GB1106220A - Improvements in or relating to information storage and retrieval - Google Patents

Abstract

1,106,220. Producing holograms. AMERICAN OPTICAL CO. Nov.18, 1965 [Dec.2, 1964], No.49025/65. Heading G2C. Apparatus for sequentially recording information from a number of transparencies 26, 28, 30, 32, one at a time, on to a single film 22 comprises a coherent light-source 12 emitting a beam 14 which is split by a mirror 16 to produce a reference beam 18 and an object beam 20, the ratio of the reference beam intensity to the object beam intensity being approximately 10:1. The object beam is diffused by a ground glass plate 24 and, after passing through one transparency (e.g. 26) interferes with the beam 18 to form a hologram of the transparency 26 on the photographic plate 22. The transparency 26 is then replaced by another (e.g. 28) in a different plane in space, a hologram of which is also formed on the plate 22. In another embodiment Fig. 3 (not shown) holograms of several opaque objects (46), (48), (50), (52) are formed on the plate (22), but in this case the ratio of the reference beam intensity to the object beam intensity is 1:10, and the objects themselves act as diffusers. Retrieval of the information stored on the film 22 is achieved by illuminating, with coherent light of variable radius wave front Fig. 2 (not shown), the film, the information content of the film then being carried by a beam (40). The radius of the wave front is varied by use of a zoom lens system (36) to produce on a screen (42) only one image at a time, the radius being varied in such a manner that the larger the radius of curvature, the nearer the object, the image of which is seen on the screen (42), to the lightsource 12. The hologram producing systems are arranged so as to give rise to off axis images to prevent "cross-talk" between different images.