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We fabricated a terahertz (THz) polarization converter using a twisted nematic (TN) liquid crystal (LC) cell. Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films coated on quartz glass substrates were used as electrode layers in the TN LC cell. The PEDOT/PSS films were rubbed unidirectionally using a rayon cloth to align the nematic LC, thereby also serving as an alignment layer. The azimuthal surface anchoring strength of the PEDOT/PSS films was measured to be 5×10-4 J/m2 using the Néel wall method, which is similar to that of typical polymeric alignment layers. The optical constants of the PEDOT/PSS film in the THz range were also characterized using the Drude-Smith model, and the results indicated that the PEDOT/PSS films could be used both as transparent electrodes in the THz range and as alignment layers for the LC. The electro-optical properties of the fabricated TN LC cell were also investigated using a polarized visible laser and THz time-domain spectroscopic system. In particular, the transmission spectra and polarization conversion property of the TN LC cell in the THz range were theoretically analyzed based on a stratified model that considers optical anisotropy, absorption, and multiple interference. This work substantiates the advantages of TN LC cells with rubbed PEDOT/PSS films useful for THz polarization converters with electrical tunability. [ABSTRACT FROM AUTHOR]

A tunable dichroic polarization beam splitter (tunable DPBS) simultaneously performs the follow functions: 1. Separation of a polarized incident beam into multiple pairs of orthogonally polarized beams; 2. Separation of the propagation direction of two wavelength incident beams after passing through the tunable DPBS; and 3. Control of both advanced polarization and wavelength separation capabilities by varying the temperature of the tunable DPBS. This novel complex optical property is realized by diffraction phenomena using a designed three-dimensional periodic structure of aligned liquid crystals in the tunable DPBS, which was fabricated quickly with precision in a one-step photoalignment using four-beam polarization interferometry. In experiments, we demonstrated that these diffraction properties are obtained by entering polarized beams of wavelengths 532nm and 633nm onto the tunable DPBS. These diffraction properties are described using the Jones calculus in a polarization propagation analysis. Of significance is that the aligned liquid crystal structure needed to obtain these diffraction properties was proposed based on a theoretical analysis, and these properties were then demonstrated experimentally. The tunable DPBS can perform several functions of a number of optical elements such as wave plates, polarization beam splitter, dichroic beam splitter, and tunable wavelength filter. Therefore, the tunable DPBS can contribute to greater miniaturization, sophistication, and cost reduction of optical systems used widely in applications, such as optical measurements, communications, and information processing. [ABSTRACT FROM AUTHOR]

Active waveband selective switches for the telecommunication wavebands are fabricated and demonstrated. This type of active waveband selective switch is composed of a guided-mode resonance filter, a twisted nematic liquid crystal (TNLC) layer, and a linear polariser. In voltage-off status, a fabricated active waveband selective switch with grating period of 893.86 nm exhibits high resonance peak with wavelength around 1311.2 nm. In voltage-on status, this switch exhibits a high resonance peak with wavelength around 1551.3 nm. The measured reflection peaks of another active waveband selective switch with grating period of 872.84 nm are located at 1309.1 and 1549.4 nm in voltage-on status and voltage-off status, respectively. Thus, light waveband can be tuned between O-band and C-band by electrically driving the TN-LC layer of this type of active waveband selective switch in real time. [ABSTRACT FROM AUTHOR]

