Detection of the optical magnetic field by circular symmetry plasmons

We report on the influence of coating a sharpened optical fiber tip with Au when observing nanofabricated dielectric structures with a Photon Scanning Tunneling Microscope (PSTM) in constant-height mode. For well-defined inci dent wavelengths and coating thicknesses, we found that such tips detect th e distribution of the magnetic field associated with the optical wave in th e near-field zone. A simple tip model indicates that this phenomenon is rel ated to the excitation of circular symmetry plasmons in Au coated tips. (C) 2000 Published by Elsevier Science B.V.