Cross-sectional Study Of Four-wave Wavefront Shearing Interferometry Detection Technique Based On Phase Grating

In traditional lateral shearing interferometry, wavefront reconstruction needs two orthogonal directional wavefront differences. So the precise adjustment is needed in order to obtain two interferograms. To meet the requirements of dynamical measurement, four-wave lateral shearing interferometry is studied to retrieve the wavefront to be tested from a single interferogram.Firstly, the scheme of wave-front measurement is presented and corresponding optical structures are designed based on theory of four-wave lateral shearing interferometry.Secondly, in order to generate wave-front splitting and improve light energy utilization efficiency, the core optical element, phase chessboard, is designed and manufactured. The diffraction efficiencies of cross phase grating and phase chessboard are analyzed using scalar diffraction theory. Simulation results show that the total (±1,±1)st orders diffraction efficiencies of phase chessboard are four times that of cross phase grating. The test results indicate that the property of the grating is accord with the design requirement.Thirdly, based on FFT algorithm and difference Zernike algorithm, the wave-front reconstruction method for demodulating four-wave lateral shearing interferogram is designed. FFT algorithm is used to obtain wavefront differences and difference Zernike algorithm is used to reconstruct original wavefront. For several primary aberrations, reconstruction accuracy and applicable dynamic range of wavefronts are analyzed using difference Zernike method. Simulation results show that this wavefront reconstruction method can apply to four-wave lateral shearing interferograms with shear ratio less than10%.Fourthly, to verify the feasibility of four-wave lateral shearing interferometry, an experimental facility is set up to test a standard lens of interferometer. The wavefront aberration of the lens is1.067λ P-V and0.265A RMS. The result basically agrees with that of SID-4wavefront sensor’s. In addition, the phase chessboard can be applied to dynamic interferometer to increase the intensity of interference beams and to improve the interferograms contrast.