Spectropolarimetry is a versatile technique that allows an observer to measure both the spectrum of an object and the polarization of each point on that spectrum. Spectropolarimeters, like other...Show moreSpectropolarimetry is a versatile technique that allows an observer to measure both the spectrum of an object and the polarization of each point on that spectrum. Spectropolarimeters, like other spectrographs, generally use a slit to restrict their field of view to a line. However, slits have a long history of polarizing the light they transmit. Although multiple theories exist, and the polarizing behavior of slits near wavelength-scale is experimentally well-tested, the polarizing behavior of the generally wider spectrographic slits is less well-known and well-tested. We present a first step towards a new general model of the polarizing effects of slits based on waveguide theory and the eigenmode expansion that already shows the general expected behavior; linear polarization perpendicular to the slit’s long axis, as well as retardation effects with a similar perpendicular fast axis. Additionally, we tried to experimentally test the model’s predictions, but our setup proved insufficient. This was due to systematic errors, which could be removed using a different method, for which we provide suggestions.Show less
