Polarization of light and diffuse/specular reflection

[SIM677]

How would polarized light behave after being reflected by a diffuse surface, such as a white wall? Would it still be completely polarized or would it be more randomly polarized? Would whatever effect takes place vary significantly with different diffuse materials?

What about a mirror? Surely that would reflect completely polarized light?

 

[Andy Resnick]

How would polarized light behave after being reflected by a diffuse surface, such as a white wall? Would it still be completely polarized or would it be more randomly polarized? Would whatever effect takes place vary significantly with different diffuse materials?

What about a mirror? Surely that would reflect completely polarized light?

As long as the light is reflecting (elastic scattering), the polarization state is maintained. However, the polarized di-directional reflectance distribution function (BRDF) can be very complicated- a simple case is a diffraction grating, it has different efficiencies for different polarization states.

Integrating spheres can depolarize light, but not always:
https://www.researchgate.net/publication/47510782_Depolarization_measurements_of_an_integrating_sphere
https://www.ncbi.nlm.nih.gov/pubmed/20577369

 

[SIM677]

Thanks Andy.
So that would mean that most common materials would reflect polarized light regardless of whether it's a diffuse or specular reflection? My knowledge of optics is fairly limited, so I just want to be clear on what you're saying.

As another hypothetical, what would you expect to happen if polarized light were passed through fog? Would it remain polarized and just be dimmed? Would the light reflected off of the fog itself still be polarized?

 

[Andy Resnick]

Thanks Andy.
So that would mean that most common materials would reflect polarized light regardless of whether it's a diffuse or specular reflection? My knowledge of optics is fairly limited, so I just want to be clear on what you're saying.

As another hypothetical, what would you expect to happen if polarized light were passed through fog? Would it remain polarized and just be dimmed? Would the light reflected off of the fog itself still be polarized?

The details can get complicated, but basically, the amount of polarization that is lost per reflection is a small non-zero number. So, if the light reflects/scatters many times, such as the case for propagation within an integrating sphere or through turbid media (for example, fog), the amount of polarization loss is much greater. Even so, polarization-sensitive imaging can be used to improve visibility of targets immersed in fog, smoke, or dirty water.

 

[DrDu]

Reflection can even completely polarise light, when it occurs at the Brewster angle.

 

[Andy Resnick]

Reflection can even completely polarise light, when it occurs at the Brewster angle.

Good point! But in the context of the OP, reflections off rough surfaces or multiple scattering through turbid media means that on average, the degree of polarization decreases.

 

[DrDu]

I was more referring to the reflection from a mirror part of the question. While a metallic mirror won't change polarisation, a dielectric mirror/ specular reflection will and might even transform a linear polarisation into a eliptic one or a circular polarisation into a linear polarisation.