Microstructure and laser performance of fine-grained Yb:CaF2 transparent ceramics prepared by two-step sintering

The 5 at.% Yb:CaF2 transparent ceramics were successfully fabricated by hot pressing (HP) combined with hot isostatic pressing (HIP) for the first time. The raw nano-powders were synthesized by the co-precipitation method and the influence of HP temperature and HIP post-treatment on the optical quality and microstructures of Yb: CaF2 transparent ceramics were investigated. After HIP post-treatment (600 degrees C x 3 h, 100 MPa Ar), the micro pores in the hot pressed ceramics were further eliminated and all ceramics revealed high optical quality. The ceramic sample hot pressed at 575 degrees C for 2 h and HIP post-treated at 600 degrees C for 3 h shows the best optical quality with the in-line transmittance of 90.5% at 1200 nm (3.9 mm thickness), and the average grain size of ceramics is only 470 nm. And the absorption and emission cross sections of ceramics were calculated. Finally, the laser performance of 5 at.%Yb:CaF2 transparent ceramics was tested. The maximum output power of ceramics was 1.12 W, which is higher than other Yb:CaF2 ceramics fabricated by pressure-assisted sintering method reported in literature, with a corresponding, slope efficiency of 11.6%.