Thin Liquid Crystal Layer Research Articles

Evolution Process of the Williams Domain in a Nematic Liquid Crystal

We have investigated the pattern formation of the Williams domain when a super-critical voltage is suddenly applied to a thin layer of a nematic liquid crystal. Analyzing about two-hundred paths of an order parameter which represents the degree of the ordering of the pattern, we have clarified the transient behavior of the most probable path and the fluctuation. It has been found that the evolution process of the Williams domain is well described by a scaling function and fluctuation enhancement takes place in a middle stage of the evolution.

Acoustic response of a twisted nematic liquid crystal cell

A thin layer of liquid crystal can be used as a simple two‐dimensional detector of ultrasound. The acoustic beam disturbs the molecular alignment of the liquid crystal, which allows changes in light transmission when the cell is placed between crossed polarizers. Most studies have concentrated on nematic liquid crystals with optic axis along the layer normal. We have studied the acoustic response of a new type of cell developed for electro‐optic displays [D. Berreman and W. Heffner, J. Appl. Phys. 52, 3032–3039 (1981)], which is a twisted nematic with oblique attachment angle at the layer surfaces. We find that this cell is generally more sensitive than the homeotropic nematic and has a faster response time. The cell has the additional feature of having two stable molecular configurations that satisfy the same boundary conditions. Under certain conditions the acoustic beam can drive the system from one state to the other, providing a memory feature for the detector.

Thin-layer liquid crystal thermometry of cells in vitro during hyperthermal microwave irradiation.

A nonperturbing technique of thin-layer liquid crystal thermometry was developed to quantitate heating of Chinese hamster ovary cells and the bacterium Serratia marcescens when exposed to 2450-MHz microwave fields at 0.2-0.5 W/cm2. Cells suspended in culture medium were injected into 5-cm glass microcapillary tubes coated on the inside with a thin layer of liquid crystal. The tubes were sealed and placed parallel to the electric field in a watertight waveguide exposure chamber where they were heated by circulating temperature-controlled water. Even at high circulation rates, liquid crystal color changes indicated local microwave capillary tube heating of 0.1-0.25 degrees C. Precision of measurement was 0.02 degrees C. Observations during microwave heating were significantly different from observations without microwaves at the 1% level, and heating increased as circulating water flow was reduced from 300 ml/s to 100 ml/s. The results of a cell survival assay following hyperthermal treatment were in good agreement with expectations based on the observations of microwave heating using liquid crystals.

Photo-induced electron transfer of a chlorophyll—liquid crystal electrode to water

A platinum plate was coated with a thin layer of chlorophyll and liquid crystal in order to make it photo-excitable. The chlorophyll—liquid crystal electrode immersed in water was found to shift its electrode potential to a more positive value on light irradiation. Furthermore light irradiation increased cathodic current. Liquid crystals such as N-( p-methoxybenzylidene)- p′-butylaniline markedly enhanced a photo-response in electrode potential and current. A prominent photo-response of the electrode appeared in an acidic solution around pH 4. A possibility of a direct electron transfer from a photo-excited chlorophyll—liquid crystal electrode to water, ie, photo-decomposition of water, is suggested.

Energy-transducing membrane : I. Photo-response of a chlorophyll-liquid crystal membrane

An energy-transducing membrane was prepared by incorporating chlorophyll into a thin layer of liquid crystal on a platinum plate. When the membrane was contacted with an acidic solution, a marked increase in positive photopotential resulted from visible light illumination. Of liquid crystals including cholesteryl oleate (COL), N-( p-methoxybenzylidene)- p'-butylaniline (MBBA), or 4'-heptyl-4-cyanobiphenyl (HCB), MBBA produced the greatest enhancement in the photopotential of the membrane. The photopotential depended sharply on the ratio of MBBA to chlorophyll. The maximum photopotential was developed at a ratio of 3. The mechanism of charge transfer within the membrane is discussed.

Spatial coherence of laser radiation transmitted by a liquid crystal near its phase transition to the isotropic liquid state

The spatial coherence of the radiation transmitted by a thin liquid-crystal layer of MBBA near its phase transition was measured very accurately. A laser beam (λ=0.633 μ) was scattered at a small angle from this layer. Attention was concentrated on the heterogeneous state in which the nematic and isotropic phases of the liquid crystal coexisted. The intensity of zero-angle scattering was determined. The dependence of the coherence radius of the transmitted radiation on the liquid crystal temperature was determined. The characteristics of a phase transition of a liquid crystal in a thin cell were analyzed.

Transmission characteristics of a twisted nematic liquid-crystal layer*

An approximate analytical expression is calculated for the transmission of thin twisted nematic layers situated between a polarizer/analyzer pair. The approximation assumes that the twist angle of the nematic liquid crystal is smaller than the maximum retardation of the cell. The direction of the incident light is assumed to be parallel to the normal of the electrode. This configuration is analyzed for a general arrangement of polarizer and analyzer; the general result is evaluated for the case of the polarizer parallel and analyzer perpendicular to the liquid-crystal optical axis on the input and output electrodes, respectively. The results show that in the case of a thin twisted nematic layer the transmission depends on the thickness of the layer, on the birefringence of the liquid crystal, and on the wavelength of the light. This is a departure from the well-known independence of the transmission on these parameters for a thick twisted nematic layer. The analysis also shows that the transmission through thin layers can be minimized by tuning the layer thickness to particular values that depend on wavelength and on liquid-crystal birefringence. In this way, high image contrast can be obtained even for thin liquid-crystal layers.

