SQUIDPOL: Seoul National University QUadruple Imaging Device for POLarimetry

TL;DR

SQUIDPOL is an affordable, multi-channel optical polarimeter that accurately measures linear polarization simultaneously, with a correction scheme for systematics, validated on-sky for bright stars, mounted on a 60-cm telescope.

Contribution

We introduce SQUIDPOL, a novel low-cost imaging polarimeter with a correction method for polarization systematics, enabling reliable polarization measurements.

Findings

Achieved 0.15% polarization accuracy on bright standard stars.

Demonstrated stable, reproducible on-sky performance.

Validated correction scheme for polarization-dependent systematics.

Abstract

We present SQUIDPOL, a low-cost, multi-channel optical imaging polarimeter that performs simultaneous linear polarization measurements using a rotating half-wave plate, a non-polarizing beam splitter, and four wire-grid filters. We show that the off-the-shelf non-polarizing beam splitter introduces measurable polarization-dependent systematics, which can bias polarimetric measurements if left uncorrected. We quantify this effect for both transmitted and reflected beams and incorporate a correction scheme into the data-analysis pipeline. On-sky validation demonstrates stable and reproducible performance, achieving a polarization accuracy of about 0.15 percent for bright polarized standard stars. Mounted on the 60-cm Ritchey-Chretien telescope (focal length 4200 mm, f/7) at the Pyeongchang Observatory of Seoul National University, SQUIDPOL provides an effective common field of view of 13.5 by 8.2 arcminutes with a pixel scale of 0.45 arcseconds per pixel and supports standard B, V, R_C, and I_C filters.