Quasi-cylindrical wave contribution in experiments on extraordinary optical transmission
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.
van Beijnum, F, Rétif, C, Smiet, C. B, Liu, H, Lalanne, P, & van Exter, M. P. (2012). Quasi-cylindrical wave contribution in experiments on extraordinary optical transmission. Nature, 492, 411–414. doi:10.1038/nature11669