Accurate Characterization of the Properties of the Rare-Earth-Doped Crystal for Laser Cooling

We present a method for calibrating a commercial thermal camera adopted to accurately measure the temperature change of the sample in a laser-induced temperature modulation spectrum (LITMoS) test, which is adopted for measuring two crucial parameters of the external quantum efficiency ηext and the background absorption coefficient αb for assessing the laser cooling grade of the rare-earth-doped materials. After calibration, the temperature resolution of the calibrated thermal camera is better than 0.1 K. For the cooling grade Czochralski-grown 5% Yb3+:LuLiF4 crystal, the corresponding values of ηext and αb are LITMoS = measured to be ηext=99.4 (±0.1)% and αb=1.5 (±0.1)×10−4 cm−1, respectively.