Two step pumped YLF:Tm blue upconversion laser

Several fluoride and oxide Tm and (Tm, Yb) doped crystals such as YLF, GLF, YAG, and YAlO3 were tested for pulsed lasing at the ID2 -+ 3 ~ 4 transition (453 nm blue) at room temperature under two step pumping by a Ti:sapphire and a dye laser. Laser operation was obtained for the fluoride crystals. The input-output curves exhibit a saturation effect of emission with respect to both pump lasers. This can be explained by a depletion of the 3 ~ 6 ground state of ~ m ~ + and the competition between the excited state absorption from the 3 ~ 4 intermediate level and the mechanisms depopulating this level. Introduction Blue laser radiation is of practical importance for many purposes, such as information processing or medical applications. Up-conversion or excited state absorption (ESA) pumping schemes are of interest in this respect because in principle powerful laser diodes in the red or infrared spectral region could be used as pump sources. Trivalent thulium presents interesting properties due to the existence of two strong blue emission transitions, -+ 3 ~ 4 and 1~~ -+ 3 ~ 6 . Recently blue laser emission of this ion was reported at cryogenic temperatures [I, 21, but there are only very few data on the emission characteristics at 300 K [2]. We investigated the possibilities to obtain blue laser emission at the transition ID2 + 3 ~ 4 tiom several fluoride( m i 4 , GdLiiq) or oxide(YAlO3, Y3Al5012) 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 ps) and a dye laser (650 nm, 40 ns). Under this excitation laser operation could be obtained in the fluoride crystals while the oxide crystals were destroyed before the laser threshold was reached. 650 nm DCM dye laser ' 0 2 ' 0.4 453 nm Tm laser