  A back action from Dirac electrons in graphene on the hybridization of
radiative and evanescent fields is found as an analogy to Newton's third law.
Here, the back action appears as a localized polarization field which greatly
modifies an incident surface-plasmon-polariton (SPP) field. This yields a high
sensitivity to local dielectric environments and provides a scrutiny tool for
molecules or proteins selectively bounded with carbons. A scattering matrix is
shown with varied frequencies nearby the surface-plasmon (SP) resonance for the
increase, decrease and even a full suppression of the polarization field, which
enables accurate effective-medium theories to be constructed for
Maxwell-equation finite-difference time-domain methods. Moreover, double peaks
in the absorption spectra for hybrid SP and graphene-plasmon modes are
significant only with a large conductor plasma frequency, but are overshadowed
by a round SPP peak at a small plasma frequency as the graphene is placed close
to conductor surface. These resonant absorptions facilitate the polariton-only
excitations, leading to polariton condensation for a threshold-free laser.
