Spatial dispersion in chiral liquid crystals. Effects of higher orders

Abstract

Spatial dispersion effects in chiral liquid crystals are reviewed. New spatial dispersion phenomena are observed in the vicinity of the Bragg reflection wavelength-an anomaly of the refractive index and an optical anisotropy of the cubic blue phases. These effects can be explained by taking into account the spatial dispersion correction of the dielectric tensor of the medium of higher orders in the ratio of the light wave vector to the structural wave vector of chiral phases.

Structural Investigations on Smectic Blue Phases

“…Another source of birefringence is the existence of Bragg reflections in the UV range, thus close to the blue wavelength, which can disturb the optical appearance of theses phases [14]. This effect is similar to the phenomenon of spatial dispersion which makes even cubic crystals birefringent [15]. Therefore, the experimental results presented in this Letter, that is three almost identical and perpendicular smectic peaks and only a very weak birefringence, lead us to conclude that the orientational symmetry of the BP Sm 1 phase is cubic.…”

A model for the Pockels effect in distorted liquid crystal blue phases

“…24,28 ) The model is crude in many respects and assumes a number of quite severe approximations: not least, it ignores completely the regions in between the DTCs. Further, it ignores spatial dispersion 25 and, as a result, is strictly only valid in the limit that the wavelength of electromagnetic radiation may be considered to be infinite with respect to the lattice dimension; in particular, the approach ignores natural optical activity, 4,25 the inherent anisotropy of the cubic structure, 25,31,32 linear electro-optic effects other than the Pockels effect, which exist on account of spatial dispersion, 33,34 and all aspects relating to selective reflection. Nevertheless, the model adequately establishes that flexoelectricity can account for the observation of the Pockels effect in mechanically distorted BPs, provides an intuitive picture of the physical origin of the effect in terms of given director distortions, and links the fundamental physical parameters (K 1 , K 3 , e 1 , e 3 , and a) with the macroscopic optical properties.…”