Misalignment error analysis in polychromatic division of focal plane Stokes polarimeters

Abstract

Snapshot imaging polarimeters are used in many different areas. Recently, division of focal plane (DoFP) polarimeters have proved useful as snapshot polarimeters for dynamic applications. For an optimal performance of polarimeters, different works dealing with the error analysis of such devices are proposed in literature. In terms of noise amplification from intensity measurements to the final polarization calculations, well-established quality metrics, as in the condition number or the equally weighted variance criteria, are used. Other studies analyze systematic errors due to deviations in the construction parameters. However, something not considered so far is the effect produced by misalignment between the various pixelated masks over the pixelated structure of the camera sensor, always occurring in experimental implementations of DoFPs. In this work, we study the effect of such misalignments in DoFP polarimeters and demonstrate how they lead to polarimetric systems composed of partially depolarized analyzers. We calculate the combined degree of polarization related to different amounts of misalignment and analyze the corresponding system performance. From this study, we show how an imaging polarimeter based on partially polarized analyzers can still lead to a robust and accurate polarimetric performance, and we also provide the misalignment limits in which an acceptable performance is obtained. We evaluate both the monochromatic and the polychromatic cases with special focus on the latter.