Localised plasmons on the aperture of a channel in a metal layer

Optical fields are studied in a planar channel inside a metal layer taking into account a complex dielectric function of the metal. An influence of an exit aperture on the incident field propagating along the channel is considered; a mathematical approach is developed for analysing the effect. Attention is paid to the fact that the incident field should not be assumed a priori known if the wave transformation at the exit is neglected. For a chosen dimension of the channel and parameters of a metal, the coefficients for the lowest mode transformation into higher modes are found. The spatial field structure at the exit aperture and on the exit surface of a metal is studied. Existence of domains possessing an anomalously high intensity is revealed.