As far as I have understood, surface plasmon can't be excited with natural light because the dispersion relation of the plasmon doesn't cross the vacuum dispersion relation of light. But, when we decrease the size (for example, we take a nanoparticle), we are now in quasistatic approximation. Thus, the electric field is uniform in the sphere and we don't have plasmon propagation on the surface. Instead, we have a localised excitation. Surface plasmon (wave propagation inside) : Localised surface plasmon (no propagation because electric field is uniform on the sphere) But then, what I don't understand is that for me we then should only have localized surface plasmon in nanoparticle. As bulk plasmon result of wave propagation and because we are in quasistatic approximation (electric field vary in time but uniform on the sphere), such modes can't occur for nanoparticle. But in an article I'm reading it seems like it is possible to have bulk excitation in nanoparticles, so I'm very confused... Here is the link for the article : doi:10.1038/nature10904 My question : what does that mean to have bulk plasmon for nanoparticle ? As the quasistatic approximation is true such modes should'nt exist ?