Laser operation of a bulk Tm3+: Germanate glass laser around 2 µm with 50 % internal slope efficiency

In this report we have presented a spectroscopic and CW laser characterization of an efficient thulium doped GPNG bulk germanate glass pumped at 792 nm by Ti: Sapphire radiation. Laser characterization gave a maximum slope efficiency of 50 % comparable to the crystalline counterparts and we believe, to the best of our knowledge, this being the best for Tm-doped bulk glass lasers. The maximum output power was of 190 mW with a 4 % OC for -500 mW of absorbed power. In this report we can confirm that Germanate glass proved a good host for 2 mum Tnr+ lasers as suggested by G. Turri et al.[9]. Given that Germanate materials possess nonlinear refractive indexes around ~ 40 x 10"16 cm2/W [10] (approximately one order of magnitude higher that the ~ 3 x 10"16 cm2/W of the Ti:Sapphire[ll]) yielding pronounced Kerr lens susceptibilities, when combined with their broad tunability further suggests that they have good potential for ultrashort pulse operation.