Surface-enhanced hyper-Raman scattering and the chirality conferral process revealed by Plasmonic Helical Metamaterial platforms
ORAL · Invited
Abstract
Chirality conferral – the transfer of handedness between different forms of matter – plays a fundamental role in both biological self-organization and nanoscale photonics. We report field-driven chirality conferral from chiral plasmonic gold nanohelices to nominally achiral crystal violet (CV) molecules, leading to the first experimental observation of hyper-Raman optical activity (HROA), a phenomenon predicted over four decades ago. The doubly resonant hybrid system was engineered so that the nanohelices and CV resonate respectively at the fundamental and second-harmonic frequencies, maximizing light–matter coupling under Fermi’s golden rule. Circular-intensity-difference spectra recorded under right- and left-circularly polarized illumination reveal intrinsic chirality, invariant under sample rotation and absent in achiral controls.
In parallel, we demonstrate exceptionally strong metasurface-enhanced Raman optical activity (meta-ROA) in this system, with polarization-resolved chiral difference ratios several orders of magnitude larger than conventional molecular ROA. We believe that it is precisely this strong meta-ROA response, reflecting intense chiral near-fields and efficient chirality conferral, that enables the detection of the weaker hyper-ROA process. Theoretical analysis extends the hyper-Raman formalism to include surface enhancement and cross-terms between electric-dipole, magnetic-dipole, and electric-quadrupole amplitudes, revealing the quantum origin of the chiroptical response.
By demonstrating chirality conferral from chiral nanostructures to achiral molecules, we have revealed the underlying physical mechanism that, by reciprocity, must also enable the reverse process – the conferral of molecular chirality onto achiral nanoparticles. Since the same near-field coupling governs both conferral directions, this corollary follows naturally from our findings. This reciprocity extends chiroptical spectroscopy toward regimes of dramatically enhanced sensitivity, where hybrid molecule–metamolecule systems act simultaneously as amplifiers and detectors of chirality.
In parallel, we demonstrate exceptionally strong metasurface-enhanced Raman optical activity (meta-ROA) in this system, with polarization-resolved chiral difference ratios several orders of magnitude larger than conventional molecular ROA. We believe that it is precisely this strong meta-ROA response, reflecting intense chiral near-fields and efficient chirality conferral, that enables the detection of the weaker hyper-ROA process. Theoretical analysis extends the hyper-Raman formalism to include surface enhancement and cross-terms between electric-dipole, magnetic-dipole, and electric-quadrupole amplitudes, revealing the quantum origin of the chiroptical response.
By demonstrating chirality conferral from chiral nanostructures to achiral molecules, we have revealed the underlying physical mechanism that, by reciprocity, must also enable the reverse process – the conferral of molecular chirality onto achiral nanoparticles. Since the same near-field coupling governs both conferral directions, this corollary follows naturally from our findings. This reciprocity extends chiroptical spectroscopy toward regimes of dramatically enhanced sensitivity, where hybrid molecule–metamolecule systems act simultaneously as amplifiers and detectors of chirality.
*This work was funded by The Royal Society, the Leverhulme Trust, and the Engineering and Physical Science Research Council (EPSRC).
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Presenters
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Ventsislav K Valev
- University of Bath