Session 3-4

Abstract

Light confined in nanostructured arrays interacts significantly with the surrounding molecules owing to its strong electromagnetic field enhancement effect. The strong light-molecule interactions are important for diverse applications, including cavity quantum electrodynamics, nonlinear enhancement, sensors, and spectroscopy. The quality (Q) factor is a measure of the energy dissipation of confined light, and both material selection and structural design play major roles in maximizing the experimental Q factors. Recently, quasi-bound states in the continuum (qBICs) in dielectric materials have attracted considerable attention owing to their design flexibility in controlling radiative losses through precise structural design.[1] Experimentally, the sharp peaks are accessible from the free-space excitation of light when the symmetry of the unit structure is broken. Here, we report an all-dielectric metasurface formed on silicon-on-insulator wafers to achieve high Q factors and demonstrate vibrational weak/strong coupling to qBICs.[2] The silicon metasurfaces are spatially and spectrally coupled with the C=O stretching mode of the polymethyl methacrylate thin films, reaching an enhancement factor of the vibrational signal as high as 104, which corresponds to the detection sensitivity at the monolayer level.[3] In addition, we show a new type of BIC metasurface with Q factors exceeding 105 in the telecom wavelength range, achieved through the use of low-contrast silicon paired nanostructures.[4] These ultrahigh-Q metasurfaces enable the successful detection of single polystyrene particles through their strong light–molecule interactions. These findings establish that all-dielectric nanostructures can serve as low-cost yet highly effective platforms for light-matter interactions, offering new opportunities for label-free molecular sensing and spectroscopy at low concentrations.