Terahertz and optical properties of nematic mixtures composed of liquid crystal isothiocyanates, fluorides and cyanides

Abstract

Several simple nematic eutectic liquid crystal mixtures composed of different two and three ring isothiocyanato compounds as well as mixtures consisting of analogous cyano and fluoro compounds were formulated. The optical properties of the thereby obtained mixtures, i.e. refractive indices, birefringence and absorption coefficients α_e and α_o are measured in the frequency range between 0.5 and 2.5 THz and in the visible range at 589 nm. Our results show that two mixtures can be identified, which seems particularly promising for applications in the terahertz (THz) range: those consisting only of isothiocyanates show the highest birefringence at THz frequencies while those consisting of isothiocyanates and cyanides have the smallest dichroic ratio over a broad THz range. We also found that in most cases, the absorption coefficients of the isothiocyanato compounds fulfill the relationship α_e > α_o while for cyano and fluoro compounds, α_o > α_e is observed as a dominating trend. Furthermore, we show that by carefully selecting constituents of both isothiocyanato and cyano compounds, we can achieve a mixture for which the values of α_o are in the same order as for α_e for THz frequencies below 2 THz.