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Nanoapertures and surface plasmon polaritons
Micro & Nano Characterization Group
MNC Group

Plasmon polaritons (SPP) are surface waves that propagate on thin metallic films, at the interface between a metal and a dielectric (the air for instance). These waves can transport light on distances much larger than the wavelength, while remaining confined in the surface region. A way to create these waves is to nanostructure the sample, for instance by creating nano-apertures. With the fluorescent particle glued at the end of the tip (see the experimental set-up in Fig. 1), we have been able to vizualize the surface waves created by nanoslit apertures made in a thin gold film.

Fig. 1: Experimental set-up.
Fig. 2: Near-field distribution between two slits in a thin gold film : XZ scan (a); XY scan (b); SEM of the structure.

We show in Fig. 2 the field distribution between two parallel slits made in a thin gold film, and illuminated in a transmission mode by a TM-polarized plane wave. The images have been obtained in a plane perpendicular to the surface (a) or on the surface (b). Each slit creates surface waves that give rise to interference fringes. Numerical simulations (performed at the Institute of Optics in Orsay by P. Lalanne), are in good agreement with the experimental data. The generated surface waves are composed of a surface plasmon polariton and of a quasi-cylindrical wave (CW) that rapidly decays when getting away from the slit.

See for instance:

- Phys. Rev. Lett. 98, 153902 (2007).                         - Appl. Opt. 48, 8573 (2007).
- Appl. Phys. Lett. 94, 011114 (2009).                       - Phys. Rev. B 83, 085422 (2011).
- Plasmonics 8, 1515 (2013).                                        - Appl. Opt. 54, 9326 (2015).

We also study the generation of surface waves by other structures : ridges, chains of nanoparticles, nanorods. Depending on the type of nanostructures and of their arrangement on the gold surface, various interference patterns can be observed. It is also possible to tune the propagation of these surface waves by adjusting the polarization or the angle of incidence.