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Articles 1 - 16 of 16

Full-Text Articles in Physics

Control Of Dispersion In Form Birefringent-Based Holographic Optical Retarders, Erica N. Montach, Philip J. Bos Dec 2005

Control Of Dispersion In Form Birefringent-Based Holographic Optical Retarders, Erica N. Montach, Philip J. Bos

Chemical Physics Publications

Holographic retarders based on form birefringence are shown to have controllable dispersion properties. Significantly, we show that the dispersion properties of these retarders can be adjusted over a large wavelength range by varying the periodicity of the index of refraction profile. These retarders with controllable dispersion characteristics are of high value for applications such as the compensation of liquid crystal displays.


Broadband Optical Phased-Array Beam Steering, Paul F. Mcmanamon, Jianru Shi, Philip J. Bos Dec 2005

Broadband Optical Phased-Array Beam Steering, Paul F. Mcmanamon, Jianru Shi, Philip J. Bos

Chemical Physics Publications

An array of phase retarders can be used as an optical phased array (OPA) to steer light [McManamon et al., Proc. IEEE 84 (2), 268 298 (1996)]. The introduction of resets enables steering to larger angles without requiring an optical path difference (OPD) greater than one wavelength. These resets, however, are correct only at the design wavelength. The beam steerer is therefore very dispersive. It has been shown theoretically that resets of an integer multiple of the wavelength will make the beam steerer less dispersive [McManamon and Watson, Proc. SPIE 4369, 140-148 (2001)]. We offer the first experimental proof that ...


Elasticity-Mediated Self-Organization And Colloidal Interactions Of Solid Spheres With Tangential Anchoring In A Nematic Liquid Crystal, Ivan I. Smalyukh, Oleg Lavrentovich, A. N. Kuzmin, A. V. Kachynski, P. N. Prasad Oct 2005

Elasticity-Mediated Self-Organization And Colloidal Interactions Of Solid Spheres With Tangential Anchoring In A Nematic Liquid Crystal, Ivan I. Smalyukh, Oleg Lavrentovich, A. N. Kuzmin, A. V. Kachynski, P. N. Prasad

Chemical Physics Publications

Using laser tweezers, we study colloidal interactions of solid microspheres in the nematic bulk caused by elastic distortions around the particles with tangential surface anchoring. The interactions overcome the Brownian motion when the interparticle separation r ->(p) is less than 3 particle diameters. The particles attract when the angle theta between r ->(p) and the uniform far-field director n(0) is between 0 degrees and approximate to 70 degrees and repel when 75 degrees less than or similar to theta(0) and, at higher concentrations, form complex kinetically trapped structures.


Nonstandard Electroconvection In A Bent-Core Nematic Liquid Crystal, D. B. Wiant, Jim T. Gleeson, Nandor Éber, Katalin Fodor-Csorba, Antal Jákli, T. Tóth-Katona Oct 2005

Nonstandard Electroconvection In A Bent-Core Nematic Liquid Crystal, D. B. Wiant, Jim T. Gleeson, Nandor Éber, Katalin Fodor-Csorba, Antal Jákli, T. Tóth-Katona

Chemical Physics Publications

We characterize three nonstandard electrohydrodynamic instabilities in nematic liquid crystals composed of bent-core molecules. In addition to their shape, another important attribute of this material is that the anisotropy in the electrical conductivity changes sign as the frequency of the applied electric field changes. These instabilities do not appear to fit within the standard model for electroconvection. The first instability creates a pattern with stripes parallel to the initial director orientation, with a wavelength about equal to the separation of the cell plates. The next is the previously reported prewavy instability. The third instability is optically and dynamically identical to ...


Optical Characterization Of The Nematic Lyotropic Chromonic Liquid Crystals: Light Absorption, Birefringence, And Scalar Order Parameter, Yuriy A. Nastishin, H. Liu, T. Schneider, V. G. Nazarenko, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2005

Optical Characterization Of The Nematic Lyotropic Chromonic Liquid Crystals: Light Absorption, Birefringence, And Scalar Order Parameter, Yuriy A. Nastishin, H. Liu, T. Schneider, V. G. Nazarenko, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We report on the optical properties of the nematic (N) phase formed by lyotropic chromonic liquid crystals (LCLCs) in well aligned planar samples. LCLCs belong to a broad class of materials formed by one-dimensional molecular self-assembly and are similar to other systems such as “living polymers” and “wormlike micelles.” We study three water soluble LCLC forming materials: disodium chromoglycate, a derivative of indanthrone called Blue 27, and a derivative of perylene called Violet 20. The individual molecules have a planklike shape and assemble into rodlike aggregates that form the N phase once the concentration exceeds about 0.1M. The ...