Two photo-activators, AAP and CAP, were synthesized with cyclohexanone oxime with methyl and cronic anhydrides. They were used to improve the liquid crystal (LC) alignment properties by increasing the surface azimuthal anchoring energy, that has been an image-sticking problems. These photo-activators were respectively mixed with twisted nematic (TN) planar alignment agent (TN-PAA) or photo-polyamic acid (P-PAA), respectively. It is remarkable that a photo-activator using crotonic anhydride (CAP) what has allyl double bond showed very high anchoring energy, 6.92 × 10−5 J/m2, which is comparable or better than that obtained with rubbing, 1.65 × 10−5 J/m2. The anchoring and the alignment properties were observed with the P-PAA were the lower than the TN-PAA. The photochemical reactions and the surface properties of the photo-polyimide (P-PI) were more complex due to more than double photochemical reactions. The fourier transform infrared spectroscopy (FT-IR), contact angle, atomic force microscope (AFM) and differential thermal analysis and thermogravimetic analysis (DTA-TGA) measurements indicated that the surface of polyimide (PI) became more hydrophobic due to the photoreactions of alkyl radicals. These radicals were generated by the photo-irradiation and the reduction of hydrophilic functional groups. The high anchoring energy was assisted by the rough and robust surface induced by carbon dioxide generation. These properties contribute to prevent the image-sticking and shorten the irradiation time with energy. [ABSTRACT FROM AUTHOR]

A hole-patterned electrode liquid crystal (LC) lens with electrically switching coaxial bi-focus and single focus modes of tuning is demonstrated. The proposed LC lens mainly consists of a two LC layer (TLCL) structure with different thicknesses to achieve higher focusing power than the conventional hole-patterned electrode LC lens with the same aperture size. In the TLCL structure, one LC layer, doped with 3 wt % RM257, was photopolymerized to achieve a fixed focusing power of 18.5 Diopter. Due to polarization dependence in TLCL lenses, an additional 90° twisted nematic (TN) cell was used to change the incident polarization in order to switch lens functions on or off. As a result, a fixed focusing power of 18.5 Diopter was achieved when voltages of 10 Vrms were applied to the 90° TN cell. In addition, the switching capabilities of the bi-focus and single focus modes were achieved when operating individually with applied voltages from 20 Vrms to 90 Vrms, and higher voltages of over 90 Vrms, respectively. The maximum focusing power in the fabricated TLCL lens is 30.9 Diopter. [ABSTRACT FROM AUTHOR]

The optimized electrooptical (EO) properties of inverse twisted nematic (ITN) liquid crystals (LCs) were demonstrated by utilizing liquid doping technique. ITN LC display is a driving system containing 90° twisted structure on homeotropic polyimide with negative dielectric anisotropic LCs. Toluene was chosen as dopant and the doped ITN LCs show improved driving voltage and response time while maintaining a very good dark state as undoped ITN LCs. Driving voltage was 1.1 V lower and the total response time was reduced by 49% after toluene doped into LCs. The main reason of these EO properties enhancement is that toluene molecules penetrate between LC molecules, and hence, the dielectric anisotropy and the visco-elastic coefficient of LCs are changed. The simplicity of liquid doping technique shows that it could be applied to a wide range of LC systems. [ABSTRACT FROM PUBLISHER]

Highly first order silane end-group difluoroterphenyl liquid crystal was added to trifluoroterphenyl host with a nematic to smectic-C phase transition to increase its first order nature, achieve a higher cone angle and reduce its temperature dependence. Increasing concentration of the additive, caused a linear decrease and eventual disappearance of the nematic phase. A smectic-A phase was injected at 35% concentration, making the transition second order. Optical studies of the mixtures showed little dependence of the highest value of cone angle on concentration. The original host showed first order cone angle behavior and was used to fabricate a twisted FLC device. [ABSTRACT FROM AUTHOR]

We propose a double frequency ultraviolet (UV) exposure process that can improve the surface anchoring energy of photopolyimide (PI) embedded with reactive mesogens (RMs) for the high speed liquid crystal modes. In experiment, we polymerize the RM materials using long wavelength UV light over 340 nm, and then accomplish the polymerization of the UV alignment layer using short UV light between 254 nm and 340 nm. As results, we demonstrate the improved surface anchoring energy and the fast response time of an in-plane switching (IPS) and a twisted nematic (TN) LC modes in this paper. [ABSTRACT FROM AUTHOR]

