Spectral analysis of periodically nanostructured metal surfaces

Abstract

ABSTRACT The enhanced transmission of square arrays of nanoholes in thin and thick metal films has been studied. We show that normal incidence transmission spectra of an array of elliptical nanoholes in a 220 nm thick gold films have reduced symmetry with respect to the four-fold symmetry found in an equivalent array of circular nanoholes. Elliptical nanoholes milled in a 40 nm thick gold film show complex oscillatory behaviour of the transmission spectrum that has properties similar to those of a two-dimensional birefingent crystal. The transmission spectrum may also be controlled by polarisation selection due to the different degrees of the elliptical polarisation of the transmitted light. The enhanced transmission through 1D arrays of stripes is studied for a range of incident angles with a polarisation perpendicular to the stripe length. Increasing the incident angle increases the number of observed peaks, and changes their spectral positions. Changing the polarisation or the angle of incidence in a 1D array of stripes or a 2D array of reduced symmetry motifs allows control of the enhanced transmission spectrum and shows great potential for numerous applications in photonic and opto-electronic devices. Keywords: surface polaritonic crystals, surface plasmon, polarisation, nano-optics. 1. INTRODUCTION Nanostructured thin metal films have been a topic of considerable interest in the last few years due to their great potential as devices for applications in optical communications and computing. Devices such as optical filters which exploit surface plasmon polariton (SPP) excitations in metal nanostructures have been designed and studied.