Relevance of Carbon Dioxide Laser to Remove Scratches on Large Fused Silica Polished Optics

Scratches at the surface of fused silica optics can be detrimental for the performance of optical systems. A carbon dioxide (CO₂) laser is an interesting tool to remove those scratches because it can melt efficiently the silica in a rapid and localized way, without generating debris. In this article, we propose a new process for optical fabrication, which uses a CO₂ laser to remove scratches between polishing and finishing steps. This is a linear process with no iterative polishing operations for scratch removal. This process is applied on an optic representative of laser megajoule facility production. Indeed, we succeed in removing a 10 μm deep scratch and we demonstrate that this laser operation increases the laser damage threshold by a factor of three in fluence.