Optical constants of two typical liquid crystals 5CB and PCH5 in the THz frequency range

The complex refractive indices of two benchmark nematic liquid crystal, 4'-n-pentyl-4-cyanobiphenyl (5CB) and 4-(trans-4'pentylcyclohexyl)-benzonitrile (PCH5) have been determined in the frequency range from 0.2 to 0.8 THz. The technique of coherent THz time-domain spectroscopy (THz-TDS) was used. We show that the birefringence of 5CB is in the range of 0.15 to 0.21, while that of PCH is from 0.01 to 0.08. Both liquid crystals exhibit relatively small absorption in this frequency range. The large birefringence of 5CB indicates possible applications of liquid-crystal-based devices for modulation and polarization control of electromagnetic radiation in the THz frequency range.