This seems fundamental, but I just can't get my head around it.
Many proposed plasmonic absorbers (2D structures metallic gratings) claim to have enhanced absorbance due to excitation of Surface Plasmon Polaritons. How are SPP excited in these cases, since there is no coupling device to increase the momentum? It's a wavefront hitting an metallic interface and that's it, for most cases.
The grating increases the momentum by any integer number of reciprocal vectors automatically.
The grating provides the additional momentum. See for instance
A.Christ et al., Phys. Rev. B 74, 155435 (2006)
Thank you all for your quick response and attention.
I realize the gratings do increase the momentum, since you can couple SPP with them. The precise underlying physical mechanism is still a bit cloudy to me.
The paper you provided were greatly elucidating, but I think I still need to read some more about i.e. how and what are the excited modes, dispersion relations and so on.
On a flat surface, the angle of reflection is equal to the angle of incidence. On a grating, there are multiple peaks in the reflection including evanescent waves. The dispersion can be obtained by substituting q with q +nQ, where Q = 2 pi/d, and n is any integer number.
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