Adiabatic Nanoplasmonic Energy Concentration*

We predict that propagation of surface plasmon polaritons (SPPs) toward a sharp edge of smoothly (adiabatically) graded metallic layer causes their slowing down and asymptotic stopping. This is accompanied by a concentration of electromagnetic energy and enhancement of local optical fields. As such a nano-concentration effect , we consider the adiabatic energy concentration in a conic nanoplasmonic waveguide ..[1]. In this case, SPPs are created in the $m=0$ plasmonic state at the wide (microscopic) edge of the system and propagate toward the tip of the conic waveguide. As local radius $R$of the cone waveguide decreases, both the phase and group velocity tend to zero $\propto R$. This asymptotic stopping lead to the accumulation of SPPs at the tip and their adiabatic transformation to the standing surface plasmons. For silver, it is possible to have local optical intensity at the tip increased by three orders of magnitude. We also discuss two- dimensional focusing nanoplasmonic waveguides. In conclusion, we will discuss the many prospective application of this effect. [1]. M. I. Stockman, \textit{Nanofocusing of Optical Energy in Tapered Plasmonic Waveguides}, Phys. Rev. Lett. \textbf{93}, 137404-1-4 (2004).