Theoretical study of near-field surface plasmon excitation, propagation and diffraction

Surface plasmons have been extensively studied by using far field techniques. Today, new experiments can be developed by using scanning probe microscopes. In optics, the tip of a scanning near-field optical microscope has been used to detect or to excite the surface plasmon in the near-field region. In this paper, we propose a theoretical study of one of these optical experiments. A 3D model of excitation and detection by scanning tunneling optical microscope (STOM) of the surface plasmon is developed. The surface plasmon is excited by a 3D polarized gaussian beam in the Kretschmann configuration. We determine its propagation length. We also present a preliminary study of the interaction of the surface plasmon with the edge of a surface defect. Our results are in good accordance with experimental ones and show new effects. (C) 1999 Elsevier Science B.V. All rights reserved.