Plasmon enhancement of third-order nonlinear optical absorption of gold nanoparticles dispersed in planar oriented nematic liquid crystals

Abstract

We report structural and nonlinear optical properties of 20 nm gold (Au) nanoparticles (NPs) that are dispersed in planar degenerate (non-oriented) and planar oriented nematic liquid crystals (4′-Pentyl-4-biphenylcarbonitrile-5CB). Taking advantage of elastic forces in the planar oriented nematic liquid crystal, we aligned AuNPs parallel to the 5CB director axis. In the case of planar degenerate, 5CB is not aligned and has no preferred orientation, forcing the AuNPs to disperse randomly. Results show that the linear optical absorption coefficient for the planar oriented 5CB/AuNPs mixture is larger than the corresponding planar degenerate sample. The nonlinear absorption coefficients are greatly enhanced in planar oriented samples at relatively high concentrations which can be attributed to plasmon coupling between the aligned AuNPs. This study demonstrates the utility of liquid crystals for developing the assembly of NPs with enhanced optical properties which may offer important insight and technological advancement for novel applications, including photonic nanomaterials and optoelectronic devices.

Polarization Z-Scan Studies Revealing Plasmon Coupling Enhancement Due to Dimer Formation of Gold Nanoparticles in Nematic Liquid Crystals

“…An efficient method for inducing twisting in NLCs involves orienting the rubbing directions of anchoring materials on two substrates perpendicular to each other [32]. Recently, we demonstrated enhanced third-order nonlinear absorption when AuNPs are dispersed in planar-oriented nematic liquid crystals (4 -Pentyl-4-biphenylcarbonitrile-5CB) [33].…”