Abstract
The measurement of the silicon lattice parameter by a separate-crystal triple-Laue X-ray interferometer is a key step for the realization of the kilogram by counting atoms. Since the measurement accuracy is approaching nine significant digits, a reliable model of the interferometer operation is required to quantify or exclude systematic errors. This paper investigates both analytically and experimentally the effect of the defocus (the difference between the splitter-to-mirror and analyser-to-mirror distances) on the phase of the interference fringes and the measurement of the lattice parameter.
Highlights
The measurement of the silicon lattice parameter at optical wavelengths by scanning X-ray interferometry opened a broad field of metrological and science applications
In addition to realizing the metre at atomic length scales (Basile et al, 2000), to determining the Avogadro constant (Fujii et al, 2018), and, nowadays, to realizing the kilogram from the Planck constant h, it was instrumental in the determination of the h/mn ratio (Krueger et al, 1998, 1999) and allowed the wavelength of Xand -rays to be referred to the metre
The assessment and further improvements of the measurement accuracy, approaching nine significant digits, require a reliable model of the interferometer operation to quantify or exclude parasitic contributions to the fringe phase originated by unavoidable aberrations
Summary
The measurement of the silicon lattice parameter at optical wavelengths by scanning X-ray interferometry opened a broad field of metrological and science applications. In addition to realizing the metre at atomic length scales (Basile et al, 2000), to determining the Avogadro constant (Fujii et al, 2018), and, nowadays, to realizing the kilogram from the Planck constant h, it was instrumental in the determination of the h/mn ratio (Krueger et al, 1998, 1999) and allowed the wavelength of Xand -rays to be referred to the metre These links resulted in improved measurements of the deuteron binding energy and neutron mass mn (Greene et al, 1986; Kessler et al, 1999) and the most accurate test of the Planck–Einstein identity h = mc (Rainville et al, 2005).
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