Fabrication, microstructure, spectral properties, and laser performance of Yb:GdxY3−xAl5O12 ceramics

Highly transparent 10 at.% Yb:GdxY3−xAl5O12 (x = 0.3, 0.5, and 0.7) ceramics were successfully fabricated by vacuum solid-state reactive sintering at 1800°C for 20 h combined with hot isostatic pressing posttreatment at 1700°C for 3 h under 176 MPa pressure in Ar atmosphere. The in-line transmittances of these ceramics with the thickness of 2.5 mm are 84.4%, 84.0%, and 83.5% at 1100 nm for x = 0.3, 0.5, and 0.7, respectively. The relationships of the Gd3+ content among the phase, microstructures, spectral, and laser properties of the Yb:GdxY3−xAl5O12 ceramics were elucidated in detail. The introduction of Gd3+ has a little influence on the crystal field strength of the Yb3+ sites in GdxY3−xAl5O12. The absorption, emission spectra, and fluorescence lifetime of the Yb3+ in these ceramics are similar, close to 10 at.% Yb:YAG ceramics. Quasi-continuous wave laser outputs of the ceramics were also achieved. The maximum laser output powers are 7.8, 7.7, and 6.6 W with the corresponding slope efficiency as 46.2%, 44.7%, and 39.2% for x = 0.3, 0.5, and 0.7, respectively. The 7.8 W laser output power is the highest value achieved so far for the Yb:GdYAG ceramics, to the best of our knowledge. The previous discussions show that not all the mixed garnets could enhance full width at half maximum of absorption and emission peaks for the active ions; however, the Yb:GdYAG ceramics are still excellent laser gain media.