Solid state optical crycoolers: Developments and prospective

摘要

Optical refrigeration (solid-state laser cooling) is based on the principle of anti-Stokes fluorescence where incident light from a coherent (low entropy) source such as laser is upconverted into high entropy fluorescence via absorption or removal of vibrational energy (phonons) [1]. This phenomenon has been termed “a laser running in reverse” as it mimics the reverse operation of a solid-state laser. Since its first experimental observation in 1995 [2], optical refrigeration in a variety of rare-earth doped glasses and crystals has been demonstrated [3]. A major milestone was achieved in 2010 by cooling a 5% Yb:YLF crystal to an absolute temperature of 155K from room temperature [4]. This represented the first demonstration of an all-solid-state cryocooler, whereby achieving lower temperatures than that of standard multi-stage Peltier coolers. Exploiting the E4-E5 electronic resonance in the Yb