Abstract
Subwavelength hole array (HA) metasurfaces support the so-called extraordinary optical transmission (EOT) resonance that has already been exploited for sensing. In this work, we demonstrate the superior performance of a different resonant regime of HA metasurfaces called anomalous EOT, by doing a thorough numerical and experimental study of its ability in thin-film label-free sensing applications in the terahertz (THz) band. A comprehensive analysis using both the regular and anomalous EOT resonances is done by depositing thin layers of dielectric analyte slabs of different thicknesses on the structures in different scenarios. We carry out a detailed comparison and demonstrate that the best sensing performance is achieved when the structure operates in the anomalous EOT resonance and the analyte is deposited on the non-patterned side of the metasurface, improving by a factor between 2 and 3 the results of the EOT resonance in any of the considered scenarios. This can be explained by the comparatively narrower linewidth of the anomalous EOT resonance. The results presented expand the reach of subwavelength HAs for sensing applications by considering the anomalous EOT regime that is usually overlooked in the literature.
Highlights
The discovery of extraordinary optical transmission (EOT) through a subwavelength hole array (HA) by Ebbesen et al [1] contributed decisively to relaunch the topic of plasmonics opening new avenues towards the use of apertures much smaller than the operation wavelength [2,3]
Before characterizing the sensing performance of the fabricated HA metasurfaces, we begin the study by analyzing the response of an ideal lossless structure
We have demonstrated the superior performance of a HA metasurface when it operates at the anomalous EOT resonance, exceeding largely the results obtained at the regular EOT in label-free thin-film sensing applications
Summary
The discovery of extraordinary optical transmission (EOT) through a subwavelength hole array (HA) by Ebbesen et al [1] contributed decisively to relaunch the topic of plasmonics opening new avenues towards the use of apertures much smaller than the operation wavelength [2,3]. Initially interpreted as the coupling of light to surface plasmons, it was soon noticed that similar peaks could be obtained even with perfect conductors [2,3,4]. This enabled the replica of the phenomenon at frequencies in which metals do not follow a Drude model (typical of the plasmonic approach), such as millimeter-waves [5]. The high field intensity near the subwavelength apertures at the EOT resonance has been exploited for sensing applications [11,12,13] and nowadays one can find in the literature several examples of EOT biosensors [14], sensors combining nanofluidics and nanoplasmonics [15], and even sensing platforms for a direct detection and monitoring of viruses [16].
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