  In this second article of the series, we apply our recently derived equation
for the electric field propagation along light rays [arXiv:2004.03496], valid
on the electromagnetic geometrical optics limit, to the special case of a toy
interferometer used to detect gravitational waves in a flat background. Such an
equation shows that, assuming the detector is in the transverse-traceless
frame, which has a local shearing relative motion due to the gravitational wave
perturbations, the electric field does not propagate as in an inertial
reference frame in Minkowski spacetime. We present the electric field at the
end of the interferometric process, for arbitrary arm configurations with
respect to the plane gravitational wave packet propagation direction. Then, for
normal incidence, we compute the interference pattern and, in addition to the
usual term associated with the difference in path traveled by light in the
arms, we deduce two new contributions to the final intensity, arising from: (i)
the round-trip electromagnetic frequency shift and (ii) the divergence of the
light beam. Their quantitative relevance is compared to the traditional
contribution and shown to be typically negligible due to the geometrical optics
regime of light. Moreover, a non-parallel transport of the polarization vector
takes place, in general, because of the gravitational wave, a feature which
could generate further contributions. However, we conclude that for the normal
incidence case such vector is parallel transported, preventing this kind of
correction.
