High precision flatness over 300 mm

Project Description

This is a comparison of flatness measurements of an optical plane with openings of 300 mm diameter.
The participants have to measure the inner opening of 300 mm with optical instruments to avoid possible scratches on the surface when measuring with tactile instruments. The achievable measurement uncertainty of the flatness measurements should be less than 15 nm (k=2).

Progress Report 2023-10-04

Intercomparison of flatness measurements of an optical flat at apertures of 300 mm in diameter.
The participants shall measure the inner aperture of 300 mm with optical instruments in order to avoid possible scratches on the surface when measured with tactile instruments. The achievable measurement uncertainty of the flatness measurements should be smaller than 15 nm (k=2). Measurements at PTB, XFEL and NMIJ are completed. Measurements are currently being carried out at NIM.
VNIIMS is currently excluded. Guided by EURAMET’s standpoint, the participants have decided to conclude the comparison without VNIIMS’s contribution unless there is a change with respect to Russia’s invasion of Ukraine. VNIIMS’s opposed to their exclusion from the comparison.

Progress Report 2022-10-05

This supplementary comparison is based on the previous successful EURAMET project “Determination of form/topography of high-quality flats”. In this EURAMET project a high quality flat made of Zerodur with a diameter of 205 mm was used as comparison artefact and the flatness measurements were evaluated on an aperture of 150 mm and 100 mm in diameter and the results were published in: Metrologia Vol 54, pp. 85-93 (2017).
Based on the experiences gained in this previous project, the EURAMET Supplementary Comparison EURAMET.L-S28 is executed using an optical flat with a diameter of 330 mm.

The participants shall measure the inner aperture of 300 mm with optical instruments only to avoid possible scratches on the surface when measured with tactile instruments. Since the comparison is intended as a high accuracy comparison, particpants shall reach an expanded uncertainty of less than 15 nm (k=2).

The participants of the comparison are:
NIM (CN), NMIJ (JP), PTB (DE), XFEL (DE);
(XFEL stands for European XFEL GmbH, which participates in the comparison informally)

Current status to be updated:
The measurements at the XFEL (DE) and the NMIJ (JP) were completed. The next station will be NIM (CN). The new schedule is that the measurements will be completed by March of next year 2023.