Abstract
Arrays of nanoholes in metal are important plasmonic devices, proposed for applications spanning from biosensing to communications. In this work, we show that in such arrays the symmetry can be broken by means of the elliptical shape of the nanoholes, combined with the in-plane tilt of the ellipse axes away from the array symmetry lines. The array then differently interacts with circular polarizations of opposite handedness at normal incidence, i.e., it becomes intrinsically chiral. The measure of this difference is called circular dichroism (CD). The nanosphere lithography combined with tilted silver evaporation was employed as a low-cost fabrication technique. In this paper, we demonstrate intrinsic chirality and CD by measuring the extinction in the near-infrared range. We further employ numerical analysis to visualize the circular polarization coupling with the nanostructure. We find a good agreement between simulations and the experiment, meaning that the optimization can be used to further increase CD.
Highlights
IntroductionPlasmonic arrays of nanoholes are able to couple light into plasmon oscillations at the metal-dielectric interface, i.e., surface plasmon polaritons (SPPs) [2]
The physics of corrugated metal films has been attracting researchers for some decades [1].At the nanoscale, plasmonic arrays of nanoholes are able to couple light into plasmon oscillations at the metal-dielectric interface, i.e., surface plasmon polaritons (SPPs) [2]
The unique coupling and subwavelength confinement properties of nanohole-based plasmonic devices have already led to many demonstrations and application proposals in subwavelength optics [5], surface enhanced
Summary
Plasmonic arrays of nanoholes are able to couple light into plasmon oscillations at the metal-dielectric interface, i.e., surface plasmon polaritons (SPPs) [2] These specific resonant electromagnetic excitations are strongly confined and lead to electromagnetic field enhancement at the interface [3]. One of the issues in plasmonic sensing is the ability to detect and characterize chirality, i.e., different interaction of the material with the left and right circularly polarized light (LCP and RCP, respectively). This difference can be characterized as normalized absorption difference between LCP and RCP, i.e., circular dichroism (CD). The two non-superimposable images of the same drug (so called enantiomers) are physically equal, but can have drastically different interactions
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