First on-sky results of the CAWS wavefront sensor on the CANARY experiment

Point-diffraction interferometers are a class of wavefront sensors which can directly measure the phase with great accuracy, regardless of defects such as vortices and disconnected apertures. Due to these properties, they have been suggested in applications such as cophasing of telescope segments, wavefront sensing impervious to the island effect and high-contrast AO and imaging. This paper presents an implementation of this class of interferometer, the Calibration & Alignment~WFS (CAWS), and the results of the first on-sky tests in the visible behind the SCAO loop of the CANARY AO experiment at the William Herschel Telescope. An initial analysis of AO residuals is performed in order to retrieve the SNR of interference fringes and assess the instrument's performance under various observing conditions. Finally, these results are used to test the validity of our models, which would allow for rapid implementation-specific modelling to find minimum-useful flux and other CAWS limits.