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Title: Development of diode pumped Alexandrite lasers
Author: Sheng, Xin
ISNI:       0000 0004 9350 9817
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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This thesis is focused on the development of diode-pumped Alexandrite lasers, especially in terms of understanding and optimizing their performance. Alexandrite possesses excellent physical properties and broad wavelength tunability (701-858 nm). Diode pumping of Alexandrite is a promising route to construct simple, compact and low-cost laser systems, which can enable a multitude of precision applications including remote sensing (LIDAR) light sources. This thesis work presents the first demonstration of a Q-switched Alexandrite laser under CW diode pumping. The Q-switched laser was operated with pulse repetition rates up to 10 kHz. Pulses with maximum peak power of 1.19 kW were obtained at 1 kHz repetition rate. By modifying the already Q-switched laser system, a cavity-dumped Q-switched system was developed to generate shorter pulses. Pulses with considerably shorter duration of 2.9 ns and increased pulse energy of 200.8 μJ were produced. These correspond to a peak power of 69.2 kW which is more than 60 times that of the standard Q-switched operation. This thesis also reports the first wavelength-tunable passively Q-switched diode-pumped Alexandrite laser using a semiconductor saturable absorber mirror (SESAM). The Q-switched wavelength tuning was achieved between 775 and 781 nm using a birefringent plate. Highly stable pulses with 73 mW average power, 6.9 μs pulse duration and 11.2 kHz repetition rate were obtained in fundamental TEM00 mode with excellent spatial quality (M2 < 1.1). Lastly, the first single-longitudinal-mode (SLM) operation of a CW Alexandrite ring laser under diode pumping was presented in this work. An ultra-compact bow-tie ring cavity with astigmatic compensation was developed. The unidirectional operation of the ring laser was realized using an optical diode consisting of a Faraday rotator and a half-wave plate, which resulted in the SLM output with power >1 W in TEM00 mode. The wavelength was tuned between 727 and 792 nm. These successful pulsed and continuous-wave operations promote the prospect of diode-pumped Alexandrite lasers in light source applications.
Supervisor: Damzen, Michael John Sponsor: Imperial College London ; China Scholarship Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral