Azzurra Volpi, a postdoctoral researcher with the University of New Mexico, and Markus Hehlen, a research scientist with Los Alamos National Laboratory and the New Mexico Consortium, recently published a paper in Optics Express titled: “Optical refrigeration: the role of parasitic absorption at cryogenic temperatures“. Co-authors on this paper include Junwei Meng, Aram Gragossian, Alexander R. Albrecht, Saeid Rostami, Alberto Di Lieto, Richard I. Epstein, Mauro Tonelli and Mansoor Sheik-Bahae.
In optical refrigeration, certain solids cool when they are excited by laser light and subsequently fluoresce. The cooling effect is achieved when the laser is tuned such that its energy is lower than the mean fluorescence energy. The respective small energy difference is extracted as heat from the solid and carried away as light, cooling the solid in the process.
Solid-state laser cooling requires the material to be of exquisite purity. Any impurity introduces “parasitic absorption” which causes laser-induced heating and offsets the cooling effect. This paper explores the change in the parasitic absorption as the material temperature decreases.
This work shows for the first time that the parasitic absorption depends on temperature and becomes less pronounced at lower temperatures. This has important implications for the laser cooling of solids to cryogenic temperatures.
This research was funded by the Air Force Office of Scientific Research.