# Can polarized light be unpolarized again?

I was just wondering if there could be a process that could unpolarize polarazied light. Is that possible?

Sure. Un-polarized light is just a superposition of many polarizations. Even if you are in vacuum you can use some beam splitters in cascade to obtain many rays, change (rotate) the polarization of each one in a different way, and then recombine the beam.

• That raises an interesting question. How many beams do you need? Is two enough? If I combine two beams with orthogonal polarization and equal intensity can I distinguish it from a randomly polarized beam? – George Herold Dec 19 '14 at 17:32
• @GeorgeHerold And, as a related and perhaps more practical question, could I use this property to transmit multiple signals at once through a fiber optic cable? – Ajedi32 Dec 19 '14 at 19:44
• @Ajedi32, I think most fibers scramble the polarization state of the light... there is special fiber. en.wikipedia.org/wiki/Polarization-maintaining_optical_fiber – George Herold Dec 19 '14 at 19:56
• @GeorgeHerold I suspect that if you use an ideal beam and split it in only two, the recombined one will be diagonal polarized or circular (elliptical) polarized according to the phase difference of the two paths. This will probably be eased if the incoming light has some incoherency/chromatics. – DarioP Dec 23 '14 at 14:37

Use the light to excite a gas. The re-emission would be un-polarized.

That is given you have enough energy in the wave to do so. That's one way I could think of off my head.

EDIT: As per DarioP's suggestion, a solid fluorescent material would be nicer, as it is certainly more opaque than a gas.I am not aware of emission characteristics of a fluoroscent material, but in general, it should emit unpolarized light

• Isn't it against the intuition? Electric field vectors from one of the planes have been absorbed by the polarizer , how can they get regenerated after hitting a gas molecule? – Swami Dec 19 '14 at 15:31
• @Swami Use another polarizer at a different angle, in combination with your original polarizer. The new direction has a component in the planes where the original vector was absorbed by the first polarizer. Nothing too surprising. – Cheeku Dec 19 '14 at 15:35
• Uhmm, this is not obvious to me. You can use a gas to polarize unpolarized light (observing at 90° - try with the Sun and the sky!) but I'm not sure if the other way somehow happens. – DarioP Dec 19 '14 at 16:28
• @DarioP I am not sure if it does, but here is my chain of logic. Excited gas produces unpolarized light(general direction). Use the polarized light to excite a gas. It hould emit unpolarized light. But, on a slightly unrelated tone on your doubt, but relevant to my previous comment, for the equations and all, with a nice connection to particle spin and quantum theory see Baym 1969, the first chapter. – Cheeku Dec 19 '14 at 16:32
• @DarioP Yeah, that'd be nice. As I mentioned in the answer, excited gas was the first thing that came to my mind. Fluoroscent solid material makes more sense. – Cheeku Dec 19 '14 at 16:50

First of all ,what is unpolarized light?

As Feynman said, ''Light is unpolarized if you cannot tell whether it is polarized or not.''

light from ordinary sources are unpolarized because our detectors only can detect the mixture of waves polarized in different directions.(not individual waves).

waves emitted by any one molecule may be linearly polarized but an ordinary light source contains large number of molecules with random orientations,so the emitted light is random mixture of waves linearly polarized in all possible transverse directions. so light from ordinary light source is unpolarized.

now to ans your question just mix light polarized in different directions so that our detectors cannot detect the individual light and you will have unpolarized light.