Laser Bandwidth Effects on Four-Wave Mixing.

Available from UMI in association with The British Library. Requires signed TDF. The effects are investigated of the field fluctuations associated with broad bandwidth lasers on the non-linear process of degenerate four-wave mixing. A theory of four -wave mixing with large bandwidth fields is developed and solutions are obtained for the steady state reflectivity and for the temporal evolution of the signal in experiments carried out with short laser pulses. The salient predictions of the theory are presented. Experiments are described which were carried out to test the predictions of the theoretical work. These involved the use of a modeless, variable bandwidth dye laser. The results, for laser intensities which do not saturate the atomic medium and zero detunings, are in good qualitative agreement with the theory. In the high intensity regime the theoretical prediction for the steady state saturation behaviour of the signal and that measured experimentally are seen to differ. Arguments are presented to account for these discrepancies. The design and construction of a novel widely tunable, single-mode, pulsed dye laser is described. The system differs from previous devices in that a multi-mode oscillator is used and mode selection is carried out outside the cavity. This is achieved using a tunable, narrow bandwidth amplifier. The performance of a prototype device is reported and modifications to the design are suggested which may enable the frequency stability and tuning range of the system to be enhanced.