The high quality Yb-doped fluoride crystals have broad prospects for optical refrigeration. We have laser cooled the Yb:LuLiF crystal to a temperature below the limit of current thermoelectric coolers (~180 K). The 5% Yb:LuLiF crystal sample has a geometry of 2 mm×2 mm×5 mm and was supported by two fibers of 200 μm in diameter. They were placed in a ~2×10<sup>-4</sup> Pa vacuum chamber with an environment temperature of ~294.5 K. The 1019 nm CW laser of power 38.7 W was adopted to irradiate the sample. The temperature of the sample was measured utilizing the DLT methods. After 20 minutes of laser irradiation, the 5% Yb:LuLiF crystal sample was cooled down to ~182.4 K. By further optimizing experimental conditions and increasing the doped Yb concentration, the Yb:LuLiF crystal might be optically cooled below the cryogenic temperature of 123K in the near future.
We report the laser cooling performance of 5 mol. % Yb3+:LuLiF4 crystal in air. Both end faces of the crystal with a size of 3×3×5 mm3 are cut by Brewster angles. A temperature drop of 11 K (from room temperature) of the sample, pumped by a 3-W/1020-nm CW fiber laser, is observed by a thermal camera. The cooling power and efficiency of the sample are estimated to be ∼14.5 mW and ∼1.9%, respectively. Our experiment results show the prospect of this crystal with laser cooling and its potential applications in earth-based optical refrigeration devices.
When pumped with a 10 W 1020 nm fiber laser, a temperature drop of 60.4 K from room temperature of a crystal in the
vacuum is observed by utilizing the differential luminescence thermometry measurement method. The crystal is doped
with 5wt.%Yb <sup>3+</sup> : LuLiF<sub>4</sub> and has a size of 3×3×5 mm<sup>3</sup>. The cooling power and the cooling efficiency of sample is
estimated to be ~50.6 mW and ~2.53%, respectively, at the 232.6 K temperature.