Measurement of complex amplitude with a point-diffraction interferometer.

We propose a pupil-plane wavefront sensor to measure instantaneous phase and amplitude aberrations, developing the configuration of the point-diffraction interferometer proposed by Imada et al. [Appl. Opt. (2015), accepted]. The previous configuration allows us to instantaneously acquire four phase-shifted interferograms, from which cosine and sine functions of the relative phase difference between the test and reference beams can be derived. Here, because the wavefront phase can be reconstructed from only its sine function when the aberration of the input beam is smaller than half that of the sensing wavelength, we directly measure the intensities of the test and the reference beams instead of two of the four interferograms. Using this proposed configuration enables reconstruction of not only the wavefront phase but also its amplitude. The conceptual design of the proposed sensor is described, and its performance is evaluated compared with the original point-diffraction interferometer through numerical simulations.