They
have a
real Jones Matrix that depend on 4 parameters and can all be
constructed as
products of matrices describing the following elementary actions (see
the proof in Appendix B):
An imperfect polariser: with the copolar (
) direction
at an angle 
from the X axis (3 parameter):
and 
are the transmission
coefficients
in the and 
directions, they verify 
and hopefully 
. The corresponding
Mueller
matrix is:
where 
, 
, and 
, with 
and 
.
A rotation of the polarisation: by
an angle 
(or of the axis by an angle 
) is described
by the
following Jones matrix (one parameter):
and the
corresponding
Mueller matrix is:
A mirror transformation: (no free parameter):
To summarise:
the most general instrument inducing no circular polarisation can be
viewed as an imperfect polarimeter in some direction followed
by a device rotating, and possibly mirroring, the polarisation. If the
instrument is just in front of the measuring bolometer, only sensitive
to the intensity, this last polarisation rotation and/or reflection is irrelevant and
the signal in the bolometer is governed by the first row of the
Mueller matrix in Eq. (14):
