Optical refrigeration of Tm3+ doped indium fluoride glass from room temperature

Abstract

Optical refrigeration has significant promise for vibration-free cryogenic cooling and radiation-balanced fiber lasers. In this paper, we report theoretical and experimental investigations of optical refrigeration in thulium (Tm3+) doped indium fluoride glass (Tm3+:InF3) from room temperature. Comprehensive spectroscopic studies of Tm3+:InF3 were conducted, and its cooling with 1875, 1900, and 1950 nm pump lasers at different power levels has been measured. Maximum cooling of 2.4 K was achieved with 4.4 W from a 1900 nm laser. The experimental results agree with our theoretical expectations. Our experiment has demonstrated that Tm3+:InF3 has better cooling efficiency than Tm3+ doped ZrF4-BaF2-LaF3-AlF3-NaF glass due to Tm3+:InF3's lower maximum phonon energy, which reduces non-radiative decay.