Patent GB-1301954-A (GB)
IPC: G02B27/50
Filed: 1971-04-19
Abstract: 1301954 Image converter CIBA-GEIGY AG 19 April 1971 [13 March 1970 12 Feb 1971] 24126/71 Heading H4F A image converter wherein focused infrared image produces local temperature differentials and hence surface distortions in a thin liquid film, and wherein such distortions are detected using a Schlieren or phase contrast optical system to provide a visible image, is characterized in that a diaphragm supporting the liquid films itself only supported at its periphery. In the embodiment of Fig. 11 the diaphragm 3 has an infra red absorbent layer 4 on one side, a specular layer 5 and the liquid film 6 on the other side, and is supported on a ring 22 in a gastight casing 23. The infra-red image is transmitted via a window 27 and a lenticular grating 2 dividing the casing into separate portions 25, 26 on to the layer 4, whence heat is conducted to deform the film 6 so that a visible light beam L is variably diffracted and reflected by the layers 6 and 5 out through a window 7 to the image forming optical system. Layers 3-6 are of suitable materials and thicknesses to prevent thermal conduction thereacross from degrading the image. Diaphragm 3 is typically 2-8 Á of ceramic, glasslike or plastics (e.g. nitrocellulose) material, and liquid 6 may be 0À2-10 Á of hexane, octane or decane. Specular layer 5 may be of dielectric material or be divided into isolated (metallic) elements, e.g. forming a grating Fig. 8 (not shown), or it may be omitted altogether, if internal reflection at the liquiddiaphragm interface is sufficient, Figs. 4 and 7 (not shown) or if the visible beam L is transmitted through the diaphragm and liquid film to the image forming system, Fig. 3 (not shown), If a specular grating is used, it constant is preferably not greater than half that of the grating 2. A pupil 21 may then be disposed so that the first order diffracted beam provided by the liquid film deformation is transmitted, but light diffracted by the specular grating 5 is obstructed. The layer 4 may be crystalline, e.g. lithium fluoride, or amorphous, e.g. "gold black", "silver black", and may be omitted if the diaphragm is infra-red absorbent, such as by encasting such materials the rein, or if the liquid film 6 is infra-red absorbent, Fig. 7 (not shown). In Fig. 4 (not shown), the visible and infra-red beams are incedent on the same side of the diaphragm, and the liquid film 6 may be on the opposite side thereof, if the diaphragm is transparent. A layer 5 may be provided. In Fig. 6 (not shown) the specular layer 5, such a reflecting grating, which is transparent to infra-red, is disposed in the other side of the diaphragm 3 from that shown in Fig. 11. Grating 2 is not necessarily lenticular, may be deposited on the infra-red window, or on the assembly of layers 3-6, and may comprise two crossed gratings active in the long and short wave infra-red regions respectively. The diffraction images will then likewise be located in two different directions and can be transformed into different coloured images using filters for example. The mean temperature of the liquid film must be maintained close to the temperature of the viewed object. In one embodiment, Fig. 9 (not shown), either window 7, 27, acts as a thermal radiator, for example having an electric resistance element. A gastight chamber (as 25 in Fig. 11) incorporating the window is filled with gas, preferably if a low thermal conductivity such as xenon. In Fig. 10 (not shown), the layers 3-6 are encircled by two half-annular radiators at different temperatures which are variably covered by a semicircular mesh to provide intermediate temperatures. In Fig. 11, the layers 3-6 are in the gastight portion 25 filled with xenon. A beam splitter 29 and photodetector 30 sense the overall field brightness and thereby control the temperature of a stream of gas A passing through the portion 26. Grating 2 is of AgCl for high thermal conductivity. Alternatively the grating may bear a conducting coating for electrical heating. A movable beam 24 is provided for obtaining the correct thickness of film 6.