ACS Photonics 1, 365–370 (2014)

The transmission of light through very small holes in metal films is known to be surprisingly efficient. A beam of light emerging from such holes can be tailored not only by adjusting the size of the hole, but also by placing diffractive elements on the film. A popular approach to enhance transmission by plasmonic effects is to use a periodic relief structure consisting of concentric rings (a bullseye structure) around the aperture. In recent work, Jue-Min Yi and colleagues from the Universities of Strasbourg and Toulouse in France have considered the effect of the incident polarization and the design of the bullseye structure on the light exiting the aperture. The researchers claim that previous studies overlooked the role of polarization on the transmission characteristics of this structure and that their work is the first extensive experimental study. The aperture and concentric grooves and rings were optimized to generate an intense beam and to tailor the directivity and 'gain' of the structure. The scientists conclude that the efficiency of surface plasmon conversion can be increased by increasing the number of rings, but that the propagation length of about 25 μm limits the maximum size of the rings.