Left: Scanning Electron Microscope image of a 40nm thick, 2.5 micrometre wide gold strip lying on a glass substrate. Right: the optical functionality is visualized by collection mode near-field optical microscopy, also called Photon Scanning Tunneling Microscope (PSTM). An extended surface plasmon, launched on the larger area by a spot (indicated by the ellipse on the left figure) generated by total internal reflection illumination (wavelength=800nm) through the substrate, is used to excite one of the strip's surface plasmon mode featuring three maxima. The PSTM image illustrates nicely that the electromagnetic field is bound to the surface of the metal. A cross-section across the strip shows that this mode is much better confined to the guiding material sustaining the mode than would be the case in dielectric based waveguides.

Images courtesy of Dr. J.C. Weeber Laboratoire de Physique de l'Université de Bourgogne.