projects FP6 NMP4-CT-2003-505699 and FP6 2002-IST-1-507879 are acknowledged. [1] H. Raether, Surface Plasmons (Springer, Berlin, 1988). [2] B. Hecht, H. Bielefeldt, L. Novotny, Y. Inouye, and D. W. Pohl, Phys. Rev. Lett. 77 , 1889 (1996). [3] S. I. Bozhevolnyi, and F. A. Pudonin, Phys. Rev. Lett. 78 , 2823 (1997). [4] H. Ditlbacher, J. R. Krenn, N. Felidj, B. Lamprecht, G. Schider, M. Salemo, A. Leitner, and F. R. Aussenegg, Appl. Phys. Lett. 80 , 404 (2002). [5] H. Ditlbacher, J. R. Krenn, G. Schider, A. Leitner, and F. R. Aussenegg, Appl. Phys. Lett. 81 , 1762 (2002). [6] A. Drezet, A. L. Stepanov, H. Ditlbacher, A. Hohenau, B. Steinberger, F. R. Aussenegg, A. Leitner, and J. R. Krenn, Appl. Phys. Lett. 86 , 074104 (2005). [7] A. Bouhelier, Th. Huser, H. Tamaru, H. -J. G¨ untherodt, D. W. Pohl, Fadi I. Baida and D. Van Labeke, Phys. Rev. B. 63 , 155404 (2001). [8] A. stepanov, J. R. Krenn, H. Ditlbacher, A. Hohenau, A. Drezet, B. Steinberger, A. Leitner, and F. Aussenegg, Opt. Lett. 30 ,1524 (2005) [9] A. Zeilinger, Am. J. Phys. 49 , 882 (1981). C. H. Holbrow, E. Galvez, and M. E. Parks, Am. J. Phys. 70 , 260 (2002). [10] H. Ditlbacher, Phd Thesis, Karl-Franzens Universit¨ at Graz (2003). [11] Each dipole generate at x, y a scalar field [12] M. Brun, A. Drezet, H. Mariette, N. Chevalier, J. C. Woehl, and S. Huant, Europhys. Lett. 64 , 634 (2003). [13] If we don’t neglect the SPP damping we obtain V$_{1}$ = 2 | R || T | / ( | R | $^{2}$e − δ/ (2 L SPP ) + | T | $^{2}$e − δ/ (2 L SPP $^{)}$) and V$_{2}$ = 2 | R || T | / ( | R | $^{2}$e − δ/ (2 L SPP ) + | T | $^{2}$e − δ/ (2 L SPP $^{)}$) for respectivelly the 10 [2, 4, 12]. r = √ ( x − x$_{s}$ ) 2 + ( y − y$_{s}$ ) 2 is the distance separating the source located at x$_{s}$, y$_{s}$ from the observation point, and Θ is the angle between the dipole P and the vector position r going from the source to the observation point. The dipole is induced by the local electric field E $_{0}$( x$_{s}$, y$_{s}$ ) and thus P = χ E $_{0}$( x$_{s}$, y$_{s}$ ) where χ is the dipole polarizability. Ψ( x, y ) ∝ cos (Θ) e ik SPP $^{r}$e − r/ (2 L SPP ) $_{/}$√$_{r}$