Abstract
Simple chiroptically active metamaterials are difficult to realize in practice but could pave the way for a range of important applications, such as sensitive optical biosensors, asymmetric catalysis, and novel polarization manipulation devices. We show that a metasurface based on a random arrangement of anisotropic but aligned gold nanoparticles can exhibit an almost perfect selectivity towards incident photon spin for evanescent excitation with visible to near-infrared light. The experimentally attained reflection contrast between left- and right-handed circularly polarized light peaks at , in excellent agreement with analytical theory. These results are important for the development of future photonic and plasmonic polarization-based technologies.
- Received 30 March 2015
DOI:https://doi.org/10.1103/PhysRevX.5.041019
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Published by the American Physical Society
Popular Summary
A chiroptically active material preferentially interacts with either left- or right-handed circularly polarized light. Although chiroptical effects are weak in natural materials, they are critically important in the detection of molecules with structures that do not superimpose with their mirror image (i.e., so-called enantiomers such as DNA). Accordingly, many researchers have attempted to develop artificial nanostructures and materials with enhanced optical activity. However, a simple-to-fabricate and effective chiroptical metasurface for the visible-to-near-infrared spectral range has not yet been reported. In this work, we show that strong chiroptical effects can be achieved in an achiral metasurface composed of oriented elongated plasmonic gold nanoparticles.
We employ a single layer of gold nanoparticles, each roughly 175 nm long and 75 nm wide, fabricated on a glass surface. We study, both experimentally and analytically, how a beam of light is absorbed and reflected from this layer based on its polarization state. We find that chiroptical effects are most pronounced when the surface is illuminated under total internal reflection conditions, in which case the extinction contrast between left- and right-handed light can reach 90% for certain combinations of nanoparticle orientations and illumination angles.
We expect that our findings will be useful for a range of novel photon-spin selective devices for optical communication technologies and biophotonics.