Application of Modified Interference Wedge Method in Measurements of Indices of Refraction and Birefringence of Nematic Liquid Crystals

Wedge cell filled with a homogeneously oriented nematic liquid crystal was exploited as an interference wedge to measuring indices of refraction. Interference fringes from the wedge were observed in polarised light in reflection or transmission mode of a polarisation microscope to determining ordinary and extraordinary indices of refraction or birefringence (i.e. anisotropy of both indices). The interference fringes close to wedge apex were uniform and could be well described in two-beam interference approximation. The refractive indices were computed with using simple formulae involving only distances between subsequent fringes in a cell filled with the liquid crystal and an empty reference cell. Several new highly-birefringent nematic mixtures produced in the Military University of Technology were investigated. The 6CHBT nematic was used as the reference material.