# Does a retroreflector depolarize light or preserve polarisation?

In case the retroreflector is just a glas window, the Fresnel equations apply and for an incidence angle of $$\theta = 0^\circ$$ the reflectivities $$R_p$$ and $$R_s$$ for parallel and perpendicular polarized light are the same (about 4%), thus the polarisation of incoming light is preserved, correct?

From the answer in Polarization and mirrors I learned that a (perfect) mirror would preserve polarisation as well.

But what about corner reflectors? Or cat's eyes on bicycles and retroreflectors on clothes like sailor jackets, life vests, working clothes etc. (no idea how these retroreflectors work at all...)?

And how is all this in case of circular polarisation instead of linear polarisation?

• The example is RF, so the "mirror" is metal $\sigma = \infty$. Still the polarization is not preserved by one reflection unless the ray is perpendicular to the surface or the the ray is parallel with the surface normal. For oblique incidence the reflected ray is not parallel with the incident so its polarization must also rotate to be orthogonal to the ray. For reflection off a dielectric interface the polarization will be similarly affected with the proviso that there is also a refracted ray that can suffer multiple internal reflections and when it finally comes out – hyportnex May 14 at 18:05