Hybrid photonic-plasmonic cavities based on the nanoparticle-on-a-mirror configuration

Hybrid photonic-plasmonic cavities have emerged as a new platform to increase light-matter interaction capable to enhance the Purcell factor in a singular way not attainable with either photonic or plasmonic cavities separately.In the hybrid cavities proposed so far,the plasmonic element is usually a metallic bow-tie antenna,so the plasmonic gap—defined by lithography-is limited to minimum values of several nanometers.Nanoparticle-on-a-mirror(NPoM)cavities are far superior to achieve the smallest possible mode volumes,as plasmonic gaps smaller than 1 nm can be created.Here,we design a hybrid cavity that combines an NPoM plasmonic cavity and a dielectric-nanobeam photonic crystal cavity operating at transverse-magnetic polarization.The metallic nanoparticle can be placed very close(<1 nm)to the upper surface of the dielectric cavity,which acts as a low-reflectivity mirror.We demonstrate through numerical calculations of the local density of states that this hybrid plasmonic-photonic cavity exhibits quality factors𝑄above 10^(3) and normalized mode volumes𝑉down to 10^(−3),thus resulting in high Purcell factors(F_(P)≈10^(5)),while being experimentally feasible with current technology.Our results suggest that hybrid cavities with sub-nanometer gaps should open new avenues for boosting light-matter interaction in nanophotonic systems.

Quantifying single plasmonic nanostructure far-fields with interferometric and polarimetric k-space microscopy

Optically resonant nanoantennae are key building blocks for metasurfaces,nanosensors,and nanophotonic light sources due to their ability to control the amplitude,phase,directivity,and polarization of scattered light.Here,we report an experimental technique for the full recovery of all degrees of freedom encoded in the far-field radiated by a single nanostructure using a high-NA Fourier microscope equipped with digital off-axis holography.This method enables full decomposition of antenna-physics in its multipole contributions and gives full access to the orbital and spin angular momentum properties of light scattered by single nano-objects.Our results demonstrate these capabilities through a quantitative assessment of the purity of the“selection rules”for orbital angular momentum transfer by plasmonic spiral nanostructures.