Enhancing Superchiral Fields and Circular Dichroism Detection with Achiral Dielectric Metasurfaces

We study achiral dielectric metasurfaces composed of symmetric silicon nanocube dimers and demonstrate that they can generate pronounced superchiral fields by engineering the electric and magnetic resonant modes. The superchiral fields exhibit an over 20-fold enhancement in optical chirality density in the visible region. While superchiral fields have been demonstrated in distinct nanostructures, it remains challenging to detect and assess them. We show that the third Stokes parameter, readily obtainable from far-field measurements, serves as an indicator of the strong chiral hot spot within the dimer gap. We further characterize the circular dichroism signals of d- and l-phenylalanine molecules in the presence of the metasurface and observe an approximately 12-fold enhancement compared to the control experiment without the metasurface. The experimental and simulation results show good agreement. The all-dielectric achiral metasurface paves a new way toward chiral molecule detection with the advantages of low loss, reduced background noise, and high sensitivity.