Highly efficient CW cascade operation of 1.47 and 1.82 mu m transitions in Tm-doped fluoride fibre laser

The 1.475 mu m selfterminating transition in a thulium-doped fluorozirconate fibre has been operated CW with thresholds as low as 3.2 mW of launched pump power. Furthermore, by enforcing oscillation at 1.475 and 1.88 mu m simultaneously, output powers of approximately 130 and approximately 115 mW, respectively, have been observed for around 325 mW of launched pump power. These results correspond to slope efficiencies of 43 and 38% or photon conversion efficiencies of 82 and 92%, respectively, for the 1.475 and 1.82 mu m transitions.