Résumé

We reconsider here the long exposure AO PSF computation based on a analytical derivation of the spatial power spectrum of the residual phase (Rigaut et al. 1998), and applied it to the case of giant telescopes with or without MCAO. This approach is proven to be faster in computation time than any other Monte-Carlo ones, for a high level of accuracy. With the addition of an interpretation of the AO PSF wings in term of the residual phase angular power spectrum, we show that both approachs, the analytical and the angular interpretation, lead to a powerful tool for assessing the effect of the different parts of the spectrum on the different parts of the AO PSF. Using this tool, we present some examples of the relationship between the spectrum and the PSF wings, for the atmospheric, noise, aliasing and anisoplanatism components, and show that the effects of the residual phase is more critical for a giant than for a modest size telescope, for which these effects are hidden by the diffraction structures.

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