Passive Q-switching of the Tm-silica fibre laser near 2 μm by a Cr2+:ZnSe saturable absorber crystal

Q-switching of a single-clad Tm-silica fibre laser operating at 1.9 μm is demonstrated using a Cr2+:ZnSe saturable absorber crystal. The Q-switching was accompanied by self-mode-locking. A Q-switched pulse duration of 330 ns and peak power of 15 W has been measured for a 1.8 m length fibre when pumped with 3.6 W launched power at 1.3 μm. The Q-switching process has been optimized for variation of the output coupler reflectively, pump power and fibre length, and the best performance found for a cavity with 4% output coupler and fibre length equal to the optimum length for CW operation laser of near 3.2 m.