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K: Fachverband Kurzzeit- und angewandte Laserphysik
K 1: New Methods - Applications
K 1.3: Talk
Thursday, September 2, 2021, 12:00–12:15, H2
Anti-Stokes laser cooling of ytterbium-doped fluorite-structure crystals — Felix Mauerhoff, Stefan Püschel, Christian Kränkel, and •Hiroki Tanaka — Leibniz-Institut für Kristallzüchtung, Berlin, Germany
We report the first laser cooling of ytterbium (Yb3+)-doped fluorite-structure crystals by antiStokes fluorescence. High quality Yb3+(5 at.%):CaF2 and Yb3+(5 at.%):SrF2 single crystals were grown by the Czochralski method. Room temperature fluorescence spectroscopy revealed the mean fluorescence wavelengths to be 997.2 nm and 994.6 nm for Yb:CaF and Yb:SrF, respectively. We characterized the crystals by laser-induced temperature modulation spectroscopy (LITMoS) in a vacuum chamber. All-side polished parallelepiped-shaped samples of both crystal were excited by wavelength-tunable laser sources: a Ti:sapphire laser and a home-built Yb3+:Lu2O3 thin-disk laser. The temperature of the samples was measured with a thermal camera through an anti-reflection coated germanium window. The Yb:CaF and Yb:SrF samples exhibited cooling down by 6.6 K and 3.9 K from room temperature under excitation at 1040 nm at few 100 mW of absorbed power. The evaluation of the external quantum efficiency, background absorption coefficient, and the expected minimum achievable temperature will be reported at the conference.