Orientador: Jorge Humberto Nicola / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-13T23:37:12Z (GMT). No. of bitstreams: 1 Wagner_PauloRicardoSteller_M.pdf: 1195255 bytes, checksum: 0ad13f7bec227bb947f9513b7e2d6406 (MD5) Previous issue date: 1991 / Resumo: Neste trabalho apresentamos o desenvolvimento de um laser de CO2 tipo guia de ondas excitado por radio freqüência. Primeiramente apresentamos um estudo teórico necessário para o entendimento dos processos envolvidos na operação do equipamento. Atenção especial foi dada a teoria relativa as perdas por acoplamento, na entrada do guia de ondas, entre os modos gaussianos do espaço livre os modos do guia de ondas. Estas perdas são inerentes da cavidade óptica escolhida. Outro ponto de interesse que mereceu maior atenção é o caso das descargas em altas freqüências, em especial na região de alta freqüência. Como resultado desse estudo construímos um protótipo que nos forneceu potência óptica de saída de 900 mW na condição de otimização dos parâmetros: posição do espelho, pressão da mistura gasosa e acoplamento elétrico / Abstract: In this work we report the development of a CO2 radio frequency excited waveguide laser. Initially we present a theorical study needed to understand the processes involved in the operation of the equipment . Special attention was given to the theory related to the coupling losses, at the entrance of the waveguide, between the Gaussians modes of the free space and the waveguide modes. These losses are inherent of the optical cavity selected. Another point that deserve higher attention is the high frequency discharges aspect, in special in the radio frequency discharge region. As result of this study we build a prototype that gave 900 mW of output optical power at optimal condition for laser parameters: mirror position, pressure of gas mixture and electrical coupling / 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 2018-07-14T17:35:55Z (GMT). No. of bitstreams: 1 Cotta_MonicaAlonso_M.pdf: 4477982 bytes, checksum: d6cf92342f4467e5f4265efd28cdad80 (MD5) Previous issue date: 1987 / Resumo: Neste trabalho, nosso objetivo é o de dar idéias físicas sobre vários fenômenos biológicos funcionais relacionados a irradiação de tecidos vivos com lasers de baixa potência, que denominamos efeitos não térmicos. Devido a diversidade de comprimento de ondas e densidades de energia com os quais foram observados anteriormente efeitos desse tipo, lançamos a hipótese de que a coerência da radiação utilizada fosse fator importante no processo. Para testar a validade dessa hipótese, dividimos o trabalho em duas partes: uma experimental onde construímos um dispositivo permitindo a irradiação de lesões criadas artificialmente no dorso de ratos por um laser de He-Ne, ou ¿ colocando-se um vidro fosco em movimento a frente do feixe laser, por radiação desse mesmo laser co seu grau de coerência diminuído. Pela observação da cicatrização das lesões, nosso teste mostrou ser a coerência da radiação relevante no processo e apontou a necessidade de estudos mais detalhados nessa área. Do ponto de vista teórico, constituindo a outra parte desse trabalho, realizamos um estudo sobre a distribuição do campo elétrico e intensidade sobre uma superfície dotada de micro-rugosidades quando irradiada por luz coerente. Em nossa opinião, uma distribuição deste tipo pode ocorrer em superfícies celulares e influir decisivamente na fisiologia da própria célula, em grande / Abstract: In this work, our objective is giving physical ideas about several functional biological effects related to the irradiation of live tissues with low power lasers, which we called non-thermal effects. Due to the diversity of wavelengths and energy densities these effects have been previously observed with, we propose that the coherence of the used radiation was an Important factor in this process. To test the validity of this hypothesis, we divided the work in two parts, one experimental and one theoretical. In the experimental part, we constructed a device which permitted the irradiation of lesions artificially created on the back of rats by an He-Ne laser, or - putting a moving ground glass in the path of the laser beam, by radiation of this same laser with its coherence degree decreased. By observation of the lesions cicatrization, our test showed that the coherence of the radiation is relevant in the process and pointed to the necessity of more detailed studies in this area. From the theoretical viewpoint, we performed a study about the electrical field and intensity distribution over a surface with micro-roughness when irradiated by coherent light. In our opinion, this kind of distribution might occur in cellular surfaces and influence decisively the cell physiology, which is to a great extent controlled by electrical phenomena at the membrane level / Mestrado / Física / Mestre em Física

No description available.

