Studies of reorientational mobility of chromophores in poled nonlinear optical polymers by secondary poling

The reorientational mobilities of molecules in nonlinear optical (NLO) polymers poled by thermal-assisted (TAP) and photo-assisted (PAP) electric-field poling are compared by measuring the temporal development of the NLO properties under a secondary poling voltage at a temperature below the glass transition temperature of the polymer. By comparing the experimental results with a theoretical model that is based on independent chromophores with a distribution of relaxation times, it was found that the secondary poling profile for a polymer poled by PAP is very well described by the theory. This shows that the chromophores can indeed be regarded as independent to each other as far as their relaxations are concerned. The secondary poling profile for a polymer poled by TAP, on the other hand, did not agree with the theory. The discrepancy of the behaviors between the two poling methods suggests that the relaxation patterns observed for polymers poled by TAP may be affected by factors not intrinsic to the polymer properties. This result may have an impact on the assessment of the long-term reliability of photonic devices based on thermally poled NLO polymers.