On the origin of the huge nonlinear response of dye-doped liquid crystals

We report the results of an investigation carried on Methyl Red-doped nematic liquid crystals with the aim of studying the basic mechanism of the extraordinarily large nonlinear response recently reported. We show that the experimental data can be explained as due to light-induced modifications of the anchoring conditions leading to director reorientation on the irradiated surface, which in turn gives rise to a bulk reorientation through the cell. We have called this phenomenon SINE (Surface Induced Nonlinear Effect) to remind that it occurs "without" (= sine in latin language) a direct optical or electric torque on the director in the bulk.