Characterization of the polishing-induced contamination of fused silica optics

Abstract : In this work, the polishing-induced contamination layer at the fused silica optics surface was studied with various interface analysis techniques: Secondary Ion Mass Spectroscopy (SIMS), Electron Probe Microanalysis (EPMA), X-Ray Photoelectron Spectroscopy (XPS), and Inductively Coupled Plasma—Optical Emission Spectroscopy (ICP-OES). Samples were prepared using an MRF polishing machine and cerium-based slurry. The cerium and iron penetration and concentration were measured in the surface out of defects. Cerium is embedded at the surface in a 60 nm layer and concentrated at 1200 ppmw in this layer while iron concentration falls down at 30 nm. Spatial distribution and homogeneity of the pollution were also studied in the scratches and bevel using SIMS and EPMA techniques. We saw evidence that surface defects, such as scratches, are specific places that hold the pollutants. This overconcentration is also observed in the chamfer. These new insights into the polishing-induced contamination of fused silica optics and it repartition have been obtained using various characterization methods. Advantages and disadvantages of each one are discussed.