Watt-level efficient 2.3  µm thulium fluoride fiber laser

We report on an efficient mid-infrared thulium (Tm) fiber laser operating on the 3 H 4 → 3 H 5 transition and featuring an upconversion pumping scheme. This laser comprises a heavily T m 3 + -doped (2.50 mol. %) zirconium fluoride glass fiber pumped by a tunable Yb fiber laser around 1.05 µm corresponding to the 3 F 4 → 3 F 2 , 3 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 3 H 4 → 3 H 5 emission with a bandwidth of 173 nm, making it very promising for femtosecond fiber oscillators at ∼ 2.3 µ m .