Liquid Crystal Colloids Studied by THz Time-Domain Spectroscopy

Abstract

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 0 -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 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.Keywords: colloid; effective medium theory; dielectric; liquid crystal; optical constant; terahertz spectroscopy Confining and dispersing soft condensed matter such as liquid crystals (LCs) has been of significant interest for more than a decade, while looking for fundamental changes in the physical properties of the material or searching for new applications. For this, colloidal particles dispersed in an LC host have attracted much attention, and also play a crucial role in LC nano-technology [1,2]. On mixing particles with a nematic LC host, an orientational topological defect is formed at the surface of a particle if the surface anchoring is sufficiently strong [3][4][5]. But, in addition to the local effects, one would also expect some of the bulk properties of an LC to change, since a single particle in an

Improvement of THz phase sensing system by using LC phase shifter under magnetic field application

“…Using a common path interferometer is one good approach because the experimental setup is very simple and the system provides greater robustness against vibration. A liquid crystal (LC) device is a good candidate for common path PSI and several groups have reported results for the visible region [15][16][17]. In this method, electromagnetic waves of ordinary and extraordinary rays are interfered in one light path.…”

Continuous wave terahertz common path phase shifting interference using a liquid crystal phase shifter

“…On the other hand, the LC materials exhibit birefringence in the THz region [18][19][20][21][22][23][24][25][26][27][28] and are quite suited for tuning the phase of a THz signal by an external electric field. However, many LCs exhibit dichroism in this region, thereby leading to unwanted variation in the polarization state of the THz phase shifter.…”