Laser cooling by over 7 K in Yb-doped ZBLAN fibers with high-power pumping at atmospheric pressure.

Anti-Stokes fluorescence (ASF) cooling has been demonstrated to be a viable method for balancing the waste heat produced in gain materials. In addition, radiation-balanced fiber lasers and amplifiers at atmospheric pressure have recently been developed. Here, we evaluate the cooling characteristics in a long section of a Yb-doped ZBLAN fiber with high pump power. The fiber has a 200-µm-diameter core and is doped with 3 wt. % Yb. As indicated by a thermal camera, cooling by over 7 K below ambient temperature was achieved by core pumping at 1030 nm. The temperature drop distribution at multiple measurement points in the fiber was evaluated with a maximum pump power of tens of watts. The results demonstrate the excellent ASF cooling performance of Yb-doped ZBLAN fibers. This study has great significance for the development of high-power radiation-balanced fiber lasers.