Dysprosium mid-infrared fibre lasers

Optical sources in the mid-infrared have enabled an increasing number of applications in fields such as sensing, materials processing, and defence. While traditional mid-IR sources have often been based on nonlinear conversion in parametric oscillator devices, these systems are bulky, costly, and inefficient. In contrast, the past few decades have seen uoride glass based mid-IR fibre lasers advance from small scale laboratory demonstration, to advanced developmental systems, and even recently commercial products. The majority of this class of lasers have been based on erbium, or to a lesser extent, holmium-doped gain media. Both systems have achieved multi-watt output power, and have been demonstrated as ultra-fast pulsed systems down to pico- and even femto-second pulse duration. However, these systems share two fundamental limitations. One, the conversion efficiency is limited to less than 50%, which has led to a distinct slowdown in output power scalability. Two, both systems are limited in bandwidth, translating to holes in the optical spectrum which can be covered by fibre lasers. There is a third dopant element which exhibits emission in the same spectral region, but has been largely ignored: dysprosium. While the few demonstrations of dysprosium-doped mid-IR fibre lasers did not exceed performance of competing systems, there is much untapped potential remaining which is what this thesis aims to address. Specifically, two novel optical pumping schemes based on near- and mid-infrared are investigated which address the limitations of the previous dysprosium efforts, and the competing erbium and holmium basedsystems. Further, the viability of progressing these systems to operation in the pulsed regime is considered. As a whole, these investigations aim to both solidify dysprosium as a viable candidate for mid-IR fibre laser emission, and deepen the collective understanding of dysprosium as an active rare earth dopant.