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

Abstract

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.

Historical perspective on fifteen years of laser damage thresholds at LLNL

“…However, even in these early years, as noted above, we observed significant improvements in thresholds both by laser conditioning and thermal conditioning. 21,22,34 From 1988 to the present we have observed steadily rising thresholds. This was attributable primarily to improved crystal-growing techniques employing ultrafiltration to produce crystals w_th bulk materials virtually free of any visible defects 2 5 lain in size.…”

Final Optic Protection Designs for ICF Containment Chambers

“…Unfortu nately, the current damage threshold for 3d) HR coatings is typically only 10-15 J/cm 2 which is 2-3 times less than the re quired damage threshold of 225-30 J/cm 2 . 5 With a strong re search effort, damage thresholds of 25-30 (/cm 3 might be attain able. A possible method to avoid this threshold problem would be to use a blow away coating that would tamp the reflective surface, thus allowing the light to be reflected off its surface before it can damage more significantly.…”