Optical Refrigeration Proves Really Cool

Richard I. Epstein, B. C. Edwards, Mansoor Sheik‐Bahae

Optical refrigerators using semiconductor material as a cooling medium, with layers of material in close proximity to the cooling medium that carries away heat from the cooling material and preventing radiation trapping. In addition to the use of semiconducting material, the invention can be used with ytterbium-doped glass optical refrigerators.

A. Rayner, N. R. Heckenberg, Halina H. Rubinsztein-Dunlop

Guang-Zong Dong, Kaishun Zou, Juncheng Liu

A theoretical cooling scheme based on pulsed excitation is presented to facilitate efficient optical refrigeration at cryogenic temperatures. The mechanism of optical refrigeration with pulsed excitation is described by a simplified cooling model founded on a density matrix. Simulated results show that for the Yb3+:YLiF4 crystal with doping concentration of 10% and background absorption of 10−4 cm−1, optical refrigeration via picosecond pulsed excitation is competitive at a temperature of lower than 100 K due to its high cooling efficiency and may advance the cooling temperature to the boiling point of nitrogen.

Manuel Vogel

Denis V. Seletskiy, Richard I. Epstein, Mansoor Sheik‐Bahae

This review discusses the progress and ongoing efforts in optical refrigeration. Optical refrigeration is a process in which phonons are removed from a solid by anti-Stokes fluorescence. The review first summarizes the history of optical refrigeration, noting the success in cooling rare-earth-doped solids to cryogenic temperatures. It then examines in detail a four-level model of rare-earth-based optical refrigeration. This model elucidates the essential roles that the various material parameters, such as the spacing of the energy levels and the radiative quantum efficiency, play in the process of optical refrigeration. The review then describes the experimental techniques for cryogenic optical refrigeration of rare-earth-doped solids employing non-resonant and resonant optical cavities. It then examines the work on laser cooling of semiconductors, emphasizing the differences between optical refrigeration of semiconductors and rare-earth-doped solids and the new challenges and advantages of semiconductors. It then describes the significant experimental results including the observed optical refrigeration of CdS nanostructures. The review concludes by discussing the engineering challenges to the development of practical optical refrigerators, and the potential advantages and uses of these refrigerators.

G. L. Mills