Fig. 1
From: Non-fluorescent nanoscopic monitoring of a single trapped nanoparticle via nonlinear point sources
3D plasmonic nanoantenna. a Schematic of the proposed 3D plasmonic nanoantenna. Squeezed photons in an extremely small volume (Vm = 6.1 × 10−8λ3) of the 3D plasmonic nanoantenna enable the trapping of a sub-5-nm particle and create strong background-free second-harmonic signal. b |E|2 profiles of the antenna mode in the xy- and yz-plane. The resonant wavelength of the antenna is 1560 nm in water. The y-polarized incident beam is pumped from the bottom to excite the resonant mode. c Scanning electron microscopy images of the fabricated 3D plasmonic nanoantenna. The central-gap size (g) and the vertical taper angle are measured to be ~5 nm and ~65°, respectively
