Optical refrigeration has been observed by subjecting single crystals of yttrium aluminum garnet and Nd-doped yttrium aluminum garnet to intense 1.064-μ laser radiation. In addition to this first observation of optical refrigeration, the present experiments yield a very accurate value for the fluorescent quantum efficiency of Nd-doped yttrium aluminum garnet.

• Received 12 September 1968

DOI:https://doi.org/10.1103/PhysRevLett.21.1172