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Can Stokes parameters be obtained directly from polarization observations?

I'm developing the observational plan for a study of magnetic fields in a protostellar disk using a new polarimeter on our telescope. The theory papers always decompose light into Stokes I, Q, U, V, but the instrument manual talks about measuring intensity at different polarizer angles. I need to bridge this gap to ensure our data reduction pipeline is correct from the start.

 

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By Neetish Answered 8 months ago

This is a crucial step that defines data quality. You never measure a Stokes parameter directly; you always infer it from a set of intensity measurements. A standard method is to use a rotating half-wave plate (or a polarizer) in front of your detector. You measure the intensity at several specific orientation angles (e.g., 0°, 45°, 22.5°, 67.5°). From these discrete intensity values, you then solve for I, Q, and U. For circular polarization (V), you typically need a quarter-wave plate. I always recommend building a detailed optical model of your entire system using Jones matrices to account for instrumental polarization before you even go to the telescope.

 

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