Adding a chiral dopant in twisted nematic (TN) liquid crystal cell can stabilize the orientation of liquid crystal molecules, particularly in high TN (HTN) or super TN (STN) liquid crystal cells. The difference in pitches in liquid crystal is induced by the chiral dopant, and these different pitches affect the orientation of liquid crystal director under an external applied voltage and influence the characteristics of microwave modulation. To illustrate this point, the microwave phase shift per unit length (MPSL) versus voltage is calculated on the basis of the elastic theory of liquid crystal and the finite-difference iterative method. Enhancing the pitch induced by the chiral dopant in liquid crystal increases the MPSLs, but the stability of the twisted structures is decreased. Thus, appropriate pitches of 100d, 4d, and 2d can be applied in TN, HTN, and STN cells with cell gap d to enhance the characteristics of microwave modulation and stabilize the structures in twisted cell. This method can improve the characteristics of liquid crystal microwave modulators such that the operating voltage and the size of such phase shifters can be decreased. [ABSTRACT FROM AUTHOR]

We present a simple and efficient way to improve the performance of the twisted nematic liquid crystal (LC) system by doping a small amount of n -alcohols. The LCs modified by n -hexanol demonstrates the optimum electro-optical properties of lower driving voltage and shorter response time. Our measurements indicate that the liquid dopant n -alcohols can be used to modify LCs for lowering zenithal anchoring energy relative to undoped LCs. Without the drawbacks of precipitation and aggregation that the nanoparticles could have, the method of doping n -alcohol liquids provides a more stable and reliable choice to apply in the various LC display systems. [ABSTRACT FROM AUTHOR]

We show that the crystal rotation method for measuring the difference between splay and bend flexoelectric coefficients (e1–e3) [Outram and Elston, Liq. Cryst.39, 149 (2012)] can be improved by using AC instead of DC fields. The field frequency is small (~0.05 Hz), yet sufficient to get rid of the difficulties connected with the migration of charge carriers. The method is sensitive enough so as to use fields with amplitudes as small as 1 V/mm. This has the advantage of avoiding the consideration of the interaction due to the dielectric anisotropy, and greatly simplifies the analysis of data. The results are extracted from a simple fitting scheme, which involves two parameters. In particular (e1–e3) is obtained from a scale factor in a one-parameter fit. Measurements of the temperature dependence of (e1–e3) are presented for two classical nematic materials. [ABSTRACT FROM AUTHOR]

Ferromagnetic nanoparticles insertions in nematic liquid crystals (NLC) in twisted configuration are studied and a theoretical model is proposed to explain the results. Experimental observation revealed that nanoparticles tend to overcrowd in long strings parallel to the rubbing direction of the alignment substrate of the LC cell. Their behavior under external field was studied and their interaction with their nematic host is described using elastic continuum theory. [ABSTRACT FROM AUTHOR]

The optical response time of a nematic liquid crystal (NLC) decreases due to incorporation of carbon nanotubes (CNTs) in the liquid-crystal host. Such reduction is believed to be due to an increase in the elastic constant of the nanotube-doped LC system. In this paper, we present the effect on optical response due to doping an NLC with octadecylamine functionalised single-walled carbon nanotubes (ODA-SWCNT) in a twisted alignment mode. The electro-optic switching amplitude of ODA-SWCNT nanocomposites of NLC decreases compared to pure NLC. A fast response time is observed with an increase in the concentration of ODA-SWCNT in NLC host. Additionally, optical response of pure NLC in a twisted nematic (TN) cell fabricated using mixtures of polyimide (PI) and ODA-SWCNT as an alignment layer is investigated. The optical response time decreased by ~75% in a TN cell fabricated with a mixture of PI and ODA-SWCNT compared to that of a TN cell prepared using a pure PI alignment layer. The presence of ODA-SWCNT in the alignment layer enhances the surface anchoring of the NLC molecules leading to an increase in the elastic constant and a decrease in the optical response time of NLC. [ABSTRACT FROM PUBLISHER]

