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Traceability of sub-nm length measurements

Traceability can be a property of a measurement result, which is said to be traceable if the measured quantity can be traced back to a primary measurement standard through a chain of calibrations. Such primary standards for various quantities are usually provided by national metrology institutes (NMI).

Length measurements are traced back to the unit metre, which in turn is defined by the speed of light in vacuum c and the unit second: "The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second".

A Nanometre (nm) is the 1 / billion (10-9) part of a metre. Sub-nm means even smaller than 1 nm. The need for improved accuracy in this range is already there or on the horizon for certain applications in metrology and industry.

This EMRP project aims to improve the traceability of laser interferometers and capacitive sensors, which are the most widely used measurement devices to measure lengths or displacements with utmost precision and accuracy today. The starting point is to develop a better understanding of the underlying effects which limit the accuracy and to develop and to validate theoretical models in order to calculate corrections to reduce measurement uncertainty.