From Weak to Strong Coupling: Quasi-BIC Metasurfaces for Mid-infrared Light-Matter Interactions

Resonant metasurfaces present extraordinary subwavelength light trapping capabilities, which have been critical to the development of high-performance biochemical sensors and surface-enhanced spectroscopy techniques. To date, metasurface-enhanced light-matter interactions in the mid-infrared region have been primarily leveraged in the weak coupling regime. Nevertheless, the strong coupling regime, characterized by the hybrid light-matter states - polaritons, has not been fully explored. Specifically, metasurfaces made from low-loss dielectric resonators underpinned by the bound states in the continuum (BIC) are well suited for quantum coherent energy exchange between their high-Q open cavities and molecules' resonant transitions. This paper delves into the light-matter interactions in metasurface cavities generated by quasi-BIC resonances at mid-infrared frequencies. We thoroughly investigate the material and cavity parameters that define the boundaries between weak and strong coupling. Our findings underscore the transformative potential of dielectric metasurfaces to harness vibrational strong coupling for applications such as cavity polaritonic chemistry, modulation of chemical reactivity with light, and highly sensitive molecular spectroscopy.