Localized CO 2 -laser treatment for mitigation of 351-nm damage growth in fused silica

Abstract

A technique for inhibiting the growth of laser-induced surface damage on fused silica, initiated and propagated at the 351-nm laser wavelength, has been investigated. The technique exposes the damage sites to single pulses of a CO<SUB>2</SUB> laser operating at the 10.6 micrometers wavelength at or near beam focus. This method results in a very localized treatment of the laser damage site and modifies the site such that laser damage does not propagate further. A laser damage site initiated with a single pulse of 355-nm laser light at approximately 45 J cm<SUP>-2</SUP> and 7.5-ns pulse duration grows rapidly upon further illumination at 8 J cm<SUP>-2</SUP> with 100% probability. Treatment of these sites with single pulses of 10.6 micrometers laser light for one second at a power level of between 17 and 37 Watts with a beam diameter of 5 mm alters the damage site such that it does not grow with subsequent 351-nm laser illumination at 8 J cm<SUP>-2</SUP> 10-ns pulse duration for > 1000 shots. The technique has been found to be 100% effective at stopping the growth of the laser damage.