Phase structure function measurement with a plenoptic camera used as wavefront sensor

Abstract

The use of the plenoptic camera as a wavefront sensor has been proposed and demonstrated in the past by our group, as especially adequate for extended objects, within the context of the design of the European Solar Telescope (EST), and also may be used with point sources and even with elongated objects like laser guide stars. The underlying concept of the plenoptic camera can be adapted to the case of a telescope by using a lenslet array of the same f-number placed at the focal plane, thus obtaining at the detector a set of pupil images corresponding to every sampled point of view. This approach will generate a generalization of Shack-Hartmann, Curvature and Pyramid wavefront sensors in the sense that all those could be considered particular cases of the plenoptic wavefront sensor, because the information needed as the starting point for those sensors can be derived from the plenoptic image. This paper quantitatively evaluates the effect of the low-pass filtering in the spatial frequencies of the wavefront, derived from the use of a limited diameter of the lenslet used in the array, which accurately explain the deviation from the 5/3 power law of the structure function of the wavefront phase.