Method of hologram recording with reduced speckle noise

• US 3,917,380 A
• Filed: 12/26/1973
• Issued: 11/04/1975
• Est. Priority Date: 12/25/1972
• Status: Expired due to Term

• Current Assignee: Makoto Kato, Yoshihiro Okino
• Original Assignee: Makoto Kato, Yoshihiro Okino
• Inventors: Okino, Yoshihiro, Kato, Makoto
• Primary Examiner(s): Stern, Ronald J.
• Application Number:
  US05/428,056
• Time in Patent Office: 678 Days
• Field of Search: 350/3.5 340/173LT,173LM 250/550
• US Class Current: 359/35
• CPC Class Codes: G03H 1/16 using Fourier transform G03H1/10, G03H1/12, G03H1/14 take precedence; analogue computers G06G, e.g. G06G7/19
• CPC Class Codes: G11C 13/046 using other storage elements storing information in the form of an interference pattern
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A sampling mask having a regular array of light transmitting areas is superimposed by a phase mask having a random array of phase shifting areas. The superimposed sampling and phase masks are holographically recorded for producing a hologram which later acts as a beam splitter to provide object and reference beams. The hologram so prepared is illuminated with a spatially incoherent broad source of light and imaged through an optical system. The zero order diffracted wave serves as the reference beam and the first order diffracted wave is used to illuminate an object transparency which is placed in the focused beam of the first order wave. Each point source of light from the spatially incoherent broad light source produces a corresponding interference fringe pattern, and it is shown that the interference pattersn exactly overlaps one upon another so that sharply defined fringe contrast results. The size of the light source is determined only by the required degree of resolution which in turn is dependent on the sampling spacing. The use of the incoherent broad light source enables uniform illumination of the object transparency, resulting in high-quality holograms with reduced speckle noise.

Claims

1. A holographic recording system for recording the hologram of an object transparency comprising:

a random phase illumination hologram receptive in use of substantially monochromatic spatially incoherent light for diffracting the incoherent light incident thereon into a zeroorder diffracted beam of light and into a first-order diffracted array of sampled, phase-shifted beams of light;

an image forming lens system receptive of the zero-order diffracted beam and the first-order diffracted array of light beams for focusing the zero-order diffracted beam and the first-order diffracted array of light beams in a focal plane which is also a Fourier transform plane with respect to said random phase illumination hologram;

a mask having a first and a second aperture and disposed in the focal plane of said image forming lens system for allowing the transmittance of only the zero-order diffracted beam and the first-order diffracted array of light beams through the first and second apertures, respectively, and beyond the focal plane;

whereby the positioning of said object transparency in the focal plane at the second aperture of said mask will result in the intensity modulation of the first order diffracted array of light beams to form a holographic interference pattern between the zero-order difrracted beam and intensity modulated firstorder diffracted array of light beams in a plane conjugate to said random phase illumination hologram with respect to said image forming lens system.

2. A holographic recording system according to claim 1 further comprising, a hologram recording plate disposed in said conjugate plane for recording the holographic interference pattern.

3. A holoGraphic recording system according to claim 1 further comprising, a source of substantially monochromatic spatially incoherent light disposed to illuminate said random phase illumination hologram.

4. A holographic recording system as claimed in claim 3 further comprising a lens interposed between said light source and said random phase illumination hologram for collimating the incoherent light incident on said random phase illumination hologram.

5. A holographic recording system as claimed in claim 3, wherein said incoherent light source extends in two dimensions to disperse each of said sampled beams outwardly with respect to the adjacent sampled beams.

6. A holographic recording system as claimed in claim 3, wherein said incoherent light source comprises means for scanning a coherent light beam in two dimensions.

7. A holographic recording system as claimed in claim 3, wherein said incoherent light source comprises means for passing a coherent light beam through a vibrating light diffusing medium.

8. A holographic recording system as claimed in claim 5, wherein said second aperture has a square shape and has an area equal to the cross-sectional area of each of said dispersed sampled beams.

9. A holographic recording system according to claim 1 wherein said image forming lens system comprises, a first Fourier transforming lens receptive of the zero-order beam and the first order diffracted array of light beams for focusing the light beams in the focal plane, and a second Fourier transforming lens aligned to receive the light beams focused by said first Fourier transforming lens and spaced a focal length from the focal plane.

10. A holographic recording system as claimed in claim 1, wherein said random phase illumination hologram is prepared by a process comprising the steps of:

a. providing a sampling mask having an array of light transmissive areas;

b. superimposing on said sampling mask a phase mask having randomly arranged groups of substantially equal numbers of phase shifting areas having phase shifts differing by discrete amounts such that each of said transmissive areas is aligned with each of said phase shifting areas;

c. illuminating said superimposed masks with a coherent light beam to provide sampled beams of light;

d. illuminating a photographic film with said sampled beams; and

e. simultaneously illuminating said photographic film with a reference light beam to produce thereon an interference fringe pattern of said sampling array.

11. A holographic recording system as claimed in claim 10, wherein the step of illuminating a photographic film with said sampled beams includes forming an optical Fourier transform of said sampling mask on said film.

12. A holographic recording system as claimed in claim 10, wherein said phase mask has a plurality of groups of recesses having depths differing by discrete amounts and arranged randomly thereon to impart a phase shift in the range from 0* to 360*, said groups each having complementary phase shift in said range.