Analysis of lateral shearing interferometry without self-imaging limitations.

In lateral shearing interferometry, interferograms with a good contrast can be obtained at any distance without self-imaging limitations based on a modified Hartmann mask (MHM) and a randomly encoded hybrid grating (REHG). The present study analyzes and compares the diffraction orders, the contrast of carrier fringes, the available spectral bandwidth, and the wavefront measurement accuracy of the lateral shearing interferometer using MHM and REHG. Numerical simulations show that the performance of the REHG is superior to that of the MHM with respect to fringe contrast, available spectral bandwidth, and wavefront measurement accuracy. For the REGH, if the phase step of the phase chessboard is within the range of (2n+1±0.2)π, the contrast of the carrier fringes is almost invariant along the propagation axis, and the wavefront reconstruction error generated from higher diffraction orders is small enough to be neglected. Optimal quantization of the REHG is also studied. When M is equal to 2 and N is not less than 5, the quantization result can meet the requirement of the measurement accuracy.