Light-induced mass transport in azobenzene functionalized polymers has been used for generation of surface relief
gratings (SRG) for different optical applications. The effect of grating formation has been ascribed to the light-induced
motion of the azobenzene chromophores involving the covalently bound polymer chains. We propose a concept of
supramolecular materials for the effective all-optical generation of surface relief structures and optical anisotropy. The
materials are based on the non-covalent interactions between charged photochromic azobenzene units and oppositely
charged polymer matrix, for example polyelectrolytes including charged alkoxysilanes. This new supramolecular
approach opens a new way for the simple, cost effective and environment friendly preparation from building blocks of a
variety of materials for the effective formation of SRG. Up to 1.65 μm deep relief gratings were inscribed onto a few
micrometers thick films of these materials. The high thermal stability of the induced structures has been explained in
terms of the network of oppositely charged ions inherent to the materials. Also 2D-structures, for example square and
hexagonal gratings, were inscribed by the successive recordings. The latter possibility was also used to generate gratings
with non-sinusoidal profiles by Fourier transform technique. A new technique to control the grating profile has been
developed based on the real-time process of grating formation in these materials. The gratings with sow-tooth like
profiles were induced by this method. The diffraction efficiencies up to 60 % in one diffraction order were achieved.
We have studied photogeneration, transport, trapping and recombination as the governing mechanisms for the saturation field strength and the time response of the photorefractive (PR) effect in PVK-based PR materials, utilizing xerographic discharge and photoconductivity experiments. Both the charge carrier photogeneration efficiency and the photocurrent efficiency were found to be independent of chromophore content, suggesting that the chromophore does not participate in carrier generation and trapping. The photoconductivity gain factor G defined as the number of charge carriers measured in photoconductivity in relation to the number of carriers initially photogenerated as determined by the xerographic experiments is found to be much smaller than unity, which indicates that the mean free path of the photogenerated charge carriers is less than the grating period. Photoconductivity data can be explained over 3 orders of magnitude in field, assuming a field-independent trap density. Based on the photoelectric data, PR response times have been predicted by Yeh's model for the build-up of space or by calculating the time, which is necessary to fill all traps by photogenerated holes. Only the latter model can reasonably well explain the observed field dependence of the PR growth time, suggesting that trap-filling essentially controls the PR onset behavior.
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