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Proceedings Paper

Visualizing enantioselective optical forces with chiral force microscopy (Conference Presentation)
Author(s): Yang Zhao; Amr Saleh; Marie-Anne van de Haar; Albert Polman; Jennifer A. Dionne

Paper Abstract

Enantiomer separation is a critical step in many chemical syntheses, particularly for pharmaceuticals, but prevailing chemical methods remain inefficient. Here, we introduce an optical technique to sort chiral specimens using coaxial plasmonic apertures. These apertures are composed of a deeply subwavelength dielectric channel embedded in silver (or gold) and can stably trap sub-20-nm dielectric specimens. Using both full-field simulations and analytic calculations, we first show that selective trapping of enantiomers can be achieved with circularly polarized illumination and proper index-matching of the immersed liquid with the particles being trapped. Opposite enantiomers experience distinct trapping forces in both sign and magnitude: one is trapped in a deep potential well while the other is repelled with a potential barrier. These potentials maintain opposite signs across a range of chiral polarizabilities and enantiomer-aperture separations. We also demonstrate how atomic force microscopy can be used to directly probe the near field optical forces from our coaxial nano-aperture. Our measurement reveals the spatial distribution of the optical near-field forces on a nanometer-sized dielectric specimen. To directly visualize the enantio-selective optical forces, we pattern silicon AFM-probes with chiral patterns. Our near-field force mapping indicates a differentiable force in the piconewton range on the chiral probes, exerted by our coaxial aperture with circularly polarized illumination. Our theoretical and experimental demonstrations indicate that the interaction of chiral light and chiral specimens can be mediated by achiral plasmonic apertures, providing a possible route toward all-optical enantiopure syntheses.

Paper Details

Date Published: 9 November 2016
PDF: 1 pages
Proc. SPIE 9918, Metamaterials, Metadevices, and Metasystems 2016, 991813 (9 November 2016); doi: 10.1117/12.2239317
Show Author Affiliations
Yang Zhao, Stanford Univ. (United States)
Amr Saleh, Stanford Univ. (United States)
Marie-Anne van de Haar, FOM Institute for Atomic and Molecular Physics (Netherlands)
Albert Polman, FOM Institute for Atomic and Molecular Physics (Netherlands)
Jennifer A. Dionne, Stanford Univ. (United States)

Published in SPIE Proceedings Vol. 9918:
Metamaterials, Metadevices, and Metasystems 2016
Nader Engheta; Mikhail A. Noginov; Nikolay I. Zheludev, Editor(s)

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