20 W passively cooled single-mode all-fiber laser at 2.8 μm

A maximum output power of 20.6 W at 2.825 mu m from an erbium-doped all-fiber laser is reported, which we believe is the highest output power for this laser transition in single-mode operation. The slope efficiency of the passively cooled laser was up to 35.4% with respect to the absorbed pump power. Accounting for an estimated round-trip intracavity loss of 1.3 dB, we calculated a theoretical conversion efficiency of 39.5%, which is 15% higher than the Stokes efficiency of 34.3%. We believe this is the first experimental confirmation of the predicted pump energy recycling for this fiber laser. The narrow laser linewidth varied from 0.09 to 0: 16nm from low to maximum output power. (C) 2011 Optical Society of America