Enhanced dipole-dipole interaction between elementary radiators near a surface

We report the results of elastic light-scattering measurements of random silver nanoparticle arrays fabricated onto structures supporting optical surface modes (i.e., surface plasmons or waveguide modes). We observe dramatic, qualitative changes in the resonance structure of the nanoparticle layer due to coupling with the propagating modes. The effect appears to arise because the underlying surface modes mediate an enhanced dipole-dipole interaction between individual nanoparticles. A calculation that supports this interpretation is described.