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Proceedings Paper

Non-contact profilometry of E-ELT segments at OpTIC Glyndwr
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Paper Abstract

Following a 'Call for Tenders' by the European Southern Observatory (ESO) a collaboration headed by OpTIC Glyndwr Ltd is producing seven prototype segments for the European Extremely Large Telescope (E-ELT). Each hexagonal segment is 1.4 m corner-to-corner with a base radius of curvature (ROC) of 84 m and the combination of 984 segments will lead to a primary mirror with a diameter of 42 m. The polishing of the prototype segments occurs in-house at OpTIC Glyndwr using a Zeeko polishing machine, while in situ interferometry is undertaken using a specifically designed optical test tower built above the polishing machine. To confirm the base radius of curvature of the prototype segments an on-machine non-contact profiler is used. The profiler attaches to the bridge of the polishing machine and is removed during polishing. The design of the profiler is based upon a nanometre optical component measuring machine (NOM) system, originating from the sychrotron optics community. This instrument determines the height at a series of points across the surface through the integration of measured slope data. This paper presents the operation of the OpTIC-NOM as both an on-machine and off-machine profiler. The accuracy of the profiler both on- and off-machine and its accuracy is compared against similar profilers through its participation in a round robin study. Radius of curvature results are presented for the master spherical segment (MSS), which is a reference optic for the E-ELT segments and highlights a standard deviation on the mean radius of curvature of 2.5 mm. Finally, a summary of future work is presented regarding the polishing of the prototype segments and the development of a stitching algorithm to produce 3D surface maps from profilometry data.

Paper Details

Date Published: 27 September 2011
PDF: 10 pages
Proc. SPIE 8126, Optical Manufacturing and Testing IX, 81260M (27 September 2011); doi: 10.1117/12.893690
Show Author Affiliations
Carolyn Atkins, Univ. College London (United Kingdom)
OpTIC Glyndwr Ltd. (United Kingdom)
John Mitchell, Cranfield Univ. (United Kingdom)
OpTIC Glyndwr Ltd. (United Kingdom)
Paul Rees, OpTIC Glyndwr Ltd. (United Kingdom)

Published in SPIE Proceedings Vol. 8126:
Optical Manufacturing and Testing IX
James H. Burge; Oliver W. Fähnle; Ray Williamson, Editor(s)

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