Abstract
In this paper, a novel absolute measurement method based on multisurface interference is proposed for a 600 mm aperture interferometer. Compared to existing 3-flat testing methods, which generally require two transmission flats and one reflection flat, our method does not require the replacement of the transmission flat with another flat and rotation of the reflection flat about the z-axis of the 600 mm aperture interferometer. Only by rotating an auxiliary parallel flat about the z-axis can we realize the in situ absolute measurement of the reference flat surface error of the interferometer without losing the medium-frequency error. The principle of absolute measurement based on the proposed novel method is discussed. The various sources of measurement error are analyzed, including the number of rotations, the rotation angle error and the pixel misalignment error of the coordinate axis. Based on these analysis results, an auxiliary rotating device for a large aperture flat is designed. Repeatability experiments were carried out on the 600 mm aperture interferometer produced by Zygo. The experimental results show that the RMS value of the repeatability precision is less than 2 nm.
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