A REAL‐TIME OPTICAL DATA PROCESSING DEVICE*

A novel liquid-crystal electro-optical device useful as a real-time input device in coherent optical data processing is described. The device is a special adaptation of an ac photoactivated liquid-crystal light valve, and utilizes a hybrid field effect (45 deg twisted nematic effect in OFF state and pure optical birefringence of the liquid crystal in ON state). A thin-film sandwich exerts photoelectric control over the optical birefringence of a thin liquid-crystal layer. Liquid-crystal layer thickness is successfully reduced without image degradation. The device offers high resolution (better than 100 lines/mm), contrast (better than 100/1), high speed (10 msec ON, 15 msec OFF), high input sensitivity, low power input, low fabrication cost, and can be operated at below 10 V rms. Preliminary measurements on device performance in level slicing, filtering, contrast reversal, and edge enhancement are under way.

A 24-digit multiplexed liquid-crystal display working in dynamic deformation mode

Matrix driving of a liquid-crystal transmissive display panel in a dynamic deformation mode is described. In this mode, a very thin homeotropic layer of negative dielectric anisotropy liquid crystal is placed between crossed polarizers. In addition, suitable selection electric-field pulses and modulation waveforms are applied to the liquid crystal in such a way that the alignment is deformed by and let relax between the pulses at a rate high enough to avoid flickering. A 24-digit display making use of a liquid-crystal layer of 3 µm ±10- percent thickness was built and operated in multiplex mode using a single 7-segrnent decoder and 24 digit-selection drivers. Quickly changing images together with good viewing angle, contrast, and efficiency have been obtained.

Non-Gaussian fluctuations in electromagnetic radiation scattered by a random phase screen. II. Application to dynamic scattering in liquid crystal

For pt.I see ibid., vol.8, 369 (1975). The authors have studied experimentally the statistical, spatial coherence and temporal coherence properties of non-Gaussian fluctuations in light scattered by a thin layer of liquid crystal (MBBA) in its dynamic scattering state. The results are consistent with the deep phase-screen theory developed in the previous paper. With 20 V applied to the sample, experimental values of the parameters of the model are: mean square phase deviation phi 2=45.6+or-8.0 rad2, phase correlation length xi =2.63+or-0.24 mu m and phase coherence time 2.2+or-0.2s. Indications are found that, while phase fluctuations in the emergent wave-front are probably dominant, amplitude fluctuations are not entirely negligible. It is argued, however, that the effects of amplitude fluctuations on the values of the above parameters are probably quite small. Taking a broader view, the results confirm that, in many scattering experiments, detailed information concerning the scattering process can be obtained from measurements in the non-Gaussian regime.

Cw thermal lens effect in thin layer of nematic liquid crystal

A cw laser induced, thermal lens effect in a thin layer of MBBA nematic liquid crystal was observed. Due to the birefringence both focusing and defocusing were obtained, depending on the polarization. A qualitative discussion of the aberrational effect in this thermal thin lens is given.

Orientation of liquid crystals by surface coupling agents

Uniformly oriented thin liquid-crystal layers are required for most liquid-crystal device applications and physical investigations. Usual methods for obtaining orientation rely on a substrate interface which has an orienting action on the liquid-crystal molecules. In previously described methods the orienting interfaces degrade chemically with time, thereby generating a corresponding degradation of the liquid-crystal orientation. In the present work, silane surface coupling agents are used to obtain chemically stable interfaces and a wide variety of liquid-crystal orientations.

Static and Transient Electric Field Effect on Homeotropic Thin Nematic Layers

Abstract The experiments presented in this paper give a way to the determination of two elastic constants K 11 and K 33 and one viscosity coefficient y 1 of a nematic liquid crystal. ac electric field stresses applied to a thin layer of nematic liquid crystal modify its cooperative molecular alignment. So, the electrically controlled rotation of molecules induces a variable birefringence as a function of applied voltage and time. The experimental results in relation with the static and dynamic behaviour lead to the determination of these previously static and dynamic behaviour lead to the determination of these previously stated parameters. Temperature dependence of these parameters is given in the nematic range.

The cholophor: A passive polarization-switched liquid crystal screen for multicolor laser displays

Cholophors are passive polarization-switched color display elements suitable for use with lasers or white light. Their hybrid structure, consisting of a thin layer of cholesteric liquid crystal over a layer of photoluminescent phosphor, provides properties of particular interest for large-screen optically scanned multicolor display applications. Cholophors permit more efficient use of available laser power while providing a solution to the problem of color registration for two-primary displays and a partial solution for three-primary displays. Two-primary or Land-color displays can be obtained with only one color of laser light and three-primary displays with only two colors. A three-primary cholophor display using a single argon ion laser would have over 7 times the efficiency of a typical state-of-the-art system using an argon-krypton mixed-gas laser. The liquid crystal layer provides polarization selectivity, and the phosphor layer produces the additional color not furnished by the laser. The liquid crystal transmits one sense of laser polarization while totally reflecting the other, thereby permitting polarization selective excitation of the underlying phosphor. The color selection information is coded into the polarization of the incident laser beam.

Electronically Scanned Analog Liquid Crystal Displays

A new analog display technique for liquid crystal display panels is demonstrated. The size, shape, and location of display patterns can be changed continuously using low power electronic control. The display consists of a thin liquid crystal layer sandwiched between high resistance transparent area electrodes. Transverse voltage gradients on the electrodes actuate the device. The display operates with either dynamic scattering liquids or quiescent scattering liquids. Experimental results are given for three prototype analog displays: a voltmeter, a flying spot scanner, and a null indicator.