Variations with Laser Pulse Duration of the Thresholds at 350-nm and 1064-nm for Bulk Damage in Crystals of KDP

Five separate laser facilities were used to measure 350-nm and 1064-nm thresholds for bulk damage in crystals of KDP. At 1064-nm, tests were made with single laser pulses having durations of 1, 9 and 25 ns and with 9-ns pulses incident at 10 Hz. At 350-nm test were made with single pulses having durations of 0.6, 5.0 and 25 ns and with 25-nm pulses incident at rates up to 50 Hz. Over the range from 0.6 to 25 ns, 350-nm thresholds increased by a factor of approximately 2, and 350-nm thresholds were almost independent of laser repetition rate. The 1064-nm thresholds increased by a factor > 3 as pulse duration increased from 1 to 25 ns. Laser hardening of thresholds was observed at both 350-nm and 1064-nm.