  We study the interaction of electromagnetic waves with electrons. Our results
can be applied to radio waves in the ionosphere or to lasers impinging on
metals causing melting. We generalize the classical analysis of Zener to the
case which includes the interactions of the electrons with lattice vibrations
or the positive ions. We use the induced polarization to give a globally
coherent and unifying analysis of the two cases, where collisions are important
and where they are negligible.
