Kirchoff's radiative balance law and polarisation of emitted light

In summary, the light reflected to me from a surface is polarised (Fresnel), but the light emitted from the surface is not. This is due to the conservation of energy law which states that energy cannot be destroyed, only transferred.
  • #1
Mark.R
3
0
I'm looking at a surface at an angle. Light reflected to me is polarised (Fresnel), does this mean light emitted to me from the surface is also polarised?

I've been told that ocean emission is polarised (when looking at an angle) because of Kirchoff's law of radiative balance (emissivity = absorptivity = 1 - transmission - reflection). They've told me that since reflection is polarised at that angle, absorption must be polarised and therefore emission is too.

But I don't see why it has to be and physically I don't see where it comes from. The only possible source I can see is something to do with the angle of observation. Can anyone help me?
 
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  • #4
Usually, both polarisations are not transmitted and reflected in the same way at a plane interface.
Therefore, the reflected light has a different polarisation mix than the incident light.

This is completely described by the Fresnel laws.
The Fresnel laws are a consequence of the Maxwell equations.

On wikipedia you can read the Fresnel laws in detail.

http://en.wikipedia.org/wiki/Fresnel_equations

There is a special angle of incidence, called the Brewster angle, where one polarisation (E field in the incidence plane) is not reflected at all. In this case, the reflected light has a perfect linear polarisation, perpendicular to the incidence plane.
See there for the details:

http://en.wikipedia.org/wiki/Brewster's_angle

The Brewster angle is a consequence of the Fresnel laws.
The Fresnel laws are a consequence of the Maxwell's equations.
The Maxwell's equations are the law of electromagnetism.
 
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  • #5
Mark.R said:
I'm looking at a surface at an angle. Light reflected to me is polarised (Fresnel), does this mean light emitted to me from the surface is also polarised?

I've been told that ocean emission is polarised (when looking at an angle) because of Kirchoff's law of radiative balance (emissivity = absorptivity = 1 - transmission - reflection). They've told me that since reflection is polarised at that angle, absorption must be polarised and therefore emission is too.

But I don't see why it has to be and physically I don't see where it comes from. The only possible source I can see is something to do with the angle of observation. Can anyone help me?

The emitted light may have a non-zero degree of polarization:

http://www.opticsinfobase.org/abstract.cfm?URI=ao-38-8-1384

Kirchoff's law is simply conservation of energy.
 
  • #6
Thanks for the replies.

I'd already checked wiki and I can derive and apply the Fresnel equations (which is how I know reflected stuff can be polarised!) I think I didn't explain my question properly, but Andy has provided exactly the sort of derivation I'm looking for. Thanks Andy!
 

1. What is Kirchoff's radiative balance law?

Kirchoff's radiative balance law, also known as Kirchoff's law of thermal radiation, states that at thermal equilibrium, the ratio of the emissive power to the absorptivity of any material is constant at a given temperature and wavelength.

2. How does Kirchoff's radiative balance law relate to the polarization of emitted light?

Kirchoff's radiative balance law does not directly relate to the polarization of emitted light. However, it does explain the behavior of polarized light when interacting with a material. According to the law, the absorptivity and emissive power of a material are dependent on its physical properties, such as its structure and composition, which can affect the polarization of light passing through it.

3. Can Kirchoff's radiative balance law be applied to all materials?

Yes, Kirchoff's law applies to all materials, regardless of their composition or physical properties. However, it is most commonly used to study the behavior of electromagnetic radiation in thermal equilibrium with solid, liquid, or gaseous materials.

4. How is Kirchoff's radiative balance law used in scientific research?

Kirchoff's law is widely used in scientific research, particularly in the fields of thermodynamics, optics, and astronomy. It helps scientists understand the behavior of thermal radiation and its interaction with different materials. It is also used to develop models and equations that can predict the behavior of light in various environments.

5. Are there any limitations to Kirchoff's radiative balance law?

While Kirchoff's law is a fundamental principle in thermal radiation, it has some limitations. For instance, it assumes that the material is in thermal equilibrium, which may not always be the case in real-world scenarios. It also does not account for some complex interactions, such as multiple reflections and scattering, which can affect the polarization of light.

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