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Freeform and advanced optics for ELT instrumentation

In this paper we share some recent work performed at REOSC in the domain of advanced optics for space and that is also directly applicable to astronomical instrumentation, e.g. for the Extremely Large Telescopes (ELT), the construction of which has already started. We present firstly the results of some design investigations performed on Three Mirror Anastigmat (TMA) imaging optics when using freeform optical surfaces clearly showing gain in performance (WFE, distortion, … ) or compactness of the optics. We separate smart freeform from more aggressive freeform offering increased level of gain in design performances. Secondly we present our development in freeform and direct off-axis high performance optical manufacturing capabilities and the industrialization efforts conducted in the frame of the European Extremely Large Telescope (E-ELT) primary mirror segments. A third subject is the demonstration of an extreme freeform surface manufacturing with the prototyping of a huge 500 mm aperture, 90° deviation angle, F/2.5 high output NA Off Axis Parabola (OAP), a unique achievement aimed to confirm the viability of potential new design opportunities involving such type of extreme optics. Finally we present in this paper our technology development on polishing layer for SiC material, named R-SiC, a polishing layer that reduces costs, risks and schedule for advanced SiC optics manufacturing for Vis and IR applications.