Full text loading...
Schematic representation of a metal-coated optical fiber scanning probe near a thin metal foil incorporated in a scanning probe microscope arrangement. The laser beam steered into a plano-convex cylindrical lens is reflected from the planar metal foil. Upon excitation of surface plasmons in the planar foil, the intensity of the reflected photons will suffer a minimum. The field associated with surface plasmons couples to a surface mode of the probe tip coating. Electrons undergoing collective oscillations in the tip coating decay to light, whereupon a photonic signal is generated in the optical fiber probe and detected in a detector.
SEM image of a gold-coated dielectric probe tip. A hyperboloid (the dashed curved) has been fitted to this image to display its boundary. The curvature of the tip and the fitted curve can be seen by further zooming into the nanometer-sized apex region.
Nonretarded surface-plasmon resonance values for the azimuthal modes , assuming an undamped Drude metal, for substrate thickness , with tip and coating boundaries set to opening angles and , respectively. The modes have been normalized using the bulk-plasmon frequency . The abscissa is the scaled surface plasmaon momentum. The effect of the inclusion of retardation can be shown28 in the cartesian limit of the curved films (i.e., as the probe and its confocal metal coating become increasingly wider) to be restricted to the small momentum region, and will pull the modes below the light dispersion in vacuum.
Experimentally observed photon tunneling via plasmon coupling. Photon tunneling in the visible for a gold substrate coating thickness , and a gold probe tip coating thickness . Incidence angles for the three examined wavelengths , 543.5, and were set to , , and . The axis displays the relative proximity of the tip to the substrate coating surface; that is, and , where is the unknown absolute distance to the surface.
Article metrics loading...