Room-temperature continuous-wave upconversion-pumped laser emission in Ho, Yb : KYF4 at 756, 1070, and 1390 nm

We report room-temperature continuous-wave laser operation in Ho(0.5%), Yb(5%):KYF4 on the S-5(2) -- \u3e I-5(7) transition at 756 nm, on the S-5(2) -- \u3e I-5(6) transition around 1070 nm, and on the S-5(2) -- \u3e I-5(5) transition at 1390 nm. Room-temperature absorption and fluorescence spectra are presented. An upconversion pumping mechanism was employed to populate the upper laser level S-5(2) of holmium. In first experiments a Ti:sapphire laser was used as pump source. Laser operation around 1070 nm and at 1390 nm was also obtained by laser diode excitation. The maximum achieved laser output power under laser diode pumping was 5 mW at 1070 nm and 1 mW at 1390 nm