A Model-based Technique for Ad Hoc Correction of Instrumental Polarization in Solar Spectropolarimetry

TL;DR

This paper introduces a model-based method for correcting instrumental polarization in solar spectropolarimetry by accurately modeling optical effects and using physical constraints, improving correction accuracy over previous methods.

Contribution

It presents a novel approach that models the optical system's Mueller matrix as a combination of elliptical diattenuator and retarder, enabling precise correction of polarization cross-talk.

Findings

Accurately corrects polarization cross-talk in solar spectropolarimetry.

Conserves the physical magnitude of the Stokes vector.

Effective even with large polarization cross-talk.

Abstract

We present a new approach for correcting instrumental polarization by modeling the non-depolarizing effects of a complex series of optical elements to determine physically realizable Mueller matrices. Provided that the Mueller matrix of the optical system can be decomposed into a general elliptical diattenuator and general elliptical retarder, it is possible to model the cross-talk between both the polarized and unpolarized states of the Stokes vector and then use the acquired science observations to determine the best-fit free parameters. Here, we implement a minimization for solar spectropolarimetric measurements containing photospheric spectral lines sensitive to the Zeeman effect using physical constraints provided by polarized line and continuum formation. This model-based approach is able to provide an accurate correction even in the presence of large amounts of polarization cross-talk and conserves the physically meaningful magnitude of the Stokes vector, a significant improvement over previous ad hoc techniques.