The birefringence and extinction coefficient of positive and negative liquid crystals in the terahertz range

Birefringence and extinction coefficients of positive nematic liquid crystal (NLC) MLC-2142 and negative NLC BHR28000-400 are measured by terahertz time-domain spectroscopy system (THz-TDS). Frequency ranging from 0.1 to 0.6 THz, the birefringence of positive NLC MLC-2142 increases with the increase of frequency, and keeps larger than 0.23, which exhibits application potential in tunable broadband LC THz device where a large birefringence is required. In contrast, the birefringence of BHR28000-400 decreases with the increased frequency, which shows a completely different optical property from the positive NLC. The extinction coefficient of the above two kinds of liquid crystals are also investigated.