We report the experimental demonstration that both the extra-ordinarily large nonlinear response and the light-induced permanent reorientation in liquid crystals doped by the azo-dye Methyl-Red originates from the modification of the charge density on the irradiated surface. By recording the sample response by applying dc or ac voltage, it is shown that in the latter case no permanent anchoring is possible. It is also demonstrated the limited role of photo-isomerization that gives a contribution to the nonlinear reorientation process only in the high dose regime. The effects on light-induced tuning of the Freedericksz transition are also reported.
"Light-induced effects in dye-doped liquid crystals: role of space charges", Proc. SPIE 9182, Liquid Crystals XVIII, 918204 (3 October 2014); doi: 10.1117/12.2059039; https://doi.org/10.1117/12.2059039