Figuring sequences on a super-smooth sample

An ion beam figuring facility is operational at the Centre Spatial de Liège since 1997. Its present capabilities are described. An extensive characterisation programme is running in order to determine the optimised parameters for various materials and operating conditions. In this frame, tests have been performed on a spherical gold-coated aluminium mirror plated in between with nickel. The nickel plating was used to be super-polished to a BRDF of 1 10-4 at 1 deg at 10 µm wavelength. Micro-roughness and etching rate measurements were realised and influence of ion bombardment on the coating has been established after removal of the gold coating. The gold coating removing was performed by using the ion beam flux.
Finally, the mirror has been figured from the original sphere to a parabola. Surface characteristics evolution is also described in terms of micro-roughness and surface error.
An overview of the research and development programmes related to this facility is given. Results of this technique and potential impact on optics fabrication are then briefly exposed.