Optical refrigerator using reflectivity tuned dielectric mirrors

Abstract

Optical refrigerator using reflectivity-tuned dielectric mirrors. Selected working materials can be optically pumped using monochromatic radiation such that the resulting fluorescence has an average photon energy higher than that of the pumping radiation; that is, net anti-Stokes fluorescence. If the quantum efficiency is sufficiently high, the working material will cool and optical refrigeration can be achieved. Parallel mirrored faces are employed to increase the optical path of the incident pumping radiation within the working material by multiple reflections. Reflectivity-tuned dielectric mirrors which allow higher-energy fluorescence photons to readily escape from the working material while inhibiting the escape of the lower-energy photons which are consequently partially trapped in the working material and ultimately reabsorbed and refluoresced at higher energies are employed. This increases the optical refrigerator efficiency. An efficient geometry for the cooling material is a disk having a large diameter and a small height, since the fluorescence can predominantly escape through the tuned mirror on one end face of the working material. An alternative cooling element could be approximately cubic with tuned mirrors on the sides as well as on one end. In another embodiment of the invention, photocells are used to convert escaping fluorescence energy into electricity, thereby reducing the power requirements of the optical refrigerator and reducing the amount of waste that must be removed from the vicinity of the working material.