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# Physics/Heat Radiation of Polarizing Filters

Question
Dear Sir,
a polarizing filter passes light of a specific polarization and blocks waves of other polarizations. Since such a polarizer absorbs radiation, it also has to emit heat radiation.
Is the heat radiation of a linear polarizer unpolarized or polarized light (and is the polarity of its radiation opposite of the polarity of light which it allows through)?
Which Kind of heat radiation will be generated from a circular polarizer?
Thanks very much!
Gerhard

Hello Gerhard,

There are several different types of polarizing filters. See the site:
http://en.wikipedia.org/wiki/Polarizer
Some accomplish the polarization by splitting the incoming light. The light to be eliminated from the beam may be deflected to the side or reflected back. In those cases (and others of the splitting type in the link) the deflected (or reflected) light is polarized opposite the passed light. But perhaps that case doesn't apply to the question since it's not heat radiation. So let's limit the discussion to the type discussed in the link's section titled "Absorptive polarizers".

These will warm up and therefore radiate heat. See this site:
Check out the 4th bullet in the section titled "Properties". I'm surprised to find that the radiated electromagnetic radiation, including heat radiated, will be polarized. However I haven't found information indicating the plane of the polarization. I would suspect that the plane would be the same as the passed light.

I would extend the principle of the above referenced 4th bullet to a circular polarizer and believe that the emitted radiation would be circularly polarized.

Optics is not my field. I had to research the subject to attempt an answer. Therefore, I suggest that you not accept this as gospel.

I hope this helps,
Steve
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Physics

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#### Steve Johnson

##### Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

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I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University