1. Context

Since the 2000s, plasmonics has been an area of intense study for its ability to concentrate light on a sub-wavelength scale. The principle consists in confining light in the form of surface plasmon-polaritons (SPP): these resonant quasi-particles result from the strong coupling between an electromagnetic wave and an electric polarization wave carried by the surface conduction electrons of certain metals. In ascending order of resonance frequencies, copper, gold, silver and aluminum exhibit plasmonic responses from near infrared (IR) to near ultraviolet (UV). The electromagnetic wave thus "hooked" onto the metal surface by the plasmonic interaction presents an evanescent wave profile on either side of the interface, and contains a very high optical power density. Light is slowed and concentrated to the sub-wavelength scale at the metal surface, available for exalted interactions with any...