Tunable single-frequency continuous-wave laser action in Co2+:KZnF3.

We have operated a tunable cw single-frequency laser based on the 4T2–4T2 transition of Co2+ in KZnF3. In single-frequency operation the laser tuned from 1.75 to 2.15 μm and produced an output power of 48 mW. Single-mode conversion efficiencies above 80% were obtained at the peak of the gain curve.