Monday

The Galway Astronomical Stokes Polarimeter (GASP) is a high-time resolution astronomical polarimeter working on the principle of division of amplitude polarimetry (DOAP) to measure the full Stokes parameters using differential photometry. The GASP instrument uses a retarding beam-splitting prism to split the incoming light from a telescope into two optical channels, these two optical channels are then split into their orthogonally polarised components resulting in four images, which are imaged simultaneously on two electron-multiplying charge-coupled devices (EMCCDs).

The GASP instrument uses a Polarisation State Generator (PSG) and the eigenvalue calibration method (ECM) to determine the Mueller matrix of the instrument. In this sense it is a complete Mueller Matrix Ellipsometer (MME) as the system is self-consistent and can unambiguously determine the optical characteristics of all of the elements contained in the system without any first-order approximations.

We will present an overview of the challenges facing high-time resolution polarimetry with respect to the calibration and characterisation methods used and the resultant accuracy of an independently calibrating imaging polarimeter with reference to measurements taken of polarimetric standards. As the GASP instrument is a full Stokes polarimeter, a concern for the future is the development of a catalogue of circularly polarised standard stars.