Optimized enhancement of electric field in a metallic hollow cylinder

Abstract

The enhancement of the electric field in a hollow metallic cylinder is optimized as a function of the angular frequency of incident light. A resonant enhancement occurs by exciting azimuthal surface plasmon (SP) and the enhancement is uniform inside the cylinder which is useful for spectroscopy. The enhancement of the electric field is numerically calculated by solving the Helmholtz equation as a function of the inner and outer radii of the cylinder from which an empirical formula for the enhancement is obtained by fitting the numerical results. The maximum enhancement occurs near the resonant condition of the SP but it is not exactly at the resonant frequency of the SP. The calculated induced charge density at the inner and outer surfaces show that the maximum enhancement occurs when the induced charge density at the outer surface becomes minimum. We suggest that such suppression of charge density at the outer boundary of the cylinder is the result of the linear combination of two intrinsic modes of the cylindrical SP.