  The physics of collective optical response of molecular assemblies, pioneered
by Dicke in 1954, has long been at the center of theoretical and experimental
scrutiny. The influence of the environment on such phenomena is also of great
interest due to various important applications in e.g. energy conversion
devices. In this manuscript we demonstrate both experimentally and
theoretically the spatial modulations of the collective decay rates of
molecules placed in proximity to a metal interface. We show in a very simple
framework how the cooperative optical response can be analyzed in terms of
intermolecular correlations causing interference between the response of
different molecules and the polarization induced on a nearby metallic boundary
and predict similar collective interference phenomena in excitation energy
transfer between molecular aggregates.
