Polarization of light and diffuse/specular reflection

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Discussion Overview

The discussion centers on the behavior of polarized light when reflected from various surfaces, specifically diffuse surfaces like white walls and specular surfaces like mirrors. Participants explore how different materials and reflection types affect the polarization state of light, including implications for practical scenarios such as light passing through fog.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question whether polarized light remains completely polarized after reflecting off diffuse surfaces, suggesting it may become more randomly polarized depending on the material.
  • Others propose that most common materials reflect polarized light, regardless of whether the reflection is diffuse or specular.
  • A participant mentions that the polarized bidirectional reflectance distribution function (BRDF) can be complex, with different efficiencies for different polarization states.
  • There is a hypothesis about the behavior of polarized light passing through fog, with questions about whether it remains polarized and how reflections off fog would behave.
  • Some participants note that reflection at the Brewster angle can completely polarize light.
  • Concerns are raised that reflections from rough surfaces or multiple scattering through turbid media generally decrease the degree of polarization.
  • A distinction is made between metallic mirrors, which do not change polarization, and dielectric mirrors, which may alter the polarization state, potentially transforming linear polarization into elliptical or circular polarization into linear polarization.

Areas of Agreement / Disagreement

Participants express differing views on how polarized light behaves after reflection, particularly regarding diffuse versus specular surfaces. There is no consensus on the extent to which polarization is maintained or altered in various scenarios.

Contextual Notes

The discussion highlights complexities such as the effects of multiple reflections, the specific characteristics of different materials, and the conditions under which polarization is preserved or lost. Limitations in participants' knowledge of optics are acknowledged, which may influence their interpretations.

Who May Find This Useful

This discussion may be of interest to those studying optics, materials science, or anyone exploring the properties of light and its interactions with different surfaces.

SIM677
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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?
 
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SIM677 said:
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
 
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?
 
SIM677 said:
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.
 
Reflection can even completely polarise light, when it occurs at the Brewster angle.
 
DrDu said:
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.
 
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.
 

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