Pressure-Assisted Sintering and Properties of Yb: CaF2 Transparent Ceramics

The 5% (atomic fraction) Yb∶CaF2 nano-powders were synthesized by chemical co-precipitation method. Following freeze-drying, the agglomeration degree of the powders reduces, and the powders exhibit cubic lamellar structures with an average particle size of approximately 40 nm. High optical quality 5% Yb ∶ CaF2 transparent ceramics were subsequently fabricated through hot pressing, supplemented by hot isostatic pressing (HIP) sintering as a post-treatment, utilizing the freeze-dried powders. The densification behaviour of the samples during the hot pressing process was investigated. The microstructure, in-line transmittance, absorption spectra, and laser performance of the ceramics were assessed and analyzed. The findings indicate that activation threshold of densification driving force occurs during the holding stage of the hot pressing process, and the HIP post-treatment effectively compresses and removes residual pores within the hot pressed ceramics, thereby significantly enhancing their optical quality. The in-line transmittance of the 5% Yb ∶ CaF2 transparent ceramics, produced through hot pressing (625 ℃ × 2 h, 50 MPa) followed by HIP post-treatment (600 ℃ × 3 h, 100 MPa Ar), is 72. 6% and 92. 2% at 400 and 1 200 nm, respectively, with a thickness of 2 mm. Additionally, the absorption cross-section at 976 nm is determined to be 0. 52 × 10 - 20 cm2 . A fiber-coupled diode laser (LD) with a wavelength of 930 nm served as the pumping source for end-face pumping of the Yb∶ CaF2 transparent ceramics, obtaining a quasi-continuous laser output with a peak power of 0. 81 W and a slope efficiency of 9. 7% .