Removal of antireflection sol-gel SiO2 coating based on Ar ion beam etching

Abstract

• We proposed a stripping method of antireflection coating based on ion beam etching. • This dry approach is greener than wet method for no waste water produced, like tritiated water. • Coating is etched 6 times faster than substrate, so ignorable modification of the optics. • This method is effective and does not degrade optics performance. • This method has been adopted to process the recycling optics of Chinese ICF facility. We proposed a new stripping method of sol-gel SiO 2 coating widely used in inertial confinement fusion facilities based on Ar ion beam etching, during which the coating is removed in the form of gaseous and solid particle. This dry approach is more environment-friendly than the conventional wet cleaning process for saving the trouble of treating tons of polluted water, especially highly toxic tritiated water. In the IBE process, porous coating is sputtered away at a constant etching rate just like other homogeneous materials. IBE parameters are systematically optimized to obtain a selective and gentle etching. The weakly bonded coating is etched 6 times faster than the fused silica substrate, which ensures the selective sputtering of coating over the underlying fine optics. Experiments on different off-line samples as well as the actual recycled optics from high power laser system show that this method is very effective. Moreover, this stripping process does not degrade the optic’s performance. Surface shape and roughness barely change after stripping. The laser damage threshold increases slightly, probably due to the removal of re-deposition layer introduced during polishing process. This method has been successfully adopted to process the optics of ICF facility in China.