A stochastic model for chromophore disorientation in guest-host nonlinear optical polymer system

Abstract

The temporal and thermal stability of nonlinear optical (NLO) properties of polymers doped with optically active chromophores has been studied by many researchers [1] because of its importance to predict the long term performance of these systems for practical applications. Until recently most of these efforts were focused on attempting to fit experimental data to empirical functions, such as stretched exponential [2] or lognormal [3], with no direct mechanistic interpretation of the parameters. It has been established that the decay of the second harmonic generation (SHG) signal after poling is clearly nonexponential, and its characteristics depend, in a complex manner, on processing and thermal history. Whereas there is general agreement that the complex character of the decay in NLO properties is caused by the coupling of the chromophores disorientation to the structural relaxation of the polymer matrix, the mechanism of this coupling is poorly understood. This research involves the application of a stochastic model, recently developed by our group, for structural relaxation in glasses [4] in order to describe orientational relaxation of chromophore particles, which is responsible for SHG decay in chromophore doped polymer glasses.