25 October 2016 λ/100 reference flat for commercially available Fizeau interferometer
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The flatness is one of the important geometric quantity such as a silicon wafer, a photo mask and ultra-precise optics for an extreme ultraviolet lithography, synchrotron radiation facilities and a gravitational wave interferometer. A Fizeau interferometer is in a high accurate flatness measurement equipment. In a Fizeau interferometer, the measurand is a gap distance between a reference flat and a specimen. The measurement accuracy of the Fizeau interferometer is limited by the flatness of the reference flat. The flatness of commercially reference flats is about λ/40 to λ/20 (15 nm - 30 nm). There is strong demand for developing that the flatness of reference flat is less than 10 nm. Thus, we developed a λ/100 (6.3 nm) reference flat which is attachable to a commercial Fizeau interferometer. The measurable diameter of the optical flat was φ100 mm. In the factory fields, the flatness of the reference flat mounted on a commercial Fizeau interferometer is required. We designed the reference flat using the finite element method (FEM) to decrease a deformation by mounting. The developed reference flat was evaluated by a scanning deflectometric profiler (SDP) and an ultra-high accurate Fizeau interferometer. Finally, the reference flat was validated through the evaluation results.
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Y. Kondo, Y. Kondo, Y. Bitou, Y. Bitou, Kazuhide Yamauchi, Kazuhide Yamauchi, } "λ/100 reference flat for commercially available Fizeau interferometer", Proc. SPIE 9687, 8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Subnanometer Accuracy Measurement for Synchrotron Optics and X-Ray Optics, 968708 (25 October 2016); doi: 10.1117/12.2242806; https://doi.org/10.1117/12.2242806

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