We normally define a mode by its effective index or propagation constant. For a mode to be excited its refractive index should be greater than the cladding ref. index (in case of fiber, waveguides, metal nanowires etc.). Is it also true in the case of localized surface plasmons?
Dear Jitender,
what you state is the fact that in order to have a guided mode the fields outside the guiding "core" have to decay exponentially. This is the case as soon as your condition is met. This is definitely also true for plasmonic modes. I recommend to read the paper by Takahara et al. (Opt. Lett. 22, 475 (1997)).
Bert
Strictly speaking, there is no "propagation constant" for a localized mode; it doesn't propagate. A surface plasmon polariton or simply a surface plasmon is a propagating mode in a structure that is translationally invariant in at least one dimension. It will have a well-defined omega-k relation. There would be less confusion in the field if the term "plasmon mode" were used to refer to localized modes such as Mie-type resonances, and "surface plasmon" used to refer to propagating modes, pinned to a surface and decaying evanescently far away.
Thanks you Dear Willes.
But non propagating characteristics of "Plasmon mode" can also be incorporated with high value of imaginary part of propagation constant let's say, in case of Ag Nanowires. If its imaginary part is very high then it will die out instantly. So the "Surface Plasmon mode" will be excited but they will not propagate at all, and we refer it as "Plasmon mode".
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