An experimental study of capillary waveguide techniques applied to nonlinear optics

Abstract

This thesis describes investigations made into the nonlinear optical processes of Stimulated Raman and Brillouin Scattering in simple gases when they are performed in various guided configurations.

In order to make a detailed comparison between experiment and theory a well defined pump beam is required. The development and operation of a laser capable of producing such a beam, the pre-lase Q-switched, Nd:YAG telescopic resonator, is described in the first part of this thesis. The output from this laser, and the harmonics derived from it, were then used to perform simple unguided SRS and SBS experiments to provide results against which the performance of the guided configurations can be compared. This also allowed a check to be made of the accuracy of the theoretical predictions of SRS and SBS in gases, so that we could be confident about extending the theory to the case of guided configurations.

The waveguiding properties of hollow, cylindrical, quartz capillaries are then described, along with the associated problems of coupling radiation into and out of them. Assuming next that a nonlinear medium is contained within the hollow core, theoretical expressions are developed for the SRS and SBS threshold powers for various configurations that include single pass, resonator and oscillator-amplifier systems. In the final part of the thesis these predictions are tested experimentally, in each case good agreement being found. The main conclusion to be made, finally, is that the use of waveguides substantially reduces the threshold powers required for these nonlinear processes.

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