Thulium sensitised holmium-doped CW fluoride fibre laser of high efficiency

CW operation of extremely high efficiency has been observed from the 2.024 μm transition of holmium in a Tm: Ho codoped singlemode fluoride fibre laser. By pumping into thulium absorption between 820 and 830 nm, output powers of 250 mW and maximum slope efficiencies of 60 % were observed. These results suggest that pump quantum, and photon conversion efficiencies of 150 and 75 % respectively, are readily attainable.