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3 March 2020 Experimental observation of cooling in Yb-doped silica fibers
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Anti-Stokes fluorescence cooling in a silica-based fiber is reported for the first time. The fiber had a core with a 20-μm diameter doped with 2.06 wt.% Yb and co-doped with 0.86 wt.% Al and 0.88 wt.% F. Core-pumping the fiber with 1040- nm light, temperature changes as large at -50 mK were measured at atmospheric pressure. Temperature measurements were performed at 12 pump wavelengths, and the measured dependence of the temperature change as a function of pump wavelength was in excellent agreement with a previously reported model. With this model, the absorptive loss in the fiber was inferred to be less than 15 dB/km, and the critical quenching concentration to be ~15.6 wt.% Yb. This combination of low loss and high quenching concentration (a factor of 16 times higher than the highest reported values for Yb-doped silica) is what allowed the observation of cooling. The temperature measurements were performed at atmospheric pressure using a custom slow-light fiber Bragg grating sensor with an improved thermal contact between the test fiber and the FBG. The improved method involves isopropanol to establish a good thermal contact between the two fibers. This eliminated a source of heating and enabled more accurate measurements of the cooled-fiber temperature. This improved temperaturemeasurement set-up also led to a new cooling record in a multimode Yb-doped ZBLAN fiber at atmospheric pressure. When pumped at 1030 nm, the fiber cooled by -3.5 K, a factor of 5.4 times higher than the previous record.
Conference Presentation
© (2020) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jenny M. Knall, Pierre-Baptiste Vigneron, Magnus Engholm, Peter D. Dragic, Nanjie Yu, John Ballato, Martin Bernier, and Michel Digonnet "Experimental observation of cooling in Yb-doped silica fibers", Proc. SPIE 11298, Photonic Heat Engines: Science and Applications II, 112980F (3 March 2020);

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