Figure 1: Sketch of the electrodynamic properties of a superconductor at : (a) in the upper panel the frequency dependence of the real and imaginary parts of the conductivity and is plotted, normalized to the normal state behavior , which basically can be assumed to be constant in the spectral range of interest, where with the quasiparticle scattering rate. (b) The second panel exhibits the frequency dependence of the relative transmission and absorption . (c) The optical reflectivity of a superconductor is compared to the reflectivity of a normal metal , assuming a dc conductivity of .