Near-field optics: Direct observation of the field enhancement below an apertureless probe using a photosensitive polymer

We report the direct observation of the optical near-field enhancement at the nanometric extremity of a metallic probe for apertureless scanning near-field optical microscopy. Our approach consists in making the "snapshot" of the spatial distribution of the optical intensity in the vicinity of the probe end via a photosensitive polymer. This distribution is coded by polymer surface topography which is characterized in situ by atomic force microscopy using the same probe. Results clearly reveal nanometric dots corresponding to local field enhancement below the tip end. The field enhancement is shown to be crucially dependent on the polarization state of the incident laser beam as well as the tip material and geometry. The experimental results are found to agree with the results of preliminary calculations. This experiment both constitutes a useful tool for investigating field enhancement below apertureless probes and has potential applications in nanophotolithography. (C) 2001 American Institute of Physics.