Mapping the Radiative and the Apparent Nonradiative Local Density of States in the Near Field of a Metallic Nanoantenna

We present a novel method to extract the various contributions to the photonic local density of states from near-field fluorescence maps. The approach is based on the simultaneous mapping of the fluorescence intensity and decay rate and on the rigorous application of the reciprocity theorem. It allows us to separate the contributions of the radiative and the apparent nonradiative local density of states to the change in the decay rate. The apparent nonradiative contribution accounts for losses due to radiation out of the detection solid angle and to absorption in the environment. Data analysis relies on a new analytical calculation, and does not require the use of numerical simulations. One of the most relevant applications of the method is the characterization of nanostructures aimed at maximizing the number of photons emitted in the detection solid angle, which is a crucial issue in modern nanophotonics.