Evanescent Waves in Optics by Mario Bertolotti Concita Sibilia & Angela M. Guzmán

Author:Mario Bertolotti, Concita Sibilia & Angela M. Guzmán
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

The maximum possible field enhancement on a smooth surface is

(5.44)

where

Elight is the electric field of the incident light, εi, εm and εs are the dielectric constant of the adjacent medium, metal, and of the prism through which the metal film is illuminated to excite SPP, respectively. For a 60 nm thick silver film illuminated with red light, the intensity enhancement can reach more than two orders.

The parallel components of the wavevector necessary for plasmon excitation can also be found if the metal surface is rough11 or are present suitably designed metallic particles. The scattered field wave-vector can match with the field component of SPP waves so that coupling to SPP can be accomplished locally.12 On a rough surface, the SPP excitation conditions can be achieved without any special arrangement. Diffraction of light on surface features can provide coupling to the SPP modes because the diffracted components of light with all wave-vectors are present. However, the conditions for excitation are hill defined and the light coupling is not efficient.

Figure 5.12 shows excitation with a SNOM probe or by diffraction on surface features.

Fig. 5.12Excitation of plasmons with a SNOM probe (upper) or by diffraction on a small particle (lower)

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