New interferometric technique for piston measurement in segmented mirrors

New interferometric technique for piston measurement in segmented mirrors full article
Agustí Pintó¹, Ferran Laguarta¹, Roger Artigas², Cristina Cadevall^2
1Sensofar Medical, S.L. (Spain)
²Universitat Politècnica de Catalunya (UPC) Rambla Sant Nebridi, 10, E-08222 Terrassa, Spain.
Published 4 November 2002 • Published under licence by IOP Publishing Ltd
Journal of Optics A: Pure and Applied Optics, Volume 4, Number 6
Citation A Pintó et al 2002 J. Opt. A: Pure Appl. Opt. 4 S369

Abstract

Present trends in the design of ground-based telescopes point towards the use of segmented primary mirrors. A major problem in this type of mirror is the achievement of proper segment positioning, as they have to be aligned with an accuracy of the order of a fraction of a wavelength for near-diffraction-limit telescope performance in the infrared. In this paper we present a new interferometric technique applied to the measurement of segment vertical misalignment (piston error) in segmented mirrors. The instrument is based on a high-aperture Michelson interferometer using a broadband light spectrum. The main innovation introduced in this instrument is the use of a novel optical fibre illumination technique that allows the system to measure piston error during the daytime with an uncertainty of 5 nm in a 30 µm range. A detailed description of the light spectrum, expected interferograms and piston extraction algorithms is presented here.