Laboratory demonstration of focal plane wavefront sensing using phase diversity: a way to tackle the problem of NCPA in SHARK-NIR

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.