Molecular properties of liquid crystals in the terahertz frequency range.

We report on a first experimental study of the molecular properties of nematic liquid crystals in the terahertz range. In the beginning, we extract the frequency and temperature dependent refractive index and absorption coefficient of the cyanobiphenyls 5CB, 6CB and 7CB from terahertz time domain spectroscopy measurements and investigate the impact of the alkyl chain length on the macroscopic liquid crystal characteristics, focusing especially on the pronounced odd and even effect. Next, we deduce the principle polarizabilities and the order parameter S by applying Vuks' approximation and Haller's approach. On this basis, we calculate the main polarizabilities along the longitudinal and transverse axis and link the observed terahertz properties to the molecular structure of the liquid crystals.

[1]  N. Vieweg,et al.  Liquid crystal based electrically switchable Bragg structure for THz waves. , 2009, Optics express.

[2]  M. Koch,et al.  Analyzing sub-100-μm samples with transmission terahertz time domain spectroscopy , 2009 .

[3]  N. Vieweg,et al.  Impact of the contact metallization on the performance of photoconductive THz antennas. , 2008, Optics express.

[4]  Mahmoud Shahabadi,et al.  Sub-terahertz on–off switch based on a two-dimensional photonic crystal infiltrated by liquid crystals , 2008 .

[5]  Ci-Ling Pan,et al.  Temperature-dependent optical constants and birefringence of nematic liquid crystal 5CB in the terahertz frequency range , 2008 .

[6]  R. Wilk,et al.  Highly Accurate THz Time-Domain Spectroscopy of Multilayer Structures , 2008, IEEE Journal of Selected Topics in Quantum Electronics.

[7]  N. Vieweg,et al.  THz Spectroscopy of Liquid Crystals from the CB Family , 2009, 2007 Joint 32nd International Conference on Infrared and Millimeter Waves and the 15th International Conference on Terahertz Electronics.

[8]  E. Cebe,et al.  Molecular dynamic study of the odd-even effect in some 4-n-alkyl-4'-cyanobiphenyls. , 2006, Physical review. E, Statistical, nonlinear, and soft matter physics.

[9]  R. Pan,et al.  A liquid-crystal-based terahertz tunable Lyot filter , 2005, 2005 IEEE LEOS Annual Meeting Conference Proceedings.

[10]  J. Sambles,et al.  Microwave liquid-crystal variable phase grating , 2004 .

[11]  Shin-Tson Wu,et al.  Temperature effect on liquid crystal refractive indices , 2004 .

[12]  C. Glorieux,et al.  Determination of the order parameter and its critical exponent for nCB (n=5–8) liquid crystals from refractive index data , 2004 .

[13]  Shin-Tson Wu,et al.  Extended Cauchy equations for the refractive indices of liquid crystals , 2004 .

[14]  H. Fujikake,et al.  Voltage-variable microwave delay line using ferroelectric liquid crystal with aligned submicron polymer fibers , 2003 .

[15]  Martin Koch,et al.  THz time-domain spectroscopy on 4-(trans-4'-pentylcyclohexyl)-benzonitril , 2001, SPIE Optics + Photonics.

[16]  B. Gestblom,et al.  On the derivation of the nematic order parameter from the dielectric relaxation times , 1999 .

[17]  Shin-Tson Wu,et al.  Absorption measurements of liquid crystals in the ultraviolet, visible, and infrared , 1998 .

[18]  T. Nozokido,et al.  Refractive index of nematic liquid crystals in the submillimeter wave region. , 1997, Applied optics.

[19]  Y. N. Murthy,et al.  Molecular Polarizabilities, Polarizability Anisotropies and Order Parameters of Nematic Liquid Crystals , 1997 .

[20]  R. Jacobsen,et al.  Generation and detection of terahertz pulses from biased semiconductor antennas , 1996 .

[21]  S. Ristori,et al.  Investigation of a liquid crystal dispersed in an ionic polymeric membrane , 1993 .

[22]  Elena Sherman,et al.  Liquid crystal birefringence for millimeter wave radar , 1993 .

[23]  R. S. McEwen.  Liquid crystals, displays and devices for optical processing , 1987 .

[24]  Wu,et al.  Birefringence dispersions of liquid crystals. , 1986, Physical review. A, General physics.

[25]  J. Lalanne,et al.  Molecular aspect of the even–odd effect in cyanobiphenyls (nCB): Theoretical studies of the molecular geometrical conformation and optical anisotropy. I. n≤6 , 1984 .

[26]  R. Williams.  Instrument Science and Technology Vol 2 , 1984 .

[27]  A. Buka,et al.  DIAMAGNETISM AND ORIENTATIONAL ORDER OF NEMATIC LIQUID-CRYSTALS , 1982 .

[28]  N. Shivaprakash,et al.  Refractive Indices, Densities, Polarizabilities and Molecular Order in Cholesteric Liquid Crystals , 1982 .

[29]  W. Haase,et al.  On the Molecular Polarizability of Nematic Liquid Crystals , 1981 .

[30]  R. Horn,et al.  Refractive indices and order parameters of two liquid crystals , 1978 .

[31]  I. Haller.  Thermodynamic and static properties of liquid crystals , 1975 .

[32]  S. Marčelja,et al.  Chain ordering in liquid crystals. II. Structure of bilayer membranes. , 1974, Biochimica et biophysica acta.

[33]  S. Marčelja.  Chain ordering in liquid crystals. I. Even‐odd effect , 1974 .

[34]  I. A. Shanks,et al.  Fast-switching twisted nematic electro-optical shutter and colour filter , 1974 .

[35]  M. Evans,et al.  Molecular motion and molecular interaction in the nematic and isotropic phases of a liquid crystal compound , 1973 .

[36]  George W. Gray,et al.  New family of nematic liquid crystals for displays , 1973 .

[37]  M. Schadt,et al.  Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal , 1971 .

[38]  N. V. Madhusudana,et al.  Orientational order in p-azoxyanisole, p-azoxyphenetole, and their mixtures in the nematic phase. , 1969 .

[39]  M. Vuks.  Determination of the Optical Anisotropy of Aromatic Molecules from the Double Refraction of Crystals , 1966 .

[40]  A. Saupe,et al.  Eine einfache molekular-statistische Theorie der nematischen kristallinflüssigen Phase. Teil l1. , 1959 .

[41]  O. Lehmann.  Über fliessende Krystalle , 1889 .

[42]  Friedrich Reinitzer,et al.  Beiträge zur Kenntniss des Cholesterins , 1888 .