ELT mirrors (M2, M3, M4, M5) production status at Safran Reosc

The European Southern Observatory (ESO) awarded Safran Reosc with the contracts for the manufacturing of the main optics for the Extremely Large Telescope (ELT) : in 2015 for the twelve ELT M4 Zerodur shells, in 2016 for the ELT M2 4.25-m diameter Zerodur convex mirror, in 2017 for the ELT M3 4-m diameter Zerodur concave mirror, and in 2019 for the ELT M5 2.7-m diameter Silicon Carbide flat mirror. We present for each of these optics their key requirements and challenges. The ELT M4 shells are thin glass sheets in Zerodur of 1.95 mm thickness with strong requirements on thickness uniformity lower than 15 μm and on surface deformation lower than 14 nm RMS. The ELT M2 and ELT M3 mirrors are large Zerodur mirrors of class 4-meter diameter with strong requirements on bonding and surface deformation, requiring dedicated WFE test benches. We present the main parameters to achieve and make an overview of their test benches developed in Safran Reosc facility. The ELT M5 mirror is a large piece of Silicon Carbide of dimension 2.7m x 2.2m that presents high challenges for its substrate manufacturing and surface deformation. We detail its main requirements and the test bench specially developed for this mirror. Finally, we summarize for each of these optics the main steps and results achieved, and the current progress status.