Linear Polarization Experiment Question

sirzerp

I'm a grad student and I got some recent results that I can't figure out. Thought I would post a question and see if I can get a quick answer.

I'm taking pictures of polarized system. Using a normal linear polarized filter that has a slip ring, so I take a picture, rotate the slip ring a few degrees and take another picture.

If I focus the camera on one of the interesting features of the system that I study, I get a dark band and bright band that cross each other. See attached figure. If I rotate the slip ring, the dark band and bright band rotate in lock step with the filter alignment.

My system has a lot of radial symmetry, so think this is the expected result.

Here's the rub, I focus on a different feature in the same system, everything else is the same and do the same actions. I still get a dark zone and bright zone that cross each other and a single frame looks very similar to my baseline.

Now, I rotate the slip ring a few degrees and take another picture. Everything looks the same but now the dark zone and bright zone has rotated the OPPOSITE DIRECTION between frames. If rotate the filter 9 degrees clockwise, my zones now rotate 9 degrees counter clockwise!

I think I understand linear polarization, circular, and elliptical polarizations.

What am I missing here? Can someone enlighten me? :)

Thanks in advance,

Sirzerp

Attached Thumbnails

 

Simon Bridge

You are missing an understanding of how those bands could form.
What is the system?

sirzerp

I was thinking of it as two zones of photons in phase and two zones of photons out of phase. Of course having the zones rotate in the wrong direction confused things a bit.

Through a process of elimination, my system must have some elliptical polarization(s) mixed in with random polarizations.

If I only observe the intensity of the frames, I get two brighter frames for 2 pi of filter rotation. I was thinking this was related to linear polarizations of the source but now I see that elliptical is the other possibility.

I'll get a circular polarization filter and confirm my findings.

Thanks for prompting me,

Sirzerp