Arbitrary vector beams (VBs) are realized by the designed polarization converters and corresponding vector-photoaligned q-plates. The polarization converter is a specific twisted nematic cell with one substrate homogeneously aligned and the other space-variantly aligned. By combining a polarization-sensitive alignment agent with a dynamic micro-lithography system, various categories of liquid crystal polarization converters are demonstrated. Besides, traditional radially/ azimuthally polarized light, high-order and multi-ringed VBs, and a VB array with different orders are generated. The obtained converters are further utilized as polarization masks to implement vector-photoaligning. The technique facilitates both the volume duplication of these converters and the generation of another promising optical element, the q-plate, which is suitable for the generation of VBs for coherent lasers. The combination of proposed polarization converters and correspondingly fabricated q-plates would drastically enhance the capability of polarization control and may bring more possibilities for the design of photonic devices. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new physical model to predict the transient responses of an active-matrix liquid crystal display (LCD) in a twisted nematic (TN) mode. For the behavioral model, three types of data are most important: 1) capacitance–voltage; 2) transmittance–voltage characteristics; and 3) time constant parameters a1 and a2 . We extract them from the physical properties of TN LC molecules, such as dielectric anisotropy, birefringence, viscosity, cell gap, and elastic constant. We describe the behavior of the TN-LCD by using the analog hardware description language, Verilog-A. We simulate optically rising responses of the TN-LCD panel by importing the behavioral circuit model in the circuit simulator. The simulation results show that the transient optical responses show excellent matches with the measurement ones. In addition, we can observe how the behaviors of optical responses change with varying the physical parameters, such as cell gap, dielectric anisotropy, and elastic constant. [ABSTRACT FROM PUBLISHER]

We demonstrate homogeneous and uniform liquid crystal (LC) alignment on poly(vinylidene fluoride-trifluoroethylene) [PVDF-TrFE] films using ion-beam (IB) irradiation and a performance improvement of twisted nematic (TN) cells using IB-irradiated PVDF-TrFE films. Spontaneous ferroelectricity of the PVDF-TrFE films was modified by IB irradiation, which affected the LC alignment properties. The variation in the pre-tilt angles of the LC molecules on the IB-irradiated PVDF films is attributed to surface reformation, including defluorination and oxidation because the pre-tilt angles of LC molecules can be controlled by adjusting the fluorine content. The results of contact angle measurements supported this phenomenon. A 58% reduction in the switching voltage was observed for TN cells, indicating that the IB-irradiated PVDF-TrFE films are a promising candidate for use as an alignment layer. [ABSTRACT FROM AUTHOR]

This paper proposes a temperature-dependent behavioral circuit model to predict optical characteristics of an active-matrix liquid crystal display (AMLCD) with twisted-nematic (TN) mode. By the simulation, we found that the movement of LCs has a linear relationship depending on the ambient temperature. The simulation results of the transient optical responses show excellent matches with the measurement ones regardless of ambient temperature. [ABSTRACT FROM AUTHOR]

We demonstrate that the supramolecular structure can be formed through the fibrous self-assembly of the polyfluorene-based polymer F8BT in liquid crystal (LC) 5CB. With the utility of alignment layer, the F8BT molecules can be aligned and formed oriented polymer network. We found that the presence of oriented polymer network makes twisted nematic LC exhibit excellent electro-optical properties (EO) of driving voltage reduction and EO bump peak elimination. The polyfluorene-based supramolecular structure provides the function of stabilizing LC molecules. We consider this functional self-assembled network has potential to apply in various devices for the ability of improving performance in operating property. [ABSTRACT FROM AUTHOR]

In this paper, doping liquid materials to enhance the electro-optical (EO) properties of twisted nematic liquid crystals (NLCs) was presented. Two polycyclic aromatic hydrocarbon (PAH) liquids, toluene and 1-methylnaphthalene, were chosen as dopants in order to lower the driving voltage and response time of the NLCs. We find that the main reason of this phenomenon is due to a large amount of reduction in the rotational viscosity of PAH liquids doped NLCs. Without the drawbacks of aggregation that the solid nanoparticles could have, the method of doping liquids provides a more reliable choice for applications in various LC display systems. [ABSTRACT FROM AUTHOR]

