  Multiconjugate adaptive optics (MCAO) systems have the potential to deliver
diffraction-limited images over much larger fields of view than traditional
single conjugate adaptive optics systems. In MCAO, the high altitude deformable
mirrors (DMs) cause a distortion of the pupil plane and lead to a dynamic
misregistration between the DM actuators and the wavefront sensors (WFSs). The
problem is much more acute for solar astronomy than for night-time observations
due to the higher spatial sampling of the WFSs and DMs, and the fact that the
science observations are often made through stronger turbulence and at lower
elevations. The dynamic misregistration limits the quality of the correction
provided by solar MCAO systems. In this paper, we present PropAO, the first AO
simulation tool (to our knowledge) to model the effect of pupil distortion. It
takes advantage of the Python implementation of the optical propagation library
PROPER. PropAO uses Fresnel propagation to propagate the amplitude and phase of
an incoming wave through the atmosphere and the MCAO system. The resulting
wavefront is analyzed by the WFSs and also used to evaluate the corrected image
quality. We are able to reproduce the problem of pupil distortion and test
novel non-linear reconstruction strategies that take the distortion into
account. PropAO is shown to be an essential tool to study the behavior of the
wavefront reconstruction and control for the European Solar Telescope.