Second harmonic(2ω₀) and three halves harmonic(3/2ω₀) are studied in the interaction of CO₂ laser of frequency ω₀, with an underdense plasma. It is shown theoretically that filamentation can lead to sizable second harmonic generation. The 2ω₀-radiation is emitted into a forward directed cone, its angle determined by the wavelength of the fundamental radiation in the plasma filament. Experimental observations confirm the theoretical predications. Aside from the forward directed emission cone, non negligable 2ω₀ power is detected over a broad angular range in the backward direction showing a broadened red shifted spectrum. The dependence of the backward emitted 2ω₀-radiation on the plasma density, and the red shifted spectrum strongly support the argument that the backward emitted 2ω₀-radiation is related to the SBS(Stimulated Brillouin scattering) instability. Based on the wave vector matching conditions, the angular distribution of 3/2ω₀-radiation is predicted. The experimental results confirm the prediction. It is shown experimentally that the fusion of three plasma waves produced in the TPD(Two Plasma Decay) instability dominates the generation of 3/2ω₀-radiation when the incident beam energy is high. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Orientador: Carlos A. Arguello / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T16:50:35Z (GMT). No. of bitstreams: 1 Megusar_Richard_M.pdf: 1458855 bytes, checksum: 838204831105c640efb9ec1d15bc921f (MD5) Previous issue date: 1973 / Resumo: Com a utilização de um filtro de I2, substância esta que possui transições de frequência situada no interior do intervalo de varredura ( 8 GHz ) do sistema, foi possível elaborar um novo método de espectroscopia próprio para pesquisas próximas à linha do laser, ângulos de observação pequenos, como Brillouin, ou Rayleigh wings e espalhamento Rayleigh. Sistema de resolução limitada pela largura de linha do I2 ( 0,85 GHz ) e pelo pequeno intervalo de varredura, mostrou ser, em contrapartida, um eficiente método de investigação, além do que, sua simplicidade traduz-se em baixos custos se comparado aos métodos "tradicionais" que implicam em uso de espectrômetro de alta resolução ou Fabry Perot / Abstract: Not informed. / Mestrado / Física / Mestre em Física

Includes bibliographical references. / An investigation is made into the major factors contributing to shot-to-shot spectral fluctuations in a broadband dye laser with a view to reducing noise in Coherent Anti-Stokes Raman Spectroscopy (CARS). Combinations of three dyes and methods of quantifying noise in spectra are investigated. Correlations between groups of modes in the dye laser are shown to exist and vary from dye to dye. Investigation is made into the effects that the insertion of scattering particles into the dye laser oscillator has on the spectral noise. A tunable, solid state Ti:Sapphire laser is assembled and spectra obtained for comparison with the dye laser spectra.

No description available.

Thesis (Ph. D.)--Oregon Graduate Institute of Science and Technology, 1992.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Laser cladding is a process that is used to improve the properties of a metal surface. The properties in question may include hardness, wear-, corrosion- and/or fatigue-resistance. The process involves fusing a thin layer of additional metal to the original surface, using a laser as the heat source. Unfortunately, residual stresses are generated due to the rapid and highly localised thermal expansion and contraction that occur during the heating-melting-solidification-cooling cycle. These residual stresses can have a detrimental effect on the final performance of the clad component, especially with respect to corrosion resistance. Detrimental tensile residual stresses can be mitigated through the use of post-processing techniques such as laser shock peening (LSP). LSP is a process that uses a pulsed laser to generate intense spots of recoil pressure on a surface, thereby introducing compressive residual stresses. Post weld heat treatment (PWHT) is another process that could be also used in laser cladding in order to relieve tensile residual stresses. In this work, laser cladding was carried out by depositing a clad layer of AISI grade 316L stainless steel on to either a S275 steel substrate or an AISI grade 316L stainless steel substrate, using different process parameters. The hardness and residual stresses in the overlay and substrate were assessed for each laser clad sample before and after being treated with LSP and PWHT. The corrosion rate and microstructure were also assessed in each case. The novelty of this work is two-fold. Firstly, to the author's knowledge, it is the first study that attempts to link process parameters to both the residual stresses and the corrosion performance of austenitic stainless steel overlays deposited by laser cladding. The second novel aspect is based on the application of both LSP and PWHT to the deposited overlay in order to investigate whether an improvement in the mechanical properties and the corrosion resistance can be realised. In this study, tensile residual stresses were generated in the clad layers. However, the magnitude of the residual stresses did not appear to be particularly sensitive to the deposition parameters. Indeed, it was found that the number of layers that is deposited is more important than the choice of process parameters. LSP was effective in reducing the tensile residual stresses and in fact it introduced compressive stresses to all the samples that were treated. In contrast, PWHT only led to satisfactory stress relief when the AISI grade 316L stainless steel was deposited on to a matching substrate material. This was related to the fact that a difference between the thermal expansion coefficients of the overlay and substrate led to the development of significant tensile residual stresses on cooling down after PWHT. The corrosion tests on the clad coupons led to the development of pits and cracks. However, after LSP only pits were found, without any sign of cracking, for the test durations that were investigated owing to the fact that compressive stresses were generated. Similar results were found after PWHT for the clad samples in which the overlay material matched the substrate material. However, signs of cracking were observed after PWHT in samples where AISI grade 316L stainless steel was deposited on to an S275 steel substrate due to tensile residual stresses remaining within the overlay. This result suggests that there may be little benefit in carrying out PWHT for components in which grade 316L stainless steel is deposited on to a steel substrate. In contrast, there appear to be clear benefits associated with carrying out LSP in order to mitigate the residual stresses and retard the onset of cracking.