Quenched optical transmission in ultrathin, plasmonic gratings

We discuss the optical properties of one-dimensional, ultrathin, sub-wavelength, metallic gratings under transverse-magnetic (TM) excitation, with particular attention to the phenomenon of quenched transmission, recently highlighted in several optical experiments. In particular, we consider a grating with thickness comparable or less than the metal skin depth, showing how the geometrical properties of the grating can dramatically modify its transmission properties, often in a counterintuitive way. We study the role played by short-range(SR)/long-range(LR) surface plasmons (SPs) and localized SP resonances, showing that quenched transmission must be ascribed to localized resonance effects, while long-range and short-range SPs play only a marginal role in this anomalous effect. As an example, we show the transmission (T) in the plane (λ, θ) for a silver grating of thickness d=10 nm, slit aperture a=200 nm, width of the metal in the elementary cell b=120 nm and period Λ=a+b=320 nm.