SAGEM has developed a line of product specific to the large-sized parts. The means available make it possible today to coat substrates of dimensions going until 1m50. Current developments address coating of substrate up to 2m20. A specific focus has been held on the wavefront deformation due to the coating. Principle contributors of this deformation are introduced and analyzed as well as some experimental results.The race with gigantism taking into consideration instrument of astronomy creates new challenges. The optical coatings are also involved in this race. With increasingly large substrates (without increase proportional in the mass), the flatness of optical surface becomes very sensitive to the stress of the optical layers deposited, whether it is at ambient or at cryogenic temperatures.
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