Leroy J. Miller

A new real-time non-coherent to coherent light image converter - The hybrid field effect liquid crystal light valve

A new, high-performance device has been developed for application to real-time coherent optical data processing. The new device embodies a CdS photoconductor, a CdTe light-absorbing layer, a dielectric mirror, and a liquid crystal layer sandwiched between indiumtin-oxide transparent electrodes deposited on optical quality glass flats. The non-coherent image is directed onto the photoconductor; this reduces the impedance of the photoconductor, thereby switching the ac vol-tage that is impressed across the electrodes onto the liquid crystal to activate the device. The liquid crystal is operated in a hybrid field effect mode. It utilizes the twisted nematic effect to create a dark off-state (voltage off the liquid crystal) and the optical birefringence effect to create the bright on-state. The liquid crystal modulates the polarization of the coherent read-out light so an analyzer must be used to create an intensity modulated output beam. Performance figures for the device include: Resolution 100 lines/mm; Input Sensitivity 160 iW/cm2 at 525 nm; Time Response on: 10. msec; off: 15 msec; Contrast >100 : 1 ; Aperture 1 inch by 1 inch.

Liquid crystal birefringence for millimeter wave radar

Abstract Many liquid crystals are found to have relatively high birefringence (Δn) values in the microwave and millimeter wave regions, as calculated from the phase shift induced by their reorientation by magnetic or electric fields. At 30 GHz, Δn values were obtained in the range of 0.08 to 0.18 for eleven liquid crystal mixtures of various types. The most favourable liquid crystal structures for high millimeter wave birefringence are highly conjugated rod-like molecules containing biphenyl, terphenyl, phenylpyrimidine, biphenylpyrimidine, and tolane groups in nematics of positive dielectric anisotropy (Δe). However, other liquid crystal structures including Schiffs base, azoxybenzene, and aromatic ester groups also have substantial birefringence, including nematics with negative and crossover Δe, as well as cholesteric nematics. The Δn varied only slightly at different frequencies of microwave millimeter wave in the 15–94 GHz range. Studies on magnetic and electrical field liquid crystal orientation in ...

Electro-optical applications of liquid crystals

Abstract The unique properties of thermotropic liquid crystals have led to the development of many new electro-optical devices, particularly for display applications. Basic properties and surface alignments of liquid crystals are reviewed with regard to these applications. Electro-optical effects based on conductivity and field effect alignment are described for both nematic and cholesteric materials. Three applications of nematics are selected for more detailed discussion: a flat panel television display using dynamic scattering activated by a semiconductor matrix, a watch display using polarization modulation of twisted nematic cells on transparent segment electrodes, and a large screen projection system using tunable birefringence in a photoactivated light valve.

Formulation and Predicted Properties of Nematic Eutectic Mixtures of Esters

Abstract Techniques are described both for formulating new nematic liquid crystal (LC) eutectic mixtures and for calculating several of their predicted properties. Ester LC components from various structure classes are used. Emphasis is placed on obtaining mixtures which have relatively short average molecular length, and which are suitable for dynamic scattering electro-optical applications. Examples are given of binary eutectic mixtures made with LC esters of essentially the same molecular length. Selection rules are described for mixing short length components, both from homologous series and from different classes of esters. Approximate class values of birefringence, dielectric anisotropy, and viscosity are assigned to each type of ester structure, based on experimental results in selected mixtures of short molecular length. Properties of multi-component eutectic mixtures are calculated, and comparisons are shown between the predicted and the observed values of melting point, clearpoint, viscosity, di...

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.

