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Polarization-induced orientational order and surface relief gratings in liquid crystalline polymers containing photosensitive azochromophores

Investigations on the polarization induced orientational order in three different azo-polymers are presented and discussed with respect to the formation of surface relief gratings induced by holographic exposure. For this purpose the birefringence induced for different polarization-states of the light, e.g. linear, elliptical or circular, has been studied. By placing the sample between crossed polarizers at various angles of incidence of the probe-laser, the symmetry and the induced amount of order is determined. The orientational order is characterized by the scalar Maier- Saupe order parameter S, known from nematic liquid crystals. By holographic exposure different kinds of polarization gratings were induced in these materials and investigated with polarization- and atomic force microscopy. The gratings are characterized by diffraction efficiencies and by depth and shape of the surface modulation. Large surface modulations (> 2.5 micrometers ) and diffraction efficiencies (> 90%) for a 5 micrometers thick film were obtained.