Abstract: This invention provides a nematic liquid crystal display device for displaying a first information in the absence of any control voltage and substituting for that another information, or successively several other informations, by application of a control voltage. Several embodiments are described, in which either rotatory polarization effect in twisted structures or dynamic scattering effect are used.

Abstract: The invention provides an optical display device, utilizing a thermo-optical effect to inscribe a transmitted image in a layer of a material exhibiting a smectic state. Recording of the image with a full range of half tones without modulation of the recording beam and quick erasure of the recorded image without reheating of the film can be obtained by directly applying, simultaneously to the whole of the film either the video signal or an erasure voltage of suitable values. By associating this display device to a projection device utilizing a very bright source, the image thus recorded can be projected onto a large screen or a photosensitive substrate.

Abstract: The invention provides a liquid crystal imaging system which employs a transitory thermo-optic effect to permit notably the reproduction of T.V. images. This transitory effect is characterized by the fleeting appearance of scattering cybotactic zones in the transparent liquid phase of a mesomorphic material, at the very beginning of the transition to a nematic transparent ordered phase. The duration of the scattering period can be considerably shortened by subjecting the mesomorphic material layer to the action of an alternating electrical field.

Abstract: This invention relates to apparatus for automatically tracing patterns under the control of a program recorded in a computer. Said apparatus comprises means for initially recording the pattern in a liquid crystal cell by a known method under the control of said computer, and means for projecting the pattern thus recorded onto a photosensitive surface which records it on a reduced scale. It may also be projected on a large scale onto a monitor screen.

Abstract: The invention provides an optical display device, utilizing a thermo-optical effect to inscribe a transmitted image in a film of a material exhibiting a smectic state. The crystal liquid layer is inserted between transparent electrodes and heated to be in the smectic mesophase. The image is recorded in the layer under the form of variations in the scattering coefficient thereof by applying the video signal transmitting the image between the electrodes, while an infra-red beam of constant intensity synchronously scans the layer at a constant rate to successively raise each point beyond the melting point of the liquid crystal material. A quick erasure of the recorded image is provided by applying between the electrodes a voltage pulse of suitable value.

Abstract: The invention concerns liquid-crystal display methods and their application to radar screens. The invention provides a method which consists in thermally writing on a layer of liquid-crystal two successive patterns which are combined in accordance with a law designated A .times. B in Boolean algebra by the way of a reorienting biasing voltage applied during the writing in of the second of said pattern.