Second and third harmonic generations in random composites of nonlinear dielectrics

We study the effective nonlinear susceptibility tensor d(- 2 omega;omega,omega) for second-harmonic generation and chi for third-harmonic generation in a nonlinear composite medium. Simple expressions for these susceptibilities in terms of the position-dependent nonlinear susceptibilities of the constituents and local field factors in a corresponding linear medium are used to evaluate the nonlinear response. These expressions are useful starring points to develop effective medium approximations. (C) 2000 Elsevier Science B.V. All rights reserved.