Within the Landaude Gennes theory, the order reconstruction of s =±1/2 twist disclinations in a twisted nematic cell is investigated, using the two-dimensional relaxation iterative method. The biaxial structure of the defect core as the cell gap decreasing is explored. At a critical value of dc* ≈ 9ξ (here ξ is the characteristic length for order-parameter changes) , the exchange solution is stable, while the defect core solution becomes metastable, where the system starts to stretch the defect structure and the biaxiality starts to propagate inside of the cell. Comparing to the case with no initial disclination, the value at which the exchange solution becomes stable increases relatively. At a critical separation of dc ≈7ξ, the system undergoes a biaxial transition, and the defect core merges into a biaxial wall with large biaxiality. The force reaches a maximum at dc ≈9ξ, and a local minimum at d≈7ξ. For weak anchoring boundary conditions, because of the weakened frustration, the asymmetric boundary conditions repel the defect to the weak anchoring boundary as the anchoring strength coefficient decreasing. [ABSTRACT FROM AUTHOR]

In order to reduce the power consumption of liquid crystal displays (LCD), the Ag nanowires-liquid crystal composites were prepared. Twisted nematic (TN) liquid crystal mode cells doped with Ag nanowires of 50 nm diameters and different concentrations were prepared. The effects of Ag nanowires on the driving voltage, response time and frequency modulation of TN LCD mode cells were investigated. It was found that the addition of Ag nanowires decreased the driving voltage remarkably, and the threshold voltage can be reduced by 14% at most. The field on response time (Ton) of TN LCD mode cells doped with Ag nanowires was higher than those of pure TN LCD mode cells. Furthermore, strong frequency modulation response of the electro-optical characteristics was alsofound in Ag nanowires doped TN LCDs. The doping of Ag nanowires into LC host improved the electro optical characteristics of TN LCDs effectively. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations offer an effective approach to modelling of optical properties of nematic liquid crystals (NLC). In this paper Monte Carlo method based on the Lebwohl-Lasher effective Hamiltonian with Rapini-Papoular term is described and main results obtained by our group using this approach are briefly presented. [ABSTRACT FROM AUTHOR]

We have developed a new microstructure film for wide viewing liquid crystal displays (LCDs). By attaching it to the surface of a conventional LCD, the viewing angle characteristics of LCD has drastically improved without causing a blur of the frontal image and a decrease in the contrast ratio under bright ambient light conditions. This film can be applied to various LC modes including twisted nematic and multidomain vertical alignment by changing its internal micrometer-size 3D structure. Further, this film can be mass-produced efficiently by self alignment roll-to-roll process. [ABSTRACT FROM AUTHOR]

We investigated the origins of the viewing angle problems caused in single-domain AH-IPS LC mode. To enhance the viewing angle property, we applied polystyrene which is well known for realizing zero pretilt angle. But polystyrene has poor alignment stability due to its low anchoring energy. In this paper, we improved alignment stability by employing UV-curable reactive mesogen and enhanced the viewing angle property by realizing zero pretilt angle with rubbing process. [ABSTRACT FROM AUTHOR]

We demonstrate a liquid crystal (LC) mode switched by combined fringe and in-plane switching (IPS) fields, which are self-adjusted by adopting a bottom floating electrode for enhanced electro-optical properties. In our LC mode structure, conventional IPS electrodes are formed as pixel electrodes and common electrodes on an insulating layer, and floating electrodes that are patterned per the sub-pixels are formed under the insulating layer. When the areas of the pixel and common electrodes are same, the voltage of the bottom floating electrode is spontaneously determined to be half the value of the pixel voltage, which ideally generates symmetric fringe fields with both pixel and common electrodes. Due to the in-plane fields additionally generated between the pixel and common electrodes, the proposed LC structure shows higher transmittance than fringe-field switching (FFS) and IPS LC modes. Transmittance of the conventional FFS and IPS LC modes is highly sensitive to the in-plane electrode's width and spacing condition, but the proposed LC mode shows good transmittance without degradation under large variation condition of the in-plane electrode's spacing-to-width ratio. [ABSTRACT FROM AUTHOR]

