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Title: Extending the wavelength coverage of frequency-doubled fibre lasers
Author: Runcorn, Timothy
ISNI:       0000 0004 7427 6608
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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The unique coherence properties of laser light has revolutionised modern life through fields as diverse as materials processing, optical communications and scientific research. Despite the enormous engineering progress made in developing laser systems into tools used in a wide range of applications, there are still many spectral regions where suitable laser sources are demanded. This thesis describes progress made towards developing practical and efficient nonlinear frequency conversion techniques to access some of these spectral regions, whilst exploiting the inherent benefits that master oscillator power fibre amplifier (MOPFA) systems offer. In particular, two of the developed sources were designed to satisfy the depletion beam requirements for stimulated emission depletion microscopy using the green fluorescent protein. The sources operated at 560 nm and were based on a frequency-doubled Raman amplifier that was pulse-pumped by an ytterbium MOPFA system. The first source developed proved that this architecture was effective at generating picosecond pulse trains at megahertz repetition rates with nanojoule pulse energy in a compact and alignment-free system. The second source improved on the design by adding temporal flexibility, increasing the efficiency and pulse energy and demonstrated that it was a completely turn-key solution. The third source extended the frequency-doubled pulse-pumped Raman amplifier concept to operation around 590 nm by utilising cascaded Raman amplification, whilst maintaining similar output characteristics. The final source developed operated around 780 nm and was based on direct frequency-doubling of an erbium MOPFA system. It was designed for subsequent nonlinear frequency conversion and featured high average power with flexible wavelength and temporal characteristics. Watt-level average powers and pulse energies of hundreds of nanojoules were obtained at every wavelength region, demonstrating that the implemented nonlinear frequency conversion techniques are a viable method for extending the wavelength coverage of MOPFA systems.
Supervisor: Taylor, James Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral