Investigation of surface plasmonic extraordinary transmission for spectral, polarimetric, and off-normal incidence

Abstract

Extraordinary transmission of surface plasmonic (SP) structures has been widely studied but lacking is a focus on the off-normal dependency of the resonant modes and how this affects the transmission spectrum. The measurements of offnormal spectral transmission for a SP structure were compared to finite-difference time-domain simulations. The SP sample is a gold/titanium thin film (50 nm) with a 2D square array of circular holes deposited on 1 μm of highly ndoped, n =2e18cm -3 , gallium-arsenide (GaAs) upon a semi-insulating GaAs substrate. Spectral transmission measurements were taken for wavelengths from 2-12μm, incident elevation and azimuthal angles of θ=0°, 20° and 40°, and φ=0° and 45°, respectively, with linearly polarized and un-polarized light. The first and second-order surface plasmon modes and their dependency on θ, φ, polarization and the grating momentum vector were identified. The measurements and simulations corroborate the theoretical analysis, giving a closed-form solution to the spectral location of lower-order modes. For off-normal incidence in a plane parallel to the array periodicity (φ=0°), the (1,0) mode as defined for p-polarization splits while the (0,1) mode as defined for s-polarization, remains essentially un-changed for all θ. For φ=45° incidence, both polarizations split the modes. Full polarimetric spectral transmission was both measured and simulated, giving a Mueller matrix representation of the spectral transmission of the SP structure at θ=0° and 20° and φ=0° and 45°, demonstrating that this structure is moderately depolarizing when resonant. The results show the dependence on incident angle and polarization of the extraordinary transmission of SP structures.