Circularly polarized light is a potentially efficient and versatile method to both sense and separate chiral molecules. However, the differential interaction of chiral light with molecules of opposite handedness is very weak, limiting practical implementation. Here, we describe the design of metasurfaces that enhance chiral light-molecule interactions by locally concentrating chiral fields. Our metasurfaces consist of arrays of high refractive index disks, which support both electric and magnetic dipolar resonances. By varying the geometry of each disk, we independently tune the electric and magnetic dipole resonant frequencies to optimize the chiral fields surrounding the metasurface. We use full-field finite difference time domain simulations to determine the local electric and magnetic field intensities and phase near a silicon array illuminated with circularly polarized light (CPL). We then utilize the spatial field distributions to calculate the optical density of chirality, C as well as Kuhn’s dissymmetry factor, g. Our calculations indicate that a spectral overlap of the electric and magnetic dipole modes produces high field intensities with an optimal phase to support the largest C enhancements, as high as 138-fold compared to CPL alone. We also find that g is enhanced up to 15-fold when dipole modes are spectrally separated, producing large external magnetic fields compared to electric fields. We then apply these results to two systems spanning chiral separation and sensing: i) the ultraviolet-to-visible photodissociation reaction of thiocamphor; and ii) detection of D-amino acid metabolites based on vibrational circular dichroism spectroscopy. For the former, we show that metasurfaces can enable an increase in enantiomer yield from &lt;0.01% to 52% (a 5000-fold increase compared to CPL) for a reaction product with a 20% enantiomeric excess. For the latter, we show how infrared-resonant metasurfaces enable the simultaneous identification of chemical fingerprints and chiral resolution of targets at low concentrations that correlate to early onset of specific diseases. We anticipate facile, direct integration of these metasurfaces with commercially available spectrometers for translation from prototypes to clinical or industrial laboratories.

Towards all-optical chiral resolution and few-molecule circular dichroism spectroscopy with dielectric metasurfaces

2019 Fall National Meeting

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