摘要： In the present chapter we explore the optical properties of plasmonic systems. The word plasmonics is often associated with the properties of metals. The reason for this association is that both the electrical and optical properties of metals are intimately related to the large number of nearly free electrons present in the conduction band of a metal. In this chapter we will primarily be concerned with the optical properties of metals, although the fundamental results that we obtain equally well describe the optical properties of other types of plasmas. The properties of nearly free electrons have been described earlier in this book, for instance as a limiting case of the Lorentz model described in Section 1.4 and also in terms of relativistic effects of plasmas as described in Section 13.7. The present chapter seeks to describe the properties of plasmonic systems in a cohesive manner. Part of the reason for interest in plasmonic systems is that they display very strong light-matter coupling, and this strong coupling leads to both linear and nonlinear properties that can be qualitatively different from those of nonplasmonic systems. This coupling leads for example to a propagating wave, known as a surface plasmon polariton (SPP), which is a mixed excitation of both electron and electromagnetic ?eld oscillations. Plasmonic systems also tend to display large nonlinear optical effects, both because metals often possess a large value ofχ (3) and because for the case of composite systems electric ?elds tend to become enhanced in regions near a metallic particle. More detailed accounts of the the role of plasmonics in nonlinear optics can be found in the accounts of Kauranen and Zayats (2012), Maier (2007), and Novotny and Hecht (2006a).