In situ absolute surface metrology for a 600 mm aperture interferometer

• Published in: Optics and lasers in engineering 2020-06, Vol.129, p.106054, Article 106054
• Main Authors: Zhou, You, Liu, Shijie, Lu, Qi, Bai, Yunbo, Wu, Fulin, Shao, Jianda
• Format: Article
• Language: English
• Subjects: Absolute measurement; Large aperture interferometer; Multisurface interference; Surface metrology
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2020.106054

•A novel absolute measurement method based on multisurface interference for a 600 mm aperture interferometer is proposed.•The proposed method is not necessary to replace the transmission flat with another flat and rotate the reflection flat about the z-axis, it just needs to rotate an auxiliary parallel flat about the z-axis.•The proposed method can realize the in situ absolute measurement of a 600 mm aperture reference flat surface error without losing the medium-frequency error. 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.