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 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 reveals SPP interferences in the vicinity of the mirror (Fig. 10 A). In Fig. 10 B we show the FIG. 11: (A) Fourier space cross-cut along the short solid line in Fig. 10 B corresponding to the L beam (see inset). Experimental data (symbols) are compared with a Lorentz fit (solid curve). The intensity is normalized by setting the maximum intensity of L to 1. (B) Direct space cross-cut along the L beam in Fig. 10 A. Data points (symbols) are compared to an exponential fit (solid line). Data from [39] ( c ○ , Appl. phys. Lett., American Institute of physics, 2006). 18 P = λ$_{SPP}$ 2 cos θ$_{SPP}$ . (24)