We investigate thin phase polarization holographic gratings recorded with two waves with orthogonal linear polarizations in materials in which illumination with linearly/circularly polarized light gives rise to linear/circular birefringence. The theoretical analysis shows that the presence of circular photoanisot-ropy changes significantly the diffraction characteristics of the gratings. The intensities of the waves diffracted in the +1 and -1 orders of diffraction and their ratio depend substantially on the reconstructing-wave polarization. Experiments with films of side-chain liquid-crystalline azobenzene polyester that is a photoanisotropic material of the considered type confirm the unusual polarization properties. It is shown that polarization holography may be used for real-time simultaneous measurement of photoinduced linear and circular birefringence.
Second-harmonic and third-harmonic waves that are generated in an azo-polymer form diffraction patterns without any material deformation. The source is a single IR laser beam at λ=1064 nm that is weakly absorbed by the polymer. If the IR power is sufficiently high, laser-induced periodic (700 nm) structures grow on the polymer surface and give rise to distinctive diffraction patterns in the visible and ultraviolet. If the IR power is low, there are no surface changes but diffraction patterns that have the same shape still appear.
The photoinduced isotropic and anisotropic changes in the refractive index of dye/polymer guest-host systems are investigated. The values obtained are compared to the diffraction efficiencies of scalar and polarization holographic gratings, recorded in the same polymer systems. It is concluded that the induced anisotropy is related to the dye molecules involved in the photoprocesses, whereas the isotropic changes, which are much stronger, are related to the polymer matrix as well.
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