After a general introduction to plasmonics, the optics of metal nanostructures, I will describe different technologies used for the fabrication of metal nanostructures with well-controlled features down to about 10 nm. Only a few plasmonic metals, such as gold, silver or aluminum, produce strong optical resonances, thus limiting the spectral range where plasmonics can be used. To extend that range, we recently developed a technology for the fabrication of Au-Ag alloyed nanostructures with well-controlled shapes that can be combined into metasurfaces to produce lenses or holograms. The working principle of these metasurfaces consists in engineering the phase associated with light scattered from metallic nanostructures to mimic the effects of gratings, lenses or phase plates.
While the metal dictates the wavelength range where plasmonic effects can occur, the dimensions and the shape of the nanostructures control the type of optical resonances that can be supported by a given nanostructure assembly. These optical resonances can be divided in essentially two families: electrical and magnetic modes. At optical frequencies, it is believed that electrical resonances always dominate the response of the system, which has led to some confusion on the so-called magnetism at optical frequencies. I will however demonstrate that it is possible to produce plasmonic systems that radiate purely magnetic light. Finally, I will share some recent results on hybrid nanostructures that combine plasmonic elements with dielectric resonators and show how they can be utilized for sensing.