Sphere diameter interferometry with nanometer uncertainty

Abstract

In this paper we present both the design details and uncertainty budget for a National Institute of Standards and Technology (NIST)-developed high-accuracy Fizeau-type interferometer specifically adapted to measurement sphere diameter. To do this, we provide some historic details of the instrument’s origins, an explanation of the clever accuracy-improving enhancements integrated into the design over the past several decades, and a detailed discussion of the role automation has played in achieving its current world-class accuracy. With utmost attention to the dominating components of a detailed uncertainty budget, we methodically improved a rather dated instrument design into a high-accuracy state-of-the-art system for sphere diameter measurement with an expanded uncertainty, U(k = 2), of less than ±10 nm for spheres with nominal diameters of between 0.4 mm and 26 mm. We conclude with a brief description of a novel application of this instrument for determining the phase-change upon reflection correction for both gauge blocks and gauge block platens. Applying corrections for phase-change upon reflection differences between different surfaces, gauge block and platen, is critically important for high-accuracy interferometric gauge block length measurements.