1460793 Holographic apparatus XEROX CORP 25 March 1974 13195/74 Heading G1A A succession of image planes of a reconstructed hologram 6 are analyzed by a photo-electric scanner 14, whose output is compared with reference data in order to control the operation of a recording station to make a record of image-planes satisfying certain criteria. The invention is particularly applicable to the analysis of a hologram of a suspension e.g. gas particles dispersed in a liquid or solid, liquid particles in a gas or solid, or solid particles in a gas, liquid or other solid, in particular: fog, silt in water, plankton, duct in air, air or gas in plastics moulding as in a liquid &c. A hologram of the suspension is taken by transmission therethrough of light from a high power e.g. ruby laser with a short exposure to freeze any motion. In readout, a continuous He-Ne gas laser 18 is directed by lens 10, to the hologram, which is moved along the optical axis. A semi-silvered mirror 12 directs separate images to the record station 14 e.g. a photo-copy machine and to the scanner 14 which may be an array of photo-cells which may be associated with optical fibres, a line of photo-cells which scan the image plane, a T.V. camera or similar scanning cathode ray tube. The scanner output is fed to a progammed comparator and if a particular image-plane contains e.g. a predetermined number, size, shape or distribution of particles &c., the photo-copier is triggered to take a copy, which is also marked with the hologram longitudinal position, by electrical, mechanical or optical (e.g. a light image) transmission techniques, so as to indicate the image-plane in relation to the holographic volume record. In an alternative arrangement, the hologram may be fixed and the optical arrangement adjusted to produce different sequential image-planes for scanning.
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