Electro-optical polarimeters for ground-based and space-based observations of the solar K-corona
2012
Polarimeters based on electro-optically tunable liquid crystals (LC) represent a new technology in the field of
observational astrophysics. LC-based polarimeters are good candidates for replacing mechanically rotating polarimeters
in most ground-based and space-based applications. During the 2006 total solar eclipse, we measured the visible-light
polarized brightness (pB) of the solar K-corona with a LC-based polarimeter and imager (E-KPol). In this presentation,
we describe the results obtained with the E-KPol, and we evaluate its performances in view of using a similar device for
the pB imaging of the K-corona from space-based coronagraphs. Specifically, a broad-band LC polarimeter is planned
for the METIS (Multi Element Telescope for Imaging and Spectroscopy) coronagraph for the Solar Orbiter mission to
be launched in 2017. The METIS science driver of deriving the coronal electron density from pB images requires an
accuracy of better than 1% in the measurement of linear polarization. We present the implications of this requirement on
the METIS design to minimize the instrumental polarization of the broad-band visible-light (590-650 nm) polarimeter
and of the other optics in the METIS visible-light path. Finally, we report preliminary ellipsometric measurements of the
optical components of the METIS visible-light path.
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