Measurement of solid-state optical refrigeration by two-band differential luminescence thermometry

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 Yb 3+ -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±0.01% at 238 K (at a pump wavelength of 1020.5 nm) is found for a ZBLANI:1% Yb3+ lasercooling sample produced from metal fluoride precursors that were purified by chelate-assisted solvent extraction and dried in hydrofluoric gas. In comparison, a ZBLANI:1% Yb 3+ sample produced from commercialgrade 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. © 2010 Optical Society of America OCIS codes: 160.5690, 300.2530, 300.6430.