In an AO system the correction to be applied to the Deformable Mirror is computed at each loop cycle from the residual
slopes on the Wavefront Sensor and the Interaction Matrix of the system DM/WFS.
But the a posteriori analysis of the DM commands and WFS slopes can also provide a wealth of information on the
closed loop behavior. In this paper we present a non-exhaustive list of what can be learned from such data. We base our
analysis on simulated data, on data recorded on ESO’s PEACE test bench, and on data recorded on the NAOS instrument
at the VLT during technical nights in 2010 and 2011, in the framework of the preparation of the algorithms for the AO
The topics presented include the reconstruction of the input turbulence in the WFS domain (pseudo open-loop slopes),
the estimation of the seeing, turbulence profile, coherence time, wind speed and direction, the measurement of LGS spot
size, the detection of vibrations via modal transfer functions, the identification of DM/WFS mis-registration and the
optimal loop gain computation.