Surface degradation effects on laser damage in KU1 quartz glass windows for LIDAR applications

For LIDAR applications in fusion devices, surface degradation effects (erosion and deposition of a thin contaminating layer) on laser damage in KU1 quartz glass material has been assessed. To study surface quality effects, roughly polished samples have been examined. For surface deposition effects, thin gold layers were deposited by sputtering on to KU1 quartz samples in order to study the influence of the layer thickness on the laser damage probability. For the thinnest layer of 5 nm a decrease in threshold to produce laser damage by several orders of magnitude is observed, implying a serious risk of breakdown for the laser window from the onset of reactor operation.