Advances in Raman-based broadband optical refrigeration

摘要

This work reports progress towards demonstrated Raman-based optical refrigeration. Previously [1] we introduced Ramanrefrigeration and its required photonic structures. Building on the previous, the mechanisms and photonic structures aredetailed and simplified proof-of-concept devices described. Three wavelength bands, two illuminated and one dark, areconsidered. The width of each of these bands is predicated upon the magnitude of the Raman shift of the active layer.Optimally, the first illuminated band is approximately one Raman shift (wavelength) in width. This illuminated band iscapped above (at shorter wavelengths) by a dark band. At longer wavelengths a second illuminated band again oneRaman shift in width is reflected by photonic structuring that forbids light propagation. The dark bands provide anexhaust through which up energy (anti-Stokes) shifted light can be emitted thereby carrying away heat. The Photonicstructure prohibits the propagation of a band of long wavelength light thereby both blocking Stoke’s shifted illuminatedband light and reflecting incident light having these wavelengths. The naturally occurring solar spectrum with its light anddark bands caused by atmospheric absorption is a good match to diamond-based Raman refrigeration. Diamond also hasextremely low absorption and large Raman cross-section especially in small grain form. Proof-of-concept devicesemploying simple one-dimensional photonic structures are the focus of present experimental effort. The prospect ofbroadband refrigeration remains a delicate balance requiring limited absorption and increased Raman cross sectionthrough phonon engineering of the Raman active layer.