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Adaptive Optics for ELTs with Low-Cost and Lightweight Segmented Deformable Mirrors

Abstract 168

Submitted by Gonçalo RODRIGUES


G. Rodrigues, R. Bastaits, A. Preumont,


Active Structures Laboratory; Université Libre de Bruxelles


Deformable mirrors have had a huge success in delivering stunning aberration corrected images in existing telescopes. However, the simple up-scaling of existing concepts up to the tens of thousands of degrees of freedom required in ELTs faces numerous difficulties. A shift in technology paradigm is very likely required. Namely, the extreme complexity of linear actuation raises issues in terms of reliability and maintenance and development and fabrication costs. Higher weight will also become an issue by increasing the dynamic coupling between the heavy and highly complex adaptive optics control system and the other control systems of the telescope.

An innovative wavefront corrector consisting of an assembly of hexagonal bimorph mirrors provides the necessary technology shift. The mirrors are fabricated by screen-printing thick films of piezoelectric ceramics on silicon wafers in a process suited to mass-production and having a low-cost which is essentially independent of the number of actuators. The simplicity of the bimorph configuration makes the proposed deformable mirror robust and lightweight while the modularity facilitates its assembly and maintenance and reduces the control effort by decoupling it between the segments. The manufacturing technique can provide an actuation pitch of about 5mm, enabling deformable mirrors 60 cm wide with 10000 actuators and weighing only about 3 kg. Previous research demonstrated that the deformable mirrors fabricated by screen-printing possess the optical controllability required for adaptive optics. A new prototype with multiple hexagonal segments is now under development for demonstrating global shape correction of the assembly by individually shaping and aligning each segment as well as co-phasing the entire set. Numerical simulations for an assembly of 7 segments showed an excellent morphing capability of the assembly with a nearly continuous transition of shape between the segments.

Reference: G. Rodrigues et al., Modular Bimorph Mirrors for Adaptive Optics, TBP in Optical Engineering, 48(3).