Polarized light carries valuable information about the various physical parameters that have been acting on it. Magnetic fields,chemical interactions, molecular structures, and mechanical stress all affect optical polarization.Applications relying on these polarization changes include astrophysics, agricultural production,electric power generation, and molecular biology.

Polarization states are linear, circular, or elliptical according to the paths traced by electric field vectors in a propagating wave train.Unpolarized light (such as from an incandescent bulb) is a combination of all linear, circular, and elliptical states. Randomly polarized light, in reference to laser output, is composed of two orthogonally linearly polarized collinear beams whose power randomly varies over time. Although random, this radiation is always linearly polarized.

Depolarized light is usually linearly polarized light that has been randomized by either temporal or spatial retardation variations across or along the beam. If the various retardations are integrated enough, the beam will appear to be depolarized. The randomization process usually varies the linear polarization in a fairly smooth and predictable manner.