Improving laser cooling efficiencies of Yb-doped yttrium aluminum garnet by utilizing non-resonant anti-Stokes emission at high temperatures

Laser cooling in solids has been demonstrated, and cooling from room temperature to cryogenic temperatures has so far been the main focus of research. However, operation at high temperatures can be advantageous. We propose that laser cooling of Yb-doped yttrium aluminum garnet ceramic discs is enhanced above 300 K. Photoluminescence (PL) spectra is evidence that the phonon-assisted energy transfer from resonant states, which exhibit a narrow PL peak, to inhomogeneously distributed energy states becomes stronger at higher temperatures. This results in an enhanced non-resonant anti-Stokes PL at high temperatures. The ideal cooling efficiency determined from the PL spectrum at 470 K is 1.7 times higher than that at 300 K.