AO4ELT5 Proceedings

Deformable Mirror configuration in MCAO: is propagation a fundamental limit on visible wavelength correction?

Farley, Ollie (Durham University), Osborn, James (Durham University), Morris, Tim (Durham University), Reeves, Andrew (Durham University), Wilson, Richard (Durham University)

To achieve the best correction using a multi-conjugate adaptive optics (MCAO) system, the sequence of the deformable mirrors must be taken into account. Since atmospheric turbulence is sampled from high to low altitude, the subsequent phase corrections must be performed in a symmetrical way (low to high altitude) to avoid aberration arising from optical propagation through the system. This is a well known problem in solar MCAO however ordering the DMs in this way requires bulky relay optics, therefore most post focal MCAO systems for night-time astronomy have been designed with the DMs ordered from high to low altitude. We show that this results in a small wavefront error that can become non-negligible in the visible. Employing an adaptive secondary mirror conjugated to the ground has the potential to alleviate this effect.

DOI: 10.26698/AO4ELT5.0091- Proceeding PDF

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