A technique for cooling macroscopic crystal or a piece of Glass via laser-induced fluorescence.

The crystal must be doped with ytterbium or thulium ions, which are excited by the Laser beam. The laser Wavelength is chosen SO that it is longer than the Average Wavelength of the resulting fluorescence. This means that the Energy of the absorbed Photons is lower than the average energy of the emitted photons, so that energy is removed from the crystal.