Gauge block measurements with nanometre uncertainty

Abstract

A fringe-pattern analysing interferometer with a resolution of 1 × 10-9, stablility of readings of about 0.1 nm, and an uncertainty owing to optical effects of less than 1 nm, has been used to study some systematic effects in gauge block length measurements. Measurements on steel and quartz plates with sub-nanometre reproducibility are reported. An accuracy of about 1 nm is demonstrated for a combination of reproducible wringing and slave-block techniques. The limitations of the present definition of the length of a gauge block are highlighted. A double-sided method for length measurement of gauge blocks has been realized, the results of which are not affected by excessive thickness of the wringing film and which incorporate a correction on the interferometer optics.