Liquid Crystal Colloids Studied by THz Time-Domain Spectroscopy

THz time-domain spectroscopy is used to measure the frequency dependent (0.2-2.0 THz) complex refractive index of a pure liquid crystal (LC), 4-n-pentyl-4-cyanobiphenyl (5CB), and its LC colloids with SiO₂ particles. While the refractive index of the pure LC is found to vary markedly due to distinct orientated domains within the sample, the LC colloids provide us with very stable and reproducible spectra, from which we can reliably deduce the optical constants of pure 5CB using effective medium theory. While the absorption coefficient is found to be very small, the refractive index of 5CB decreases considerably over our probe frequency range.