Highly efficient dual-wavelength mid-infrared CW Laser in diode end-pumped Er:SrF(2) single crystals

The spectral properties and laser performance of Er:SrF(2) single crystals were investigated and compared with Er:CaF(2). Er:SrF(2) 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(3+):(4)I(11/2) level) than those of Er:CaF(2) crystals. Dual-wavelength continuous-wave (CW) lasers around 2.8 μm were demonstrated in both 4at.% and 10at.% Er:SrF(2) 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(2) with a low threshold of 0.100 W, a high slope efficiency of 22.0%, an maximum output power of 0.483 W.