Conception de lois de commande à hautes performances pour l'optique adaptative des grands / très grands télescopes

Abstract : Adaptive optics (AO) enables to correct the effects induced by atmospheric turbulence, which affect telescopes' resolution and hence image quality. Introduced in the 1990s, AO systems become tomographic, allowing to analyze turbulence in volume in order to achieve wide-field correction. For future large telescopes, this goes together with a sharp increase in complexity. New AO concepts, often exhibiting large number of degrees of freedom (LNDF), require innovative control laws compatible with real-time constraints. Several original aspects are addressed. For LNDFs, the entry point is the selection of a basis for the turbulent phase. Two directions are explored: with a zonal formulation, Fourier methods for static wavefront reconstruction are investigated; a new strategy combining Fourier and iterative methods is developed to adapt optimal Linear Quadratic Gaussian (LQG) control to LNDFs. The issue of large deformable mirror's temporal dynamics is addressed. For linear dynamics, the optimal control minimizing residual variance is obtained as the solution of a discrete-time LQG problem. This also enables to quantify the degradation in performance with suboptimal controllers. This approach is applied to the control of tip-tilt mirrors developed for large telescopes. It is shown that neglecting dynamics results in significant performance degradation. Another application is dealt with: the coordination of slow and fast mirrors (woofer-tweeter concept).
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Submitted on : Sunday, September 12, 2010 - 9:50:04 PM
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Carlos Correia. Conception de lois de commande à hautes performances pour l'optique adaptative des grands / très grands télescopes. Astrophysique [astro-ph]. Université Paris-Nord - Paris XIII, 2010. Français. ⟨tel-00516866⟩

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