Molecular-field-enhanced optical Kerr effect in absorbing liquids and liquid crystals

While the optically induced reorientation of nematic liquid crystals - as a result of the optically induced torque due to the anisotropic polarizability of the molecules - has been known for several years and is well understood, a new effect could be one important driving force for further developments: the recently discovered enhancement of the nonlinear optical sensitivity by up to two orders of magnitude in some dye doped nematic liquid crystal systems. To investigate the origin of this new effect without the complications of collective effects in the nematic phase we have studied the molecular-field enhanced nonlinearity in the isotropic phase of LC. For the first time we have found a large enhancement of the optical Kerr-effect, which is attributed to the generation of an anisotropic intermolecular force field by excited dye molecules. The orientational performance of this field contributes to the direct optical torque and depends significantly on the dye itself