Molecular reorientation in cross polarization gratings formed in thin photoreactive-polymer–liquid-crystal films

We present the results from some experimental and theoretical studies aimed at revealing the mechanism leading to the diffraction properties of two-dimensional cross polarization gratings in photocrosslinkable polymer liquid crystals. Although the polarization gratings are overwritten at the same place, each polarization grating works independently in our material system. The above-mentioned characteristic of our cross polarization gratings originates in the grating formation mechanism in the photocrosslinkable polymer liquid crystals, in which the molecules in the solid-state polymeric materials are not reoriented during exposure and reorientation is generated during the annealing process after multiple exposure.