The polarization state of an electromagnetic wave can conveniently be described by a set of Stokes parameters. On the left, the polarization ellipse describes the motion of the optical electric field (
) in a plane transverse to the light propagation direction. On the right are the corresponding Stokes parameters defined in terms of intensity difference measurements
where the intensities of the polarization components (
: horizontal,
: vertical, ±45
: along diagonals,
: circular left,
: circular right) are normalized to the total light intensity. The parameters that you can vary are the orientation of the ellipse, its degree of linear polarization
, where
and
are the intensities measured along the major and minor axes, and its handedness (direction of rotation). For 100% polarized light, the endpoint of the Stokes vector
lies on a unit sphere called the Poincaré sphere.
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