Development of speckle shearing interferometer error analysis as an aperture function of wavefront divergence

Increasing the confidence in whole-field speckle-based optical metrology transducers requires a detailed understanding of the error sources of the respective instruments. The analysis of error contributions to the optical phase output of a Michelson-based speckle shearing interferometer have been modelled. Specific attention has been paid to the effect of the aperture at the image plane, with respect to collimated and non-collimated object illumination. This modelling presents an advance on a previous modelled analytical relationship, which includes partial displacement derivative terms and components as a function of illumination geometries and, importantly, aperture effects. The work has identified a phase error contribution due to the aperture function of between 0.15% and 1.48%, dependent on the object distance, when considering a planar object undergoing predominantly surface to normal deformation.