  The Advanced Space-based Solar Observatory (ASO-S) mission aims to explore
two most spectacular eruptions in the Sun: solar flares and coronal mass
ejections (CMEs), and their magnetism. For the studies of CMEs, the payload
Lyman-alpha Solar Telescope (LST) has been proposed. It includes a traditional
white-light coronagraph and a Lyman-alpha coronagraph which opens a new window
to CME observations. Polarization measurements taken by white-light
coronagraphs are crucial to derive fundamental physical parameters of CMEs. To
make such measurements, there are two options of Stokes polarimeter which have
been used by existing white-light coronagraphs for space missions. One uses a
single or triple linear polarizers, the other involves both a half-wave plate
and a linear polarizer. We find that the former option subjects to less
uncertainty in the derived Stokes vector propagated from detector noise. The
latter option involves two plates which are prone to internal reflections and
may have a reduced transmission factor. Therefore, the former option is adopted
as our Stokes polarimeter scheme for LST. Based on the parameters of the
intended linear polarizer(s) colorPol provided by CODIXX and the half-wave
plate 2-APW-L2-012C by Altechna, it is further shown that the imperfect maximum
transmittance of the polarizer significantly increases the variance
amplification of Stokes vector by at least about 50% when compared with the
ideal case. The relative errors of Stokes vector caused by the imperfection of
colorPol polarizer and the uncertainty due to the polarizer assembling in the
telescope are estimated to be about 5%. Among the considered parameters, we
find that the dominant error comes from the uncertainty in the maximum
transmittance of the polarizer.
