Plasmonic nanoconfined light source
The extraordinary properties of surface plasmon polaritons (SPP) can be used for delivering, controlling and confining light on the nanoscale. We demonstrated the realization of a novel nanoscopic light source by grating-coupled excitation of SPP onto the shaft of conical nanoscopic metallic tips which upon propagation on the tip surface converge in a highly localized light spot at the ultrasharp apex region.
Linear gratings are written more than 10 Âµm away from the apex by focused ion beam milling. Broad-band laser excitation of the grating results in resonant excitation of SPP with spectral characteristics corresponding to the illumination conditions (incident angle, polarization) and grating period:
In the context of using this intense nanscopic light source for near-field optical experiments, we characterized the field distribution around the apex region by studying the optical coupling of the tip-scattered light to smooth Au surfaces. Strong increase in the optical response is observed for incident polarization orthogonal to the grooves (p-in) on a lenghtscale of about 10 nm, comparable to the tip apex radius:
This adiabatic nanofocusing on nano-designed tips provides a spectrally tunable nanoscopic light source suitable for background-free apertureless near-field microscopy and spectroscopy. By taking advantage of the ultrafast laser pulses, this may offer temporal resolution down to the 10 fs level, together with the nanometer spatial resolution.