Research on fabrication of mirror segments for E-ELT

Research output: Chapter in Book/Report/Conference proceedingConference contribution

8 Citations (Scopus)

Abstract

The next generation ground-based giant telescope, the European Extremely Large Telescope (E-ELT), under development by the European Southern Observation (ESO) 1, will have nearly 1000 hexagonal segments of 1.45m across the flats. Fast processing of these segments with high form and edge specifications has proven to be a challenge. The Zeeko Precessions sub-aperture bonnet polishing plays an important role providing capability for polishing the surface and correcting the form to meet this target 2,3. BoXTM grinding has been adopted. This technology has the advantage of fast generating of aspheric surface with very low subsurface damage (SSD) 4. This will avoid the need of removing thick layer of stock at polishing stage to remove SSD. However the result grinding signatures has proven to be problematic for direct polishing with Zeeko's standard bonnet technology. A novel 'grolishing' process which stands between 'grinding' and 'polishing' has been developed to deal with mid-spatial features left by BoXTM grinding. This tool is designed base on Zeeko's R80 bonnet which will fits directly into the company's IRP series machines. The process parameters have been optimised to have signatures less than 10 nm PV. The edge profile is 1μm upstand within 40 mm edge zone. The 'grolished' surface can be directly pre-polished together with all the form corrections. To meet the fabrication time target, R160 bonnet is used with 50 mm polishing spot, this will provide removal rate of 9.8 mm3/minute, which can be employed at pre-polishing stage and some form correction. Process parameters have been developed to leave slow upstand at edge zone without any form of sharp edge downturn. The following form correction stage, which employs smaller polishing spot of about 20 mm diameter, will continue to remove form errors of spatial frequency between 0.02 - 0.05 1/mm. Furthermore, the upstand edge will be, to a large part, removed at this stage. It is demonstrated that the form specs can be achieved after this process. The following smoothing process will improve surface textures and remove edge errors. Local edge rectification is normally necessary to bring the edge at same level. A final smoothing process will bring the bulk area and edge zone to meet all the specifications.

Original languageEnglish
Title of host publication6th International Symposium on Advanced Optical Manufacturing and Testing Technologies
Subtitle of host publicationAdvanced Optical Manufacturing Technologies
Volume8416
DOIs
Publication statusPublished - 1 Dec 2012
Externally publishedYes
Event6th International Symposium on Advanced Optical Manufacturing and Testing Technologies - Xiamen, China
Duration: 26 Apr 201229 Apr 2012
Conference number: 6
https://spie.org/OMT/conferencedetails/advanced-optical-manufacturing-technologies (Link to Conference Details )

Conference

Conference6th International Symposium on Advanced Optical Manufacturing and Testing Technologies
CountryChina
CityXiamen
Period26/04/1229/04/12
Internet address

Fingerprint

Extremely Large Telescopes
Polishing
Telescopes
Fabrication
Mirror
Mirrors
polishing
telescopes
mirrors
fabrication
Grinding
grinding
Subsurface Damage
Process Parameters
Smoothing
Signature
smoothing
Specification
specifications
Aspheric Surface

Cite this

Yu, G., Walker, D., & Li, H. (2012). Research on fabrication of mirror segments for E-ELT. In 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies (Vol. 8416). [841602] https://doi.org/10.1117/12.2009290
Yu, Guoyu ; Walker, David ; Li, Hongyu. / Research on fabrication of mirror segments for E-ELT. 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies. Vol. 8416 2012.
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Yu, G, Walker, D & Li, H 2012, Research on fabrication of mirror segments for E-ELT. in 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies. vol. 8416, 841602, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies, Xiamen, China, 26/04/12. https://doi.org/10.1117/12.2009290

Research on fabrication of mirror segments for E-ELT. / Yu, Guoyu; Walker, David; Li, Hongyu.

6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies. Vol. 8416 2012. 841602.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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Yu G, Walker D, Li H. Research on fabrication of mirror segments for E-ELT. In 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies. Vol. 8416. 2012. 841602 https://doi.org/10.1117/12.2009290