HOLOGRAPHIC SPATIAL FILTERS AND METHOD OF MAKING SAME

• US 3,581,280 A
• Filed: 06/27/1966
• Issued: 05/25/1971
• Est. Priority Date: 06/27/1966
• Status: Expired due to Term

• Current Assignee: John M. Holeman
• Original Assignee: John M. Holeman
• Inventors: Holeman, John M.
• Application Number:
  US04/560,418
• Time in Patent Office: 1,793 Days
• US Class Current: 382/210
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G03G 16/00 Electrographic processes using deformation of thermoplastic layers layers for surface-deformation imaging G03G5/022; Apparatus therefor shaping of plastic objects with thermoplastic memory effect B29C61/00; digital stores using thermoplastic elements G11C11/46; television signal recording using deformable thermoplastic recording medium H04N5/82
• CPC Class Codes: Y10S 359/90 Methods

Abstract

This invention relates to holography, and more particularly to a method and apparatus for rapidly making highly efficient spatial filters for holography.

Claims

1. In an object recognition system including a source of substantially coherent light, means for illuminating objects to be recognized with said source of light, light sensing means, and a holographic spatial filter positioned so that light emanating from said objects impinges on said filter, the improvement wherein said hologram recorded on a photoconductive transparent thermoplastic medium of substantially uniform transmissivity as a pattern of deformations defining the object to be recognized.

2. The apparatus of claim 1 wherein said spatial filter is positioned between said source of substantially coherent light and said light sensing means.

3. The apparatus of claim 1 and further including means for applying an electrostatic charge to said medium prior to impinging light thereon and means for heating said medium after impinging said light thereon.

4. The apparatus of claim 3 wherein said spatial filter is positioned between said source of substantially coherent light and said light sensing means.

5. The method of making an improved holographic spatial filter comprising the steps of:

generating first and second beams of coherent light;

directing the first of said beams onto an optical image of an object desired to be recognized so as to modulate said first beam with image information;

directing said second beam and said modulated first beam in directions to interfere with each other and impinge on an electrostatically charged, photoconductive, thermoplastic medium to produce a residual charge pattern thereon; and

heating said medium to a temperature sufficiently high to soften said medium and allow said medium to deform in accordance with the residual charge pattern thereon and recorded as a pattern of deformations a phase hologram of the object to be recognized.

6. The method of making an improved holographic spatial filter of claim 5 wherein said step of directing the first of said beams onto an optical image of an object desired to be recognized comprises the step of passing the first of said beams through a transparency containing an image of said object so as to modulate said first beam with image information.

7. The method of making an improved holographic spatial filter comprising the steps of:

uniformly electrostatically charging a transparent, photoconductive, thermoplastic medium;

generating first and second beams of coherent light;

directing the first of said beams onto an optical image of an object desired to be recognized so as to modulate said first beam with image information;

directing said second beam and said modulated first beam in directions to interfere with each other and impinge on said medium so as to selectively electrostatically discharge said medium according to a pattern determined by said optical image of an object desired to be recognized; and

heating said medium to a temperature sufficiently high to allow said medium to deform in accordance with said pattern and record a phase hologram of said object.

8. The method of making an improved holographic spatial filter of claim 7 wherein said step of directing the first of said beams onto an optical image of an object desired to be recognized comprises the step of passing the first of said beams through a transparency containing an image of said object so as to modulate said first beam with image information.

10. The method of reusing a photoconductive thermoplastic, holographic spatial filter in a holographic recognition system by substItuting a new image thereon while said filter is maintained stationary in said system, said method comprising the steps of:

heating said filter to a first temperature sufficiently high to soften the surface material thereon and render said surface material conductive;

cooling said filter in order to reharden said surface material;

uniformly electrostatically charging the surface of said filter;

generating first and second beams of coherent light;

directing the first of said beams onto an optical image of an object desired to be recognized so as to modulate said first beam with image information;

directing said second beam and said modulated first beam in directions to interfere with each other and impinge on the surface of said filter so as to selectively electrically discharge said surface according to a predetermined pattern; and

reheating said filter to a second temperature below said first temperature but sufficiently high to soften the surface material thereon and allow said material to deform in accordance with said predetermined pattern, all of said steps being carried out without removing said spatial filter from its operative location in the holographic recognition system.