Investigation of dipole alignments by swelling in poled thin films of a side-group polymer using second harmonic generation

This paper deals with relations between solvent diffusion and changes in se cond harmonic generation (SHG) in a side-group polymer with nonlinear optic al (NLO) chromophores. The SHG signal of poled polymer thin films was measu red as a function of time during the swelling process with methanol. The re sults indicated that the diffusion process was Fickian. The topographic res ults obtained by atomic force microscopy, together with the SHG data, also demonstrated the existence of the domain layer formed during poling that ga ve rise to the principal SHG intensity for this sample. Also, a noncentrosy mmetric chromophore ordering was induced by swelling in the absence of a po ling electric field. This time-varying SHG signal upon swelling was discuss ed in terms of dipolar and polar alignments of the side-group NLO chromopho res. (C) 1999 John Wiley & Sons, Inc.