Surface profile dependence of surface plasmon band gaps on metallic gratings

When surface plasmon polaritons propagate on a corrugated surface, an energy gap opens up in the dispersion of the surface mode. We present the results of an experimental technique that directly images this gap. The technique is used to measure the width and the central frequency of the gap as a function of the grating profile. The experimental results agree well with the predictions of a recently published analytic model. In particular the results confirm that the central frequency of the gap drops as the grating amplitude increases. This is a previously unconfirmed prediction, over which there has been some debate. We also demonstrate that it is possible to observe gaps that are an order of magnitude wider than those reported elsewhere. (C) 1996 American Institute of physics.