In general, light propagating an inhomogeneous liquid crystal (LC) cell can be modeled as ‘bundle rays’ because the LC cell consists of many birefringence layers. In order to calculate the optical path of the propagating light in the inhomogeneous LC cell, we multidimensionally calculated the wavevector,k, and the Poynting vector,S, of an ordinary and an extraordinary ray at LC grid interfaces, which are isotropic to a uniaxial medium and a uniaxial-to-uniaxial medium, by using the phase matching method. Furthermore, we also investigated the transmission coefficients and transmittance of the ordinary and the extraordinary rays as a function of difference of the optical axes of the facing birefringence medium at the interface to obtain the significant rays in the LC cell. Finally, we could calculate the exact path of the significant rays in the inhomogeneous LC cell, and compared the ray path in an electrically controlled birefringence (ECB) mode and a twisted nematic (TN) LC mode. [ABSTRACT FROM AUTHOR]

The paper presents the results of comparative research on the roughness and tool life of the machined surface when steel and cast iron work pieces were turned, reamed and tapped and the cutting zone was lubricated by various coolants (mineral oils, oil emulsions) with and without twisted nematic liquid crystals. The tested liquid crystals were taken from the same homologous series (fatty acid cholesterol esters) but had different molecular mass. It has been established that the most positive tribological effect of liquid crystalline additives is achieved when high-molecular liquid crystals are used in operations characterized by the largest tool-work piece interface area (reaming, threading). Santrauka Straipsnyje pateikti apdirbto paviršiaus šiurkštumo ir įrankių patvarumo matavimo rezultatai, kai plieno ir ketaus paviršiai buvo tekinami, plečiami ir sriegiami sriegikliais, pjovimo zoną tepant ir aušinant įvairiais tepimo ir aušinimo skysčiais su cholesterinių skystųjų kristalų priedais ir be priedų. Buvo naudojami skirtingos molekulinės masės vienos homologinės eilės cholesteriniai skystieji kristalai (cholesterolio esteriai) ir skirtingi tepimo ir aušinimo skysčiai: tepalai ir mineralinių tepalų vandens emulsijos. Nustatyta, kad didžiausias teigiamas skystųjų kristalų priedų efektas pasiekiamas tų operacijų metu, kai įrankio ir detalės kontakto plotas yra didesnis (pvz., plečiant, sriegiant). Taip pat nustatyta, kad didžiausiu tribologiniu efektu pasižymi didesnės molekulinės masės skystieji kristalai. Raktiniai žodžiai: cholesteriniai skystieji kristalai, tepimo ir aušinimo skystis, tekinimas, plėtimas, sriegimas

The twisted nematic (TN) mode is often employed when using three-dimensional active retarder (3DAR) technology, owing to its many merits such as low operating voltage, high aperture ratio and large cell-gap tolerance. However, an unexpected problem with the TN mode is that it leads to an asymmetric contrast ratio (CR) between the normally white TN (NW-TN) mode and normally black TN (NB-TN) mode due to the dispersion characteristics caused by the 90° twist angle. To overcome this problem, we designed a film compensation method using numerical calculations and validated it through experiments. Using our optical configuration, asymmetric CRs can be drastically improved. [ABSTRACT FROM AUTHOR]

The article presents a study which examines a general method which is based on a nematic (N) phase and applicable for compounds without N phase but exhibit helical nanofilament (HNF) B4 phase. It states that to confirm deracemization occurrence in the Bx phase, circular dichroism (CD) measurements were performed. It concludes that a high excess of homochiral HNF domains in the Bx phase from a N-Bx phase sequence mixture was obtained by cooling twisted nematic (TN) cells.

