Role of upconversion in optical refrigeration: A theoretical study of laser cooling with Ho3+ doped fluoride crystals

We present a generalized model for optical refrigeration with Ho3+ doped fluoride crystals in which the dopant concentration dependent upconversion is considered. Based on the spectrum properties of candidate rare-earth ions (Ho3+, Tm3+, and Er3+) for optical refrigeration, a common criterion for upconversion assisted cooling is derived. The cooling performances of Ho3+:YLiF4 crystals are simulated to reveal the practical dopant concentration range for cooling. It is found that the optimal dopant concentration is determined by a balancing consideration of heat loads induced by background absorption and fluorescence quenching. The appropriate pump wavelengths for optical refrigeration with Ho3+:YLiF4 crystals are also indicated. (C) 2013 Optical Society of America