Abstract

As first discussed by Pringsheim in 1929, continual cooling of a material may occur via anti- Stokes luminescence. However, not until recently was net cooling actually observed experimentally in a solid. By pumping Yb³⁺ to the lower Stark levels of the ²F_5/2 manifold, followed by population redistribution across this manifold and fluorescence to the ground state, removal of heat from a ZBLAN-derived fluoride host was achieved. The Yb-doped ZBLANP host demonstrated a temperature drop of 0.33 K at 1008 nm via infrared evaluation. Photothermal deflection spectroscopy (PTDS) was employed to measure the relative cooling efficiency (DC laser power to cooling power), which was determined to be 2.03%. Due to constraints on the doping levels in ZBLAN-derived hosts, other high rare earth concentration fluoride hosts are presently being investigated as potential coolers. BIZYT-derived hosts, with Yb concentrations as high as 26%, have been shown to contain similar spectral characteristics to that of ZBLAN, and thus sufficient spectral overlap for anti-Stokes fluorescent behavior. In general, the potential for high levels of net cooling in Yb-doped fluoride glasses makes these hosts attractive candidates for the development of a first- generation optical cryocooler for astronomical remote sensing applications.

© 1997 Optical Society of America