Electromagnetic Waves

Stokes Parameters
The polarization content of an EM wave is known if it can be written in
the form of either (18) or (24) with known coefficients (E1, E2) or
(E−, E+) .
In practice, the converse problem arises i.e. given a wave of the form (6),
how can we determine from observations on the beam the state of
polarization?
A useful tool for this are the four Stokes parameters. These are
quadratic in the field strength and can be determined through intensity
measurements only. Their measurements determines completely the state
of polarization of the wave.
For a wave propagating in the z-direction the scalar products
ɛ1 · E , ɛ2 · E , ɛ ∗ + · E , ɛ ∗ − · E (25)
are the amplitudes of radiation respectively, with linear polarization in
the x-direction, linear polarization in the y-direction, positive helicity
and negative helicity.
The squares of these amplitudes give a measure of the intensity of each
type of polarization.
The phase information can be taken by using cross products
Electromagnetic Waves