Static spectropolarimeter concept adapted to space conditions and wide spectrum constraints

TL;DR

This paper introduces a static, wide-spectrum spectropolarimeter concept suitable for space applications, utilizing birefringent wedges for spatial polarization modulation, enabling single-shot full-Stokes measurements across UV to millimeter wavelengths.

Contribution

The paper presents an innovative static spectropolarimeter design that replaces temporal modulation with spatial modulation using birefringent wedges, suitable for space conditions and broad spectral ranges.

Findings

Theoretical modeling and simulations support the concept.

Laboratory validation confirms feasibility.

Application to the Arago mission demonstrates practical potential.

Abstract

The issues related to moving elements in space and instruments working in broader wavelength ranges lead to a need for robust polarimeters, efficient on a wide spectral domain, and adapted to space conditions. As part of the UVMag consortium, created to develop spectropolarimetric UV facilities in space, such as the Arago mission project, we present an innovative concept of static spectropolarimetry. We studied a static and polychromatic method for spectropolarimetry, applicable to stellar physics. Instead of modulating the polarization information temporally, as usually done in spectropolarimeters, the modulation is performed in a spatial direction, orthogonal to the spectral one. Thanks to the proportionality between phase retardance imposed by a birefringent material and its thickness, birefringent wedges can be used to create this spatial modulation. The light is then spectrally cross-dispersed, and a full-Stokes determination of the polarization over the whole spectrum can be obtained with a single-shot measurement. The use of Magnesium Fluoride wedges, for example, could lead to a compact, static polarimeter working at wavelengths from 0.115 mm up to 7 mm. We present the theory and simulations of this concept, as well as laboratory validation and a practical application to Arago.