Janne Simonen

We demonstrate third- (THG) and second-harmonic generation (SHG) microscopy of individual silver nanocones using tightly focused cylindrical vector beams (CVBs). Although THG is expected to be a weaker process than SHG, the yield for THG with radial polarization was higher than for SHG. We also found an excellent correlation between the imaging properties of THG and SHG, suggesting that both are governed by the same overall features of the individual nanocone. We also found that the transverse spatial resolution of THG with CVBs, particularly RP, exceeds that of SHG. Our work establishes the potential of THG microscopy with CVBs for structure-sensitive imaging of three-dimensional (3D) metal nano-objects.

We introduce an imaging technique based on second-harmonic generation with cylindrical vector beams that is extremely sensitive to three-dimensional orientation and nanoscale morphology of metal nano-objects. Our experiments and second-harmonic field calculations based on frequency-domain boundary element method are in very good agreement. The technique provides contrast for structural features that cannot be resolved by linear techniques or conventional states of polarization and shows great potential for simple and cost-effective far-field optical imaging in plasmonics.

Resonant waveguide gratings (RWG) consist of a surface waveguide and a surface grating that diffracts light both into and out of the waveguide mode for a particular angle of incidence. On resonance, the field diffracted out of the waveguide mode interferes with the directly transmitted and reflected fields in such a way that it is possible (at least theoretically) to obtain 100% reflection. Significantly, RWGs can also lead to strong local fields within the structure, which can enhance two-photon fluorescence or second-harmonic generation (SHG). Here, we report on SHG from an all-dielectric sub-wavelength RWG made of SiNχ that allows for a 1000x enhancement compared to a thin-film of the same material of comparable thickness and in optimum geometry.

Here, we show that second harmonic generation (SHG) imaging using cylindrical vector beams permits highly sensitive mapping of the local response in a gold nanocone array. Our sample consists of gold nanocones on a silicon substrate fabricated using UV-nanoimprint lithography.

We present two silver nanocones separated by 450 nm, well beyond the typical gap spacing of coupled nanoantennas, and connected by a metal bridge to facilitate plasmonic coupling between them. The tip-enhanced Raman scattering from crystal violet molecules is found to be almost an order of magnitude higher from the bridged cones than from individual cones. This result is supported by local-field calculations of the two types of structures. The bridged nanocones are easily fabricated by a nanoimprint-based process, thus offering a faster and simpler approach compared to other fabrication techniques.