Pulsed Fibre Lasers Beyond 3 Micron
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(Thesis)
Date
2021
Authors
Bawden, Nathaniel
Editors
Advisors
Ottaway, David
Henderson-Sapir, Ori
Henderson-Sapir, Ori
Journal Title
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Thesis
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Abstract
The mid-infrared spectral region between 3 μm and 5 μm contains the absorption features of many different organic and biological compounds, which leads to a wide range of potential applications for sources of mid-infrared radiation. Historically, this part of the spectrum has been difficult to access, which has limited the development of these applications. Fibre based lasers offer long gain lengths, effective thermal management and robustness. This thesis explores pulsed operation of fibre lasers using the ⁴F(9/2) → ⁴I(9/2) transition in erbium, which is currently the only fibre laser source to directly generate light in the 3.4 μm to 3.8 μm region. This thesis explores lasers that generate pulses in the nanonsecond, picosecond and femtosecond regimes through use of both Q-switching and mode-locking techniques. The Q-switched systems utilise acousto-optic devices to modulate the resonator losses and produce pulsed laser output. These systems included the first actively Q-switched fibre laser at 3.5 μm. Mode-locked pulses with electronically tunable wavelength were generated via the frequency shifted feedback technique, using an acousto-optic tunable filter. The non-linear polarisation rotation method was used to generate ultrafast mode-locked pulses. This was the first time that this technique had been used on the 3.5 μm erbium transition, which resulted in the first subpicosecond pulses from a fibre laser at this wavelength, with a duration of 580 fs and an energy of 3.2 nJ. The resulting peak power of 5.5kW is the highest of any 3.5 μm fibre laser system. The ultrashort pulses are used to demonstrate non-linear spectral broadening in a highly non-linear fibre. This thesis concludes with a summary of results and suggestions for future work.
School/Discipline
School of Physical Sciences
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2021
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