Theory of second harmonic generation in composites of nonlinear dielectrics

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