Resonant Coupling of an Infrared Metasurface with PMMA
Finch, Michael Francis
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Resonance coupling between a metasurface or planar metamaterial and PMMA’s, polymethyl methacrylate, phonon resonance corresponding to the C=O molecular bond at 1733 cm-1 (52 THz) is investigated. Two metasurfaces, nano rod and nano slot, are modeled using ANSYS HFSS and measured material optical properties for gold and PMMA in inferred spectrum. Both metasurfaces exhibited normal mode splitting also known as avoidance crossing, quantum level repulsion, or vacuum Rabi splitting. Normal mode splitting is shown to be a result of coupling between the PMMA phonon resonance and the resonance of the metasurface. Analytical models, which are tied to physical descriptions, are explored for normal mode splitting. The description varies from simple coupled pendulum oscillators to quantum electrodynamics descriptions like exciton-polaritons in microcavities. The analytical model produces an anti-crossing or avoidance crossing dispersion plot of hybrid modes from a system of differential Equations or uses a Hamiltonian matrix for the coupled oscillator or Rabi description respectively. The Hamiltonian approach, in line with a quantum state description, was employed and solved for equations that describe the eigenfrequancies. A Fano resonance explanation tried together with a description of normal mode splitting is presented. A comparison is drawn between the complementary metasurface pairs with a discussion of Babinet's Principle. Couple resonates have applications in biosensing, surface-enhanced infrared absorption (SEIRA), and infrared imaging.