Architecting, Implementing and Observing with a Metasurface vector Zernike wavefront sensor on the Keck Telescope

The ability to directly detect faint companions orbiting nearby stars using ground-based telescopes has made incredible strides in the past couple of decades. This has been enabled by a suite of methods working closely and in concert with one another. These methods include: 1) adaptive optics to correct for the earth's turbulent atmosphere, 2) stellar corongraphs to suppress the light from the bright host star, and 3) precision wavefront sensing. In this paper we concentrate on the later. We describe a vector Zernike wavefront sensor (vZWFS) that is fabricated using the emerging technology of metasurfaces. We describe the engineering aspects of the design and implementation of this wavefront sensor on the Keck II telescope. We conclude by highlighting results of using this sensor in two different modes: 1) internal wavefront sensing and control on the adaptive optics bench, 2) sensing and control of the segment phasing errors on the Keck II primary mirror.