Development and Performance Evolution of Medium-Pressure He/SF6/O2-Based Plasma and Wet Chemical Etching Process for Surface Modification of Fused Silica

• Published in: Plasma chemistry and plasma processing 2024-03, Vol.44 (2), p.1083-1104
• Main Authors: Yadav, Hari Narayan Singh, Das, Manas
• Format: Article
• Language: English
• Subjects: Astronomical instruments; Characterization and Evaluation of Materials; Chemical etching; Chemistry; Chemistry and Materials Science; Classical Mechanics; Contact pressure; Fused silica; Inorganic Chemistry; Mechanical Engineering; Optical components; Original Paper; Plasma etching; Raman spectroscopy; Substrates; Surface roughness
• ISSN: 0272-4324; 1572-8986
• DOI: 10.1007/s11090-024-10447-x

The rising demand for precision optics widely employed in ground and space-based astronomical instruments and other scientific instrumentation requires highly efficient advanced fabrication methods. Due to complex-shaped fused silica substrate surfaces like freeform or aspheres with strong curvatures or very small-sized components, a novel non-contact medium-pressure plasma-based method is developed to finish optical components. The present study critically compares the polished optical surfaces of a prism with a medium-pressure plasma process and wet chemical etching to provide insight into their smoothing. The results show that surface roughness ( R a ) increases from 0.54 to 2.61 nm and 0.53 to 0.57 nm at 5 and 20 mbar total pressures, respectively, using a plasma process without surface contamination. However, wet chemical etching increases surface roughness ( R a ) from 0.52 to 15.9 nm. The substrates' surface morphology, elemental composition, and surface topography are analyzed using FESEM, EDX, and AFM. Moreover, subsurface improvements are analyzed using Raman spectroscopy analysis.