Temperature dependence of the director reorientation of dye-doped nematic liquid crystals subjected to an optical field and its relation with the non-linear absorption coefficient

The temperature behaviour of the torque amplification factor η in the E48-D4 dye-host/liquid crystal-guest dyed system illuminated by a laser beam has been investigated using a single beam Z-Scan experimental technique. A plot of η versus temperature showed a monotonic aspect, different from other anthraquinone dyed liquid crystals. This behaviour, in our case, is consistent with the monotonic dependence on temperature of the linear αo and non-linear β optical absorption coefficients. In particular, the non-linear optical absorption coefficient related to the reorienting process is negative and of the order of-0.25 mm W-1. The temperature dependence of η seems to be directly correlated to β and not to αo. Since drastic conformational modifications on dye molecules are not expected on passing from the ground to the excited state, the role of the electronic structure seems to be dominant in the reorienting process in dyed nematics.