chapter  6
Infrared Surface Plasmon Resonance
Pages 26

Drude conductor, Ag and Au have plasma frequencies of 2.18 and 2.183 × 1015 s-1, respectively, [8]. However, it is important to note that the Drude model does not describe the optical properties of the noble metals accurately and the model can only be used to describe the lower frequency region of the dielectric functions where the real part becomes less than zero. The Drude model does not capture inter-and intraband transitions, which define the optical properties of those metals in the UV-Vis region of the electromagnetic spectrum. Clearly, the noble metals have plasma frequencies far above the infrared region. The vast majority of plasmonic applications have therefore been in the visible region of EM spectrum to take advantage of relatively large optical response due to Au when the index of refraction changes near an Au surface excited in an appropriate configuration [1-3].