Implementation of Laser-Induced Anti-Stokes Fluorescence Power Cooling of Ytterbium-Doped Silica Glass published May 2021 https://pubs.acs.org/doi/10.1021/acsomega.1c00116 Abstract Laser cooling of a solid is achieved when a coherent laser illuminates the material, and the heat is extracted by annihilation of phonons resulting in anti-Stokes fluorescence. Over the past year, net solid-state laser cooling was successfully demonstrated for the first time in Yb-doped silica glass in both bulk samples and fibers. Here, we report more than 6 K of cooling below the ambient temperature, which is the lowest temperature achieved in solid-state laser cooling of silica glass to date to the best of our knowledge. We present details on the experiment performed using a 20 W laser operating at a 1035 nm wavelength and temperature measurements using both a thermal camera and the differential luminescence thermometry technique.
https://en.wikipedia.org/wiki/Laser_cooling#Anti-Stokes_cooling Anti-Stokes cooling The idea for anti-Stokes cooling was first advanced by Pringsheim in 1929.[14] While Doppler cooling lowers the translational temperature of a sample, anti-Stokes cooling decreases the vibrational or phonon excitation of a medium. This is accomplished by pumping a substance with a laser beam from a low-lying energy state to a higher one with subsequent emission to an even lower-lying energy state. The principal condition for efficient cooling is that the anti-Stokes emission rate to the final state be significantly larger than that to other states as well as the nonradiative relaxation rate. Because vibrational or phonon energy can be many orders of magnitude larger than the energy associated with Doppler broadening, the efficiency of heat removal per laser photon expended for anti-Stokes cooling can be correspondingly larger than that for Doppler cooling. The anti-Stokes cooling effect was first demonstrated by Djeu and Whitney in CO2 gas.[15] The first anti-Stokes cooling in a solid was demonstrated by Epstein et al. in a ytterbium doped fluoride glass sample.[16]
