Abstract
Laser cooling of solids has many potential applications in communications, surveillance and medical science, etc. This paper reviews our recent work on laser refrigeration of solids in stoichiometric hexa-chloroelpasolite crystals with high concentrations of erbium. Our results are one to two orders of magnitude improvements over any previously reported cooling in erbium based materials. We have seen bulk crystal cooling by as low as 6 degrees Celsius below room temperature in elpasolite crystals. The high efficiency and low temperatures of cooling have been attributed to a high concentration of erbium, as high as 80% by formula, in the crystal. This cooling has been achieved by pumping near the IR transition at 870 nm which is the weakest transition of erbium. We report cooling in the 1.5 micron transition as well, using a diode laser to pump this transition. The result is cooling by only a fraction of a degree from room temperature.
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