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Proceedings Paper

Deflectometry for optics evaluation: free form segments of polynomial mirror
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Paper Abstract

Deflectometry is a well-known method for astronomical mirror metrology. This paper describes the method we developed for the characterization of free-form concave mirrors. Our technique is based on the synergy between deflectometry and ray-tracing. The deflectometrical test is performed by illuminating the reflecting surface with a known light pattern in a Ronchi – like configuration and retrieving the slope errors by the observed rays deflection. The ray-tracing code allows us to measure the slopes and to evaluate the mirror optical performance. This technique has two main advantages: it is fast and it is applicable on-site, as an intermediate step in the manufacturing process, preventing that out-of-specification mirrors may proceed towards further production steps. Thus, we obtain a considerable time and cost reduction.

As an example, we describe the results obtained measuring the primary mirror segments of the Cherenkov prototypal telescope manufactured by the Italian National Institute for Astrophysics in the context of the ASTRI Project. This specific case is challenging because the segmentation of the polynomial primary mirror lead to individual mirrors with deviations from the spherical optical design up to a few millimeters.

Paper Details

Date Published: 28 July 2014
PDF: 13 pages
Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91510T (28 July 2014); doi: 10.1117/12.2056108
Show Author Affiliations
Giorgia Sironi, INAF - Osservatorio Astronomico di Brera (Italy)
Rodolfo Canestrari, INAF - Osservatorio Astronomico di Brera (Italy)
Giovanni Pareschi, INAF - Osservatorio Astronomico di Brera (Italy)
Carlo Pelliciari, INAF - Osservatorio Astronomico di Brera (Italy)

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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