  The photoinduced 3D orientational structures in the films of liquid
crystalline polyester, containing azobenzene side groups, are studied both
experimentally and theoretically. By using the null ellipsometry and the UV
absorption methods, preferential in-plane alignment of the azobenzene fragments
and in-plane reorientation under irradiation with polarized UV light are
established. The uniaxial and biaxial orientational configurations of the
azobenzene chromophores are detected. The biaxiality is observed in the
intermediate stages of irradiation, whereas the uniaxial structure is
maintained in the photosaturated state. The components of the order parameter
tensor of the azobenzene fragments are estimated for the initial state and
after different doses of irradiation. The proposed theory takes into account
biaxiality of the induced structures. Numerical analysis of the master
equations for the order parameter tensor is found to yield the results that are
in good agreement with the experimental dependencies of the order parameter
components on the illumination time.
