Strong coupling assisted high-Q and giant chiroptical responses at near-ultraviolet frequency in planar metasurfaces.

Circular dichroism (CD) spectroscopy represents a crucial technique for probing the structural details of chiral molecules. In recent years, emerging chiral metasurfaces have emerged as a promising platform by generating localized, intense chiral fields. Nevertheless, current metasurfaces predominantly function within the visible and near-infrared spectra with limited response in the ultraviolet (UV) spectrum due to materials and fabrication challenges. In this study, we report the attainment of a remarkably high Q factor of 1200, concomitant with a relatively pronounced planar chirality with a CD value of 0.67 under normal incidence in chiral all-dielectric Ta2O5 metasurfaces in the near-UV region. This achievement is realized through the strong coupling between magnetic dipole resonances and Mie surface lattice resonances, which occurs when the two resonance modes are both spatially and spectrally coincident. Our findings not only chart a novel trajectory for the realization of high-performance chiral metasurfaces in the UV region but also hold substantial potential for diverse chiral nanophotonic applications, such as sensing, lasing, and nonlinear optics investigations.