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Proceedings Paper

Metrology and surface figuring of the LMT secondary mirror
Author(s): David Castro Santos; Lizeth Cabrera Cuevas; Emilio Hernández Rios; Josefina Lázaro Hernández; Andrea Leon-Huerta; Maribel Lucero Alvarez; Carlos Tzile Torres; David M. Gale; David R. Smith
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Paper Abstract

The Large Millimeter Telescope Alfonso Serrano (LMT) is a 50-meter (currently 32m) diameter single-dish telescope optimized for astronomical observations at millimeter wavelengths in the range 0.85 mm < λ < 4 mm. During initial operation, the LMT makes use of the central 1.7 meters of a 2.5m hyperbolic secondary reflector constructed of cast and machined aluminum. Following the first light campaign in 2011, a program of iterative surface sanding was carried out to reduce the surface error of the central area to a level compatible with that presently achieved for the primary reflector. Metrology during the sanding process was conducted using a Leica laser tracker. A total of 22 sanding iterations were interspersed with tracker measurements at differing spatial resolutions, allowing the RMS surface error to be reduced from 63 to 35 microns. Maps for the final iterations were repeated for distinct scan patterns to check for systematic variance. Since the work was carried out in early 2013, repeat measurements of the dismounted secondary have confirmed the stability of this reflector.

In this paper we present details of the surface improvement program with emphasis on the metrology techniques used throughout the process. We discuss issues such as data sampling, measurement geometry, and mirror orientation. We also consider the steps taken to ensure tight control of the sanding task itself, since this process was carried out entirely by hand. Finally we present some comparative metrology results obtained using our laser tracker and photogrammetry equipment.


Paper Details

Date Published: 28 July 2014
PDF: 15 pages
Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91513R (28 July 2014); doi: 10.1117/12.2056857
Show Author Affiliations
David Castro Santos, Gran Telescopio Milimétrico, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
Lizeth Cabrera Cuevas, Gran Telescopio Milimétrico, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
Emilio Hernández Rios, Gran Telescopio Milimétrico, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
Josefina Lázaro Hernández, Gran Telescopio Milimétrico, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
Andrea Leon-Huerta, Gran Telescopio Milimétrico, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
Maribel Lucero Alvarez, Gran Telescopio Milimétrico, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
Carlos Tzile Torres, Gran Telescopio Milimétrico, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
David M. Gale, Gran Telescopio Milimétrico, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)
David R. Smith, MERLAB, P.C. (United States)


Published in SPIE Proceedings Vol. 9151:
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation
Ramón Navarro; Colin R. Cunningham; Allison A. Barto, Editor(s)

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