THz time-domain spectroscopy of liquid crystal colloids

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 SiO 2 particles. While the refractive index of the pure LC is found to vary markedly due to distinct spatial inhomogeneities consisting of oriented domains within the sample, the LC colloids provide us with a spatially much more homogeneous dielectric response which is very stable and reproducible, 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.