Ion beam figuring of precision aspheric optical surfaces

An ion beam figuring facility is fully operational at the Centre Spatial de Liège since 1997. Ion beam figuring principle is briefly reminded and the present capabilities of the technique are described. An extensive characterisation programme is running in order to determine the optimised parameters for numerous materials and operating conditions. In this frame, tests have been performed on various optics to demonstrate the capability of the technique to figure aspheric shapes on glass or metallic substrates.
At first, an aspherisation on a spherical gold-coated aluminium mirror plated in between with Nickel is presented. After removal of the gold coating with the ion beam, micro-roughness and etching rate measurements have been performed on the substrate material. Finally, the mirror has been figured from the original sphere to a parabola. The surface characteristics evolution is described in terms of micro-roughness and surface error. Other examples of complex aspherical figuring (polynomials of high order, ...) are shown.
In conclusion, the potential impact and the results of this technique on optics fabrication, especially for exotic shapes, are exposed. The integration of the ion beam figuring process in a classical optics manufacturing sequence will be discussed, identifying the potential time and money savings.