Electrorotation Of Colloidal Particles In Liquid Crystals, Guangxun Liao, Ivan I. Smalyukh, J. R. Kelly, Oleg D. Lavrentovich, Antal Jakli Sep 2005

Electrorotation Of Colloidal Particles In Liquid Crystals, Guangxun Liao, Ivan I. Smalyukh, J. R. Kelly, Oleg D. Lavrentovich, Antal Jakli

Chemical Physics Publications

We present the first observations of dc electric-field-induced rotational motion of finite particles in liquid crystals. We show that the electrorotation is essentially identical to the well-known Quincke rotation, which in liquid crystals triggers an additional translational motion at higher fields. In the smectic phase the translational motion is confined to the two-dimensional geometry of smectic layers, in contrast to the isotropic and nematic phases, where the particles can move in all three dimensions. We demonstrate that by a proper analysis of the electrorotation, one can determine the in-plane viscosity of smectic liquid crystals. This method needs only a small ...


Dielectric Torque And Orientation Dynamics Of Liquid Crystals With Dielectric Dispersion, Y. Yin, Sergij V. Shiyanovskii, A. B. Golovin, Oleg Lavrentovich Aug 2005

Dielectric Torque And Orientation Dynamics Of Liquid Crystals With Dielectric Dispersion, Y. Yin, Sergij V. Shiyanovskii, A. B. Golovin, Oleg Lavrentovich

Chemical Physics Publications

We demonstrate that the finite rate of dielectric relaxation in liquid crystals which has been ignored previously causes profound effects in the fast dielectric reorientation of the director. We propose a theory of dielectric response in which the electric displacement depends not only on the present (as in the standard theory) but also on the past values of electric field and director. We design an experiment with a dual-frequency nematic in which the standard "instantaneous" model and our model predict effects of opposite signs; the experimental data support the latter model.


Optically Isotropic Liquid-Crystal Phase Of Bent-Core Molecules With Polar Nanostructure, Guangxun Liao, S. Stojadinovic, Gerhard Pelzl, Wolfgang Weissflog, Samuel N. Sprunt, Antal Jakli Aug 2005

Optically Isotropic Liquid-Crystal Phase Of Bent-Core Molecules With Polar Nanostructure, Guangxun Liao, S. Stojadinovic, Gerhard Pelzl, Wolfgang Weissflog, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

We found that the optically isotropic (I-M) mesophase observed recently below the nematic phase of the bent-core liquid crystal 4-chlororesorcinol bis[4-(4-n-dodecyloxybenzoyloxy)benzoate] shows ferroelectric-type switching. Polarizing microscopic, electric current, dielectric, and dynamic light scattering studies lead us to propose that the I-M phase is composed of interconnected orthoconic racemic smectic (Sm-CaPF) nanodomains with random layer orientations. Near the nematic phase, where the polarization can be saturated by electric fields, the system responds in a fashion analogous to the granular structure of a magnetic spin glass-in particular, we observed that the relaxation back to the nonpoled structure follows a ...


Short Pitch Cholesteric Electro-Optical Device Stabilized By Nonuniform Polymer Network, Sang Hwa Kim, Liang-Chy Chien Apr 2005

Short Pitch Cholesteric Electro-Optical Device Stabilized By Nonuniform Polymer Network, Sang Hwa Kim, Liang-Chy Chien

Chemical Physics Publications

We have developed a method for stabilization of the uniform lying helix (ULH) texture of short pitch cholesterics in an electro-optical device, based on the flexoelectro-optic effect in such a texture. By using a small concentration of photoreactive liquid crystal monomer (less than 5 wt. %) and selecting the illumination conditions, we were able to create a nonuniform polymeric network in the liquid crystal bulk (localized essentially at both substrate surfaces) which stabilized efficiently the amplitude and the phase modulation modes of the device. Most importantly, the effect of the residual birefringence of the polymeric network in the field-unwound state of ...


Modeling And Design Of An Optimized Liquid-Crystal Optical Phased Array, Xinghua Wang, Bin Wang, Philip J. Bos, Paul F. Mcmanamon, John J. Pouch, Felix A. Miranda, James E. Anderson Apr 2005

Modeling And Design Of An Optimized Liquid-Crystal Optical Phased Array, Xinghua Wang, Bin Wang, Philip J. Bos, Paul F. Mcmanamon, John J. Pouch, Felix A. Miranda, James E. Anderson

Chemical Physics Publications

In this paper, the physics that determines the performance limits of a diffractive optical element based on a liquid-crystal(LC) optical phased array(OPA) is investigated by numerical modeling. The influence of the fringing electric fields, the LC material properties, and the voltage optimization process is discussed. General design issues related to the LCOPA configuration, the diffraction angle, and the diffraction efficiency are discussed. A design for a wide-angle LCOPA is proposed for high-efficiency laser beam steering. This work provides fundamental understanding for a light beam deflected by a diffractiveliquid-crystal device.


What Aligns Liquid Crystals On Solid Substrates? The Role Of Surface Roughness Anisotropy, Satyendra Kumar, Jae-Hoon Kim, Yushan Shi Feb 2005

What Aligns Liquid Crystals On Solid Substrates? The Role Of Surface Roughness Anisotropy, Satyendra Kumar, Jae-Hoon Kim, Yushan Shi

Physics Publications

The mechanism responsible for liquid crystal (LC) alignment on mechanically buffed or UV exposed polymer films is poorly understood. A comprehensive study of LC alignment on variously prepared substrates unequivocally shows that the anisotropy in the surface roughness of the substrate completely determines the direction of LC alignment. In all the cases studied, including those where an anchoring transition occurs with temperature, the LC director (re)aligns in the directions of low roughness.


