Abstract

In order to redefine the kilogram, the Avogadro constant is determined by means of the X-ray crystal density method, where the lattice constant, density and mean molar mass of a single crystal silicon sphere are absolutely measured [1]. The density of the silicon sphere, whose diameter and mass are approximately 93.6 mm and 1 kg respectively, is obtained by the accurate diameter and mass. To measure the absolute diameter, laser interferometry is the most promising method with nanometer resolutions and traceable measurement results. However, the 2π ambiguity range limits the measurement range. In this contribution, a chain of temporal synthetic wavelengths, generated by use of a frequency-tunable diode laser calibrated by an optical frequency comb, is used to measure the absolute diameter with an accuracy of 3 nm in air, where the fractional interference phase is measured by phase-shifting interferometry.

© 2013 IEEE