Photo-induced phase-matched second-harmonic generation in azodye-doped polymer films by nonresonant dual-frequency coherent excitation

Abstract

All-optical control of the noncentrosymmetry of azodye-doped polymer films was demonstrated by nonresonant dual-frequency coherent excitation. Three kinds of noncentrosymmetries of the polymer films were optically tailored using appropriate combinations of the writing beam polarizations. The characteristic kinetics of the photoinduced molecular polar orientation and the tensor analysis were performed by monitoring SHG of the films. The SHG conversion efficiency of a 105)mum thick film was estimated to be about 2%. It was observed that when polarizations of the writing beams were changed from the linear polarization to the circular polarization the saturated SHG signals were enhanced even at the same readout condition. A relaxation retardation effect of the photoinduced (chi) (2 ) was also observed in the thick films. The quadratic dependence of SHG on film thickness showed that a (chi) (2 )grating satisfying the phase-matching condition for SHG was optically induced in the polymer films, indicating this nonresonant all-optical poling can be used to tailor the symmetry of bulk samples.