Reconstruction of computer generated holograms (CGHs) addressed on a spatial light modulator (SLM) is an effective way to dynamically generate designed light field distributions. Based on the classic Gerchberg-Saxton (GS) algorithm, we proposed a technique, which can greatly reduce the computation cost to about 60 % in calculating CGHs for three-dimensional (3D) structures but with little degradation of reconstructed light field compared with the classic GS algorithm. The CGHs calculated by our method were displayed on a twisted nematic liquid crystal display, working as a phase-only-modulation SLM, and 3D structures of optical fields, e.g., 3D array of optical traps and vortices, were reconstructed with high efficiency and high quality. Besides, the possibility for 3D holographic display or projection was also demonstrated with this algorithm by reconstruction several images simultaneously in distinct axial planes. [ABSTRACT FROM AUTHOR]

A new method to improve the response time of twisted nematic (TN) liquid crystal displays (LCDs) with liquid crystalline (LC) materials of pitch length shorter than twice the cell gap is proposed. It was known that by using LC materials possessing shorter pitch length, the response time could be improved. However, in previous studies, the pitch length p was limited to values larger than the twice of the cell gap d. This is because 90° TN arrangements become unstable and transform into a 270° super-twisted nematic (STN) arrangement for p < 2d. It was found that by applying voltage to 270° STN arrangement, the 90° TN arrangement could be formed and the obtained TN-LCDs could be stabilised by photopolymerisation. This is because the 270° STN arrangement contains splay deformation. The obtained TN-LCDs exhibit a fast response. By using this method, fast-response TN-LCDs could be realised maintaining moderate driving voltage. [ABSTRACT FROM AUTHOR]

Recently the effect of photoinduced molecular reorientation of nematic liquid crystal molecules originating from dispersed gold nanoparticles (NP) in twisted geometry above the Freedeericksz threshold was reported experimentally via optical Kerr effect studies [1]. In this paper we work out the Monte Carlo approach suitable for modelling of this effect using standard Lebwohl–Lasher–Rapini model with an additional term responsible for photoinduced molecular reorientation. The influence of local electric field enhancement on transmission coefficient is studied for chosen cases. [ABSTRACT FROM PUBLISHER]

The paper presents the results of comparative research on the roughness and tool life of the machined surface when steel and cast iron work pieces were turned, reamed and tapped and the cutting zone was lubricated by various coolants (mineral oils, oil emulsions) with and without twisted nematic liquid crystals. The tested liquid crystals were taken from the same homologous series (fatty acid cholesterol esters) but had different molecular mass. It has been established that the most positive tribological effect of liquid crystalline additives is achieved when high-molecular liquid crystals are used in operations characterized by the largest tool-work piece interface area (reaming, threading). [ABSTRACT FROM AUTHOR]

We present a fully automated system which unites CCD camera technology with liquid crystal technology to create a polarization camera capable of sensing the partial linear polarization of reflected light from objects at pixel resolution. As polarization sensing not only measures intensity but also additional physical parameters of light, it can therefore provide a richer set of descriptive physical constraints for the understanding of images. Previously it has been shown that polarization cues can be used to perform dielectric/metal material identification, specular and diffuse reflection component analysis, as well as complex image segmentations that would be significantly more complicated or even infeasible using intensity and color alone. Such analysis has so far been done with a linear polarizer mechanically rotated in front of a CCD camera. The full automation of resolving polarization components using liquid crystals not only affords an elegant application, but significantly speeds up the sensing of polarization components and reduces the amount of optical distortion present in the wobbling of a mechanically rotating polarizer. In our system two twisted nematic liquid crystals are placed in front of a fixed linear polarizer placed in front of a CCD camera. The application of a series of electrical pulses to the liquid crystals in synchronization with the CCD camera video frame rate produces a controlled sequence of polarization component images that are stored and processed on Datacube boards. We present a scheme for mapping a partial linear polarization state measured at a pixel into hue, saturation and intensity producing a representation for a partial linear polarization image. Our polarization camera currently senses partial linear polarization and outputs such a color representation image at 5 Hz. The unique vision understanding capabilities of our polarization camera system are demonstrated with experimental results showing polarization-based dielectric/metal material classification, specular reflection and occluding contour segmentations in a fairly complex scene, and surface orientation constraints. [ABSTRACT FROM PUBLISHER]

We propose a method for fast switching of a vertical alignment (VA) liquid crystal (LC) cell by forming polymer networks at a low temperature. We found by experiment that the response time of a VA cell can be reduced by low-temperature curing. The turn-off time of the fabricated VA cell was reduced by 54% when the polymers were cured at -20°C. [ABSTRACT FROM AUTHOR]

