Stokes Polarimetry of a Polarized Standard Star

[Jashcraf]

Back when I was at SCExAO we had worked on a project to install a pupil-viewing lens on the bench. With the VAMPIRES upgrade that came to fruition! Now we can take images like this:

(Left) VCAM1, (Middle) VCAM2, (Right) Difference.

The idea with this kind of hardware upgrade was to be able to do stokes polarimetry on distant targets. If we can measure the polarization state across the pupil, we might be able to determine the presence of polarization aberrations.

We got some data of a polarized standard star, and took images from VCAM1 and VCAM2 at different HWP cycles. We can then apply single-differencing to determine the Stokes parameters.

Single-Difference VCAM1

Single-Difference VCAM2

Double-Difference

So we are seeing some ~% level effects. Need to ping Rebecca about the calibrated Mueller Matrix to go forward.

[Jashcraf]

Note that the same analysis was applied to single difference 1 and 2, so the stokes parameters are rotated by 90 degrees probably

[Jashcraf]

Note also that part of the processing pipeline involves a low-pass filter to get rid of the speckly stuff from the AO residuals, and the fact that we are a little out of focus

[Jashcraf]

This is what happens to the double-difference if you don't really low-pass filter them