Reactive ion beam etching-based planarization of optical aluminium surfaces

The surface error topography of optical aluminium surfaces after common manufacturing by single-point diamond turning meets the requirements for applications in the infrared spectral range. However, for short-wavelength applications in the (E)UV spectral range the requirements in the optical surface quality increase immensely. Reactive ion beam etching (RIBE) is a promising process route, which allows direct surface machining rather than the use of a NiP coating. Lowenergy ion beams driven by a reactive process control permit a roughness preservation up to 1 μm etching depth. The effect of RIBE machining on roughness features is evaluated suggesting a model scheme for smoothing of high-frequency features.