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Dielectric nanoparticles with both strong electric and magnetic dipole (ED and MD) resonances offer unique opportunities for efficient manipulation of light-matter interactions. Here, based on numerical simulations, we show far-field diffractive coupling of the ED and MD modes in a periodic rectangular array. By using unequal periodicities in the orthogonal directions, each dipole mode is separately coupled and strongly tuned. With this method, the electric and magnetic response of the dielectric nanoparticles can be deliberately engineered to accomplish various optical functionalities. Remarkably, an ultra-sharp MD resonance with sub-10 nm linewidth is achieved with a large enhancement factor for the magnetic field intensity on the order of ∼103. Our results will find useful applications for the detection of chemical and biological molecules as well as the design of novel photonic metadevices.

With a view to biomedical and environmental applications, we investigate the plasmonic properties of a rectangular gold nanodisk array in water to boost surface enhanced Raman scattering (SERS) effects. To control the resonance wavelengths of the surface plasmon polariton and the localized surface plasmon, their dependence on the array period and diameter in water is studied in detail using a finite difference time domain method. A good agreement is obtained between calculated resonant wavelengths and those of gold nanodisk arrays fabricated using electron beam lithography. For the optimized structure, a SERS enhancement factor of 7.8 × 107 is achieved in water experimentally.

We investigate the plasmonic properties of gold nanorings in close proximity to a gold film. The rings have been fabricated using nanosphere lithography and are optimized to boost their near-infrared surface enhanced Raman scattering (SERS) effects. A SERS enhancement factor as large as 1.4×107 has been achieved by tuning the separation between the gold nanorings and the gold film. In addition, we have numerically and experimentally demonstrated an enhanced tunability of the plasmon resonance wavelength and a narrowing of the plasmon linewidth for increasing ring-film interaction.

We study the spectral properties of a triangular plasmonic nanoslit-cavity with periodic triangular grooves to optimize the field enhancement inside the nanoslit. This work is mainly based on numerical calculations and also partly supported by experimental evidence. In the nanoslit-cavity, we can distinguish following three main contributions to the field enhancement: electrostatic interaction in the nanoslit, surface plasmon polariton standing waves in the cavity and excitation, and reflection of surface plasmon polaritons by the grating. The importance of phase matching between surface plasmons generated at the nanoslit and the gratings is also investigated in order to optimize the local field intensity in the nanoslit.

We demonstrate excitation and detection of Raman scattering of a silicon substrate through a 15 nm gold nanoslit. Along with the nanoslit, a plasmonic cavity is fabricated to optimize optical transmission through the slit. Using a polarization analysis we prove that the plasmons enhanced transmission is responsible for the detection of the Raman scattered photons of the silicon substrate through the nanoslit. The optical cavity between the nanoslit and the Si substrate further enhances this backward photon transmission. This opens up prospects for new tools for near-field Raman spectroscopy and sub-wavelength measurements.