  Bohmian mechanics allows to visualize and understand the quantum-mechanical
behavior of massive particles in terms of trajectories. As shown by
Bialynicki-Birula, Electromagnetism also admits a hydrodynamical formulation
when the existence of a wave function for photons (properly defined) is
assumed. This formulation thus provides an alternative interpretation of
optical phenomena in terms of photon trajectories, whose flow yields a
pictorial view of the evolution of the electromagnetic energy density in
configuration space. This trajectory-based theoretical framework is considered
here to study and analyze the outcome from Young-type diffraction experiments
within the context of the Arago-Fresnel laws. More specifically, photon
trajectories in the region behind the two slits are obtained in the case where
the slits are illuminated by a polarized monochromatic plane wave. Expressions
to determine electromagnetic energy flow lines and photon trajectories within
this scenario are provided, as well as a procedure to compute them in the
particular case of gratings totally transparent inside the slits and completely
absorbing outside them. As is shown, the electromagnetic energy flow lines
obtained allow to monitor at each point of space the behavior of the
electromagnetic energy flow and, therefore, to evaluate the effects caused on
it by the presence (right behind each slit) of polarizers with the same or
different polarization axes. This leads to a trajectory-based picture of the
Arago-Fresnel laws for the interference of polarized light.
