Can polarized light be unpolarized again? I was just wondering if there could be a process that could unpolarize polarazied light. Is that possible?
 A: 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
A: 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.
A: 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.
