Watt-level efficient 2.3 µm thulium fluoride fiber laser.

We report on an efficient mid-infrared thulium (Tm) fiber laser operating on the → transition and featuring an upconversion pumping scheme. This laser comprises a heavily -doped (2.50 mol. %) zirconium fluoride glass fiber pumped by a tunable Yb fiber laser around 1.05 µm corresponding to the → excited-state absorption transition. The laser generates 1.24 W at 2269-2282 nm with a slope efficiency of 37% in the quasi-continuous-wave regime. The Tm-glass fiber exhibits a broadband → emission with a bandwidth of 173 nm, making it very promising for femtosecond fiber oscillators at ∼2.3µ.