Simultaneous multi-wavelength polarimetry without spectral splitting: proof of concept of a single channel dual-wavelength polarimeter

Spectro-polarimeters in solar astronomy usually require splitting different wavebands into separate monochromatic arms that operate as independent sub-instruments. We demonstrate a concept for a polarimeter that operates at two wavebands simultaneously, using a single channel of optical components and a single detector. By using chromatic zero-order waveplates, polarized light propagates differently through the instrument depending on its wavelength, allowing to measure the polarization in both wavebands simultaneously. We present Stokes vectors measurements with ∼ 1% relative error using standard off-the-shelf components, thus demonstrating the relevance of this concept for fields like solar astronomy and space instrumentation.