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Title: Exploiting nonlinearity in optical fibres and nanomaterials for short-pulse laser technology
Author: Woodward, Robert
ISNI:       0000 0004 5918 5521
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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The importance of short-pulse laser technology in all branches of science and engineering continues to grow, increasing demands on their performance. In this thesis, we explore approaches for advancing such technologies using optical nonlinearity in emerging nanomaterials and fibres to manipulate the spectral and temporal properties of light. Firstly, we introduce a long-cavity mode-locked fibre laser architecture for generating high-energy pulses with a giant chirp at low repetition rates. Chirped fibre Bragg gratings are developed for pulse compression (and peak-power enhancement) by a factor of a hundred and the system is shown to be an ideal pump source for low-threshold supercontinuum generation in photonic crystal fibre (PCF). Experimental work is supported by numerical simulations to reveal insight into the pulse dynamics. Two-dimensional nanomaterials, specifically few-layer transition metal dichalcogenides such as MoS2 are then considered. We report a harmonic generation microscopy technique for rapidly characterising the structure and optical properties of nanomaterial samples. These materials are then integrated into fibre lasers to act as saturable absorbers for pulse generation by Q-switching and mode-locking. We present a range of sources with pulse durations from femtoseconds to microseconds and kilohertz to megahertz repetition rates, operating throughout the near-infrared, highlighting the wide parameter space that can be accessed. We also propose a theory based on edge states to explain the wideband saturable absorption. Finally, we study stimulated Brillouin scattering in PCF with a focus on the role of acoustic dynamics. With careful choice of wavelength relative to the microstructured fibre length scales, PCFs are shown to exhibit a stronger Brillouin response than conventional fibre, which we use to develop a compact self-mode-locked Brillouin laser. We conclude that emerging nanomaterials and optical fibre designs could be leveraged to yield tangible benefits for short-pulse laser technology and we place our results in context of ongoing research.
Supervisor: Popov, Sergei Sponsor: Engineering and Physical Sciences Research Council ; IPG Photonics
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available