  We investigate the dynamics of photon echo exhibited by exciton-plasmon
systems under strong coupling conditions. Using a self-consistent model based
on coupled Maxwell-Bloch equations we investigate femtosecond time dynamics of
ensembles of interacting molecules optically coupled to surface plasmon
supporting materials. It is shown that observed photon echoes under two pulse
pump-probe sequence are highly dependent on various material parameters such as
molecular concentration and periodicity. Simulations of photon echoes in
exciton-plasmon materials reveal a unique signature of the strong
exciton-plasmon coupling, namely a double-peak structure in spectra of recorded
echo signals. This phenomenon is shown to be related to hybrid states (upper
and lower polaritons) in exciton-plasmon systems under strong coupling
conditions. It is also demonstrated that the double-peak echo is highly
sensitive to mild deviations of the coupling from resonant conditions making it
a great tool for ultrafast probes.
