FEM analysis of bonding process used for minimization of deformation of optical surface under Metis coronagraph mirrors manufacturing

High demands on the final surfaces micro-roughness as well as great shape accuracy have to be achieved under the manufacturing process of the precise mirrors for Metis orbital coronagraph. It is challenging engineering task with respect to lightweight design of the mirrors and resulting objectionable optical surface shape stability. Manufacturing of such optical elements is usually affected by number of various effects. Most of them are caused by instability of temperature field. It is necessary to explore, comprehend and consequently minimize all thermo - mechanical processes which take place during mirror cementing, grinding and polishing processes to minimize the optical surface deformation. Application of FEM simulation was proved as a useful tool to help to solve this task. FEM simulations were used to develop and virtually compare different mirror holders to minimize the residual stress generated by temperature changes and to suppress the shape deformation of the optical surface below the critical limit of about 100 nm.