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Full-Text Articles in Physics

Physical Limitations And Fundamental Factors Affecting Performance Of Liquid Crystal Tunable Lenses With Concentric Electrode Rings, Liewi Li, Doug Bryant, Tony Van Heugten, Philip Bos Mar 2013

Physical Limitations And Fundamental Factors Affecting Performance Of Liquid Crystal Tunable Lenses With Concentric Electrode Rings, Liewi Li, Doug Bryant, Tony Van Heugten, Philip Bos

Philip J. Bos

A comprehensive analysis of fundamental factors and their effects on the performance of liquid crystal (LC)-based lenses is given. The analysis adopts numerical LC director and electric field simulation, as well as scalar diffraction theory for calculating the lens performance considering different variable factors. A high-efficiency LC lens with concentric electrode rings is fabricated for verifying and enriching the analysis. The measurement results are in close agreement with the analysis, and a summary of key factors is given with their quantitative contributions to the efficiency.


Near-Diffraction-Limited Tunable Liquid Crystal Lens With Simplified Design, Liwei Li, Doug Bryant, Tony Van Heugten, Dwight Duston, Philip Bos Mar 2013

Near-Diffraction-Limited Tunable Liquid Crystal Lens With Simplified Design, Liwei Li, Doug Bryant, Tony Van Heugten, Dwight Duston, Philip Bos

Philip J. Bos

A high-efficiency tunable refractive lens based on liquid crystals with concentric electrode rings and a simple unique design of a resistor network is reported, and used to assess the performance of an optimized electrically tunable lens. It has a large number of phase control points to be able to accurately control the phase profile and produce high efficiency. The lens design uses resistors between neighboring electrodes to minimize external connections. The lens optical path difference is measured as a near perfect parabolic shape and the Strehl ratio of about 80% is obtained (comparing to a high-quality glass lens). Image evaluations ...


Designing Dupin Cyclides In Micro And Macro Worlds, Oleg Lavrentovich Jan 2013

Designing Dupin Cyclides In Micro And Macro Worlds, Oleg Lavrentovich

Oleg Lavrentovich

No abstract provided.


Polar Bent-Shape Liquid Crystals - From Molecular Bend To Layer Splay And Chirality, Antal Jakli, A. Eremin Oct 2012

Polar Bent-Shape Liquid Crystals - From Molecular Bend To Layer Splay And Chirality, Antal Jakli, A. Eremin

Antal Jakli

Considerable progress has been achieved in understanding the fascinating structure and physical properties of the ferroelectric liquid crystalline phases formed by bent-core liquid crystals (BLC). In this review, we discuss a manifold of polar structures and phases found in BLCs such as orthogonal and tilted ferro-/antiferroelectric phases, smectic phases, switchable columnar phases, modulated structures and phases stabilised by a periodic lattice of defects such as dark conglomerate and nanofilament phases. We review the theoretical aspects of ferroelectricity in BLCs including existing microscopic theories and computer simulations, polarity and chirality phenomena. The last part of the paper is devoted to ...


Hybrid Rod-Like And Bent-Core Liquid Crystal Dimers Exhibiting Biaxial Smectic A And Nematic Phases, Yan Wang, Hyung Yoon, Hari Bisoyi, Satyendra Kumar, Quan Li Jan 2012

Hybrid Rod-Like And Bent-Core Liquid Crystal Dimers Exhibiting Biaxial Smectic A And Nematic Phases, Yan Wang, Hyung Yoon, Hari Bisoyi, Satyendra Kumar, Quan Li

Satyendra Kumar

Liquid crystal hybrid dimers involving bent-core units and rod-like units were designed, synthesized and investigated by a combination of polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction studies. All the four unsymmetrical dimers 1–4 exhibited stable nematic phases over a wide temperature range. Moreover, dimer 1exhibited the biaxial smectic A (SmA) phase and dimer 2 exhibited a highly ordered mesophase below the nematic (N) phase. Two rod-like and bent-core nematogenic units were covalently linked in dimers 3 and 4 to furnish exclusively the nematic phase. The observation of the biaxial SmA phase underlying the nematic phase ...


