Patent GB-1173122-A (GB)
Title: Image Intensifier for Optically Produced Images
IPC: G02B23/12
Filed: 1968-02-28
Abstract: 1,173,122. Light modulators. GES. ZUR FÍRDERUNG DER FORSCHUNG AN DER EIDGENÍSSISCHEN TECHNISCHEN HOCHSCHULE. 28 Feb., 1968 [17 March, 1967], No. 9632/68. Heading H4F. Relates to an improvement in a device for increasing the intensity of an image such as that disclosed in Specifications 741,154, 987,867 and 1,114,162 where the image is employed to cause deformation of a control layer bearing a reflecting surface which is located in a Schlieren optical system for modulating light from a separate light source, the deformation being effected by means of a photoconductive layer which is illuminated by the image and produces variations in an electrostatic field to which the control layer is subjected in correspondence with the resistance variations imparted by the image. In accordance with the invention the device includes an isosceles glass prism 11, Fig. 5, cemented to a glass backing plate 12 on which is mounted an electrode grid comprising two interlaced comb-like grid elements 13a and 13b respectively connected to the poles of a voltage source U K . A soft deformable layer 14 e.g. siliconized rubber, is located in direct contact with the electrode grid 13a, 13b, and has a totally reflecting surface ABCD. An air gap 15 is left next to layer 14 followed by a photoconductive layer 17, e.g. antimony sulphide, an electrode grid comprising interlaced comb-like grid elements 18a and 18b respectively connected to the poles of a voltage source U T , mounted on a glass or quartz plate 19, and an optical raster e.g. a line-form optical raster 20 comprising thin metal strips which are equidistantly spaced and which are carried on a transparent plate 21. A further voltage source U L  is connected between grid elements 18b and 13b. The device is positioned in a Scblieren optical system (Fig. 1, not shown) and the light from a light source is directed via a strip-form diaphragm into prism 11 and is reflected from surface ABCD back via prism 11 and the same or another strip-form diaphragm on to a projection screen, the image to be projected being directed via optical raster 20 on to photoconductive layer 17. The device is substantially the same as the device described in Specification 987,867 but with the addition of grid elements 13a and 13b whose number, length, orientation and spacing of their longitudinal centre-lines is the same as for grid elements 18a and 18b. Grid elements 13a, 13b may be narrower than grid elements 18a and 18b. Both sets of grid elements are arranged to be at right-angles to the strips of the diaphragm of the Schlieren optical system and the strips of optical raster 20 are preferably 45 degrees thereto. As in Specification 987,867 grid elements 18a and 18b cause a wave-like deformation of surface ABCD and thus by switching on U T , U L  and U K  a superimposition of two deformations caused by elements 18a, 18b, 13a and 13b takes place on surface ABCD. The resulting total deformation is again waveshaped and by moving plate 12 having elements 13a, 13b in a direction perpendicular to the direction of the elements, the total deformation is carried between a maximum and a minimum. The position of plate 12 and the ratio of U T  to U K  are chosen so that the deformation of surface ABCD is a minimum i.e. the deformation comprises small wave-like curves in the surface which have a period half as great as the contributory deformations and have small amplitude. With this arrangement elements 13a and 13b compensate for the deformation produced by elements 18a and 18b and causes the diffracted images to be in close proximity to the undiffracted image and thus enables low intensity images to be intensified and produce a bright image on the projection screen without the diffracted images being at a considerable distance from the undiffracted image. In a second embodiment, Fig. 7, deformable layer 14 (and air gap 15) is replaced by two electrically insulating elastically deformable layers 24 and 25 and an intermediate conductive liquid mirror layer 26. Layers 24 and 25 comprise a silicon polymer with an added plasticizer e.g. siliconized rubber with plasticizer, and mirror 26 comprises a liquid metal or metal alloy, or mercury or an amalgam with indium. In addition to D.C. voltage sources U T  and U K , A.C. voltage sources U L  and UL<SP>1</SP> having the same frequency and phase although their amplitudes may differ are connected as shown between mirror 26 and grid elements 18b and 13b. The device may be used in a Schlieren optical system using a reflecting strip diaphragm (Fig. 6, not shown), prism 11 not being required. Voltage sources U L  and UL<SP>1</SP> are A.C. voltage sources since the liquid mirror layer 26 must reproduce point for point on the surface II only time-wise changing deformations of surface I in controlled dependence on the photoconductive layer 17 (see Specification 1,114,162).