Efficient 2.96 micron dysprosium-doped ZBLAN fibre laser pumped at 1.3 micron

Wavelengths around 1.15 μm, 1.3 μm and 1.7 μm can be used to pump Dy-doped ZBLAN fibre in order to generate ∼3 μm with high efficiency. Previously the generation of 2.9 μm from the Dy-ZBLAN fibre was demonstrated by pumping with 1.1 μm Yb-silica fibre laser sources. The laser slope efficiency and lasing threshold demonstrated was about ∼5% and ∼1.78 W. In this investigation, the longer wavelength absorption band (⁶H _9/2, ⁶F_11/2) centred at 1.3 μm of Dy ³⁺-doped ZBLAN is utilised and the lasing transition around ∼3 μm takes places from ⁶H_13/2 → ⁶H _15/2. With this pumping scheme the Stokes' efficiency is expected to be up to ∼45%. A quasi-continuous wave Dy³⁺-ZBLAN fibre laser pumped by a ∼1.3 μm Nd:YAG laser and operating at 2.96 μm with a bandwidth (FWHM) of ∼14 nm has been demonstrated. For a 60cm fibre length, a threshold of 0.5W and a slope efficiency of ∼20% with respect to the absorbed pump power was observed. The overall pump absorption in the fibre was around 84%. The cavity reflectivities at 2.9 μm were 99% and 50%. The demonstrated slope efficiency was 45% of the Stokes' limit. The slope efficiency was around four times higher and the threshold around 3.6 times lower than the previous performance demonstrated by using the 1.1 μm Yb fibre laser pumping scheme. The higher performance achieved compared to the 1.1 μm pump scheme is due to the higher Stokes' limit, lower pump ESA losses and higher cavity reflectivity. About 590 cm^-1 Raman Stokes shift has also detected by using 514.5 nm and 488 nm Ar ion laser as excitation pump sources.