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.
We demonstrate an instantaneous phase-shift, point diffraction interferometer that achieves high accuracy and is capable of measuring a single pulse of light at NA greater than 0.8.
A new method of optical, non-contact profiling of rough surfaces is described that utilizes interferometric techniques as well as digital signal processing algorithms to produce fast, accurate, repeatable 3-D surface profile measurements. When combined with more traditional phase-shifting measurement techniques, this produces an instrument capable of profiling surfaces with rms roughness, Rq, ranging from 1 angstrom to 20 micrometers , and measurement of steps up to 100 micrometers . Sample data are discussed and a comparison with other surface profiling techniques is presented.
Conference Committee Involvement (6)
Optical Manufacturing and Testing X
26 August 2013 | San Diego, California, United States
Optical Manufacturing and Testing IX
22 August 2011 | San Diego, California, United States
Optical Manufacturing and Testing VIII
4 August 2009 | San Diego, California, United States
Optical Manufacturing and Testing VII
28 August 2007 | San Diego, California, United States
Optical Manufacturing and Testing VI
31 July 2005 | San Diego, California, United States
Optical Manufacturing and Testing V
3 August 2003 | San Diego, California, United States
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.