Research On Surface Testing Algorithm Based On Wavelength-Shifting Interferometry

Phase shifting interferometry is one of the important means of modern optical testing technology.The phase shifting interferometry can be divided into the traditional phase-shifting interferometry and the wavelength-shifting interferometry according to the different ways of phase shifting. The wavelength-shifting interferometry is high-precision by changing the wavelength of the light source to realize the phase shifting. It is without any moving parts and can eliminate the nonlinear phase error caused by the movement of parts in the system. This has important implications for the measurement of large aperture optical element, so it is necessary to study the wavelength-shifting shift interferometry. The surface detection algorithms based on the wavelength-shifting interferometry are mainly studied in this paper. The main contents of this paper are:The basic principle of the phase shifting interferometry, the wavelength-shifting interferometry and phase shifting calibration principle are introduced; The measurement precision of four step phase shifting algorithm and the phase demodulation algorithm based on iteration are simulated and analyzed by using Matlab software; the wavelength shifting-Fizeau interferometry testing platform is built, the interference fringes with different phase shifting are acquired, and using different phase demodulation algorithm to solve the wrapped phase, then the surface information can be obtained by the phase unwrapping and Zernike fitting.For the problem of wavelength-shifting interferometry phase calibration, a new wavelength-shifting interferometry phase calibration method has been proposed in this paper. The extremum points of the error function are solved to calibrate the phase in this method. The whole sampling points of the interference pattern are considered in this phase calibration method, it can be very good to avoid the random error. At the same time, in the process of phase calibration, the nπ/2phase shift points are calibrated respectively, so the cumulative error does not exist in this calibration method because each point do not be influenced by each other. Simulation results verify the correctness of the phase calibration method principle. And the simulations show that the calibration method have higher calibration precision.Because of the existence of the phase shift error in measurings, in order to reduce the influence on the measurement precision, a phase demodulation algorithm based on iteration has been used in wavelength-shifting interferometry in this paper. This iteration algorithm does not need calibrating the phase of the test system, and it can obtain the testing phase and phase shifts through alternate iteration method when the testing phase and phase shift are unknown. A series of simulations and experiments have been done. The results show that, the precision of this algorithm is better than the traditional four step phase shifting algorithm.