Measurement of Solid-State Optical Refrigeration by Two-Band Differential Luminescence Thermometry
NEW MEXICO UNIV ALBUQUERQUE
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We present a non-contact optical technique for the measurement of laser-induced temperature changes in solids. Two-band differential luminescence thermometry TBDLT achieves a sensitivity of 7 mK and enables a precise measurement of the net quantum efficiency of optical refrigerator materials. The TBDLT detects internal temperature changes by decoupling surface and bulk heating effects via time-resolved luminescence spectroscopy. Several Yb3-doped fluorozirconate ZrF4-BaF2-LaF3-AlF3-NaF-InF3, ZBLANI glasses fabricated from precursors of varying purity and by different processes are analyzed in detail. A net quantum efficiency of 97.39 or -0.01 at 238 K at a pump wavelength of 1020.5 nm is found for a ZBLANI1 Yb3 laser-cooling sample produced from metal fluoride precursors that were purified by chelate-assisted solvent extraction and dried in hydrofluoric gas. In comparison, a ZBLANI1 Yb3 sample produced from commercial-grade metal fluoride precursors showed pronounced laser-induced heating that is indicative of a substantially higher impurity concentration. The TBDLT enables rapid and sensitive benchmarking of laser-cooling materials and provides critical feedback to the development and optimization of high-performance optical cryocooler materials.