Fe:ZnSe passive Q-switching of 2.8-μm Er:Cr:YSGG laser cavity

The use of Fe:ZnSe polycrystals as passive Q-switches for the Er:Cr:YSGG laser operating at 2.8&mgr;m is introduced. Fe:ZnSe samples with 1-7cm^-1 coefficients of absorption were prepared using thermal diffusion of iron in CVD grown polycrystalline ZnSe. A flashlamp pumped Er:Cr:YSGG laser with a variable (40 - 80% reflectivity) output coupler (OC) was used as a test bed for passive Q-switching. Using a 90% initial transmission Fe:ZnSe placed at the Brewster angle we obtained a single giant pulse lasing with a pulse duration of ~65 ns and a maximum output of 13 mJ under 30 J of flashlamp pump. Multi-pulse (19 pulses) output was obtained with 85 mJ total output energy at a pump energy of 30 J. The saturation curve of Fe:ZnSe was measured. Fitting this data with a theoretical model results in absorption crosssection of 0.56 × 10^-18 cm², which is close to the value of the absorption cross-section obtained from spectroscopic measurements (0.85 × 10-18 cm² at 2.8 &mgr;m).