Tuning localized plasmons in nanostructured substrates for surface-enhanced Raman scattering

Comprehensive reflectivity mapping of the angular dispersion of nanostructured arrays comprising of inverted pyramidal pits is demonstrated. By comparing equivalently structured dielectric and metallic arrays, diffraction and plasmonic features are readily distinguished. While the diffraction features match expected theory, localised plasmons are also observed with severely flattened energy dispersions. Using pit arrays with identical pitch, but graded pit dimensions, energy scaling of the localised plasmon is observed. These localised plasmons are found to match a simple model which confines surface plasmons onto the pit sidewalls thus allowing an intuitive picture of the plasmons to be developed. This model agrees well with a 2D finite-difference time-domain simulation which shows the same dependence on pit dimensions. We believe these tuneable plasmons are responsible for the surface-enhancement of the Raman scattering (SERS) of an attached layer of benzenethiol molecules. Such SERS substrates have a wide range of applications both in security, chemical identification, environmental monitoring and healthcare

Optical spectroscopy of neodymium-doped tantalum pentoxide slab waveguides

Neodymium doped tantalum pentoxide (Nd:Ta2O5) waveguides were fabricated by RF sputtering from a Nd doped Ta2O5 target. Waveguide losses, absorption spectra, fluorescence spectra and excited-state lifetime were measured, and show promise for realisation of waveguide lasers

Nd:Ta₂O₅ rib waveguide lasers

Ta2O5 waveguides offer great potential for high-density active photonic crystal circuits and their combination with rare-earth dopants for active devices is of interest for increasing their potential functionality. To this end, neodymium-doped Ta2O5 rib waveguide lasers have been fabricated on an oxidized silicon wafer by rf sputtering and argon ion-beam milling and laser action in this material has been demonstrated. Lasing was observed at wavelengths between 1060 and 1080 nm and an absorbed pump power threshold of 87 mW was obtained