What is unpolarized monochromatic light?

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Discussion Overview

The discussion revolves around the concept of unpolarized monochromatic light, exploring its definition, characteristics, and implications in the context of polarization. Participants examine the nature of unpolarized light, its relationship with polarization states, and the conditions under which it can be considered monochromatic.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants suggest that the most general case for monochromatic light is elliptically polarized light, questioning whether unpolarized monochromatic light could be considered elliptically or circularly polarized.
  • One participant defines unpolarized light as the superposition of electromagnetic waves from uncorrelated sources with respect to polarization.
  • Another participant seeks clarification on what is meant by sources being uncorrelated with respect to polarization and the consequences of this condition.
  • It is proposed that unpolarized light means randomly polarized light, and that sending it through any polarizer results in half of the light passing through, unlike light with a fixed polarization.
  • A viewpoint is presented that unpolarized light can be conceptualized as the non-coherent addition of two monochromatic waves with horizontal and vertical polarizations, respectively, with a random phase difference.
  • One participant argues that a perfectly monochromatic beam cannot be unpolarized, as a plane wave has a definite polarization, and that true unpolarization implies a spread in frequency or direction.

Areas of Agreement / Disagreement

Participants express differing views on the definition and characteristics of unpolarized monochromatic light, with no consensus reached on whether it can exist as a perfectly monochromatic state or how to accurately describe its nature.

Contextual Notes

There are unresolved questions regarding the definitions of polarization states, the implications of coherence, and the conditions under which light can be considered unpolarized while still being monochromatic.

center o bass
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I've gotten the impression that the most general case for monochromatic light is elliptically polarized light. But what do one mean when one states that some kind of light is unpolarized monochromatic light? Does one mean that it is elliptically polarized?
Or is circularly polarized light the more reasonable canidate?
 
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It's the superposition of electromagnetic waves from uncorrelated (at least with respect to polarization) sources.
 
What do you mean by sources being uncorrelated with respect to polarization and what would be the consequence?
 
Unpolarized light means randomly polarized.

If you send unpolarized light through any polarizer (linear, circular, elliptical, etc) then half will go through. This would not be the case for any particular fixed polarization.
 
You can think of it as one monochromatic wave with a horizontal polarization and traveling in the z direction added non-coherently to another monochromatic wave with a vertical polarization traveling in the z direction. Non-coherently in this case means that there is a random phase difference between the waves.
 
A monochromatic beam is a plane wave and a plane wave has definite polarization. Add two monochromatic beams together, you get another monochromatic beam, so you cannot have a perfectly monochromatic beam that is unpolarized. There has to be some (small) spread in frequency or direction, or both. When an atom emits light, it does not emit a monochromatic beam. There is a spread in frequency and direction. When you add these waves up, their phases are random and you get an approximately monochromatic beam with random phase angles, which is called unpolarized.
 

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