Defocused travelling-fringes in scanning triple-Laue x-ray interferometry

TL;DR

This paper analyzes how defocus affects phase measurements in triple-Laue x-ray interferometry, which is crucial for precise silicon lattice parameter determination used in redefining the kilogram.

Contribution

It provides an analytical and experimental investigation of defocus effects on interference fringes in triple-Laue x-ray interferometry, enhancing measurement accuracy.

Findings

Defocus causes measurable phase shifts in interference fringes.

Modeling defocus improves the reliability of lattice parameter measurements.

Experimental results confirm the analytical predictions.

Abstract

The measurement of the silicon lattice parameter by a separate-crystal triple-Laue x-ray interferometer is a key step for the kilogram realisation by counting atoms. Since the measurement accuracy is approaching nine significant digits, a reliable model of the interferometer operation is demanded to quantify or exclude systematic errors. This paper investigates both analytically and experimentally the effect of defocus (a difference between the splitter-to-mirror distance on the one hand and the analyser-to-mirror one on the other) on the phase of the interference fringes and the measurement of the lattice parameter.