Body-of-revolution FDTD simulations of improved tip performance for scanning near-field optical microscopes

Recently, it has been proposed to attach a nanometric metallic sphere at the apex of a scanning near-field optical microscope (SNOM) tip in order to enhance its efficiency [Appl. Phys. Lett. 76 (15) (2000) 2134]. In this paper, we use a home-made body-of-revolution FDTD code to compare the emission of conventional metal coated tip with and without this nanoparticle. In both cases, our calculation establishes the occurrence of a cylindrical surface plasmon that propagates along the taper. When it is excited, the surface plasmon of the sphere strongly modified both the temporal and the spectral responses of the tip. In the near field, a 100x exaltation of the field intensity, at the resonant wavelength, is shown. In the far field, an interference phenomenon between the core guided pulse and the cylindrical surface plasmon leads to a channeled transmitted spectrum. (C) 2003 Elsevier B.V. All rights reserved.