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The fibre laser has revolutionised modern technology, underpinning applications as diverse as materials processing, communications, and medical imaging. Demand has grown for fibre-based laser sources across a wide range of spectral regions. This thesis outlines progress towards extending the spectral coverage of fibre laser technology, through efficient nonlinear conversion techniques such as stimulated Raman scattering, four-wave mixing, and second-harmonic generation. We target two distinct areas of research: nonlinear frequency conversion in bulk crystals, and four-wave mixing in photonic crystal fibre. We begin by introducing an architecture for generating nanosecond pulsed, MHz repetitionrate pulses at 1240 nm based on stimulated Raman scattering in phosphosilicate fibre. The resulting amplifier has ideal properties as a pump for subsequent nonlinear conversion in crystals. We demonstrate the use of this phosphosilicate Raman amplifier as the pump system for three novel nonlinear sources. The first of these utilises seeded optical parametric generation in a cadmium silicon phosphide crystal to generate nanosecond pulsed, MHz repetition-rate, mid-infrared radiation between 4.2–4.6 μm. The second source we present delivers watt-level average powers at 620 nm, based on the direct frequency-doubling of the 1240 nm amplifier system, with ideal properties for stimulated-emission depletion microscopy. The third source extends the concept of the frequency-doubled Raman amplifier system at 620 nm to 743 nm, by utilising cascaded Raman amplification in phosphosilicate fibre. Lastly, we outline an architecture for generating short, tuneable pulses at 794–828 nm based on fibre optical-parametric chirped pulse amplification, a technique which utilises four-wave mixing in photonic crystal fibre. This architecture aims to generate ultrashort pulses in spectral regions not traditionally well served by existing fibre lasers. We underpin the work with both experimental results and simulations, discussing the design, implementations and limitations of this architecture, as well as presenting avenues for the future research and development of similar systems. Open Access |
