LAUSR

Abstract In this work Thermal Lens Spectroscopy (TLS) is used for sensitive characterization of absorption in optical materials with particular application for solid-state laser cooling (optical refrigeration). TLS is used to characterize key parameters involved in 4f-4f transition in Yb3+:YLF and 4f-5d transition in Ce3+:YAG systems. The results confirm the excellent laser cooling results found in previous works on Yb3+:YLF crystal. In addition, although no cooling effect was observed in Ce3+:YAG sample, the TLS showed that this material exhibits promising characteristics towards laser cooling applications, such as high external quantum efficiency (>92%), and low parasitic background absorption of (1.2 ± 0.2) × 10−4 cm−1 at 885 nm. The key mechanisms that appear to inhibit net cooling in Ce3+:YAG are attributed to the intrinsic excited state absorption and/or 4f-4f transitions between the two lowest levels of Ce3+. This investigation was turned possible due to the high sensitivity of TLS for very low absorptions.