Abstract
We have measured the frequency dependence and temperature dependence of the optical constants of a liquid crystal 4′ -n -pentyl-4-cyanobiphenyl (5CB) in both nematic and isotropic phases by using terahertz time-domain spectroscopy. The extinction coefficient of 5CB is less than 0.02 and without sharp absorption features in the frequency range of 0.2-1.0 THz. The extraordinary and ordinary indices of refraction at 25 °C are around 1.77 and 1.58, respectively, giving rise to a birefringence of 0.20±0.02 in this frequency range. The temperature-dependent order parameter extracted from birefringence agrees with the results from the visible region quite well. © 2008 American Institute of Physics.