Experimental studies of the length dependence of second-order nonlinear optical responses of conjugated molecules

We present experimental results on the study of the length dependence of molecular second-order nonlinear optical responses based on a new class of heteroaromatic compounds. We observed a power-law dependence of the second-order molecular susceptibility on the length of the molecule with an exponent of 2. The exponent value observed is in agreement with that obtained from the equivalent internal-field model using recently reported data for third-order susceptibility [Thienpont et al., Phys. Rev. Lett. 65, 214 (1990)].