  We study the transport properties of a topological system coupled to an AC
electric field by means of Floquet-Keldysh formalism. We consider a
semi-infinite chain of dimers coupled to a semi-infinite metallic lead, and
obtain the density of states and current when the system is out of equilibrium.
Our formalism is non-perturbative and allows us to explore, in the
thermodynamic limit, a wide range of regimes for the AC field, arbitrary values
of the coupling strength to the metallic contact and corrections to the
wide-band limit. We find that hybridization with the contact can change the
dimerization phase, and that the current dependence on the field amplitude can
be used to discriminate between them. We also show the appearance of side-bands
and non-equilibrium zero-energy modes, characteristic of Floquet systems. Our
results directly apply to the stability of non-equilibrium topological phases,
when transport measurements are used for their detection.
