Temperature-dependent optical constants and birefringence of nematic liquid crystal 5CB in the terahertz frequency range

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 degrees 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. (C) 2008 American Institute of Physics.