Direct wavefront phase measurement using a point diffraction interferometer with application to large scale AO

Interferometric techniques are attractive in wavefront sensing because they give a direct measure of the phase (as opposed to the first or second derivative) which means they are useful for use with a piston-only wavefront corrector (such as a liquid crystal spatial light modulator, or some MEMS mirrors). In this paper we describe (also described in ref 1) a novel method of implementing a common-path phase-shifting point diffraction interferometric wavefront sensor suitable. The sensor simultaneously gives two phase-shifted outputs which can be used to drive a phase-only wavefront corrector. The device can also give a null output which can be used to calibrate any scintillation.