Abstract
We present the first angle resolved measurements of extraordinary optical transmission (EOT) through hole array gratings in a gold film. Varying the lattice spacing of the arrays and looking at higher diffraction orders, we retrieve the angular emission pattern of the constituent holes with better signal to noise ratio than with single-hole experiments. We present a method to determine separately the angular dependence of the direct and resonant contribution to EOT by using the spectral features of the diffraction orders together with an established model. The comparison of our results with the known angular transmission of a single hole in a metal film yields a good agreement for s-polarized light. Deviations are found for illumination with p-polarized light and we address the discrepancy with Coupled Mode Model calculations and Finite Difference Time Domain simulations. These measured deviations are currently not fully understood.
Highlights
Metal nano-structures can strongly localize optical fields in a charge-field coupled oscillation at the metal-dielectric interface, or surface plasmon (SP)
Extensive studies were conducted to understand how this phenomeon depends on the material [7], size [8, 9] and shape [10] of the holes and how surface waves propagate and couple to contribute to the spectral features of Extraordinary Optical Transmission (EOT) [11, 12]
The first way is looking at T (λ, θ) at constant wavelength; the angular response of the system results in multiple peaks corresponding to the different diffraction orders, as shown in Fig. 1(b) for different values of the spacing factor q
Summary
Metal nano-structures can strongly localize optical fields in a charge-field coupled oscillation at the metal-dielectric interface, or surface plasmon (SP). The physical picture of EOT is based on transmission of the electromagnetic field through nanoholes aided by resonant surface waves of the patterned structure [13]. These waves can be understood, in metal films, from the multiple scattering of SPs on holes at the flat interfaces; plasmons play the biggest role [14], together with the so called quasi-cylindrical wave (QCW) [15,16,17,18]
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