Alignment By Langmuir/Schaefer Monolayers Of Bent-Core Liquid Crystals, Wilder Iglesias, Timothy Smith, Prem Basnet, Sharon Stefanovic, Carsten Tschierske, Daniel Lacks, Antal Jakli, Elizabeth Mann Aug 2011

Alignment By Langmuir/Schaefer Monolayers Of Bent-Core Liquid Crystals, Wilder Iglesias, Timothy Smith, Prem Basnet, Sharon Stefanovic, Carsten Tschierske, Daniel Lacks, Antal Jakli, Elizabeth Mann

Antal Jakli

Langmuir films of bent-core molecules at the air/water interface are transferred onto a solid surface by the inverse-Langmuir-Schaefer (ILS) technique. Previous work by the authors demonstrated that ILS films of a symmetric bent-core molecule can serve as effective planar alignment layers for a nematic bent-core liquid crystal cell, but the Langmuir films were unstable and formed multilayers at very low pressures. Here, films of bent-core molecules with one hydrophilic end connected to the bent core by a short aliphatic chain are tested as alignment layers. The hydrophilic group led to much more stable Langmuir films, and also to a ...


Chiral Symmetry Breaking By Spatial Confinement In Tactoidal Droplets Of Lyotropic Chromonic Liquid Crystals, Luana Tortora, Oleg Lavrentovich Mar 2011

Chiral Symmetry Breaking By Spatial Confinement In Tactoidal Droplets Of Lyotropic Chromonic Liquid Crystals, Luana Tortora, Oleg Lavrentovich

Oleg Lavrentovich

In many colloidal systems, an orientationally ordered nematic (N) phase emerges fromthe isotropic (I) melt in the form of spindle-like birefringent tactoids. In cases studied so far, the tactoids always reveal a mirror-symmetric nonchiral structure, sometimes even when the building units are chiral. We report on chiral symmetry breaking in the nematic tactoids formed in molecularly nonchiral polymer-crowded aqueous solutions of low-molecular weight disodium cromoglycate. The parity is broken by twisted packing of self-assembled molecular aggregates within the tactoids as manifested by the observed optical activity. Fluorescent confocal microscopy reveals that the chiral N tactoids are located at the boundaries ...


Self-Organized Photochromic Dithienylcyclopentene Organogels, Krishnamurthy Rameshbabu, Lu Zuo, Chanjoong Kim, Augustine Urbas, Quan Li Jan 2011

Self-Organized Photochromic Dithienylcyclopentene Organogels, Krishnamurthy Rameshbabu, Lu Zuo, Chanjoong Kim, Augustine Urbas, Quan Li

Quan Li

A series of photochromic organogelators based on dithienylcyclopentene amides with a phenylene unit as a bridge between the amide and long alkyl chain were synthesized, their gelation behaviors were characterized by rheology, FT-IR, H-1 NMR, SEM, optical microscopy, UV-Vis and fluorescence spectroscopy. These organogelator molecules were found to be able to induce gelation in apolar solvents such as benzene, toluene and p-xylene to form entangled networks driven by intermolecular hydrogen bonding together with pi-pi interactions. Their excellent reversible photochromism with thermal stability in both solution and gel states was observed, and the thermally reversible property in sol-gel transition was exhibited.


Liquid Crystalline Amorphous Blue Phase And Its Large Electrooptical Kerr Effect, Khoa Le, Satoshi Aya, Yuji Sasaki, Hyunhee Choi, Fumito Araoka, Kenji Ema, Jozef Mieczkowski, Antal Jákli, Ken Ishikawa, Hideo Takezoe Jan 2011

Liquid Crystalline Amorphous Blue Phase And Its Large Electrooptical Kerr Effect, Khoa Le, Satoshi Aya, Yuji Sasaki, Hyunhee Choi, Fumito Araoka, Kenji Ema, Jozef Mieczkowski, Antal Jákli, Ken Ishikawa, Hideo Takezoe

Antal Jakli

An amorphous blue phase III with low and wide thermal range (similar to 20 degrees C) including room temperature is induced by doping a bent-core nematic with a strong chiral material. We confirm that the electrooptical response is due to the Kerr effect, with the Kerr constant being up to two orders of magnitude larger than conventional Kerr materials such as nitrobenzene.


