Dressed State in Solids and Optical Resonance Saturation

The concept of the dressed-atom is extended to electronic system in solids under nearly resonant coherent laser field, which is in contact with phonon and photon fields. Optical resonance saturation and nonlinear optical free induction decay are discussed in terms of this dressed state. The effective temperature is defined in terms of population ratio between the doublet of the dressed states and is related to the optical phenomena from the aspect of an open system far from thermal equilibrium.