Investigation on process stability of laser beam figuring for single nanometer ablation on fused silica

The processing of optical components surfaces is usually performed by grinding and polishing and is characterized by an increasingly fine gradation of the ablative processing. The aim of this step is to adjust shape errors, low- and mid-spatial-frequency errors caused by the previous grinding and polishing steps. These corrective polishing processes are associated with extreme accuracy requirements and thus with high equipment, process costs and long process times. A new and cost-effective approach for correction polishing is the so-called Laser Beam Figuring (LBF). By controlling the pulse duration of a highly stable CO2 laser beam source and thus the pulse energy of each individual laser pulse, the ablation depth can be locally adjusted in a targeted manner. In this way, site-selective ablation is possible to reproducibly correct the surface of a fused silica sample or to structure it with an ablation depth of ≤ 5 nm.