recorded of NH₃ and CH₄ both individually and as components of a mixture. A minimum detection level for this system was determined to be 4.3 μbar m^-1 for CH₄, a sensitivity increase of 300 over similar measurements performed in the near-IR.

<p>There has been a long-standing need in the marketplace for the economic production of small lots of components that have complex geometry. A potential solution is additive manufacturing (AM). AM is a manufacturing process that adds material bottom-up. It has the distinct advantages of low preparation cost and high geometric creation capability. Components fabricated via AM are now being selectively used for less-demanding applications in motor vehicles, consumer products, medical products, aerospace devices, and even some military projects.</p><p><br></p> <p>For engineering applications, high value-added components require consistency in the fatigue properties. However, components fabricated by AM have large variation in the fatigue properties compared to those by conventional manufacturing processes. To alleviate unpredictable catastrophic failures of components, it is essential to study and predict fatigue life. Previous study reported that fatigue crack initiation process accounts for a large portion of fatigue life, especially for low loading amplitude and high cycle fatigue. However, this major portion of fatigue life prediction is mostly ignored by main stream researchers working on fatigue modeling. For industrial applications, engineers often specify a lower stress condition to obtain a higher safety factor. Under these circumstances, fatigue crack initiation becomes even more important, so it is essential to further study of crack initiation.</p><p><br></p> <p>The objective of this research is to develop a fatigue crack initiation model for metal components produced by AM. To improve life prediction accuracy, the model must incorporate the effect of different microstructures, which are typically produced by AM due to a large number of repetitive cycles of re-heating and re-cooling processes. To fulfill this objective, the tasks are separated into three studies: (1) developing a temperature model to simulate temperature history, (2) modeling the component’s microstructure for the potential crack initiation zone, and (3) developing a fatigue crack initiation model for life estimation. A summary of each task is provided in the following.</p> <p>First, the role of temperature model is to understand the mechanism that leads to the variation of microstructures. The existing temperature models are computationally expensive to obtain an accurate prediction of the temperature history due to repetitive heating and cooling. The main reason is that these models considered entire boundary conditions of all the material points. In this section, we proposed and employed the concept of effective computation zone, which can save the computational time significantly for AM process. </p><p><br></p> <p>Second, it is critical to include the effect of microstructure in the fatigue life model since the microstructure variation at different locations within the real AM component is large. The grain size variation is modeled by using representative volume element, which is defined as a volume of heterogeneous material that is sufficiently large to be statistically representative of the real component’s microstructure. Regarding phase transformation, a continuous cooling transformation (CCT) diagram is a useful tool that can be used with a thermal model for microstructure design and manufacturing process control. However, traditional CCT diagrams are developed based on slow and monotonic cooling processes such as furnace cooling and air cooling, which are greatly different from the repetitive heating and cooling processes in AM. In this study, a new general methodology is presented to create CCT diagrams for materials fabricated by AM. We showed that the effect of the segmented duration within the critical temperature range, which induced precipitate formation, could be cumulative. </p><p><br></p> <p>Third, the existing fatigue crack initiation life model has poor accuracy. One of the reasons for the poor accuracy is the coefficients change due to the variation in microstructure is not accounted for. In this section, a semi-empirical fatigue crack initiation model is presented. The important coefficients include maximum persistent slipband width, energy efficiency coefficient, resolved shear stress and plastic slip rate per cycle. These coefficients are modeled and determined as a function of microstructure, which can improve the accuracy of life estimation.</p><p><br></p> <p>The contribution of this study is to provide a new engineering tool for designing the melting AM process based on scientific research. With this tool, the fundamental mechanism contributing to a large variation of the fatigue life of the metal components made by AM process can be understood, attributed, predicted and improved. The seemly ‘stochastic’ nature of fatigue life of the AM components can be changed to be more deterministic and predictable. This approach represents a major advance in fatigue research on AM materials. The model developed is considered as a tool for research, design, and control for laser-based AM process applications. </p>