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In the same context we developed in recent years a systematic approach using far-field 

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microscopy to analyze quantitatively the interaction between SPPs and plasmonic devices by using LRM. The nanodevices studied were all fabricated by electron beam lithography (EBL) allowing the precise and reproducible tailoring of metal and dielectric surfaces on a lateral size dimension down to 20 nm [37]. As an example we show in Fig. 8 B a LRM image obtained by using a gold ridge (50 nm height, 150 nm width) lithographed on a 50 nm thick gold film to launch two well collimated and counter propagating SPP beams. These beams are launched by focussing a laser beam with a microscope objective (10x, numerical aperture NA = 0 . 3) on the gold ridge. Scattering by the nanostructure gives rise to evanescent waves supplying the right amount of momentum necessary for generating a SPP wave. The optical LRM setup is sketched in Fig. 8 A. Leakage radiation emitted through the glass substrate is collected by an immersion oil objective (63x, numerical aperture, NA = 1 . 3). Light is subsequently refocussed on a charge coupled device (CCD) camera. The direct mapping of 