Real-Time Microbe Detection Based On Director Distortions Around Growing Immune Complexes In Lyotropic Chromonic Liquid Crystals, Sergij V. Shiyanovskii, T. Schneider, Ivan I. Smalyukh, T. Ishikawa, G. D. Niehaus, K. J. Doane, C. J. Woolverton, Oleg Lavrentovich Feb 2005

Real-Time Microbe Detection Based On Director Distortions Around Growing Immune Complexes In Lyotropic Chromonic Liquid Crystals, Sergij V. Shiyanovskii, T. Schneider, Ivan I. Smalyukh, T. Ishikawa, G. D. Niehaus, K. J. Doane, C. J. Woolverton, Oleg Lavrentovich

Chemical Physics Publications

We describe director distortions in the nematic liquid crystal (LC) caused by a spherical particle with tangential surface orientation of the director and show that light transmittance through the distorted region is a steep function of the particle's size. The effect allows us to propose a real-time microbial sensor based on a nontoxic lyotropic chromonic LC (LCLC) that detects and amplifies the presence of immune complexes. A cassette is filled with LCLC, antibody, and antigen-bearing particles. Small and isolated particles cause no macroscopic distortions of the LCLC. Upon antibody-antigen binding, the growing immune complexes distort the director and cause ...


Light-Induced Changes Of Optical And Electrical Properties In Bent-Core Azo Compounds, Antal Jakli, V. Prasad, D.S.S. Rao, Guangxun Liao, I. Janossy Feb 2005

Light-Induced Changes Of Optical And Electrical Properties In Bent-Core Azo Compounds, Antal Jakli, V. Prasad, D.S.S. Rao, Guangxun Liao, I. Janossy

Chemical Physics Publications

We have studied the optical and electrical properties of two bent-core substances with an azo linkage in their cores. Pump-probe laser studies, direct textural observations, and spectrophotometric recordings show an initial decrease of light transmission, which at larger light intensities (similar to 1 mW/mm(2)) is followed by a bleaching. Simultaneously the electrical properties (electric conductivity, antiferroelectric polarization, switching threshold, and switching time) decreased monotonically with increasing light intensities. The monotonic decrease of electrical properties indicates that the darkening and bleaching have the same origin, namely, the photochemical isomerization of the azo linkage from the trans to the cis ...


Submillisecond Switching Of Nematic Liquid Crystal In Cells Fabricated By Anisotropic Phase-Separation Of Liquid Crystal And Polymer Mixture, Qingbing Wang, Satyendra Kumar Feb 2005

Submillisecond Switching Of Nematic Liquid Crystal In Cells Fabricated By Anisotropic Phase-Separation Of Liquid Crystal And Polymer Mixture, Qingbing Wang, Satyendra Kumar

Physics Publications

Liquid crystal (LC) cells consisting of a very thin (submicrometer) nematic LC layer switch with time response smaller than 1 ms. The total response time, i.e., sum of the turn-on and turn-off times, can be made as small as 1.3 ms. Such devices were prepared by a photoinduced anisotropic phase separation of mixtures of the LC and prepolymer. The formation of the LC-polymer bilayer in these devices was confirmed by polarized light microscopy and scanning electron microscopy. The phase separation method permits one to fine-tune the LC film thickness by varying the LC concentration in the mixture. This ...


Fast Birefringent Mode Stressed Liquid Crystal, John L. West, Guoqiang Zhang, Anatoliy Glushchenko, Yurii Reznikov Jan 2005

Fast Birefringent Mode Stressed Liquid Crystal, John L. West, Guoqiang Zhang, Anatoliy Glushchenko, Yurii Reznikov

Chemistry & Biochemistry Publications

We report a stressed liquid crystal (SLC) that produce a large shift in phase retardation at submillisecond speeds. The SLC consists of uniformly aligned micro-domains of a liquid crystal dispersed in a polymer structure. Mechanical stress produces uniform alignment, essentially eliminates light scattering, and substantially improves the electro-optic performance. A 22-μm-thick SLC film switches more than 2μm of phase retardation in less than 1ms. The system has a linear voltage response with essentially no hysteresis.


Optical Trapping Of Colloidal Particles And Measurement Of The Defect Line Tension And Colloidal Forces In A Thermotropic Nematic Liquid Crystal, Ivan I. Smalyukh, A. N. Kuzmin, A. V. Kachynski, P. N. Prasad, Oleg Lavrentovich Jan 2005

Optical Trapping Of Colloidal Particles And Measurement Of The Defect Line Tension And Colloidal Forces In A Thermotropic Nematic Liquid Crystal, Ivan I. Smalyukh, A. N. Kuzmin, A. V. Kachynski, P. N. Prasad, Oleg Lavrentovich

Chemical Physics Publications

We demonstrate optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystal with low birefringence. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. The three-dimensional director fields and positions of the particles manipulated by laser tweezers are visualized by fluorescence confocal polarizing microscopy.