Dielectric response, nonlinear-optical processes, and the Bloch–Maxwell equations for polarizable fluids

Reduced equations of motion, which generalize the Bloch–Maxwell equations to polarizable fluids with intermolecular interactions, are derived. Local-field effects are analyzed using the solvable limiting case of a perfect crystal. The dielectric function ∊(k, ω) and the nonlinear susceptibility χ(3) are explicitly evaluated for a model system. Two four-wave mixing techniques, which provide a direct probe for transport processes, are analyzed: the transient grating and its frequency-domain analog. A unified picture is provided for transport phenomena, cascading, and polariton effects.