A nickel-carbon-fibre composite for large adaptive mirrors: fabrication methods and properties

We present results from our recent research into carbon-fibre composite (CFC) mirror fabrication for optical and infra-red applications. In particular this research is aimed towards the next generation of extremely large telescopes to offer an alternative to thin glass shell adaptive secondary mirrors. We address the issues involved with CFC mirror production, in particular the accuracy of the form replication process, a suitable surface for polishing to optical quality, no fibre print-through, environmental stability (shape change due to thermal and moisture variations), material uniformity and lifetime. We have performed experiments into the effectiveness of cold electroplating thick nickel coatings to totally encapsulate the CFC base substrate; the manufacturing procedure and properties of the Ni-CFC mirror are described here.