Quasi-total funneling of light in high aspect ratio gold grooves

Here, we demonstrate the total extinction of the reflectivity for a transverse magnetic polarized wave on a gold surface etched on a tiny portion of its area by both narrow and deep grooves. At the resonance, the incident energy is funneled towards the grooves aperture and is then dissipated on the grooves sidewalls. Thanks to the decomposition of the electromagnetic field into its propagative and evanescent parts, we unambiguously show that the funneling is not due to plasmonic waves flowing toward the grooves, but rather to the magnetoelectric interference of the incident wave with the evanescent field. This evanescent field is mainly due to the resonant wave escaping from the groove. These high aspect ratio metallic grooves were fabricated using a mold cast technique based on an electrolytic growth of gold. They exhibit a nearly total absorption due to a Fabry-Perot like resonance inside the grooves. We also evidence the incidence-invariance of their spectral response, which undoubtedly shows the localized nature of the resonances. These experimental results confirm the prediction of total funneling of light in very narrow grooves.