content_image/331054.jpg content_image/331052.jpg
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 

<img src='content_image/331054.jpg'>

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 

<img src='content_image/331052.jpg'>

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 

