Snapshot spectropolarimeter based on a six-fold separating prism operating from 360 nm to 1 µm

Abstract

We describe a new type of spectropolarimeter in which light is separated to simultaneously measure six spectra carrying polarimetric information on a 2D CMOS camera. The polarization separation along one of the camera axes was obtained using a novel prism, and the spectral dispersion along the other camera axis was obtained using an imaging spectrometer. An ideal version of the six-fold separating prism is first described, in which polarimetric separation is performed along the canonical polarization states used to define the Stokes vector, and it can be explained without any math. The real version is then presented, with math that is simple for those familiar with polarization. The operation of the spectropolarimeter is described. Experimental results show that the polarimetric accuracy is a few 10−3, and noise (mainly due to shot noise) is in the same range for a single acquisition. The spectral resolution depends on the entrance pinhole width and can be as low as 2 nm. Several examples are presented that feature how informative snapshots, high spectral resolution, spectropolarimetric measurements can be. The anticipated applications of this spectropolarimeter and, more broadly, for this novel polarization-separating prism are discussed. Technical details, such as the calibration procedure, noise levels, and consistency checks, are presented as supplementary material.