Research On Optical Parameters Measurement Of Parallel Flat Plate Based On Weighted Multi-step Phase-shifting Algorithm

Optical transmission materials are an important part of optical materials,and their main parameters include surface shapes,optical thickness variation and optical homogeneity.The inconsistency of optical parameters will cause the deviation of transmission wavefront and influence the performance of the optical system.Therefore,it is necessary to achieve highprecision measurement of the optical parameters of optical materials.Among many measurement methods,the interference method is widely used due to its high sensitivity and high accuracy.However,when measuring parallel plates,the multi-surface interference of the parallel plates will bring difficulties to the measurement of optical parameters.Therefore,this paper uses wavelength-tuning interference method combined with phase-shifting algorithm to achieve accurate extraction of the target frequency signal information.On the basis of comparing the common wavelength phase-shifting algorithms and analyzing their advantages and disadvantages,this paper proposes a method for measuring the optical parameters of parallel plates based on weighted multi-step wavelength phase-shifting algorithms.First,the theory of the multi-surface interference technology is studied combined with the two-step wavelength tuning absolute testing method.Three groups of 25-sample phaseshifting algorithms are designed based on the principle of characteristic polynomials and characteristic diagrams to extract and calculate the surface shape,thickness variation and optical homogeneity information of the parallel plates respectively,and the evaluation function of the phase-shifting algorithm and its Fourier representations are used to show the algorithm's immunity to errors.Then the measurement process of the optical parameters of the parallel plates is simulated,and the simulation results show that the algorithm can accurately extract the target frequency signal information.Finally,the calculation results of the 25-sample phaseshifting algorithm are compared with the results measured by the Zygo phase-shifting interferometer.The two results are basically the consistent,which verifies the correctness and feasibility of the algorithm.The research shows that the harmonic suppression order of the algorithm is high,and it is not sensitive to the phase shift error and the coupling error between the phase shift error and the harmonic error.Moreover,it requires fewer interferograms and has high detection efficiency,which is suitable for the high-precision measurement of the optical parameters of the parallel plate.