Improvement of the optical properties after surface error correction of aluminium mirror surfaces

• Published in: Journal of the European Optical Society. Rapid publications Vol. 17; no. 1; pp. 1 - 13
• Main Authors: Ulitschka, M., Bauer, J., Frost, F., Arnold, T.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 04.01.2021; EDP Sciences
• Subjects: Aluminium; Aluminum; Chemical composition; Chemical-mechanical polishing; Classical Electrodynamics; Diamond machining; Diamonds; Error correction; Error correction & detection; Ion beam etching; Ion beam smoothing; Ion beams; Mirrors; Nitrogen; Optical properties; Oxygen; Physics; Physics and Astronomy; Roughness; Smoothing; Surface properties; Surface stability; Turning (machining); Ultraviolet spectra; Ion beam etching; Oxygen; Aluminium; Ion beam smoothing; Mirrors; Nitrogen
• ISSN: 1990-2573; 1990-2573
• DOI: 10.1186/s41476-020-00143-6

Ion beam finishing techniques of aluminium mirrors have a high potential to meet the increasing demands on applications of high-performance mirror devices for visible and ultraviolet spectral range. Reactively driven ion beam machining using oxygen and nitrogen gases enables the direct figure error correction up to 1 μm machining depth while preserving the initial roughness. However, the periodic turning mark structures, which result from preliminary device shaping by single-point diamond turning, often limit the applicability of mirror surfaces in the short-periodic spectral range. Ion beam planarization with the aid of a sacrificial layer is a promising process route for surface smoothing, resulting in successfully reduction of the turning mark structures. A combination with direct surface smoothing to perform a subsequent improvement of the microroughness is presented with a special focus on roughness evolution, chemical composition, and optical surface properties. As a result, an ion beam based process route is suggested, which allows almost to recover the reflective properties and an increased long-term stability of smoothed aluminium surfaces.