Sub-nanometre displacements calibration using X-ray interferometry

Abstract

The technology of X-ray interferometry has been applied to the calibration of micro displacement transducers at sub-nanometre levels. Using the lattice spacing of high perfection silicon of semiconductor industry grade as a reference, the system provides a portable, absolute length standard with an accuracy of 1 part in 10⁶ traceable to primary standards, a demonstrated resolution of 10 picometres and a double-beam phase-quadrature output for providing sensitivity to the direction of motion of the moving interferometer blade. The system and its performance are discussed in detail, methodologies for the analysis of data are presented and an application to the calibration of Talystep transducers (both absolute and comparative between models) for overall accuracy and thermal drift is reported. The design and performance of a portable instrument using a miniature X-ray source is also reported.