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Title: Control of the stability of pulsed 2 μm lasers
Author: Brooks, James
ISNI:       0000 0004 7972 3040
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2019
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Pulse-to-pulse uctuations in the output of Q-switched 2 μm lasers are a major obstacle to commercialisation. This jitter is present in all pulse parameters: build-up time, pulse duration, peak power and energy. The severity of the jitter is dependent on how far above threshold the laser can be pumped; lower gain coupled with reabsorption losses contribute to the level of jitter observed in 2 μm lasers. This thesis presents a detailed investigation into the jitter in a Q-switched Tm:YAP laser and tests methods of reducing the jitter. Target jitter levels of <1 ns for the build-up time and < 3% for the energy were identified based on similar commercial Nd-based systems. A full characterisation of the level of jitter in all pulse parameters was undertaken and the results were used as a benchmark to gauge the efficacy of subsequent improvements. The use of etalons to limit the laser mode content increased the build-up time jitter by an order of magnitude and the energy jitter by a factor of three. This is thought to be due to increased mode competition. The cavity was transferred to a ruggedised housing with the minimum degrees of freedom required for alignment. This was done to reduce the variation of losses due to mechanical vibrations and was successful in reducing the jitter. This housing also allowed the purging of the cavity with dry air to reduce atmospheric water absorption. Through this combination, the build-up time jitter was reduced to 1.9 ns and pulse energy jitter to 1.8 %, representing the best performance achieved in this work. The pre-lase technique was employed to enforce laser oscillation on a single longitudinal mode. Pre-lase is a two-step process that allows the build-up of a weak single-frequency pulse that seeds the main output. This led to increased jitter in the build-up time (to 19 ns) and energy (to 16 %) due to the inherent levels of jitter in the high-threshold seed pulse.
Supervisor: Bonner, Gerald ; Stothard, David ; Kemp, Alan Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral