Local-field enhancement and quantum yield of metallic dimer

The nanostructure of a metallic dimer, a pair of metallic (Au or Ag) nanoscatterers containing a molecule within its gap, is studied for the purpose of the enhancement of a single molecule's fluorescence due to the coupling surface plasmon resonance of the dimer. For simplicity, a two-dimensional transverse magnetic model is used for simulation, and a set of new surface integral equations is developed for the calculation of the electromagnetic field. The process of fluorescence is simply divided into two stages, the excitation and the emission, for analysis. For the former, an incident plane wave illuminating the structure to excite the molecule is simulated. For the latter, another model, an electric dipole within the gap of the dimer, is used to simulate the excited molecule interacting with the dimer. The results show that a metallic dimer behaves as a nanolens to provide a strong local electric field in the gap to excite the molecule, and its quantum yield behaves as a low-pass filter as well as an orientizer for the fluorescence emission.