Twenty Years of Laser Cooling of Solids

Abstract

Laser induced cooling of solids or optical refrigeration is an area of optical science investigating interaction of light with condensed matter. This addresses a very important practical issue: design and construction all optical solid-state cryocoolers, which are compact devices, free from mechanical vibrations, moving parts, or fluids. They are based on reliable diode pump technology and in the most part free from electromagnetic interference in the cooled area. The optical cryocooler has a broad range of applications such as in the development of biomedical sensing, magnetometers for geophysical sensors and other sensors, satellite instrumentations where compactness and the lack of vibration are key parameters. The operation of these devices is based on anti-Stokes fluorescence also known as luminescence upconversion, in which light quanta in the red tail of the absorption spectrum are absorbed in a material from a pump laser and by adding thermal energy, blue-shifted photons are spontaneously emitted. Laser cooling of solids can be realized in rare-earth doped low phonon energy glasses and crystals as well as in direct band gap semiconductors. Both of these areas are very interesting and important and are discussed in this article.