Extremely aspheric surfaces: toward a manufacturing process based on active optics

The evolution of astrophysical needs in the era of extremely large telescopes calls more and more complex instrumental systems and sub-systems. A promising solution would be to propose compact reflective optical systems, with less optical surfaces than classical optical designs. This is made possible if the designs are not limited by the use of known conics or symmetrical optical surfaces. Recent studies have shown that the use of highly aspherics could strongly reduce the number of optical surfaces and also the size of instruments, while improving the global system performances. The aim of this article is to study the feasibility of the design and manufacturing of highly aspheric optical mirrors, toward freeform mirrors, thanks to the combination of different active optics techniques: stress deformations up to plasticization phenomenon to provide the optical shape during the manufacturing and actuator corrections to compensate for residual errors during the operation phase of the instrument. A first step consists in structural mechanics analysis to understand as possible the non-linear behaviors of materials and its particular effects which depend on the material chosen, the global dimensions and the boundary conditions parameterized for the manufacturing process.