Static spectropolarimeter concept adapted to space conditions and wide spectrum constraints

Issues related to moving elements in space and instruments working in broader wavelength ranges lead to the need for robust polarimeters that are efficient on a wide spectral domain and adaptable to space conditions. As part of the UVMag consortium, which was 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, which is applicable to stellar physics. Instead of temporally modulating the polarization information, as is 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 up to 7 μm. We present the theory and simulations of this concept as well as laboratory validation and a practical application to Arago.