Damage thresholds of fused silica, plastics and KDP crystals measured with 0.6-ns 355-nm pulses

Three hundred fifty-five-nm and 0.6-ns pulses were focused to a beam diameter of approximately 1 mm to measure the laser damage thresholds for surfaces of bare polished samples of several types of fused silica, for the bulk of crystals of potassium dihydrogen phosphate (KDP), and for a few plastics. Surface damage thresholds for fused silica ranged from 1 to 14 J/cm(2), and were least for surfaces with residual subsurface polishing fractures. Thresholds for inclusion damage in KDP crystals were 2 to 4 J/cm(2). Test volumes in these same crystals had thresholds from 1.5 to 7.0 J/cm(2) when they were laser hardened by repeated subthreshold irradiation. FEP teflon films had thresholds of 3 J/cm(2), which were the greatest threshold observed for a plastic.