Demonstration of an optical cryocooler

We present the first observation of cryogenic operation in an all-solid-state refrigerator. A temperature drop of ~150 K is demonstrated in a 0.2 cm³ rare-earth doped fluoride crystal (Yb:YLF) using anti-Stokes fluorescence, at a record cooling power of 110 mW. Lowest electronic transition within Yb³⁺ Stark manifold along with cavity enhanced absorption and thermal-load management were key in achieving this operation. We show that temperatures down to 100 K are achievable in this arrangement given sufficient absorbed laser power at 1020 nm.