Abrasion Resistant Anti-Reflective Sol-Gel Coatings

Many optics in both the OMEGA and OMEGA EP lasers are coated with anti-reflective (AR) silane sol-gel to maximize their transmittance. Although these coatings are highly resistant to both airborne contaminants and laser damage, they are susceptible to mechanical damage by abrasion, and thus require extra care during the handling, installation and alignment of sol-gel optics. Previous “hardened” sol-gel AR formulations achieved physical robustness through exposure to ammonia, but were highly susceptible to degradation by atmospheric contaminants. In this work, alternate cross-linking agents for improving both mechanical robustness and contamination resistance were studied. The effectiveness of acryloyl chloride and glyoxal as “hardening” agents was evaluated through both solution and vapor-phase exposure. A drag-wipe testing protocol was developed for these chemically modified sol-gel AR coatings to determine their abrasion resistance as a function of hardening agent and exposure time. Results showed that glyoxal modification of AR coatings is effective in improving abrasion resistance, while contamination resistance and laser damage resistance need to be explored further.