Increased laser damage threshold by protecting and cleaning optics using first contact polymer stripcoatings: preliminary data

Abstract

Statistically based Laser Damage Testing (LDT) was performed on clean, polished silicon wafers before and after First Contact Polymer was applied and removed. Polymer removal results in surfaces that are nearly atomically clean as evidenced by XPS data and may be a starting basis for developing an LDT based surface cleanliness test. A LabView controlled nanosecond YAG based LDT system with motion control stages was built and used to demonstrate significant difference in surface laser damage threshold following cleaning of already "clean" surfaces. These initial results represent the beginning of a systematic study on a variety of surfaces to include glass, silicon, germanium, coatings and nonlinear optical crystals as well as diffraction gratings. Recent independent testing lab results demonstrate YAG laser damage thresholds after polymer removal, indistinguishable from that of new high power laser optics, on coated BK7 of 15J/cm² at 20ns and 20Hz. Our initial data indicate a significant increase, as much as 10% in LDT post cleaning.