Damage Thresholds of Fused Silica, Plastics and KDP Crystals Measured with 0.6-ns 355-nm Pulses

We used 355-nm, 0.6-ns pulses 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 1–14 J/cm², and were least for surfaces with residual subsurface polishing fractures. Thresholds for inclusion damage in KDP crystals were 2–4 J/cm². Test volumes in these same crystals had thresholds from 2.5–7.0 J/cm² when they were laser hardened by repeated subthreshold irradiation. FEP teflon films had thresholds of 3 J/cm², which were the greatest threshold observed for a plastic.