Effects of Electric Field Induced Dipolar Orientation on First- and Second-OrderOptical Susceptibilities in Organic Guest/Host Systems

摘要

Orientational order parameters induced in polymer guest/host systems consistingof nonlinear optical chromophores dispersed in poly(methyl methacrylate) been investigated by using the electrochromic (EC) and second-harmoinc generation (SHG) techniques. The order parameter associated with the EC study is and those with SHG are and , where Pn is the Legendre polynomial of order n. The order parameters are studied as a function of chromophore concentration and temperature. Intermolecular interactions are found to play an important role in affecting the order parameters. The Pockels electrooptical coefficient r13 is calculated from the EC data and compared with that deduced from the SHG results. Real time EC and SHG signal decay curses are obtained. Both types of decay curses are not single exponential; they can be adequately fit to a stretched exponential function, characterized by a relaxation time and a width parameter. Below the glass transition temperature (Tg) the width parameter is temperature dependent tending toward 1 above Tg . The average relaxation time is calculated from the decay curse and is found to display a non-Arrhenius temperature dependence. As the EC decay is compared with the SHG signal decay, it is found that upon removal of the poling field, the SHG signal assumes a longer decay than the EC decay by at least 1 order of magnitude. Fundamental differences between EC and SHG processes as well as effects due to surface-trapped charges are considered to be the causes for the difference in the decays. (AN).