18 July 2014 FAME: Freeform Active Mirrors Experiment: manufacturing process development
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Abstract
Extreme freeform mirrors couple a non-axisymmetrical shape and an extreme asphericity, i.e. more than one millimeter of deviation from the best fit sphere. In astronomical instrumentation, such a large asphericity allows compact instruments, using less optical components. However, the lack of freeform mirrors manufacturing facilities is a real issue. We present the concept and development of an innovative manufacturing process based on plasticity forming which allow imprinting permanent deformations on mirrors, following a pre-defined mold. The aim of this activity, pursued in the frame of the OPTICON-FAME (Freeform Active Mirrors Experiment) project, is to demonstrate the suitability of this method for VIS/NIR/MIR applications. The process developed can operate on thin and flat polished initial substrates. Three study cases have been highlighted by FEA (Finite Element Analysis) and the real tests associated were performed on thin substrates in AISI420b stainless steel with 100 mm optical diameter. A comparison between FEA and tests is performed to study the evolution of the mechanical behaviour and the optical quality. The opto-mechanical results will allow a fine tuning of FEA parameters to optimize the residual form errors obtained through this process to converge toward an innovative and recurrent process.
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Zalpha Challita, Zalpha Challita, Emmanuel Hugot, Emmanuel Hugot, Lars Venema, Lars Venema, Hermine Schnetler, Hermine Schnetler, Marc Ferrari, Marc Ferrari, Jean-Gabriel Cuby, Jean-Gabriel Cuby, } "FAME: Freeform Active Mirrors Experiment: manufacturing process development", Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 915133 (18 July 2014); doi: 10.1117/12.2056656; https://doi.org/10.1117/12.2056656
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