Optical properties of a conductor Why do metals reflect so well? Modification for conductor: A For bound charges, the spring limits the displacement r What limits r for free charges?

displacement r for bound, unbound charges

Optical properties of a conductor First, start with (opposite case!) of dielectric: (insulator) A Modification for conductor:

Typical plasma frequencies   density N (m-3) (Hz) metals 1028 1016 semicond. (pure) 1024 1014 semicond. (doped), fusion expts 1020 1012 ionosphere (60 to 450 km) 1011 107 interplanetary space 105

Optical properties of a conductor Case of very little damping g<<w: A For w< wp , check the sign of . Which must be nonzero? n b) k

Optical properties of a conductor Since wo 0, can we simply shift n(w), k (w)?

n,k for metal. Plasma frequency divides two regimes g=wp/10 g=0 n, k g=wp/10 n, k A Which frequencies are transmitted well? Which are reflected well?

Reflectance vs. Wavelength Plasma frequency of silver

Poynting Vector energy density in a vacuum Its magnitude is the intensity: Power/area What equation does this look like? So S is an energy flow vector: energy/area/time

Directions of vectors

S, irradiance, intensity For a plane wave in index n, derive the time average intensity

The following are always true (definition and basic MaxEqn for plane wave) Which vector pair is not guaranteed to be perpendicular? E, S E, k E, B S, E B, k

Preview:

Wave equation P. is a solution to It is also a solution to ____: 1) 2) eqn 1 eqn 2 both neither