One- and biphotonic reorientational nonlinearities in dye-doped nematic and cholesteric liquid crystals

Abstract

This investigation elucidates one- and biphotonic reorientational nonlinearities in dye-doped nematic liquid crystals (DDNLCs) and dye-doped cholesteric liquid crystals (DDCLCs) using the Z-scan technique. Three cases—DDNLCs stimulated by one green beam polarized linearly parallel and perpendicular to the LC director and DDCLCs stimulated by one circularly polarized green beam—are considered without and with simultaneous stimulation by one linearly polarized red beam. Green-beam-induced dye reorientation through trans-cis isomerization and red-beam-induced suppression of dye reorientation by cis-trans back isomerization are responsible for the one- and biphotonic nonlinearities, respectively. The nonlinear refractive indices obtained herein are two orders of magnitude larger than those obtained elsewhere [Fuh et al., Opt. Exp. 13, 10634 (2005)]. The induced biphotonic nonlinearities can be modulated by controlling the intensity of the red beam in different ways due to the difference among the capabilities of the red beam to suppress the reorientation of the dyes and LCs in the three cases.