Astropolarimetry with a polarization-holographic imaging Stokes polarimeter

Abstract

We present an innovative imaging Stokes polarimeter. The main unit of the polarimeter is an integral polarization-holographic diffraction element, which enables the instant complete analysis of the polarization state of light in real time. An element is recorded by a special holographic schema using circularly and linearly polarized beams. As a result, it decomposes an incoming light into orthogonal circular and linear diffraction orders. We then capture diffraction orders using a CCD and transform the measured intensities into the Stokes images through the calibration parameters. The Stokes images are used to determine polarization state of a point or an extended space object in different spectral ranges. The operating spectral range of the polarimeter is 500 to 1600 nm with diffraction efficiency equal to 50% at 532 nm, 30% at 635 nm, and 5% at 1550 nm. The theoretical model of relations between measured intensities in different diffraction orders and Stokes parameters was used to calibrate the polarimeter. The calibration observations of day time sky show that the resulting errors are near of 10 − 3 order.