Share Email Print
cover

Proceedings Paper • new

Interferometric characterization of Keck segment edge errors
Format Member Price Non-Member Price
PDF $14.40 $18.00
cover GOOD NEWS! Your organization subscribes to the SPIE Digital Library. You may be able to download this paper for free. Check Access

Paper Abstract

The Keck telescope segments were manufactured by stressed mirror polishing of large circular pieces of Zerodur that were then cut into hexagons and finished by Ion Beam Figuring (IBF). It has long been believed that this process results in segments with little or no edge effects. As a result, this same general approach is planned for segment manufacturing for the Thirty Meter Telescope (TMT) and the European Extremely Large Telescope (E-ELT). However, recent measurements at the Keck telescope suggest that at least some of the Keck segments have significant aberrations within 60 mm of the edge. These aberrations impact the telescope phasing and the overall telescope image quality. We present interferometric measurements of multiple Keck segments, characterizing the surface errors near the edges over spatial periods from ~5 cm down to ~1 mm. We show that the largest phasing and image quality effects are due to plateaus of unremoved material, left behind after IBF as a result of obscuration by the IBF supports. Apart from these plateaus, the edge quality is relatively good, though not as good as in the segment interiors. Some residual phasing and image quality effects remain, and these are not currently understood.

Paper Details

Date Published: 6 July 2018
PDF: 13 pages
Proc. SPIE 10700, Ground-based and Airborne Telescopes VII, 107000M (6 July 2018); doi: 10.1117/12.2314568
Show Author Affiliations
Mitchell Troy, Jet Propulsion Lab. (United States)
Gary Chanan, Univ. of California, Irvine (United States)
Mark Colavita, Jet Propulsion Lab. (United States)
Stephen J. Martinek, 4D Technology Corp. (United States)


Published in SPIE Proceedings Vol. 10700:
Ground-based and Airborne Telescopes VII
Heather K. Marshall; Jason Spyromilio; Roberto Gilmozzi, Editor(s)

© SPIE. Terms of Use
Back to Top