Alignment and retardance errors, and compensation of a channeled spectropolarimeter

A channeled spectropolarimeter's alignment and retardance errors are theoretically analyzed. The channels of Stokes parameters are mixed by the alignment and retardance errors, and a mathematical basis for selecting optimal channels to reconstruct full Stokes parameters is provided. The reconstructed Stokes spectra would be distorted by the alignment errors. Quantifying the alignment errors as well as eliminating the retardance terms can be achieved by using two polarized reference beams sequentially. A general compensation procedure is proposed to account for the alignment errors, which also considers the potential misalignment in the two polarized reference beams. An analytical treatment is given, followed by a numerical example to demonstrate the effectiveness of this method.