Optical resonances in relief metalized 1D gratings

Recently, Ebbesen et al. (Nature v.391, p.667, 1998), have reported an 'extraordinary optical transmission' (EOT) enhancement of several orders of magnitude in thin metallic films with perforated circular subwavelength holes. Later, it was shown that this phenomenon does not require the existence of apertures. Continuous thin metal films with constant thickness give a similar EOT, provided they are 1D or 2D modulated. Still there is no detailed understanding of the physical nature of this transmission enhancement. It could be explained by plasmon-polariton interactions; yet another hypothesis suggests that it occurs from waveguide mode resonance. In this communication, we report experimental data on the optical response of a simple 1D relief grating structure with EOT. We have studied the transmission wavelength dependence as well as the angular dispersion of the grating reflection. Our experimental results are consistent with the involvement of p-polarized resonant modes.