The design, simulation, and fabrication of two electrically tunable Fabry-Perót (FP) microcavities filled with Twisted Nematic Liquid Crystal (TNLC), based on different mirror materials are demonstrated theoretically and experimentally in the near-infrared (NIR) regime. Owing to the polarization-independent property of TNLC, the wavelength-selection and tunable property of the Liquid Crystal Tunable Filter (LCTF) is independent on polarization state of incoming light beam in the tuning range. The experimentally measured full width at half maximum (FWHM) of the first aluminum mirrors device at a voltage of 10.39 V is ∼ 2.5 nm while the other device composed of gold mirrors showed ∼ 5.5 nm at an applied voltage of 12.72 V. An overall ∼ 53.6 nm spectral shift is observed in first device at 12.72 V with seven and five distinct spectral channels are found with an overall spectral shift of ∼ 27.9 nm at 15.29 V applied voltage in second device over the desired spectral band. The simulated work on LCTFs is found in complete agreement with experimental results. • Design, simulation, and fabrication of two Electro-Optic tunable filters are demonstrated in NIR regime. • Computations of switch-on time of TNLC filled cavity with applied voltages and active cell thicknesses are reported. • Experimentally measured spectral positions, linewidths (FWHM) and transmittances of GF-Al and GG-Gold devices agree completely with simulated results. • GF-Al device shows superior spectral properties than GG-Gold. [ABSTRACT FROM AUTHOR]

Abstract: We have studied molecular director reorientation in a twisted nematic liquid crystal induced by a two-dimensional temperature gradient. We studied the effect of rate change between the temperature gradients in two directions. Our obtained director reorientations are in the range that can be observed experimentally very easily. [Copyright &y& Elsevier]

Of interest here is the fully three-dimensional analysis of the Freedericksz transition for the twisted nematic device (TND), which is widely used in liquid-crystal display monitors. Using a coupled electromechanical variational formulation, the problem is treated as a bifurcation instability triggered by an externally applied electric field. More specifically, we study a finite thickness liquid-crystal layer, anchored between two infinite parallel plates relatively rotated with respect to each other by a given twist angle and subjected to a uniform electric field perpendicular to these bounding plates. The novelty of the proposed analysis lies in the fully three-dimensional formulation of the TND problem that considers all possible bounded perturbations about the principal solution. By scanning a wide range of the liquid crystal's material parameter space, we establish whether the Freedericksz transition is global, i.e., has an eigenmode depending solely on the layer thickness coordinate, or local (also termed the periodic Freedericksz transition), i.e., has an eigenmode with finite wavelengths in one or both directions parallel to the plate. It is found that global modes are typical for low values, while local modes appear at large values of the twist angle. Moreover, for certain TND's, the increase in twist angle can lower the critical electric field, findings that could be useful in guiding liquid-crystal selection for applications. [ABSTRACT FROM AUTHOR]

We herein report the results of a study of a power generating reflective-type liquid crystal display (LCD), composed of a 90° twisted nematic (TN) LC cell attached to the top of a light-absorbing polymer solar cell (PSC), i.e., a Solar-LCD. The PSC consisted of a polymer bulk-heterojunction photovoltaic (PV) layer of poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] and [6,6]-phenyl C71 butyric acid methyl ester (PCDTBT:PCBM70), and showed a high power conversion efficiency of about 5%. In order to improve the visibility of the Solar-LCD, between the TN-LC and the PV cells we inserted a reflective polariser of a giant birefringent optical (GBO) film. The reflectivity from the Solar-LCD was observed to be considerably increased by more than 13-15% under illumination by visible light. The Solar-LCD also exhibited a significantly improved contrast ratio of more than 17-19. We believe there is a clear case for using such Solar-LCDs in new power-generating reflective-type displays; taken as a whole these results also demonstrate the possibility of their application in a number of energy-harvesting opto-electrical display devices. [ABSTRACT FROM AUTHOR]