Quasi-cylindrical wave contribution in experiments on extraordinary optical transmission

TLDR: From the measured transmission spectra, microscopic scattering parameters are determined which allow us to show that quasi-cylindrical waves affect EOT only for high densities, when the hole spacing is roughly one wavelength.

Abstract: Results on light scattering from metal hole arrays show the relative importance of surface plasmon polaritons and quasi-cylindrical waves in extraordinary optical transmission. Over a decade ago, the 'extraordinary optical transmission' effect was discovered, in which a metal film perforated by a regular array of subwavelength holes shows unexpectedly high light transmittance at specific wavelengths. The effect was found, in part, to depend on surface plasmons, stimulating a renewed interest in plasmonics, but more recently so-called quasicylindrical waves have also been implicated. A detailed study by Frerik van Beijnum et al., involving hole arrays in metal films with varying hole density, now provides definitive quantitative evidence for the respective roles of surface plasmons and quasicylindrical waves, bringing a more complete understanding of the extraordinary optical transmission effect and opening up new possible design strategies. A metal film perforated by a regular array of subwavelength holes shows unexpectedly large transmission at particular wavelengths, a phenomenon known as the extraordinary optical transmission (EOT) of metal hole arrays1. EOT was first attributed to surface plasmon polaritons, stimulating a renewed interest in plasmonics2,3,4 and metallic surfaces with subwavelength features5,6,7. Experiments soon revealed that the field diffracted at a hole or slit is not a surface plasmon polariton mode alone8. Further theoretical analysis9 predicted that the extra contribution, from quasi-cylindrical waves10,11,12,13, also affects EOT. Here we report the experimental demonstration of the relative importance of surface plasmon polaritons and quasi-cylindrical waves in EOT by considering hole arrays of different hole densities. From the measured transmission spectra, we determine microscopic scattering parameters which allow us to show that quasi-cylindrical waves affect EOT only for high densities, when the hole spacing is roughly one wavelength. Apart from providing a deeper understanding of EOT, the determination of microscopic scattering parameters from the measurement of macroscopic optical properties paves the way to novel design strategies.