Optical Refrigeration for Dramatically Improved Cryogenic Technology

ABSTRACT: Optical refrigeration is currently the only demonstrated all-solid-state cryocooling technology. Optical cryocoolers are devices that use laser light to cool small crystal or glass cooling elements. The cooling element absorbs the laser light and reradiates it at higher energy, an example of anti-Stokes fluorescence. The difference between the energy of the outgoing and incoming light comes from the thermal energy of the cooling element, which in turn becomes colder. In Phase I of this STTR program, the collaboration of ThermoDynamic Films LLC (TDF) and the University of New Mexico (UNM) has cooled an optical-refrigerator cooling element comprised of an ytterbium-doped yttrium lithium fluoride crystal from room temperature to 123 K with about 2% efficiency. This is the world record in optical refrigeration and an important step toward revolutionizing cryogenic systems for sensor applications. This Phase II proposal addresses the improvement and integration of the key components of an optical cryocooler to enable the transition of this scientific breakthrough into DoD sensor applications. The TDF/UNM collaboration will improve the performance of optical refrigerators by making them more efficient, less massive and more reliable for space-born applications. BENEFIT: Rugged, compact, quiet cryogenic refrigerators are essential for a wide range of emerging space-borne and ground-based defense and non-proliferation applications. Optical refrigerators have the potential to meet both national security and commercial needs. In particular, cryogenic optical refrigerators are well suited to cooling space-borne radiation detectors and infrared imagers in small satellites where low weight and a lack of vibrations are especially important. For example, optical cryocoolers could cool infrared detectors for the Department of Defense's Space-Based Infrared System. After the successful completion of this Phase II project, TDF, together with a strategic partner, will be prepared to build and market optical cryocoolers for space-based missions and for ground-based applications such as medical devices and handheld thermal imagers.