Study of polarization-dependent energy coupling between near-field optical probe and mesoscopic metal structure

We present an experimental study of the coupling of light from a probe of a scanning near-field optical microscope ~SNOM! into a mesoscopic structure consisting of gold stripes with varying separations. We demonstrate that the coupling efficiency depends upon the polarization direction in the probe relative to the stripes as well as the separation between the lines. Two possible explanations for a contrast reversal effect in between sand p-polarized light are given. One is based on the excitation of a quasi-transverse electric and magnetic mode in the mesoscopic transmission line. For this explanation we have made a prediction of the condition of the maximum coupling efficiency through the approach of impedance matching. The second explanation is based on surface plasmon excitation in the gold structure. The present results can also be of importance in the development of new concepts of probes for SNOM. © 2004 American Institute of Physics. @DOI: 10.1063/1.1649453#