Efficient 2.76 μm continuous-wave laser in extremely lightly Er-doped CaF2 single-crystal fiber

Rare-earth-doped single-crystal fibers are promising for use in developing high-power lasers due to their improved thermal management and excellent optical properties. In this work, Er-doped CaF(2)single-crystal fibers of good optical quality were successfully grown by a modified temperature gradient technique method. For the characteristic clustering effect of trivalent rare earth ions within fluorite crystals, a high-efficiency 2759.1 nm laser was obtained in a 1 at.% Er-doped CaF(2)crystal fiber. Moreover, even in an extremely lightly doped crystal fiber with a concentration of 0.5 at.%, a continuous-wave (CW) 2758.2 nm laser with a slope efficiency of 20% was achieved. Without the cascade lasing, a similar to 2.8 mu m CW laser operation pumped by a laser diode was first demonstrated in the case of a Er(3+)doping concentration below 1 at.%. The results suggest that Er-doped CaF(2)single-crystal fibers are promising for mid-infrared lasers.