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Extreme Adaptive Optics in the mid-IR: the METIS AO system

Abstract 115

Submitted by Remko STUIK


R. Stuik (1), L. Jolissaint (1), S. Kendrew (1), S. Hippler (2), B. Brandl (1), L. Venema (3), the METIS team.


(1) Leiden Observatory, Leiden University ; (2) MPIA Heidelberg ; (3) ASTRON


Adaptive Optics at mid-IR wavelengths has long been seen as either not necessary or easy. The impact of atmospheric turbulence on the performance of 8-10 meter class telescopes in the mid-IR is relatively small compared to other performance issues like sky background and telescope emission. Using a relatively low order AO system, Strehl Ratios of larger than 95% have been reported on 6-8 meter class telescopes.

Going to 30-42 meter class telescopes changes this picture dramatically. High Strehl Ratios require what is currently considered a high-order AO system. Furthermore, even with a moderate AO system, first order simulations show that the performance of such a system drops significantly when not taking into account refractivity effects and atmospheric composition variations. Reaching Strehl Ratios of over 90% at L, M and N band will require special considerations and will impact the system design and control scheme of AO systems for mid-IR on ELTs.

In this paper we present an overview of the effects that impact the performance of an AO system at mid-IR wavelengths on an ELT, simulations on the performance and potential solutions to mitigate these effects and we will present a first order design of such an AO system for METIS, the mid-IR instrument for the E-ELT.