LD pumped high-power mid-infrared solid state lasers based on 1.3at.%Er³⁺: CaF₂ crystal (Invited)

3 μm wavelength laser is an ideal laser source for high precision laser surgery, and can be an effective pump source for mid-infrared optical parametric oscillations. The mid-infrared laser in 2.7-3 μm band can be obtained by laser diode (LD) directly pumping Er³⁺-doped crystal, which has advantages of low cost, compact and simple structure. The Er³⁺doping concentration is generally high to solve the laser self-termination. However, high concentration causes strong light absorption and up-conversion, which could enhance the thermal effect of laser crystal and hinder the improvement of laser output power. The characteristic fluorite structure of low phonon energy CaF₂ crystals makes trivalent rare earth ions easily form “clusters”. A laser gain medium with high thermal conductivity can be obtained by lightly doping Er³⁺ into the CaF₂ crystal. In this work, high quality 1.3at.%Er³⁺: CaF₂ laser crystals were successfully grown by temperature gradient method, diode pumped continuous-wave Er³⁺: CaF₂ laser with maximum output power of 2.2 W was achieved, this is the highest output power in the LD end pumped lightly doping crystals. Furthermore, we demonstrated the 2.8 μm laser continuous-wave performance pumped by 1532 nm LD. The research of the LD direct pumped high power laser is expected to promote the development of the long-wavelength mid-infrared laser towards the direction of compact structure and low cost.