Solid-state optical refrigeration is an emerging cooling technology that can provide vibration free and reliable refrigeration to cryogenic temperatures in a lightweight and compact device. The technology has matured over the past two decades and is currently being considered for applications where the mechanical vibrations, limited reliability, or insufficient portability of existing cooling technologies pose challenges. Possible applications include satellite-borne infrared imaging, laser metrology, and gamma-ray spectroscopy as well as high-reliability cooling of semiconductors and high-temperature superconductors. The best results achieved so far have been in cooling rare-earth-doped solids, especially materials doped with ytterbium. We discuss the fundamental physical principles of solid-state laser cooling, the resulting material and device design requirements, and the estimated payload heat lift of an optical cryocooler.
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