Adaptive Optics Systems: A Challenge for Closed Loop Subspace Identifcation

Adaptive optics allows to obtain pictures of the sky (stars and galaxies) on ground telescopes with a resolution close to those obtained from telescopes outside the atmosphere, for example the Hubble telescope. This requires controlling a deformable mirror in order to compensate for the distortion introduced by the atmosphere. In this paper the problem of obtaining a model based on which controllers can be designed is discussed. This problem is particularly challenging for many reasons, among which the high dimensions of the input and output spaces. The system has 60 inputs (piezoelectric actuators on the mirror) and 60 outputs (avalanches photodiodes sensing the wavefront "slope"). Some promising preliminary results are reported using a recently developed subspace method which allows identification to be performed in closed loop.