Effect of doping concentration on the performance of 2.8 µm Er:CaF₂ lasers

The effect of rare-earth doping on the spectroscopy and mid-infrared laser performance of Er³⁺:CaF₂ crystals was investigated. An optimum doping level of 3-5 at.% was identified owing to ion clustering. Pumped by a high-brightness Yb-fiber laser at 976 nm, a continuous-wave 5 at.% Er³⁺:CaF₂ laser generated 1.22 W at 2798 nm with a slope efficiency of 38.3% exceeding the Stokes limit, and the laser wavelength was continuously tunable across 2690-2830 nm (tuning range: 140 nm). The ratio of energy-transfer upconversion rates from ⁴I_11/2 and ⁴I_13/2 states was quantified relating to the energy recycling process.