Polarimeter

The Polarimeters are mounted at the direct Gregorian mounts in place of the MODS. The polarimeters are only available in specific pre-scheduled blocks. Spectropolarimetry is not permanently available.

Two science modes are currently implemented. Firstly, all Stokes parameters are taken consecutively with both telescopes simultaneously. In this mode, SX and DX give a combined 11.8 aperture. Secondly, circular Stokes V polarization on SX and linear Stokes QU on DX simultaneously (each with an 8.4 m aperture). With this method, it takes 2 spectra for Stokes V and 4 for Stokes QU.

Circular Polarization is measured by inserting a retarder in front of a Foster prism located in each beam. Linear polarization is measured by removing the retarders. This means that there is no cross-talk between measured circular and linear polarization.

In polarization mode, all four fibers (target and sky) will simultaneously direct two ordinary and two extraordinary light beams to the spectrograph.