High-resolution absorption measurement at the zero phonon line of Yb:YAG between 80 K and 300 K

We present measurements of the temperature dependence of the absorption crosssection of Yb:YAG at the zero phonon line (ZPL) near 969 nm. Experiments were carried out on a 1.08 mm thick, ceramic, 1.1 at-% Yb-doped YAG sample over a temperature range between 80 K and 300 K. Results show that the ZPL characteristics strongly depend on temperature. The absorption cross section increases from 0.8 10^-20 cm² to above 49 10^-20 cm² as temperature is decreased from 300 K to 80 K. The full-width at half maximum of the absorption line decreases with temperature, from 2.38 nm at 300 K to 0.05 nm at 80 K. The absorption peak shifts from 969.04 nm at 300 K to 968.39 nm at 80 K. To the best of our knowledge, this is the first time that the ZPL of Yb:YAG has been characterised with enough resolution at cryogenic temperatures and we expect that this data will assist in the design and optimisation of Yb:YAG lasers pumped on this absorption line.