Stable Amorphous Blue Phase Of Bent-Core Nematic Liquid Crystals Doped With A Chiral Material, Stefanie Taushanoff, Khoa Le, Jarrod Williams, Robert Twieg, B. Sadashiva, Hideo Takezoe, Antal Jakli Jun 2010

Stable Amorphous Blue Phase Of Bent-Core Nematic Liquid Crystals Doped With A Chiral Material, Stefanie Taushanoff, Khoa Le, Jarrod Williams, Robert Twieg, B. Sadashiva, Hideo Takezoe, Antal Jakli

Antal Jakli

We report an induction of the blue phase III (BPIII) at a relatively low and wide ( over 20 degrees C) temperature range in nematogenic achiral bent-core liquid crystals doped with a high twisting power chiral material. The pitch decreases with increasing chiral dopant ratio, and easily reaches the ultraviolet wavelength, so that completely dark texture is obtained under crossed polarizers. Electrooptical switching was achieved in a time range of a few to a few tens of milliseconds. We propose for the stabilization of BPIII that broad-temperature range smectic nano-clusters inhibit the long-range order of the double twisted helical structures, and ...


Light-Driven Nanoscale Chiral Molecular Switch: Reversible Dynamic Full Range Color Phototuning, Ji Ma, Yannian Li, Timothy White, Augustine Urbas, Quan Li Mar 2010

Light-Driven Nanoscale Chiral Molecular Switch: Reversible Dynamic Full Range Color Phototuning, Ji Ma, Yannian Li, Timothy White, Augustine Urbas, Quan Li

Quan Li

A light-driven nanoscale chiral molecular switch was found to impart its chirality to an achiral liquid crystal host to form a self-organized, optically tunable helical superstructure capable of fast and reversible phototuning of the structural reflection across the entire visible region.


Odd-Even Effects In Bent-Core Compounds Containing Terminal N-Alkyl Carboxylate Groups, S. Umadevi, Antal Jakli, B. Sadashiva Oct 2006

Odd-Even Effects In Bent-Core Compounds Containing Terminal N-Alkyl Carboxylate Groups, S. Umadevi, Antal Jakli, B. Sadashiva

Antal Jakli

A homologous series of eleven five-ring symmetrical bent-core compounds containing terminal n-alkyl carboxylate groups were synthesized, characterized and their dielectric and electro-optical properties have been investigated. The lower homologues (n = 6-11) of the series show B-2 structures with an interesting odd-even effect concerning their local director tilt and polar arrangements. This odd-even effect probably is due to steric (entropic) reasons, which are not suppressed by the relatively low polar interaction. Three of the middle homologues display a B-7' phase, which is bistable and shows linear electro-optical switching with a transition to the chiral antiferroelectric smectic phase at a lower temperature ...


Electrically Tunable Lens Based On A Dual-Frequency Nematic Liquid Crystal, Oleg Pishnyak, Susumu Sato, Oleg Lavrentovich Jul 2006

Electrically Tunable Lens Based On A Dual-Frequency Nematic Liquid Crystal, Oleg Pishnyak, Susumu Sato, Oleg Lavrentovich

Oleg Lavrentovich

We report on an electrically controlled liquid-crystal-based variable optical lens filled with a dual-frequency nematic material. The lens design employs a hole-patterned electrode structure in a flat nematic cell. In order to decrease the lens switching time we maximize the dielectric torque by using a dual-frequency nematic material that is aligned at an angle approximately 45 degrees with respect to the bounding plates by obliquely deposited SiOx, and by using an overdrive scheme of electrical switching. Depending on the frequency of the applied field, the director realigns either toward the homeotropic state (perpendicular to the substrates) or toward the planar ...


Fluorine Containing Nonsymmetrical Five-Ring Achiral Banana-Shaped Compounds With Columnar And Synclinic Antiferroelectric Layered Phases, Channabasaveshwar Yelamaggad, Indudhara Shashikala, Uma Hiremath, Guangxun Liao, Antal Jakli, Doddamane Shankar Rao, Subbarao Prasada, Quan Li Jun 2006

Fluorine Containing Nonsymmetrical Five-Ring Achiral Banana-Shaped Compounds With Columnar And Synclinic Antiferroelectric Layered Phases, Channabasaveshwar Yelamaggad, Indudhara Shashikala, Uma Hiremath, Guangxun Liao, Antal Jakli, Doddamane Shankar Rao, Subbarao Prasada, Quan Li

Antal Jakli

The phase transitional behavior of two homologous series of five-ring banana-shaped compounds comprising fluorine substituents synthesized through covalent linking of two chemically dissimilar rod-like anisometric cores (arms) to central 1,3-phenylene is reported. The novelty of these molecules originates from the fact that the molecules are highly nonsymmetrical. One of the arms, which is either salicylaldimine or Schiff base core, possesses two vicinal fluorine atoms at the terminal ring having a n-decyloxy tail; while the n-alkyl tail attached to the other arm was varied to realize a homologous series of compounds. The mesophases have been characterized by several complementary studies ...


