Investigations of rare earth doped fluorozirconate fibre lasers and amplifiers
This thesis presents the results of a three year study into the use of thulium and praseodymium doped fluorozirconate fibres as low threshold, potentially miniature laser sources at a variety of wavelengths from the visible to the infrared. Thulium doped fluorozirconate fibre is also investigated as a high gain optical amplifier at 810nm. Pumped at the semiconductor diode compatible wavelength of 790nm, laser emission has been demonstrated at 1.9µm, 2.3µm, 1.47µm and 810nm in thulium doped fluorozirconate fibres, with diode pumped operation achieved at 1.91µm. The transition at 810nm has been operated as an optical amplifier where single pass gains in excess of 22dB have been demonstrated for less than 60mW of pump power. The gain characteristics of this transition have been modelled and show good agreement with the experimentally observed performance. Operated as a laser emitting around 810nm, this transition has demonstrated both high efficiencies (> 70%), low thresholds (< 13mW of pump power) and tunability over 30nm. A Judd-Ofelt analysis has been carried out for thulium-doped fluorozirconate fibre to extract spectroscopic data for explanation of the system performance. In praseodymium doped fluorozirconate fibre, visible laser emission has been observed at 635nm, 605nm, 520nm and 491nm both when pumped by an argon ion laser at 472.7nm and by upconversion pumping when using two Ti:sapphire pump lasers tuned to 1.01µm and 835nm. An analytical model of the performance of these upconversion pumped visible fibre laser transitions is presented and shows good agreement with experiment. Pump power requirements for laser action on the high gain 635nm transition have been shown to be as low as 20mW from each pump laser and there exists, therefore, the possibility of semiconductor laser diode pumping.