Strongly localized chiral optical fields can enhance the chiral light–matter interaction. In article number 1901038, Qiaoqiang Gan, Qiwen Zhan and co‐workers present a design for the generation of superchiral optical field using symmetric metamaterial superabsorber structures and demonstrate its application in enhanced circular dichroism (CD) spectroscopy. Simulations reveal that the optical chirality density and the CD signal can be enhanced by 80‐ and 1300‐fold, respectively, revealing a strategy to develop scalable platforms for chiroptical applications.

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Structural color utilizing microscale concave interfaces has been reported in several publications, but the explanation is currently incomplete. Within this work, the physics behind this coloration technique is clarified using multiple light sources and simulations.

Metallic nanostructures with nanogap features can confine electromagnetic fields into extremely small volumes. In particular, as the gap size is scaled down to sub-nanometer regime, the quantum effects for localized field enhancement reveal the ultimate capability for light-matter interaction. Although the enhancement factor approaching the quantum upper limit has been reported, the grand challenge for surface enhanced vibrational spectroscopic sensing remains in the inherent randomness, preventing uniformly distributed localized fields over large areas. Here we report a strategy to fabricate high-density random metallic nanopatterns with accurately controlled nanogaps defined by atomic-layer-deposition and self-assembled-monolayer processes. As the gap size approaches the quantum regime of ~0.78 nm, we demonstrate its potential for quantitative sensing based on a record-high uniformity with the relative standard deviation of 4.3% over a large area of 22 mm × 60 mm. This superior feature paves the way towards more affordable and quantitative sensing using quantum-limit-approaching nanogap structures.

We unambiguously define the physics behind structural coloration induced by microscale concave interfaces using both white light, and single wavelength illumination.