Stressed Liquid-Crystal Optical Phased Array For Fast Tip-Tilt Wavefront Correction, Bin Wang, Guoqiang Zhang, Anatoliy Glushchenko, John West, Philip Bos, Paul Mcmanamon Dec 2005

Stressed Liquid-Crystal Optical Phased Array For Fast Tip-Tilt Wavefront Correction, Bin Wang, Guoqiang Zhang, Anatoliy Glushchenko, John West, Philip Bos, Paul Mcmanamon

John L West

A liquid-crystal optical phased-array technology that uses stressed liquid crystals provides a new type of tip-tilt wavefront corrector. It demonstrates a very fast time response (10 kHz) and high beam-steering efficiency (similar to 91%). The new technology presented here will allow for a nonmechanical, high-speed correction with simple device construction.


Finite-Difference Time-Domain Calculations Of A Liquid-Crystal-Based Switchable Bragg Grating, Bin Wang, Xinghua Wang, Philip Bos Jun 2004

Finite-Difference Time-Domain Calculations Of A Liquid-Crystal-Based Switchable Bragg Grating, Bin Wang, Xinghua Wang, Philip Bos

Philip J. Bos

A polymer-wall-confined transmissive switchable liquid crystal grating is proposed and investigated by two-dimensional finite-difference time-domain optical calculation and liquid-crystal-director calculation, to our knowledge for the first time. The results show how to obtain optimized conditions for high diffraction efficiency by adjusting the liquid crystal parameters, grating geometric structure, and applied voltages. The light propagation direction and efficiency can be accurately calculated and visualized concurrently.


Multispectrum, Spatially Addressable Polarization Interference Filter, Salman Saeed, Philip Bos Jan 2002

Multispectrum, Spatially Addressable Polarization Interference Filter, Salman Saeed, Philip Bos

Philip J. Bos

We review current synthesis techniques for generating and improving birefringent filters. The relationship between wave-plate orientation and the resulting spectral output is shown to be that of a simple Fourier transform. By using this relationship and starting from the fan Sole configuration, we easily generated plate orientations providing lower sidelobe levels and improved finesse. We outline a method by which filters can be constructed to provide from 0 to 100% of the desired passband in a continuous fashion. Such a filter can be stacked to allow rapid control of any number of passbands and is shown, as an example in ...


Ultraviolet Lasing In Cholesteric Liquid Crystals, A. F., Peter Palffy-Muhoray, B. Taheri Jun 2001

Ultraviolet Lasing In Cholesteric Liquid Crystals, A. F., Peter Palffy-Muhoray, B. Taheri

Peter Palffy-Muhoray

We report the observation of stimulated emission and mirrorless lasing in pure cholesteric liquid crystals. The lasing action is attributed to the combination of the fluorescence and the distributed feedback that are due to the inherent periodic structure of the liquid crystal. If the reflection band matches the intrinsic emission of the cholesteric liquid crystal, the crystal becomes a natural laser material, which will self-lase, without any optical elements or the addition of dyes, under picosecond excitation at 355 nm. Samples have been made to lase at different wavelengths in the near UV by shifting of the edge of the ...


Optical Vortices Generated By Dislocations In A Cholesteric Liquid Crystal, D. Voloschenko, Oleg Lavrentovich Mar 2000

Optical Vortices Generated By Dislocations In A Cholesteric Liquid Crystal, D. Voloschenko, Oleg Lavrentovich

Oleg Lavrentovich

We report the observation of optical vortices in a laser beam propagating through the stripe pattern of a cholesteric liquid crystal. The liquid crystal is confined in a cell with homogeneous boundary conditions and forms a diffraction phase grating. Optical vortices are produced by edge dislocations of the cholesteric grating. The vortices show up as spots of zero light intensity in the diffraction maxima. There is one spot in each +1 and -1 diffraction maximum and two spots in diffraction maxima +2 and -2. (C) 2000 Optical Society of America. OCIS codes: 160.3710, 050.1940, 180.1790, 070.4690.