PHOTOINDUCED NONLINEAR OCTUPOLAR POLARIZATION - TRANSIENT AND PERMANENT REGIMES

An original poling method using purely optical means and based on a du al-frequency interference process is presented. We show that the coher ent superposition of two beams at fundamental and second-harmonic freq uencies results in a polar field with an irreducible rotational spectr um containing both a vector and an octupolar component. This enables t he method to be applied even to molecules without a permanent dipole s uch as octupolar molecules. After a theoretical analysis of the proces s, we describe different experiments aiming at light-induced noncentro symmetry performed respectively on one-dimensional Disperse Red 1 and octupolar Ethyl Violet molecules. Macroscopic octupolar patterning of the induced order is demonstrated in both transient and permanent regi mes. Experimental results show good agreement with theory.