Thesis (M.S.)--University of Northern British Columbia, 1998. / Includes bibliographical references (leaves 74-81).

Düsseldorf, Universiẗat, Diss., 2002.

published_or_final_version / abstract / Chemistry / Master / Master of Philosophy

Acoustic resonances leading to high unsteady pressure levels may occur in flow past cavities. The resonance involves a coupling between the downstream-propagating instability wave on the shear layer spanning the open face of the cavity, and acoustic waves propagating within and external to the cavity. These elements of the disturbance field are coupled by the scattering processes that occur at the upstream and downstream ends of the cavity. We develop a theoretical prediction method that combines propagation models in the central region of the cavity with scattering models for the end regions. In our analyses of the scattering processes at the cavity ends, the square-corner geometry is treated exactly, by a method employing the Wiener--Hopf technique. The shear layer is approximated as a vortex sheet in the edge scattering analyses, but finite shear-layer thickness is accounted for in analyzing the propagation of the waves along the length of the cavity. The global analysis leads to a prediction for the resonant frequencies which has a form similar to the Rossiter formula, but contains no empirical constants. In addition to prediction of the frequency, our theory determines the temporal growth or decay rate of each mode. Finally, our theory also predicts the influence of secondary feedback loops involving other components of the unsteady field. Comparisons of the predictions with existing experimental data are made.

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An investigation in to a novel pivot point free external cavity tunable laser (PPI ECTL). Existing external cavity tunable lasers are constructed using tunable optics, such as Bragg gratings to manipulate the cavity length. These elements although functional provide instability with prolonged use as they are defined by a centre of rotation or pivot point. The aim of this research was to provide a lab demonstrator of a new concept tunable laser based on conventional designs. The novel approach to the system design was in the removal of a defined pivot point, whilst still maintaining a moving optical component. The demonstration system will investigate the improvements upon traditional methods of tuning whilst providing greater tuning range and stability. The main defect of conventional systems was the reliance on the defined pivot point of the movable optics. By changing the position of the pivot point, the cavity length will change and the laser mode will change or hop to a side mode. This was known as a mode hop. The objective of the research was to design and implement a durable ECTL with a large tuning range (>200GHz), mode hop free tuning, fibre coupled, circular output beam and a wavelength in the visible. Design and production of a prototype PPI ECT laser that demonstrate the process of mode hop free tuning without the need of a defined pivot point. The impact of the research may lead in to the integration in to lower cost and more reliable commercial applications.