In this paper, we mainly use the basic principle of Fizeau interferometer, because Fizeau type interferometer has the advantage of common optical path, which can reduce the influence of some system errors to a certain extent, and the requirements for environmental changes are relatively low, and then use zemax optical simulation software to simulate the cat's eye position, confocal position and confocal rotation 180 degree position in the three position absolute detection method, and establish the absolute measurement model . Through the combination of simulation and simulation, it is concluded that the measurement error mainly includes tilt error, translation error and defocus error. Among them, the tilt error and translation error have negligible impact on the system measurement results, and the defocus error has a greater impact on the measurement results. Finally, the defocus error is removed by a new higher-order defocus removal method.
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