Ultra-low Damping of Surface Plasmon Polaritons in Atomically Smooth Epitaxial Ag Films: An Extraordinary Optical Transmission Study

When an electro-magnetic radiation field couples strongly to surface plasmons, a surface plasmon polariton (SPP) is formed. In recent years, studies of SPPs in metal films perforated with hole lattices have revealed broad technological implications ranging from exotic metamaterials for sub-wavelength resolution microscopy to ultra-compact plasmonic waveguides for optical interconnects, as well as many other exciting technological applications. Thus far, most investigations have employed dielectric/metal hybrid structures with granular polycrystalline metal films. Although many conceptual devices have been demonstrated, one factor significantly limits their technological potential: the strong damping of SPP propagation. By using atomically smooth, epitaxial Ag films we show that such a damping effect can be mostly eliminated, resulting in nearly ideal extraordinary optical transmission (EOT) through sub-wavelength hole arrays in the mid-infrared range. This also allows us to map out very detailed SPP band structure, with analogy to the electronic band structure in solids.