Photoisomerization of azo-dyes in nematic liquid crystals

The photoisomerization of azo dyes in nematic liquid crystals is investigat ed. Using a pump-probe technique, the absorption coefficients of the trans and cis isomers are evaluated separately and the dye order parameters of bo th forms are determined. It is shown that as a consequence of the differenc e of the trans and cis orientational order, the trans-cis equilibrium can b e controlled through the polarization direction of the pump beam.