Single fluoride crystals as materials for laser cooling applications

摘要

We report the successful growth and the laser cooling results of Yb~(3+)-doped single fluoride crystals. By investigating the mechanical and thermal properties of Yb-doped BaY_2F_8 and LiYF_4 crystals and using the spectroscopic data we collected from our samples, the theoretical and experimental cooling efficiency of fluoride crystals are evaluated and compared with respect to those of ZBLAN. Two different methods, a thermal camera and a fluorescence intensity ratio technique, have been used to monitor the temperature change of the samples. The temperature change is clearly exponential, as expected from theory, and the temperature drops are 6.3 K and 4 K for Yb:LiYF_4 and Yb:BaY_2F_8 respectively in single-pass configuration, corresponding to a cooling efficiency of about 2% and 3%. This last value is slightly larger than that observed in Yb-ZBLAN in similar experimental condition.