The application of freeform diamond machining techniques to the manufacture of precision optics for astronomical
instrumentation has opened up a wide range of exciting new design possibilities. Freeform surfaces, not limited by
symmetry considerations, and complex multi-faceted mirror arrays can be precisely machined. This capability has
removed many constraints from the design process and has enabled the fulfilment of radical instrument designs.
However, this flexibility poses a significant challenge for component characterisation. Accurate measurement of the
form accuracy of surfaces lacking symmetry is particularly difficult using standard interferometric techniques.
Furthermore, the accurate 3 dimensional characterisation of complex multi-faceted components presents an added
challenge. The authors describe techniques that have been applied to the measurement of complex surfaces in Integral
Field Units (IFUs). In particular, we present novel approaches for the measurement of the form of complex non-radially
symmetric surfaces to an accuracy of a few nanometres. These measurements use a Twyman-Green Interferometer
configured in a variety of non-standard arrangements. In addition, the authors consider the difficulties in the
measurement of multifaceted surfaces, and the accurate determination of the geometric relations between these surfaces.
The authors discuss the use of confocal gauge techniques in the characterisation of these surfaces.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.