Configurational disorder and the local field effects in nonlinear optical systems

We argue that in nonlinear optical systems with atoms randomly distributed in crystals or amorphous hosts one should go beyond the Clausius-Mossoti limit in order to take into account the effect of local field fluctuations induced by configurational disorder in atom position. This effect is analyzed by means of a random local mean field approach with neglect of correlations between dipole moments of different atoms. The formalism is applied to 3-level Λ type systems with quantum coherence possessing an absorptionless index of refraction and lasing without inversion. We. show that the effect of configurational fluctuations results in the suppression of the atom susceptibility compared with the predictions based on the Clausius-Mossoti equation.