Microstructure and laser emission of Yb:CaF2 transparent ceramics fabricated by air pre-sintering and hot isostatic pressing

Transparent ytterbium doped calcium-fluoride (Yb:CaF2) ceramics were successfully fabricated by air pre-sintering and hot isostatic pressing (HIP) post-treatment from the powders synthesized by the co-precipitation method. The influence of pre-sintering temperature on the densification, microstructures and optical quality of 5 at.% Yb:CaF2 ceramics was systematically investigated. The ceramic sample pre-sintered at 650 °C for 2 h and HIP post-treated at 650 °C for 1 h shows the best transparency with the in-line transmittance of 90% at 1200 nm. The upper level lifetime of the Yb3+ in Yb:CaF2 ceramics was evaluated to be 1.95 ms by the pinhole method. In addition, the laser emission from an optimized 5 at.% Yb:CaF2 ceramic sample yields in the maximum output power of 0.81 W with a maximum slope efficiency of 22.6% at 1028.5 nm under quasi-CW pumping.