Kenneth John Harrison

Measurement of x(3) in novel liquid-crystal materials

In this paper we describe measurements of the third order nonlinear susceptibility and the response time for a large number of novel liquid crystal materials, in their isotropic phase, at temperatures close to the isotropic to nematic phase transition. By examining the dependence of the length of the alkyl chain part of the molecule, for the cyanobiphenyl and alkoxy- cyanobiphenyl homologous series, it is shown that the small alkyl chain materials have a superior nonlinear response. Unfortunately in these materials the large nonlinear effects close to the nematic phase are inaccessible because the solid phase is formed directly on cooling the isotropic liquid. An alternative route to large effects is to increase the molecular anisotropy in polarizability, while maintaining approximately the same molecular dimensions. It is shown that a significant increase in the size of the nonlinear response can be achieved by changing the various chemical constituents.