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Method for distinguishing similar subjects using discriminating holograms

  • US 3,899,240 A
  • Filed: 12/09/1970
  • Issued: 08/12/1975
  • Est. Priority Date: 08/13/1965
  • Status: Expired due to Term
First Claim
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1. In a process for forming a reference hologram of a pattern having both an element in common with any other pattern and a distinctive element that comprises the steps of:

  • interfering on a recording medium two beams of light for a suitable exposure one of which beams is modulated by the pattern to be recorded, thereby forming on the recording medium a set of interference fringes, a first part of which is related to the common element in the pattern to be recorded and a second part of which is related to the distinctiive element;

    the fringes having a location on the recording medium that is dependent on the phase relation between the two beams;

    the improvement characterized by;

    forming the first part of the set of interference fringes by projecting onto the recording medium a first and a reference beam of light, the first beam being modulated by the common element of the pattern to be recorded; and

    forming a different second part of the set of interference fringes by projecting onto the medium a third and a reference beam of light, the third beam being modulated by the distinctive element of the pattern to be recorded; and

    the phase relation between the third and reference beams being different from the phase relation between the first and reference beams.

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