Influence of Material Parameters on the Optical Excitation of Surface Plasmon Polaritons

We present a study of the efficiency of excitation of surface plasmon polaritons (SPP) at a vacuum-metal interface as a function of the permittivity of the metal. The results of the efficiency, obtained using two types of coupling structures, are presented as maps in complex permittivity space. We find that the efficiency reaches a maximum value of approximately 50% for low loss metals, and that this value decreases monotonically as the imaginary part of the permittivity increases. The similarity between the maps of the excitation efficiency and the SPP propagation length shows that the latter, which is much easier to calculate and is by itself an important characteristic of SPP, provides a fairly complete description of the relative performance of plasmonic materials in different regions of the spectrum.