Recent developments in cooling thulium-doped heavy-metal fluoride glass are presented. Thulium-doped fluorozirconate (ZBLANP) is cooled to 19 K below ambient with a multiple-pass pump scheme. This represents over an order of magnitude increase from the previously reported single-pass geometry. The results agree with a simple model for anti-Stokes fluorescence cooling that includes considerations of quantum efficiency and parasitic heating mechanisms. Issues relating to a practical optical

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