Abstract
X-ray interferometry established a link between atomic and macroscopic realisations of the metre. The possibility of measuring the silicon lattice parameter in terms of optical wavelengths opened the way to count atoms, to determine the Avogadro constant with unprecedented accuracy, and, nowadays, to realise the kilogram from the Planck constant. Also, it is a powerful tool in phase-contrast imaging by X-rays and, combined with optical interferometry, in linear and angular metrology with capabilities at the atomic scale. This review tells the history of the development of this fascinating technology at the Istituto Nazionale di Ricerca Metrologica in the last forty years. Eventually, it highlights its contribution to the redefinition of the International System of Units (SI).
Highlights
In 1963, Egidi [1] figured a natural mass standard realised by counting the atoms in a crystal, ‘‘scaled so to result outside in the form of a cube with faces parallel to the reticular planes’’
It is a powerful tool in phase-contrast imaging by X-rays and, combined with optical interferometry, in linear and angular metrology with capabilities at the atomic scale
It highlights its contribution to the redefinition of the International System of Units (SI)
Summary
In 1963, Egidi [1] figured a natural mass standard realised by counting the atoms in a crystal, ‘‘scaled so to result outside in the form of a cube with faces parallel to the reticular planes’’ He stated that the crystal should be prepared with a mass near to 1 kg and should be a mononuclidic element, with impurities not exceeding 0.1 nmol/mol and dislocations or other defects not exceeding a similar concentration. The X-ray and optical interferometers project the analyser motion on the normals to the diffracting planes and front mirror. Both projections must be equal to within 1 nm/m fractional error. To ensure temperature uniformity and stability and to eliminate the adverse influence of the refractive index of air, the apparatus is hosted in a thermovacuum chamber
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