Reactive ion beam etching – based finishing of optical aluminium surfaces

Abstract

Reactively driven low-energy ion beam machining is a widely used finishing technique for optical aluminium surfaces. Direct RIBE machining with oxygen or nitrogen process gas permits figure error correction of diversely shaped aluminium optics while preserving the initial roughness up to 1 µm etching depth. Those optical surfaces are appropriate for applications in the infrared spectral range. For increasing demands on optical surfaces for short - wavelength applications in the visible and ultraviolet spectral range ion beam polishing techniques with the aid of a sacrificial layer are a promising process route. Turning marks situated in the high-to –mid spatial frequency range are remarkably reduced while preserving the initial microroughness resulting in an enhancement of the full range roughness.