Tunability of third-order nonlinear response in nematic liquid crystal E7 via SnO₂ nanoparticle doping: a structured...

This study investigates the temperature- and concentration-dependent linear and third-order nonlinear optical properties of SnO₂-doped nematic liquid crystal E7. Refractive index measurements confirm that nanoparticle incorporation modifies both ordinary and extraordinary indices while preserving positive birefringence throughout the nematic phase. Kerr-effect analysis shows a pronounced enhancement of nonlinear response at 0.1 wt% SnO₂, where the Kerr constant increases from 2.73 × 10^-10 m V^-2 (pure E7) to 6.94 × 10^-10 m V^-2, corresponding to an enhancement of approximately 154%. The third-order nonlinear optical susceptibility reaches its maximum value of 7.62 × 10^-18 m² V^-2 at the same concentration near the nematic-isotropic transition temperature. At higher nanoparticle loadings, both the Kerr constant and χ⁽³⁾ decrease, which may be attributed to nanoparticle aggregation and partial disruption of molecular ordering. Inverse Kerr analysis indicates a shift in pre-transition temperature from 332.2 to 332.7 K (ΔT⁓0.5 K), suggesting subtle modifications in the critical behavior near the phase transition. Therefore, these results demonstrate the potential of SnO₂-E7 nanocomposites in nonlinear optical applications.