Effect of air annealing on the optical properties and laser performance of Yb:YAG transparent ceramics

Highly transparent 5 at.% Yb:YAG ceramics were fabricated by a solid-state reactive sintering method. Aiming to eliminate the color centers, annealing treatments of the 4 mm × 4 mm × 3 mm samples from 1250 °C to 1500 °C for 5–40 h in air were conducted. The effects of annealing temperature and holding time on the optical transmittance as well as the laser performance of Yb:YAG transparent ceramics were investigated. The experimental results showed that the prepared ceramics had a dense and homogeneous structure with the average grain size of 26.8 μm. Annealing at 1250 °C for 40 h, 1350 °C for over 10 h or higher than 1400 °C for 5 h made the samples turn to colorless. For the Yb:YAG ceramics vacuum sintered at 1750 °C for 50 h and then annealed at 1350 °C for 20 h under air atmosphere, the in-line transmittance of the sample with the thickness of 3 mm was about 83.5% at 400 nm. Continuous-wave (CW) laser at 1031.5 nm was demonstrated and the maximum output power of 4.4 W with a slope efficiency of 27.5% was achieved.