A moir  fringe interpolator of high resolution

Abstract

A moire fringe interpolator capable of dividing one fringe into a thousand equal parts is described. Two photoelectric signals in phase quadrature are derived from the grating system and are applied to a sine-cosine potentiometer. The grating displacement is determined from the setting of the potentiometer at which its output vanishes. For displacements of 2 × 10-3 in. this system and a Fabry-Perot interferometer were found to agree to within ±5 × 10-7 in. r.m.s. A detailed description is given of possible sources of error and the means adopted to eliminate them.