Topper, B.B.TopperPeysokhan, M.M.PeysokhanAlbrecht, A.R.A.R.AlbrechtFlores, A.S.A.S.FloresKuhn, S.S.KuhnHässner, D.D.HässnerHein, S.S.HeinHupel, C.C.HupelNold, J.J.NoldHaarlammert, N.N.HaarlammertSchreiber, T.T.SchreiberSheik-Bahae, M.M.Sheik-BahaeMafi, A.A.Mafi2022-05-062022-05-062021https://publica.fraunhofer.de/handle/publica/41613410.1364/OL.444709An ytterbium doped silica optical fiber with a core diameter of 900µm has been cooled by 18.4 K below ambient temperature by pumping with 20 W of 1035 nm light in vacuum. In air, cooling by 3.6 K below ambient was observed with the same 20 W pump. The temperatures were measured with a thermal imaging camera and differential luminescence thermometry. The cooling efficiency is calculated to be 1.2±0.1%. The core of the fiber was codoped with Al3+ for an Al to Yb ratio of 6:1, to allow for a larger Yb concentration and enhanced laser cooling.en620535journal article