The quantity Ip+In+Inp, where Ip is the intensity (amplitude
squared) of the electric vector in the plane of polarization,
In is the intensity (amplitude squared) of the electric vector
in the plane of the normal to the plane of polarization,
and Inp is the intensity (amplitude squared) of the
non-polarized (incoherent) electric vector.
This is an average or other representative sample of the
This is the first of the Stokes polarization parameters,
I, Q, U, V [also known as I, M, C, S; see Berry et al. (1977)].
If the absolute intensity is not known, the value 1.0
is assumed for I, and all four Stokes parameters are
dimensionless. When the absolute intensity is known,
all four Stokes parameters are in units of watts per
Note that, if the polarized intensity Ip+In is required,
(Ip+In)2 is the sum of Q2+U2+V2.
Berry, H. H., Gabrielse, G. & Livingston, A. E. (1977).
'Measurement of the Stokes parameters of light',
Appl. Optics, 16:12, 3200 -- 3205.