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In this work, we investigate intrinsically chiral optical effects – specifically absorption circular dichroism (CD) at normal incidence – in elliptical nanohole arrays (ENHAs) with square lattice realized in thin films of silver, gold, and aluminum on glass. Our purpose is twofold: first, we aim at clarifying the origin of CD and its relation to surface plasmon polariton (SPP) properties upon symmetry reduction in the plasmonic metasurface. Second, we optimize the parameters for CD enhancement, with specific attention on aluminum in the visible-near UV spectral range. The choice of the square lattice (as compared to our previous study on ENHA in Au with a triangular lattice [Petronjievic et al. Opt. Quantum Electronics (2020) 52:176]) yields a more complete picture of chiral properties in ENHAs, and it allows comparing the results of two different simulation methods under ideal conditions, as discussed below. The results shed light on the subtle interplay between two concurring mechanisms of symmetry reduction, namely elliptical nanohole shape and tilting of nanohole axis with respect to the symmetry axes of the array. Moreover, they give guidelines for optimizing the CD from the near-IR (using Au or Ag) to the UV spectral region (using Al metal). Thus, the present work sets the bases for applications of the ENHA to chiroptical spectroscopies, notably in the near-UV region which is especially interesting for various kinds of biomolecules.
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