Experimental characterization of the birefringent point-diffraction interferometer wavefront sensor

We propose a new wavefront sensor with a birefringent point-diffraction interferometer (b-PDI) for extreme adaptive optics and report the experimental results. It has a phase mask made with birefringent crystal TiO₂ and simultaneously generates interferograms with three different phase-shifts. The statistical error of the b-PDI was consistent with a simple error propagation model. The error due to photon noise was 1.4 times larger than that of the Zernike wavefront sensor (ZWFS). The b-PDI could determine the wavefront phase up to ∼1 wavelength without ambiguity. The range is two times larger than that of the ZWFS, which is affected by the ambiguity of the sine of the phase.