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Techn. Univ., Diss.--Ilmenau, 1999.

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Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xiv, 170 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 159-164).

Chemnitz, Techn. Univ., Diplomarb., 2002.

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Universiẗat, Diss., 1999--Kassel.

Techn. Hochsch., Diss., 2005--Aachen.

Light-based therapies are becoming increasingly important and widely applied within the clinical practice. Their advantages over more traditional therapies have created an expanding market which is driving the development of more efficient and sophisticated devices. These devices allow a more precise control of the characteristics of the optical output to maximise benefits of the treatment. Although many studies have been conducted on light, and more specifically lasers, both from a therapeutic and a technological perspective, there is still much research to be undertaken. Laser systems have been used for more than two decades for the treatment of vascular lesions. Indeed the application of selective photothermolysis utilising the monochromaticity of the laser system has become the treatment of choice. However the treatment of larger blood vessels remains problematic. Many workers have, for theoretical and clinical reasons, elected to choose the YAG laser for the treatment of larger thread veins and vascular lesions containing larger vessels. The therapeutic output has been mixed and the need for further work identified. This thesis describes the design of a novel approach to the control of the temporal profile of the YAG laser. The design aspect of the work includes a computer modelling study which shows that careful control of the temporal parameters can in principle improve the therapeutic output. A novel approach to the digital control of the flashlamps pumping the YAG crystal is also described. The digital control of the flashlamp translates to sensitive control of the temporal profile of the laser output in a way that has not been described to date. The thesis therefore concludes that control of the temporal output of the YAG laser, if possible, should give improved therapeutic output and that the necessary level of control can be achieved by advanced digital techniques. Future clinical work should prove improved therapeutic results.

Neste trabalho foi desenvolvido e caracterizado um aparato óptico para geração de padrões de perfurações em escala micrométrica em diversas classes de materiais. Este sistema, fundamentado nas técnicas de percussão e trepanação, foi acoplado a um laser industrial nanopulsado de Nd:YAG operando em 532 nm. Sua viabilidade foi analisada em amostras de alumínio metálico, cerâmica de α−alumina, poli(cloreto de vinila) (PVC) e silício cristalino. Verificou-se que as melhores condições para a obtenção de microperfurações de precisão são proporcionadas pelo método de trepanação assistido por um alto fluxo de ar. Micrografias eletrônicas comprovaram que estes parâmetros resultam em microperfurações simétricas, precisas e, geralmente, desprovidas de rebarbas. Suas dimensões, comparadas ao método de percussão, são evidentemente superiores devido à maior quantidade de material processado nesta técnica. Verificou-se que os diâmetros de microperfurações por percussão variaram de 25 a 200 µm enquanto que pelo método de trepanação estes resultados foram de aproximadamente 50 a 240 µm, dependendo das propriedades do material e da fluência aplicada. Um estudo sobre a velocidade de perfuração em função da fluência incidente comprovou a alta dependência da taxa de ablação com relação às propriedades térmicas e ópticas dos materiais. A análise de secções retas transversais em microperfurações obtidas por percussão e trepanação também indicou a formação de deformações internas em materiais com baixas velocidades de perfuração, tais como alumínio metálico e α−alumina. Esse fenômeno está diretamente associado ao plasma formado no interior de algumas microcavidades, sobretudo pelo método de trepanação sob baixos regimes de fluência. Estudos da região termicamente afetada em silício cristalino por espectroscopia micro−Raman também indicaram a ausência de tensões induzidas por ambas as técnicas empregadas e evidências de transições cristalinas entre a fase cúbica do diamante (Si−I) e hexagonal compacta (Si−IV); as quais foram mais pronunciadas em altos regimes de fluências. De maneira geral estes resultados contribuíram para a comprovação da eficiência e viabilidade do sistema desenvolvido e para a caracterização de microperfurações de precisão em materiais metálicos, cerâmicos e poliméricos / In this work, it was developed and characterized an optical apparatus that was used to generate holes in micrometric scale in several classes of materials. This system, based on the techniques of percussion and trepanning drilling, was connected to an industrial nanopulsed Nd:YAG laser operating in 532 nm. Its viability was analyzed for metallic aluminum, α−alumina ceramic, poly(vinyl chloride) (PVC) and single crystalline silicon samples. It was verified that the trepanning method assisted by intense air jet had given the best conditions for the attainment of precise microdrillings. Electronic micrographs has proved that this technique results in symmetrical and precise microholes, generally without burrs. Their dimensions are evidently superior to those obtained by the percussion method, probably due to the different amounts of material processed in each technique. It was verified that the microholes diameters had varied approximately from 25 to 200 µm for percussion, while for the trepanning method they has varied from 50 to 240 µm, depending on the material properties and the applied fluence. A study about the drilling velocity in function of the incident fluence had proved the high dependence of the ablation rate with relation to the thermal and optical materials properties. The analysis of transversal cross−sections in microholes obtained by percussion and trepanning methods has also indicated the formation of internal deformations in materials with low drilling velocities, such as metallic aluminum and α−alumina. This phenomenon is directly associated with the plasma formed inside of some microcavities, mainly appling the trepanning method under lower fluence regimes. Studies in the thermally affected region in crystalline silicon, by micron-Raman spectroscopy, has also indicated the absence of induced tensions for both techniques employed, as well as indications of crystalline transitions between the cubic phase of the diamond (Si−I) and compact hexagonal (Si−IV); which were more pronounced in high incident fluences. In general way these results has contributed to the verification of the efficiency and viability of the developed system and to the precise characterization of microholes in metallic, ceramic and polymeric materials