LASER COOLING OF BULK MATTER. For many years laser light has been used to slow down and thereby cool individual atoms in traps. But laser light can now also be used to cool bulk matter. This happens by a process called anti-Stokes fluorescence. In the solid certain molecules reside in vibrational states which make them somewhat warmer than their neighbors. If now specially tuned laser light hits these molecules, they will emit a photon whose energy is greater than the one they absorbed. Thus heat energy is carried away as light energy (New Scientist, 18 January 1997). In this way gases and liquids have been cooled, and now researchers at Los Alamos have cooled a solid ytterbium-doped optical fiber from a temperature of 298 to 282 K, a difference of 16 K. Applied on a large scale, this principle could lead to a laser refrigerator. (C.E. Mungan et al., Physical Review Letters, 10 February 1997.)