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 POLARIS facility

This facility offers polishing machines for mirrors manufacturing up to 2.5m in diameter.

A well-adapted approach for the manufacturing process of strongly-aspherical optics with large dimensions is to combine two state-of-the-art methods for which the LAM and Thales SESO company have acquired important and internationally-acclaimed know-how: active optics and robotic polishing . Following this statement, the LAM and Thales SESO made the decision to develop a new technology facility named POLARIS (POLishing Active and Robotic Integrated System).

Johan FLORIOT: +33 (0) 491 055 935
Marc FERRARI: +33 (0) 495 044 191

With this technology facility, the LOOM team and SESO, its industrial partner, have the possibility to share their know-how concerning aspherical optics. The aim is both to build a unique technology facility and to validate our conceptual approach.
One crucial point for the future Extremely Large Telescopes (ELTs) concerns the possibility to manufacture large and strongly-aspherical mirrors or off-axis aspherical segments with an easier and faster method than existing ones. The same challenge exists for the manufacturing of large spatial optics for Earth observation, or for high-energy physics projects.
Nowadays, aspherical surfaces tend to be more and more distorted. For that, the polishing technologies implemented on POLARIS will allow a significant gain in production time, and consequently a cost reduction, by shortening the duration of the lapping and aspherical polishing steps.
The current manufacturing process of a strongly-aspherical surface follows 3 steps :
a) surface lapping : a form closed from the desired aspherical one is obtained ; the larger the sample, more difficult to obtain is the aspherical form. The limitations rely on the accuracy of the large machining machines used for mechanical manufacturing, i.e. a few tens of µm,
b) surface polishing : low-frequency defects are corrected first with the robotic tool, achieving a few-µm disparity from the desired aspherical form,
c) surface finishing with the robotic tool when specifications in the 10nm-rms range are required. An iterative approach (with intermediate measurements) is necessary to reach such performances.
The POLARIS facility can perform step a) and step b) with the LAM-patented active optics method. In this case, after active deformation of the mirror, the surface to be lapped and polished (steps a and b) results in a sphere. Thus, the main difficulty due to the aspherical form of the surface is replaced by the (relative) simplicity of polishing a spherical surface.
This adaptation/simplification constitutes the significative gain in production time for the manufacturing of the aspherical surface. Moreover, this “spherical” polishing process has a better convergence than existing ones, resulting in the decreasing of the number of intermediate measurements required. Step c) is necessary to finish the part.

This facility, co-financed by the INSU, Thales SESO, the Région PACA, and Europe (Feder funds) in the framework of the new facilities of the laboratory, has been labeled in 2006 by the cluster « OPTITEC : Systèmes complexes d’optique et d’imagerie » .
The facility is currently at the end of its mechanical and electronic integration at the LAM premises, at the “Technopôle de Château-Gombert”.
The implementation of this tool for the manufacturing of large and strongly-aspherical optics will be a key asset for our partners in the context of future large-optics projects at the 2015-2020 horizon.

© LAM - Laboratoire d’Astrophysique de Marseille

Pôle de l’Étoile Site de Château-Gombert
38, rue Frédéric Joliot-Curie 13388 Marseille cedex 13 FRANCE

Phone : +33 4 91 05 59 00
Fax : +33 4 91 62 11 90