LASER COOLING OF A SOLID BY 21 K STARTING FROM ROOM-TEMPERATURE

A fluorozirconate glass doped with trivalent ytterbium ions has been l aser cooled in vacuo from 298 to 277 K by optical pumping of the ions at 1015 nm. The cooling effect arises from anti-Stokes fluorescence of the laser-excited ions and by virtue of the near-unit fluorescence qu antum efficiency for Yb3+ in sufficiently pure solid hosts. The sample temperatures in the experiment are determined by measurement of the Y b3+ emission spectrum; the value of the observed temperature change fr om room temperature as a function of pump wavelength is successfully e xplained in terms of a simple two-level model that includes the effect of optical saturation. (C) 1998 Optical Society of America.