Here is what I understood from the plasmons:
Bulk plasmon: we need longitudinal electric wave to excite them. Then it is not possible to excite them with natural light.
Surface plasmon: we can't "directly" excite them with natural light. Indeed the vacuum dispersion relation of light and the dispersion relation of the surface plasmon don't cross. We thus need to increase the parallel of the surface component of the EM wave (to do it we can use evanescent waves for example).
Localised surface plasmon: It is a surface plasmon on a small particle (spherical nanoparticle). Using Mie theory we can see that natural light can excite them.
What I don't understand is: Why for localized surface plasmon we don't have the problem of the dispersion relation of light must cross the dispersion relation of the surface plasmon? Does the dispersion relation of the surface plasmon change if the particle start to be very small? I don't understand?