Abstract 187

Submitted by Fabien MOMEY

Authors

F. Momey, M. Tallon

Affiliations

CRAL - Obs. Lyon

Abstract

The classical models of a Shack-Hartmann wavefront sensor (e.g. Fried’s model) approximate its measurements by finite differences between samples of the wavefront at particular locations with respect to the subapertures (e.g. at the corner of the subapertures for Fried’s model). In the context of atmospheric tomography, the samples of the wavefronts in the turbulent layers can be hardly aligned with the subapertures after propagation down to the wavefront sensors (WFS), for any positions of the guide stars. Further, the sampling step is enlarged from the layers to the WFS when modeling laser guide stars but is unchanged with natural guide stars. Such effects yield the need to resample the wavefronts after propagation introducing errors and still using an approximate response of the WFS.

We present another approach where the wavefronts are represented on a basis of continuous functions in the turbulent layers. The gradient measurements of the WFS are then computed analytically. With this method, we do not need to perform any interpolation and an accurate continuous model of WFS is used. Assuming that the functions of the basis are separable on the two dimensions, we obtain a sparse operator that can be factorized in two components, acting respectively on each dimension of the wavefront. This factorization could allow this approach to be used for Wide Field AO systems on ELTs. A study of the computational load of this method is performed, and compared with a standard method using resampling and Fried’s model of WFS. We also studied the performances of the model, in terms of precision of measurements and quality of wavefront reconstruction.