THEORY OF 2ND-HARMONIC GENERATION IN COMPOSITES OF NONLINEAR DIELECTRICS

We consider the effective nonlinear susceptibility tensor d(-2 omega;o mega,omega) for second harmonic generation in a nonlinear composite me dium. We derive a simple expression for this susceptibility in terms o f the position-dependent tensor d, and three factors that describe the local field enhancement in a corresponding linear medium. The resulti ng expression can be used to calculate the local-field enhancement of d in many geometries. In the dilute limit, the general expression redu ces to a result previously derived. (C) 1997 American Institute of Phy sics.