Highly efficient dual-wavelength mid-infrared CW Laser in diode end-pumped Er:SrF single crystals.

The spectral properties and laser performance of Er:SrF single crystals were investigated and compared with Er:CaF. Er:SrF crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections and much longer fluorescence lifetimes of the upper laser level (Er:I level) than those of Er:CaF crystals. Dual-wavelength continuous-wave (CW) lasers around 2.8 μm were demonstrated in both 4at.% and 10at.% Er:SrF single crystals under 972 nm laser diode (LD) end pumping. The laser wavelengths are 2789.3 nm and 2791.8 nm in the former, and 2786.4 nm and 2790.7 nm in the latter, respectively. The best laser performance has been demonstrated in lightly doped 4at.% Er:SrF with a low threshold of 0.100 W, a high slope efficiency of 22.0%, an maximum output power of 0.483 W.