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.

Date Published: 23 July 2008
PDF: 12 pages
Proc. SPIE 7018, Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 70183S (23 July 2008); doi: 10.1117/12.789332

Published in SPIE Proceedings Vol. 7018:
Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation
Eli Atad-Ettedgui; Dietrich Lemke, Editor(s)