CiaoCiao WFS: sensing phase discontinuities at the ELT

The upcoming extremely large telescopes will have to deal with the so-called ''pupil fragmentation'' effect: for what concerns the Extremely Large Telescope (ELT), the presence of thick spider legs supporting the secondary mirror may induce unseen phase discontinuities across the pupil sectors that could limit the performance of the adaptive optics correction. In this context, we propose a wavefront sensor (WFS), the CiaoCiao WFS, consisting in a rotational shearing interferometer to sense phase differences between the pupil sectors. In this work, we present the CiaoCiao WFS concept and the first analyses carried out through numerical simulations. In particular, we analyze the performance of such a wavefront sensor in case the phase discontinuities are induced by low-wind effect during observations with the Multiconjugate adaptive Optics Relay For ELT Observations (MORFEO).