Matter’s sensitivity to light polarization is classically characterized by linear and circular dichroism. Nanophotonics now provides the tools to strongly confine and guide light on the nanoscale, such as the evanescent near-fields surrounding waveguides in photonic circuits. However, matter’s inherent sensitivity to the full range of polarization states that can be found in evanescent waves has not been explored, leaving an opening for observing novel light-matter interactions. Trochoidal, or cartwheeling, field motion is relatively unexplored and can be found in interference fields, tightly focused Gaussian beams, and evanescent waves produced via total internal reflection. Unlike the helical field motion of circular polarization, trochoidal polarization consists of rotational motion confined to a plane. We develop the trochoidal analog of the Born-Kuhn model for understanding circular dichroism, where a key distinction is the planar confinement. This system is experimentally realized via a coupled pair of plasmonic dipole scatterers. We find that the plasmon mode hybridization between the pair depends on the rotational direction of the trochoidal excitation field. This observation constitutes a novel geometric basis for dichroism that fundamentally differs from circular dichroism, which we name trochoidal dichroism. Future applications of trochoidal dichroism could involve radiative reporting of near-field polarization phenomena and interfacial molecular geometry, accessing previously unseen information due to this unique polarization.<br/>

Observation of trochoidal dichroism

2019 Fall National Meeting

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