Precision in ground based solar polarimetry: Simulating the role of adaptive optics

TL;DR

This paper uses numerical simulations to analyze how adaptive optics influence polarization measurement accuracy in ground-based solar observations, revealing that higher order corrections improve signal quality but do not reduce cross-talk caused by atmospheric turbulence.

Contribution

The study demonstrates through simulations that higher order adaptive optics corrections do not decrease seeing-induced polarization cross-talk, but do enhance signal-to-noise ratio.

Findings

Cross-talk is independent of the degree of AO correction.

Higher order AO improves the signal-to-noise ratio.

Atmospheric turbulence remains a key challenge for polarization accuracy.

Abstract

Accurate measurement of polarization in spectral lines is important for the reliable inference of magnetic fields on the Sun. For ground based observations, polarimetric precision is severely limited by the presence of Earth's atmosphere. Atmospheric turbulence (seeing) produces signal fluctuations which combined with the non-simultaneous nature of the measurement process cause intermixing of the Stokes parameters known as seeing induced polarization cross-talk. Previous analysis of this effect (Judge et al., 2004) suggests that cross-talk is reduced not only with increase in modulation frequency but also by compensating the seeing induced image aberrations by an Adaptive Optics (AO) system. However, in those studies the effect of higher order image aberrations than those corrected by the AO system was not taken into account. We present in this paper an analysis of seeing induced cross-talk in the presence of higher order image aberrations through numerical simulation. In this analysis we find that the amount of cross-talk among Stokes parameters is practically independent of the degree of image aberration corrected by an AO system. However, higher order AO corrections increase the signal-to-noise ratio by reducing the seeing caused image smearing.