Photochemical and Thermal Stability Studies on a Liquid Crystal Mixture of Cyanobiphenyls

Liquid crystals (LCs) have unique properties that allow them to be used in information display devices.1 In particular, LCs are useful for displays used in wrist watches, calculators, message boards, flat-panel television, and large-screen projection systems.2 The choice of materials is often dictated by the desired application. The use of LCs in electro-optical devices exposed to high-intensity light must meet not only the usual criteria for these devices such as birefringence, dielectric and conductivity anisotropy, and alignment qualities, but must be photochemically stable to long exposures of visible light and thermally stable to heat generated by exposure to visible and near infrared light. Large-screen projection displays that use liquid crystal light valves3 have more severe photochemical stability requirements to achieve long lifetime displays than many other devices. Even very small absorption “tails” of the LCs that extend into the visible region of the spectrum can cause lifetime problems (should photo-decomposition occur) because of the high intensity of light used. Figure 1 shows a light valve projection system.3

Liquid Crystal Alignment Method for Long Lifetime Tilted-Perpendicular Light Valves

Abstract A new technique for tilted-perpendicular alignment (TPA) of liquid crystals on surfaces greatly improved the photostability of the photoactivated liquid crystal light valves (LCLVs) with negative dielectric anisotropy liquid crystals. The operation of surface-perpendicular aligned LCLVs provided a very dark off-state, high contrast images, and high light throughput efficiency. Alkoxy groups bonded on angle-deposited SiO2 gave controlled TPA, in which the tilt angle of LC on the treated surfaces was primarily dependent on the thickness of the shallow-angle deposited SiO2 layer. We have demonstrated improved photostability to high intensity light exposures using this TPA method in hermetically sealed cells. Projection LCLVs with very high contrast and with greater than 10,000 hours of operational stability at 2000 lumens, were obtained using this new TPA method and more stable liquid crystal mixtures.

Conductive Polymer-Based Transducers as Vapor-Phase Detectors

Publisher Summary This chapter discusses the development of conductive polymer-based transducers for the detection of volatile organic compounds (VOCs) and other gaseous pollutants for application in environmental monitoring. In the experiment described in the chapter, highly sensitive sensor elements derived from polyaniline (PANI) are demonstrated for NO2 and other VOCs. A figure of merit is defined to allow the comparison of the response of different sensors to particular challenge vapors at various concentrations. The use of excess silane coupling agents to modify the surface of the sensor substrates in combination with excess of a sulfonic acid used to convert PANI to its conductive state results in highly sensitive, stable, and reversible VOC sensors, along with some polythiophene derivatives, for the detection of ketones, esters, and aromatic hydrocarbons. Individual sensors show different sensitivities to each class of VOC used in the study so that an array of these sensors generated a characteristic signature for each class demonstrating selectivity and classification.

Poly(methacrylic anhydride) positive electron beam resist

Poly(methacrylic anhydride) (PMAH) is a positive resist for use in electron beam (e‐beam) lithography. It is derived by heating coatings of the precursor polymer, poly(tert‐butyl methacrylate) or PtBMA, on the wafer. Crosslinks are introduced during the thermal conversion. The sensitivity and line profiles of PMAH e‐beam images are significantly affected by the synthesis route, the pre‐exposure processing, and the development method. Development with organic solvents can swell and soften the resist, especially in areas that received some exposure to radiation. This causes the walls of the image to expand or flow into the image cavity, thereby limiting the sensitivity at which high resolution can be achieved. However, the use of a new, nonswelling, basic developer gives PMAH a sensitivity of 2.5 μC/cm2 with better than 0.5 μm resolution.

A New Method for Inducing Homeotropic and Tilted Alignments of Nematic Liquid Crystals on Silica Surfaces

Homeotropic alignment of a nematic liquid crystal on a silica surface can be induced by means of a prior treatment of the surface with a long-chain aliphatic alcohol or a mixture of such an alcohol and an amine. The treatment is presumed to replace some or all of the hydroxy groups normally attached to silicon atoms at the surface with alkoxy groups derived from the alcohol, thereby reducing the critical surface tension of the surface. As the chain length of the alcohol is decreased, the director of the nematic tilts away from the perpendicular orientation. The direction of tilt can be controlled by shallow angle ion beam etching the silica surface prior to the alcohol treatment, in which case the nematic molecules are uniformly tilted toward the ion beam source. The tilt angle is a function of both the length of the alcohol chain and the composition of the liquid crystal. Tilted homeotropic alignment is essential for obtaining optimum performance of field effect devices that use nematics with a negative dielectric anisotropy.