T. C. Brunold, H. U. Güdel, S. Kück and G. Huber
Excited-state absorption and laser potential of Mn⁶⁺-doped BaSO₄ crystals
J. Opt. Soc. Am. B 14, 2373-2377 (1997)                 

Abstract: Room-temperature E||b and Eb polarized excited-state absorption (ESA) measurements on Mn⁶⁺ -doped crystals of BaSO₄ in the 530 - 1800-nm spectral region are reported. ESA transitions from the metastable ²T₂ ligand-field state to the lowest-energy ligand-to-metal charge transfer states involve two-electron excitations and thus carry low intensity. A strong ESA band owing to the first one-electron ligand-to-metal charge transfer transition peaks near 600 nm. Between 700 and 900 nm, ground-state absorption is stronger than ESA, and near-infrared pumping by laser diodes is thus possible. The stimulated-emission cross section is larger than the ESA cross section over the whole range of spontaneous emission. Our results indicate that tunable laser action between 920 nm and 1.6 mm should, in principle, be achievable. The effective peak stimulated-emission cross section at 1100 nm is 3 × 10^–19 cm² .