Monolithic highly efficient 272 W nested-ring structured-core thulium fiber laser at 1940 nm

A novel, to the best of our knowledge, thulium-doped silica fiber with a non-uniform core doping profile has been utilized to demonstrate a high-power monolithic laser oscillator system. The fiber laser achieved a continuous-wave (CW) output power of 272 W at 1940 nm with slope efficiencies of 68% and 71% with respect to launched and absorbed pump power, respectively. This novel Tm fiber design enabled the generation of the highest reported output power from a single-mode, small core ($<$15 µm diameter) non-pedestal fiber. Moreover, the slope efficiency achieved is the maximum reported to date for a single-mode thulium fiber laser operating at >100 W output power level.