Anomalous intensity dependence of optical reorientation in azo dye-doped nematic liquid crystals

Istvan Janossy ,Marta Becchi ,Shankar Rao 2,David Statman 3

Research Institute for Solid State Physics and Optics, Budapest, Hungary
Dipartimento di Fisica, Politechnico di Torino, 10129 Torino, Italy
2Centre for liquid Crystal Research, Jalahalli, 560013 Bangalore, INDIA
3Department of Physics, Allegheny College, PA16335 Meadville, US

The intensity dependence of optical nonlinearity in a nematic liquid crystal doped with an azo-dye is investigated. The reorientational part of the nonlinearity changes from self-defocusing to self-focusing character while the intensity passes through the saturation value of trans-cis photoisomerization. This observation, in accordance with previous models, indicates that the optical torque generated by the trans isomers is of opposite sign than the torque generated by the cis isomers. At very low intensities a further reorientational nonlinearity was found, which is attributed to light-induced orientational redistribution of adsorbed molecules at the surface.

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