Multiple-wave lateral shearing interferometry with a liquid-crystal geometric phase grating

A multiple-wave lateral shearing interferometer extends upon the traditional lateral shearing interferometry by producing multiple sheared copies of the incoming light. By using a special grating instead of a shear plate, it is able to produce fringes in multiple directions at the same time. This makes it possible to do single-shot reconstruction of both phase and amplitude aberrations. Instead of a surface relief grating, we propose to use a patterned half-wave plate manufactured using direct-write techniques that acts as a liquid-crystal geometric phase grating. We demonstrate its wavefront sensing capabilities with laboratory measurements with an ALPAO-97 deformable mirror in monochromatic light. Finally, we present on-sky measurements performed at the William Herschel Telescope, showing broadband operation in unpolarized light.