Enhanced magnetic second-harmonic generation in an ultra-compact plasmonic nanocavity.

Light Sci Appl

Department of Materials Science and Engineering, Centre for Functional Photonics, and Hong Kong Branch of National Precious Metals Material Engineering Research Centre, City University of Hong Kong, Hong Kong, China.

Published: September 2025


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Article Abstract

Observation of the second-harmonic generation (SHG) from subwavelength metallic structures is often hindered by the interrelations of higher-order multipolar contributions. In particular, the magnetic Lorentz contribution to SHG is often neglected due to the ineffective magnetic field enhancement in electrically resonant structures. Here, we demonstrate a strong Lorentz-driven SHG output at the plasmon-induced magnetic dipolar resonance in inversion-symmetry-broken plasmonic nanocavities. We observe experimentally tenfold enhancement in the SHG intensity when the magnetic dipole mode is excited, with polarization-resolved measurements confirming the significant role of the hydrodynamic Lorentz-driven second-order nonlinear response. The enhancement originates from a significant spatial overlap between the electric and magnetic fields within the nanometer-scale cavity gaps. Our findings outline the critical role played by the resonant Lorentz-driven optically induced magnetic nonlinearities in metallic nanocavities, and it paves the way towards developing highly efficient nanoscale nonlinear photonic devices.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC12411620PMC
http://dx.doi.org/10.1038/s41377-025-01962-3DOI Listing

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Observation of the second-harmonic generation (SHG) from subwavelength metallic structures is often hindered by the interrelations of higher-order multipolar contributions. In particular, the magnetic Lorentz contribution to SHG is often neglected due to the ineffective magnetic field enhancement in electrically resonant structures. Here, we demonstrate a strong Lorentz-driven SHG output at the plasmon-induced magnetic dipolar resonance in inversion-symmetry-broken plasmonic nanocavities.

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