Abrasion Resistant Anti-Reflective Sol-Gel Coatings

Anti-reflective sol-gel coatings are deposited on many of the optical surfaces in both the OMEGA and OMEGA EP laser systems. These coatings are responsible for yielding the maximum transmission of UV light as it passes from air into the glass optics. One issue with these coatings resides in their lack of abrasion resistance. An unmodified sol-gel coating will be scratched if subjected to a very small mass dragged across its surface ( ~ 6 g), making it necessary to handle optics containing these coatings with extreme caution during installation and alignment. In an effort to increase the abrasion resistance of sol-gel coatings, organosilane modified sol-gel particles have been crosslinked with dithiols. This process increases abrasion resistance because the dithiol crosslinkers bond sol-gel particles to each other and to the coated substrate, resulting in a robust sol-gel network that can withstand greater abrasive forces. The most promising results have been demonstrated using a 15 mol % solution of the organosilane modifier 3-methacryloxypropyltriethoxysilane (MOTOS) in combination with the crosslinker pentanedithiol. A substrate coated with this solution demonstrated little to no damage after a mass of 36 g was dragged across its surface (simulating abrasive forces that the coating may endure during handling) while maintaining 96 % transmission. A reduction in transmission of the coating was observed with increasin