Displacement uncertainty in interferometric radius measurements

Interferometric radius measurements may be completed using a radius bench, where radius is defined as the displacement between the confocal and cat's eye nulls (identified using a figure measuring interferometer). Measurements of a Zerodur sphere have been completed on the X-ray Optics Calibration interferometer (XCALIBIR) and a coordinate measuring machine. Larger recorded disagreements than indicated by the current uncertainty analysis call for an exploration of the analysis model. This paper details uncertainties associated with the use of multiple displacement measuring interferometers (DMIs) to record motion in a single axis by treating the specific case of displacement measurement on XCALIBIR using three DMIs equally spaced around the optical axis.