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It seems clear that a photon stream as well as single photons behind a well designed slit - the right slit width for a given wavelength - are polarized. Means, the electric fields of such photons are aligned. What are the theoretical explanations and was this proofed by experiments?

HolgerFiedler
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2 Answers2

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The simplest answer to this is based on Huygens principle Check the wikipedia link here. According to this principle each wavefront after the slit is made up of small wavelets, each emitted from the wavefront before the slit (see figure).

enter image description here

These wavelets inherit all the properties of the wavefront before the slit, that among them is polarization.

I am not sure if a specific experiment is done to prove this.

Amin
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    Please think about a polarizer foil, this is nothing else than a lot of slits or pairs of double slits. This is the proof, that behind every slit as well as behind every edge the involved photons (those, who are close enough to the edges to interact with them) are polarized. – HolgerFiedler Dec 05 '15 at 09:01
  • Huygens analogy from water waves to light has included a unnoticed difference between the behavior of this to phenomenons. Water waves are polarized in front of the wall and this is a condition to see the dispersion behind edges. Light has to be point like and monochromatic for the best results to get fringes, but their polarization in front of the slit is not necessary. So your statement " wavelets inherit all the properties of the wavefront before the slit, that among them is polarization" is not logical. – HolgerFiedler Dec 05 '15 at 09:10
  • BTW, another difference is, that the wavefront of water waves does not stand still, the min and max points in the sketch are not showing, that they are moving all the time (https://en.wikipedia.org/wiki/Interference_%28wave_propagation%29#/media/File:Two_sources_interference.gif). That is not the case for the intensity distribution behind edges, they stand still. – HolgerFiedler Dec 05 '15 at 09:15
  • I did not speak of water. Huygens principle is valid for optical waves as well. And polarization of water waves is a new thing that I never heard of. About your first comment I am not sure if you are answering your own question or not. :-) – Amin Dec 05 '15 at 09:17
  • The last part of my answer was not correct (you are right, with unpolarized light, like the normal room light, you can have the fringes). Sorry! – Amin Dec 05 '15 at 09:20
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As John Rennier wrote in his answer to the question about Why does the electric field dominate in light?

"The reason we tend to concentrate on the electric field (of the light) is that it interacts strongly with charges, e.g. electrons, and there are a lot of electrons around."

More in detail anna v according to Wikipedia pointed out, that

"A wire-grid polarizer converts an unpolarized beam into one with a single linear polarization."

So yes, photons which are influenced by sharp edges are polarised. And the reason for this phenomenon is the interaction between the electric field component of the photon and the surface electrons of the edge.

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HolgerFiedler
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  • by definition, a polarizer is a spin-filter, see the 1/2 coeff that appears in the Malus law for a randow flow –  Dec 30 '15 at 06:38
  • @igael I would say, that a polarizer influences the orientation of the electric field component of a photon. Your comment is to cryptic to me, to get the message. Please describe in more details your point. – HolgerFiedler Dec 30 '15 at 07:43
  • a polarizer doesn't convert a polarization in another one. It stops the bad orientations in regard of its angle and orientation. Polarifilter would be a better name for the device. I'm very interested by your idea of polarizer = many double slits. Do you please have a reference ? –  Dec 30 '15 at 08:46
  • @igael Crossed polarizers: no light goes through (for some range of wavelengths of course). Third polarizer under 45° between them: light goes through. How to explain this without rotation of the electric field component of the light? – HolgerFiedler Dec 30 '15 at 09:40
  • it's matter of QM states basis and of the cos law. Read the Ernie and Floris answers here. –  Dec 30 '15 at 17:18