Electric field effects in polymer thin films for second order nonlinear optics

Researchers have been actively involved in developing nonlinear optical polymers for device applications. Much research has focused on improving the polymer properties, but little research has been done on studying the poling process and its effect on the second order nonlinear optical properties of the doped polymer. Understanding the electric field effects during poling is crucial in the development of optimal poling procedures for second order nonlinear optical devices. The purpose of this research was to characterize the electric field through doped polymer films and to study its effects on the orientational stability of the chromophores using novel optical and electrical techniques. Specific issues, such as the effects of poling parameters and processing conditions upon the local electric field, the polarization distribution and the orientational stability of the chromophores, were studied. Electrochromism was used to obtain the average local electric field through the doped polymer film under different poling conditions. In addition, thermal pulse measurements were performed to obtain the polarization distribution under similar conditions. Hence, by combining these two techniques, a qualitative description of the local electric field distribution through the polymer film was obtained and compared to the frequently used Lorentz expression for the local electric field. In addition, the effects of poling conditions on the orientational stability of the chromophores was studied using two second order nonlinear optical techniques, second harmonic generation, and electrochromism. Average orientational relaxation times for the chromophores were obtained under different poling conditions. Dielectric relaxation was also performed on the doped polymer film in order to obtain polymer relaxation information. By examining the second order nonlinear optical properties of the doped polymer films as a function of time and temperature, and dielectric relaxation as a function of frequency and temperature, information concerning the local mobility and the relaxations of the polymer film was obtained. The results obtained in this study are critical to the development of optimal poling procedures for second order nonlinear optical devices