Laser-induced fluorescent cooling of rare-earth-doped fluoride glasses

Continual cooling of a material by anti-Stokes luminescence has been experi mentally observed in a solid material. Net cooling was achieved by pumping to the lower levels of the F-2(5/2) manifold of Yb3+ followed by population redistribution across this manifold via thermalization and fluorescence to the ground state, Fluoride glass hosts in the ZBLAN and BaF2-InF3-GaF3 (BI G) families have been used in these experiments. Temperature decreases of 0 .33 K in a bulk glass sample and 16 K in a fiber sample were obtained in ZB LANPb:Yb3+. Net cooling was achieved when an electrochemical purification s tage was incorporated into the glass fabrication process to decrease the ex trinsic absorptive component of the host glass in the 1.0 mu m region. Reso nant laser ablation experiments showed the positive and negative effects of electrochemical processing on fluoride glasses in reducing transition meta l content which is detrimental to successful fluorescent cooling. Reduction in copper, iron, and chromium content of 18, 4.2, and 5.5 were determined for the ZBLANPb sample via RLA. However, reductions in transition metal con tent were only 1.9 for copper and a negligible amount for iron and chromium in the BIG glasses, (C) 1999 Elsevier Science B.V. All rights reserved.