Formation of Enhanced Uniform Chiral Fields in Symmetric Dimer Nanostructures

TL;DR

This paper demonstrates that simple plasmonic dimer nanostructures can generate uniform, highly enhanced chiral fields suitable for sensing applications, offering a practical alternative to complex nanostructures.

Contribution

The study introduces a simple plasmonic dimer design that produces uniform, enhanced chiral fields, explained by an analytical dipole model, improving chiral sensing efficiency.

Findings

Achieved 30-fold volume-averaged chiral field enhancement.

Generated opposite-handedness chiral fields by polarization control.

Provided uniform chiral fields in the nanogaps under linearly polarized light.

Abstract

Chiral fields with large optical chirality are very important in chiral molecules analysis, sensing and other measurements. Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals. However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications. Plasmonic helical nanostructures and blocked squares have been proved to provide uniform chiral near-fields, but structure fabrication is a challenge. In this paper, we show that very simple plasmonic dimer structures can provide uniform chiral fields in the gaps with large enhancement of both near electric fields and chiral fields under linearly polarized light illumination with polarization off the dimer axis at dipole resonance. An analytical dipole model is utilized to explain this behavior theoretically. 30 times of volume averaged chiral field enhancement is gotten in the whole gap. Chiral fields with opposite handedness can be obtained simply by changing the polarization to the other side of the dimer axis. It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule.