I have a problem with understanding of these sentences:
We have indicated in the opening paragraph of the Introduction that surface plasmon polaritons are solutions of Maxwell’s equations in which the effects of retardation—the finiteness of the speed of light—are taken into account. An important subclass of surface plasmon polaritons are surface plasmons. These can be viewed as the limiting case of surface plasmon polaritons when the speed of light is allowed to become infinitely large.
Nano-optics of surface plasmon polaritons (1.1.2) - Anatoly Zayats et.al.
How can we allow c be infinite? Why is it correct in case of surface plasmons?
The article is available online, easy to find with Google Scholar