Laser damage in triglycine sulfate: Experimental results and thermal analysis

An investigation of the effects of 10.6-μm laser radiation on triglycine-sulfate (TGS) crystals determined that the primary irreversible damage mechanisms in TGS pyroelectric detectors are cracking and thermal decomposition (charring). Irradiation thresholds for cracking and charring were determined for TGS crystals of typical detector dimensions as a function of laser power density and irradiation time. These energy density thresholds exhibit two distinct regions of behavior: For short irradiation times E0 is independent of τ while for long times E0 varies as τ1/2. The thresholds are given empirically by E0 (crack) = [0.65 + 22(τ)1/2] J/cm2 and E0(char) = [4.0 + 34 (τ)1/2] J/cm2. A theoretical model describing thermally induced damage in irradiated crystals is presented. The energy density damage thresholds obtained from this model are compared to the experimental results. These results on material damage are used to predict damage thresholds in operating TGS detectors. These predictions are in good agreement with experimentally determined detector thresholds.