81, 1762 (2002). [5] M. Born and E. Wolf, Principles of Optics (Cambridge University Press, Cambridge, 1999). [6] 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). [7] A. Bouhelier, Th. Huser, H. Tamaru, H.-J. G¨ untherodt, D. W. Pohl, F. I. Baida, and D. Van Labeke, Phys. Rev. B 63, 155404 (2001). [8] V. Coello, T. Søndergaard, and S. I. Bozhevolnyi, Opt. Commun. 240, 345 (2004). [9] M. Brun, A. Drezet, H. Mariette, N. Chevalier, J. C. Woehl, and S. Huant, Europhys. Lett. 64, 634 (2003). [10] The reflected intensity in F 2 depends on the angular distribution of the protrusions consti- tuting the mirror and on the variation of the damping with the different SP propagation path. [11] The [cos ( θ )] 2 law is in fact valid for every point located on the long ellipse axis. While the intensity at F 2 equals zero theoretically (as can be observed by zooming on this point in the simulation) the LR images in Fig. 3 do not have sufficient spatial resolution to observe this effect. Consequently, the experimental data in Fig. 5 represent the average of the data points around F 2 . 5