Near-field optical images of subwavelength annular aperture arrays exhibiting an extraordinary transmission.

In this paper, we present near-field optical images of nanostructures exhibiting an extraordinary transmission. These structures consist of annular aperture arrays engraved in a metallic film: they are quite promising structures for nanophotonics because of their high transmission directly linked to a guided mode mediated by each annular aperture. We first briefly explain our fabrication process (focused ion beam milling), then we expose the experimental setup of the near-field optical microscope working both in reflection and transmission modes. For the reflection mode, the 'coffee-bean' structure of the electromagnetic field predicted by the theory has been quite well reproduced. For the transmission mode, we present preliminary experimental results concerning the influence of the wavelength and the polarization of the incident beam on the obtained near-field images.