# What is unpolarized monochromatic light?

by center o bass
Tags: light, monochromatic, unpolarized
 P: 339 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?
 Sci Advisor Thanks P: 1,754 It's the superposition of electromagnetic waves from uncorrelated (at least with respect to polarization) sources.
 P: 339 What do you mean by sources being uncorrelated with respect to polarization and what would be the consequence?
P: 1,781

## What is unpolarized monochromatic light?

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.
 P: 617 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.
 P: 786 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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