1.87 μm laser operation by 980 nm pumping in Yb,Tm:CaF2

We report the first laser operation of an Yb:Tm:CaF2 crystal around 1.9 μm after pumping at 980 nm. A maximum power of 140 mW was obtained corresponding to a slope efficiency of 14.5% with respect to the incident pump power. The spectroscopic study of this laser medium allows the optimization of the Yb/Tm concentration ratio to achieve laser operation and tune the energy transfers efficiency between Yb and Tm ions.