Investigation into phenomena observed during the interaction of a focused high-energy laser beam with high voltage electric fields

West, Nicholas John
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The work presented in this thesis extends and contributes knowledge to the field of laser-induced breakdown of a spark gap in air. Previous work has shown that laser- triggering of a spark gap is very effective in the case of a coaxially triggered spark gap (where the beam is directed along the axis of the gap). Although a coaxially triggered gap presents a very intuitive approach, it is not practical. Therefore, the main focus of this work is to investigate how effective laser-triggering is in the case of an orthogonally arranged gap (beam at right angles to the gap axis). The effects of the laser beam intensity, the gap length used and the position of the plasma in the gap were found to play important roles in the breakdown process of an orthogonally triggered gap. It was found that directing and focusing the laser beam at right angles to the gap axis reduces the breakdown voltage of the gap dramatically. An almost 70% reduction of the breakdown voltage of a 50 mm gap was recorded. Also, the spatial and temporal relation between the laser-induced plasma and the resulting arc was investigated. Although the laser-triggered arc was expected to attach to the conductive laser-induced plasma, experiments showed that this is not the case. Whether attachment occurs depends on the relative timing of the initiation of the plasma and the high voltage arc and on the overall breakdown probability of the spark gap. This represents a unique and valuable contribution to engineers working in the field of triggered spark gaps and other high voltage triggering applications.