AOTF based spectro-polarimeter for observing Earth as an Exoplanet

TL;DR

This paper presents the design and calibration of an AOTF-based spectro-polarimeter for observing Earth's spectro-polarimetric signatures, aiming to simulate exoplanet observations and optimize instrument performance for lunar orbit deployment.

Contribution

It introduces a novel AOTF-based spectro-polarimeter design, including calibration results and simulation-based optimization for Earth observation in exoplanet-like conditions.

Findings

Achieves <0.3% polarimetric accuracy for linear polarization

Demonstrates feasibility of Earth observation from lunar orbit

Provides calibration and simulation data for instrument optimization

Abstract

Earth is the only known habitable planet and it serves as a testbed to benchmark the observations of temperate and more Earth-like exoplanets. It is required to observe the disc-integrated signatures of Earth for a large range of phase angles, resembling the observations of an exoplanet. In this work, an AOTF (Acousto-Optic Tunable Filter) based experiment is designed to observe the spectro-polarimetric signatures of Earth. The results of spectroscopic and polarimetric laboratory calibration are presented here along with a brief overview of a possible instrument configuration. Based on the results of the spectro-polarimetric calibration, simulations are carried out to optimize the instrument design for the expected signal levels for various observing conditions. The usefulness of an AOTF based spectro-polarimeter is established from this study and it is found that, in the present configuration, the instrument can achieve a polarimetric accuracy of $<0.3$\% for linear polarization for an integration time of 100 ms or larger. The design configuration of the instrument and the planning of conducting such observations from Lunar orbit are discussed.