In figure 3 of this document, there is data relating $\Re(\sigma(\omega))$ to the Fermi energy. It is claimed that $\Re(\sigma(\omega))$ is determined via reflectivity measurements. How is this done? ...
How does the nonlinear absorption coefficient depend on the band gap? How can that coefficient be calculated theoretically? (Preferably with an example)
In the two Phys.SE questions What is the mechanism behind the slowdown of light/photons in a transparent medium? and Why glass is transparent? transparent media were discussed. But I'd like to clarify ...