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constitutes a one-dimensional lattice of parallel gold ridges (50 nm height, 140 nm width) separated by a distance P defining the period of the lattice. The period P is connected to the SPP wavelength by λ$_{SPP}$ = 2 π/k$_{SPP}$ < λ and to the angle of incidence reflection θ$_{SPP}$ of the SPP beam relatively to the (in plane) normal to the lattice by 

<img src='content_image/369197.jpg'>

In the present case shown in Fig. 10 the Bragg mirror is optimized for λ = 800 nm (i. e., λ$_{SPP}$ = 785 nm ) and for θ$_{SPP}$ = 45 ◦ incidence angle which means P ≃ 555 nm . The experimental analysis of such a Bragg mirror when the resonance condition ( λ , θ$_{SPP}$ ) is fulfilled reveals a very high reflectivity of R ≃ 95% (see, for example, [34] for some earlier results on SPP Bragg mirrors studied with fluorescence microscopy). However, in the present experiment we choose an incident angle θ = 65 ◦ . As a consequence the reflectivity was much lower (see Fig. 10 A and more details in [39]). This configuration 

<img src='content_image/369198.jpg'>

reveals SPP interferences in the vicinity of the mirror (Fig. 10 A). In Fig. 10 B we show the 

