Long-pulse 4.4-4.6 μm laser oscillations of Fe²⁺ ions in a Zn_1-xMn_xSe (x = 0.3) crystal pumped by a 1940 nm Tm fiber laser through Cr²⁺ → Fe²⁺ energy transfer

Millisecond-pulse laser operation of Fe²⁺ ions at 78 K is demonstrated in the Zn_1-xMn_xSe:Fe²⁺,Cr²⁺ (x=0.3) crystal under a Tm fiber 1940 nm laser pumping through a Cr²⁺→Fe²⁺ energy transfer process for the first time, to the best of our knowledge. The laser slope efficiency was 1% with respect to absorbed pumping energy at 1940 nm. The laser central wavelength shift from 4450 nm at 78 K up to 4510 nm at 110 K was observed. Tunability from 4350 up to 4670 nm at 78 K was achieved using an intracavity tuning element.