DYNAMICAL DENSITY-MATRIX THEORY OF MULTIPHOTON TRANSITIONS IN SEMICONDUCTORS

A dynamical theory of multiphoton transitions in semiconductors is dev eloped using a density matrix approach. It is shown that, in dipole ap proximation, these transitions require a mixed parity of the basis sta les and that band-diagonal coupling's of the electromagnetic field to Bloch electrons have to be included. The general theory is outlined us ing the simple, but solvable model of a diatomic tight-binding chain. Possible extensions and applications of the approach are discussed.