Propagation effects in apertureless near-field optical antennas

Abstract

We report a direct observation of the electromagnetic wave propagation on optical antennas. A free-space broadband terahertz pulse is coupled into a propagating mode along the shaft of an optical antenna acting as an apertureless near-field probe. We determine the spatial extent of this guided mode and its velocity. In addition, we consider the possibility of multiply reflected modes propagating along the near-field probe, an effect which will be significant in near-field spectroscopic measurements.