Research On Wavefront Reconstruction Of Four-wave Lateral Shear Interferometer

Meeting the requirements of transient wavefront sensing, four-wave lateral shearing interferometry can be used for real-time wavefront testing with high precision. But with the method, only the differences of the wavefront are measured and the wavefront cannot be obtained directly. A full set of algorithms is presented for wavefront reconstruction from one single four-wave lateral shearing interferogram using which the phase distribution can be retrieved effectively and accurately.Firstly, in order to determine the whole reconstruction process, basic principles of four-wave lateral shearing interferometry have been studied.Secondly, the method based on Fourier transform is applied to shearing interferogram to extract the differences of two orthogonal directions. To reduce the error caused by spectrum leakage, some research on filter selection method and Gerchberg-type iterative extrapolate technique has been done. Corresponding discussions and analysis are given in detail based on relative simulations.Thirdly, wavefront reconstruction algorithm based on Fourier expansion in the complex plane has been adopted to retrieve the original phase distribution and extension of the difference data based on the duplication and antisymmetrization is performed before reconstruction to avoid the artifacts caused by the discontinuities. Wavefront reconstruction simulation was carried on one interferogram which contained information of one wavefront with several kinds of aberration. The RMS of reconstruction error is 3.97×10-3λ and PV is 4.67 × 10-2 λ which verifies the effectiveness of the full set of algorithms.Finally, an experimental setup was established and the exit wavefront of a standard lens of interferometer was measured. Both the RMS or PV value and the 35 terms Zernike coefficients of the reconstructed phase distribution show a great agreement with those of the phase measured by the SID4 wavefront sensor which proves the feasibility and validity of our system and reconstruction algorithms.