UNITED STATES NAVAL ACADEMY Carl E. Mungan, Associate Professor Development of a Fluorescent Cryocooler Presented at the Ninth Annual American Institute of Astronautics & Aeronautics Utah State University Conference on Small Satellites on September 20, 1995 in Logan, UT. Authors: B.C. Edwards, M.I. Buchwald, R.I. Epstein, T.R. Gosnell, and C.E. Mungan. Abstract ( #abstract ) Introduction ( #introduction ) Anti-Stokes Fluorescent Cooling ( #principles ) First-Generation Fluorescent Cryocooler ( #design ) Future Directions ( #plans ) Conclusions ( #conclusions ) References ( #references ) Abstract Recent work at Los Alamos National Laboratory has demonstrated the physical principles of a new type of solid-state cryocooler based on anti-Stokes fluorescence. Design studies indicate that a vibration-free, low-mass "fluorescent cryocooler" could operate for years with efficiencies and cooling powers comparable to current commercial systems. This paper presents concepts for a fluorescent cryocooler, design considerations, and expected performance. Introduction Recent laboratory measurements have demonstrated laser-induced anti-Stokes fluorescent cooling of a solid [ 1 ( #one ) ]. Combining this laboratory work with computer simulations and information on available technology, we expect that a practical, first-generation, all-solid-state fluorescent cryocooler will have the following properties: no vibrations does not produce and is not susceptible to electromagnetic interference cools to 77 K is ~1% efficient (DC power to cooling power) weighs less than 3 kg/W has a lifetime of 10 years continuous operation. This first-generation cryocooler will employ material with a demonstrated fluorescent cooling capability (ytterbium-doped ZBLANP). With improved cooling materials and designs, future cryocoolers could be over twice as efficient at 77 K and cool to lower temperatures. Anti-Stokes Fluorescent Cooling Anti-Stokes fluorescence is the phenomena in which a substance that is excited by radiation at one wavelength fluoresces at a shorter wavelength. This results in more energy being radiated than is absorbed for each photon. Utilizing this process for cooling may, at first, appear to violate common sense: a multi-watt laser is focused into a mostly transparent material, and yet the material cools. A closer look at a specific cooling process reveals how it works. Consider a glass doped with a rare-earth ion that has spectrally broad ground and excited states (see Fig. 1 ( #fig1 ) ). Each energy state, or manifold, consists of several closely spaced levels that are in thermal equilibrium among each other. (Since we will be discussing glasses the energy levels are actually inhomogeneously broadened bands, but for simplicity we will refer to them INTRANET Development of a Fluorescent Cryocooler :: User Sites :: USNA http://usna.edu/Users/physics/mungan/Publications/Pub-AIAA.php 1 of 8 5/9/14 11:44 AM