Upconversion cooling of Er-doped low-phonon fluorescent solids

We report on a mechanism for laser cooling of fluorescent solids based on infrared-to-visible upconversion often found in rare-earth-doped low-phonon materials. This type of optical cooling presents some advantages with regard to conventional anti-Stokes cooling. Among them, it allows us to obtain cooling in a broader range of frequencies around the barycenter of the infrared emitting band.