12th International Conference on Optics, Photonics & Lasers
Laboratoire Charles Fabry - Institut d’Optique Graduate School-CNRS, France
Title: What high performance control can do for you? The example of adaptive optics
Biography: Caroline Kulcsár
Adaptive optics (AO) systems aim at compensating in real time optical aberrations induced by atmospheric turbulence, so as to retrieve quasi diff raction-limited imaging on ground-based telescopes. A deformable mirror is inserted in the optical path, and actuators, located under its reflecting surface, are controlled thanks to measurements of the wavefront aft er correction. Th e fi rst on-sky demonstration of AO was realized in 1989 at the Observatoire de Haute Provence (France) on a 1.52 m telescope, by a French-ESO consortium (European Southern Observatory). Twelve years aft er, in 2001, an AO system was installed on ESO’s Very Large Telescope (VLT) in Chile. First light results were impressive, with this system operating at a loop frequency of 600 Hz and controlling in real time 185 actuators from 270 measurements. Nevertheless, unexpected guests invited themselves with the atmospheric turbulence: vibrations (propagated from the telescope structure due to wind, vans, coolers, etc.) induced sometimes a severe performance loss. Recent and future AO systems thus feature high performance controllers designed to mitigate the many spurious signals affecting imaging quality. They are about to replace, at least partially,the so-called “integrator”, a standard controller prized for its simplicity. Why do integrators work (or not)? What can be expected from high performance controllers? When should they be considered as a relevant alternative for optical systems feedback loops? And at last, are they really implementable in real-time, in the era of giant telescopes featuring AO systems with thousands of degrees of freedom? Qualitative answers will be proposed, along with many illustrative examples.