A 1-metre Ni coated CFRP demonstrator for large deformable mirrors

¹ Physics and Astronomy Department, University College London, Gower Street, London, WC1E 6BT, UK
² Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

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Abstract

We present results from our current project to develop an alternative substrate for large deformable mirrors, particularly with the European Extremely Large Telescope (E-ELT) in mind. Our mirror substrate consists of a carbon-fibre reinforced polymer (CFRP) core encapsulated in a thick (50µm) coating of nickel; the coating entirely covers the CFRP front, back and edges. The benefits of CFRP are: that it has high tensile strength, making it exceptionally resistant to breakage and able to withstand high inter-actuator forces; that it can be fabricated in large sections, allowing the production of a 2.6 m monolithic mirror, simplifying system control and eliminating additional diffraction/scattering introduced by segmented mirror systems; its low density (< 1800 kgm^-3 for a Ni coated substrate). By the end of summer this year (2009) we aim to have constructed a 19 cm diameter fully actuated (37 piezo-stack actuators on a 29 mm triangular grid) prototype and a 1.0 m diameter substrate mounted on a static set of points to demonstrate the scalability of the technology. We discuss the processes involved in forming a Ni-CFRP mirror, the results obtained so far and a current status update.