Elucidating the surface damage behavior of sol-gel silica anti-reflective films during low-pressure plasma cleaning

Plasma has been widely used in the in situ removal of organic contaminants on the surface of large aperture optical components by physical bombardment and chemical reaction. Since the plasma is usually generated by ionizing gas through the electric field, the charged reactive species are accelerated to bombard the surface when passing through the surface sheath. After the organic contaminants on the surface of the optical components are completely removed, the surface film of the optical components may be eroded by long-time plasma irradiation. Therefore, the surface damage characteristics induced by plasma cleaning on optical components were studied to apply the technology of plasma in situ cleaning in the inertial confinement fusion facilities. Firstly, the effect of the amount of organic contaminants on the performance of optical components was investigated. Then, the influence of plasma cleaning time on the transmittance and wavelength peak of fused quartz optical components coated with sol-gel anti-reflection film was analyzed. The plasma cleaning experiments illustrated that the film thickness had a damage accumulation effect after the long plasma irradiation, and the surface pores gradually increased. The surface damage mechanism of plasma action was discussed. Finally, the research on the surface damage mechanism of sol-gel anti-reflective film during plasma cleaning lays a foundation for the realization of nondestructive in situ cleaning of optical components.