Plasmons, which are excited by an evanescent wave and localized in a narrow slit between two metallic cylinders overlying a dielectric substrate, are found by numerical solution of Maxwell equations. The simulation is carried out by a modified boundary elements method with the Green function for layered medium. For the wave incident from a dielectric to its border near the angle of total internal reflection, the amplitude of plasmon resonance is shown to change sharply with the incidence angle. The effect allows one to tune up the field enhancement factor. The control over plasmons is promising for applications in "smart" adaptive plasmonic optical elements.
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