Patent GB-902384-A (GB)
Title: Apparatus for light control
IPC: G02F1/19
Filed: 1958-10-01
Abstract: 902,384. Light modulating. AGFA A.G. Oct. 1, 1958 [Oct. 19, 1957], No. 31356/58. Class 40 (3). [Also in Groups XXXVI and XL (a)] An apparatus for light control includes a light transmitting medium having components that wander in the medium under the influence of an electric field, thereby causing local concentration variations, with corresponding variations of the refraction index in a boundary layer of said medium, means for applying to the medium an electric field have said influence, said field being variable in accordance with a variable signal, and means for rendering a light beam incident upon the boundary layer in such manner that the variations of refractive index in said layer caused by concentration variations can be used for controlling the beam so that a resulting light beam is produced having intensity variations corresponding to the concentration variations. The medium may comprise an aqueous or non-aqueous solution of electrolyte, an aqueous or non-aqueous colloid as either a sol or a gel, a macro-molecular substance or dyestuffs, a polystyrene emulsion, or a solubilized system, for example, chlorobenzine in aqueous dimethylamine hydrochloride solution. In addition to the use of variations of refractive index, reference is also made to the use of the thickness of the boundary layer. The refractive index variations may be utilized to control light in accordance with Schlieren, phase contrast or dark field methods. As illustrated in Fig. 3, a colloid solution 16 is bounded by membranes 15 and 17 and is subjected to an electric field applied by source 23 between electrodes 11 and 19. Electrolyte solutions 14 and 18 provide conducting paths between the membranes and electrodes 12 and 19. A semi-conductor layer 12 is between electrodes 11 and 13. In response to incident radiation 20, the electrical resistance of layer 12 varies and causes a corresponding variation in the strength of the electric field appearing across colloid solution 16. As a result, the concentration in a thin layer bounded by membrane 17 changes and with it the refractive index. The concentration may be arranged to be increased or decreased. If, for example, the refractive index of electrolyte solution 18 is normally made equal to that of the colloid solution, a beam of radiation 21 which is normally transmitted via membrane 17 may be caused to be reflected in response to a reduction in the refractive index of the colloid solution. As an alternative, the apparatus may be arranged so that the radiation 21 is normally reflected and is transmitted in response to the application of radiation 20. Reversal of the concentration variations may be effected by diffusion, by a counteracting electric field or supersonic waves. The apparatus may be employed as an image intensifier or image converter for which purpose elements 13, 14 and 16 are preferably divided into elemental cells with insulating partitions between to prevent concentration equalization between adjacent elements of the image. Reference is made to the use of the apparatus with incident radiation in the form of electromagnetic waves, e.g. X-rays, ultra-violet, visible and infra-red rays, and corpuscular radiation, e.g. electrons or ions. For use with electrons, elements 11, 12 and source 23 may be dispensed with and electrode 13 constructed in grid form of a large number of -mutually insulated elements on which the electrons induce charges. The controlled radiation 21 may comprise infra-red, visible or ultra-violet rays. Reference is made to the use of polarized light. Another embodiment of the invention, Fig. 1 (not shown), comprises only the colloid solution and electrolytes between electrodes, variation in the field strength being effected directly by controlling the electric circuit by electrical, mechanical, magnetic, electromagnetic or thermoelectric means.