Mid-infrared superchiral field induced by quasi-guided mode in diamond metasurface

The superchiral field that enables ultrasensitive detection and discrimination of chiral matter beyond that of circularly polarized light by its field structure has emerged as a powerful tool in chiroptical spectroscopy, spin photonics, and analytical chemistry. Specially, the superchiral field at the wavelength beyond 15 μm is indispensable for various mid-infrared applications, such as ultrasensitive chiroptical sensing in the molecular fingerprint region. Here we propose and present a new strategy to realize the superchiral field with a Kuhn’s dissymmetric factor up to ~90 at the wavelength beyond 15 μm. This is enabled by the high-quality (up to ~10⁴) multipole resonance induced by Brillouin-zone-folding-driven quasi-guided mode in a diamond metasurface. This work opens up a new avenue towards realizing mid-infrared superchiral fields at the wavelength beyond 15 μm.