Abstract: Recently, it has been proposed to attach a nanometric metallic sphere at the apex of a scanning near-.eld optical microscope (SNOM) tip in order to enhance its e.ciency [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 modi.ed both the temporal and the spectral responses of the tip. In the near .eld, a 100 exaltation of the .eld intensity, at the resonant wavelength, is shown. In the far .eld, an interference phenomenon between the core guided pulse and the cylindrical surface plasmon leads to a channeled transmitted spectrum.
Abstract: With the use of optical near-field techniques, it is now possible to excite or observe surface plasmons with high lateral resolution. A theoretical study is presented of surface plasmon excitation by near-field optical probes and the influence of well-defined structures on surface plasmon propagation and surface plasmon detection in the far field. The generation and the diffraction of the surface plasmon is calculated by using a theoretical scheme founded upon a first-order perturbation expansion of the RayleighFano method. A very good agreement is obtained between numerical and experimental results. The theoretical tools used should prove a useful guideline for future experiments of nanooptics with surface plasmons.
Abstract: 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.
Abstract: The influence of a focused polarized Gaussian beam on image formation was studied. We show that the position of the tip with reference to the center of the beam involves asymmetry in the intensity map. A comparison between s and p polarization can be made, owing to the definition of both a three-dimensional polarized Gaussian beam and a three-dimensional object. This result implies that the best way to scan a sample consists in moving it and not the tip; moreover, focusing the incident light to get a higher signal-to-noise ratio must be done carefully with respect to the sample period.
Abstract: We present a compact stand-alone near-field optical microscope combined with force detection in which manufactured atomic force microscope (AFM) microcantilevers are used for both optical and force detection. Because of the stand-alone design, the combination allows a great variety of operation modes, including the scanning tunneling optical microscope (STOM), and possibly the reflection scanning near-field optical microscope modes. The first images obtained in the AFM and the STOM mode are presented. A polarization study is carried out to confirm the optical nature of the detected signal and to discuss possible artifacts.
