Many nontransparent materials used in optics and optoelectronics devices show frequency-dependent complex electrical permittivity in the visible domain. The complex refractive index of bulk material is an important parameter that determines the optical behavior of a given material and in many cases any nanophotonic structure that might be fashioned from such a material. The complex refractive index for materials in the visible domain is given by the square root of the electrical permittivity [Eq. (8.36)]. The complex refractive index constitutes an important simulation parameter in optics and photonics. The imaginary parts of the refractive index and the electrical permittivity are associated with the absorption and the conductivity of the material, respectively. It is also important to understand that the implementation of FDTD depends on the actual relations among various components of the electric and magnetic fields, which in turn are determined by the nature of material properties. In this chapter we develop a simple dispersive algorithm that can be used when metal nanostructures need to be simulated in the visible domain.
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