High Quality Factor Dielectric Metasurfaces for Ultraviolet Circular Dichroism Spectroscopy

Abstract

Chiral-optical spectroscopies, such as circular dichroism, are critical in the biomedical, pharmaceutical, and agrochemical industries for revealing structural information about molecules and determining the purity of chemical samples. Emerging nanophotonic platforms have been shown to increase the intrinsically weak interaction between circularly polarized light and chiral molecules through the concentration of the local density of optical chirality, C . However, enhancements in C have been limited to infrared and visible frequencies, while the chiral absorption features of most small molecules are in the ultraviolet. Furthermore, achievable C enhancements in nanophotonic systems remain relatively low, especially when averaged across the sample volume. Here, we use full-field simulations to design a high quality factor (high Q ) diamond metasurface that enhances C by over 3 orders of magnitude in the ultraviolet regime. The diamond nanostructures enable ultraviolet Mie resonances while a biperiodic disk lattice activates high Q resonances that significantly increase the electromagnetic field intensities. When a high Q electric dipole and magnetic dipole mode are spatially and spectrally overlapped, a Kerker-like condition emerges that enables uniform sign C enhancements that are locally as high as 1130-fold. Even when averaged across the unit cell and 40 nm away from the surface, enhancements in C exceed 100-fold. We show how the quality factor and C can be further tuned by adjusting the structural asymmetry via the diameter offset in the biperiodic lattice. Our results pave the way for ultrasensitive chiral spectroscopy and efficient light-mediated enantiomer separation.