Abstract

Trivalent thulium presents interesting properties for visible upconversion-lasers due to the existence of two strong blue emission transitions, ¹D₂ → ³F₄ and ¹G₄ → ³H₆. Recently blue laser emission of this ion was reported at room tempera tures.^1,2,3 We investigated the possibilities to obtain bluelaser emission at the transition ¹D₂ → ³F₄ from several fluoride- (YLiF₄, GdLiF₄) or oxide- (YA1O₃, Y₃A1₅O₁₂) crystals doped with Tm or double-doped with Tm and Yb, by two-step pumping using a pulsed Ti:sapphire laser (tuned to 780 nm, pulse duration 60 μs) and a dye laser (650 nm, 40 ns) (Fig. 1). Under this excitation, laser operation was obtained in the fluoride crystals while the oxide crystals were destroyed before the laser threshold was reached. The best results were obtained for Tm(1%), Yb(10%): YLF; the maximum output power at 300 K was 2.5 μJ; the crystal absorbed 1.5 mJ at 780 nm and 370 μJ at 650 nm.

© 1994 IEEE