Excitation of the thulium (1)G(4) level in glass

The (1)G(4)-level of Thulium seems to be an interesting candidate to realiz e a IR pumped blue upconversion fibre laser. Ytterbium is needed to sensiti ze the excited state absorption. Spectral properties of glass samples with various Thulium and Ytterbium concentration are investigated in the range o f 300 up to 2300 nm. Different wavelengths art: used to excite the (1)G(4) level. Peak absorption is found to be at 788 nm with maximum fluorescence a t 472 nm. A lifetime of 165 mus of the (1)G(4) level is measured. The input output characteristics are linear.