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Circularlypolarized light

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

Unpolarized light

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.

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

Difference betweenpolarized and unpolarized lightsunglasses

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

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