Calibration of displacement sensors up to 300 mu m with nanometre accuracyand direct traceability to a primary standard of length

A new class of sensor has recently appeared: nanometre sensors. These senso rs are characterized by nanometre or sub-nanometre resolution and an uncert ainty of a few nanometres over a range of at least several micrometres. Ins truments such as capacitive or inductive sensors, laser interferometers, ho lographic scales, and scanning probe microscopes belong to the class of nan ometre sensors. Linearity errors and drift in the mechanical and electronic system limit the accuracy of all these sensors. In order to determine thes e errors in a traceable way, the instrumentation described in this paper wa s developed. The heart of the system consists of a Fabry-Perot cavity. One mirror of this cavity generates the required displacement. A so-called slav e laser is stabilized to the cavity length. The frequency of this slave las er is compared with the frequency of a primary length standard. In this way the displacement is measured with a resolution of a few picometres, a rang e of 300 mu m and an uncertainty of about 1 nm. Experiments confirm the per formance of this instrument and show typical deviations of the probe system s investigated.