The chromophore orientation distribution in photoaddressable bis-azo copolymer thin films is investigated as a function of the poling temperature and the chromophore concentration. The first, second, and third order parameters are deduced from the linear electro-optic coefficients and the linear dichroism by free-beam interferometry and angle-resolved spectroscopy, respectively. Absorption spectra obtained by density-functional calculations are compared with the experimentally observed ones and support the picture of differently aligned bis-azo dye molecules in a trans,trans-configuration. The various kinds of ordering in samples poled at different temperatures is confirmed by complementary wide-angle X-ray scattering. Furthermore, we show that a higher thermal stability for applications can be reached by fractionating the polymer, and how such a material can be successfully employed to build a large-area Fabry-Perot-Modulator using the electro-optic effect.
Investigating dynamics in a disordered solid material below, at, and well above glass transition temperature, we show that (1) to describe glass dynamics entirely it has to be regarded over a long
range on logarithmic time scale, (2) a single stretched exponential function (Kohlrausch-Williams-Watts) can never describe the data, (3) stretching exponents do not cover the ranges previously suggested (from 0 to 1, e.g. as a sigmoid function). Optically recorded dynamics (measured by ellipsometry) is brought into connection with dielectric spectroscopy.
The relaxational response of a photorefractive polymer subjected to different poling voltages slightly above the glass transition temperature is measured using ellipsometry. We discuss our results using a new curve-fit function, which provides a good description of the experimental data. Using this new function we examine how the poling voltage influence the poling behavior of the chromophores. Furthermore, it is shown that the characteristic time for turn-off behavior is strongly influenced by the time span elapsed since turn-on.