Measurements of optical refrigeration in ytterbium-doped crystals

We measured anti-Stokes fluorescence cooling (optical refrigeration) in ytterbium-doped yttrium aluminum garnet (YAG). Pumping the 2.3% Yb3+:YAG crystal with 1.8 W of 1030 nm laser light produced a temperature drop of 8.9 °C from room temperature. The high thermal conductivity and ruggedness of this crystal make it an attractive material for use in optical refrigerators. Our spectral studies show that pure crystals of this material could be efficient for optical refrigeration at temperatures above ∼100 K. Photothermal deflection measurements show that our current crystals can cool at ∼250 K. Additionally, we measured optical refrigeration in a 5% Yb3+:Y2SiO5 crystal when pumped at 1050 nm.