Characterization of Solar Telescope Polarization Properties Across the Visible and Near-Infrared Spectrum. Case Study: The Dunn Solar Telescope

TL;DR

This study provides a detailed multi-wavelength characterization of the Dunn Solar Telescope's polarization properties, improving calibration methods for current and future large-aperture solar telescopes.

Contribution

It introduces a more accurate telescope model for polarization characterization and explores novel calibration techniques using time-varied polarimeter data.

Findings

The proposed model better describes wavelength dependence of aluminum-coated mirrors.

Calibration data at different times of day can effectively characterize telescope properties.

Results align with entrance window polarizer measurements, aiding future telescope calibration.

Abstract

Accurate astrophysical polarimetry requires a proper characterization of the polarization properties of the telescope and instrumentation employed to obtain the observations. Determining the telescope and instrument Muller matrix is becoming increasingly difficult with the increase in aperture size of the new and upcoming solar telescopes. We have carried out a detailed multi-wavelength characterization of the Dunn Solar Telescope (DST) at the National Solar Observatory/Sacramento Peak as a case study and explore various possibilites for the determination of its polarimetric properties. We show that the telescope model proposed in this paper is more suitable than that in previous work in that it describes better the wavelength dependence of aluminum-coated mirrors. We explore the adequacy of the degrees of freedom allowed by the model using a novel mathematical formalism. Finally, we investigate the use of polarimeter calibration data taken at different times of the day to characterize the telescope and find that very valuable information on the telescope properties can be obtained in this manner. The results are also consistent with the entrance window polarizer measurements, opening very interesting possibilities for the calibration of future large-aperture solar telescopes such as the ATST or the EST.