1.45–1.49-µm tunable thulium-doped silica fiber laser quasi-continuous-wave cladding-pumped at 0.79 µm

A silica-based thulium-doped fiber (TDF) laser emitting on the 3 H 4 → 3 F 4 transition is continuously tunable in the range 1.45–1.49 µm. We designed and fabricated a double-clad TDF and incorporated it into a cavity formed between a perpendicular fiber facet and a Littrow-configured diffraction grating for tunable wavelength-selective feedback. The TDF was cladding-pumped quasi-continuous-wave with up to 644 W of instantaneous launched power at 0.79 µm from three pigtailed diode lasers, operating with a pump duty cycle of 0.95 % in 190-µs rectangular pulses. This pump power readily overcomes the fast decay of 3 H 4 in silica. The highest instantaneous output power reached approximately 58 W at 1464 nm, exhibiting a slope efficiency of around 11.6 % relative to the launched pump power. The optical-to-optical conversion efficiency at 1464 nm was 9.0 % at full power. Concurrent emission at 1.9 µm, on the 3 F 4 → 3 H 6 transition, was required to deplete the 3 F 4 level and thus enhance the population inversion. Our work represents the first demonstration of a cladding-pumped silica-based TDF laser in this wavelength range.