associated with a given hole show clearly that the QD excitation is mediated by SPPs propagating on the aluminum film. Fig. 6B shows the radial dependence of the collected intensity. These results agree well with a 2D SPP dipole model supposing an effective dipole located at the tip apex [8, 22] (see also the discussions concerning the Bethe-Bouwkamp [24–26] theory of diffraction by a small aperture in a metal film in [27–31]). Following this model the SPP wave can be theoretically modelled by a scalar wave Ψ( ρ, θ ) given by FIG. 6: (A) Sketch of the experiment using a NSOM tip to excite SPPs on an aluminum film with nanoholes. The film containing 240 nm diameter holes covers a CdTe/ZnTe system of QDs whose spectral luminescence induced by SPP excitation is characteristic of a given hole. The laser excitation wavelength is 514.5 nm. (B) Radial mapping of the SPP intensity. The SPP intensity is proportional to the QDs luminescence of a given hole. The curve represents the evolution of the total luminescence collected (using a detector in the optical far field) as a function of the distance R separating the NSOM (source) from the hole (probe). The experiment is made at 4.2 K [22] ( c ○ Europhys. Lett., EDP, 2003). where k$_{SPP}$ = k ′ $_{x}$+ ik ′′ x is given by Eq. 3, ρ, φ are polar coordinates on the metal film and the origin of the coordinate is taken at the dipole position. φ is the angle between the dipole associated with the NSOM tip (parallel to the polarization of the laser beam injected in the Ψ( ρ, φ ) = const. e ik SPP $^{ρ}$cos φ √ ρ , (22) 13