Experiments on a laser cooled Cr3+:LiSrAlF6 using an allowed transition

Thermal lens spectroscopy has been performed with a single-mode Ti:sapphire laser in a fluoride doped with trivalent transition metal ions. In samples with background absorption as high as 10-3 cm-1 an experimental quantum efficiency of 100% was determined at room temperature and the cooling efficiency via anti-Stokes fluorescence on an electric dipole transition has been shown to reach threshold in the near infrared spectral range. Cooling efficiencies as high as 20% are predicted for these fluoride crystals with impurity absorption coefficients reduced to 10-4 cm-1.