The Galway Astronomical Stokes Polarimeter: An All-Stokes Optical Polarimeter with Ultra-High Time Resolution

TL;DR

The Galway Astronomical Stokes Polarimeter (GASP) enables high-time-resolution, all-Stokes polarimetric observations of astronomical sources, overcoming previous limitations to observe a broader range of objects and polarization components.

Contribution

GASP is a novel all-Stokes polarimeter with microsecond time resolution, capable of measuring all polarization components simultaneously over a broad wavelength range.

Findings

GASP can measure Stokes parameters to <1% accuracy under poor atmospheric conditions.

The instrument operates effectively over 400-800nm wavelength range.

Preliminary observations demonstrate GASP's capability for high-precision polarimetry.

Abstract

Many astronomical objects emit polarised light, which can give information both about their source mechanisms, and about (scattering) geometry in their source regions. To date (mostly) only the linearly polarised components of the emission have been observed in stellar sources. Observations have been constrained because of instrumental considerations to periods of excellent observing conditions, and to steady, slowly or periodically-varying sources. This leaves a whole range of interesting objects beyond the range of observation at present. The Galway Astronomical Stokes Polarimeter (GASP) has been developed to enable us to make observations on these very sources. GASP measures the four components of the Stokes Vector simultaneously over a broad wavelength range 400-800nm., with a time resolution of order microseconds given suitable detectors and a bright source - this is possible because the optical design contains no moving or modulating components. The initial design of GASP is presented and we include some preliminary observational results demonstrating that components of the Stokes vector can be measured to <1% in conditions of poor atmospheric stability. Issues of efficiency and stability are addressed. An analysis of suitable astronomical targets, demanding the unique properties of GASP, is also presented.