Of elliptically polarized incident
radiation, these are given by
where

and

specify the
irradiances of the incident light polarized with their electric vectors vibrating perpendicular
and parallel to the
scattering, respectively and

is the phase difference between these electric vectors.
Source:
PAC, 1983, 55, 931
(Definitions, terminology and symbols in colloid and surface chemistry. Part 1.14:
Light scattering (Provisional))
on page 933