Comparing experiment and theory in plasmonics

Progress in plasmonics has been greatly assisted by developments in experimental techniques and in numerical modelling. In this paper I look at some of the difficulties that emerge when comparisons are made between experiment and theory. Using four examples I illustrate what some of these difficulties are, from the perspective of both experiment and of modelling. Although there are many aspects to consider, two seem to be of particular concern at the time of writing; identifying the most appropriate relative permittivity (dielectric function) to describe the optical response of the metals used, and how best to make space discrete when using numerical models that rely on this approach.