Variation of nonlinear refractive index in dye-doped liquid crystals by local and nonlocal mechanisms

Abstract

We report in this work on the simultaneous presence of both positive and negative nonlinear optical (NLO) refractive indexes measured in methyl-red dye doped 5CB liquid crystal (LC). Characterization of these materials was performed according to the Z-Scan technique under cw He–Ne laser irradiation, taking into account the polarization and temperature dependence of the NLO-refractive index, and how these parameters are related to local and nonlocal mechanisms. The experimental conditions and a possible explanation for the simultaneous presence of positive and negative nonlinear refractive indexes are carefully discussed.