Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Second-order nonlinearity studies on organic polymeric materials
Abstract
Second order nonlinear optical (NLO) properties of organic polymer thin films were studied by optical second harmonic generation (SHG) and electrooptical measurements. The polar orientational order parameters (POP) were deduced from the second order susceptibilities and from the first order electrooptical coefficients. It is found, in the guest/host system, that the POP is NLO chromophore concentration and external electric poling field dependent. By monitoring the in situ SHG intensity change, we are able to study the temporal stability of the polymer systems under different preparation and different poling conditions. The decay of SHG signal is found to be affected by surface/trapped space charges as well as polymer chain conformational changes induced by the electric field. It is shown that reproduceable relaxation experiment can not be obtained unless the sample has been successively poled. In guest/host systems at temperatures above the glass transition temperature ($T\sb{g}$), a two single exponential decay function is found to give a good fit to the SHG intensity decay curve. On the other hand, the SHG intensity decay curve from a main-chain polymer system is found to follow a Kohlrausch-Willams-Watts (KWW) equation. It is also shown that above $T\sb{g}$, the temperature dependence of the steady-state average relaxation time is not Arrhenius; the Vogel-Fulcher-Tammann equation gives a satisfactory fit to the temperature dependence data. It is shown that the SHG relaxation is different from that obtained by bireferengence, dielectric, or absorption recovery techniques. The SHG technique is also successfully applied to investigate the physics of pure blank polymers in the presence of a high electric field. Finally, the Mach Zehnder interferometry technique has also been used to determine the Pockels and Kerr coefficients.
Subject Area
Chemistry|Polymers
Recommended Citation
Guan, Hann-Wen, "Second-order nonlinearity studies on organic polymeric materials" (1994). ETD collection for University of Nebraska-Lincoln. AAI9430169.
https://digitalcommons.unl.edu/dissertations/AAI9430169