Laboratory demonstration of focal plane wavefront sensing using phase diversity: a way to tackle the problem of NCPA in SHARK-NIR: Part II: new characterization tests and alternative wavefront sensing strategies

Phase diversity is a focal-plane wavefront sensing technique. Two or more images of whatever object are required, differing in the amount of a well-calibrated injected aberration (typically a pure defocus). We present here new results concerning 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 tested the sensor both on a new dedicated testbed and on the instrument bench itself, which is now fully integrated. We characterized the behavior of the sensor in several conditions, in view of its application to sense SHARK-NIR non-common path aberrations at the telescope. We also investigated some alternative wavefront sensing strategies, such as a curvature-like sensor.