Absolute interferometric testing of a flat surface based on the Laplacian method

In the present study, a method is introduced for absolute interferometric testing. An interferometer is used to measure the phase difference distributions at five positions of the reference surface with respect to the test surface. The Laplacian of the phase distribution is calculated from the measured phase difference distributions. Then, the reference phase distribution is reconstructed by solving the Laplacian equation by the Fourier method. The accuracy of the method with respect to the amount of the displacement and noise is investigated by simulation and compared with the conjugate differential method. It is shown that the spatial frequencies of the phase distributions reconstructed by the Laplacian method are less filtered out with respect to the conjugate differential methods. Finally, the experimental result is presented.