  In a previous paper we showed how higher-order strong-field-QED processes in
long laser pulses can be approximated by multiplying sequences of "strong-field
Mueller matrices". We obtained expressions that are valid for arbitrary field
shape and polarization. In this paper we derive practical approximations of
these Mueller matrices in the locally-constant- and the
locally-monochromatic-field regimes. We allow for arbitrary laser polarization
as well as arbitrarily polarized initial and final particles. The spin and
polarization can also change due to loop contributions (the mass operator for
electrons and the polarization operator for photons). We derive Mueller
matrices for these as well.
