| 摘要 |
1,218,148. Holography. INTERNATIONAL BUSINESS MACHINES CORP. April 11, 1969 [July 12, 1968], No. 18705/69. Heading G2J. Information, e.g. of a ship 10, is recorded in a storage medium 11, e.g. a photographic plate, by interfering an information bearing beam 12 of radiation with a plurality of reference beams 13 of coherent radiation in the medium to form holograms, the reference beams being collinear with respect to one another and interfering in time sequence with different portions of the information bearing beam. Preferably a laser beam is split into three portions 16, 17, 18, of which 17, 18 are directed on to the object 10 and then to recording medium 11. The object 10 has dimensions greater than the coherence length of the radiation. The reference portion 16 is divided at 30 into two ports 33, 34 polarized at right angles to each other, the port 34 passing through a quartz crystal for example, to retard it relative to 33 and give a path length difference between portions 33, 34 not greater than the coherence length of the radiation. The portions 33, 34 are made collinear by a crystal 31 to give two reference beams 13 which will respectively interfere with different portions of the information beam 12, each portion of the information beam representing a part of the object having dimensions not exceeding the coherence length of the light. The reference beams may interfere with the information beam from the same or the opposite side of recording medium 11. If desired any number of reference beams may be used provided that the path length between successive beams does not exceed the coherence length of the radiation. The information may be read out of medium 11 after its processing by a reference beam collinear with reference beams 13.
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