Phase diversity is a wavefront sensing technique that makes use of images in the scientific channel to derive the instrumental aberrations. Two images of whatever object are required, with a well-calibrated differential aberration (typically a pure defocus) between the two. We present here the laboratory demonstration of this concept in the specific context of SHARK-NIR, the new-generation high contrast imager for the Large Binocular Telescope. We investigated the behavior of the sensor in presence of several aberrations of variable amplitude and we optimized the retrieval algorithm parameters by comparing the results with the ones of a Shack-Hartmann sensor. We illustrate the challenges and the perspectives of this technique in view of its application to sense non-common path aberrations in SHARK-NIR.
LINC-NIRVANA at the LBT has a dual MCAO system using solely natural guide stars. A multi pyramid WFS provides the slopes to close two independent loops for ground and high layer correction, as foreseen by the Layer Oriented scheme. The projection of the deformable mirrors actuators pattern on the WFS cameras rotates, since mechanical (ground) and optical (high) derotation provides the field rotation correction needed to keep the WFS on the reference stars. We reported in the previous conferences that we succeed in obtaining valid control matrices through numerical interpolation of a few calibrated interaction matrices registered for different clocking angle. We successfully tested a different approach based on a synthetic WFS and DM model. We proved that control matrices computed by the inversion of the interaction matrices generated from the model were effectively working on the real system closing high-order correction loop on the sky, providing better performance.
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