Optical refrigeration of payloads to T < 125†K.

A modified all-solid-state optical cryocooler prototype based on anti-Stokes fluorescence in a 10%-doped Yb:YLF crystal cooled a payload to temperatures below 125 K starting from room temperature. To achieve this record performance, the optical refrigerator employed a novel, to the best of our knowledge, textured-MgF2 thermal link to improve the thermal transport and fluorescence escape. Additionally, it used spectrally selective, high-reflection coatings in the pump circulator cavity to suppress parasitic lasing and amplified spontaneous emission.

Open-aperture Z-scan study for absorption saturation: accurate measurement of saturation intensity in YLF:Yb for optical refrigeration.

Knowledge of saturation intensity of gain or absorption plays a fundamental role in a variety of applications ranging from lasers to many nonlinear optical processes. Here, we present an analytical expression for open-aperture Z-scan transmission for accurately measuring the saturation intensity in the low absorbance samples but at arbitrary pump intensities. We exploit this formalism to investigate the absorption saturation of LiYF4:Yb3+ (YLF:Yb) in the anti-Stokes excitation region for optical refrigeration at high pump intensities. An absorption saturation intensity of 14.5±1kW/cm2 was measured in YLF:Yb at 1020 nm (E||c) at room temperature.