OBSERVATION OF LASER-INDUCED FLUORESCENT COOLING OF A SOLID

THE possibility that an object might cool through its interaction with radiation vas suggested as early as 1929 by Pringsheim(1) After Landa u(2) established the basic thermodynamic consistency of such a process , certain aspects of fluorescent cooling were vigorously pursued(3-11) . In particular, laser 'Doppler' cooling of gas-phase atoms and ions h as today grown into a robust research area In contrast, attempts to co ol solids with light have met with limited success; non-radiative heat ing effects tend to dominate, and fluorescent cooling has at best resu lted in a reduction in overall heating rates(6). Here we report the ex perimental realization of net cooling of a solid with radiation. The c ooling efficiencies achieved (up to 2%) are more than 10(4) times thos e observed in Doppler cooling of gases. By pumping a fluorescent cooli ng element with a high-efficiency diode laser, it may be possible to c onstruct a compact, solid-state optical cryocooler, thereby allowing w idespread deployment of cryogenic electronics and detectors in space a nd elsewhere(16).