Observation of Fabry-Perot-type surface plasmon on Ag film with perforated short-range 3x3 hole array arranged in long-range periodic structure

This letter elucidates enhanced optical transmission through a Ag film with perforated short-range 3x3 hole arrays arranged in a long-range periodic structure. The 3x3 squared hole array constitutes an individual microcell. The measured transmission peak wavelength reveals that the surface plasmons are generated by Fabry-Perot-type waveguide resonances with integer order. The ratio of periodicity between the superperiodic structure p and the 3x3 microcell d determines the integer order. Namely, when p/d > 3, the order 3, 4, and 5 surface plasmon modes with average hole spacings p/3, p/4, and p/5 are observed. The transmission intensities of order 3 modes are the strongest, and those of order 5 modes are barely seen. But as p/d approaches 4, the order 3 modes gradually disappear with the emergence of order 4 and 5 modes. These phenomena suggest that the surface plasmons are Fabry-Perot-type resonance within a super unit cell.(c) 2007 American Institute of Physics.