New method for interferometric measurement of gauge blocks without wringing onto a platen

A new method, using a novel double-ended interferometer, is described for the highly efficient calibration of gauge blocks. Unlike the conventional Kosters interferometric method, the new method does not require wringing of the gauge block onto an auxiliary platen. Although the gauge block length defined by International Standard 3650 (Gauge blocks) can be obtained using the Kosters method, the wringing operation is a laborious process, which requires skill, sometimes causes contact errors and decreases measuring efficiency, and prevents a fully automated measuring operation. The new interferometer can also be used as a conventional Kosters interferometer by changing some of the optical systems. Thus, after preliminary investigations measuring some samples using the Kosters method, we can determine an accurate correction value, dependent on the phase shift of light at the reflecting surface, to obtain the gauge block length defined by ISO 3650. The results, obtained from experimental work and theoretical analysis, show that the combined standard uncertainty of a gauge block length up to 100 mm is less than 16 nm, and this value is nearly the same as that obtained by the conventional Kosters method.