Gap surface plasmon

It is the form under which light propagates inside an extremely thin gap between two metals (having the same nature or not).

The distance between the metallic area has to be typically smaller than 50 nm in order to noticeably slow the guided mode.

Devices based on gap-plasmon, such as resonators, present a typical size which is of the order of the effective wavelength.

Such structures (see picture) present a very small volume compared to the wavelength is vacuum (which allow to reach a very important Purcell effect).

Such resonators can then be used to design metasurfaces, fabricate reflection holograms or for subwavelength color printing.