Compact Lateral Shearing Interferometer Based On Circular Modified Hartmann Mask

A compact lateral shearing interferometer (LSI) based on circular Modified Hartmann Mask (cMHM) is proposed for the measurement of wavefront aberrations. A cMHM grating consists of a circular apertures amplitude grating and a phase chessboard grating. By choosing the radius of the circular aperture of the amplitude grating to be the first positive root of Bessel function, residual diffraction orders are suppressed. As a result, the diffraction field of cMHM is close to that of the ideal quadriwave lateral shearing interference which only contains +/- 1 orders in two orthogonal directions. An interferometer adopting cMHM as the diffraction element exhibits a diminished Talbot effect on the detection plane as those adopting the conventional Modified Hartmann Mask (MHM) grating or the improved Randomly Encoded Hybrid Grating (REHG). Compared with the REHG, the cMHM requires non-strict manufacturing process. Numerical simulations shows a better diffraction efficiency compared with that using the conventional MHM grating. In the experiments, the interferograms captured by the cMHM-LSI exhibit the same level of contrast as those by MHM-LSI.