Second and third order nonlinear optical properties of organic polymeric materials

The importance of induced orientational dipolar order is investigated by considering its connection to the dynamic poling process. The temporal stability studies showed a non-Arrhenius temperature dependence for the relaxation of the poled order measured by second harmonic generation, and that the dipolar orientational relaxation time was dependent upon the dopant level, with increasing relaxation times with larger dopant levels. The orientational order parameters were also shown to depend on dopant level; however the dependence was nonlinear. The thermal stability of the induced order was enhanced by a photocrosslinked NLO epoxy functionalized system that was synthesized, and characterized. This polymer was stable at high temperatures (100\sp\circC) and appeared not to degrade upon photolysis. Electrochromism was also used to characterize the temporal stability in the guest/host system. It was shown that the activation energy obtained from the temperature dependent curves was affected by the dopant level. The increase in activation energy as a function of concentration was explained in terms of orientational pair correlation. Second and third order NLO effects were investigated by linear and quadratic electro-optic effects. The increase in the linear electro-optic coefficient upon increasing dopant level was shown to be nonlinear. A novel technique called electro-absorption was developed for the investigation of the imaginary part of the Pockels and Kerr coefficients. With this novel technique the complete dispersion of the second and third order effects could be obtained. The quadratic electro-absorption measurement gave information concerning the mechanism of the third order effect. A proposed elastic model depicting the mechanism of the third order effect in polymers was tested for a guest/host system. At low temperature there was an electronic, but no orientational, contribution to the total mechanism. However, at temperatures above the glass transition, orientational effects dominated the mechanism. In both cases (Pockels and Kerr), the correct expressions of the NLO coefficients were presented for the first time