Mode splitting and resonant coupling between a slot metasurface and PMMA
Finch, Michael F.
Lail, Brian A.
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A slot metasurface (metascreen) designed to have resonance that couples with the 1733 cmˉ¹ absorption peak of the C=O molecular bond of PMMA (polymethyl methacrylate) is presented. The metasurface is made of a gold layer perforated with periodically-placed slots and stood off above a reflective ground plane with silicon substrate. The metasurface is modeled using ANSYS HFSS and including measured optical properties for gold, silicon and PMMA in the infrared spectrum. PMMA forms a thin overcoat and exhibits a strong absorption resonance at wavenumber 1733 cmˉ¹. Coupling between the metasurface and PMMA is observed via normal mode splitting. Mode splitting has been analyzed from classical coupled mass spring oscillators to exciton-photons coupling in microcavities. The coupled systems can be described with a Hamiltonian matrix and solved for the eigenfrequencies. Parametric analysis of coupled response as a function of the design geometry is provided. Coupling energy, reflectance spectrum, and dispersion plots showing the anticrossing behavior of hybrid modes are presented as characterization of resonance coupling and normal mode splitting. Slot metasurface results are compared to the complementary structure (nanorod metasurface) in order to explore the duality of the complentary metasurfaces and their coupled responses. Coupled resonances have application in biosensors for molecule detection, surface-enhanced infrared absorption (SEIRA), and infrared imaging.