Superresolution imaging of the local density of states in plasmon lattices

Periodic plasmonic nanostructures have been found promising in controlling photoluminescence directivity and efficiency for a wide variety of applications. Because of the inhomogeneous spatial distribution of the photonic resonances of periodic plasmonic nanostructures, their influence on emission is strongly dependent on the position of emitters relative to the nanostructures. Therefore, mapping the local dependence of directivity, efficiency, and emission rate enhancements is key to understanding and optimizing the devices. We introduce a method of mapping the local enhancement of spontaneous emission rates of emitters coupled to periodic nanostructures based on stochastic superresolution imaging. As an example, we show superresolved measurements of the local density of states (LDOS) at 605 nm induced by a hexagonal lattice of aluminum nanoantennas with a spatial resolution of 40 nm, defined by the size of the colloidal nanosources we use as randomly dispersed probes. We demonstrate that our method is superior to near-field mapping of emission rates. Comparison with electrodynamic simulations indicates that the variation of the decay rate of the emitters in the investigated sample is hardly influenced by the lattice modes and mainly governed by single-particle LDOS variations and nearest-neighbor interactions.