Efficient and high-power operation of Tm~(3+)-doped silica fibre laser based on enhanced cross-relaxation process

We describe a high-power and ultra-efficient cladding-pumped Tm-doped silica fibre laser with Tm3+ concentration and core composition optimised for efficient 'two-for-one' cross-relaxation.The fibre laser had a threshold pump power of 4.8 W and yielded a maximum output power of 81.5 W at 2.03 μm for 137 W launched pump power at ~ 790 nm,corresponding to a slope-efficiency of 62.5% with respect to launched pump power.The prospects for further improvement in performance are discussed.