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

Abstract 167

Submitted by Samantha THOMPSON


S. J. Thompson(1), A. P. Doel(1), D. Brooks(1), M. Strangwood(2)


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


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 ( 50 microns) 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 as large sections, allowing the production of a 2.5m 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 19cm diameter fully actuated (37 piezo-stack actuators on a 30mm triangular grid) prototype and a 1.0m diameter substrate mounted on a similarly spaced, static set of points to demonstrate the scalability of the technology. We discuss the processes involved in forming a Ni-CFRP mirror and the results obtained so far, including materials analysis, optical form and surface quality, system simulations and comparisons with the laboratory constructed prototypes.